Fractional-readout oversampled image sensor

Patent metadata

Field	Value
Publication number	US-11284034-B2
Application number	US-202016859243-A
Country	US
Kind code	B2
Filing date	Apr 27, 2020
Priority date	Sep 21, 2015
Publication date	Mar 22, 2022
Grant date	Mar 22, 2022

Abstract

Signals representative of total photocharge integrated within respective image-sensor pixels are read out of the pixels after a first exposure interval that constitutes a first fraction of a frame interval. Signals in excess of a threshold level are read out of the pixels after an ensuing second exposure interval that constitutes a second fraction of the frame interval, leaving residual photocharge within the pixels. After a third exposure interval that constitutes a third fraction of the frame interval, signals representative of a combination of at least the residual photocharge and photocharge integrated within the pixels during the third exposure interval are read out of the pixels.

First claim

What is claimed is:

1. A method of operation within an integrated-circuit image sensor having a pixel array, the method comprising:
clearing accumulated photocharge from the pixel array to commence a first sub-frame interval;
executing a first partial readout of the pixel array at conclusion of the first sub-frame interval to (i) generate first sub-frame readout values indicative of photocharge accumulation within respective pixels of the pixel array in excess of a first threshold, and (ii) commence a second sub-frame interval having a duration that is scaled relative to duration of the first sub-frame interval based at least in part on the first threshold; and
executing a second partial readout of the pixel array at conclusion of the second sub-frame interval to generate second sub-frame readout values indicative of photocharge accumulation within the respective pixels of the pixel array in excess of a first threshold.

2. The method of claim 1 wherein the duration of the second sub-frame interval is scaled relative to the duration of the first sub-frame interval based on a relation between the first threshold and full-well capacity of the pixels of the pixel array.

3. The method of claim 2 wherein the first threshold represents a fraction of full-well capacity of the pixels of the pixel array, and wherein the duration of the second sub-frame interval is inversely proportional to magnitude of the fraction of full-well capacity represented by the first threshold.

4. The method of claim 1 wherein the duration of the second sub-frame interval is shortened relative to the duration of the first sub-frame interval by a scaling factor, the scaling factor being a ratio of a difference value and full-well capacity of the pixels of the pixel array, and the difference value being a difference between the full-well capacity and a fraction of the full-well capacity represented by the first threshold.

5. The method of claim 1 further comprising summing the first and second sub-frame readout values to generate constituent values within a pixel image, the pixel image corresponding to a frame interval that spans at least the first and second sub-frame intervals.

6. The method of claim 1 wherein clearing accumulated photocharge from the pixel array comprises generating, by executing a full readout of the pixel array following an initial sub-frame interval that precedes and is longer than the first sub-frame interval, full readout values indicative of total photocharge accumulation within respective pixels of the pixel array during the initial sub-frame interval.

7. The method of claim 1 wherein executing the second partial readout commences a third sub-frame interval, the method further comprising executing a full readout of the pixel array at conclusion of the third sub-frame interval to generate third sub-frame readout values indicative of total photocharge resident within the respective pixels of the pixel array.

8. The method of claim 7 wherein the second and third sub-frame intervals have equal durations.

9. The method of claim 7 further comprising summing the first, second and third sub-frame readout values to generate constituent values within a pixel image, the pixel image corresponding to a frame interval that spans at least the first, second and third sub-frame intervals.

10. The method of claim 7 wherein clearing accumulated photocharge from the pixel array comprises generating, by executing a full readout of the pixel array following an initial sub-frame interval that precedes and is longer than the first sub-frame interval, full readout values indicative of total photocharge accumulation within respective pixels of the pixel array during the initial sub-frame interval, the method further comprising selectively combining the full readout values with the first, second and third sub-frame readout values to generate constituent values within a pixel image, the pixel image corresponding to a frame interval that spans at least the initial sub-frame interval and the first, second and third sub-frame intervals.

11. An integrated-circuit image sensor comprising:
a pixel array; and
imaging circuitry to:
clear accumulated photocharge from the pixel array to commence a first sub-frame interval;
execute a first partial readout of the pixel array at conclusion of the first sub-frame interval to (i) generate first sub-frame readout values indicative of photocharge accumulation within respective pixels of the pixel array in excess of a first threshold, and (ii) commence a second sub-frame interval having a duration that is scaled relative to duration of the first sub-frame interval based at least in part on the first threshold; and
execute a second partial readout of the pixel array at conclusion of the second sub-frame interval to generate second sub-frame readout values indicative of photocharge accumulation within the respective pixels of the pixel array in excess of a first threshold.

12. The integrated-circuit image sensor of claim 11 wherein the duration of the second sub-frame interval is scaled relative to the duration of the first sub-frame interval based on a relation between the first threshold and full-well capacity of the pixels of the pixel array.

13. The integrated-circuit image sensor of claim 12 wherein the first threshold represents a fraction of full-well capacity of the pixels of the pixel array, and wherein the duration of the second sub-frame interval is inversely proportional to magnitude of the fraction of full-well capacity represented by the first threshold.

14. The integrated-circuit image sensor of claim 11 wherein the duration of the second sub-frame interval is shortened relative to the duration of the first sub-frame interval by a scaling factor, the scaling factor being a ratio of a difference value and full-well capacity of the pixels of the pixel array, and the difference value being a difference between the full-well capacity and a fraction of the full-well capacity represented by the first threshold.

15. The integrated-circuit image sensor of claim 11 wherein the imaging circuitry further comprises circuitry to add the first and second sub-frame readout values to generate constituent values within a pixel image, the pixel image corresponding to a frame interval that spans at least the first and second sub-frame intervals.

16. The integrated-circuit image sensor of claim 11 wherein the imaging circuitry to clear accumulated photocharge from the pixel array comprises circuitry to generate, by executing a full readout of the pixel array following an initial sub-frame interval that precedes and is longer than the first sub-frame interval, full readout values indicative of total photocharge accumulation within respective pixels of the pixel array during the initial sub-frame interval.

17. The integrated-circuit image sensor of claim 11 wherein the imaging circuitry to execute the second partial readout comprises circuitry to commence a third sub-frame interval, the imaging circuitry further comprising circuitry to execute a full readout of the pixel array at conclusion of the third sub-frame interval to generate third sub-frame readout values indicative of total photocharge resident within the respective pixels of the pixel array.

18. The integrated-circuit image sensor of claim 17 further comprising summing the first, second and third sub-frame readout values to generate constituent values within a pixel image, the pixel image corresponding to a frame interval that spans at least the first, second and third sub-frame intervals.

Assignees

• Rambus Inc

Inventors

• Endsley Jay
• Vogelsang Thomas
• Smith Craig M
• Guidash Michael
• Schneider Alexander C

Classifications

• H04N25/531 Primary

  by controlling rolling shutters in CMOS SSIS · CPC title

• H04N25/58

  involving two or more exposures · CPC title

• H04N25/583

  with different integration times · CPC title

• H04N23/741

  by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors · CPC title

• H04N25/78

  Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters · CPC title