An Auto-zeroing In-pixel Voltage Comparator for High Accurate PWM Micro-LED Displays Based on LTPO TFTs

An auto-zeroing in-pixel voltage comparator with high dc-gain is proposed for high-accuracy pulse width modulation (PWM) Micro-LED pixel circuits based on low temperature poly-silicon and oxide (LTPO) thin-film transistors (TFTs). The high dc-gain over $78 \mathrm{~dB}$ is resulted from the good match of subthreshold regions and threshold voltages $\left(\mathrm{V}_{\mathrm{TH}}\right)$ of LTPS and oxide TFTs, by adjusting the voltage level of the secondary gate of the dual-gate oxide TFTs. The high-gain LTPO voltage comparator is used to convert data voltage into PWM waveforms, with the falling-time reduced to 21µs, which is about 10% of the previous Micro-LED pixel circuits using p-type voltage comparator. Furthermore, self-zero adjusting procedures are introduced to compensate for $\mathrm{V}_{\mathrm{TH}}$ variations.