A BiCMOS Active Quencher Using an Inverter-Based Differential Amplifier in the Comparator

For fast switching off of a firing single-photon avalanche diode, an active quenching circuit in 0.35 μm BiCMOS technology with a very fast quenching slew rate is introduced. Quenching transients measured at an integrated small prober pad are shown. An NPN transistor as quenching switch leads to an active quenching time of 250 ps and a quenching slew rate of 21.1 V/ns. A self-biased two-inverter differential amplifier used in the comparator makes this fast quenching possible. By the implementation of cascoding, the excess bias voltage of the integrated SPAD can be doubled to 6.6 V with respect to the nominal supply voltage of 3.3 V of the BiCMOS process used. Active resetting of the SPAD is achieved in 725 ps. The power consumption of the BiCMOS quenching circuit is 16.3 mW at 40 Mcounts/s and 3 mW in the idle state.