7.3 A 189×600 Back-Illuminated Stacked SPAD Direct Time-of-Flight Depth Sensor for Automotive LiDAR Systems

Abstract

There have been many developments in Light Detection And Ranging (LiDAR) sensors used in Autonomous Driving (AD) and Advanced Driver Assistance Systems (ADAS) to measure the precise distance to an object, recognize the shape of an intersection, and classify road types. These LiDAR sensors can achieve fantastic results day and night without any loss of performance. In the past, Time-Correlated Single Photon Counting (TCSPC) and complete digital signal processing (DSP) have been used in to achieve a 100m range Time-of-Flight (ToF) sensor [1]. Background (BG) noise-rejection techniques [2] have been used to improve the signal-to-noise ratio (SNR), leading to detection of objects at a 6km range. Single Photon Avalanche Diode (SPAD)-based architectures implement per-pixel level histogramming, Time-to-Digital Conversion (TDC) and signal processing [3], [4]. Another ToF sensor has been shown that enables significantly higher resolution, $1200 \times 900$ pixels [5]. With the emerging need for a highresolution solid-state LiDAR using a scanning 2D-SPAD array [6], we report a SPAD direct Time-of-Flight (dToF) depth sensor [1] –[5] to realize long-distance 300m range and high resolution over an automotive-grade temperature range of -40 to $125 ^{\circ}{C}$. This microelectromechanical systems (MEMS)-based SPAD LiDAR can measure over ranges up to 150m with 0.1% accuracy for a 10%-reflectivity target and 200m with 0.1% accuracy for a 95%-reflectivity target. This paper presents a back-illuminated stacked SPAD dToF depth sensor deployed with passive quenching and recharge (PQR) frontend circuitry, TCSPC, and on-chip DSP. Under 117klux sunlight conditions, the MEMS-based SPAD LiDAR measures distances up to 200m with $168 \times 63$ resolution at 20 frames/s.