Highly Uniform and Flicker-Free Pixel Circuit for Wide Variable Refresh Rate AMOLED Displays

This letter proposes a 9T2C AMOLED pixel circuit that achieves high luminance uniformity and low flicker across a wide variable refresh rate (VRR) range of 15 to 360 Hz using LTPS TFTs. To enhance uniformity, the circuit compensates for threshold voltage (Δ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_TH</i>) and subthreshold slope (Δ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i>) variations of the driving TFT by securing sufficient compensation time and employing a diode-connected current sink method. Flicker is significantly reduced by alleviating the effects of switching TFT leakage current, driving TFT hysteresis, and OLED parasitic capacitance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_OLED</i>) through a pulse-referenced method and maximum refresh rate (MRR) driving method. The circuit was fabricated on a 14-inch 4K AMOLED panel and experimentally verified. The measured worst-case spatial emission current errors (SECEs) were +2.8/-2.9 LSB and +0.4/-0.4 LSB at high and low gray levels, respectively. Regarding flicker, the worst temporal errors (TECEs) were measured to -1.7 LSB and +0.3 LSB at high and low gray levels, respectively.