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TWI404016B - Display drive apparatus,display apparatus and drive method - Google Patents
Display drive apparatus,display apparatus and drive method Download PDF
TWI404016B
TWI404016B TW97110915A TW97110915A TWI404016B TW I404016 B TWI404016 B TW I404016B TW 97110915 A TW97110915 A TW 97110915A TW 97110915 A TW97110915 A TW 97110915A TW I404016 B TWI404016 B TW I404016B
TW97110915A
TW200901134A (en
Jun Ogura
Casio Computer Co Ltd
2008-03-27 Application filed by Casio Computer Co Ltd filed Critical Casio Computer Co Ltd
2009-01-01 Publication of TW200901134A publication Critical patent/TW200901134A/en
2013-08-01 Publication of TWI404016B publication Critical patent/TWI404016B/en
230000000875 corresponding Effects 0 abstract 1
G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
G09G3/3275—Details of drivers for data electrodes
G09G2320/029—Improving the quality of display appearance by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
G09G2320/0295—Improving the quality of display appearance by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel by monitoring each display pixel
A display drive apparatus includes a detection voltage applying circuit that applies a predetermined detection voltage to the drive element of the pixel drive circuit, a voltage detecting circuit that detects a voltage value corresponding to a device characteristic unique to the drive element after a predetermined time elapses after the application of the detection voltage to the drive element by the pixel drive circuit, and a gradation designating signal generating circuit that generates a gradation designating signal based on an absolute value of a voltage component according to a gradation value of display data and a value, acquired by multiplying an absolute value of the voltage value detected by the voltage detecting circuit, by a constant greater than 1, and applies the gradation designating signal to the pixel drive circuit, whereby a change in device characteristic.
Display driving device, display device, and driving method
The present invention relates to a display driving device, a display device using the same, and a driving method, and more particularly to a current control type (or current) that can be applied to align a plurality of currents in a gray scale by supplying a current corresponding to the data to be displayed. A display driving device for a display panel (display pixel array) comprising a light-emitting element of a driving type, a display device using the same, and a driving method for the display device.
In recent years, the second generation of display devices are being actively provided with organic electroluminescent elements (organic EL elements) and inorganic electroluminescent elements (inorganic EL elements) or light-emitting diodes (LEDs). Research and development of a light-emitting element type display device (light-emitting element type display) in which a current-driven light-emitting element such as a display panel is arranged in a matrix.
In particular, a light-emitting element type display to which an active matrix driving method is applied has a display reaction speed faster than that of a well-known liquid crystal display device, and has a small viewing angle dependency, and does not require a backlight and a light guide plate as required for a liquid crystal display device. Therefore, it is expected to be applied to various electronic devices in the future.
In an organic EL display device using an organic EL device for a light-emitting element type display device using an active matrix driving method, it is known to control a luminance gray scale by using a voltage signal to control a current flowing into the light-emitting element. By.
In this case, a thin film transistor for current control is provided in each display pixel, and a voltage signal corresponding to the display data is applied to the gate, which will have The current of the current value of the voltage value of the voltage signal flows into the light-emitting element; and the thin film transistor for switching is switched for supplying a voltage signal corresponding to the pixel data to the gate of the thin film transistor for current control.
However, in the organic EL display device for controlling the luminance gray scale, the electric characteristics of the thin film transistor for current control are set in the organic EL display device for controlling the luminance gray scale by the voltage value of the voltage signal applied in response to the display of the data. The threshold is subject to change at any time. When such a threshold change occurs, even if the voltage value of the voltage signal applied in response to the display of the data is the same, the current value of the current flowing into the light-emitting element fluctuates, and the luminance of the light-emitting element fluctuates, and the display characteristics deteriorate.
The present invention provides a display driving device capable of compensating for variations in device characteristics of a driving element for displaying pixels, in order to display a suitable gray scale of data, and a display device using the same, and a driving method using the same, Therefore, there is an advantage that it is possible to provide a display device having a long-term display image quality and a driving method using the same.
In order to obtain the above advantages, the display driving device for driving a display pixel according to the present invention includes: the display pixel includes: an optical element; and a pixel driving circuit having one end of the current path connected to the optical element The display drive device includes: a detection voltage application circuit that applies a specific detection voltage to the drive element of the pixel drive circuit; and a voltage detection circuit that applies the detection voltage from the detection voltage application circuit to the After driving the component, after a lapse of a specific time, detecting a voltage value corresponding to the component characteristic inherent in the driving component; and a gray scale designation signal generating circuit that sets an absolute value of the voltage component detected by the voltage detecting circuit to a constant value larger than 1 by an absolute value of a voltage component corresponding to a gray scale value of the display data And generating a gray scale designation signal to be applied to the aforementioned pixel drive circuit.
In order to obtain the above advantages, the display device for displaying image information of the present invention includes a display driving device having: a display pixel having: an optical element; and a pixel driving circuit having one end of the current path connected to a driving element of the optical element; a data line connected to the pixel driving circuit of the display pixel; and a voltage applying circuit for detecting, wherein the pixel driving circuit of the display pixel is displayed via the data line The driving element applies a specific detection voltage, and the voltage detecting circuit detects the voltage from the detecting voltage application circuit to the driving element, and after detecting the driving element for a predetermined period of time, detects the driving element through the data line. a voltage value corresponding to the inherent component characteristic (Vth); and a gray scale designation signal generating circuit that is detected by the voltage detecting circuit according to the absolute value of the voltage component (Vd0) corresponding to the gray scale value of the displayed data The absolute value of the aforementioned voltage value (Vth) is set to a value that is a constant multiple of 1 to generate a gray scale designation signal (Vpix). And applied to the aforementioned pixel driving circuit via the aforementioned data line.
In order to achieve the above advantages, the driving method of the display driving device of the present invention is a driving method of a display device for displaying image information, and includes the steps of: applying a specific data line connected to the pixel driving circuit via a display pixel The detection voltage is applied to the driving element of the pixel driving circuit, and the display pixel has an optical element and a current path The end is a pixel driving circuit connected to the driving element of the optical element; after applying the detection voltage to the driving element, after a lapse of a specific time, detecting a characteristic of the element corresponding to the driving element through the data line (Vth) voltage value; based on the absolute value of the voltage component (Vd0) corresponding to the gray scale value of the data to be displayed, and the absolute value of the voltage value (Vth) detected by the voltage detecting circuit is set to be larger than 1 The value of the constant multiple produces a gray scale designation signal (Vpix); and the gray scale designation signal is applied to the pixel drive circuit via the data line.
Hereinafter, the display driving device, the display device using the same, and the driving method of the present invention will be described in detail based on the embodiments shown in the drawings.
<Display of important parts of pixels>
First, the configuration of important parts of the display pixels applicable to the display device of the present invention and the control operations thereof will be described with reference to the drawings.
Fig. 1 is an equivalent circuit diagram showing the construction of an important part of a display pixel suitable for the display device of the present invention. Here, a description will be given of a case where a current-driven light-emitting element that displays a pixel is used, and an organic EL element is applied as appropriate.
As shown in Fig. 1, the circuit configuration of the display pixel to be applied to the display device of the present invention includes a pixel circuit unit (corresponding to a pixel driving circuit DC to be described later) DCx, and an organic EL of a current-driven light-emitting element. Element OLED. The pixel circuit portion DCx has a 汲 terminal and a source terminal respectively connected to a power supply terminal TMv and a contact point N2 to which a power supply voltage Vcc is applied, and a gate terminal connected to a driving transistor T1 of the contact point N1; a 汲 terminal and a source extreme The sub-terminal is respectively connected to the power terminal TMv (the terminal of the driving transistor T1) and the contact point N1, the gate terminal is connected to the holding transistor T2 of the control terminal TMh, and the gate and the source terminal connected to the driving transistor T1. Capacitor Cx between (between contact N1 and contact N2). Further, the organic EL element OLED is connected to the above-mentioned contact N2 at the anode terminal, and a voltage Vss is applied to the cathode terminal TMc.
Here, as described in the control operation described later, the power supply voltage TMcc having different voltage values depending on the operating state is applied to the power supply terminal TMv in response to the operation state of the pixel (pixel circuit unit DCx). A certain voltage (reference voltage) Vss is applied to the cathode terminal TMc of the element OLED, a hold control signal Shld is applied to the control terminal TMh, and a data voltage corresponding to the gray scale value of the display data is applied to the data terminal TMd connected to the contact N2. Vdata.
Further, the capacitor Cx may be a parasitic capacitance formed between the gate and the source terminal of the driving transistor T1, or may be a capacitor element connected in parallel between the contact point N1 and the contact point N2 in addition to the parasitic capacitance. Further, the element structure and characteristics of the driving transistor T1 and the holding transistor T2 are not particularly limited, and the case where an n-channel type thin film transistor is applied is shown here.
<Display control action of pixels>
Next, a description will be given of a control operation (control method) in the display pixel (pixel circuit unit DCx and organic EL element OLED) having the above-described circuit configuration.
Fig. 2 is a signal waveform diagram showing a control operation of a display pixel applied to the display device of the present invention.
As shown in Fig. 2, the operation state in the display pixel (pixel circuit unit DCx) having the circuit configuration shown in Fig. 1 can be roughly divided into: the voltage component corresponding to the grayscale value of the displayed data is written. a write operation of the capacitor Cx; in the write operation, the write voltage component is held in the capacitor Cx; and the voltage component contained in the hold operation flows into the organic EL device OLED The illuminating driving current of the gray scale value causes the organic EL element OLED to emit light in response to the gray scale of the brightness of the displayed data. Hereinafter, each operation state will be specifically described with reference to the timing chart shown in FIG.
(write action)
The writing operation is performed by writing a voltage component corresponding to the gray scale value of the data to be displayed in the capacitor Cx in a light-off state in which the organic EL element OLED is not turned on.
3A and B are schematic diagrams showing an operation state in which a pixel is displayed during a write operation.
Fig. 4A is a characteristic diagram showing the operational characteristics of the driving transistor when the pixel is in the writing operation, and Fig. 4B is a characteristic diagram showing the relationship between the driving current and the driving voltage of the organic EL element.
The solid-line SPw-type driving transistor T1 shown in Fig. 4A is applied to an n-channel type thin film transistor, and the drain-to-source voltage Vds and the drain-source-source current Ids in the initial state when the diode is connected The characteristic line of the relationship. Further, the broken line SPw2 shows an example of a characteristic line when the characteristic change of the driving transistor T1 occurs with the driving experience. Details will be described later. The point PMw on the characteristic line SPw represents the operating point of the driving transistor T1.
As shown in Fig. 4A, the threshold voltage Vth of the driving transistor T1 (the threshold voltage between the gate and the source = the threshold voltage between the drain and the source) is on the characteristic line SPw, the drain When the inter-source voltage Vds exceeds the threshold voltage Vth, the drain-to-source current Ids is accompanied by an increase in the drain-to-source voltage Vds rather than linearity. That is, in the drain-to-source voltage Vds, the voltage represented by Veff_gs in the figure effectively forms a voltage component of the drain-to-source current Ids, and the drain-source-to-source voltage Vds is as in (1) It is shown as the sum of the threshold voltage Vth and the voltage component Veff_gs.
Vds=Vth+Veff_gs‧‧‧(1)
The solid line SPe shown in FIG. 4B shows the relationship between the driving voltage Voled applied between the anode and the cathode of the organic EL element OLED in the initial state, and the driving current Ioled flowing between the anode and the cathode of the organic EL element OLED. Characteristic diagram. Further, the one-point chain line SPe2 shows an example of a characteristic line when the organic EL element OLED has a characteristic change accompanying the driving experience. Details will be described later. When the threshold voltage Vth_oled is on the characteristic line SPe and the driving voltage Voled exceeds the threshold voltage Vth_oled, the driving current Ioled increases with the increase of the driving voltage Voled instead of the linearity.
In the write operation, first, as shown in FIGS. 2 and 3A, the hold level control signal Shld is applied to the control terminal TMh of the holding transistor T2 to turn on the holding transistor T2. action. Thereby, the gate and the terminal of the driving transistor T1 are connected (short-circuited), and the driving transistor T1 is set to the diode connection state.
Continuing, a first power supply voltage Vccw for a write operation is applied to the power supply terminal TMv terminal, and a corresponding data is applied to the data terminal TMd. The data voltage of the gray scale value is Vdata. At this time, a current Ids corresponding to a potential difference (Vccw - Vdata) between the drain and the source terminal flows between the drain and the source terminal of the driving transistor T1. The data voltage Vdata is set such that the current Ids flowing between the drain and the source terminal is a voltage value for causing the organic EL element OLED to emit light in response to the gray scale of the gray scale value of the data to be displayed.
At this time, since the diode is connected to the driving transistor T1, as shown in FIG. 3B, the drain-to-source voltage Vds of the driving transistor T1 is equal to the gate-source voltage Vgs, and is formed as (2). As shown in the formula.
Vds=Vgs=Vccw-Vdata‧‧‧(2)
Then, the gate-source voltage Vgs is written into the capacitor Cx (charge).
Here, the conditions required for the value of the first power supply voltage Vccw will be described. Since the driving transistor T1 is of the n-channel type, in order to flow the drain current and the source current Ids, the gate potential of the driving transistor T1 must be positive (high potential) to the source potential, and the gate potential is equal to the drain potential. Since the first power supply voltage Vccw is used and the source potential is the data voltage Vdata, the relationship of the equation (3) is established.
Vdata<Vccw‧‧‧(3)
Further, the contact point N2 is connected to the data terminal TMd, and is connected to the anode terminal of the organic EL element OLED. When writing, in order to turn off the organic EL element OLED, the potential of the contact point N2 (data voltage Vdata) must be organic The potential difference of the voltage Vss of the cathode terminal TMc of the EL element OLED is the illuminating threshold voltage of the organic EL element OLED Vth_oled Hereinafter, the potential of the contact point N2 (data voltage Vdata) must satisfy the formula (4).
Vdata-Vss≦Vth_oled‧‧‧(4)
Here, when Vss is the ground potential of 0 V, it is (5).
Vdata≦Vth_oled‧‧‧(5)
Secondly, from equations (2) and (5), equation (6) is obtained. Vccw-Vgs≦Vth_oled‧‧‧(6)
Furthermore, since the equation (1) is Vgs=Vds=Vth+Veff_gs, the equation (7) is obtained.
Vccw≦Vth_oled+Vth+Veff_gs‧‧‧(7)
Here, since the equation (7) must be established even if Veff_gs=0, when Veff_gs=0, the equation (8) is obtained.
Vdata<Vccw≦Vth_oled+Vth‧‧‧(8)
In other words, in the write operation, the value of the first power supply voltage Vccw is set to a value satisfying the relationship of the equation (8) in the state in which the diodes are connected. Next, the influence of the change in characteristics of the driving transistor T1 and the organic EL element OLED accompanying the driving experience will be described. It is known that the threshold voltage Vth of the driving transistor T1 increases as the driving progresses. The broken line SPw2 shown in Fig. 4A shows an example of a characteristic line when a characteristic change occurs by a driving experience, and ΔVth represents a variation amount of the threshold voltage Vth. As shown in the figure, the initial characteristic line becomes a shape that moves substantially in parallel as the characteristic changes experienced by the driving of the driving transistor T1. Therefore, in order to obtain the light-emission drive current (drainage, source-to-source current Ids) in response to the gray scale value of the displayed data, the value of the required data voltage Vdata must be increased by the amount of change ΔVth of the threshold voltage Vth.
Further, it is known that the organic EL element OLED is increased in resistance as the driving progresses. The dot chain line SPe2 shown in FIG. 4B shows an example of a characteristic line when a characteristic change occurs in association with a driving experience, and the characteristics characteristic change due to high resistance due to the driving experience of the organic EL element OLED, the initial characteristic line The direction of the drive current Ioled decreases in the direction in which the increase rate of the drive voltage Voled decreases. In other words, since the driving current Ioled required to emit light in order to cause the organic EL element OLED to emit light in accordance with the gray scale value of the gray scale value of the data is supplied, the driving voltage Voled increases only the extent of the characteristic line SPe2 to the characteristic line SPe. This increased portion is shown as ΔVoledmax in Fig. 4B, and becomes maximum when the drive current Ioled becomes the highest gray scale of the maximum value Ioled(max).
(keep the action)
5A and B are schematic diagrams showing the operation state of the pixel when the pixel is held.
Fig. 6 is a characteristic diagram showing the operational characteristics of the driving transistor when the pixel is held in the holding operation.
As shown in FIG. 2 and FIG. 5A, the holding operation is performed by applying the OFF level (low level) holding control signal Shld to the control terminal TMh, and the holding transistor T2 is turned off (cut). In the non-connected state, the gate and the terminal of the transistor T1 are driven to disconnect the diode. As a result, as shown in FIG. 5B, in the above-described address operation, the voltage Vds (= gate and source-to-source voltage Vgs) between the drain and source terminals of the driving transistor T1 charged in the capacitor Cx is held. .
The solid line SPh shown in Fig. 6 releases the diode of the driving transistor T1. The characteristic line when the gate voltage and the source-to-source voltage Vgs are constant voltages (such as the voltage held in the capacitor Cx during the sustain operation). Further, the dotted line SPw type diode shown in Fig. 6 is connected to the characteristic line when the transistor T1 is driven. The operating point PMh at the time of holding becomes the intersection of the characteristic line SPw when the diode is connected and the characteristic line SPh when the diode is disconnected.
One dot chain line SPo shown in Fig. 6 is introduced as the characteristic line SPw-Vth, and the intersection point Po of the one-point chain line SPo and the characteristic line SPh shows the pinch-off voltage Vpo. Here, as shown in FIG. 6, in the characteristic line SPh, the region where the drain-to-source voltage Vds is from 0 V to the pinch-off voltage Vpo becomes an unsaturated region, and the drain-to-source voltage Vds is a pinch-off voltage. The area above Vpo becomes a saturated area.
(lighting action)
7A and B are schematic explanatory views showing an operation state in which a pixel is displayed during a light-emitting operation.
8A and B are characteristic diagrams showing the operational characteristics of the driving transistor when the pixel is illuminated, and a characteristic diagram showing the load characteristics of the organic EL element.
As shown in FIG. 2 and FIG. 7A, the state in which the hold level control signal Shld of the off level (low level) is applied to the control terminal TMh (the state in which the diode connection state is released) is maintained, and the power supply terminal TMv is placed. The power supply voltage Vcc is switched from the first power supply voltage Vccw for writing to the second power supply voltage Vcce for light emission. As a result, the current Ids held in the voltage component Vgs of the capacitor Cx flows between the drain and the source terminal of the driving transistor T1, and the current is supplied to the organic EL element OLED, and the organic EL element OLED causes The light-emitting operation is performed by the brightness of the current value to be supplied.
The solid line SPh-based gate and source-to-source voltage Vgs shown in Fig. 8A is a characteristic line of the driving transistor T1 when a constant voltage (such as a voltage held in the capacitor Cx from the sustain operation period to the light-emitting operation period). Further, the solid line SPe represents the load line of the organic EL element OLED, and the potential difference between the power supply terminal TMv and the cathode terminal TMc of the organic EL element OLED, that is, the value of Vcce-Vss is used as a reference to drive the organic EL element OLED. The voltage Voled-drive current Ioled characteristic is reversed to the plot.
