Intelligent System for Optimal Hold-Off Time Selection in an Active Quench and Reset IC

A signal processing circuit using autocorrelation statistics that intelligently selects the optimal hold-off time in an active quench and reset integrated circuit (AQR-IC) is presented. This circuit optimizes the hold-off time to reduce afterpulsing effects in any Geiger-mode avalanche photodiode (GM-APD). The described AQR-IC has a maximum count rate of 20 Mcounts/s, includes a subnanosecond comparator for quickly detecting incident photons, and incorporates a novel technique, based on silicon delay lines, for selecting 1 of 16 predefined, discrete, hold-off times between 5 and 660 ns. The accompanying hold-off time autotuning circuit sets the optimal hold-off time by assigning a 4-b output to the AQR-IC corresponding to the minimization of afterpulse effects in the GM-APD. The configuration sequence completes in a maximum time of 20 s, without operator intervention, and only requires repeating if the GM-APD is changed.