A Compact Amorphous In-Ga-Zn-Oxide Thin Film Transistor Pixel Circuit With Two Capacitors for Active Matrix Micro Light-Emitting Diode Displays

Abstract

In this paper, we propose a novel amorphous In-Ga-Zn-oxide (a-IGZO) thin film transistor (TFT) pixel circuit for pulse width modulation (PWM) driving active matrix micro light-emitting diode (LED) displays. The proposed pixel circuit compensates for wavelength shifts according to gray level and threshold voltage (VTH) variation of TFTs with only two capacitors. This compact operation can be achieved by simultaneous compensation for VTH along with data input in the constant current generation (CCG) circuit and the PWM circuit, which consist the pixel. Since the VTH variation in TFTs is compensated, the proposed pixel circuit can supply a uniform and stable current to the LED throughout all gray levels. The compensation accuracy was verified by HSPICE with an oxide TFT model based on the measurement data.In addition, we analyzed the optimization method to improve the PWM driving by controlling the electrical properties of TFT, and verified this approach by simulation.