Refreshable Delay Coincidence Detection Circuit for Direct Time-of-Flight Depth Sensors

Abstract

This letter introduces a refreshable delay coincidence detection circuit for direct time-of-flight (DToF) depth sensors. Although the conventional coincidence detection structure can suppress noise pulses from background light, it results in significant attenuation of signal pulses, compromising the accuracy (ACC) of depth acquisition. In this work, the authors propose a refreshable delay coincidence detection structure, which integrates a refreshable delay unit to achieve automatic adjustment of the time window width. Additionally, the initial time window width of the refreshable delay unit can be externally configured, facilitating its application in various background light environments. The proposed structure was implemented and verified in an Artix-7 FPGA. The measurements show that the refreshable structure effectively suppresses noise and performs better in retaining signal pulses and improving peak position accuracy. At an 18 m distance and 150 klx illumination, it captures 161 signal pulses over 300 frames, 60 more than the conventional structure. After 100 repeated measurements, the refreshable structure achieves 91% peak accuracy, outperforming the conventional structure's 72%. The refreshable delay structure enhances depth sensing robustness, flexibility and adaptability, making it ideal for high-precision applications such as robotics and autonomous driving.