A Dual-Mode Readout Circuit for SPAD Imaging Applications

CMOS single-photon avalanche diodes (SPADs) have recently emerged as promising components in various high-detection-rate imaging applications, including low-light imaging and light-detection and ranging (LiDAR). To reduce the dead time and enhance the timing resolution, each SPAD is equipped with a passive quenching active reset (PQAR) circuit, which includes a logic control circuit for self-restoration. Then a readout tree (RT) circuit is included to accommodate different imaging requirements. The RT circuit introduces two operating modes: single-hit mode and multi-hit mode, enabling pre-processing of the photon-induced signals to meet diverse imaging requirements. A test chip with an effective 1×64 pixels has been designed and fabricated. Measurement results show a reduction in the jitter of the photon-induced signal width of the PQAR circuit to 29.5 ps. Furthermore, a decrease in the dark count rate (DCR) to 0.53 cps/µm² for the multi-hit mode and an improvement in the photon detection efficiency (PDE) to 9.96% for the single-hit mode has been demonstrated.