Patent ID: 7738019

Claim:
An automatic gain control system for an imaging device comprising: an image sensor with a plurality of active pixels, each of said active pixels comprising: a photosensitive device configured to generate an electrical signal in response to impinging light; and a storage device electrically connected to said photosensitive device to store an accumulated signal of said electrical signal during an exposure period; an integration circuit including an output transistor electrically connected to said storage device of each of said active pixels to receive a combined signal of said accumulated signal stored in said storage device of each of said active pixels, said output transistor being connected to produce a comparison signal corresponding to said combined signal, wherein said output transistor of said integration circuit is connected in series with a current source on a signal path between a first voltage rail and a second voltage rail; a comparator connected to said integration circuit to receive said comparison signal, said comparator being configured to compare said comparison signal with a threshold signal; and a counter operably connected to said comparator, said counter being configured to measure the duration for said comparison signal to become equal to said threshold signal, said duration being used to derive a shutter value for subsequent image capture.