Patent ID: 7479995
Filing Date: 2009-01-20
Classification: H04N

Abstract:
1. A method of correcting for fixed pattern noise, comprising: providing a pixel having a photodiode; providing a first sample and hold circuit and a second sample and hold circuit, wherein said first sample and hold circuit and said second sample and hold circuit each comprise a first FET having a source, a drain, and a gate; a first capacitor having a first terminal connected to said drain of said first FET and a second terminal connected to ground potential; a second capacitor having a first terminal connected to said drain of said first FET and a second terminal; a second FET having a source connected to said second terminal of said second capacitor, a drain connected to ground potential, and a gate; and a third FET having a source connected to said source of said second FET, a gate, and a drain connected to an output bus; allowing light to impinge on said photodiode during an integration period; performing a first readout of said photodiode after said integration period has been completed and storing a first signal in said first sample and hold circuit wherein said first signal is related to the potential of said photodiode during said first readout of said photodiode; resetting said photodiode after performing said first readout of said photodiode; performing a second readout of said photodiode, after resetting said photodiode after performing said first readout of said photodiode, and storing a second signal in said second sample and hold circuit wherein said second signal is related to the potential of said photodiode during said second readout of said photodiode; resetting said photodiode after said second readout of said photodiode to prepare for the next integration period; subtracting said second signal from said first signal, thereby producing a signal related to the amount of light incident on said photodiode during said integration period corrected for fixed pattern noise.