The operating point of the driving transistor T1 during the light-emitting operation is moved from PMh at the time of the holding operation to PME at the intersection of the characteristic line SPh of the driving transistor T1 and the load line SPe of the organic EL element OLED. Here, as shown in FIG. 8A, the operating point PMe indicates that the voltage of Vcce-Vss is applied between the power supply terminal TMv and the cathode terminal TMc of the organic EL element OLED, and the voltage is at the drain of the driving transistor T1. The point between the source terminals and the anode-cathode of the organic EL element OLED. That is, at the operating point PMe, a voltage Vds is applied between the drain and source terminals of the driving transistor T1, and a driving voltage Voled is applied between the anode and the cathode of the organic EL element OLED.
Here, in order not to change the current Ids (expected value current) flowing between the drain and source terminals of the driving transistor T1 during the writing operation and the driving current Ioled supplied to the organic EL element OLED during the light-emitting operation, the operating point PMe Must be maintained in the saturated area of the characteristic line. Voled became the largest Voled(max) at the highest gray level. Thus, in order to maintain the aforementioned PMe in the saturation region, the value of the second power supply voltage Vcce must satisfy the condition of the formula (9).
Vcce-Vss≧Vpo+Voled(max)‧‧‧(9)
Here, when Vss is the ground potential of 0 V, it is (10).
Vcce≧Vpo+Voled(max)‧‧‧(10)
<Relationship between changes in characteristics of organic EL elements and voltage-current characteristics>
As shown in FIG. 4B, the organic EL element OLED is increased in resistance as the driving progresses, and changes in the direction in which the driving current Ioled decreases in the rate of increase of the driving voltage Voled. In other words, the direction in which the slope of the load line SPe of the organic EL element OLED shown in FIG. 8A decreases is changed. In the eighth drawing, it is noted that the load line SPe of the organic EL element OLED changes with the driving experience, and the load line changes from SPe → SPe2 → SPe3. As a result, the operating point of the driving transistor T1 thus moves in the direction of PMe→PMe2→PMe3 on the characteristic line SPh of the driving transistor T1 as the driving progresses.
At this time, when the operating point is in the saturation region on the characteristic line (PMe→PMe2), the driving current Ioled maintains the value of the expected value current during the writing operation. However, when entering the unsaturated region (PMe3), the driving current Ioled is written. The expected value current at the time of the input operation is reduced. In other words, since the difference between the current value of the drive current Ioled flowing into the organic EL element OLED and the current value of the expected value current during the write operation is significantly different, the display characteristics are changed. In Fig. 8B, the pinch-off point Po is at the boundary between the unsaturated region and the saturated region, that is, the potential difference between the operating point PMe and the pinch-off point Po at the time of light emission, and is used to maintain the light emission of the organic EL. The compensation range of the OLED drive current. In other words, in each of the Ioled levels, the potential difference on the characteristic line SPh of the driving transistor sandwiched between the track Po of the pinch-off point and the load line SPe of the organic EL element becomes the compensation range. As shown in FIG. 8B, the compensation range is reduced as the value of the drive current Ioled increases, and is applied to the power supply terminal. The voltage Vcce-Vss between the TMv and the cathode terminal TMc of the organic EL element OLED increases.
<Relationship between variation of TFT element characteristics and voltage-current characteristics>
Further, in the voltage gray scale control using a transistor suitable for the display pixel (pixel circuit portion), the drain voltage and the source-to-source voltage Vds and the drain of the transistor which are initially set in advance are used. The data voltage Vdata is set in the characteristic (initial characteristic) of the source-to-source current Ids. However, as shown in FIG. 4A, the threshold voltage: Vth is increased in response to the driving experience, and is supplied to the light-emitting element (organic EL element OLED). The current value of the light-emitting drive current does not correspond to the display data (data voltage), and the light-emitting operation cannot be performed with an appropriate gray scale. In particular, it is known that an electro-crystalline system is applied to an amorphous germanium transistor, and variation in device characteristics remarkably occurs.
Here, in the amorphous germanium transistor having the design value shown in Table 1, when the display operation of 256 gray scales is performed, the initial characteristics of the drain-to-source voltage Vds and the drain-source-source current Ids are shown. An example of (voltage-current characteristics).
The voltage-current characteristic in the n-channel amorphous germanium transistor, that is, the drain-to-source voltage Vds and the drain-source current Ids shown in FIG. 4A In the relationship, the driving experience and the change with time occur, and the gate electric field is offset against the gate electric field of the gate insulating film to cause an increase in Vth (from the initial state: SPw to the high voltage side: SPw2 shift) . As a result, when the drain voltage and the source-to-source voltage Vds applied to the amorphous germanium transistor are constant, the drain current and the source current Ids are reduced, and the luminance of the light-emitting element is lowered.
In the variation of the characteristics of the device, the voltage V-th of the amorphous germanium transistor is increased, and the voltage-current characteristic (VI characteristic line) of the amorphous germanium transistor is a shape in which the characteristic line in the initial state is substantially parallel. The VI characteristic line SPw2 can be a certain voltage corresponding to the variation amount ΔVth of the threshold voltage Vth (about 2 V in the figure) to the drain-to-source voltage Vds of the VI characteristic line SPw in the initial state ( The voltage-current characteristics corresponding to the compensation voltage Vpth) which will be described later are uniformly added in the same manner (that is, when the VI characteristic line SPw is moved by ΔVth in parallel).
In other words, when the display element is displayed on the display pixel (pixel circuit unit DCx), the element characteristics (predicted voltage) corresponding to the driving transistor T1 provided in the display pixel are added. A constant voltage (compensation voltage Vpth) of the amount of change ΔV is compensated by applying a corrected data voltage (corresponding to a grayscale designation voltage Vpix described later) to the source terminal (contact N2) of the driving transistor T1. When the voltage-current characteristic is shifted due to the fluctuation of the threshold voltage Vth of the driving transistor T1, the driving current Iem having the current value corresponding to the data to be displayed can be flowed into the organic EL element OLED, and the desired gray scale can be performed. Light action.
In addition, the holding operation of switching the hold control signal Shld from the on level to the off level may be performed synchronously, and the power supply voltage Vcc is applied from the voltage. Vccw is switched to the light-emitting action of voltage Vcce.
Next, an embodiment of a display device including a display panel in which a plurality of display pixels including an important portion of the pixel circuit portion are arranged in two dimensions is displayed will be specifically described.
<display device>
Fig. 9 is a schematic block diagram showing an embodiment of a display device of the present invention.
Fig. 10 is a view showing an essential part of a data driver (display driving device) and a display pixel (pixel driving circuit and light-emitting device) which can be applied to the display device of the embodiment.
Further, in Fig. 10, a part of a data driver for displaying a specific display pixel of a display panel of a display device and a light-emitting drive for controlling the display pixel will be described. Here, the symbols corresponding to the circuit configuration of the pixel circuit unit DCx (see FIG. 1) are collectively displayed. Further, for convenience of explanation, various signals, data, and applied voltages which are sent between the respective configurations of the data driver are displayed, and as will be described later, such signals, data, voltages, and the like are not limited to being simultaneously sent or applied.
As shown in FIG. 9 and FIG. 10, the display device 100 of the present embodiment includes a plurality of selection lines Ls disposed in the row direction (left-right direction of the drawing) and arranged in the column direction (pattern In the vicinity of each intersection of the plurality of data lines Ld in the vertical direction, an important portion including the pixel circuit portion DCx is arranged in a matrix of n columns × m rows (n, m is an arbitrary positive integer) (see The plural display of Fig. 1 shows the display area 110 of the pixel PIX; the selection drive of the selection signal Ssel is applied to each of the selection lines Ls at a specific timing. a driver 120; a power driver 130 that applies a power supply voltage Vcc of a specific voltage level at a specific timing on a plurality of power supply voltage lines Lv arranged in the row direction parallel to the selection line Ls; specific to each data line Ld The data driver (display driving device) 140 that supplies the gray scale designation signal (gray scale designation voltage Vpix); generates at least the control selection driver 120, the power source driver 130, and the data according to the timing signal supplied from the display signal generating circuit 160, which will be described later. The system controller 150 outputs the selection control signal, the power control signal, and the data control signal of the operating state of the driver 140; and generates display data composed of digital signals according to the image signal supplied from the outside of the display device 100 (luminance gray scale) The data is supplied to the data driver 140, and based on the display data, a timing signal (system clock, etc.) for displaying image information in the display area 110 is extracted or generated, and the display signal supplied to the system controller 150 is displayed. a generating circuit 160; and a display formed by a substrate provided with the display area 110, the selection driver 120, and the data driver 140 Panel 170.
In addition, in FIG. 9, the power source driver 130 is connected to the display panel 170 via a film substrate, but may be disposed on the display panel 170. Alternatively, one of the data drivers 140 may be disposed on the display panel 170, and the other portion may be outside the display panel 170, such as a structure connected via a film substrate. At this time, a part of the data driver 140 in the display panel 170 may be an IC chip, or may be configured by a transistor fabricated together with each transistor of a pixel driving circuit DC (pixel circuit portion DCx) to be described later. Further, the selection driver 120 may be an IC chip or may be constructed by a transistor fabricated together with each transistor of a pixel driving circuit DC (pixel circuit portion DCx) to be described later. to make.
Hereinafter, each of the above configurations will be described.
(display panel)
In the display device 100 of the present embodiment, a plurality of display pixels PIX arranged in a matrix form in the display region 110 at the center of the display panel 170 are provided. As shown in FIG. 9, the plural display pixel PIX is grouped into an upper area (upper side of the drawing) and a lower area (lower side of the drawing) of the display area 110, and the display pixel PIX included in each group is connected to the difference. Individual supply voltage lines Lv. Then, the respective power supply voltage lines Lv of the group in the upper region are connected to the first power supply voltage line Lv1, and the respective power supply voltage lines Lv of the group in the lower region are connected to the second power supply voltage line Lv2, the first power supply voltage line Lv1 and the second power supply. The voltage lines Lv2 are electrically independent of each other and are connected to the power source driver 130. In other words, the display pixel PIX of the first to n/2th columns (where n is an even number) in the upper region of the display region 110 is commonly applied with the power supply voltage Vcc via the first power supply voltage line Lv1. The display pixel PIX of the n/2+1~nth column of the region is supplied with the power supply voltage Vcc that is commonly applied via the second power supply voltage line Lv2, and is independently output to different groups by the power supply driver 130 at different timings. Power supply voltage line Lv.
(display pixels)
The display pixel PIX suitable for the present embodiment is disposed in the vicinity of the intersection of the selection line Ls connected to the selection driver 120 and the data line Ld connected to the data driver 140. As shown in FIG. 10, it has a current-driven type of illumination. The organic EL element OLED of the element is composed of an important portion including the pixel circuit portion DCx (see FIG. 1), and the organic EL element is driven for light emission. An OLED, and a pixel driving circuit DC that generates a light-emitting driving current.
The pixel driving circuit DC has a gate terminal connected to the selection line Ls, a 汲 terminal connected to the power supply voltage line Lv, and a source terminal connected to the transistor Tr11 of the contact N11 (a transistor for diode connection); The terminal is connected to the selection line Ls, the source terminal is connected to the data line Ld, the 汲 terminal is connected to the transistor Tr12 of the contact N12 (selective transistor); the gate terminal is connected to the contact N11, and the 汲 terminal is connected to the power supply a voltage line Lv, a source terminal connected to the transistor Tr13 of the contact N12 (driving transistor); and a capacitor Cs connected between the contact N11 and the contact N12 (between the gate and the source terminal of the transistor Tr13) Capacitor element).
Here, the transistor Tr13 corresponds to the driving transistor T1 shown in the first part of the pixel circuit portion DCx (Fig. 1), and the transistor Tr11 corresponds to the holding transistor T2, and the capacitor Cs corresponds to the capacitor Cx. The contacts N11 and N12 correspond to the contact N1 and the contact N2, respectively. Further, the selection signal Ssel applied from the selection driver 120 to the selection line Ls corresponds to the above-described hold control signal Shld, and the gray scale designation signal (gray scale designation voltage Vpix) applied from the data driver 140 to the data line Ld corresponds to the above Data voltage Vdata.
Further, the anode terminal of the organic EL element OLED is connected to the contact N12 of the pixel driving circuit DC, and a predetermined low voltage reference voltage Vss is applied to the cathode terminal TMc. Here, in the driving operation of the display device to be described later, the gray scale is applied from the data driver 140 during the writing operation period in which the gray scale designation signal (gray scale designation voltage Vpix) corresponding to the display data is supplied to the pixel drive circuit DC. Order specified voltage Vpix, reference voltage Vss, and The power supply voltage Vcc (=Vcce) applied to the high potential of the power supply voltage line Lv during the light-emitting operation satisfies the relationship of the above equations (3) to (10), and thus the organic EL element OLED is not lit at the time of writing.
In addition, the capacitor Cs may be a parasitic capacitance formed between the gate and the source terminal of the transistor Tr13, or may be a capacitor connected to the transistor Tr13 between the contact N11 and the contact N12 in addition to the parasitic capacitance. Both of these can be.
Further, the transistors Tr11 to Tr13 are not particularly limited. For example, an n-channel type amorphous germanium film transistor can be used by all of the n-channel type field effect type transistors. At this time, using the established amorphous germanium manufacturing technique, the pixel driving circuit DC composed of the amorphous germanium thin film transistor which is stable in element characteristics (electron mobility, etc.) can be manufactured in a relatively simple process. In the following description, the case where the n-channel type thin film transistor is applied to all of the transistors Tr11 to Tr13 will be described.
Further, the circuit configuration for displaying the pixel PIX (pixel driving circuit DC) is not limited to that shown in FIG. 10, and at least the driving transistor T1 and the holding transistor T2 corresponding to the first figure are provided. The element of the capacitor Cx may be connected to the current-driven light-emitting element (organic EL element OLED) in series with the current path of the driving transistor T1, or may have other circuit components. Further, the light-emitting element that is driven to emit light by the pixel driving circuit DC is not limited to the organic EL element OLED, and may be another current-driven type light-emitting element such as a light-emitting diode.
(select drive)
The selection driver 120 is controlled according to the selection supplied from the system controller 150. The display signal sets the display pixels PIX of the respective rows to the selected state by applying a selection signal Ssel of the selection level (the high level in the display pixel PIX shown in FIG. 10) to each of the selection lines Ls. Specifically, in the display pixel PIX of each row, in the threshold voltage detection period Tdec and the display operation period Twrt in the display driving period Tcyc, which will be described later, each row is sequentially executed at a specific timing to select the level. The selection signal Ssel of the (high level) is applied to the selection line Ls of the column, and the display pixels PIX of the respective rows are sequentially set to the selection state (selection period).
Further, the selection driver 120 is applicable to include a shift register that sequentially outputs a shift signal corresponding to the selection line Ls of each row in accordance with a selection control signal supplied from a system controller 150 to be described later; The signal is converted into a specific signal level (selection level), and the selection signal Ssel is sequentially output to the output circuit portion (output buffer) of the selection line Ls of each row. Here, as long as the driving frequency of the driver 120 is selected to be a range in which the amorphous germanium transistor can operate, a part or all of the transistors included in the selection driver 120 and the transistors Tr11 to Tr13 in the pixel driving circuit DC may be selected. Together they are manufactured as amorphous tantalum transistors.
(power driver)
The power source driver 130 performs a write operation in at least the operation period (the threshold voltage detection period Tdec and the display drive period Tcyc) in each of the power source voltage lines Lv in accordance with the power source control signal supplied from the system controller 150. In the period Twrt), a low-potential power supply voltage Vcc (=Vccw) is applied, and during the light-emitting operation, a power supply voltage Vcc (=Vcce>Vccw) higher than the low-potential power supply voltage Vccw is applied.
Here, in the present embodiment, as shown in FIG. 9, since the display pixels PIX are grouped into the upper region and the lower region of the display region 110, the individual power supply voltage lines Lv of the respective groups are arranged. The power driver 130 supplies the power supply voltage Vcc to the display pixel PIX arranged in the upper region via the first power supply voltage line Lv1 during the operation of the group in the upper region, and the second power supply voltage during the operation period of the group in the lower region. The line Lv2 outputs the power supply voltage Vcc to the display pixel PIX arranged in the lower area.
In addition, the power driver 130 is applicable to: a timing generator that generates timing signals corresponding to the power supply voltage lines Lv of the respective regions (groups) according to the power supply control signals supplied from the system controller 150 (for example, sequentially outputting the shift signals The shift register or the like, and the output circuit portion that converts the timing signal into a specific voltage level (voltage values Vccw, Vcce) and outputs the power supply voltage Vcc to the power supply voltage line Lv of each region. In the case of the first power supply voltage line Lv1 and the second power supply voltage line Lv2, when the number of lines is small, the power supply driver 130 may be disposed on one of the system controllers 150 without being disposed on the display panel 170.
(data drive)
The data driver 140 corrects the signal voltage (gray effective voltage Vreal) of each display pixel PIX supplied from the display signal generating circuit 160 to be described later in response to the display data (light grayscale data), corresponding to the use of the above-described light-emitting driving. a data voltage (gray scale designation voltage Vpix) of a voltage fluctuation (voltage characteristic inherent in the pixel drive circuit DC) caused by the light-emitting driving operation of each display pixel PIX of the transistor Tr13 (corresponding to the driving transistor T1), and via The data line Ld is supplied to each display pixel PIX.
As shown in FIG. 10, the data driver 140 is provided with a shift register. The data register unit 141 displays the data latch unit 142, the gray scale voltage generating unit 143, and the threshold detection voltage analog-digital converter (hereinafter simply referred to as "detection voltage ADC", which is denoted as "VthADC" in the figure) 144. a compensation voltage digital-to-analog converter (hereinafter referred to as "compensation voltage DAC", which is denoted as "VthDAC" in the figure) 145, and a threshold data latching portion (hereinafter referred to as "Vth data latching portion") 146, The frame memory 147, the voltage adding unit 148, and the data line input/output switching unit 149.
Here, the display data latch unit 142, the gray scale voltage generating unit 143, the detection voltage ADC 144, the compensation voltage DAC 145, the threshold data latch unit 146, the voltage adder unit 148, and the data line input/output switching unit 149 are arranged in columns. The data lines Ld are provided separately, and the display device 100 of the present embodiment is provided with m groups. Further, the shift register, the data register unit 141, and the frame memory 147 are provided with 1 or a complex array (<m group) in common for the plurality of rows of data lines Ld (for example, all rows).
The shift register and data register unit 141 includes: a shift register that sequentially outputs a shift signal according to a data control signal supplied from the system controller 150; and sequentially acquires the shift signal according to the shift signal A data register of luminance gray scale data composed of at least a digital signal supplied from the outside.
More specifically, any one of the following operations is selectively performed: sequentially, the display pixels PIX of the respective columns corresponding to the one column portion of the display region 110 are sequentially supplied from the display signal generating circuit 160 as serial data. Displaying data (bright grayscale data) and transferring them in parallel to the display data latching portion 142 provided in each column; or, by detecting the voltage ADC 144 Converting to a digital signal, and sequentially obtaining the threshold voltage (threshold detection data) of the display pixel PIX held in one column of the threshold data latching portion 146, and transferring it to the frame memory 147 The operation is performed by sequentially acquiring the threshold compensation data of the specific one column display pixel PIX from the frame memory 147 and transferring it to the threshold data latching unit 146. In addition, each of these actions is detailed later.
The display data latch unit 142 holds the column display pixels that are transferred from the outside by the shift register and the data register unit 141 in accordance with the data control signal supplied from the system controller 150. PIX display data (bright grayscale data).
