Amplification with feedback capacitance for photodetector signals

• US 7,199,349 B2
• Filed: 02/10/2006
• Issued: 04/03/2007
• Est. Priority Date: 03/31/2004
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Rossi, Giuseppe, Fossum, Eric R., Olsen, Alf
• Primary Examiner(s): Luu; Thanh X.
• Assistant Examiner(s): YAM, STEPHEN K
• Application Number:
  US11/351,036
• Publication Number:
  US 20060124830A1
• Time in Patent Office: 417 Days
• Field of Search: 250/208.1, 250/214.R, 250/214.A, 348300-302
• US Class Current: 250/208.1
• CPC Class Codes: H03F 3/08 controlled by light
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• CPC Class Codes: H03F 3/087 with IC amplifier blocks H03F3/085 takes precedence
• CPC Class Codes: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• 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

Abstract

Signals from an imager pixel photodetector are received by an amplifier having capacitive feedback, such as a capacitive transimpedance amplifier (CTIA). The amplifier can be operated at a low or no power level during an integration period of a photodetector to reduce power dissipation. The amplifier can be distributed, with an amplifier element within each pixel of an array and with amplifier output circuitry outside the pixel array. The amplifier can be a single ended cascode amplifier, a folded cascode amplifier, a differential input telescopic cascode amplifier, or other configuration. The amplifier can be used in pixel configurations where the amplifier is directly connected to the photodetector, or in configurations which use a transfer transistor to couple signal charges to a floating diffusion node with the amplifier being coupled to the floating diffusion node.

Claims

1. A method of obtaining a signal from a pixel cell comprising:

generating charges with a photodetector during an integration period;

resetting a charge storage node that receives charges generated by said photodetector to a reset level;

resetting a capacitive transimpedance amplifier associated with the pixel cell;

biasing the capacitive transimpedance amplifier with a first voltage level to place the amplifier in a high power operating mode;

with the storage node at the reset level, reading and sampling a first output signal from the capacitive transimpedance amplifier having an input coupled to said storage node;

biasing the capacitive transimpedance amplifier with a second voltage level to place the amplifier in a low power operating mode;

receiving charges at said charge storage node generated by said photodetector during the integration period;

biasing the capacitive transimpedance amplifier with the first voltage level to place the amplifier in the high power operating mode; and

reading and sampling a second output signal from said capacitive transimpedance amplifier after said integration period.

2. The method of claim 1 further comprising obtaining a difference signal indicating a difference between said first and second output signals.

3. The method of claim 1 in which resetting said storage node and reading and sampling the first output signal are performed before reading and sampling the second output signal.

4. The method of claim 1 further comprising operating said capacitive transimpedance amplifier in an open loop during said integration period.

5. The method of claim 1, wherein said resetting resets a capacitor of said capacitive transimpedance amplifier.

6. The method of claim 1, wherein said charge storage node is part of said photodetector.

7. The method of claim 1, wherein said charge storage node is a floating diffusion node which receives charges from said photodetector and said resetting resets said floating diffusion node.

8. The method of claim 1, wherein the low power operating mode is a no power operating mode wherein the capacitive transimpedance amplifier is halted during said integration period.

9. The method of claim 1 further comprising controlling a charge transference from the photodetector to said storage node with a transfer gate transistor.

10. The method of claim 1 further comprising operating at least a portion of said capacitive transimpedance amplifier outside of a pixel cell.

11. The method of claim 1 further comprising operating a portion of said capacitive transimpedance amplifier outside of a pixel cell and a portion of said capacitive transimpedance amplifier inside a pixel cell.

12. The method of claim 1 further comprising operating a capacitive transimpedance amplifier inside a pixel cell.