LTPO-based pixel circuit with highly uniform luminance and low flicker for variable refresh rate in AMOLED displays.

Low-temperature polycrystalline silicon and oxide (LTPO)-based pixel circuits are increasingly being adopted in medium-sized active-matrix organic light-emitting diode (AMOLED) displays due to their power-saving advantages. However, conventional pixel circuits originally developed for mobile displays face challenges when applied to larger panels, due to aggravated IR-drop and residual luminance at black levels. To address these issues, we propose a novel pixel circuit composed of nine thin-film transistors (TFTs) and one storage capacitor (CST). The proposed design compensates for luminance non-uniformity caused by IR-drop in the VDD line and ensures stable variable refresh rate (VRR) operation without requiring an additional compensation scheme, such as the on-bias voltage (OBV) used in conventional designs, which causes residual luminance in dark states. To validate the effectiveness of the proposed circuit, a 13-inch LTPO AMOLED panel was fabricated. Flicker was measured to be below − 50 dB at a 10 Hz refresh rate under both 140 nits and 6 nits conditions. In addition, luminance uniformity was significantly improved from 69% to 89% under the high luminance condition of 1,600 nits. These results demonstrate that the proposed pixel circuit achieves improved luminance uniformity and stable VRR performance.