CMOS Single-Photon Avalanche Diode Pixel Design for a Gun Muzzle Flash Detection Camera

We present the architecture and design of a CMOS single-photon avalanche diode (SPAD) pixel that was selected to be the basis for a gun muzzle flash detection camera. The SPAD sensor and auxiliary circuitry are fabricated in a standard 0.18-mu m CMOS image sensor technology. The pixel integrates a 25-mu m pitch SPAD, a variable-load quenching circuit implemented with a 1.8-V pMOS, and digital processing electronics providing an 8-bit output bus. The SPAD is low noise (around 100-Hz dark count rate at 1.8-V excess voltage) and has a real peak photon detection efficiency (not averaged on pixel pitch) of 9.2% at 450 nm (1.8-V excess voltage). The pixel delivers intensity information through photon counting, up to 256 counts per frame with down to 5-mu s integration time for the full dynamic range. The pixel memories enable parallel processing and global-shutter readout, preventing motion artifacts and partial exposure effects. The pixel can acquire very fast optical events at a high frame-rate (up to 200 kilo frames/s) and at a single-photon level. The pixel has an 8-bit parallel output bus.