The gray scale voltage generating unit (gray scale designation signal generating circuit, gray scale voltage generating unit, and non-light emitting display voltage applying circuit) 143 has a function of selectively supplying any one of the following voltages: for causing the organic EL element (current control type of light emission) The OLED has a gray-scale effective voltage Vreal having a specific voltage value corresponding to a luminance gray scale of the display material, or is set to a black display without causing the organic EL element OLED to perform a light-emitting operation (lowest The luminance-free grayscale state (no illumination operation) has a non-light-emitting display voltage Vzero having a specific voltage value.
Here, the gray-scale effective voltage Vreal having the voltage value corresponding to the display data is supplied, and is applicable to be provided in the display data latch unit in accordance with a gray-scale reference voltage supplied from a power supply circuit (not shown). a digital signal voltage of each of the display data of 142, converted into a digital-to-analog converter (D/A converter) of analog signal voltage; and at a specific timing, the analog signal voltage is input as the gray-scale effective voltage Vreal The composition of the output circuit. In addition, the gray scale effective voltage Vreal will be described later in detail.
Further, the non-light-emitting display voltage Vzero is written in order to generate the gray-scale designated voltage Vpix(0) generated by the voltage addition unit 148 by adding the compensation voltage Vpth as shown in a driving method (non-light-emitting display operation) to be described later. In the operation, the electric charge stored in the gate and the source terminal (capacitor Cs) of the light-emitting driving transistor Tr13 constituting the pixel driving circuit DC of the display pixel PIX is sufficiently discharged to cause the voltage between the gate and the source. Vgs (potential of both ends of the capacitor Cs) is at least equal to the threshold voltage Vth13 inherent in the transistor Tr13, and should be set to 0 V (or approximately 0 V), and set to any desired voltage value. Here, the gray scale reference voltage of the non-light-emitting display voltage Vzero and the write current Iwrt for generating the minute current value corresponding to the black display is supplied as in the above-described power supply circuit or the like, which is not shown.
The detection voltage ADC (voltage detection circuit) 144 acquires (detects) the light-emission drive transistor Tr13 that supplies the light-emission drive current to the light-emitting element (organic EL element OLED) provided in each display pixel PIX (pixel drive circuit DC). The threshold voltage (or the voltage component corresponding to the threshold voltage) is converted into a threshold detection data (voltage value data) composed of a digital signal voltage as an analog signal voltage.
The compensation voltage DAC (detection voltage application circuit, gray scale designation signal generation circuit, compensation voltage generation unit) 145 is constituted by a digital signal voltage for compensating for the threshold voltage of the above-described transistor Tr13 provided in each display pixel PIX. The threshold compensation data is generated by the analog signal voltage Recharge the voltage Vpth. Further, as shown in the driving method to be described later, the operation of the threshold voltage of the transistor Tr13 (the threshold voltage detecting operation) is performed by the detection voltage ADC 144, and the gate and source of the transistor Tr13 are used. The specific detection voltage Vpv can be outputted so that the potential difference between the terminals (the both ends of the capacitor Cs) is higher than the threshold voltage of the switching element of the transistor Tr13.
The threshold data latching unit 146 selectively performs any one of the following operations: each of the display pixels PIX of the one column portion is obtained by the threshold detection data generated by the conversion of the detection voltage ADC 144, and the threshold value is maintained. The detection data is sequentially transferred to the frame memory 147 described later via the shift register and the data register unit 141; or the frame memory 147 is sequentially obtained from the frame memory 147. The threshold value compensation data of each display pixel PIX of the column portion is held, and the threshold compensation data is transferred to the operation of the compensation voltage DAC 145.
The frame memory (memory circuit) 147 passes through the shift register and the data register unit 141 before the operation of writing the display data (luminance gray scale data) to each display pixel PIX arranged in the display area 110. According to the detection voltage ADC 144 and the threshold data latching unit 146, the threshold value detection data of the threshold voltage detected by each display pixel PIX of one column is used, one frame (one frame) Each of the display pixels PIX is individually memorized, and the threshold detection data is sequentially output as the threshold compensation data via the shift register and the data register unit 141, or the output threshold value is outputted. The threshold compensation data of the detection data is transferred to the threshold data latching portion 146 (compensation voltage DAC 145).
The voltage addition unit (gray-order designation signal generation circuit, arithmetic circuit unit) 148 includes a voltage component output from the gray-scale voltage generation unit 143 and a voltage component output from the compensation voltage DAC 145, and is switched via a data line input/output to be described later. The portion 149 outputs a function to the data line Ld disposed in the column direction of the display region 110. Specifically, when the threshold voltage detecting operation for detecting the threshold voltage in each display pixel PIX is provided, the detection voltage Vpv outputted from the compensation voltage DAC 145 is outputted, and the pixel PIX (light-emitting element) is displayed. In the gray scale display operation of the light-emitting operation, the gray-scale effective voltage Vreal output from the gray-scale voltage generating unit 143 is compared with the compensation voltage Vpth outputted from the compensation voltage DAC 145 (the gray-scale voltage generating unit 143 is provided with D/A conversion). When adding, the voltage component of the sum is output as the grayscale designation voltage Vpix, and the non-light-emitting display operation (black display operation) without the display of the pixel PIX (light-emitting element) is not performed. The non-light-emitting display voltage Vzero output from the step voltage generating unit 143 is added with the compensation voltage Vpth, and the non-light-emitting display voltage Vzero is also output as the gray-scale designation voltage Vpix(0) (=Vzero).
The data line input/output switching unit (signal path switching circuit) 149 includes a voltage detecting side switch SW1 for setting a threshold voltage of the light-emitting driving transistor provided in each display pixel PIX via the data line Ld. Or the voltage corresponding to the threshold voltage is obtained by the detection voltage ADC 144; and the voltage application side switch SW2 is for detecting the voltage Vpv selectively outputted from the voltage addition unit 148 via the data line Ld. The gray scale designation voltage Vpix or the gray scale designation voltage Vpix(0) (=Vzero) is supplied to each display pixel PIX.
Here, the voltage detecting side switch SW1 and the voltage application side switch SW2 can be configured by a field effect type transistor (thin film transistor) having different channel polarities. As shown in FIG. 10, the voltage detecting side switch SW1 can be applied to p. The channel type thin film transistor, in addition, the voltage application side switch SW2 can be applied to an n channel type thin film transistor. The gate terminals (control terminals) of the thin film transistors are connected to the same signal line, and the on and off states are respectively controlled according to the signal level of the switching control signal AZ applied to the signal lines.
Further, the wiring resistance and capacitance from the data line Ld to the voltage detecting side switch SW1 are set to be substantially equal to the wiring resistance and capacitance from the data line Ld to the voltage application side switch SW2, respectively. Therefore, since the voltage of the data line Ld falls, the voltage detecting side switch SW1 and the voltage application side switch SW2 are equal.
(system controller)
The system controller 150 supplies a selection control signal, a power control signal, and a data control signal for controlling the operating state to each of the selection driver 120, the power driver 130, and the data driver 140, and causes each driver to operate at a specific timing to generate The selection signal Ssel of a specific voltage level, the power supply voltage Vcc, the grayscale designation voltage Vpix, and the like are output, and a series of drive control operations (voltage application operation, voltage convergence) for each display pixel PIX (pixel driving circuit DC) are performed. The threshold voltage detecting operation of the operation and voltage reading operation and the display driving operation having the writing operation and the light emitting operation control the specific image information according to the image signal to be displayed on the display area 110.
(display signal generation circuit)
The display signal generating circuit 160 extracts a luminance gray scale signal component from a video signal supplied from the outside of the display device 100, and displays one column of each region of the display region 110, and uses the luminance grayscale signal component as a display material composed of a digital signal (luminance). The gray scale data is supplied to the shift register of the data driver 140 and the data register unit 141. Here, in the case where the video signal such as a television broadcast signal (mixed video signal) includes a timing signal component that defines a display timing of the image information, the display signal generating circuit 160 not only extracts the function of the luminance grayscale signal component, but also It may have a function of extracting the timing signal component and supplying it to the system controller 150. In this case, the system controller 150 generates respective control signals individually supplied to the selection driver 120, the power source driver 130, and the data driver 140 in accordance with the timing signals supplied from the display signal generation circuit 160.
<Drive method of display device>
Next, a driving method for performing gray scale display by causing a light-emitting element that displays a pixel to emit light in a display device having the above configuration will be described with reference to the drawings.
The driving operation in the display device 100 of the present embodiment substantially includes a threshold voltage detecting operation (threshold voltage detecting period), and any timing before the display driving operation (writing operation, lighting operation) to be described later. The threshold voltage Vth13 (inherent element characteristic) of the transistor Tr13 for light-emission driving of each display pixel PIX (pixel driving circuit DC) arranged in the display region 110 is measured, and each pixel PIX memory is displayed. And a display driving operation (display driving period), after the threshold voltage detecting operation is completed, by driving the light for driving in each display pixel PIX In the crystal Tr13, a voltage component which is written in a gray-scale effective voltage Vreal having a specific voltage value corresponding to the display data, and a threshold voltage which is inherent in the transistor Tr13 is a constant β times (compensation voltage Vpth=β Vth13) (β>1)), and the generated gray scale designates the voltage Vpix to cause the organic EL element OLED to emit light in response to the desired luminance gray scale of the data.
Hereinafter, each control operation will be described.
(probability voltage detection action)
Fig. 11 is a timing chart showing an example of a threshold voltage detecting operation applied to the driving method in the display device of the embodiment.
Fig. 12 is a conceptual diagram showing a voltage application operation applied to the driving method in the display device of the embodiment.
Fig. 13 is a conceptual diagram showing a voltage convergence operation applied to the driving method in the display device of the embodiment.
Fig. 14 is a conceptual diagram showing a voltage reading operation applied to the driving method in the display device of the embodiment.
Fig. 15 is a view showing an example of the current characteristics between the drain and the source when the gate-to-source voltage is set to a specific condition in the n-channel type transistor. Picture.
As shown in FIG. 11, the threshold voltage detection operation in the display device of the present embodiment is set to include a voltage application period (detection voltage application step) Tpv in the specific threshold voltage detection period Tdec, Voltage convergence period Tcv and voltage reading period (voltage detection step) Trv (Tdec≧Tpv+Tcv+Trv).
During the voltage application period Tpv, during the specific threshold voltage detection period In the Tdec, the voltage for detecting the threshold voltage (detection voltage Vpv) is applied to the display pixel PIX from the data driver 140 via the data line Ld, and is driven by the pixel driving circuit DC of the display pixel PIX. The voltage component corresponding to the detection voltage Vpv is held between the gate and the source terminal of the transistor Tr13 (that is, the charge corresponding to the detection voltage Vpv is stored in the capacitor Cs).
In the voltage convergence period Tcv, a portion of the voltage component (the charge stored in the capacitor Cs) held between the gate and the source terminal of the transistor Tr13 during the voltage application period Tpv is discharged, and only corresponds to the transistor Tr13. The voltage component (charge) of the threshold voltage Vth13 between the pole and the source current Ids is held between the gate and the source terminal of the transistor Tr13 (remaining in the capacitor Cs).
In the voltage reading period Trv, the voltage component held between the gate and the source terminal of the transistor Tr13 after passing through the voltage convergence period Tcv (the voltage value according to the charge remaining in the capacitor Cs; the threshold voltage Vth13) is measured. , converted into digital data, and stored (memorized) in a specific memory area of the frame memory 147.
Here, the threshold voltage Vth13 of the drain and the source-to-source current Ids of the transistor Tr13 is a drain of the transistor Tr13 by applying a slight voltage between the drain and the source terminal. The gate and source voltage Vgs of the transistor Tr13 at the operation boundary where the source-to-source current Ids starts to flow.
In particular, the threshold voltage Vth13 measured in the voltage reading period Trv of the present embodiment indicates that the threshold voltage of the transistor Tr13 in the initial state of manufacture is generated by the driving experience (light emission history), the use time, and the like. After the change (Vth shift), the threshold voltage at the time of the threshold voltage detection operation is executed.
Next, each operation period of the threshold voltage detecting operation will be described in more detail.
(during voltage application)
First, in the voltage application period Tpv, as shown in FIGS. 11 and 12, a selection level Ssel of a selection level (high level) is applied to the selection line Ls of the pixel driving circuit DC, and further, at the power supply voltage line Lv A low-potential power supply voltage Vcc (=Vccw) is applied. Here, the low-potential power supply voltage Vcc (=Vccw) only needs to be a voltage lower than the reference voltage Vss, and may also be a ground potential GND.
Further, in synchronization with the timing, the switching control signal AZ is set to a high level, the voltage application side switch SW2 is set to the ON state, and the voltage detection side switch SW1 is set to the OFF state, and by stopping or cutting off The gray scale voltage generating unit 143 outputs the detection voltage Vpv of the threshold voltage output from the compensation voltage DAC 145 via the voltage adder 148 and the data line input/output switching unit 149 (voltage application side switch SW2). Line Ld.
Thereby, the transistors Tr11 and Tr12 provided in the pixel driving circuit DC constituting the display pixel PIX are turned on, and the power supply voltage Vcc (=Vccw) is applied to the gate terminal of the transistor Tr13 via the transistor Tr11. One end side of the capacitor Cs (contact point N11), and the above-described detection voltage Vpv applied to the data line Ld is applied to the source terminal of the transistor Tr13 and the other end side of the capacitor Cs via the transistor Tr12 (contact point N12). .
Here, in the pixel PIX (pixel drive circuit DC), the n-channel type transistor Tr13 that supplies the light-emission drive current to the organic EL element OLED is a specific gate and source-to-source voltage Vgs. When verifying the variation characteristics of the drain and source-to-source current Ids when the buckling pole and the source-to-source voltage Vds are modulated, the characteristic map shown in Fig. 15 can be used.
In Fig. 15, the horizontal axis represents the partial pressure of the transistor Tr13 and the partial pressure of the organic EL element OLED connected in series, and the vertical axis represents the current value of the drain of the transistor Tr13 and the current Ids between the sources.
In the figure, one of the dotted lines is a boundary line between the gate and the source terminal of the transistor Tr13, and the left side of the boundary line is an unsaturated region, and the right side is a saturated region. The solid line indicates that the gate voltage and the source-to-source voltage Vgs of the transistor Tr13 are respectively fixed to the voltage Vgsmax when the light-emitting operation is performed at the highest luminance gray scale, and the luminance gray scale is irradiated with any (different) luminance gray scale below the highest luminance gray scale. When the voltages Vgs1 (<Vgsmax) and Vgs2 (<Vgs1) during the operation, the characteristics of the variation of the drain and the source current Ids at the time of the drain of the transistor Tr13 and the voltage Vds between the sources are modulated. The dotted line is a load characteristic line (EL load line) when the organic EL element OLED performs a light-emitting operation, and the voltage on the right side of the EL load line is a voltage between the power supply voltage Vcc and the reference voltage Vss (for example, 20 V in the figure) The partial pressure of the organic EL element OLED is such that the left side of the EL load line corresponds to the voltage Vds between the drain and source terminals of the transistor Tr13. The partial pressure of the organic EL element OLED increases with the gray scale of the luminance, in other words, as the current value of the drain of the transistor Tr13 and the current Ids of the source (the light-emitting driving current ≒ gray-scale current) increases, it gradually increases. .
In Fig. 15, the unsaturated region is even if the gate of the transistor Tr13 is When the source-to-source voltage Vgs is set to be constant, the drain-source and source-to-source voltages Vds of the transistor Tr13 increase, and the current value of the drain-to-source current Ids significantly increases (changes). In the saturation region, when the gate voltage and the source-to-source voltage Vgs of the transistor Tr13 are set to be constant, even if the drain-to-source voltage Vds is increased, the drain-to-source current Ids of the transistor Tr13 does not increase. And roughly keep it.
Here, in the voltage application period Tpv, the detection voltage Vpv applied from the compensation voltage DAC 145 to the data line Ld (more preferably, the source terminal of the transistor Tr13 of the pixel PIX (pixel driving circuit DC)) is much larger than the above-mentioned detection voltage Vpv. The power supply voltage Vcc (=Vccw) set to a low potential is low, and in the characteristic diagram shown in Fig. 15, the gate and source-to-source voltage Vgs of the transistor Tr13 is set to a drain which can obtain a region exhibiting saturation characteristics. The voltage value of the voltage Vds between the sources. In the present embodiment, the detection voltage Vpv may be set to a maximum voltage that can be applied from the compensation voltage DAC 145 to the data line Ld.
Further, the detection voltage Vpv is set to satisfy the following formula (11).
|Vgs-Vpv|>Vth12+Vth13‧‧‧(11)
In the above formula (11), Vth12 is a threshold voltage between the drain and source terminals of the transistor Tr12 when the selection signal Ssel of the on-level is applied to the gate terminal of the transistor Tr12. In addition, since a low-potential power supply voltage Vcc (=Vccw) is applied to both the gate terminal and the gate terminal of the transistor Tr13, and substantially equipotential to each other, the drain and source voltages of the Vth13-based transistor Tr13 are obtained. The threshold voltage is also the threshold voltage between the gate and source terminals of the transistor Tr13. In addition, although Vth12+Vth13 gradually increases with the passage of time, it is always set to satisfy the formula (11) (Vgs The potential difference of -Vpv) becomes large.
Thus, by applying a potential difference Vcp larger than the threshold voltage Vth13 of the transistor Tr13 between the gate and the source terminal of the transistor Tr13 (that is, at both ends of the capacitor Cs), a large current of the voltage Vcp is required. The detection current Ipv is forcibly flowed from the power supply voltage line Lv through the drain and source terminals of the transistor Tr13 to the compensation voltage DAC 145 of the data driver 140. Therefore, the charge corresponding to the potential difference according to the detection current Ipv (that is, the charging voltage Vcp in the capacitor Cs) is quickly stored at both ends of the capacitor Cs. Further, in the voltage application period Tpv, in addition to the charge stored in the capacitor Cs, in the other capacitance components forming or parasitic from the current path from the power source voltage line Lv to the data line Ld, the charge is also caused by flowing into the detection current Ipv. Storage.
At this time, since the reference voltage Vss (= GND) exceeding the power supply voltage Vcc (= Vccw) applied to the low potential of the power supply voltage line Lv is applied to the cathode terminal of the organic EL element OLED, the anode of the organic EL element OLED - The cathode is set to have no electric field state or reverse bias state, and the organic EL element OLED does not flow into the light-emission drive current, and does not perform the light-emitting operation.
(during voltage convergence)
Next, in the voltage convergence period Tcv after the end of the voltage application period Tpv, as shown in FIGS. 11 and 13, the selection signal Ssel of the on-level is applied to the selection line Ls, and further, the power supply voltage line Lv When the power supply voltage Vcc (=Vccw) of the low potential is applied, the switching control signal AZ is switched to the low level, the voltage detecting side switch SW1 is set to the ON state, and the voltage application side switch SW2 is set to the OFF state. Open state. Further, the detection of the detection voltage Vpv from the compensation voltage DAC 145 is stopped. Thereby, since the transistors Tr11 and Tr12 are kept in the ON state, the display pixel PIX (pixel driving circuit DC) maintains the electrical connection state with the data line Ld, but since the voltage is applied to the data line Ld, Therefore, the other end side (contact point N12) of the capacitor Cs is set to a high impedance state.
