Based on a driving mean, Organic Light-Emitting Diode (OLED) can be categorized into Passive Matrix OLED (PMOLED) and Active Matrix OLED (AMOLED). PMOLED, due to be configured to emit light only in a data writing period, can have a simple circuit structure, a lower cost and a simple circuit design; and thus, the early display industries much focus on the development of PMOLED technology. However, the PMOLED, due to the driving mean, may have some serious problems, such as having relatively high power consumption and a relatively short life when the PMOLED is applied to large-size displays. Therefore, basically the PMOLED is only used in medium-size or small-size displays.
The AMOLED is different to the PMOLED in that each pixel has a capacitor configured to store data and thereby keeping each pixel operated in a light-emitting state. Compared with the PMOLED, the AMOLED has several advantages, such as having lower power consumption and having a driving mean which is adapted to be used in a large-size and high-resolution display. Therefore, the AMOLED today is the mainstream technology in the display field.
Even the AMOLED consumes less power and is suitable for some large-size and full-color applications in displays; the AMOLED still has some design problems. For example, when an OLED or a Thin Film Transistor (TFT) functioned as a switch or a driving component in the AMOLED has a material property variance or a material aging issue, a uniform problem may occur on the associated display. According to a number of documents and disclosures, the uniform problem can be improved by a compensation circuit; wherein the compensation circuit basically is categorized into a voltage type and a current type.
The voltage-type compensation circuit, configured to compensate the threshold voltage (VTH) of TFTs, still has some problems, such as having a complicate circuit design and requiring a relatively large number of components therein.
In contrast, although the current-style compensation circuit can have its device characteristics without being affected by the flowing-through current, but the current, as the data input format, cannot be configured to be as accurate as the voltage source is. In addition, the current-style compensation circuit also requires more time for charging/ or discharging capacitors therein while being operated in a low grayscale.
Moreover, a pixel circuit is required to switch displays in a relatively high frequency while it uses a temporal division of 3D display; accordingly, the high frame rate may limit the compensation effect of the current-type or voltage-type compensation circuits and consequently limit the time for writing data voltages, as illustrated in FIG. 1; wherein 1H represents a period while a pixel circuit is enable (or, a horizontal scan line is turned-on). According to the existing compensation technologies, the data resetting, the VTH compensation and the data writing must be complete within the period 1H; thus, there will be no sufficient time for the data writing if the pixel circuit has a relatively high frame rate. However, it is understood that a display panel cannot normally write data as well as display the data without a sufficient data writing period; therefore, the frame rate of a display is limited to be higher if it has a limited data writing period.
Therefore, it is desirable to provide a pixel circuit in an AMOLED to prevent the above-mentioned problem.