A 512×512 SPAD Laser Speckle Autocorrelation Imager in Stacked 65/40nm CMOS

We present a single-photon avalanche diode (SPAD) autocorrelation imager implemented in 65/40nm 3D-stacked CMOS for laser speckle blood flow monitoring. The shared per-pixel SRAM architecture provides a compact 41.68 µm pitch 128×128 resolution parallel autocorrelation function operating at 0.5T Op/s and a lag-time of 1 µs. SNR gains due to high BSI SP AD NIR sensitivity and on-chip averaging extends source-detector separation to 40 mm indicative of the sensitivity required to discriminate extracerebral artifacts from deep-tissue blood flow in future wearable neuromonitoring systems.