Single-Photon Imagers with In-Pixel, Area-Efficient Time-to-Digital Converters

Single-photon avalanche diodes in CMOS technology are a key enabling technology for the realization of monolithic time-resolved image sensors for a broad range of applications. By combining avalanche detectors with integrated logic for counting and timestamping, photon arrays can extract the spatiotemporal characteristics of an optical signal in the spatial and temporal domains. This chapter focuses on the implementation of two sensor architectures with in-pixel, area-efficient time-to-digital converters with integrated ring-oscillator. The first design is based on a timestamping circuit with analog oversampling of the ring phases, achieving 19.46% fill factor. The second design implements the smallest ring-oscillator in the literature (12 transistors only), and its scalability has been demonstrated in a 60 k pixel array.