Compact SPAD Pixels with Analogue Counter for Ultraviolet Imaging

A compact actively quenched and recharged n+/p-well SPAD pixel circuit for ultraviolet (UV) imaging is being reported in this paper. This circuit is designed using a high volt-age CMOS process. The pixel includes a 10-bit analogue counter utilizing only five transistors for photon counting applications. The hold -off time of the pixel can be tuned between 2.28 ns to 67 ns using an in-pixel voltage-tuneable delay circuit, thereby, minimizing the possibility of after-pulsing effects. Simulation results show a fast quenching and recharge time of 1.32 ns and 0.96 ns, respectively. The pixel occupies an overall area of 27 µm x 31 µm and has a fill factor of 9.5%.