Patent ID: 7936039

Claim:
A backside illuminated CMOS image sensor with a front side and a back side, the backside illuminated CMOS sensor comprising: a photosensitive element on the back side, for releasing charge when light strikes the photosensitive element; a photo gate on the front side, the photo gate having a potential well for receiving the released charge from the photosensitive element; a sense diffusion for receiving the released charge from the potential well; a readout circuit coupled to the sense diffusion, for measuring a voltage corresponding to the released charge transferred to the sense diffusion; a drain switch adjacent the photo gate on the front side, for draining excess charge from the photo gate; and comparison circuitry arranged to compare the voltage measured by the readout circuit to a threshold voltage; said readout circuit further arranged to: generate a first corresponding readout voltage based on the voltage at said sense diffusion prior to the transfer of said released charge from said photo gate to said sense diffusion when the voltage at said sense diffusion prior to the transfer of said released charge is greater than a threshold voltage, and to generate a second corresponding readout voltage based on the voltage at said sense diffusion after the transfer of said released charge from said photo gate to said sense diffusion when the voltage at said sense diffusion prior to the transfer of said released charge is less than said threshold voltage.