A novel self-adaptive photosensing active-pixel structure with tunable sensitivity for high performance CMOS image sensors

In this paper, a novel self-adaptive photosensing active-pixel structure with tunable sensitivity has been proposed and demonstrated for the first time, which is implemented by using a standard 0.35-mu m CMOS logic process. For the desired performance characteristics of the proposed pixel structure, a new photogate structure is incorporated into the photodiode active-pixel structure. The sensitivity of the proposed pixel structure can be controlled due to tunable sensitivity operation by varying the bias voltage at the photogate (V-PG). At a low voltage level of the photogate (V-PG = OV), the pixel sensitivity of the new photogate pixel structure is improved by more than two-times compared to the conventional pixel. At a high voltage of V-PG = 3V, the dynamic range of the new structure is increased by more than 10 dB. Consequently, the new pixel structure allows performance tunability as well as optimization in both the dynamic range and the sensitivity of the image sensor cell.