Patent ID: 7508434

Claim:
A circuit for use in an image sensor, the circuit comprising: a floating gate semiconductor device having a floating gate, a control gate, a drain and a source; a photosensitive semiconductor device positioned for exposure to electromagnetic radiation from an image; a pixel control circuit connected to direct said floating gate semiconductor device and said photosensitive semiconductor device to a plurality of controlled modes; said photosensitive semiconductor device is a photodiode having an anode and a cathode; said pixel control circuit including: a transistor switch connected between said anode and cathode of said photodiode, said transistor switch having a control terminal for controlling the conductive state of said transistor switch; and a diode connected to drain at least a portion of a charge from said floating gate of said floating gate semiconductor device in response to an erase signal; said controlled modes including: an erase mode in which at least a portion of an electric charge is removed from said floating gate to place said floating gate semiconductor device in an initialized state, an exposure mode in which said floating gate is charged at least partially in response to a voltage at a terminal of said photosensitive semiconductor device, said voltage at said terminal corresponding to exposure of said photosensitive semiconductor device to said electromagnetic radiation from said image, a data retention mode in which the charge on said floating gate of said floating gate semiconductor device acquired during said exposure mode is maintained thereon notwithstanding further exposure of said photosensitive semiconductor device to said electromagnetic radiation from said image, and a read mode in which current flow between said source and drain of said floating gate semiconductor device is detected as an indicator of the charge on said floating gate.