I. Introduction
Single-photon avalanche diodes (SPADs) can resolve individual photons with high temporal accuracy. In recent years, various imaging systems exploiting the time-resolving features of SPADs have been demonstrated with increasing spatial resolution. Prominent application domains of SPADs include time-of-flight (ToF) imaging [1]–[3] and biophotonics [4]–[6] In particular, the use of ToF SPAD imagers for range-finding has gained increased interest from the automotive and mobile industries [7], [8]. The application benefits from the integration of SPADs into uniform arrays. Infrared illumination is preferred for the reduction of solar background noise and for complying with eye-safety regulations [9].