Passive CMOS Single Photon Avalanche Diode Imager for a Gun Muzzle Flash Detection System

We present the architecture and design of a novel 64×64 CMOS single-photon avalanche diode (SPAD)-based imager for gun muzzle flash detection. The imager is fabricated in a standard front side illuminated 0.18μ m CMOS image sensor process. Each pixel comprises a 25μ m diameter SPAD, a variable-load passive quenching circuit implemented with 1.8 V PMOS, an 8-bit counter, an 8-bit latch register, and digital processing electronics, and feeds an 8-bit output bus. The array delivers two-dimensional intensity data through photon counting, with integration time as low as 5μ s over the full dynamic range. Per-pixel digital memory enables fully parallel processing and global-shutter mode readout. The imager can acquire fast optical events at high frame rate (up to 200 kfps) and at single-photon sensitivity. The imager has an 8-pixel (64-bit) parallel output bus. This imager enables for the first time the detection and arrival-direction determination of individual muzzle flashes in real time, and even in the case of bursts of flashes, at a moderate cost and size. The presented results confirm the feasibility of gun muzzle flash online detection in the visible or NIR spectrum by uncooled silicon SPAD detectors using standard CMOS technology.