Abstract: In order to suppress the effects of ambient light and the dark count of single-photon avalanche diode (SPAD) on the performance of readout circuits, a readout circuit with photon coincidence detection function was designed for InGaAs SPAD in this work. In the design, the quenching circuit integrates the photon coincidence detection circuit, which can operate in 4 different detection levels according to the intensity of ambient light. Only when the number of pulses detected within the time window reaches a threshold, it is determined to be an effective photon event, which effectively reduces the influence of ambient noise. And the signal to background ratio of the readout circuit can reach 5.44. Additionly, the time-to-digital converter (TDC) in the design adopts a dynamic allocation circuit, which reduces the number of TDCs, and decreases the power consumption and data volume to 62.5% and 60% of anon-dynamic allocation TDC circuit, respectively. The simulation verification results show that, under the SMIC 180 nm BCD process, the TDC can achieve a resolution of 250 ps at different process angles and temperatures through precise control of the delay-locked loop. The worst-case conversion linearity values are as follows: the differential nonlinearity is −0.6 times the least significant bit (LSB), and the integral nonlinearity is 0.2 LSB, both of which are better than ±1 LSB.

Key words: single-photon avalanche diode, photon coincidence detection, dynamic allocation, time-to-digital converter