title: Compact SPAD-Based Pixel Architectures for Time-Resolved Image Sensors.
abstract: This paper reviews the state of the art of single-photon avalanche diode (SPAD) image sensors for time-resolved imaging. The focus of the paper is on pixel architectures featuring small pixel size (<25 μm) and high fill factor (>20%) as a key enabling technology for the successful implementation of high spatial resolution SPAD-based image sensors. A summary of the main CMOS SPAD implementations, their characteristics and integration challenges, is provided from the perspective of targeting large pixel arrays, where one of the key drivers is the spatial uniformity. The main analog techniques aimed at time-gated photon counting and photon timestamping suitable for compact and low-power pixels are critically discussed. The main features of these solutions are the adoption of analog counting techniques and time-to-analog conversion, in NMOS-only pixels. Reliable quantum-limited single-photon counting, self-referenced analog-to-digital conversion, time gating down to 0.75 ns and timestamping with 368 ps jitter are achieved.
authors.affiliation: Integrated Radiation and Image Sensors, Fondazione Bruno Kessler, Trento 38123, Italy. perenzoni@fbk.eu.
authors.forename: Matteo
authors.initials: M
authors.lastname: Perenzoni
authors.affiliation: Department of Industrial Engineering, University of Trento, Trento 38123, Italy. lucio.pancheri@unitn.it.
authors.forename: Lucio
authors.initials: L
authors.lastname: Pancheri
authors.affiliation: Integrated Radiation and Image Sensors, Fondazione Bruno Kessler, Trento 38123, Italy. stoppa@fbk.eu.
authors.forename: David
authors.initials: D
authors.lastname: Stoppa
keywords: SPAD; single-photon avalanche diode; time-gating photon counting; time-resolved imaging