At this time, in the voltage application period Tpv, the gate voltage of the transistor Tr13 is held by the charge stored in the capacitor Cs (Vgs=Vcp>Vth13), since the transistor Tr13 remains in the on state and is in the drain Since the current continues to flow between the source terminals, the potential of the source terminal side of the transistor Tr13 (the contact point N12; the other end side of the capacitor Cs) gradually rises to a potential close to the 汲 terminal side (the power supply voltage line Lv side). .
Thereby, a part of the electric charge stored in the capacitor Cs is discharged, the gate voltage and the source-to-source voltage Vgs of the transistor Tr13 are lowered, and finally converge to the threshold voltage Vth13 of the transistor Tr13. Further, the drain and source-to-source current Ids of the transistor Tr13 are reduced, and finally the flow of the current is stopped.
In the voltage converge period Tcv, since the potential of the anode terminal (contact point N12) of the organic EL element OLED has a potential equal to or lower than the reference voltage Vss on the cathode terminal side, the organic EL element OLED is still absent. The organic EL element OLED does not emit light when a voltage or a reverse bias is applied.
(during voltage reading)
Next, in the voltage reading period Trv after the voltage convergence period Tcv has elapsed, as shown in FIGS. 11 and 14, similarly to the voltage convergence period Tcv, the selection signal Ssel is applied to the selection line Ls. In addition, A low-potential power supply voltage Vcc (=Vccw) is applied to the power supply voltage line Lv, and the detection voltage ADC 144 and the threshold data latch electrically connected to the data line Ld are connected in a state where the switching control signal AZ is set to a low level. The lock portion 146 measures the potential of the data line Ld (detection voltage Vdec).
Here, the data line Ld after the voltage convergence period Tcv is connected to the source terminal (contact point N12) side of the transistor Tr13 via the transistor Tr12 set to the ON state, and further, As described above, the potential on the source terminal (contact point N12) side of the transistor Tr13 corresponds to the potential on the other end side of the capacitor Cs in which the electric charge corresponding to the threshold voltage Vth13 of the transistor Tr13 is stored.
Further, the potential on the gate terminal (contact point N11) side of the transistor Tr13 is the potential of the one end side of the capacitor Cs storing the electric charge corresponding to the threshold voltage Vth13 of the transistor Tr13, and is set to The transistor Tr11 in the on state is connected to the state of the low-level power supply voltage Vcc.
Thereby, the potential of the data line Ld measured by the detection voltage ADC 144 corresponds to the potential of the source terminal side of the transistor Tr13 or the potential corresponding to the potential, and therefore, the set voltage is determined in advance based on the detection voltage Vdec. The difference (potential difference) of the low-potential power supply voltage Vcc (such as Vccw=GND) can detect the gate and source-to-source voltage Vgs of the transistor Tr13 (the potential across the capacitor Cs), that is, the threshold of the transistor Tr13 The value voltage Vth13 is a voltage corresponding to the threshold voltage Vth13.
Then, the threshold voltage Vth13 (analog signal voltage) of the transistor Tr13 thus detected is converted into a digital signal by the detection voltage ADC 144. After the threshold value detection data is temporarily held in the threshold data latching unit 146, the shift register and the data register unit 141 sequentially read each display pixel PIX of one column. The threshold detection data is stored (memorized) in a specific memory area of the frame memory 147. Here, the threshold voltage Vth13 of the transistor Tr13 of the pixel driving circuit DC of each display pixel PIX is varied (Vth shift) depending on the driving experience (lighting history) or the like in each display pixel PIX. Since the degree is different, the threshold detection data inherent to each display pixel PIX is memorized in the frame memory 147.
Further, in the driving method of the display device of the present embodiment, the series of threshold voltage detecting operations are sequentially performed at different timings for the display pixels PIX of the respective rows. Further, such a series of threshold voltage detecting operations are performed at any timing before the display driving operation to be described later, such as when the system (display device) is started and when the rest state is resumed, and the driving method is also described later. In the specific example, all of the display pixels PIX arranged in the display area 110 are executed during the specific threshold voltage detection period.
(display drive action: grayscale display action)
First, a driving method in which a light-emitting element emits light (a gray scale display operation) with a desired luminance gray scale in a display device and a display pixel having the above configuration will be described with reference to the drawings.
Fig. 16 is a timing chart showing a driving method when the gray scale display operation is performed in the display driving device of the embodiment.
Fig. 17 is a conceptual diagram showing a writing operation in the driving method (gray scale display operation) of the embodiment.
Fig. 18 is a conceptual diagram showing a holding operation in the driving method (gray scale display operation) of the embodiment.
Fig. 19 is a conceptual diagram showing a light-emitting operation in the driving method (gray scale display operation) of the embodiment.
As shown in FIG. 16, the display drive operation (gray scale display operation) in the display device of the present embodiment is set such that the display operation period cyc includes a write operation period (gray scale designation signal writing step) Twrt and a hold operation. During the period of Thld and the illuminating action (gray scale display step) Tem (Tcyc ≧ Twrt + Thld + Tem).
In the write operation period Twrt, the gray scale effective voltage Vreal according to the display data is applied to the display pixel PIX from the data driver 140 via the data line Ld during the specific display operation period cyc (one processing cycle period). The voltage of the specific compensation voltage Vpth (described later), such as the voltage applied to the gray-scale effective voltage Vreal plus the compensation voltage Vpth, as the gray-scale designation voltage Vpix, the write current according to the gray-scale designation voltage Vpix ( The drain and source current Ids of the transistor Tr13 for driving the light is supplied to the pixel driving circuit DC of the display pixel PIX, and is held (written) between the gate and the source terminal of the transistor Tr13, which will be described later. In the light-emitting operation, the light-emission drive current (drive current) Iem flowing from the pixel drive circuit DC to the organic EL element OLED is not affected by the fluctuation of the threshold voltage of the transistor Tr13, but can be illuminated in accordance with the luminance gray scale of the display data. The voltage component of the current value of the action.
In the sustain operation period Thld, the transistor Tr13 set in the pixel driving circuit DC set to the display pixel PIX is written by the writing operation. The voltage component of the gray scale designation voltage Vpix between the gate and the source terminal, in other words, the transistor Tr13 flows into the charge of the write current level, and is held in the capacitor Cs for a specific period.
During the light-emitting operation period Tem, the light-emitting drive current having the current value corresponding to the display data flows into the organic EL element OLED according to the voltage component (the charge stored in the capacitor Cs) held between the gate and the source terminal of the transistor Tr13. And the light-emitting action is performed with a specific brightness gray scale.
Here, the period required for displaying the image information of one pixel portion of one frame image in the pixel PIX is set in one processing cycle period of the display operation period cyc in the present embodiment. In other words, as described in the driving method of the display device to be described later, when one frame image is displayed in a display panel in which the plurality of display pixel PIXs are arranged in the row direction and the column direction, the above-described one processing is performed. The period period Tcyc is set to a period required for the display pixel PIX of one column to display one of the partial image images of one frame image.
Hereinafter, each operation period in which the driving operation is displayed will be described in more detail.
(during write operation)
First, in the write operation period Twrt, as shown in FIGS. 16 and 17, the selection driver L is applied from the selection driver 120 to the selection line Ls of the specific column of the display region 110 as shown in FIGS. 16 and 17 . A level (high level) selection signal Ssel, and a power source of a low potential is applied from the power source driver 130 to the power source voltage line Lv arranged in parallel with the selection line Ls in accordance with a power source control signal supplied from the system controller 150. Voltage Vcc (= Vccw ≦ reference voltage Vss; such as ground potential GND).
Thereby, the transistors Tr11 and Tr12 of the pixel driving circuit DC provided in the display pixel PIX of the column are turned on, and the low-potential power supply voltage Vcc (=Vccw) is applied to the transistor Tr13 via the transistor Tr11. The gate terminal (contact N11; one end side of the capacitor Cs), and the source terminal of the transistor Tr13 (contact N12; the other end side of the capacitor Cs) is electrically connected to the data line Ld via the transistor Tr12.
In addition, in synchronization with the timing, the switching control signal AZ supplied from the system controller 150 as a data control signal is set to a high level, the voltage application side switch SW2 is set to an ON state, and the voltage detection side switch SW1 is set to be off. Open state. Further, the voltage addition unit 148 outputs the compensation voltage Vpth generated by the compensation voltage DAC 145 in accordance with the data control signal supplied from the system controller 150 (compensation voltage generation step), and is temporarily stored in accordance with the slave display signal generation circuit 160. The display data (luminance gray scale data) obtained by the data storage unit 141 and the data latch unit 142 is output by the gray scale voltage generating unit 143 to generate a gray scale effective voltage Vreal having a specific voltage value (gray) Step voltage generation step).
In the voltage addition unit 148, the compensation voltage Vpth output from the compensation voltage DAC 145 is added to the gray-scale effective voltage Vreal output from the gray-scale voltage generating unit 143, and the sum of the voltage components is used as the gray-scale designation voltage Vpix via the data line. The voltage application side switch SW2 of the input/output switching unit 149 is applied to the data line Ld (gray scale designation signal writing step). Here, the voltage polarity of the gray scale designation voltage Vpix flows from the power source voltage line Lv via the transistor Tr13, the contact point N12, the transistor Tr12, and the data line Ld to the data driver 140 (voltage addition unit 148). Way and as follows The mode of the formula (12) is set to a negative polarity (Vpix < 0). In addition, the gray scale effective voltage Vreal is a positive voltage of Vreal>0.
Vpix=-(Vreal+Vpth)‧‧‧(12)
Thereby, as shown in FIG. 17, the gray scale designation voltage Vpix set to be lower than the power supply voltage Vcc (Vccw) via the data line Ld is applied to the source terminal side of the transistor Tr13 (contact point N12; capacitor The other end side of Cs) maintains a difference (Vccw-Vpix) corresponding to the power supply voltage Vcc of the gray-scale designated voltage Vpix and the low potential between the gate and the source terminal of the transistor Tr13 (both ends of the capacitor Cs). The voltage component Vgs (the voltage component corresponding to the grayscale designation voltage Vpix in the case where the power supply voltage Vcc is the ground potential GND) (the gray scale designation signal writing step).
In other words, a voltage component (compensation voltage Vpth) corresponding to the threshold voltage Vth13 inherent in the transistor Tr13 is generated by both ends of the capacitor Cs connected between the gate and the source terminal of the transistor Tr13. The potential difference of the sum of the gray-scale effective voltages Vreal (Vreal+Vpth), and the charge due to the potential difference is stored. In the address operation, the potential difference between the gate and the source terminal formed in the transistor Tr13 increases the voltage value of the threshold voltage Vth13 which is specific to the transistor Tr13. Therefore, the transistor Tr13 is turned on. The write current Iwrt flows from the power supply voltage line Lv to the data driver 140 (voltage adder 148) via the transistor Tr13, the contact N12, the transistor Tr12, and the data line Ld.
Here, in the write operation period Twrt, the compensation voltage Vpth output from the compensation voltage DAC 145 is individually detected in the frame memory 147 in accordance with the detection of the display pixel PIX in the above-described threshold voltage detection operation. The threshold detection data is set to a voltage value of the threshold voltage Vth13 which is specific to the transistor Tr13 of each display pixel PIX (pixel driving circuit DC). Specifically, as shown in the following formula (13), the threshold voltage Vth13 generated based on the above-described threshold detection data is set to a voltage β Vth13 which is a constant β times. Here, β is a constant of β>1.
Vpix=-(Vreal+Vpth)=-(Vreal+β Vth13)‧‧‧(13)
Thereby, the gray scale designation voltage Vpix of the total voltage of the compensation voltage Vpth and the grayscale effective voltage Vreal is applied to the display pixel PIX via the respective data lines Ld, so that the gate and the source terminal of the transistor Tr13 can be made. The voltage component of the current value of the light-emission drive current during the compensation light-emitting operation is maintained as shown below, and the voltage of the threshold voltage Vth13 of the transistor Tr13 at the time of the write operation is not compensated. ingredient.
In other words, as described above, the transistors Tr11 to Tr13 which are provided in the pixel driving circuit DC of the display pixel PIX are suitable for the amorphous semiconductor film of the n-channel type. Element characteristics of the phenomenon of the threshold voltage variation (Vth shift) of the crystal. Here, since the fluctuation amount of the threshold voltage in the Vth shift is caused by the driving experience and the use time of the thin film transistor, the amount of fluctuation of each thin film transistor is different.
Therefore, in the present embodiment, first, the light-emitting driving transistor Tr13 for setting the light-emitting luminance of the organic EL element (light-emitting element) OLED is set in each display pixel PIX by the threshold voltage detecting operation, individually. Detecting the threshold voltage at the time when the threshold voltage detection operation is performed, that is, the initial threshold voltage or the threshold voltage due to the Vth shift, and is stored in the frame memory as the threshold detection data. 147, secondly, the display When the pixel PIX writes the display data, the threshold voltage which is unique to each of the transistors Tr13 is added, and when it is set to correspond to the light-emitting operation, the light-emission drive current supplied to the organic EL element OLED via the transistor Tr13 is written. The voltage component of the current value of the brightness gray scale of the display data is held between the gate and the source terminal of each transistor Tr13.
Here, in the present embodiment, the gray scale designation voltage Vpix applied in the data driver 140 and applied via the data line Ld is held by the illumination driving of each display pixel PIX (pixel driving circuit DC). The voltage Vgs (Vccw = 0, source potential = -Vd) between the gate and the source terminal of the transistor Tr13 used is set to satisfy the following formula (14), and can compensate for the pixel driving circuit DC during the light-emitting operation. The current value of the light-emission drive current flowing into the organic EL element OLED.
Vgs=0-(-Vd)=Vd0+γ Vth13‧‧‧(14)
Here, the constant γ is defined as the following formula (15).
γ=(1+(Cgs11+Cgd13)/Cs)‧‧‧(15)
Vd0 in the above formula (14) is applied to the voltage Vgs between the gate and the source of the transistor Tr13 for driving light emission by the gray scale designation voltage Vpix outputted during the writing operation, according to the specified gray scale The voltage component that changes (digital bit), γ Vth13 depends on the voltage component of the threshold voltage. Here, Vd0 in the formula (14) corresponds to the first voltage component of the present invention, and γ Vth13 corresponds to the second voltage component of the present invention.
Here, in the 24th drawing to be described later, as shown by the equivalent circuit of the pixel driving circuit DC, the Cgs11-type contact N11 in the above formula (15) (that is, the source terminal of the transistor Tr11 and the transistor Tr13) Gate terminal) and contact N13 (i.e., the parasitic capacitance between the gate terminals of the transistors Tr11 and Tr12), and Cgd13 is the parasitic capacitance between the contacts N11 and N14 (i.e., between the gate of the transistor Tr13 and the gate terminal). In addition, in Fig. 24, the parasitic capacitance of the wiring of the Cpara-based data line Ld and the pixel parasitic capacitance of the Cpix-based organic EL element OLED. The relationship between the gray-scale designation voltage Vpix shown in the above formula (13) and the gate-to-source voltage Vgs of the transistor Tr13 shown by the formula (14) will be described later.
Thereby, even if the threshold voltage Vth13 of the transistor Tr13 is shifted by Vn due to the light-emission experience (driving experience) or the like (in other words, although the threshold voltage Vth13 fluctuates due to the Vth shift), it is still during the writing operation. The organic EL element OLED is rapidly written into the Twrt, and the voltage component of the light-emitting operation can be performed in accordance with the appropriate brightness gray scale of the displayed data. In other words, this embodiment does not compensate for the threshold voltage of the transistor Tr13 for light-emission driving during the writing operation, and compensates for the current value of the light-emission drive current supplied to the organic EL element OLED during the light-emitting operation.
In addition, at this time, since a low-potential power supply voltage Vcc (=Vccw) is applied to the power supply voltage line Lv, and a gray-scale designated voltage Vpix lower than the power supply voltage Vcc is applied to the contact N12, it is applied to the organic EL element OLED. Since the potential of the anode terminal (contact point N12) is equal to or lower than the potential of the cathode terminal (reference voltage Vss = GND), a reverse bias is applied to the organic EL element OLED, and current does not flow into the organic EL element OLED, and the light-emitting operation is not performed.
(during the action period)
Next, in the holding operation period Thld after the end of the writing operation, as shown in FIG. 16, the selection line in the above-described writing operation is performed. A selection signal Ssel of a non-selected level (low level) is applied to Ls, and as shown in FIG. 18, the transistors Tr11 and Tr12 are turned off, the diode connection state of the transistor Tr13 is released, and the transistor is cut off. The source terminal of the Tr13 (contact N12) is electrically connected to the data line Ld, and continues to be supplied to the organic EL element while being compensated for the light-emitting operation between the gate and the source terminal of the transistor Tr13 (both ends of the capacitor Cs). The state of the voltage component (Vgs=Vd0+γVth13) of the current value of the OLED light-emitting drive current. Further, in synchronization with the timing, the data driver 140 stops the output operation of the grayscale designation voltage Vpix corresponding to the display pixel PIX in which the address operation is performed (that is, the grayscale in the grayscale voltage generating section 143). The effective voltage Vreal and the output operation of the compensation voltage Vpth in the compensation voltage DAC 145).
Further, in the driving method of the display device of the present embodiment, as shown in a specific example of the driving method to be described later, the display pixel PIX for a specific column (for example, the i-th column; i is a positive integer of 1≦i≦n) In the holding operation period Thld after the completion of the above-described writing operation, the selection line Ls from the selection driver 120 to the next column (for example, the (i+1)th column) is sequentially applied at different timings. The level (high level) selection signal Ssel is set to the selected state after the next display pixel PIX, and the same write operation as described above is sequentially performed in the same manner as the display pixel PIX of the i-th column.
Thereby, in the holding operation period Thld of the display pixel PIX in the i-th column, the above-described holding operation is continued until the display pixel PIX of all the other columns in the same group to which the same power supply voltage Vcc is applied as shown in FIG. 9 is sequentially applied. Write the voltage component (grayscale specified voltage Vpix) corresponding to the displayed data.
(during the illuminating action)
Next, in the light-emitting operation period Tem after the end of the writing operation period Twrt, as shown in FIGS. 16 and 19, the selection signal Ssel of the non-selected level (low level) is applied to the selection line Ls of each row. The power supply voltage Vcc (=Vcce>Vss) which is higher than the reference voltage Vss of the light-emitting operation level (positive voltage) is applied to the power supply voltage line Lv of the display pixel PIX which is connected in common to each row.
Here, the power supply voltage Vcc (=Vcce) applied to the high potential of the power supply voltage line Lv is set to be larger than the transistor Tr13 by the potential difference Vcce-Vss as in the case of the seventh and eighth figures. The sum of the saturation voltage (pinch voltage Vpo) and the driving voltage (Voled) of the organic EL element OLED is large, and the transistor Tr13 operates in the saturation region. Further, by applying a voltage component (Vgs=Vd0+) set between the gate and the source terminal of the transistor Tr13 by the above-described address operation, the anode side (contact point N12) of the organic EL element OLED is applied. The positive voltage of γ Vth13), and the reference voltage Vss (such as the ground potential GND) is applied to the cathode terminal TMc, and the organic EL element OLED is set to a positive bias state. Therefore, as shown in Fig. 19, the power supply voltage line Lv is supplied from the power supply voltage line Lv. In the organic EL element OLED, in the organic EL element OLED, the light-emission drive current Iem (the drain and the source of the transistor Tr13) is set so as to be in accordance with the luminance gray scale of the display data (gray scale designation voltage Vpix). The current is Ids), and the light is emitted in a desired gray scale.
