A 32 x 30 SPAD-Based Scanless LiDAR Sensor with In-Pixel Histogram Array

Abstract

Department of Electrical EngineeringRecently, low cost image sensors have been rapidly developed and applied to various applications. Particularly, the interest in self-driving technology that can drive without a driver beyond the common sense that such applications just help the driver to drive gets attention. Many sensors are required to accurately detect the surrounding situation, and in particular, a LiDAR sensor capable of quickly and accurately measuring mid-range detection is essential to prevent immediate accidents. However, the current LiDAR sensors are expensive due to technical problems with process and rotation issue. It is urgent to introduce a low-cost 3D LiDAR sensor to solve this problem. A single photon avalanche diode(SPAD) is a sensitive device that can generate a signal in response to a single photon and measure a long distance. However, since the SNR of the SPAD is low, histogram which solves the problem through numerous measurements is required. Unfortunately, pixel array cannot be designed due to a memory of histogram, and then SPAD-based LiDAR sensors are currently used as a line sensor. Line sensors using scanning method result in low frame rate, high structural cost for rotation, and low durability issues. This thesis is based on a new concept using a binary search, a successive approximation registrar (SAR) histogram technique, which eliminates the histogram memory and then designs a low-cost solid-state SPAD-based LiDAR sensor with small size in-pixel histogram. And in order to solve the problem of increasing measurement by eliminating memory, the problem was solved by exponential counting by measuring spatiotemporal correlation using multi-SPADs. A 30 x 32 in-pixel histogram array and associated circuitry have been designed in a 0.11um DBH CMOS process. The sensor has dynamic range of 96m and 0.75m precision for coarse resolution sensor with conventional p-well guard ring (GR) SPAD and advanced virtual guard-ring for high spec dark count rate (DCR) photon detection probability (PDP), 7%, at infrared (IR) -wave. The in-pixel histogram occupies 165um x 115um area by eliminating memory for histogram.clos