Image sensor with depletion-level pixel charge transfer control
AssigneeRambus Inc.
InventorsMichael Guidash, John Ladd
Life of this patent
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Abstract
A pixel circuit within an integrated-circuit image sensor includes a photodiode having a pinning layer of a first conductivity type, a floating diffusion node and a transfer gate disposed between the photodiode and the floating diffusion node. A first control input is coupled to the transfer gate, and a second control input is coupled to the pinning layer of the photodiode to enable the depletion potential of the photodiode to be raised and lowered.
Claims20
An integrated-circuit image sensor comprising:
- a photodiode having a pinning layer;
- a floating diffusion node;
- a transfer gate disposed between the floating diffusion node and the photodiode, adjacent to the pinning layer of the photodiode;
- a first control input coupled to the transfer gate;
- a second control input coupled to the pinning layer of the photodiode to enable a depletion potential of the photodiode to be raised and lowered;
- and
- readout circuitry to;
- determine whether accumulated photocharge within the photodiode exceeds a threshold;
- assert a first control pulse on the first control input during a readout interval to enable transfer of the accumulated photocharge from the photodiode to the floating diffusion node;
- and
- if the accumulated photocharge is determined not to exceed the threshold, assert a second control pulse on the second control input, concurrently with assertion of the first control pulse, to prevent the transfer of the accumulated photocharge otherwise enabled by assertion of the first control pulse.
A method of operation within an integrated-circuit image sensor having a pixel array, the method comprising:
- determining whether accumulated photocharge within a photodiode of a pixel within the pixel array exceeds a threshold;
- asserting a first control pulse on a row control line during a readout interval to enable transfer of the accumulated photocharge from the photodiode to a floating diffusion node of the pixel;
- and
- if the accumulated photocharge is determined not to exceed the threshold, asserting a second control pulse on a pinning-layer control line coupled to a pinning layer of the photodiode concurrently with assertion of the first control pulse to prevent the transfer of the accumulated photocharge otherwise enabled by assertion of the first control pulse.
An integrated-circuit image sensor comprising:
- a photodiode having a pinning layer;
- a floating diffusion node;
- a transfer gate disposed between the floating diffusion node and the photodiode, adjacent to the pinning layer of the photodiode;
- a first control input coupled to the transfer gate;
- a second control input coupled to the pinning layer of the photodiode to enable a depletion potential of the photodiode to be raised and lowered;
- and
- means for:
- determining whether accumulated photocharge within the photodiode exceeds a threshold;
- asserting a first control pulse on the first control input during a readout interval to enable transfer of the accumulated photocharge from the photodiode to the floating diffusion node;
- and
- if the accumulated photocharge is determined not to exceed the threshold, asserting a second control pulse on the second control input, concurrently with assertion of the first control pulse, to prevent the transfer of the accumulated photocharge otherwise enabled by assertion of the first control pulse.
Dependencies are inferred from the claim text.