Patent ID: 7781719

Claim:
A pixel structure, comprising: a photogate; and a photodiode, wherein an integration capacitance characteristic of the pixel structure is controlled by applying a constant bias voltage (V PG ) to the photogate during an integration period of the pixel structure, an integration capacitance of the pixel structure switches between a low value and a high value, thereby changing a sensitivity and a dynamic range of the pixel structure, the constant bias voltage V PG satisfies the relationship V reset >V PG −V th , with V reset being a reset level and V th being a threshold voltage of the photogate, the photodiode is isolated from a defective field oxide border to reduce a dark current, the integration capacitance of the pixel structure in a first state is equal to an integration capacitance of the photodiode, the integration capacitance of the pixel structure in a second state is equal to a sum of the integration capacitance of the photodiode and an integration capacitance of the photogate, during the integration period, photo-generated majority carriers are collected at an integration node, decreasing a voltage (V int ) at the integration node below V reset , and when V int >V PG −V th , a cathode region of the photodiode is disconnected from a depletion layer of the photogate due to a pinch-off phenomena, thereby causing the integration capacitance to equal an integration capacitance of the photodiode, and causing high sensitivity at a low illumination intensity.