The illuminating operation continues for the next processing cycle period Tcyc until the start of the writing operation level from the power driver 130 (negative power) The timing of the power supply voltage Vcc (= Vccw).
In the driving method of the series of display devices, the holding operation will be described later, and after the display pixel PIX writing operation for all the columns in each group is completed, the display pixels PIX of the group are collectively illuminated. When driving control, it is set between the writing operation and the lighting operation. At this time, the length of the Thld during the hold operation is different for each line. Further, in the case where such drive control is not performed, the holding operation may not be performed.
As described above, when the display device and the display pixel of the present embodiment are used, the constant corresponding to the threshold voltage Vth13 is maintained between the gate and the source terminal of the transistor Tr13 during the writing operation of the display data. β times, and a voltage component (Vgs=Vcc=Vpix=Vd0+γVth13) corresponding to the sum of the gray-scale effective voltages Vreal (Vpix=-(Vreal+β Vth13)) corresponding to the displayed data, substantially has a response display The light-emission drive current Iem of the current value of the data (gray effective voltage Vreal) flows into the organic EL element (light-emitting element) OLED, and a driving method of a voltage gray scale designation method of performing a light-emitting operation with a specific luminance gray scale can be applied.
Therefore, compared with the gray scale designation method in which the display data is insufficiently written in response to the luminance gray scale (especially the low gray scale operation) when the light emitting element performs the light emitting operation, even in the low gray scale operation, the The grayscale designation signal (the grayscale designation voltage) is quickly written into each display pixel, and in all the luminance grayscales, an appropriate illumination operation corresponding to the display data can be realized.
Further, in the present embodiment, in the threshold voltage detecting operation performed before the display driving operation, the pixel driving circuit DC (the source of the transistor Tr13) applied to each display pixel PIX is applied during the voltage application period Tpv. The detection voltage Vpv of the terminal side) is configured and driven by the display device applied to the data line Ld from the compensation voltage DAC 145 via the voltage addition unit 148 and the voltage application side switch SW2. However, the present invention is not limited thereto. As described below, a dedicated power source for applying the detection voltage Vpv to the data line Ld may be provided.
Fig. 20 is a view showing the configuration of an essential part of another configuration example of the display driving device of the embodiment.
Here, the configuration that is the same as the above embodiment is omitted, and the description thereof is omitted.
As shown in FIG. 20, the display device of the configuration example includes a compensation voltage DAC 145a and a detection voltage source for outputting the detection voltage Vpv (see FIG. 10). The voltage application circuit 145b has a configuration, and the source of the voltage component to the voltage addition unit 148 has a compensation voltage DAC 145a (compensation voltage Vpth) and a gray scale voltage generation unit 143 (gray effective voltage Vreal, no light emission display voltage Vzero). In addition to this, the detection voltage source 145b (detection voltage Vpv) is connected.
Thereby, in the voltage application period Tpv, the detection from the detection voltage source 145b can be detected by controlling only the state of stopping or cutting off the output from the compensation voltage DAC 145a and the gray scale voltage generating unit 143. Since the voltage Vpv is applied to the data line Ld via the voltage adder 148, it is possible to suppress an increase in the processing load for outputting the detection voltage Vpv in the compensation voltage DAC 145a and to complicate the circuit configuration.
(display drive action: no light display action)
Next, a display device and display having the above configuration will be described with reference to the drawings In the pixel, a driving method is performed in the case of a non-light-emitting display (black display) operation in which the light-emitting element does not emit light.
Fig. 21 is a timing chart showing an example of a driving method when a non-light-emitting display operation is performed in the display device of the embodiment.
Fig. 22 is a conceptual diagram showing a write operation in the driving method (non-light-emitting display operation) of the embodiment.
Fig. 23 is a conceptual diagram showing the non-light-emitting operation in the driving method (non-light-emitting display operation) of the embodiment.
Here, the drive control equivalent to the above-described gray scale display operation is simplified or omitted.
In the display driving operation (non-light-emitting display operation) in the display device of the present embodiment, as shown in FIG. 21, after the threshold voltage detecting operation (threshold voltage detecting period Tdec), there will be charging or remaining. The voltage component of the gate and the source terminal (capacitor Cs) of the transistor Tr13 for driving the display pixel PIX is discharged, and can be kept far lower than the threshold voltage Vth13 inherent in the transistor Tr13. The non-light-emitting display voltage Vzero of a certain voltage value of the voltage component (more preferably 0V; the contact point N11 and the contact point N12 is equipotential) is applied to the data line Ld as the gray-scale designated voltage Vpix(0). In the operation period Tem, the transistor Tr13 is completely turned off, and the current supplied to the organic EL element OLED is cut off to perform a display driving operation (display driving period Tcyc) set to a non-lighting state.
That is, in order to realize such a voltage state, when the driving method of the current gray scale designation method is applied, it is necessary to supply a minute current value corresponding to the black display. The gray scale current is used for the write operation, and it takes a long time to sufficiently discharge the charge stored in the capacitor Cs to bring the gate voltage and the source-to-source voltage Vgs to a desired charge amount (voltage value). In particular, during the previous display driving period (one processing period), the writing operation period Twrt of Tcyc is stored in the capacitor Cs because the voltage component (potential at both ends) charged to the capacitor Cs is closer to the highest luminance gray scale voltage. The greater the amount of charge, the longer it takes to discharge the charge in order to reach the desired voltage value.
Therefore, in the display device of the present embodiment, as shown in FIG. 10, a gray-scale effective voltage Vreal for generating an organic EL element (light-emitting element) OLED for emitting light with a specific luminance gray scale corresponding to the display material is formed. In addition to the function of the gray scale voltage generating unit 143, the function of supplying the non-light-emitting display voltage Vzero for performing the darkest display (black display) operation without causing the organic EL element OLED to emit light is provided. At the lowest luminance gray scale (black display state), the non-light-emitting display voltage Vzero is applied to the data line Ld as the gray-scale designation voltage Vpix(0).
In addition, in the present embodiment, as shown in FIG. 22, the grayscale voltage generating unit 143 outputs a non-light-emitting display voltage Vzero, and the present invention is not limited thereto, such as a grayscale voltage. The generating unit 143 is further provided with a dedicated power source for outputting the non-light-emitting display voltage Vzero.
In the display driving operation after the threshold voltage detecting operation is completed, as shown in FIG. 21, the driving method in the display device having such a configuration is set to a specific display driving period (one processing cycle period). ) Tcyc contains: display voltage in the display pixel PIX by no light emission The gray scale designation voltage Vpix(0) formed by Vzero is held (residual) in the charge between the gate and the source terminal (both ends of the capacitor Cs) of the transistor Tr13 for light-emission driving of the pixel driving circuit DC. In the mean, the gate voltage and the source-to-source voltage Vgs of the transistor Tr13 are set to 0 V in the address operation period Twrt, and the gate and source-to-source voltage Vgs of the transistor Tr13 are set to 0 V. The holding operation period Thld; and the light-emitting operation period Tem (Tcyc≧Twrt+Thld+Tem) in which the organic EL element OLED is not subjected to the light-emitting operation (the non-light-emitting operation is performed).
In other words, similarly to the drive control operation when the gray scale display operation is executed, the write operation period Twrt, as shown in Fig. 22, is from the data driver 140 (the gray scale voltage generation unit 143), for example, with the low potential The gray scale designation voltage (no light-emitting display voltage) Vpix(0) of the power supply voltage Vcc (=Vccw) and the like is directly applied to the display pixel PIX (pixel) via the data line input/output switching unit 149 and the data line Ld. The gate and source terminal (capacitor Cs) of the transistor Tr13 for driving the driving circuit DC) are specifically applied directly to the source terminal side (contact point N12) of the transistor Tr13, and The gate-source voltage Vgs (the potential across the capacitor Cs) is set to 0V.
As described above, since substantially all of the charge stored in the capacitor Cs is discharged, the gate-to-source voltage Vgs of the transistor Tr13 is set to a voltage value (0 V) which is much lower than the threshold voltage Vth13 inherent to the transistor Tr13. Therefore, when the write operation period Twrt (including the hold operation period Thld) shifts to the light-emitting operation period Tem, even if the power supply voltage Vcc is indexed from the low potential (Vccw) to the high potential (Vcce), the gate potential of the transistor Tr13 (contact N11 As shown in Fig. 23, the transistor Tr13 is not turned on (holds off), and the light-emission drive current Iem is not supplied to the organic EL element OLED, and the light-emitting operation is not performed. Illumination state).
Thereby, substantially all of the charge stored in the capacitor Cs connected between the gate and the source terminal of the transistor Tr13 is discharged by supplying the gray scale current having the current value corresponding to the non-light-emitting display material via the data line Ld. In comparison with the method, the time required for the writing operation of the non-light-emitting display material can be shortened, and the non-light-emitting state of the organic EL element OLED (no light-emitting display operation) can be surely realized.
Therefore, in addition to the display driving operation for performing the above-described normal gray scale display, by controlling the display driving operation for performing the non-light-emitting display in response to the display of the material (the luminance gray scale data), the hope can be realized with high brightness and vividness. The illuminating action of the gray scale (such as 256 gray scale).
Further, in the display pixel PIX of the present embodiment, the transistors Tr11 to Tr13 provided in the pixel driving circuit DC shown in Fig. 10 are described as being applicable to the n-channel type amorphous germanium film transistor. It can also be used for polycrystalline germanium film transistors, and it can also be used for all p-channel amorphous germanium film transistors. Here, when all of the p-channel type is applied, the ON level, the OFF level, and the low inversion of each signal are set.
<Verification of Driving Method of Display Device>
Next, the driving method of the display device and the display driving device (data driver) is specifically verified.
The above embodiment is shown by the light-emitting element (organic EL) In the element OLED), a pixel drive circuit DC having a light-emission drive current Iem corresponding to the current value of the data to be displayed is supplied, and a threshold voltage Vth13 inherent in the transistor Tr13 for driving light emission detected in advance is applied via the data line Ld, Correcting the gray scale designation voltage Vpix (=-(Vreal+β Vth13)) generated in response to the gray scale effective voltage Vreal of the display data, and maintaining the gate and source terminals of the transistor Tr13 for flowing into the above A gray-scale control method of a voltage-specified type in which the voltage component Vgs (=Vd0+γVth13) of the light-emission drive current Iem is displayed in response to the current value of the data.
Here, when it is mounted on a mobile phone, a digital camera, a walkman, etc., when a panel having a small panel size and requiring high-definition image quality is reviewed, it may not be possible to reduce the size of each display pixel by formation. The area is set, and the set capacitor (storage capacitor) Cs is much larger than the parasitic capacitance of the display pixel. Therefore, when the voltage component (writing voltage) written and held in each display pixel fluctuates from the writing operation state to the lighting operation state, the transistor Tr13 for driving the light is driven in response to the parasitic capacitance. When the gate voltage and the source-to-source voltage Vgs fluctuate, the current value of the light-emission drive current Iem supplied to the light-emitting element (organic EL element OLED) fluctuates, and the display pixels (light-emitting elements) cannot be made in accordance with the appropriate luminance gray scale corresponding to the display data. The light-emitting action may cause deterioration of the display quality.
Specifically, in the display pixel PIX including the pixel drive circuit DC having the circuit configuration shown in the above embodiment (see FIG. 10), in order to control the transition from the write operation state to the light emission operation state, The selection signal Ssel applied to the selection line Ls is switched from a high level to a low level, and further, the power supply voltage Vcc applied to the power supply voltage line Lv is switched from a low level to a low level. The high level may vary in the voltage component held between the gate of the transistor Tr13 and the source terminal (capacitor Cs).
Therefore, in the present embodiment, the fluctuation of the threshold voltage Vth13 of the transistor Tr13 for light-emission driving is not directly compensated, and the grayscale designation voltage Vpix (=Vreal+βVth13) is applied to the write operation. The data line Ld is set to Vgs=Vd0 as shown in the above formula (14) by the gate-to-source voltage (that is, the voltage component held in the capacitor Cs) Vgs of the transistor Tr13 for light-emission driving. + γ Vth13 compensates the current value of the light-emission drive current Iem supplied to the light-emitting element (organic EL element OLED) at the time of the light-emitting operation.
Next, a specific derivation method is shown in order to define the gate and source-to-source voltage Vgs (=Vd) of the transistor Tr13 flowing into the light-emission drive current Iem of the light-emitting element (organic EL element OLED) during the light-emitting operation.
Fig. 24A and Fig. B are diagrams showing an equivalent circuit diagram of the capacitance component parasitic to the pixel driving circuit of the present embodiment.
25A, B, C, and D show an equivalent circuit diagram showing a change in the capacitance relationship between the pixel component of the pixel driving circuit of the present embodiment and the display voltage operation and the voltage operation during the light-emitting operation.
Fig. 26 is a simplified model circuit for explaining the charge amount invariance rule applied to the verification of the driving method of the display device of the embodiment.
The 27A and B drawings are model circuits for explaining the charge holding state in the display pixel to be applied to the verification of the driving method of the display device of the present embodiment.
In addition, for easy understanding, the power supply voltage will be written into the action. Vcc (=Vccw) is described as the ground potential as follows.
In the display pixel PIX (pixel driving circuit DC) shown in FIG. 10, at the time of the writing operation, as shown in FIG. 25A, the selection signal Ssel of the selection level (high level) is applied to the selection line Ls. (=Vsh), in a state where the low-voltage power supply voltage Vcc (=Vccw=GND) is applied, the data driver 140 (voltage adding unit 148) applies a negative voltage lower than the power supply voltage Vccw (= GND). The gray scale specifies the voltage Vpix.
Thereby, the transistors Tr11 and Tr12 are turned on, and the power supply voltage Vccw (= GND) is applied via the transistor Tr11 at the gate (contact point N11) of the transistor Tr13, and is at the source of the transistor Tr13. On the terminal (contact N12), a negative gray scale designation voltage Vpix is applied via the transistor Tr12, a potential difference is generated between the gate and the source terminal of the transistor Tr13, and the transistor Tr13 is turned on, and the write current is applied. Iwrt flows into the data line Ld from the power supply voltage line Lv to which the low-level power supply voltage Vccw is applied, via the transistors Tr13 and Tr12. The voltage component Vgs (write voltage; Vd) at which the current value of the current Iwrt should be written is held in the capacitor Cs formed between the gate and the source terminal of the transistor Tr13.
Here, in Fig. 25A, when the gate voltage (selection signal Ssel) of the Ggs11'-based transistor Tr11 changes from a high level to a low level, an effective parasitic capacitance occurs between the gate and the source terminal of the transistor Tr11, and the Cgd13 system When the voltage between the drain and the source of the transistor Tr13 for driving light is in a saturated region, the parasitic capacitance between the gate and the gate terminal of the transistor Tr13 for driving light is generated.
Secondly, in the light-emitting action, as shown in Fig. 25B, in the selection line Ls A selection signal Ssel of a non-selected level (low level) voltage (-Vsl<0) is applied, and a high-potential power supply voltage Vcc (=Vcce; such as 12-15 V) is applied, and the slave data driver 140 is cut off (voltage addition) The portion 148) applies a gray scale designation voltage Vpix to the data line Ld.
Thereby, the transistor Tr11 and Tr12 are turned off, the supply voltage Vcc is applied to the gate of the transistor Tr13 (contact point N11), and the source (contact point N12) of the transistor Tr13 is cut off. The gray scale designation voltage Vpix is maintained in the capacitor Cs due to the potential difference (0-(-Vd) generated between the gate and the source of the transistor Tr13 during the address operation, thereby maintaining the gate of the transistor Tr13. The potential difference between the pole and the source, the transistor Tr13 continues to be turned on, and the light source driving current Iem is applied to the gate of the transistor Tr13 and the voltage Vgs (=0-(-Vd) between the sources, from the power source to which the high potential is applied. The power supply voltage line Lv of the voltage Vcce flows into the organic EL element OLED via the transistor Tr13, and the organic EL element OLED emits light with a luminance gray scale corresponding to the current value.
Here, in FIG. 25B, the potential of the contact point N12 (Vn12-Vss) in the Voel-based light-emitting operation is the light-emitting voltage of the organic EL element OLED, and the gate voltage (selection signal Ssel) of the Cgs11-based transistor Tr11 is When the low level (-Vsl) occurs, the parasitic capacitance between the gate and the source terminal of the transistor Tr11 occurs. Further, the relationship between Cgs11' and Cgs11 described above is as shown in the formula (16). Cch11 is the channel capacitance of the transistor Tr11.
Cgs11'=Cgs11+1/2×Cch11×Vsh/Vsh1‧‧‧(16)
The voltage Vsh1 is a voltage difference (voltage range; Vsh1 = Vsh - (-Vsl)) between the high level (Vsh) and the low level (-Vsl) of the selection signal Ssel.
Further, in the writing operation of the above-described driving method, the voltage component Vgs (=0) is maintained between the gate and the source terminal of the transistor Tr13 for driving light emission by applying the grayscale designation voltage Vpix from the data driver 140. - (-Vd)) The voltage level of the setting selection signal Ssel and the power supply voltage Vcc is switched in accordance with the transition to the light-emitting operation state, and is varied as shown in the equation (17) ([Expression 1]). Here, in the present invention, when the voltage Vgs of the pixel driving circuit DC is changed as the voltage state applied to the display pixel PIX (pixel driving circuit DC) changes (transfers), The tendency to change is called "the voltage characteristic inherent in the pixel drive circuit."
In the above formula (17), cgd, cgs, and cgs' are normalized by the capacitance of the capacitor Cs, and cgd=Cgd13/Cs, cgs=Cgs11/Cs, cgs', respectively. =Cgs11'/Cs.
The equation (17) can be applied before and after switching of the control voltage (selection signal Ssel, power supply voltage Vcc) applied to each display pixel PIX (pixel driving circuit DC) by applying the "law of constant charge amount". Export.
In other words, as shown in Fig. 26, in the capacitance components (capacitors C1 and C2) connected in series, when the voltage applied to one end side is changed from V1 to V1', the charge amounts Q1 and Q2 of the capacitance components before and after the state change are obtained. And Q1' and Q2' can be expressed by the formula (18) ([Expression 2]).
In the formula (18), the "law of constant charge amount" is applied, and the relationship between the potentials V2 and V2' at the connection points between the capacitance components C1 and C2 is calculated by calculating -Q1+Q2=-Q1'+Q2'. It can be represented by the formula (19) ([Expression 3]).
Therefore, the potential derivation method similar to the above equations (18) and (19) is applied to the display pixel PIX (pixel driving circuit DC and organic EL element OLED) of the present embodiment, and the transistor Tr13 when switching the setting selection signal Ssel is reviewed. When the potential of the gate terminal (contact point N11) is Vn11, it can be represented by the equivalent circuit shown in Fig. 24A, Fig. 25, Fig. 25A~D to Fig. 27A, B, and therefore can be as follows (20) The formula is expressed by the formula (23) ([Expression 4]).
Here, FIG. 27A shows a charge holding state when a selection signal Ssel of a selection level (high level voltage Vsh) is applied to the selection line Ls, and a power supply voltage Vcc (=Vccw) of a low potential is applied, and FIG. 27B shows A selection signal Ssel of a non-selected level (low level voltage Vs1) is applied to the selection line Ls, and a charge holding state at a low potential power supply voltage Vcc (= Vccw) is applied.
