Reducing image sticking in AMOLED displays with time-ratio gray scale by analog calibration

Abstract

Early loss of image uniformity has been a critical drawback of active-matrix organic lightemitting- diode (AMOLED) displays operated in time-ratio gray-scale mode. This problem is addressed with an analog calibration technique which measures the voltage across eachOLED for a given current and subsequently controls the supply voltage of pixels and the voltage drop across the driving thin-film transistor (TFT) of each OLED. The uniformity of test cells, which were aged to produce image sticking in a chessboard pattern, were improved. A measure of image sticking, called the extracted imagesticking value (EISV), was formulated, which is developed and used for the quantitative evaluation of the calibration method. OLED voltages over a range of about 0.35 V were compensated to produce more uniform OLED currents than those before aging. The variation of luminance associated with image sticking was reduced by about 40% for a full-white image after between 2 and 10 hours of accelerated aging with a constant voltage of 8 V across an OLED.