Multi-laser source interference suppression using the time-coding method for SPAD-based flash DToF systems

Flash-type direct time-of-flight (DToF) image sensors use an in-pixel successive approximation register time-to-digital converter (SAR TDC) for time quantization. However, in a scene where multiple DToF systems exist simultaneously, different laser signals from multiple sources will produce mutual signal interference between DToF systems, causing the DToF system's incorrect measurement. In this paper, we present a method called time coding, which inserts delay time bins between different working periods to suppress the interference laser together with the SAR TDC. The time-coding method is designed using a 110 nm complementary metal oxide semiconductor (CMOS) technology and verified by behavioral model and circuit simulation. Regardless of traditional systems or systems equipped with time coding, DToF systems with certain patterns of time coding can reduce interference noise by at least 95%, maintaining a measurement accuracy of 99% or higher at long distances.