A new method to enhance the driving TFT Vth compensation of OLED pixel internal compensation circuit

This article presents a novel voltage-programmed pixel circuit using a-IGZO TFTs to effectively compensate threshold voltage (Vth) variations of driving TFT. The compensation is very important to maintain the pixel brightness of active matrix organic light-emitting diodes (AMOLED) displays. The proposed pixel design uses four-phase clocking schemes: initial period, compensation period (Vth detection), data input period and emission period. To maintain uniformity in phases, the duration of all the phases is taken to be same which results in easier design of the multi-phase clock. Moreover, the circuit has been extensively simulated with control signal and the operation has been verified using SPICE from Aether EDA. The key of this paper is changing the compensation timing of the pixel circuit, which can greatly broaden the Vth compensation range of the driving TFT from -0.30~0.30 to -0.85~1.45V by means of simulation.