A New Pixel Circuit for Micro-Light Emitting Diode Displays with Pulse Hybrid Modulation Driving and Compensation

Abstract

A new pixel circuit consisting of eleven n-type IGZO transistors (TFTs) and four capacitors is proposed and applied for micro light emitting diode (MLED) displays. The circuit is driven by pulse hybrid modulation (PHM), combining pulse amplitude modulation (PAM) and pulse width modulation (PWM). In purpose, high grayscales are achieved by PAM mode and low grayscales are achieved by PWM mode, which keep the driving current of LED out of the small value range so as to avoid unstable luminance performance. It is conducted that the MLED display driven by PHM demonstrate a stable luminance at low grayscale with well suppressed luminance errors of over 30% decrease, in comparison with the display driven by PAM. Moreover, both threshold voltage (VTH) shifts of driving TFTs for PAM mode and PWM mode could be well compensated in this circuit. As revealed by simulations, the driving current variations of LED could be retained within 10% when VTH shifts in the ranges from -1 to 2 V for PAM driving TFT and from -1 to 1.5 V for PWM driving TFT, respectively. In practice, a good brightness uniformity over 90% after 240-hours aging of the MLED display could be realized.