A SPAD detection strategy based on the inter-arrival time of photons for enhanced long distance LiDAR applications

In this work, we present a detection strategy for Single Photon Avalanche Diode (SPAD)-based direct Time of Flight (d-ToF) depth measurement systems designed to improve the state of the art in terms of capability to withstand intense background light and thus increasing the maximum achievable measurement range. The proposed detection strategy differs with respect to existing approaches as it is based on an active search of the photon-related timestamp with the maximum likelihood of belonging to the reflected laser pulse. Designed to be implemented with an asynchronous SPAD driving scheme, the technique is based on the selection of the photon timestamp associated to the shortest inter-arrival time, therefore inherently maximizing the probability of detection of the correct ToF value. The technique is demonstrated by means of simulation results, based on a physical model for the computation of the optical power budget and a numerical Monte Carlo engine for the generation of the simulated train of timestamps. We consider a set of realistic parameters for a wide range, SPAD-based, d-ToF sensor for an autonomous driving scenario, showing an increase in the maximum achieved measurement range of up to +46% compared to a standard detection approach, under extremely challenging background illumination of ≈ 100 kiloLux.