(20) represents the capacitance components Cgs11, Cgs11b, Cgd13, and Cpix shown in Fig. 27A and B, and the amount of charge held in the capacitor Cs. The equation (22) indicates that the equation (20) is applied to the equation (21). The potentials Vn11 and Vn12 of the respective contacts N11 and N12 are calculated by the "law of constant charge amount".
Here, in Fig. 27B, the capacitance component Cgs11 between the contacts N11 and N13 is a gate and a source-parasitic capacitance Cgso11 other than the capacitance in the channel of the transistor Tr11, and in the 27A, the contact points N11 and N13 are provided. The capacitance component Cgs11b is defined as 1/2 of the channel capacitance Cch11 of the transistor Tr11. The sum of Cgs11 (=Cgso11) above (Cgs11b=Cch11/2+Cgs11). Further, Cgs11' in the formula (22) is defined as in the above formula (16), and D is defined as shown in the formula (23).
The method of deriving such a potential is applied to each process from the writing operation to the light-emitting operation of the present embodiment as described below.
Fig. 28 is a schematic flow chart showing the processes from the writing operation to the lighting operation in the display pixel of the embodiment.
When the driving method of the display device of the present embodiment is analyzed in detail, as shown in FIG. 28, it is possible to classify the selection signal Ssel by applying a selection level to the selection line Ls (contact N13 shown in FIG. 25). Writing a selection operation for the write operation of the voltage component corresponding to the display data (S101); applying the non-selection level selection signal Ssel, switching to the non-selected state non-selection state switching process (S102); maintaining the write voltage a non-selected state holding process of components (S103); a power supply voltage switching process of switching the power supply voltage Vcc from a writing operation level (low potential) to a lighting operation level (high potential) (S104); The luminance gray scale causes the light-emitting element to perform a light-emitting process of the light-emitting operation (S105). Alternatively, the non-selected state holding process (S103) may be omitted depending on the driving method, or the non-selected state switching process (S102) may be synchronized with the power supply voltage switching process (S104).
(Selection process S101 → non-selection state switching process S102)
Fig. 29A and Fig. B are equivalent circuit diagrams showing changes in the voltage relationship between the selection process and the non-selection state switching process in the display pixel of the embodiment.
Figure 29A shows the selection of the transistor Tr11, the transistor Tr12, and A state diagram in which the write current Iwrt flows between the drain and the source of the transistor Tr13, and FIG. 29B shows a state in which the transistor Tr11 and the transistor Tr12 are switched to a non-selection state. In Fig. 29A, the potentials of the contact N11 and the contact N12 are defined as Vccw (ground potential) and -Vd, respectively. In Fig. 29B, the potentials of the contact N11 and the contact N12 are defined as -V1, -V, respectively.
In the non-selected state switching process S102 in which the display pixel PIX shifts from the selected state (selection process S101) to the non-selected state, as in the equivalent circuit shown in FIGS. 29A and B, since the selection signal Ssel is from the high potential of the positive potential The quasi (Vsh) is switched to the low level (-Vsl) of the negative potential. Therefore, the gate and source voltages (potential difference between the contacts N11 and N12) Vgs' of the transistor Tr13 for driving the light are as described above (22). (23) and (16) to (24) ([Expression 5]), the voltage between the gate and the source of the transistor Tr13 from the write operation (contacts N11, N12) The potential difference between the two, that is, the write voltage) Vd, is expressed in the form of the voltage shift - ΔVgs. Further, the voltage shifting portion ΔVgs is expressed by Cgs11' CpixVsh1/D.
In other words, ΔVgs is a displacement of the potential difference between the contact point N11 and the contact point N12 when switching from the selected state to the non-selected state.
Here, in the non-selected state switching process S102, the capacitance component Cs' between the contacts N11 and N12 shown in FIG. 29B is a capacitance component formed outside the gate and source capacitance of the transistor Tr13. , (22), (23) As shown in Fig. 24B, the Cs shown in the equation is a gate-to-source parasitic capacitance Cgso13 other than the capacitance in the channel of the capacitor component Cs' and the transistor Tr13, and an intra-gate gate of the transistor Tr13 in the saturation region. The inter-source capacitance, that is, the sum of 2/3 of the channel capacitance Cch13 of the transistor Tr13 (Cs=Cs'+Cgso13+2Cch13/3), and the Cgd13 is between the gate and the drain in the channel in the saturated region. Since the capacitance is regarded as zero, it is only the gate-to-drain parasitic capacitance Cgdo13 other than the capacitance in the channel of the transistor Tr13. The Cgs11' shown in the formula (24) is defined as the gate and the inter-source parasitic capacitance Cgso11 other than the capacitance in the channel of the transistor Tr11, and the channel of the transistor Tr11 when Vds=0. The sum of the gate and source capacitances, that is, the sum of the voltage of the channel capacitance Cch11 of the transistor Tr11 and the voltage ratio of the selection signal Ssel (Vsh/Vsh1) (Cgs11'=Cgso11+Cch11Vsh/2Vsh1).
(non-selected state holding process S103)
30A and B are equivalent circuit diagrams showing changes in the voltage relationship of the non-selected state holding process in the display pixel of the embodiment.
In the state in which the potential of the contact point N12 is lower than the power supply voltage Vcc (Vccw) at a negative potential (-V), a state in which the drain current and the source current Ids flows into the transistor Tr13 is shown, and FIG. 30B is shown in FIG. A state diagram in which the potential of the contact point N12 rises as a result of the transistor Tr13 continuing to flow into the drain and source current Ids.
Thus, in the holding process of displaying the non-selected state of the pixel PIX, the equivalent circuit as shown in FIGS. 30A and B is transferred from the selection process (writing operation) to the non-selection process, and is held in the transistor Tr13. Gate, source The voltage Vgs' between the terminals (capacitance component Cs'), the transistor Tr13 continues to be turned on, and the drain-source-source current Ids flows from the drain of the transistor Tr13 to the source, and the voltage relationship changes to the transistor Tr13. The direction of the drain voltage (the potential of the contact N14) and the source voltage (the potential of the contact N12, Vn12) are not different. The time it takes for this change is ten μsec. Thereby, the gate potential V1' of the transistor Tr13 is affected by the change in the source potential, and the equations (22) and (23) are changed to the equation (25) ([Expression 6]).
The Cs" in the above formula (25) is as shown in Fig. 25D, and the internal gate and source capacitance of the transistor Tr13 when Vds=0 is added to the aforementioned Cs' and Cgso13, that is, One half of Cch13, and is shown in (26a).
Cs"=Cs'+Cgso13+Cch13/2=Cs-Cch13/6‧‧‧(26a)
In addition, as shown in FIG. 25C, Cgd13' is an intra-channel gate and a drain capacitance of the transistor Tr13 when Vds=0 is added to the aforementioned Cgd13, that is, one half of Cch13 is added, and is displayed on (26b) in the formula.
Cgd13'=Cgd13+Cch13/2‧‧‧(26b)
Further, -V1 and V1' in the equation (25) are not V1 and V1' shown in Fig. 26, but are potentials Vn11 of the contact point N11 in Fig. 30A and Fig. 30B, respectively.
Here, in the non-selected state retention process, the contact shown in Figure 30 The capacitance component Cgd13' between N11 and N14 is the sum of the gate capacitance of the transistor Tr13 other than the capacitance of the channel, the parasitic capacitance Cgdo13 between the drain electrodes, and the channel capacitance Cch13 of the transistor Tr13 (Cgd13'=Cgdo13+ Cch13/2=Cgd13+Cch13/2).
(Non-Selected State Holding Process S103 → Power Supply Voltage Switching Process S104 → Lighting Process S105)
31A, B, and C are equivalent circuit diagrams showing changes in the non-selected state holding process, the power supply voltage switching process, and the voltage relationship of the light-emitting process in the display pixel of the present embodiment.
Fig. 31A shows a state diagram in which the transistor Tr13 has no potential difference between the drain and the source, and does not flow into the drain and source Ids, and the 31st shows that the power supply voltage Vcc is switched from the low potential (Vccw) to the high potential. (Vcce) state diagram, FIG. 31C shows a state diagram in which the light-emission drive current Iem flows into the organic EL element OLED via the transistor Tr13.
Thus, in the process of switching the display pixel PIX from the non-selected state holding process to the power supply voltage, as shown in the 31A-C equivalent circuit, the drain of the transistor Tr13 is maintained during the non-selected state maintaining process. After the source-to-source voltage is changed (or approximated) by 0V, during the power supply voltage switching, since the power supply voltage Vcc is switched from the low potential (Vccw) to the high potential (Vcce), the gate terminal of the transistor Tr13 The potentials Vn11 and Vn12 of the sub- (contact point N11) and the source terminal (contact point N12) rise, respectively, and can be expressed by the equation (27) ([Expression 7]).
In the above formula (27), V1" and V" are the potential Vn11 of the contact point N11 and the potential Vn12 of the contact point N12 in Fig. 31B, respectively.
Next, in the process of displaying the pixel PIX, the equivalent circuit shown in FIGS. 31B and C is converges by the potential Vn11 generated at the gate terminal (contact N11) of the transistor Tr13 by the power supply voltage switching process. The voltage V1" and V" shown by the above formula (27) can be expressed by the formula (28) ([Expression 8]).
V1c in the above formula (28) is the potential Vn11 of the contact point N11 in Fig. 31C, respectively.
As described above, in the voltage change from the writing operation to the light-emitting operation shown in FIG. 25, all of the voltage components described in the above equations (24) to (28) are rewritten to be in the non-selected state switching process. The voltage sign in the middle, the gate voltage and the source voltage Vgs of the transistor Tr13 for illumination driving can be from the above (24) The formula is expressed as (29). Further, in the formula (29), V is expressed from the formula (22), and ΔVgs is recombined from the equation (24) into the equation (30) ([Expression 9]).
The Vd in the above formula (29) is generated by the voltage between the gate and the source of the transistor Tr13 at the time of writing, and the potential of the contact N12 in FIG. 29A is -Vd, and ΔVgs is switched from the 29th diagram. The change in potential difference between the contact point N11 and the contact point N12 in the case of Fig. 29B.
Next, in accordance with the above formula (29), the influence of the threshold voltage Vth on the gate voltage and the inter-source voltage Vgs of the transistor Tr13 for light-emission driving (Vth dependency of Vgs) is examined.
In the above formula (29), when the values of ΔVgs, V, and D are substituted for the finishing, the following formula (31) is obtained, and in the formula (31), the capacitance components Cgs11, Cgs11', and Cgd13 are represented by capacitance components. The Cs is normalized and reorganized, and the following formula (32) can be derived.
Here, the capacitance components Cgs11, Cgs11', Cgd13, Cs are all the same as those shown in the above-described non-selection state switching process. (32), The first term on the right side depends on the specified gray scale according to the display data and the threshold voltage Vth of the transistor Tr13, and the second term on the right is a constant term applied to the gate and source voltage Vgs of the transistor Tr13. The voltage-specified compensation Vth, that is, in order to form Vgs-Vth (the value of the driving current Ioel at the time of light emission) at the time of light emission does not depend on the form of Vth, and solves how to determine the source potential of -Vd at the time of writing. problem.
If Vgs=0-(-Vd)=Vd is maintained while illuminating, Vgs-Vth=Vd0+Vth-Vth=Vd0 is obtained in order to form Vd=Vd0+Vth without Vgs-Vth depending on Vth. The illuminating current is expressed only by Vd0 which does not depend on Vth. Further, in the case where the Vgs during writing is changed from the time of writing, in order to form Vgs-Vth in the case of light emission, Vd=Vd0+εVth is required.
Here, cgd, cgs, and cgs' of the above formula (32) are identical to cgd, cgs, and cgs' of the formula (17).
In the above formula (32), the dependence of the luminescence voltage Voel of the organic EL element OLED included in the first item on the right side is strictly determined by the relationship shown in the following formula (33). Here, in the formula (33), f(x), g(x), and h(x) respectively show a function of the coefficient x, and the gate and source voltage Vgs of the transistor Tr13 can be used as the illuminating voltage Voel. The function indicates that the illuminating drive current Iem can be expressed as a function of (Vgs-Vth13), and the illuminating voltage Voel can be expressed as a function of the illuminating driving current Iem, and the illuminating voltage Voel of the organic EL element OLED also has parasitic display pixels. The capacitance component of the PIX (pixel driving circuit DC) depends on the characteristic of the threshold voltage Vth13.
As described above, in the address operation, the source voltage (the contact point N12) of the transistor Tr13 for driving the light is supplied with the data voltage of the voltage component (gray scale voltage) according to the display data, and is not dependent on the data voltage. The term Vth is Vd0, and the threshold voltage of the transistor Tr13 at time t1 is Vth(t1), and the threshold voltage at time t2 which is sufficiently late than time t1 is Vth(t2), and is applied at time t1. When the organic EL element OLED is in the light-emitting operation, the anode-cathode is Voel1, and when the anode-cathode of the organic EL element OLED is applied to the light-emitting operation at time t2, it is Voel2. Vth(t2)>Vth(t1), and when the voltage difference of the organic EL element OLED applied to the light-emitting operation at time t2 and time t1 is ΔVoel=Voel2-Voel1, in order to compensate for the fluctuation of the threshold voltage ( Vth shift) ΔVth, by compensating for Vth, ΔVoel is infinitely close to 0. In the above formula (32), it is only necessary to set the write voltage Vd included in the first term on the right side as in (34).
Vd≒Vd0+(1+c Gs +c Gd )△Vth‧‧‧(34)
In the above formula (34), when the threshold voltage variation ΔVth is a difference from the threshold voltage Vth13=0, it can be expressed as ΔVth=Vth13, and since cgs+cgd is a design value, The constant ε is defined as ε = 1 + cgs + cgd, and the voltage component Vd can be expressed by the following formula (35). Further, when the threshold value variation of the initial state of each of the transistors Tr13 in the display region 110 is also regarded as one of ΔVth, it is considered to be a change from Vd0.
Vd≒Vd0+(1+c Gs +c Gd )△Vth=Vd0+ε△Vth‧‧‧(35)
According to the equation (35), the equation (36) is obtained from the above equation (32), and a voltage relational expression that does not depend on the threshold voltage Vth13 of the transistor Tr13 can be derived. Further, in the formula (36), the illuminating voltage Voel of the organic EL element OLED when the threshold voltage Vth13=0V is Voel=Voel0. The above formulas (14) and (15) are derived from the formula (35).
Here, in the black display state of the 0th gray scale, the condition that the voltage of the threshold voltage Vth13 or more is not applied between the gate and the source terminal of the transistor Tr13 is obtained (that is, the organic EL element OLED does not flow in). When the voltage condition of the light-emission drive current Iem is), it can be expressed as (37). Thereby, in the non-light-emitting display operation shown in FIG. 22, the non-light-emitting display voltage Vzero output from the gray-scale voltage generating unit 143 of the data driver 140 can be specified (determined).
-Vd0(0)=Vzero≧cgdVcce-cgs' Vsh1‧‧‧(37)
Next, the grayscale designation voltage Vpix outputted by the data driver 140 of the present embodiment is reviewed.
Fig. 32 is an equivalent circuit diagram showing the voltage relationship at the time of the writing operation in the display pixel of the embodiment.
In order to compensate for the portion shifted by the gate and source voltages Vgs of the transistor Tr13 for light-emission driving due to other parasitic capacitances, etc., during the writing operation period Twrt (gray scale designation) In the application time of the voltage Vpix, the gray scale designation voltage Vpix output from the voltage adder 148 is set to the following equation (48).
Vpix=-(Vd+Vds12)=-Vreal-β Vth13‧‧‧(38)
Here, the Vds12 is a drain-to-source voltage of the transistor Tr12.
In the write operation shown in Figure 32, the inflow transistor can be The write current Iwrt between the drains and source terminals of Tr13 and Tr12 is expressed by equations (39) and (40), respectively.
Further, Vdse12 and Vsat12 can be defined by the following formula (41) according to the above formulas (39) and (40).
Here, in the equations (39) to (41), the mobility of the μFET-based transistor, the capacitance of the transistor gate per unit area of the Ci system, and the channel width and channel length of the transistor Tr12 by W12 and L12, respectively, W13 L13 is the channel width and channel length of the transistor Tr13, the voltage between the drain and the source of the Vds12-type transistor Tr12, the threshold voltage of the Vth12-type transistor Tr12, and the effective voltage of the transistor Tr13 when the Vdse13 is written. The voltage between the drain and the source, p and q are intrinsic parameters (fitting parameters) suitable for the characteristics of the thin film transistor. Further, in the formula (40), the drain of the transistor Tr12 and the voltage Vdse12 between the sources are defined as (41). In the equations (39) and (40), in order to distinguish the transistor Tr12 from the transistor The threshold voltage of Tr13 is denoted as Vth12 and Vth13, respectively. Vsat12 is an effective drain and source voltage of the transistor Tr12 at the time of writing.
In addition, due to the shift amount of the threshold voltage of the n-channel amorphous germanium transistor, the longer the transistor is in the on state (the time when the voltage between the gate and the source is positive), the longer the tendency is. Therefore, the transistor Tr13 is turned on in the light-emitting operation period Tem in which the ratio in the Tcyc is high during one processing cycle period, and the threshold voltage is further shifted to the positive side voltage as time passes, and the resistance is easily increased. Further, since the transistor Tr12 is in the ON state in the selection period Tsel in which the ratio in the Tcyc is low during only one processing cycle, the threshold value of the threshold value is smaller than that of the transistor Tr13. Therefore, in the above-described method of deriving the gray-scale designation voltage Vpix, since the fluctuation of the threshold voltage Vth12 of the transistor Tr12 is small, the fluctuation of the threshold voltage Vth13 of the transistor Tr13 is negligibly small, and therefore, it is not changed. To handle.
Thus, equations (39) and (40) are fitted by the TFT characteristics of q and p, and the transistor size parameters (W13, L13, W12, L12), the gate thickness of the transistor, and the mobility of the amorphous germanium. The processing parameters and the voltage setting value (Vsh) are formed.
Then, by numerically analyzing the Iwrt of the formula (39) and the equation of the Iwrt of the formula (40), the threshold of the drain and the source Vds12 of the transistor Tr12 can be obtained from Vpix=-Vd-Vds12. The grayscale specified voltage Vpix is derived.
When the voltage addition unit 148 outputs the obtained gray scale designation voltage Vpix in the address operation period Twrt, -Vd is written in the source (contact point N12) of the transistor Tr13. Thus, the gate of the Twrt transistor Tr13 during the write operation The pole-source-to-source voltage Vgs and the drain and source-to-source current Ids=0-(-Vd)=Vd0+εΔVth of the transistor Tr13 can compensate for the influence of parasitic capacitance and the like during the light-emitting operation period Tem. The write current Iwrt of the drive current Ioled of the shift portion flows in during the write operation period Twrt.
Next, the specific experimental results are shown to explain the effects of the display device and the driving method thereof according to the present embodiment.
Fig. 33 is a characteristic diagram showing the relationship between the data voltage of the input data and the effective voltage of the gray scale in the writing operation of the display pixel of the embodiment.
As described above, in the address operation, the potential of the source terminal (contact N12) is generated by writing the voltage component Vgs held between the gate and the source terminal of the transistor Tr13 for driving the light-emitting (- Vd) is set (determined) according to the above formula (14) based on the constant γ times of the data voltage Vd0 and the threshold voltage Vth13 (Vd=-Vd0-γ Vth13).
