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US 2008/0164549 A1Published application
Low dark current pixel with a guard drive active photodiode
AssigneeAptina Imaging Corporation
InventorsIsao Takayanagi, Junichi Nakamura
Life of this patent
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Abstract
A method and apparatus for reducing thermally generated dark current in a CMOS imaging device is disclosed. A photodiode within the imaging device is kept zero-biased, so that the voltage is equal at both ends of the photodiode. This zero-biasing is accomplished using several different techniques, including, alternatively: a transistor operating at its sub-threshold level; a leaky diode; a short-channel MOSFET; or ramping charge injection.
Claims10
1-64. (canceled)
An imaging pixel comprising:
- a photo conversion device for producing an electrical signal at a first node thereof in response to incident light energy;
- a biasing transistor operating at sub-threshold level and connected to a second node of said photo conversion device, for maintaining a zero-bias across said photo conversion device;
- an NMOS source follower transistor located remotely from said photo conversion device and connected to said first node of said photo conversion device, for reading a signal from said photo conversion device;
- an NMOS selection transistor connected to said NMOS source follower transistor, for selecting a pixel of said imaging pixel;
- an electrical circuit for receiving said electrical signal at said first node and producing an imaging pixel output signal;
- and
- a circuit path for providing said imaging pixel output signal to said second node of said photo conversion device.
4 more elements
An imaging pixel comprising:
- a photo conversion device for producing an electrical signal at a first node thereof in response to incident light energy;
- a biasing transistor operating at sub-threshold level and connected to a second node of said photo conversion device, for maintaining a zero-bias across said photo conversion device;
- an PMOS source follower transistor located remotely from said photo conversion device and connected to said first node of said photo conversion device, for reading a signal from said photo conversion device;
- an PMOS selection transistor connected to said PMOS source follower transistor, for selecting a pixel of said imaging pixel;
- an electrical circuit for receiving said electrical signal at said first node and producing an imaging pixel output signal;
- and
- a circuit path for providing said imaging pixel output signal to said second node of said photo conversion device.
4 more elements
A method for operating an imaging pixel comprising:
- producing an electrical signal at a first node of a photodiode in response to incident light energy;
- maintaining a zero voltage bias across said photodiode contained within said imaging pixel by operating said photodiode at a sub-threshold level;
- resetting said photodiode;
- reading out said electrical signal;
- and
- using said electrical signal to produce an imaging pixel output signal with a conversion gain, wherein said conversion gain is determinable.
3 more elements
Dependencies are inferred from the claim text.