A 0.37W 143dB-Dynamic-Range 1Mpixel Backside-Illuminated Charge-Focusing SPAD Image Sensor with Pixel-Wise Exposure Control and Adaptive Clocked Recharging

Abstract

Demands for single-photon-sensitive high-dynamic-range (HDR) imaging in security, automotive, and medical applications have driven development of scalable single-photon avalanche diode (SPAD)-based image sensors. In recent years, 3D-stacking technology combined with advanced CMOS processes has enabled pixel-parallel photon counting in sub-10µm SPAD pixels. A major technical challenge in realizing high-definition SPAD image sensors lies in a trade-off between power consumption and dynamic range (DR). SPAD pixels inherently consume a considerable amount of power due to the high-voltage operation and high current gain. Power consumption from the SPAD array (PSPAD) grows significantly with increasing incident photon flux, and often dominates over that from the readout circuit under high light conditions. Restricting maximum photon counts per frame could suppress the maximum PSPAD, at the expense of DR. To address this issue, a recharging circuit architecture must be carefully considered. Passive recharging has been widely employed for HDR imaging SPADs [1]–[3], but it is not a viable option for megapixel implementation due to the huge PSPAD, typically reaching tens of watts at excess illuminance. A clocked recharging architecture provides a scalable solution thanks to its compact circuitry and greatly reduced PSPAD at excess illuminance [4]–[6], but to date no existing SPAD sensor has simultaneously achieved megapixel resolution, sub-watt total power consumption, and > 120dB DR.