ToF Image Sensor with Pulse-Frequency-Modulation Pixel for In-Pixel Code Discrimination

This paper presents a time-of-flight (ToF) CMOS image sensor with pulse-frequency-modulation (PFM) pixel for in-pixel code discrimination (CD). One of ToF's main problem is interference between multiple sensors or malicious one by third party. CD is a function that discriminates signal light from the others with code modulation, which will be an effective countermeasure against such interference. Proposed pixel contains a PFM circuit and counters, with which in-pixel CD and distance measurement (DM) is tried to be realized. In this paper, methods of CD and DM, circuit implementation are shown, and HSPICE and C simulation demonstrates signal-to-background ratio rejection of -7dB and 8dB signal-to-interference ratio for 128-bit CD with less than 0.08% error.