256×8 SPAD Array with 256 Column TDCs for a Line Profiling Laser Radar

Abstract

A receiver circuit for pulsed time-of-flight line profiling laser radar has been designed in 0.35μ m CMOS technology. The receiver consists of a line detector array with 256× 8 SPADs with a pitch of 41.6μ m. The diameter of the SPAD's active area is 25.6μ m, which gives a fill factor of 0.35. Each column has 8 SPADs and a TDC with a range and resolution of 640 ns and 20 ps, respectively. The TDCs are based on the Nutt interpolation method where cyclic converters are utilized as fine converters. A compact demonstrator system has been built with a horizontal FOV of about 37°, which gives a column-wise angular resolution of about 0.15°. This solid-state system uses a pulsed laser diode with cylindrical transmitter optics to illuminate the full FOV of the receiver with a single laser pulse. The system can measure distances up to 30 m @ 28 fps with an accuracy and precision of few millimeters in typical indoor lighting conditions. Outdoors, in direct sunlight conditions, the measurement range is decreased to 5 m. Outdoor range, however, can be increased if frame rate is lowered and more laser shots are accumulated per frame.