Further, the grayscale designation voltage Vpix generated in the data driver 140 (voltage addition unit 148) is set (determined) according to the constant β times of the grayscale effective voltage Vreal and the threshold voltage Vth13 as shown by the equation (13). (Vpix=-Vreal-β Vth13).
In the above formulas (14) and (13), when the relationship between the data voltage Vd0 which does not depend on the constants γ, β and the threshold voltage Vth13 and the gray-scale effective voltage Vreal is verified, as shown in FIG. 33, corresponding to The change tendency of the input data (specified gray scale) of the gray-scale effective voltage Vreal generated by the gray-scale voltage generating portion 143 of the data driver 140 is used for displaying the pixel PIX (pixel driving circuit DC) A data voltage of a voltage component (gray scale voltage) corresponding to the display data (input data) is given to the source terminal of the crystal Tr13 The change in the input data of Vd0 tends to have a higher voltage difference in the high gray scale region. Specifically, in the 0th gray scale (black display state), the data voltage Vd0 and the gray scale effective voltage Vreal are both Vzero (=0 V), and in the 255th gray scale (highest luminance gray scale), the data voltage Vd0 and gray The order effective voltage Vreal produces a voltage difference of 1.3 V or more. The larger the Vpix is, the larger the current value at the time of writing, and the voltage between the source and the drain of the transistor Tr12 is also increased.
Here, in the verification experiment shown in Fig. 33, the power supply voltage Vcc (= Vccw) at the time of the write operation is the ground potential GND (=0 V), and the power supply voltage Vcc (= Vcce) at the time of the light-emitting operation is 12 V. The voltage difference (voltage range) Vsh1 between the high level (Vsh) and the low level (-Vsl) of the selection signal Ssel is 27V, and the channel width W13 of the transistor Tr13 for light emission driving is 100 μm, the transistor Tr11 and the transistor Tr12 The channel width W11, W12 is 40 μm, the pixel size is 129 μm × 129 μm, the numerical aperture of the pixel is 60%, and the display pixel PIX of the capacitor (storage capacitor) Cs is 600 fF (= 0.6 pF). .
Fig. 34 is a characteristic diagram showing the relationship between the grayscale designation voltage and the threshold voltage of the input data in the writing operation of the display pixel of the embodiment.
Next, in the above formula (13), the gray scale designation voltage Vpix depending on the constant β and the threshold voltage Vth13 is verified under the same experimental conditions as in the case of the above-mentioned Fig. 33, as shown in Fig. 34. As shown, the change tendency of the input data (specified gray scale) of the gray scale designation voltage Vpix generated by the voltage addition unit 148 of the data driver 140 is set to a constant β. At the time of constant value, as the threshold voltage Vth13 becomes larger, the voltage value of the grayscale designation voltage Vpix decreases to the extent of the threshold voltage Vth13 in all the grayscale regions. Specifically, when the constant value β is set to β=1.08, and the threshold voltage Vth13 is changed from 0 V→1 V→3 V, the characteristic line in each threshold voltage Vth13 of the grayscale designation voltage Vpix is specified. Move in parallel in the low voltage direction. Further, in the 0th gray scale (black display state), the gray scale designation voltage Vpix is Vzero (=0 V) regardless of the threshold voltage Vth13.
35A and B are diagrams showing the input data in the light-emitting operation of the display pixel of the embodiment (the grayscale value of the displayed data, where the lowest luminance grayscale is "0", and the highest luminance grayscale is "255"). A characteristic diagram of the relationship between the illuminating drive current and the threshold voltage.
Next, the gray scale designation voltage Vpix shown in the above formula (13) is applied from the data driver 140 to each display pixel PIX (pixel driving circuit DC), and the gate and source terminals of the transistor Tr13 for light emission driving are applied. When the voltage component Vgs (write voltage; 0-(-Vd)=Vd0+γVth13) shown in the above formula (14) is written and written, the light-emission drive to the organic EL element OLED is driven when the light-emitting operation is performed. When the dependence of the constant γ of the current Iem and the threshold voltage Vth13 of the transistor Tr13 is verified by the same experimental conditions as those in the above-described FIG. 33, as shown in FIG. 35, it is found that the constant γ is set to be rough. In the case of a certain value, in each of the gray scales, the light-emission drive current Iem having a substantially equal current value is supplied to the organic EL element OLED regardless of the threshold voltage Vth13.
Specifically, the constant γ is set to γ as shown in Fig. 35A. =1.07, when the threshold voltage Vth13 is set to 1.0V, the constant γ is set to γ=1.05 as shown in Fig. 35B, and when the threshold voltage Vth13 is set to 3.0V, a comparison review is made. As for the limit voltage Vth13, a characteristic line having substantially the same characteristics is obtained, and as shown in Table 2, the luminance change (luminance difference) with respect to the theoretical value in all the gray-scale regions is suppressed to 1.3% or less in outline. Here, in the present patent application, the voltage component Vgs (writing voltage; 0-(-Vd)=Vd0+γVth13) which is constant according to the constant γ shown in the formula (14) is written by writing as described above. In addition, the luminance change (luminance difference) of the theoretical value in each gray scale is suppressed to 1.3% or less in general, and it is expediently described as "γ effect" for convenience of explanation.
36A, B, and C are characteristic diagrams showing the relationship between the light-emission drive current and the threshold voltage (Vth shift) of the input data in the light-emitting operation of the display pixel of the present embodiment.
Next, when the dependence of the γ effect on the fluctuation of the threshold voltage Vth13 (Vth shift) is verified, as shown in FIGS. 36A to 36C, when the constant γ is set to a constant value, the threshold voltage Vth13 is determined. The larger the variation (Vth shift), the higher the gray level, and the initial threshold voltage Vth13 The smaller the difference between the current values of the optical drive current Iem.
Specifically, when the constant γ is set to γ=1.1, and the comparison check is performed to change the threshold voltage Vth13 from 1.0 V to 3.0 V as shown in FIGS. 36A and B, as shown in FIGS. 36A and 36C, When the limit voltage Vth13 is changed from 1.0V to the characteristic line when it is set to 5.0V, it is determined that the larger the variation (Vth shift) of the threshold voltage Vth13 is, the closer the characteristic line is. As shown in Table 3, the outline is all gray scales. The luminance change (luminance difference) of the region with respect to the theoretical value is suppressed to be extremely small (to be roughly 0.3% or less).
Here, in order to demonstrate the superiority of the effect of the present embodiment, a voltage component that does not depend on the constant γ in the above formula (14) is written and held between the gate and the source terminal of the transistor Tr13 for driving light emission. In the state of Vgs (write voltage; 0-(-Vd)=Vd0+Vth13), the experimental results when the threshold voltage Vth13 is set differently are reviewed as a comparative example.
37A and B are characteristic diagrams showing the relationship between the light-emission drive current and the threshold voltage of the input data (Comparative Example) when the γ effect of the present embodiment is not provided.
Specifically, even if the constant γ (=1+(Cgs11+Cgd13)/Cs=1+cgs+cgd) is set to γ=1.07 as shown in Fig. 37A, the threshold will be imposed. When the value voltage Vth13 is set to 1.0 V and 3.0 V, or the constant γ is set to γ=1.05 as shown in FIG. 37B, and the threshold voltage Vth13 is set to 1.0 V and 3.0 V, it is determined that each ash is obtained. Regardless of the constant γ, the higher the threshold voltage Vth13 of the transistor Tr13 is, the smaller the current value of the illuminating drive current Iem is, and as shown in Table 4, it is shown in the general gray-scale region to the theoretical value. The luminance change (brightness difference) is 1.0% or more, and particularly, the intermediate gray scale or more (the 256 gray scale in the figure is 127 gray scale or more) is 2% or more.
According to various verifications by the inventors of the present invention, it is found that when the constant γ is not corrected, the luminance change (luminance difference) of the theoretical value in each gray scale is roughly 2% or more in the intermediate gray scale, and the image is sintered at this time. In the comparative example described above, when the voltage component Vgs (writing voltage Vd=-Vd0-Vth13) which is not dependent on the constant γ is written and held, the deterioration of the display image quality is caused.
Further, in the present embodiment, the voltage component Vgs (writing voltage; 0-(-Vd)=Vd0+γVth13) depending on the constant γ as shown in the equation (14) is held by writing, as in the 35th As shown in Fig. 36, Table 2, and Table 3, the luminance change (luminance difference) of the theoretical value in each gray scale can be greatly suppressed, so A display device that can prevent image sintering and achieve excellent display quality.
Next, the relationship between the gray-scale designation voltage Vpix shown in the above formula (41) and the gate-to-source voltage Vgs of the transistor Tr13 will be specifically described.
Fig. 38 is a characteristic diagram showing the relationship between the constant set and the input data for realizing the effects of the present embodiment.
As described above, the gray scale designation voltage Vpix shown in the equations (13) and (14) is related to the gate voltage and the source voltage Vgs of the transistor Tr13 because of the source terminal (contact point N12) of the transistor Tr13. The potential difference of the on-resistance portion of the transistor Tr12 exists between the data lines Ld. Therefore, in order to maintain the voltage of the γ times the threshold voltage Vth13 of the transistor Tr13 on the contact point N12, the voltage is added to the data voltage Vd0. The designated voltage Vpix is a voltage at which a voltage equal to β times the threshold voltage Vth is added to the gray-scale effective voltage Vreal.
In the relationship between the gray-scale designation voltage Vpix and the gate-to-source voltage Vgs of the transistor Tr13, the relationship between the γ Vth13 of the Vgs change portion when the Vpix is turned off and the β Vth13 is set is verified. The value of the constant β and γ of the input data (specified gray scale) when the value voltage Vth13 is changed from 0V to 3V, as shown in Fig. 38, the constant β of the specified gray-scale designated voltage Vpix is constant for all input data (in the figure) In the solid line note, the constant γ of the gate voltage and the source-to-source voltage Vgs of the threshold voltage Vth13 is set to have a substantially constant slope change in the input data (indicated by a thick solid line in the figure). Here, as in the middle gray scale (in the vicinity of 128 gray scales in the 256 gray scale shown in Fig. 38), in order to make the constant γ reach the ideal value (indicated by a two-point chain line in the figure), when β=1.08, It is only necessary to set γ=1.097, and since it can be set to a value that approximates the constant β and γ, it can be set to a constant β in practical use. = γ.
Based on the above verification results, the inventors of the present invention have carried out various review results, and have obtained the following conclusion: the constant γ (=β) of the gate-to-source voltage Vgs of the transistor Tr13 for illuminating driving is preferably 1.05 or more, and is written. The voltage component Vgs (write voltage Vd) held in the source terminal (contact N12) of the transistor Tr13 is the gray scale designation voltage Vpix of the voltage (-Vd0-γVth13) expressed by the equation (14), and is input data. In the specified grayscale, you only need to set at least one grayscale.
In addition, at this time, the following conclusion is obtained: the maximum current value in the initial state before the change of the threshold voltage Vth13 is caused by the change of the light-emission drive current Iem due to the fluctuation of the threshold voltage Vth13 (Vth shift) The outline is 2% or less, and the size of the transistor Tr13 for light-emitting driving (that is, the ratio of the channel width to the channel length; W/L) and the voltage of the selection signal Ssel (Vsh, -Vsl) are set.
The gray scale designation voltage Vpix is further added to the drain-to-source voltage portion of the transistor Tr12 in -Vd of the source potential of the transistor Tr13. Since the absolute value of the power supply voltage Vcc-gray-order designated voltage Vpix is larger, the current value of the current flowing between the drain and the source of the transistor Tr12 and the transistor Tr13 during the writing operation is larger, so the difference between Vpix and -Vd Become bigger. However, if the influence of the voltage between the drain and the source of the transistor Tr12 on the voltage drop is lowered, the effect of β times the threshold voltage Vth can be reflected in the γ effect as it is.
In other words, as long as the formula (14) is satisfied, the voltage component γ Vth depending on the threshold voltage can be set, and the fluctuation of the current value of the light-emission drive current Iem when shifting from the write operation state to the light-emitting operation state can be compensated. Need to test Consider the influence of the voltage between the drain and the source of the transistor Tr12.
As shown in Fig. 33, when the voltage between the drain and the source of the transistor Tr12 is at the maximum luminance gray scale, in other words, when the voltage between the drain and the source of the transistor Tr12 is maximum, The transistor Tr12 is designed in a manner of 1.3V.
Fig. 38 is a characteristic diagram of the constant in the pixel driving circuit DC of the characteristic diagram of Fig. 33, which enables the constant γ (≒1.07) and the highest luminance gray level "255" at the lowest luminance gray scale "0". The difference of the constant γ (≒1.11) is sufficiently small and approximates the β of the formula (22).
In other words, the voltage component Vd0 of the gate and the source-to-source voltage Vgs of the transistor Tr13 in the power supply voltage Vcc-gray scale designation voltage Vpix becomes the gray-scale effective voltage Vreal, and the compensation voltage Vpth is added to the gray-scale effective voltage Vreal ( =β Vth13) If the negative polarity is formed, the gray scale designation voltage Vpix is set to the equation (13) when the write operation is performed, and the maximum voltage between the drain and the source of the transistor Tr12 is appropriately set. The constant γ can be approximated to β, and the gray scale display can be performed with high precision from the lowest luminance gray scale to the highest luminance gray scale.
In addition, the change characteristic (VI characteristic) of the pixel current of the organic EL element OLED (pixel size: 129 μm × 129 μm, numerical aperture: 60%) which is applied to the verification of the above-described series of effects is as shown in FIG. In the region where the driving voltage is a negative voltage, the pixel current is relatively small (smallly 1.0E-3μA~1.0E-5μA size), the driving voltage is roughly 0V, the pixel current is the lowest, and the driving voltage is positive. In the region of the voltage, the pixel current tends to increase sharply with an increase in the voltage value.
Here, Fig. 39 shows a voltage-current characteristic diagram of an organic EL element which is suitable for verification of a series of action effects.
Fig. 40 is a graph showing the voltage dependence of the parasitic capacitance in the channel of the transistor used for the display pixel (pixel driving circuit) of the present embodiment.
Here, according to the parasitic capacitance in the thin film transistor TFT, the Meyer capacitance model generally referred to is displayed under the condition that the gate voltage and the source voltage Vgs are larger than the threshold voltage Vth (Vgs>Vth). That is, the capacitance characteristics under the condition that a channel is formed between the source and the drain.
The parasitic capacitance Cch in the channel of the thin film transistor is substantially composed of the parasitic capacitance Cgs ch between the gate and the source terminal and the parasitic capacitance Cgd ch between the gate and the gate terminal, and the voltage between the gate and the source Vgs is The ratio of the threshold voltage Vth (Vgs-Vth) to the drain-to-source voltage Vds (voltage ratio; Vds/(Vgs-Vth)), and the gate and source occupied by the channel capacitance Cch of the transistor The relationship between the parasitic capacitance Cgs ch between the terminals, or the ratio of the parasitic capacitance Cgd ch between the gate and the 汲 terminal (capacitance ratio; cgs ch/Cch, Cgd ch/Cch), as shown in Fig. 40, has a voltage When the ratio is 0 (that is, when the voltage between the drain and the source is Vds=0V), there is no difference between the source and the drain. The capacitance is equal to Cgs ch/Cch and Cgd ch/Cch, and both occupy 1/2. In the state of increasing ratio (that is, the state in which the drain voltage and the source-to-source voltage Vds reach a saturated region), the capacitance ratio Cgs ch/Cch roughly accounts for 2/3, and the capacitance ratio Cgd ch/Cch is close to zero.
As described above, when the write operation of the pixel PIX is displayed, the data driver 140 generates the gray scale designation voltage Vpix having the voltage value indicated by the above formula (41), and is applied via the data line Ld, in the transistor. Tr13 Between the gate and the source terminal, in addition to the display data (luminance gray scale value), the voltage component Vgs which is set to include the influence of the voltage change in the (expected) pixel drive circuit DC can be compensated for during the illumination operation. The current value of the light-emission drive current Iem to the organic EL element OLED. Therefore, since the light-emission drive current Iem having the current value corresponding to the display data can be flown into the organic EL element OLED, the light-emitting operation can be performed in accordance with the luminance gray scale of the display data, thereby suppressing the luminance in each display pixel. A display device that achieves excellent display quality by deviation of gray scale.
<Specific example of driving method>
Next, a specific driving method of the display device 100 including the display region 110 shown in FIG. 9 will be specifically described.
In the display device (Fig. 9) of the present embodiment, the plurality of display pixels PIX arranged in the display region 110 are grouped into two groups consisting of an upper region and a lower region of the display region 110, and each group is divided into individual groups. Since the power supply voltage lines Lv1 and Lv2 are applied with the independent power supply voltage Vcc, the display pixels PIX of the plurality of rows included in each group can be illuminated together.
Fig. 41 is a timing chart showing an operation example of a specific example of the driving method in the display device having the display region of the embodiment.
In addition, in FIG. 41, for convenience of explanation, it is expedient to arrange display pixels of 12 lines (n=12; 1st line to 12th line) in the display area, and the 1st to 6th lines (corresponding to The operation timing chart when the display pixels of the above-mentioned upper region) and the 7th to 12th rows (corresponding to the lower region described above) are grouped into two groups as a group.
As shown in FIG. 41, the driving method in the display device 100 of the present embodiment first performs a display driving operation (display driving period shown in FIG. 16) for displaying image information in the display region 110. In the pixel driving circuit DC provided in each of the display pixels PIX arranged in the display region 110, a threshold voltage detecting operation (threshold voltage detecting period Tdec) is performed, and the detection and control of the organic EL element (light emitting element) is performed. a threshold voltage Vth13 (or a voltage component corresponding to the threshold voltage Vth13) of the transistor Tr13 for driving the light-emitting state of the OLED, and thereafter, within one frame period Tfr (about 16.7 msec), In the display pixel PIX (pixel driving circuit DC) of each row of the display region 110, the compensation voltage Vpth corresponding to the constant value β of the transistor Tr13 is kept constant, and the gray scale corresponding to the data is displayed. The voltage component Vgs (written display data) of the gray scale designation voltage Vpix formed by the effective voltage Vreal is applied to the display pixel PIX (organic EL element OLED) of the first to sixth rows or the seventh to the twelfth rows of the pre-grouping The timing of the end of the write operation, by each The group is sequentially (interactively displayed in the display device 100 shown in FIG. 9) repeatedly in response to the brightness gray scale of the displayed data, so that all the displayed pixel PIXs included in the group are processed together, and the display area is displayed. 110 image information of one screen part.
Here, in the same manner as in the above-described embodiment, the threshold voltage detecting operation (the threshold voltage detecting period Tdec) is a display pixel PIX (pixel driving circuit DC) for each row of the display region 110, and each row has a specific timing. The serial drive control is performed by one of the following operations: a voltage application operation (voltage application period Tpv) for applying a specific detection voltage Vpv; The voltage component of the detection voltage Vpv converges to a voltage convergence operation (voltage convergence period Tcv) of the threshold voltage Vth13 of each transistor Tr13 at the detection time point; and measures (reads) the voltage in each display pixel PIX The threshold voltage Vth13 after convergence, the voltage reading operation (voltage reading period Trv) in which each of the display pixels PIX is stored as the threshold detection data.
