ATLAS: a large array, on-chip compute SPAD camera for multispeckle diffuse correlation spectroscopy

We present ATLAS, a 512 x 512 single-photon avalanche diode (SPAD) array with embedded autocor relation computation, implemented in 3D-stacked CMOS technology, suitable for single-photon correlation spectroscopy applications, including diffuse correlation spectroscopy (DCS). The shared per-macropixel SRAM architecture provides a 128 x 128 macropixel resolution, with parallel autocor relation computation, with a minimum autocor relation lag-time of 1 mu s. We demonstrate the direct, on-chip computation of the autocor relation function of the sensor, and its capability to resolve changes in decor relation times typical of body tissue in real time, at long source-detector separations similar to those achieved by the current leading optical modalities for cerebral blood flow monitoring. Finally, we demonstrate the suitability for in-vivo measurements through cuff-occlusion and forehead cardiac signal measurements.