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

IF 2.2 Q3 COMPUTER SCIENCE, HARDWARE & ARCHITECTURE IEEE Solid-State Circuits Letters Pub Date : 2025-01-13 DOI:10.1109/LSSC.2025.3528962

Liheng Liu;Tianxiang Qu;Hao Li;Dan Li;Gan Guo;Zhiliang Hong;Jiawei Xu

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Abstract

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.

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