Anomalous-Pulsewidth Modulation of Single-Contact Light-Emitting Diode for Grayscale Control

Due to the simple structure, single-contact light-emitting diode (SC-LED) holds promise for applications in ultrahigh resolution micro-displays. However, the required alternating current (ac) operation poses challenges for grayscale modulation in image display applications. Therefore, it is of great significance to develop a potential grayscale control technology for the ac-driven SC-LEDs. In this work, the optical and electrical characteristics of the SC-LEDs are investigated, and an anomalous pulsewidth modulation (A-PWM) technology is proposed. In the A-PWM mode, the brightness decreases with the increasing pulsewidth, which is totally different from conventional pulsewidth modulation. The carrier transport model and the circuit model are established to clarify the A-PWM mechanism. Furthermore, the brightness division is carried out on the basis of the A-PWM, and the human eye brightness perception model is established. Nonlinear correction is applied to align the brightness change with the characteristics of human eye perception. This work proposes a brightness modulation method suitable for SC-LEDs, which is expected to be applied to ac-driven nano-pixel light-emitting displays.