Photogate active pixel sensor with high fill factor and correlated double sampling

• US 6,624,850 B1
• Filed: 12/30/1998
• Issued: 09/23/2003
• Est. Priority Date: 12/30/1998
• Status: Expired due to Term

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Eastman Kodak Company
• Inventors: Guidash, Robert M.
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): WHIPKEY, JASON T
• Application Number:
  US09/223,039
• Time in Patent Office: 1,728 Days
• Field of Search: 257/292, 257/291, 348/301, 348/307, 348/308, 348/243, 348/302
• US Class Current: 348/308
• 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: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
• CPC Class Codes: H04N 25/766 comprising control or output lines used for a plurality of functions, e.g. for pixel output, driving, reset or power

Abstract

The present invention provides a high fill factor Photogate Active Pixel Architecture with the capability to perform Correlated Double Sampling, (CDS). The functionality of a 4 transistor pixel is maintained while eliminating the separate row select transistor. This is done by using the same control signal for the photogates and the Row Select signal. The preferred embodiment of the invention employs a floating diffusion as the charge to voltage conversion node and specifically envisions embodiments wherein the source of the reset transistor is a floating diffusion and the drain of the reset transistor is connected to the photogate control bus. The invention further employs a first predetermined signal combination to the photogate control bus and the reset control bus that connects the amplifier to the output signal column bus, and a predetermined second signal combination on the photogate control bus and reset control bus that enables setting the charge to voltage conversion node to a second predetermined potential that disconnects the amplifier from the output signal column bus.

Claims

1. An active pixel sensor having a plurality of pixels with at least one pixel comprising:

a photogate photodetector operatively connected to a charge to voltage conversion node;

a reset transistor having a source that is connected to the charge to voltage conversion node;

a reset gate on the reset transistor connected to a reset control bus and a drain on the reset transistor connected to the photogate and a photogate control bus;

an amplifier operatively connected to the charge to voltage conversion node.

2. The invention of claim 1 wherein the charge to voltage conversion node is a floating diffusion.

3. The invention of claim 1 wherein the source of the reset transistor is a floating diffusion.

4. The invention of claim 1 wherein the amplifier is a source follower amplifier.

5. The invention of claim 1 wherein a first predetermined signal to the photogate control bus and a second predetermined signal connected to the reset control bus enables transfer of electrons from the photogate to the charge to voltage conversion node and sets the charge to voltage conversion node to a predetermined first potential that turns the amplifier off.

6. The invention of claim 1 wherein a first predetermined signal to the photogate control bus enables transfer of electrons from the photogate to the charge to voltage conversion node.

7. The invention of claim 1 wherein a first predetermined signal to the photogate control bus and a second predetermined signal connected to the reset control bus sets the charge to voltage conversion node to a predetermined first potential that turns the amplifier on.

8. An Active pixel sensor having a plurality of pixels with at least one pixel comprising:

a photogate photodetector operatively connected to a charge to voltage conversion node;

a reset transistor having a source that is connected to the charge to voltage conversion node;

a reset gate on the reset transistor connected to a reset control bus and a drain on the reset transistor connected to the photogate and a photogate control bus;

an amplifier operatively connected to the charge to voltage conversion node and an output signal column bus.

9. The invention of claim 8 wherein a first predetermined signal to the photogate control bus and a second predetermined signal connected to the reset control bus disconnects the amplifier from the output signal column bus.

10. The invention of claim 8 wherein a first predetermined signal to the photogate control bus and a second predetermined signal connected to the reset control bus enables resetting of the charge to voltage conversion node to a predetermined first potential that connects the amplifier to the output signal column bus.

11. An active pixel sensor having a plurality of pixels arranged in rows and columns such that the rows are read out sequentially with at least one pixel comprising:

a photodetector operatively coupled to a charge to voltage conversion means;

a reset device electrically connected to the charge to voltage conversion means;

a first signal bus operatively connected to the photodetector and the reset device, and a second signal bus connected to the reset device;

an amplifier operatively connected to the charge to voltage conversion means; and

means for activating the reset device such that the charge to voltage conversion means is sequentially set to a first potential and a second potential;

wherein the means for activating the reset device further comprises a combination of signals on the first and second signal bus that operates to deselect the row associated with the pixel.

12. The active pixel sensor of claim 11 wherein the means for activating the reset device further comprises a combination of signals on the first and second signal bus that operates to reset the charge to voltage conversion means.

13. The active pixel sensor of claim 11 wherein the means for activating the reset device further comprises a combination of signals on the first and second signal bus that operates to select the row associated with the pixel.

14. The active pixel sensor of claim 11 wherein the means for activating the reset device further comprises:

a first combination of signals on the first and second signal bus operates to reset the charge to voltage conversion means and also selects the row associated with the pixel; and

a second combination of signals on the first and second signal bus deselects the row associated with the pixel.

15. The active pixel sensor of claim 11 wherein the reset device further comprises:

a reset transistor having a drain connected to the first signal bus and a source connected to the charge to voltage conversion means; and

a gate to the reset transistor connected to the second signal bus.

16. The invention of claim 11 wherein the amplifier is a source follower amplifier having a gate coupled to the charge to voltage conversion means.

17. A method of making an active pixel sensor:

providing a pixel having a photodetective element operatively coupled to at least a charge to voltage conversion means;

creating a reset transistor within the pixel having a drain coupled to the photodetector on a first signal bus and a gate to the reset transistor connected to a second signal bus and a source connected to the charge to voltage conversion means; and

forming an amplifier that is coupled to both the charge to voltage conversion means and a the reset transistor;

wherein the step of creating further comprises creating means for applying a combination of signals on the first and second signal bus that operates to deselect the row associated with the pixel.

18. The method of claim 17 wherein the step of creating further comprises creating means for applying a combination of signals on the first and second signal bus to reset the charge to voltage conversion means.

19. The method of claim 17 wherein the step of creating further comprises creating means for applying a combination of signals on the first and second signal bus that operate to select the row associated with the pixel.