Single Photon Avalanche Diode Circuits For Ultra-Violet Imaging

A compact CMOS single-photon avalanche diode (SPAD) pixel for ultra-violet imaging is reported using a standard high-voltage CMOS process with a dedicated passivation opening for the diode. An active quenching circuit is proposed to increase the speed and reliability of avalanche quenching and recharge. A 9-bit digital counter is also provided in each pixel to perform photo-counting operations. The designed pixel has a size of $35 \times\ 40\ \mu\mathrm{m}$ , with a fill factor of 8%.