IR drop-independent 8T1C LTPS pixel circuit for medium-sized AMOLED displays

Abstract

OLED displays have been widely used in mobile devices due to their numerous advantages. The pixel circuits of OLED displays typically employ low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) for their high mobility and reliability. However, LTPS TFTs suffer from threshold voltage (VTH) variation, sometimes leading to OLED current error (OCE) and non-uniform display. A diode connection method was used in the conventional OLED pixel circuit to compensate for this limitation. However, the impact of IR drop in the metal lines necessitates developing a new circuit to eliminate the adverse effect of IR drop. Accordingly, this paper proposed an 8T1C LTPS pixel circuit, featuring an additional reference voltage for VTH compensation independent of IR drop. Simulation results demonstrate that the suggested circuit effectively compensates for VTH, ensuring uniform OLED performance regardless of IR drop. This circuit design also enables consistent image quality, particularly in medium-sized displays, where IR drop would be severe, by maintaining uniform OLED current across the entire panel.

Keywords

• Organic light emitting diode (OLED) display
• pixel circuit
• low-temperature poly-Si (LTPS) thin-film transistor (TFT)
• threshold voltage
• IR drop
• Display Circuits and Systems