Method, apparatus and system providing a storage gate pixel with high dynamic range
A method, apparatus and system are described providing a high dynamic range pixel. An integration period has multiple sub-integration periods during which charges are accumulated in a photosensor and repeatedly transferred to a storage node, where the charges are accumulated for later transfer to another storage node for output.
1. An imager circuit comprising:
at least one pixel circuit, the at least one pixel circuit comprising—
a photosensor having a charge storage capacity, the photosensor configured to accumulate charge,
a first transistor connected to the photosensor for transferring charge from the photosensor,
a storage node selectively coupled to the photosensor for receiving charge from the photosensor via the first transistor, the storage node having a charge storage capacity that is greater than the charge storage capacity of the photosensor, and
a second transistor connected to the storage node for transferring charge from the storage node to a floating diffusion node; and
a control circuit operably coupled to the first transistor, the control circuit configured to—
define a plurality of successive integration periods during an image capture in which charges produced by the photosensor in each of the integration periods are successively stored and accumulated in the storage node, and
operate the second transistor to transfer charges accumulated in the storage node for the integration periods to the floating diffusion region.
2. The circuit of claim 1 wherein the storage node has a storage capacity of at least about twice the storage capacity of the photosensor.
3. The circuit of claim 1 , further comprising a readout circuit connected to the floating diffusion node to output a signal based on the charge stored at the floating diffusion node.
4. The circuit of claim 3 wherein the readout circuit further comprises:
a reset transistor connected to the floating diffusion node for resetting the charge on the floating diffusion node;
a source-follower transistor having a gate for receiving charge from the floating diffusion-node; and
a row-select transistor connected to the source-follower transistor for outputting a signal produced by the source-follower transistor.
5. The circuit of claim 4 , further comprising an anti-blooming transistor electrically connected to the photosensor for draining charge from the photosensor.
6. The circuit of claim 4 wherein the control circuit is operable to apply a constant voltage to a gate of the anti-blooming transistor during the plurality of successive integration periods.
7. An imaging device comprising:
a pixel array comprising a plurality of pixels, wherein at least some of said pixels comprise—
a photosensor having a charge storage capacity, the photosensor configured to accumulate charge,
a first transistor connected to the photosensor for transferring charge from the photosensor,
a storage node coupled to the photosensor for receiving charge from the photosensor via the first transistor, and
a second transistor connected to the storage node for transferring charge from the storage node to a floating diffusion node; and
a control circuit operably coupled to the first transistor, the control circuit configured to—
define a plurality of successive integration periods during an image capture in which charges produced by the photosensor in each of the integration periods are successively stored and accumulated in the storage node, and
transfer charges accumulated in the storage node for the integration periods to the floating diffusion region.
8. The imaging device of claim 7 wherein the storage node charge storage capacity is at least about twice the storage capacity of the photosensor.
9. The imaging device of claim 7 , further comprising a readout circuit connected to the floating diffusion node to output a signal based on the charge accumulated at the floating diffusion region.
10. A processing system comprising:
an array of pixels, each of the pixels including a photosensor for generating charges;
a first transistor connected to the photosensor for transferring charge from the photosensor;
a storage node selectively coupled to the photosensor for receiving charge from the photosensor via the first transistor, the storage node having a charge storage capacity that is greater than a charge storage capacity of the photosensor;
a second transistor connected to the storage node for transferring charge from the storage node to a floating diffusion node; and
a control circuit operably coupled to the first transistor, the control circuit configured to—
define a plurality of successive integration periods during an image capture in which charges produced by the photosensor in each of the integration periods are successively stored and accumulated in the storage node, and
operate the second transistor to transfer charges accumulated in the storage node for the integration periods to the floating diffusion region.
11. The system of claim 10 wherein the storage node charge storage capacity is at least about twice the storage capacity of the photosensor.
12. The system of claim 11 wherein the readout circuit further comprises:
a reset transistor connected to the floating diffusion node for resetting the charge on the floating diffusion node;
a source-follower transistor having a gate for receiving charge from the floating diffusion node; and
a row-select transistor connected to the source-follower transistor for outputting a signal produced by the source-follower transistor.
13. The system of claim 12 further comprising an anti-blooming transistor electrically connected to the photosensor for draining charge from the photosensor.
14. The circuit of claim 12 wherein the control circuit is operable to apply a constant voltage to a gate of the anti-blooming transistor during the plurality of successive integration periods.
15. The system of claim 12 wherein the system is a camera processor system.
16. The system of claim 10 further comprising a readout circuit connected to the floating diffusion node to output a signal based on the charge accumulated at the floating diffusion gate.