New Pixel Circuit Based on Silicon Backplane for Micro-Organic Light-Emitting Diode Employing Hybrid Program Method

Abstract

A new pixel circuit based on silicon backplane technologies for organic light-emitting diode (OLED) microdisplays is proposed for a micro-OLED with several thousand pixels per inch (ppi) and several µm pixel pitch. Because the current level of each pixel for the 63rd gray is approximately 1 nA and the minimum voltage unit at mid-gray is approximately 1 mV for high-ppi micro-OLEDs, the pixel circuit must have highly accurate current control ability. The new pixel circuit can precisely control tiny currents by employing a hybrid programming method that combines current and voltage programming. The proposed current programming based on the current mirror can compensate for short-range transistor variations even under small-current conditions, and the capacitive voltage divider can expand the data voltage range N times. A simulation program with integrated circuit emphasis (SPICE) was employed to evaluate circuit operation and performance. The simulation results indicated N times extended input data voltage range and a low current error rate of 5% for an OLED anode variation of 10 mV.