1. Technical Field
The disclosure relates to a touch display panel, and more particularly, to an optical touch display panel.
2. Related Art
With development of science, currently many consumer electronic products (for example, a personal digital assistant (PDA), a mobile phone, and a tablet computer etc.) widely use a touch display panel as a communication interface of man-machine data. The touch display panel may detect a position on which a user touches the touch display panel by using different sensing technologies, for example, resistance type, capacitance type, and optical sensing type.
FIG. 1 is a schematic view of detection of an optical sensing touch display panel 100. FIG. 2 is a schematic view of another detection of the optical sensing touch display panel 100. FIG. 3 is a schematic view of optical sensing signals generated by the optical sensing element 110 after receiving different light intensities.
As shown in FIG. 1, the optical sensing touch display panel 100 includes an optical sensing element 110, configured to detect variation of an outside light source. In typical situations, the optical sensing element 110 detects an ambient light L to generate an optical sensing signal LS1 (as shown in FIG. 3).
Please refer to FIG. 1, in which when a finger 120 contacts or approaches the optical sensing touch display panel 100 to shield the optical sensing element 110 from receiving the ambient light L, the optical sensing element 110 correspondingly generates an optical sensing signal LS2 (as shown in FIG. 3).
Please refer to FIG. 2, in which when a light pen 130 approaches or contacts the optical sensing touch display panel 100, in addition to receiving the ambient light L, the optical sensing element 110 receives a light output by the light pen 130, and correspondingly generates an optical sensing signal LS3 (as shown in FIG. 3).
As shown in FIG. 3, the optical sensing element 110 is, for example, a thin-film transistor (TFT), when a gate (G) source (S) voltage (that is, Vgs) of the optical sensing element 110 is smaller than 0 volt, the greater the light intensity received by the optical sensing element 110 is, the larger a drain source current Ids is.
FIG. 4 is a circuit diagram of detection of the optical sensing element 110. FIG. 5 is a schematic view of a gate source voltage Vgs corresponding to a reading signal RO of a voltage level of a first end Va of a storage capacitor under irradiation of different light sources.
As shown in FIG. 4, the optical sensing element 110 is connected electrically to the storage capacitor Cs1, when the optical sensing element 110 generates different optical sensing signals (that is, the drain source current Ids), after detecting different light sources, the voltage level of the first end Va of the storage capacitor Cs1 is reduced accordingly. By reading the voltage level of the first end Va of the storage capacitor Cs1, it may be determined whether touch input exists.
For example, the light pen 130 as shown in FIG. 2 is configured to perform touch input, before the touch input, the optical sensing element 110 only receives irradiation of the ambient light L, so that the reading signal RO generated after the voltage level of the first end Va of the storage capacitor Cs1 is read is a dark state voltage V1 (as shown in FIG. 5). During the touch input, in addition to receiving the ambient light L, the optical sensing element 110 receives the light output by the light pen, so that the reading signal is a bright state voltage V2 (as shown in FIG. 5). Through determining whether a voltage difference ΔV between the bright state voltage V2 and the dark state voltage V1 exceeds a preset threshold value, it is determined whether the touch input exists.
After the voltage level of the first end Va of the storage capacitor Cs1 is read, in order to detect the touch input again, the voltage of the storage capacitor Cs1 needs to be reset, that is, the storage capacitor Cs1 is charged to a reset voltage. However, in order to synchronize a touch interface and a display picture, usually a touch detection frequency is the same as a picture update frequency (that is, a frame rate). The frame rate is limited, so charging time (hereafter referred to as reset time), of the storage capacitor Cs1 is limited, so that the voltage level after the storage capacitor Cs1 is reset is not high enough, therefore, the level of the dark state voltage is relatively low. Under the situation that the level of the bright state voltage is not changed, the voltage difference ΔV is smaller, so that a signal to noise ratio becomes lower, thereby resulting in misjudgment during a touch detection event.
Additionally, usually the multiple optical sensing elements 110 in the same direction may be connected electrically to the same resetting signal line Sn, so as to receive the reset signal fed by the resetting signal line Sn. However, a delay effect of the capacitor and the resistor results in that the voltage of the reset signal received by the storage capacitor Cs1 connected to each optical sensing element 110 is further lowered. Furthermore, the storage capacitors Cs1 are connected in parallel through the resetting signal lines Sn, so that resistor-capacitor (RC) loading borne by each position on the resetting signal line Sn are not the same, particularly, a difference of the RC loading between a head end and a tail end is larger. For these reasons, the voltage level after the storage capacitor Cs1 of each optical sensing element 110 is reset is relatively low and inconsistent.
FIG. 6A is a schematic view of reset signals of the head end and the tail end of the resetting signal line Sn. FIG. 6B is a schematic view of charging of the storage capacitor Cs1 of the head end of the resetting signal line Sn. FIG. 6C is a schematic view of charging of the storage capacitor Cs1 of the tail end of the resetting signal line Sn.
As shown in FIG. 6A, a curve A is a waveform of the reset signal measured at the head end (that is, one end near a signal source sending the reset signal), of the resetting signal line Sn, a curve B is a waveform of the reset signal measured at the tail end (that is, one end away from the signal source sending the reset signal), of the resetting signal line Sn. It may be known that the curve A is original a pulse, when being delivered to the tail end of the resetting signal line Sn, the reset signal is distinctly varied because of the delay effect of the capacitor and the resistor (as shown in the curve B). Therefore, at 0.02 ms in FIG. 6A, a voltage of the curve A is approximately 29 volts, and a voltage of the curve B is lowered to be approximately 19 volts.
As shown in FIG. 6B, a curve C is a voltage variation waveform of the storage capacitor Cs1 of the head end of the resetting signal line Sn after being reset; and as shown in FIG. 6C, a curve D is a voltage variation waveform of the storage capacitor Cs1 of the tail end of the resetting signal line Sn after being reset. It may be known that at 0.02 ms, the voltage of the curve C is approximately 18 volts, and the voltage of the curve D is approximately 10 volts (at D). From the difference between the reset voltages of the storage capacitor Cs1 at the head and the tail ends, it may be known that the voltage after the storage capacitor Cs1 on the same resetting signal line Sn is reset is not uniform, so that sensing sensitivity of each touch position of the optical sensing touch display panel 100 is inconsistent, thereby resulting in the misjudgment.