A Novel Voltage Driving Method Using 3-TFT Pixel Circuit for AMOLED

A novel voltage driving method using three thin-film transistors (TFTs) for active-matrix organic light-emitting diodes (OLEDs) is presented and verified by automatic integrated circuit modeling SPICE simulation. The proposed novel 3-TFT pixel circuit, which successfully compensates for the threshold voltage variations, uses few TFTs with simplified control signals, and the current nonuniformity of the proposed circuit is 0.19% to 1.99% throughout the entire data range. To compensate for variations in OLED current, the proposed circuit utilizes a novel driving scheme that uses a diode connection current source with a biased voltage.

I. Introduction

Organic light-emitting diode (OLED) displays have a simple thin structure, wide viewing angle, fast response time, high degree of brightness, and high contrast ratio [1], [2]. Specifically, the threshold voltage variation of driving thin-film transistor (TFT) for active-matrix OLED (AMOLED) affects the drain current resulting in nonuniform phenomena. Numerous compensation methods have been developed such as voltage modulation [1]– [6] and current programming methods [2], [7]– [9]. Ashtiani et al. [7] recently presented a 3-TFT current-programmed pixel circuit and analyzed the impact of shift on the OLED drive current. Based on their analysis, circuit degradation was successfully reduced. However, these current-programmed methods require a long settling time at a low data current and inconvenient constant current sources that control submicrometer ampere-level current in peripheral drivers.