Analog PWM Method With Sweep Generation Structure Based on P-Type LTPS TFTs for Micro-LED Displays

Abstract

This work proposes a novel pixel circuit using analog pulse width modulation (PWM) for micro light-emitting diode (micro-LED) displays. The proposed circuit generates uniform sweep waveforms and driving currents to control micro-LED emission precisely by compensating for threshold voltage (VTH) variations of p-type low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) and VDD current-resistance drops (I-R drops). Driven by the PWM method, micro-LED can operate with high wall-plug efficiency (WPE), leading to low power consumption. To analyze the circuit performance, the electrical characteristics of a micro-LED and LTPS TFTs are measured to establish the simulated models. The HSPICE simulation results present that the current error rates and time shift rates of emission currents are below 1.65% and 2.75%, respectively, with ±0.3 V variations in VTH and 1.2 V drops in VDD. Furthermore, the power improvement relative to a 7T1C pulse amplitude modulation (PAM) circuit is higher than 19.05% at all gray levels, confirming that the proposed circuit is suitable for use in micro-LED displays.

Keywords

• Low-temperature polycrystalline silicon thin-film transistor (LTPS TFT)
• micro light-emitting diode (micro-LED)
• pulse width modulation (PWM)
• power consumption