Imager pixel with capacitance circuit for boosting reset voltage

1. A pixel circuit comprising:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a reset transistor for resetting said floating diffusion region to a reset voltage state;

a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a readout circuit for reading out a signal based on charges stored at said floating diffusion region; and

a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said reset voltage state, said voltage boost circuit comprising a second capacitance circuit.

2. The pixel circuit of claim 1 , wherein said voltage boost circuit is coupled between said floating diffusion region and said readout circuit.

3. The pixel circuit of claim 1 , wherein said second capacitance circuit comprises a capacitor.

4. The pixel of claim 3 , wherein said capacitor is at least partially formed over a pixel isolated region.

5. The pixel circuit of claim 1 , further comprising a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

6. The pixel circuit of claim 1 , further comprising a row select transistor acting as a switching device coupled to said voltage boost circuit.

7. The pixel circuit of claim 1 , further comprising a source follower transistor coupled to said floating diffusion region.

8. The pixel circuit of claim 1 , wherein said photo-conversion device comprises a photodiode.

9. A method of fabricating an integrated circuit comprising:

forming a photo-conversion device;

forming a floating diffusion region for receiving and storing charge from said photo-conversion device;

forming a reset transistor for resetting said floating diffusion region to a reset voltage state;

forming a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

forming a readout circuit for reading out a signal based on charges stored at said floating diffusion region; and

forming a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said reset voltage state, voltage boost circuit comprising a second capacitance circuit.

10. The method of claim 9 , wherein said step of forming a voltage boost circuit comprises coupling said voltage boost circuit to said floating diffusion region and to said readout circuit.

11. The method of claim 9 , further comprising a step of forming a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

12. The method of claim 9 , further comprising a step of forming a row select transistor coupled to said voltage boost circuit.

13. The method of claim 9 , further comprising a step of forming a source follower transistor coupled to said floating diffusion region.

14. A method of operating a pixel comprising the steps of:

receiving light in a photo-conversion device, said photo-conversion device converting said light into electrical charge;

resetting a floating diffusion region to a reset voltage state;

boosting a voltage on said floating diffusion region above said reset voltage state to a boosted reset voltage with a first capacitance circuit operating in response to a switching state of a switching device;

reading out said boosted reset voltage;

storing charge from said photo-conversion device in said floating diffusion region and in a second capacitance circuit coupled to said floating diffusion region; and

reading out a signal based on stored charge at said floating diffusion region from said photo-conversion device.

15. The method of claim 14 , further comprising a step of delivering said charge from said photo-conversion device through a transfer transistor to said floating diffusion region.

16. The method of claim 14 , further comprising operating a row select transistor to generate a boosted voltage at said floating diffusion region.