Abstract
ABSTRACTA pixel circuit that compensates for the non-uniform thin-film transistor (TFT) characteristics across a display panel is inevitably used in the organic light-emitting diode (OLED) display to exhibit uniform brightness. The existing pixel circuits aim to compensate only for the non-uniformity of the threshold voltage (Vth). They do not compensate for the deviation of the other parameters, such as the mobility and the subthreshold swing. In this study, how the OLED current changes when the mobility of a TFT in the Vth compensation circuit increases was examined. If the mobility increases, the enhanced drain current drives the TFT into a deeper subthreshold mode during the Vth compensation phase, and the |VGS| of the TFT decreases compared with the normal mobility case. The resultant OLED current, however, can be higher or lower than the normal mobility case depending on the gray level because the effects of the current increase due to the higher mobility and of the current decrease due to the reduced |VGS| appear simultaneously but differently depending on the VGS value of the TFT. The analysis results show that the OLED current increases for the high gray level but decreases for the low gray level. It remains almost unaffected by the mobility increase for the mid-gray level.
Highlights
The organic light-emitting diode (OLED) displays recently replaced the liquid crystal displays (LCDs) for mobile devices such as smartphones, owing to the high flexibility, better image quality, and lower power consumption of OLED
To exhibit uniform brightness on the OLED display panel compared with the LCD because the brightness of the OLED pixel is determined by the current in each pixel rather than by the voltage stored in a capacitor, which is the method used in the LCD
The OLED current of the double-mobility case, could be larger or smaller compared with the reference case because the mobility as well as the VGS determined the current simultaneously according to Equation (1)
Summary
The organic light-emitting diode (OLED) displays recently replaced the liquid crystal displays (LCDs) for mobile devices such as smartphones, owing to the high flexibility, better image quality, and lower power consumption of OLED. It is troublesome, to exhibit uniform brightness on the OLED display panel compared with the LCD because the brightness of the OLED pixel is determined by the current in each pixel rather than by the voltage stored in a capacitor, which is the method used in the LCD. In the case of the OLED display; an additional conversion process from the data voltage to the pixel current is required.
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