Methods of operating photodiode-type pixel and imager device

• US 7,209,173 B2
• Filed: 06/12/2006
• Issued: 04/24/2007
• Est. Priority Date: 02/17/1998
• Status: Expired due to Fees

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Fossum, Eric R.
• Primary Examiner(s): MOE, AUNG SOE
• Application Number:
  US11/450,362
• Publication Number:
  US 20060227233A1
• Time in Patent Office: 316 Days
• Field of Search: 348/308, 348/309, 348/301, 348/302, 348/303, 348/313, 348/314, 348/362, 348/296, 348/297, 257/292, 257/291, 257/237, 257/239, 257/216, 250/208.1
• 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 25/62 Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels
• CPC Class Codes: H04N 25/626 Reduction of noise due to residual charges remaining after image readout, e.g. to remove ghost images or afterimages
• CPC Class Codes: H04N 25/672 between adjacent sensors or output registers for reading a single image

Abstract

Operation for global electronic shutter photodiode-type pixels. In a first mode of operation, lag is reduced through global reset of the photodiode array and fixed pattern noise is eliminated through comparison of the photosignal level and the reset level of the floating drain. In a second mode of operation, simultaneous integration and readout processes are achieved through cessation of spill charges over the transfer gate. In a third mode of operation, regulation of the reset photodiode and transfer gate enables voltage gain between the photodiode and the sense node.

Claims

1. A method of operating an imager device:

performing a first reset operation on a plurality of pixels, wherein the first reset operation charges photo diodes of the plurality of pixels to an initial level substantially equal to a gate voltage of a corresponding transfer transistor coupling the photo diodes to floating diffusion regions;

collecting photoelectrons with the photo diodes, wherein a portion of the photoelectrons exceeding the initial level is coupled through the transfer transistor to a corresponding floating diffusion region of the plurality of pixels;

sampling a first voltage level of the floating diffusion region to determine a photosignal;

performing a second reset operation on the plurality of pixels, wherein the second reset operation charges the photo diodes to the initial level; and

following the second reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.

2. The method of claim 1, wherein the acts of performing a first reset operation and collecting photoelectrons with the photo diodes are performed simultaneously for every pixel in said imager device.

3. A method of operating an imager device comprising a photo diode and a floating diffusion region coupled through a transfer transistor, the photo diode is coupled to a bias transistor and the floating diffusion region is coupled to a reset transistor, the method comprising:

performing a first reset operation of the photo diode and floating diffusion region, the first reset operation comprises;

activating the reset transistor to bias the floating diffusion region to a positive voltage level coupled to the reset transistor, and applying a gate bias voltage to the transfer transistor to couple the photo diode to the floating diffusion region such that the photo diode is biased to the positive voltage level, and

changing a voltage coupled to the reset transistor to drain at least some charge from the photo diode and floating diffusion region, wherein the photo diode remains charged to an initial level substantially equal to the gate bias voltage applied to the transfer transistor;

following the first reset operation, turning off the reset transistor and collecting photoelectrons with the photo diode, wherein a portion of the photoelectrons exceeding the initial level is coupled through the transfer transistor to the floating diffusion region;

activating the bias transistor to terminate collection of photoelectrons with the photo diode;

sampling a first voltage level of the floating diffusion region to determine a photosignal;

performing a second reset operation on the plurality of pixels, wherein the second reset operation comprises;

activating the reset transistor to bias the floating diffusion region to the positive voltage level coupled to the reset transistor, and applying the gate bias voltage to the transfer transistor to couple the photo diode to the floating diffusion region such that the photo diode is biased to the positive voltage level, and

changing a voltage coupled to the reset transistor to drain at least some charge from the photo diode and floating diffusion region, wherein the photo diode remains charged to the initial level substantially equal to the gate bias voltage applied to the transfer transistor; and

following the second reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.

4. A method of operating an imager device:

performing a first reset operation on a plurality of pixels, wherein the first reset operation charges photo diodes of the plurality of pixels to an initial level substantially equal to a reset gate voltage of a corresponding transfer gate coupling the photo diodes and floating diffusion regions;

lowering a voltage of the transfer gate from the reset gate voltage to an integration gate voltage;

collecting photoelectrons with the photo diodes while the integration gate voltage is applied to the transfer gate;

raising the voltage of the transfer gate from the integration gate voltage to the reset gate voltage to couple a portion of the photoelectrons exceeding the initial level through the transfer gate to a corresponding floating diffusion region of the plurality of pixels;

sampling a voltage level of the floating diffusion region to determine a photo signal;

performing a second reset operation on the diffusion regions; and

following the second reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.

5. The method of claim 4, wherein the acts of performing a first reset operation and collecting photoelectrons with the photo diodes are performed simultaneously for every pixel in said imager device.

6. A method of operating an imager device comprising a photo diode and a floating diffusion region coupled through a transfer transistor, the floating diffusion region is coupled to a reset transistor, the method comprising:

performing a first reset operation of the photo diode and floating diffusion region, the first reset operation comprises;

activating the reset transistor to bias the floating diffusion region to a positive voltage level coupled to the reset transistor, and applying a reset gate bias voltage to the transfer transistor to couple the photo diode to the floating diffusion region such that the photo diode is biased to the positive voltage level, and

changing a voltage coupled to the reset transistor to drain at least some charge from the photo diode and floating diffusion region, wherein the photo diode remains charged to an initial level substantially equal to the gate bias voltage applied to the transfer transistor;

following the first reset operation, turning off the reset transistor and the transfer transistor;

collecting photoelectrons with the photo diode;

applying the reset gate bias voltage to the transfer transistor to couple a portion of the photoelectrons exceeding the initial level through the transfer transistor to the floating diffusion region;

sampling a voltage level of the floating diffusion region to determine a photosignal;

performing a second reset operation on the diffusion regions; and

following the second reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.

7. A method of operating an imager device:

collecting photoelectrons with the photo diodes and floating diffusion regions of a plurality of pixels;

sampling a first voltage level of the floating diffusion region to determine a photo signal;

performing a reset operation on the plurality of pixels, wherein the reset operation discharges the photo diodes and floating diffusion regions to a reset level; and

following the reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.

8. The method of claim 7, wherein the act of collecting photoelectrons comprises collecting said photoelectrons in said photo diodes and transferring said collected photoelectrons to said respective floating diffusion regions.

9. The method of claim 7, wherein the act of collecting photoelectrons is performed simultaneously for every pixel in said imager device.

10. The method of claim 9, wherein the performing a reset operation is done simultaneously for every pixel in said imager device.

11. A method of operating an imager device comprising a photo diode and a floating diffusion region coupled through a transfer transistor, the floating diffusion region is coupled to a reset transistor, the method comprising:

activating the transfer transistor;

performing a first reset operation to discharge the photo diode and the floating diffusion region;

collecting photoelectrons with the photo diode and the floating diffusion region;

sampling a voltage level of the floating diffusion region to determine a photosignal;

performing a second reset operation to discharge the photo diode and the floating diffusion region; and

following the second reset operation, sampling a second voltage level of the floating diffusion region to determine a reset level, wherein a voltage difference between a signal level of the photosignal and the reset level represents the photoelectrons collected by the photo diode.