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US 9,319,613 B2Granted
Image sensor having NMOS source follower with P-type doping in polysilicon gate
AssigneeOmniVision Technologies, Inc.
InventorTiejun Dai
Life of this patent
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Abstract
An image sensor array has a tiling unit comprising a source follower stage coupled to buffer signals from a photodiode when the unit is read onto a sense line, the source follower stage differs from conventional sensor arrays because it uses an N-channel transistor having a P-doped polysilicon gate. In embodiments, other transistors of the array have conventional N-channel transistors with N-doped polysilicon gates.
Claims10
An image sensor array comprising
- a tiling unit comprising a source-follower stage coupled to buffer a signal from a photodiode when read onto a sense line, wherein the source-follower stage comprises a source-follower transistor having source and drain doped as opposite doping type from a polysilicon gate of the same transistor, while at least a second transistor of the tiling unit has a transistor with source, drain, and polysilicon gate all doped with the same doping type;
- the source-follower transistor having greater threshold voltage than the second transistor.
An image sensor array comprising
- a tiling unit comprising a source-follower stage coupled to buffer a signal from a photodiode when read onto a sense line, wherein the source-follower stage comprises an N-channel source-follower transistor having an N-type source, an N-type drain, and a P-doped polysilicon gate;
- a first selection transistor coupled to pass a signal from the photodiode to the source-follower stage, the first selection transistor being an N-channel transistor having an N-doped polysilicon gate;
- wherein the source-follower transistor has greater threshold voltage than the selection transistor.
A method of sensing a photodiode in a photodiode array image sensor comprising:
- passing charge from the photodiode through a pass device to a source-follower device, the pass device having a same type drain dopant type as a primary dopant type in a gate of the pass device;
- buffering signal from the pass device in the source-follower device, the source-follower device having an opposite polarity drain dopant type as a primary dopant type in a gate of the source-follower;
- the source-follower device having a higher threshold than the pass device.
Dependencies are inferred from the claim text.