Extended dynamic range image sensor system

• US 6,441,852 B1
• Filed: 02/04/2000
• Issued: 08/27/2002
• Est. Priority Date: 05/29/1998
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Levine, Peter A., Sauer, Donald J., McCaffrey, Nathaniel J.
• Primary Examiner(s): NGUYEN, LUONG TRUNG
• Application Number:
  US09/497,898
• Time in Patent Office: 935 Days
• Field of Search: 348/294, 348/296, 348/297, 348/298, 348/299, 348/302, 348/308
• US Class Current: 348/302
• CPC Class Codes: H04N 25/575 with a response composed of multiple slopes
• 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 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

An extended dynamic range imager. An array of pixels provides an output signal for each pixel related to an amount of light captured for each pixel during an integration period. A row of extended dynamic range (XDR) sample and hold circuits having an XDR sample and hold circuit for each column of the array captures an XDR signal related to a difference between the output signal and an XDR clamp level to which the pixel is reset at a predetermined time before the end of the integration period. A row of linear sample and hold circuits having a linear sample and hold circuit for each column of the array captures a linear signal related to a difference between the output signal and an initial output signal to which the pixel is reset at the beginning of the integration period.

Claims

1. An extended dynamic range (XDR) imager, comprising:

an array of pixels for providing an output signal for each pixel related to an amount of light captured for each pixel during an integration period;

circuitry that resets the pixels in a selected row of the array to an initial output signal value before the integration period begins and that applies an XDR clamp level signal to the pixels in a selected row of the array of pixels at a predetermined time before the integration period ends;

a row of sample and hold circuits having a sample and hold circuit for each column of the array for capturing, during a first time interval, an XDR signal for each

column of the selected row that is related to a difference between the output signal and the XDR clamp level signal, and for capturing, during a second time interval distinct from the first time interval, a linear signal for each column of the selected row, the linear signal being related to a difference between the initial output signal and the greater of the output signal and the XDR clamp level signal.

2. An XDR imager according to claim 1, wherein:

the circuitry that applies the XDR clamp level to the pixels in a selected row of the array of pixels applies a plurality of respectively different XDR clamp level signals, including a first XDR clamp level signal, to the selected row at a respective plurality of times before the integration period ends; and

the row of sample and hold circuits captures, during a plurality of successive distinct time intervals, a respective plurality of XDR signals, each related to a respective one of the plurality of XDR clamp level signals and captures, during a further time interval distinct from the plurality of successive time intervals, a linear signal for each column of the selected row, the linear signal being related to a difference between the initial output signal and the greater of the output signal and the first XDR clamp level signal.

3. An XDR imager according to claim 2, wherein each of the sample and hold circuits includes first and second correlated double-sampling (CDS) circuits for storing respective ones of the XDR signals and the linear signals.

4. An XDR imager according to claim 3, wherein the first and second CDS circuits are switched capacitor CDS circuits.

5. An XDR imager according to claim 2, wherein the pixels are complementary metal-oxide semiconductor (CMOS) pixels each having a photodiode having a photodiode voltage that decreases from an initial photodiode voltage in response to light signals impinging on the photodiode.

6. An XDR imager according to claim 2, wherein the imager is characterized by a piece-wise linear signal response having a linear portion corresponding to the entire integration period and having a plurality of XDR portions corresponding to the respective plurality of times before the integration period ends.

7. An XDR imager according to claim 1, wherein the initial output signal is approximately 5V and the XDR clamp level is approximately 3.5V.

8. An extended dynamic range (XDR) pixel for capturing light during an integration period, comprising:

a photodetector to accumulate electric charge responsive to the light during the integration period and generate an output signal based on an amount of the accumulated charge; and

a reset circuit having a drain electrode coupled to a voltage source, the reset circuit coupled to the photodetector to set the photodetector to a predetermined level one of i) before the integration period and ii) during the integration period,

wherein a control signal is provided to a gate electrode of the reset circuit, the control signal having a voltage level at a beginning of the integration period such that the photodetector has a potential equal to the predetermined level, and during the integration time the gate of the reset circuit is set to a voltage less than that necessary to set the potential of the photodetector to the predetermined level,

whereby when the amount of charge accumulated by the photodetector provides a potential that exceeds a further predetermined level, the reset circuit sets the photodetector to the predetermined level.

9. An XDR pixel according to claim 8, wherein the control signal has a varying voltage.

10. An XDR pixel according to claim 8, wherein the control signal has a plurality of levels during the integration period.

11. An XDR pixel according to claim 8, further comprising a signal amplifier coupled to the photodetector to amplify the output signal of the photodetector.

12. An XDR pixel according to claim 8, wherein the XDR pixel is one of a plurality of XDR pixels.

13. An XDR pixel according to claim 12, wherein the plurality of XDR pixels is a linear array of XDR pixels coupled to a scan register.

14. An XDR pixel according to claim 12, wherein the plurality of XDR pixels is a two dimensional array, a first dimension of the array coupled to a row scanner and a second dimension of the array coupled to a column scanner.

15. An XDR pixel according to claim 12, wherein the plurality of XDR pixels are complementary metal-oxide semiconductor (CMOS) pixels.

16. An XDR pixel according to claim 8, wherein the XDR pixel is a complementary metal-oxide semiconductor (CMOS) pixel.

17. An XDR pixel according to claim 8, wherein the photodetector is a photodiode.