Pixel Circuit With Leakage Prevention Scheme for Low-Frame-Rate AMOLED Displays

Chih-Lung Lin,Li-Wei Shih,Sung-Chun Chen,Jui-Hung Chang,Mao-Hsun Cheng,Po-Cheng Lai

doi:10.1109/jeds.2020.2974576

Abstract

This work proposes a new pixel circuit for active-matrix organic light-emitting (AMOLED) smartwatch displays with a low frame rate. Within the long emission period, the leakage current of a low-temperature polycrystalline silicon thin-film transistor (LTPS TFT) is reduced to suppress the distortion of the driving voltage at the gate node of the driving TFT. Based on the measured electrical characteristics of a fabricated p-type LTPS TFT, the HSPICE model is established to verify the feasibility of the proposed circuit. The analytical results indicate that the relative OLED current error rates are all below 4.73%, as the threshold voltage of TFT varies by ±0.5 V. Notably, the OLED current varies by only 2.94% during the emission period of 66.7 ms at a medium gray level, demonstrating the effectiveness of the leakage prevention scheme.

Highlights

Active-matrix organic light-emitting diode (AMOLED) displays have recently received considerable attention due to their favorable properties such as wide viewing angle, fast response, high brightness, thinness, and compactness [1]
Variations of the threshold voltage (VTH) of LTPS TFTs that are caused by fluctuations of the laser beaming in the excimer laser annealing (ELA) process severely reduce the uniformity of OLED currents [5], [6]
The conventional pixel circuit consisting of two LTPS TFTs and one capacitor without compensation for the VTH variation of the driving TFT generates non-uniform currents that flow through OLED devices, leading to the severe image distortion

Summary

Introduction

Active-matrix organic light-emitting diode (AMOLED) displays have recently received considerable attention due to their favorable properties such as wide viewing angle, fast response, high brightness, thinness, and compactness [1]. The conventional pixel circuit consisting of two LTPS TFTs and one capacitor without compensation for the VTH variation of the driving TFT generates non-uniform currents that flow through OLED devices, leading to the severe image distortion.

Results

Conclusion