A 0.86 mW 17 fA/√Hz, 129-dB DR Current-Sensing Front-End for Under-Display Ambient Light Sensor With Zero-Compensated Logarithmic TIA

This letter presents a low-noise, power-efficient, and pulsatile-interference stabilized photocurrent readout circuit for under-display ambient light sensors (ALS). To achieve pA-level input noise and seven decades of input current dynamic range (DR) simultaneously, a logarithmic transimpedance amplifier (TIA) with a diode-connected MOS feedback is set as the first stage of the ALS. An auto-tracking zero, implemented in the amplifier of the TIA, improves the phase-margin and reduces the settling time against pulsatile interference without extra power consumption. The TIA output is then quantized by a first-order 9-bit incremental delta-sigma modulator. Fabricated in a standard 0.18- $\mu $ m CMOS process, the proposed ALS achieves the best-in-the-class input-referred current noise of $0.6~\rm {pA}_{\mathrm {rms}}$ within a 400- $\mu $ s readout time. The total input range of $1.7~\rm {pA}_{\mathrm {PP}}$ – $5~\mu \rm {A}_{\mathrm {PP}}$ corresponds to a DR of 129 dB while consuming 0.86 mW at a 1.8-V supply.