Optimal readout schemes in SPAD-based time-correlated event detection sensor for quantum imaging applications

CMOS SPAD imagers are potentially good candidates for detection of entangled photons in Quantum Imaging applications thanks to their sub-nanosecond time-resolved capabilities and highly parallel readout. In this context, the low number of photons that are typically detected corresponds to a very sparse data matrix. A full readout of raw data is therefore a waste of time and power. We have implemented a sensor architecture to improve the efficiency of the observation up to 8.46% in a TDC-based pixel structure. A tunable current source is used per pixel to establish a global current. This global current presents a real-time status of the whole pixel array in terms of triggered SPADs. The proposed solution requires minimal extra pixel electronics, with little impact on the fill factor and allows an observation rate of up to 8.5 Mfps.