A New PWM Operational Scheme for MicroLED Displays Using Inverter and Dynamic SWEEP Signal Slope for Low Gray Level Expression

Abstract

In this paper, we present a novel pulse width modulation (PWM) operational scheme for micro-light-emitting-diode ( $\mu$ LED) displays using inverter and dynamic SWEEP signal slope. In the proposed PWM operational scheme, the slope of the SWEEP signal steepens as the gray level decreases. This adjustable SWEEP signal slope further shortens the falling time compared to the inverter-only strategy, leading to an exceptional capability to express extremely low gray levels. We implement the proposed scheme with a low-temperature poly-Si oxide (LTPO) thin-film transistor (TFT) pixel circuit and verify the operation through HSPICE based on measured TFT data. The simulation results show that the proposed scheme can significantly shorten the falling time to under $\mu$ s level. The gray level of 14 G is accurately expressed without wavelength shift or pulse distortion, achieving a falling time of $\mu$ s. In addition, we also verify the compensation accuracy of the pixel circuit, and the results indicate that the proposed pixel circuit can reliably compensate for TFT variations.

Keywords

• MicroLED
• LTPO
• TFT
• pixel circuit
• PWM
• inverter