Design Considerations for Current-Assisted Photonic Demodulator (CAPD) in Time-of-Flight CMOS Image Sensor

Time-of-Flight (TOF) optical ranging technique, which correlates the reflected active illumination arrival time (or phase delay) with the distance of the object, is one solution to capture a 3D image in realtime and with high-depth accuracy [1], Current-Assisted Photonic Demodulator (CAPD) is one of the widely popular electro-optical demodulator implementations [2], CAPD extracts the phase information in the digital charge domain (Fig. 1) by mixing the reflected IR signal with two 180° out of phase electrical control signals. By linking the phase delay with the time of flight, the distance between an object and the camera is resolved. The said demodulation scheme can be performed in real-time using CAPD as the transport of photogenerated carriers are assisted by drift. Because of a lack of physical model for CAPD, guidelines in designing the structure and selecting its biasing conditions have not been established yet. With this, we analyzed the carrier transport mechanism and I-V characteristics of CAPD using 3D Atlas numerical simulations and define design considerations for its physical structure and biasing, accordingly.