Another solution of D-ToF is the so-called Indirect ToF (Indirect ToF, I-ToF, hereinafter referred to as I-ToF), and the principle of I-ToF is more complicated. In I-ToF, what is emitted is not a light pulse, but modulated light. There is a phase difference between the received reflected modulated light and the emitted modulated light. By detecting the phase difference, the flight time can be measured and the distance can be estimated. The round trip time is indirectly extrapolated from the time-gated measurement of light intensity. In this case, there is no need for an accurate stopwatch, but a time-gated photon counter or charge integrator, which can be implemented at the pixel level, requiring less computational work and silicon area. I-ToF is a natural solution for electronic and photo hybrid devices based on ToF cameras.
i-ToF, or indirect ToF, analyzes the signal phase through the proportional relationship between the energy values collected by the sensor in different time windows, indirectly measures the time difference between the transmitted signal and the received signal, and then obtains the depth. According to different modulation methods, i-ToF can be divided into two types: continuous wave modulation (CW-iToF) and pulse modulation (PL-iToF), which respectively emit continuous sine signals and repetitive pulse signals; the former is by parsing sine signals The phase resolves the depth, and the latter resolves the depth by analyzing the phase of the pulse signal.
