A 160x120 Pixel Analog-Counting Single-Photon Imager With Time-Gating and Self-Referenced Column-Parallel A/D Conversion for Fluorescence Lifetime Imaging

A single-photon, time-gated, 160 × 120 pixel imager is presented for its application in fluorescence lifetime imaging microscopy. Exploiting single-photon avalanche diodes and an extremely compact pixel circuitry-only seven MOSFETs and one MOSCAP-the imager is capable of gathering information about photon position, number, and time distribution, enabling cost-effective devices for scientific imaging applications. This is achieved thanks to the photon counting and time-gating capabilities implemented in the analog domain, which in turn enable a 15 μm pixel with a 21% fill-factor. A reconfigurable column circuitry supports both the analog conventional readout and a self-referenced analog-to-digital conversion, able to cancel out the pixel-to-pixel nonuniformities, and speeding up the framerate to 486 fps. The imager, featuring also a delay locked loop to stabilize the internal waveform generation for reliable timing performance, has been implemented in a standard high-voltage 0.35 μm CMOS technology. Measurements in a fluorescent lifetime setup have been performed, comparing the results with single-point acquisitions made with commercial time-correlated equipment.