PHOTOELECTRIC CONVERSION DEVICE AND IMAGING SYSTEM

• US 20180309946A1
• Filed: 04/17/2018
• Published: 10/25/2018
• Est. Priority Date: 04/24/2017
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ohya, Takeru, Koizumi, Satoshi, Kobayashi, Masahiro
• Granted Patent: US 10,659,706 B2
• Time in Patent Office: Days
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 23/80 Camera processing pipelines; Components thereof
• CPC Class Codes: H04N 25/622 by controlling anti-blooming drains
• CPC Class Codes: H04N 25/626 Reduction of noise due to residual charges remaining after image readout, e.g. to remove ghost images or afterimages
• CPC Class Codes: H04N 25/767 Horizontal readout lines, multiplexers or registers
• 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 25/771 comprising storage means other than floating diffusion

Abstract

A photoelectric conversion device includes a plurality of pixels each of which includes a photoelectric converter that generates charges by photoelectric conversion, a first transfer unit that transfers charges in the photoelectric converter to a first holding portion, a second transfer unit that transfers charges in the first holding portion to a second holding portion, an amplifier unit that outputs a signal based on charges held in the second holding portion, and a third transfer unit that transfers charges of the photoelectric converter to a drain portion; and a control unit that, in an exposure period in which signal charges are accumulated in the photoelectric converter, changes a potential barrier formed by the third transfer unit with respect to the signal charges accumulated in the photoelectric converter from a first level to a second level that is higher than the first level.

Claims

1. A photoelectric conversion device comprising:

a plurality of pixels each of which includes a photoelectric converter that generates charges by photoelectric conversion, a first transfer unit that transfers charges in the photoelectric converter to a first holding portion, a second transfer unit that transfers charges in the first holding portion to a second holding portion, an amplifier unit that outputs a signal based on charges held in the second holding portion, and a third transfer unit that transfers charges of the photoelectric converter to a drain portion; and

a control unit that, in an exposure period in which signal charges are accumulated in the photoelectric converter, changes a potential barrier formed by the third transfer unit with respect to the signal charges accumulated in the photoelectric converter from a first level to a second level that is higher than the first level.

2. The photoelectric conversion device according to claim 1, wherein the first level is lower than a level of a potential barrier formed by the first transfer unit with respect to the signal charges accumulated in the photoelectric converter in the exposure period.

3. The photoelectric conversion device according to claim 1, wherein the second level is lower than or equal to a level of a potential barrier of the first transfer unit with respect to the signal charges.

4. The photoelectric conversion device according to claim 1, wherein the exposure period includes a first period in which charges held by the first holding portion of pixels arranged on a plurality of rows of the plurality of pixels are transferred to the second holding portion sequentially on a row-by-row basis.

5. The photoelectric conversion device according to claim 4, wherein the exposure period further includes a second period in which accumulation of the signal charges is continued after the first period.

6. The photoelectric conversion device according to claim 5, wherein the control unit changes the potential barrier of the third transfer unit with respect to the signal charges from the first level to the second level in the first period of the exposure period.

7. The photoelectric conversion device according to claim 6, wherein the control unit changes the potential barrier of the third transfer unit with respect to the signal charges from the first level to the second level sequentially from a pixel on a row on which an operation of transferring charges held by the first holding portion to the second holding portion has ended.

8. The photoelectric conversion device according to claim 5, wherein the control unit changes the potential barrier of the third transfer unit with respect to the charges from the first level to the second level after the first period ends.

9. The photoelectric conversion device according to claim 5, wherein the first transfer unit transfers charges of the photoelectric converter to the first holding portion between the first period and the second period.

10. The photoelectric conversion device according to claim 1, wherein the control unit changes the potential barrier of the third transfer unit with respect to the signal charges continuously from the first level to the second level.

11. The photoelectric conversion device according to claim 1, wherein the control unit changes the potential barrier of the third transfer unit with respect to the signal charges stepwise from the first level to the second level.

12. The photoelectric conversion device according to claim 1, wherein, at the end of the exposure period, the potential barrier of the third transfer unit with respect to the signal charges is the same level as the potential barrier of the first transfer unit with respect to the signal charges.

