Fast and compact time-correlated single photon counting system for high-speed measurement with low distortion

Time Correlated Single Photon Counting (TCSPC) is a widely diffused technique used in scientific experiments requiring the analysis of optical pulses with high timing precision. One of the major limitations affecting this tool are distortion phenomena at high count rates happening due to pile-up. As a result, experiments must be carried out at a slower operating rate than the laser excitation frequency (1%-5%). It has been recently demonstrated that matching the detector dead time with the duration of the laser excitation period allows to overcome the aforementioned speed limitation, while still keeping distortion low. Theoretical results envision a speed improvement by almost an order of magnitude. In this work we present dedicated integrated electronics to implement the proposed idea. The selected detector for this design is a custom technology SPAD in order to achieve high performance. The SPAD is externally driven by an Active Quenching Circuit (AQC) that senses the avalanche current and provides a prompt quenching and reset of the detector. The AQC features a finely tunable dead time and a low reset time, two key aspects to achieve a very-low distortion regime and high efficiency. The detector electric signal is read out by a fully differential pick-up circuit, delivering a timing differential signal with picosecond precision and rejecting disturbances thanks to a dummy cell. A fast time-to-amplitude converter is used to measure the time of arrival of the photons with picoseconds precision and high linearity.