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Gated operation of InGaAs SPADs with active quenching and fast timing circuits

InGaAs and Germanium devices employed as Single-Photon Avalanche-Diodes (SPAD) for the infrared spectral range must be cooled to low temperature for reducing the dark-counting rate due to thermal generation and are plagued by strong avalanche carrier trapping. Released trapped carriers re-trigger the avalanche and generate correlated afterpulses. This effect can be counteracted by reducing the avalanche pulse charge and by covering the trapped carrier release transient with a hold-off time after quenching. Gated operation is employed, but simple gated passive circuits are suitable only for short gate intervals (few nanoseconds). For longer gate times, we investigated gated operation of a SPAD under the control of an active quenching circuit, which yielded accurate timing performance. We designed an integrated active quenching circuit (iAQC) suitable for gated mode for operating the SPAD down to cryogenic temperature. The iAQC senses the avalanche and swiftly quenches it, without waiting the end of the gate interval. Operation with longer gate times (100 ns and more) is achieved with remarkably reduced afterpulsing with respect to passive gated circuits. We expressly designed fast circuits for processing the avalanche pulse, cancelling spurious spikes due to gate transients and accurately extracting the photon timing information, with less than 50 ps jitter.