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

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 (P
SPAD
) 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 P
SPAD
, 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 P
SPAD
, typically reaching tens of watts at excess illuminance. A clocked recharging architecture provides a scalable solution thanks to its compact circuitry and greatly reduced P
SPAD
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.