32 × 32 CMOS SPAD Imager for Gated Imaging, Photon Timing, and Photon Coincidence

We present the design and simulations of a single-photon sensitive imager based on single photon avalanche diodes (SPADs) with an innovative pixel architecture that includes four separate SPADs with independent active time-gating and quenching circuit, a shared time-to-digital converter (TDC) with 50-ps resolution, four independent photon counters, and multiple operation modes. The TDC is driven by smart arbitration logic, which preserves spatial information among the four detectors; furthermore, an alternative operation mode exploits photon-coincidence on multiple detectors to reduce the effect of high background levels, e.g., in light detection and ranging applications with strong ambient light. Key features are the ability to operate in simultaneous photon counting and timing modes for capturing 2-D and 3-D images of the scene in a single shot (frame), the option of a counting-only mode, reducing power consumption, and increasing achievable frame-rate when timing information is not needed, and the ability to individually shut down noisy detectors or to enable just some regions of interests.