Integrated sensor for single-photon readout of avalanche diodes in standard CMOS

We report a novel sensor for ultra-low light detection incorporating a single photon avalanche diode (SPAD) with active circuitry for robust sensing, control, and readout of photon counts in a standard CMOS process. The circuit senses an avalanche event, quenches the avalanche, resets the SPAD voltage bias following a programmable holdoff time, and reports the output signal on a shared communication bus. Two novel aspects of the circuit are the method of holdoff time generation and the introduction of an output interface. The holdoff time is implemented using discrete summation of an oscillatory signal onto a capacitive node, and it achieves linear increments with highly adjustable granularity. The onset of the output signal is simultaneous with the local quenching mechanism, with adjustable pulse width for system-level readout flexibility.