High Resolution LiDAR based on Single Chip SPAD Array 2019-01-0119
It is important that Advanced Driver Assistance Systems (ADAS) and Automated Driving Systems (AD) detect on-road objects, road vehicles and pedestrians. The typical detection devices mounted on ADAS and AD include a camera, a millimeter-wave radar and a Light Detection And Ranging (LiDAR). Since LiDAR can obtain accurate distance and fine spatial resolution due to its short wavelength, it is expected that small objects such as a tire can be detected. However, the conventional LiDAR is equipped with multiple light transmitters and light receivers such as avalanche photo diodes. This causes LiDAR system to be expensive and large in size. Aiming to reduce the cost and size of LiDAR, we employed Single-Photon Avalanche Diode (SPAD) which can be fabricated by CMOS process and easily arrayed. We also developed “Single Chip SPAD Array“ in which the two-dimensional array of SPAD and a signal processing block of range calculation were integrated into a single chip. The light-receiving area was composed of 260x12 SPAD-pixels array. In order to verify the principles, we designed a prototype of LiDAR on which a single chip SPAD array, a micro-electro-mechanical systems (MEMS) mirror as a scanner and 100W laser diode were mounted. The field-of-view was 55x9.1 degrees (HxV) and the vertical angular resolution split by SPAD array was 0.76 degrees. Using the prototype, we were able to detect the target of 10% reflectivity at a distance of 50m. Therefore, we succeeded in verifying the principles of sensitivity improvement by SPAD-LiDAR and simulated its behavior. Moreover, based on this result, we optimized SPAD pixels and LiDAR configuration and confirmed that it is possible to detect a piece of broken tire of around 4% reflectivity by the simulation on the assumption of an actual road scene under daylight.