Imager pixel with capacitance circuit for boosting reset voltage

• US 7,777,169 B2
• Filed: 09/09/2008
• Issued: 08/17/2010
• Est. Priority Date: 12/03/2004
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Hong, Sungkwon C.
• Primary Examiner(s): Epps; Georgia Y
• Assistant Examiner(s): Ko; Tony
• Application Number:
  US12/207,040
• Publication Number:
  US 20090001255A1
• Time in Patent Office: 707 Days
• Field of Search: 250/208.1, 348/302
• US Class Current: 250/208.1
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 25/779 Circuitry for scanning or addressing the pixel array
• CPC Class Codes: H04N 3/1512 for MOS image-sensors, e.g. MOS-CCD H04N3/1581 takes precedence
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

A pixel cell in which a capacitance is coupled between a storage node and a row select transistor and another capacitance is coupled between a storage node and a voltage supply or ground source potential to boost a reset voltage.

Claims

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.