Superconducting nanowire single photon detectors (SNSPDs) have emerged as a leading choice for high performance single photon detectors due to their low timing jitter, high detection efficiency, and low dark count rates. SNSPDs have typically been biased using a passive quenching scheme in which the bias current of the device is shunted through a resistive load to allow for recovery after a detection event. To prevent latching, the shunting resistor must be approximately an order of magnitude smaller than the peak normal domain resistance of the SNSPD. Consequentially, the pulse amplitude (∝IBRL) and recovery time (∝LK/RL) are both negatively impacted. In this talk, we will describe a novel approach to the bias and read-out of SNSPDs based upon active quenching. We will present detailed design considerations for an active quenching architecture and will show that such an approach has the potential to improve count rates while increasing signal swings to the point where external amplification is no longer required. A silicon germanium (SiGe) active-reset chip design has been designed, implemented, and integrated with a NbTiN SNSPD. The procedure for the SiGe chip design will be described and simulation results will be presented. Finally, detailed measurement results of the complete system will be shown and compared to measurements of the same detector when biased and read-out using a standard passive quenching scheme. It will be shown that the active quenching configuration enables a considerable enhancement to the system performance.
There is a growing interest in developing systems employing large arrays of SNSPDs. To make such instruments practical, it is desirable to perform signal processing before transporting the detector outputs to room temperature. We present a cryogenic eight-channel pixel combiner circuit designed to amplify, digitize, edge detect, and combine the output signals of an array of eight SNSPDs. The circuit has been fabricated and measurement results agree well with expectation. The paper will conclude with a summary of ongoing work and future directions.