Design of a voltage-programmed VTH compensating pixel circuit for AMOLED displays using diode-connected a-IGZO TFT

Abstract

This study presents a novel voltage-programmed, amorphous-indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT)-based active-matrix organic light-emitting diode (AMOLED) pixel circuit. The circuit utilises the threshold voltage (VTH) sensing ability of a diode-connected transistor to compensate for the spatial as well as the temporal variation of the threshold voltage of the driving transistor and supply a constant current to the OLED. The circuit has been simulated in Cadence Spectre using a-IGZO TFT and OLED simulation program with integrated circuit emphasis (SPICE) models, and the analysis is presented to prove the VTH compensating capability of the proposed circuit. For small currents, about 50 nA, the error is suppressed to <9% whereas for large currents, about 2.5 µA, the error is only 1.05%. This performance has been achieved using only five TFTs and two storage capacitors.