Patent ID: 7443427
Filing Date: 2008-10-28
Classification: H04N

Abstract:
1. A method of operating a pixel circuit, comprising: collecting photogenerated charge at an integration node in response to a pixel signal during a charge integration period; operating a first transistors, in a shut-off mode, during said integration period when the amount of said collected charge is below a threshold value to cause charge to be linearly collected at said node; operating said first transistor, in a sub-threshold mode, during said integration period when said collected charge is above said threshold to cause charge to be logarithmically collected at said integration node; prior to a reset operation, injecting charge into a pixel capacitor coupled to said integration node; during the time said first transistor is operating in the sub-threshold mode, draining excess charge from said integration node through the first transistor; separating said collected charge into color and brightness components; processing said color component; recombining said brightness and color components; dividing said logarithmic charge-accumulation phase into first and second logarithmic phases corresponding to lower and higher saturation levels respectively; and for said second logarithmic phase, eliminating a color signal from an output of said pixel during the processing of said color component.