Method for power reduction of demodulation driver circuit in indirect time-of-flight CMOS image sensor

To improve the depth accuracy of an indirect time-of-flight CMOS image sensor, high modulation frequency is often adopted. It will result in high power consumption of an on-chip demodulation driver, and this problem will be much more serious when the resolution of the sensor is much higher. In this paper, a power reduction method that can lower the power consumption of the demodulation driver circuit during the integration time while obtaining accurate high-resolution depth maps is proposed and analyzed theoretically. The method decreases the number of driven pixels at a high-modulation frequency by a programmable resolution adjustment circuit to obtain an accurate low-resolution depth map. A low-depth accuracy high-resolution depth map is obtained at a low modulation frequency, and then a modified super-resolution algorithm is used to obtain an accurate high resolution solution depth map. To demonstrate the effectiveness of the proposed method, a model is established based on the actual indirect time-of-flight sensor architecture, then the depth error and power consumption are analyzed by the simulation results of the model. In the simulation, 25 MHz and 100 MHz are used as the low modulation frequency and high modulation frequency, respectively. With the best scenario in depth accuracy kept, average power consumption decreases 38.47% and peak power consumption decreases 49.83% while the depth error that is represented by RMSE merely increases 8.08%.