A 560μW 6fA/√Hz 146dB-DR Ultrasensitive Current Readout Circuit for PWM-Dimming-Tolerant Under-Display Ambient Light Sensor

This paper presents an ultra-low-noise, power-efficient, and PWM-dimming-tolerant photocurrent readout circuit for under-display ambient light sensors (ALS). To achieve a pA resolution, a transimpedance amplifier (TIA) with a feedback diode is used to provide GΩ resistance and input current noise of 6fA/√Hz. To resolve instability and noise folding with low power, the TIA utilizes a signal-dependent auto-tracking zero for frequency compensation, and a low-pass filter to suppress high frequency current noise. To accurately extract ambient light from the interference of PWM dimming, the readout can operate in an under-sampling mode to remove the interference through algorithm. Fabricated in a 180nm CMOS technology, this work achieves best-in-class resolution of 0.36pApp and 146dB DR in a readout time of 0.84ms, reaching an excellent FoM-DR of 206.3dB. ALS optical measurement with PWM dimming interference has been successfully demonstrated.