Compact readout circuits for SPAD arrays

Single Photon Avalanche Diodes (SPADs) create a very short duration voltage pulse whenever a photon is detected. The resulting high sensitivity and temporal resolution makes them useful in a range of applications. In this paper two different analogue circuits are reported that are suitable for imaging applications that can record the number of detected photons in the limited area available between SPADs in a two dimensional array. With further development, these circuits could be used in imagers capable of imaging in very low light levels.