  Most active quench circuits used for single-photon avalanche photodetectors
(APDs) are designed either with discrete components which lack the flexibility
of dynamically changing the control parameters, or with custom ASICs which
require a long development time and high cost. As an alternative, we present a
reconfigurable and robust hybrid design implemented using a System-on-Chip
(SoC), which integrates both an FPGA and a microcontroller. We take advantage
of the FPGA's speed and reconfiguration capabilities to vary the quench and
reset parameters dynamically over a large range, thus allowing our system to
operate a variety of APDs without changing the design. The microcontroller
enables the remote adjustment of control parameters and calibration of APDs in
the field. The ruggedized design uses components with space heritage, thus
making it suitable for space-based applications in the fields of
telecommunications and quantum key distribution (QKD). We demonstrate our
circuit by operating a commercial APD cooled to -20{\deg}C with a deadtime of
35ns while maintaining the after-pulsing probability at close to 3%. We also
showcase its versatility by operating custom-fabricated chip-scale APDs, which
paves the way for automated wafer-scale characterization.

Instrumentation and Detectors