An All-Digital Cmos Ambient Light Sensor Using A Single Photon Avalanche Diode

Ambient light sensors are increasingly used in low-power and portable devices to provide real-time response to changing light conditions, from modulating screen brightness to detecting user proximity. These sensors typically use an array of reverse-biased photodiodes coupled to an analog front-end and digitization circuits. In this work, we present an all-digital ambient light sensor, which leverages the pulse-based output of a CMOS-integrated single-photon avalanche diode (SPAD). Using only simple digital circuits to detect and count pulses minimizes circuit area and power. By limiting light reaching the SPAD using a metal filter structure, the detector operates across a broad ambient light range without saturation. Sensitivity is sufficient to enable sensing from a single SPAD device, resulting in further area savings. Measured performance from a fabricated 130 nm CMOS circuit implementation is provided, demonstrating operation in ambient light from 100-25,000 lux with less than 125 microwatts of active power consumption.