An In-Pixel Ambient Suppression Method for Direct Time of Flight

Abstract

This letter proposes a novel single photon avalanche diode (SPAD)-based pixel, designed for direct Time-of-Flight (ToF) imaging with in-pixel averaging, which provides a promising advancement in low-power and potentially high image resolution for outdoor applications. By utilizing a laser pulse and two orthogonal sinusoidal signals, the pixel averages out the detected ambient light while accumulating the laser pulse round-trip time. A prototype pixel array was fabricated using a 180 nm CMOS process, featuring a commercial SPAD cell. By characterizing one pixel and employing a 100 klux solar emulator as an ambient light source with a fixed 40 ambient-to-signal ratio over a 360 $^{\circ }$ phase shift, equivalent to 6 m detection range, the maximum detected accuracy error was 3.3%, with a 5 cm precision.