Time-of-flight (ToF) optical ranging technique is a 3-D imaging solution which captures the depth information in a given scene for applications such as autonomous navigation, ambient-assisted living, industry assembly, and gesture control interface for human-machine interaction. A widely popular ToF sensor implementation is the current-assisted photonic demodulator (CAPD). While CAPD has been being used in ToF systems, its operation characteristics are difficult to predict because of a lack of a compact model describing its output current as a result of the incident light and modulating voltages. This problem further poses difficulty in establishing design considerations to achieve a good tradeoff in sensitivity, power, speed, and efficiency for such photonic demodulator.

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Time-of-flight (ToF) optical ranging technique is a 3-D imaging solution which captures the depth information in a given scene for applications such as autonomous navigation, ambient-assisted living, industry assembly, and gesture control interface for human-machine interaction. A widely popular ToF sensor implementation is the current-assisted photonic demodulator (CAPD). While CAPD has been being used in ToF systems, its operation characteristics are difficult to predict because of a lack of a compact model describing its output current as a result of the incident light and modulating voltages. This problem further poses difficulty in establishing design considerations to achieve a good tradeoff in sensitivity, power, speed, and efficiency for such photonic demodulator.

In this work, a compact model for CAPD describing both the static and dynamic behavior of the device is proposed. An analytical expression relating the optical photogenerated current to the input bias and incident light intensity is derived by solving the continuity and drift-diffusion equations along the optical window of CAPD. The model has been extensively verified with numerical simulations, as well as with published experimental data. Based on the developed model, a new figure-of-merit is proposed to define the operational efficiency of CAPD with respect to the peak modulation voltage. In the end, the functionality of the full compact model is demonstrated by simulating the dynamics of electro-optical mixing in a ToF pixel. This will then enable ToF circuit designers to carry out a system level simulation, including the readout and signal processing circuitry, of their image sensor design in a circuit simulator framework.