Specifically, as shown in FIG. 41, the first power supply voltage line that is commonly connected to the display pixel PIX of the group is connected to the group of display pixels PIX of the first to sixth rows of the display area 110. In the state where the power supply voltage Vcc (=Vccw) of the low potential is applied, the above-described threshold voltage detection operation (voltage application operation, voltage convergence operation, and voltage convergence operation) is repeatedly performed for each row from the display pixel PIX of the first row. In the group of the display pixels PIX of the seventh to twelfth rows, the second power supply voltage line Lv2 that is commonly connected to the display pixel PIX of the group is applied with a low potential power supply. In the state of the voltage Vcc (= Vccw), the above-described threshold voltage detecting operation is repeatedly performed for each row from the display pixel PIX of the seventh row. Thereby, the threshold detection data corresponding to the threshold voltage Vth13 of the transistor Tr13 for illumination driving provided in the pixel driving circuit DC is obtained for each display pixel PIX, and is stored in the frame memory. 147.
Here, in the timing chart shown in FIG. 41, the shaded portions of the respective lines of the threshold voltage detection period Tdec are shown by oblique lines, and the voltage application operation, the voltage convergence operation, and the voltage reading described in the above embodiments are respectively shown. In the series of threshold voltage detection operations formed by the operation, the threshold voltage detection operations of the respective rows are sequentially executed in a manner that the time is not overlapped and the timing is shifted.
Secondly, the display drive action (display drive period Tcyc), also with In the same manner as described in the embodiment, in one frame period Tfr, the display pixels PIX (light-emitting drive circuits DC) of the respective rows of the display region 110 are sequentially executed in a sequence of steps to perform a series of drive control at a specific timing: By the threshold voltage detecting operation, the transistor Tr13 of each display pixel PIX (pixel driving circuit DC) is detected, and the data is detected according to the threshold value of the memory, and each display pixel PIX is generated as a threshold. The voltage Vth13 is a constant β times the compensation voltage Vpth, and the voltage component according to the compensation voltage Vpth and the gray-scale effective voltage Vreal corresponding to the data to be displayed, such as the voltage component of the sum of the write compensation voltage Vpth and the gray-scale effective voltage Vreal ( Write operation of gray scale designation voltages Vpix and Vpix(0)) (write operation period Twrt); hold operation of holding voltage component of write (hold operation period Thld); and at specific timing, in response to the above display A light-emitting operation (light-emitting operation period Tem) in which each display pixel PIX (organic EL element OLED) emits light, in accordance with the luminance gray scale of the data (gray effective voltage).
Specifically, as shown in FIG. 41, the first power supply voltage line that is commonly connected to the display pixel PIX of the group is connected to the group of display pixels PIX of the first to sixth rows of the display area 110. Lv1, in a state where a low-potential power supply voltage Vcc (=Vccw) is applied, the writing is repeatedly performed from the display pixel PIX of the first row in sequence, and the compensation voltage Vpth=β Vth13 is added to the gray-scale effective voltage Vreal. The write operation of the gray scale designation voltage Vpix and the display pixel PIX of the end of the write operation hold the hold operation of the voltage component Vgs corresponding to the grayscale designation voltage Vpix.
Then, in the pixel PIX of the sixth row, a high potential is applied through the first power supply voltage line Lv1 of the group at the timing when the writing operation ends. The power supply voltage Vcc (=Vcce) is based on the grayscale designation voltage Vpix written in each display pixel PIX, so that the display pixel PIX of the 6-line portion of the group is illuminated together in response to the brightness gray scale of the displayed data. This lighting operation continues to the timing of starting the display driving operation (writing operation) for the display pixel PIX of the first row (the lighting operation period Tem of the first to sixth rows). Further, in the driving method, the display pixel PIX which is the sixth line of the last line of the group does not shift to the holding operation (the holding operation period Thld) after the writing operation, and the light-emitting operation is performed.
Here, in the timing chart shown in Fig. 41, the shaded portions indicated by the cross-webs of the respective driving periods Tcyc are displayed, and the writing operation of the display material shown in the above embodiment is shown, in particular, in the present embodiment, each row The writing operation is performed in a staggered manner in a temporal manner without overlapping, and in the display driving operation of each row, only the light-emitting operation is temporally overlapped (at the same timing) between the respective lines.
In addition, in the display pixel PIX of the first to sixth rows, at the timing when the writing operation ends (or the timing at which the display pixel PIX starts to emit light in the first to sixth rows), the seventh to the twelfth rows are In the group of the pixel PIX, the second power supply voltage line Lv2 of the display pixel PIX of the group is connected in common, and a low-potential power supply voltage Vcc (=Vccw) is applied, from the seventh row. The display operation of the grayscale designation voltage Vpix generated by adding the compensation voltage Vpth=β Vth13 to the grayscale effective voltage Vreal and the display of the line ending the writing operation are performed by sequentially displaying the pixels PIX. The pixel PIX holds the holding operation corresponding to the voltage component Vgs of the grayscale designation voltage Vpix.
Then, in the display pixel PIX of the 12th line, a high-potential power supply voltage Vcc (=Vcce) is applied through the second power supply voltage line Lv2 of the group at the timing of completion of the writing operation, and each display is written in accordance with the display. The gray scale of the prime PIX specifies the voltage Vpix, so that the display pixel PIX of the 6-line portion of the group is illuminated together in response to the brightness gray scale of the displayed data. This lighting operation continues to the timing of starting the display driving operation (writing operation) for the display pixel PIX of the sixth row (lighting operation period Tem of the seventh to twelfth rows).
In this manner, the display pixels PIX are arranged in a matrix in the display area 110, and the display pixel PIX of each row performs the threshold voltage detection operation in advance, and the display pixels of the respective rows after the display pixel PIX obtains the threshold detection data. The PIX sequentially performs a continuous process including a write operation and a hold operation, and sets each group set in advance so that the write operation is completed when the display pixel PIX of all the rows included in the group ends. All of the pixels showing the pixel PIX emit light together are driven and controlled.
In the driving method of the display device, all of the pixels (light-emitting elements) in the group are displayed during the writing operation (and the holding operation) in the display pixels of the respective rows in the same group before the light-emitting operation period Tem. ) The light-emitting operation is not performed, and the light-free state (black display state) is set.
In other words, in the operation timing chart shown in FIG. 41, since the display pixels PIX constituting 12 rows of the display region 110 are grouped into two groups, it is controlled that the respective groups perform the light-emitting operation together at different timings. The ratio (black insertion ratio) of the black display period of the one frame period Tfr by the above-described non-light-emitting operation is set to 50%. Here, in the naked eye, in order to clearly recognize the animated image without blurring, in general, it is 30% Since the black insertion rate is standard, the display device having a relatively good display image quality can be realized by the driving method.
Further, in the display region 110 of the display device 100 shown in FIG. 9, the display of the continuous plural display pixels PIX (the upper region and the lower region of the display region 110) is divided into two groups, but the present invention It is not limited to this, and it is also possible to group the groups by the rows of the odd lines and the odd lines. Further, the plurality of display pixel PIXs arranged in the display area 110 may be grouped into any number of groups such as three groups and four groups, whereby the light emission time and the black display period (black display) can be arbitrarily set in accordance with the number of groups of the group. State), and can improve the display quality. Specifically, when the groups are grouped into three groups, the black insertion rate can be roughly set to 33%, and when the groups are grouped into four groups, the black insertion rate can be roughly set to 25%.
Further, the plurality of display pixels PIX arranged in the display region 110 may not be grouped as described above, and each of the rows may be individually connected (connected) with a power supply voltage line, and the power supply voltage Vcc may be independently applied at different timings to display the display. The PIX is illuminated by various lines. Thereby, since the display driving operation described above is executed in units of rows, the light-emitting operation can be sequentially performed at an arbitrary timing from the end of the writing operation. In addition, in other forms, all of the display pixels PIX arranged in one screen portion of the display area 110 may be provided together with the entire display pixel PIX of one screen portion of the display area 110 by applying the common power supply voltage Vcc together. Illuminated actor.
100‧‧‧ display device
110‧‧‧Display area
120‧‧‧Select drive
130‧‧‧Power Driver
140‧‧‧Data Drive
141‧‧‧Shift register ‧data register
142‧‧‧Display data latch
143‧‧‧ Grayscale voltage generation unit
144‧‧‧ threshold detection voltage analog-digital converter
145‧‧‧Compensated voltage digital-to-analog converter
145a‧‧‧Compensated voltage DAC
145b‧‧‧Detection voltage supply
146‧‧‧Proportional data latching
147‧‧‧ Frame memory
148‧‧‧Voltage Addition Department
149‧‧‧Data line input/output switching unit
150‧‧‧System Controller
160‧‧‧Display signal generation circuit
170‧‧‧ display panel
Fig. 1 is a view showing a display pixel suitable for the display device of the present invention. The equivalent circuit diagram of the important part.
4A and 4B are characteristic diagrams showing the operational characteristics of the driving transistor when the pixel is in the writing operation, and the characteristic diagram of the relationship between the driving current and the driving voltage of the organic EL element.
Figs. 8A and 8B are characteristic diagrams showing the operational characteristics of the driving transistor when the pixel is illuminated, and the characteristic diagram of the load characteristics of the organic EL element.
Fig. 10 is a view showing an essential part configuration of an example of a data driver and a display pixel which can be applied to the display device of the embodiment.
Fig. 12 is a view showing a drive suitable for use in the display device of the embodiment. A conceptual diagram of the voltage application action of a moving method.
Fig. 21 is a timing chart showing an example of a driving method when a non-light-emitting display operation is performed in the display driving device of the embodiment.
Fig. 35A and Fig. B are characteristic diagrams showing the relationship between the light-emission drive current and the threshold voltage of the input data in the light-emitting operation of the display pixel of the embodiment.
Fig. 39 is a graph showing the voltage-current characteristics of the organic EL element which is applied to the verification of the effect of the series of one embodiment of the present embodiment.
141‧‧‧Shift register. Data register unit
A display driving device for driving a display pixel, comprising: the display pixel comprising: an optical element; and a pixel driving circuit having a driving element having one end of the current path connected to the optical element; the display driving device comprising: a detection voltage applying circuit that applies a specific detection voltage to the driving element of the pixel driving circuit; and the voltage detecting circuit applies the detection voltage to the driving element from the detection voltage applying circuit, and then passes the specific After the time, detecting a voltage value corresponding to the characteristic of the element inherent in the driving element; and a gray scale designation signal generating circuit based on the absolute value of the voltage component corresponding to the gray scale value of the displayed data, and the voltage detecting circuit by the foregoing The detected absolute value of the voltage value is set to a value larger than a constant value of 1 to generate a gray scale designation signal, and is applied to the pixel drive circuit.
The display driving device of claim 1, further comprising a memory circuit for storing voltage value data corresponding to the voltage value detected by the voltage detecting circuit, wherein the gray scale designating signal generating circuit reads and memorizes The aforementioned voltage value data of the foregoing memory circuit, and according to the foregoing display data The absolute value of the voltage component of the gray scale value is set to a value equal to the constant value of the voltage value data read from the memory circuit to generate the gray scale designation signal.
The display driving device of claim 1, wherein the constant is set to 1.05 or greater.
The display driving device of claim 1, wherein the driving element is a driving transistor having a control terminal and a capacitance component disposed between the control terminal and one end of the current path, wherein the voltage detecting circuit is The detection voltage is applied to the driving element from the detection voltage application circuit, and the charge corresponding to the detection voltage is stored in the capacitance component, and then the connection between the detection voltage application circuit and the pixel driving circuit is cut off. During a certain period of time, a part of the electric charge is discharged, and after the lapse of the specific time, a voltage corresponding to the electric charge remaining in the capacitance component is detected as a voltage value corresponding to the characteristics of the aforementioned element.
The display driving device according to claim 1, wherein the detection voltage has a polarity in which a current flows from the display pixel side to the detection voltage application circuit side, and has an absolute value which is a voltage value corresponding to a characteristic of the element. The absolute value is a certain voltage value.
The display driving device according to claim 5, wherein the detection voltage application circuit includes a detection voltage source that outputs the detection voltage of the constant voltage value.
The display driving device of claim 1, wherein the grayscale designation signal generating circuit comprises: a grayscale voltage generating portion that generates a grayscale effective voltage, the grayscale effective voltage having a grayscale value corresponding to the display data a luminance gray scale, a voltage value for causing the optical element to emit light; a compensation voltage generating portion that generates a compensation voltage having an absolute value of the voltage value detected by the voltage detecting circuit set to the constant multiple a voltage value; and an arithmetic circuit unit that generates the gray scale designation signal based on a value obtained by adding an absolute value of the gray scale effective voltage to an absolute value of the compensation voltage.
The display driving device according to claim 1, wherein the optical element is a current control type light emitting element, wherein the driving element is a driving transistor having a control terminal and is disposed at one end of the control terminal and the current path. The capacitance component between the components of the pixel driving circuit is the threshold voltage of the driving transistor.
A display device for displaying image information, comprising: a display driving device, comprising: a display element having: an optical element; and a pixel driving circuit having a driving element having one end of the current path connected to the optical element; a data line connected to the aforementioned pixel driving circuit of the display pixel; and a detection voltage applying circuit that applies a specific detection voltage to the driving element of the pixel driving circuit that displays the pixel via the data line; and the voltage detecting circuit is applied from the detection voltage applying circuit After the detection voltage is applied to the driving element, after a lapse of a specific time, a voltage value corresponding to a characteristic of the device inherent in the driving element is detected via the data line; and a gray-scale designation signal generating circuit is provided according to the gray of the corresponding data The absolute value of the voltage component of the step value is set to a value which is a constant multiple of the absolute value of the voltage value detected by the voltage detecting circuit, and a gray scale designation signal is generated and applied to the data line via the data line. The aforementioned pixel driving circuit.
The display device of claim 9, wherein the display driving device further comprises a memory circuit for storing voltage value data corresponding to the voltage value detected by the voltage detecting circuit, and the gray scale designating signal generating circuit Reading the voltage value data stored in the memory circuit, and setting an absolute value of the voltage value data read from the memory circuit to the constant according to an absolute value of a voltage component corresponding to a gray scale value of the display data The value of the multiple is generated to generate the aforementioned gray scale designation signal.
The display device of claim 9, wherein the aforementioned constant is set to 1.05 or a value larger than the display device.
The display device of claim 9, wherein the driving element in the pixel driving circuit drives the electro-crystal The body has a control terminal and a capacitance component provided between the control terminal and one end of the current path, and the voltage detecting circuit in the display driving device is applied from the detection voltage applying circuit via the data line The detection voltage is applied to the pixel driving circuit, and after the electric charge corresponding to the detection voltage is stored in the capacitance component, the connection between the detection voltage application circuit and the pixel driving circuit is cut off, and the specific During the time period, one of the charges is discharged, and after a predetermined period of time, a voltage corresponding to the charge remaining in the capacitance component is detected as a voltage value corresponding to the characteristics of the element via the data line.
The display device of claim 12, wherein the component characteristic inherent in the pixel driving circuit is a threshold voltage of the driving transistor.
A display device according to claim 12, further comprising: a display panel in which a plurality of selection lines are arranged in a column direction, and a plurality of the data lines are arranged in a row direction, in the vicinity of intersections of the plurality of data lines and the plurality of selection lines a plurality of the display pixels are connected to the data lines and the respective selection lines; and a selection driver that sequentially applies a selection signal to each of the selection lines to display the display of each column of the display panel The pixels are set to select the states in order.
The display device of claim 14, wherein the pixel driving circuit in the display pixel further comprises: a selection transistor connected to the driving transistor and the foregoing Between the feed lines, the control terminal is connected to the selection line; and the diode for diode connection has a control terminal connected to the selection line, and the drive transistor is in a diode connection state.
The display device of claim 15, wherein the component size of the selection transistor and the voltage value of the selection signal are set to be written and held by the control terminal of the driving transistor according to the gray scale designation signal. The voltage component between one of the terminals of the current path flows through the current path of the driving transistor, and flows into the driving current of the optical element, and the amount of fluctuation of the current value that fluctuates with the threshold voltage of the driving transistor In the entire luminance gray scale of the light emission of the optical element, the maximum current value in the initial state in which the threshold voltage fluctuation of the drive transistor is not generated is within 2%.
The display device of claim 9, wherein the optical element is a current-controlled light-emitting element.
The display device according to claim 9, wherein the detection voltage has a current flowing from the display pixel side to the detection voltage application circuit side via the data line, and has an absolute value ratio corresponding to the component characteristics. The absolute value of the voltage value is also a certain voltage value.
The display device according to claim 18, wherein the detection voltage application circuit of the display drive device includes a detection voltage source that outputs the detection voltage having the predetermined voltage value.
The display device of claim 9, wherein the gray scale designation signal generating circuit in the display driving device comprises: a gray scale voltage generating portion that generates a gray scale effective voltage, the gray scale effective voltage having a display corresponding to the foregoing a luminance gray scale of the gray scale value of the data, and a voltage value for causing the optical element to emit light; and a compensation voltage generating portion that generates a compensation voltage having an absolute value of the voltage value to be detected by the voltage detecting circuit a voltage value of the constant multiple; and an arithmetic circuit unit applied to the data line to generate the gray scale designation signal according to a value obtained by adding an absolute value of the gray scale effective voltage to an absolute value of the compensation voltage .
A driving method for driving a display device for displaying image information, comprising the steps of: applying a specific detection voltage to the pixel driving circuit via a data line connected to the pixel driving circuit of the display pixel In the driving element, the display pixel has an optical element, and a pixel having one end of the current path is a pixel driving circuit connected to the driving element of the optical element; after the predetermined voltage is applied to the driving element, after a lapse of a specific time And detecting, by the foregoing data line, a voltage value corresponding to a characteristic of a component inherent in the driving element; an absolute value of a voltage component according to a grayscale value of the display data, and an absolute value of the voltage value to be detected by the foregoing Setting a value that is a constant multiple of 1 to generate a grayscale designation signal; and The gray scale designation signal is applied to the pixel driving circuit via the aforementioned data line.
The driving method of claim 21, wherein the display device further comprises a memory circuit for storing a voltage value corresponding to the component characteristic by using the voltage value data corresponding to the detected voltage value And the step of storing the detected voltage value in the memory circuit, and generating the grayscale designation signal, comprising the step of reading the voltage value data stored in the memory circuit.
The driving method of claim 21, wherein the aforementioned constant is set to 1.05 or a value larger than the above.
The driving method of claim 21, wherein the driving element in the pixel driving circuit is a driving transistor having a control terminal and a capacitance component disposed between the control terminal and one end of the current path, The step of applying the detection voltage includes a step of storing a charge corresponding to the detection voltage in the capacitance component, and the step of detecting a voltage value corresponding to the component characteristic includes the step of: applying the detection voltage by applying a step of storing a charge corresponding to the detection voltage in the capacitance component, and cutting off the connection between the detection voltage application circuit and the pixel drive circuit; and, in the specific time, a part of the charge is placed After a predetermined period of time, the voltage corresponding to the electric charge remaining in the capacitance component is detected as a voltage value corresponding to the characteristic of the element.
The driving method of claim 21, wherein the step of generating the gray scale designation signal comprises the step of generating a gray value of a voltage value for emitting the optical element with a gray scale corresponding to a gray scale value of the display data. a step effective voltage; generating a compensation voltage having a voltage value that sets the absolute value of the detected voltage value to the constant multiple; and a value obtained by adding an absolute value of the gray-scale effective voltage to an absolute value of the compensation voltage And generating the aforementioned gray scale designation signal.
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