A SPAD-Based Random Number Generator Pixel Based on the Arrival Time of Photons

A quantum random generator based on photon detection is here presented. The system consists of a source of photons, typically a commercial LED, coupled with a detector with single photon detection capability. The detector in this case is represented by a single pixel consisting of a SPAD and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation increases the efficiency of random bit extraction and reduces the afterpulsing probability, which can introduce undesirable correlation to the measurement. Preliminary results are reported, showing that the pixel has a flat behavior for a relevant range of intensity of the light, which makes the pixel robust against variations of external PVT parameters.