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

• US 7,050,094 B2
• Filed: 10/26/2001
• Issued: 05/23/2006
• Est. Priority Date: 10/26/2000
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Krymski, Alexander I.
• Primary Examiner(s): Ho, Tuan
• Assistant Examiner(s): Vieaux, Gary C.
• Application Number:
  US10/053,110
• Publication Number:
  US 20020080263A1
• Time in Patent Office: 1,670 Days
• Field of Search: 348/308, 348/362, 348/364, 348/297, 348/317, 348/221, 348/229, 348/221.1
• 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 CMOS sensor with a freeze-frame shutter 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 an analog 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 prior to collecting the short image signal.

4. The method of claim 1, further comprising resetting the analog 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 1, further comprising reading the total image signal from the CMOS sensor.

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

8. A freeze-frame pixel using wide dynamic range operating comprising:

a photodetector having a memory;

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

9. The freeze-frame pixel of claim 8, wherein the second time period is longer than the first time period.

10. The freeze-frame pixel of claim 9, wherein the second time period includes the first time period.

11. The freeze-frame pixel of claim 8, further comprising a readout section to transfer the total image signal.

12. A method of operating a CMOS image sensor comprising:

resetting an analog memory of the image sensor by activating a first switch and connecting the analog memory 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 memory 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 memory by activating the third switch; and

creating a total image signal in the analog memory by combining the first and the second image signals.

13. The method of claim 12, further comprising reading out the total image signal through a readout circuit.

14. An array of image sensor cells comprising:

a plurality of pixels arranged in an array and comprising;

a photodetector having a memory;

an analog memory; 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 the analog memory for permitting transfer of a first and a second image signal collected in the photodetector during a respective first and second collection time period, wherein the analog memory is constructed such that it can create a total image signal based on the first and the second image signals; and

a third switch for connecting the analog memory to a reset voltage source, wherein the third switch is different than either the first or the second switch.

15. The array of claim 14, wherein:

the first collection time period is identical for each of the plurality of pixels; and

the second collection time period is identical for each of the plurality of pixels.

16. The array of claim 15, wherein the second collection time period includes the first collection time period.

17. The array of claim 14, wherein the plurality of pixels are arranged in rows and columns in said array, the array further comprising a column readout circuit constructed to read out a total image signal from each of the plurality of pixels, one row at a time.