Patent ID: 7616242

Claim:
A method of operating a pixel circuit, comprising: linearly collecting photogenerated charge using a transistor when the amount of said collected charge is below a threshold value; logarithmically collecting said photogenerated charge by operating said transistor in a sub-threshold mode when the amount of said collected charge is above said threshold value; controlling a sub-threshold current flowing through said transistor during said logarithmically collecting by having previously selected a value of a first capacitive element positioned between a gate terminal and a source terminal of said transistor so as to provide a desired sub-threshold current coefficient of said transistor, wherein said controlling includes enlarging said sub-threshold current coefficient of said transistor when said transistor is operated in said sub-threshold mode by operating said transistor in a floating-gate state wherein said transistor has a second capacitive element connected to said gate thereof; and controlling a capacitance of said second capacitive element based on a level of illumination of said pixel circuit.