SPAD-based Light Detection and Ranging for 3D imaging

Abstract

In this work, a SPAD-based LiDAR system is studied. In particular, the system employs a direct time-of-flight (dToF) method to reconstruct a target-reflected pulses using histogram, from which the distance to the target is estimated. More particularly, a time correlated single photon counting (TCSPC) method has been used to record the flight time of pulses. Such method assumes and successfully reconstructs the returned pulses in a photon starved condition, but fails under strong background noise. The increase in average photon counts per detection range limits the detection range, thereby rendering the system impractical for an automotive application where strong sunlight is present. The techniques proposed in this work, namely the asynchronous gating technique and the adaptive TDC gating technique, have been simulated for the SPAD-based LiDAR system and achieves a reliable detection range of 74m and reduces the required memory size by at least a factor of 14 in comparison to the system without a data compression technique, respectively.

In-pixel time-to-digital (TDC) converters are further studied in this work. In doing so, a novel Figure-of-Merits (FoM) is proposed, which illustrates a logarithmic relation between the proposed FoM and the technology node and that the ring oscillator architecture achieves a small form factor. Accordingly, a ring oscillator architecture is studied with various delay cell topologies, which are simulated and compared against each other. The stacked-inverter topology, biased by current sources, consumes the lowest power and suceptibilty to supply variation, while exhibiting comparable supply sensitivity and jitter with respect to compared topologies. It is therefore concluded that the stacked-inverter topology shall be considered as a delay cell topology when designing a ring oscillator based large array of in-pixel TDCs.