Amplification with feedback capacitance for photodetector signals

• US 7,652,243 B2
• Filed: 12/15/2008
• Issued: 01/26/2010
• Est. Priority Date: 03/31/2004
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Fossum, Eric R., Rossi, Giuseppe, Olsen, Alf
• Primary Examiner(s): Sohn; Seung C
• Application Number:
  US12/334,805
• Publication Number:
  US 20090266976A1
• Time in Patent Office: 407 Days
• Field of Search: 250/214.A, 250/208.1, 250/214.R, 348300-302
• US Class Current: 250/214.00A
• 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 operating a pixel cell, the method comprising:

generating photogenerated charges with a photodetector during an integration period;

operating a capacitive transimpedance amplifier at a first power level during said integration period;

amplifying said charges generated by said photodetector with said capacitive transimpedance amplifier operating at a second power level during a readout period; and

resetting, before the integration period, the capacitive transimpedance amplifier and a storage node used for storing the charges generated by the photodetector using a voltage received over a column bus.

2. The method of claim 1, wherein said first power level equals zero watts.

3. The method of claim 1 further comprising biasing the photodetector to a sufficient voltage before the integration period to maintain the photodetector in a reverse bias condition during said integration period.

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

5. A method of operating a pixel cell, the method comprising:

generating photogenerated charges with a photodetector during an integration period;

halting operation of a capacitive transimpedance amplifier during said integration period;

activating the operation of the capacitive transimpedance amplifier to amplify the charges generated by the photodetector during a readout period; and

resetting, before the integration period, the capacitive transimpedance amplifier and a storage node used for storing the charges generated by the photodetector using a voltage received over a column bus.

6. The method of claim 5, wherein the act of halting operation of the capacitive transimpedance amplifier comprises applying a power level equal to zero watts to the amplifier.

7. The method of claim 5, wherein the act of activating the operation of the capacitive transimpedance amplifier comprises applying a power level greater than zero watts to the amplifier.

8. The method of claim 5 further comprising the step of biasing the photodetector to a sufficient voltage before the integration period to maintain the photodetector in a reverse bias condition during the integration period.

9. A method of operating a pixel cell, the method comprising:

resetting, before an integration period and using a voltage received over a column bus, a capacitive transimpedance amplifier and a charge storage node;

reverse biasing a photodetector before the integration period;

generating photogenerated charges with the photodetector during the integration period;

operating the capacitive transimpedance amplifier at a first power level during the integration period; and

amplifying the charges generated by the photodetector with the capacitive transimpedance amplifier operating at a second power level greater than the first power level during a readout period.