A 150nm fully integrated active quenching circuit driving custom technology SPAD at 250Mcps

Single Photon Avalanche Diodes (SPADs) are the enabling device for different kind of applications in which low noise, high photon detection efficiency, and compactness are required. They are capable of providing high photon count rate and picosecond timing precision. Furthermore, they can be fabricated in arrays, unlocking very high-count rates and the possibility to retrieve also incident photon’s spatial information. For these reasons, SPADs are the sensors of choice in many applications such as Light detection and ranging (LiDAR), Time Correlated Single Photon counting (TCSPC) and quantum key distribution (QKD). Whether the SPAD is implemented in a custom technology, allowing detector tailoring on specific application constraints, or in a CMOS process, with great benefits in terms of large-scale integration and compactness, a quenching circuit is always required, and it sets the ultimate performance that can be extracted from this sensor. The custom approach for SPAD fabrication poses a challenge in the design of the external quenching circuit mainly due to the parasitics (capacitance, wire-bonding inductance, etc.) that intrinsically come with having the detector and the circuit on two separate silicon dies, which is potentially a limiting factor for speed and timing precision. In this work, we present a fully-integrated active quenching circuit capable of driving external custom SPADs up to 250 Mcps. The circuit has been fabricated exploiting a 150nm high voltage technology and extensively tested with a custom SPAD.