Single-photon detection using analog in-pixel histogramming

Achieving real-time and high-resolution photon timing in a compact system remains a key challenge in biomedical sensing and photonics. We present a CMOS SPAD sensor integrating in-pixel analog histogramming for direct fluorescence lifetime acquisition. The 12 × 16 SPAD array features 16-bin analog memories and a tunable delay line with bin widths down to 470 ps. A dual-stage isolation scheme ensures analog stability, achieving average leakage rates of 0.33 mV ms−1 and enabling integration times up to 256 μs without degradation. The sensor was first validated using Alexa Fluor 568 and QDot 705, demonstrating accurate extraction of both short- and long-lifetime decays. It was subsequently evaluated in a compact lens-less platform with QDot 605 and QDot 705, confirming consistent lifetime extraction in a fully integrated configuration. Lifetime extraction was possible using as few as four bins, enabling fast and adaptive acquisition. In-pixel calibration maintains uniform bin linearity, further supporting robust analog histogramming across all temporal configurations. This work establishes a scalable solution for time-resolved fluorescence sensing, with potential for point-of-care diagnostics and compact bioanalytical systems.