Wide dynamic range operation for CMOS sensor with freeze-frame shutter

• US 7,209,166 B2
• Filed: 04/13/2006
• Issued: 04/24/2007
• Est. Priority Date: 10/26/2000
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Krymski, Alexander I.
• Primary Examiner(s): Vu; Ngoc-Yen
• Assistant Examiner(s): Vieaux; Gary C.
• Application Number:
  US11/402,923
• Publication Number:
  US 20060181624A1
• Time in Patent Office: 376 Days
• Field of Search: 348/308, 348/364, 348/362, 348/221.1, 348/297, 348/229
• US Class Current: 348/221.1
• CPC Class Codes: H04N 25/589 with different integration times, e.g. short and long exposures
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

Wide dynamic range operation is used to write a signal in a freeze-frame pixel into the memory twice, first after short integration and then after long integration. The wide dynamic range operation allows the intra-scene dynamic range of images to be extended by combining the image taken with a short exposure time with the image taken with a long exposure time. A freeze-frame pixel is based on voltage sharing between the photodetector PD and the analog memory. Thus, with wide dynamic range operation, the resulting voltage in the memory may be a linear superposition of the two signals representing a bright and a dark image after two operations of sampling.

Claims

1. A method of obtaining an image signal using a solid state sensor, the method comprising:

collecting a short image signal during a first time period;

sampling the short image signal after the first time period;

collecting a long image signal during a second time period;

sampling the long image signal after the second time period; and

combining the short image signal and the long image signal in a memory in the sensor to create a total image signal.

2. The method of claim 1, wherein the second time period includes the first time period.

3. The method of claim 1, further comprising resetting a photodetector in the sensor prior to collecting the short image signal.

4. The method of claim 1, further comprising resetting the memory containing the total image signal prior to collecting the short image signal.

5. The method of claim 1, further comprising simultaneous sampling of the short image signal while collecting the long image signal.

6. The method of claim 5, wherein the short image signals and the long image signals are not collected during the reading of the total image signal.

7. The method of claim 1, wherein the memory is a capacitor.

8. The method of claim 7, wherein the acts of collecting include operating a switch that selectively connects said capacitor to a photodetector.

9. The method of claim 1, wherein the second time period is longer than the first time period.

10. A pixel sensor comprising:

a photodetector having a first memory element;

a second memory element; and

a plurality of switches including;

a first switch constructed to connect the photodetector to a reset voltage source;

a second switch constructed to connect the photodetector to second memory element for permitting transfer of a first and a second image signal collected in the photodetector during a respective first and second collection time period; and

a third switch for connecting the second memory element to a reset voltage source, wherein the third switch is different than either the first or the second switch, and wherein the second memory element is constructed such that it is able to combine the first image signal and the second image signal to create a total image signal.

11. The pixel of claim 10, wherein the second time period includes the first time period.

12. The pixel of claim 10, further comprising a readout circuit to readout the total image signal from said second memory element.

13. The pixel of claim 10, wherein each of said first memory elements and said second memory elements comprise capacitors.

14. A method of operating an image sensor comprising:

resetting a capacitive structure by activating a first switch by connecting the capacitor to a reset voltage source;

resetting a photodetector of the image sensor by activating a second switch;

integrating charge at the photodetector during a first integration period to generate a first image signal;

transferring the first image signal from the photodetector to the capacitive structure by activating a third switch;

integrating charge at the photodetector during a second integration period to generate a second image signal;

transferring the second image signal from the photodetector to the capacitive structure by activating the third switch; and

creating a total image signal by combining the first and the second image signals in the capacitive structure.

15. The method of claim 14, further comprising reading out the total image signal through a readout circuit.