13. The photoelectric conversion device according to claim 1, wherein the control unit controls a level of the potential barrier of the third transfer unit with respect to the signal charges in accordance with a light amount of an incident light.

14. The photoelectric conversion device according to claim 13, wherein the control unit controls a potential of the third transfer unit with respect to the signal charges so that, when an amount of charges accumulated in the photoelectric converter during the exposure period under a constant light amount is equal to a saturation charge amount defined by the potential barrier of the first transfer unit, charges accumulated in the photoelectric converter does not exceed the potential barrier of the third transfer unit.

15. The photoelectric conversion device according to claim 1,

wherein the plurality of pixels include pixels used for image capture and pixels used for correction, and

wherein the control unit controls a potential barrier of the third transfer unit with respect to charges accumulated in the photoelectric converter to a third level higher than or equal to a potential barrier of the first transfer unit during the exposure period for the pixels used for correction.

16. The photoelectric conversion device according to claim 1,

wherein the plurality of pixels include pixels used for image capture and pixels used for correction, and

wherein an exposure period for a correction signal applied to the pixels used for correction is shorter than the exposure period applied to the pixels used for image capture.

17. The photoelectric conversion device according to claim 1, further comprising an amplifier circuit that amplifies a signal based on the signal charges at a gain that can be selected from a plurality of set values,

wherein the control unit sets the first level in accordance with the gain.

18. The photoelectric conversion device according to claim 1, wherein the control unit controls the potential barrier of the third transfer unit with respect to the signal charges by a voltage supplied to a gate of a transistor forming the third transfer unit.

19. The photoelectric conversion device according to claim 1, wherein the control unit controls the potential barrier of the third transfer unit with respect to the signal charges by a voltage supplied to the drain portion.

20. The photoelectric conversion device according to claim 1, wherein each of the plurality of pixels further includes a third holding unit that collects and holds at least a part of charges overflowed from the photoelectric converter.

21. The photoelectric conversion device according to claim 1, wherein

the exposure period includes a period which starts at a first time point when both the first and third transfer units become in an off state on at least one of the first and third transfer units turning off and ends at a second time point when the first transfer unit turns on for a first time after the first time point,

the control unit changes the potential barrier from the first level to the second level within the period.

27. An imaging system comprising:

the photoelectric conversion device according to claim 1; and

a signal processing unit that processes signals output from the plurality of pixels of the photoelectric conversion device.

28. The imaging system according to claim 27, wherein, when an image acquired from the photoelectric conversion device includes a region in which an output is at a saturation level in a frame and an output is at an intermediate level in a next frame, the signal processing unit corrects an output of the region of the next frame to a saturation level.

29. A movable object comprising:

the photoelectric conversion device according to claim 1;

a distance information acquisition unit adapted to acquire distance information of a distance to an object based on signals from the photoelectric conversion device; and

a controlling unit adapted to control the movable object based on the distance information.

22. A photoelectric conversion device comprising:

a plurality of pixels each of which includes a photoelectric converter that generates charges by photoelectric conversion, a first transfer unit that transfers charges in the photoelectric converter to a first holding portion, a second transfer unit that transfers charges in the first holding portion to a second holding portion, an amplifier unit that outputs a signal based on charges held in the second holding portion, and a third transfer unit that transfers charges of the photoelectric converter to a drain portion;

an amplifier circuit that amplifies a signal based on signal charges by a gain that can be selected from at least a first gain and a second gain different from the first gain; and

a control unit that controls a potential barrier formed by the third transfer unit with respect to the signal charges accumulated in the photoelectric converter to a first level when the gain is the first gain and controls a potential barrier of the third transfer unit with respect to the signal charges to a second level different from the first level when the gain is the second gain.

23. The photoelectric conversion device according to claim 22,

wherein the first gain is higher than the second gain, and

wherein the first level is lower than the second level.

24. The photoelectric conversion device according to claim 22, wherein at least one of the first level and the second level is lower than a level of a potential barrier formed by the first transfer unit with respect to the signal charges accumulated in the photoelectric converter in an exposure period.

25. The photoelectric conversion device according to claim 22, wherein the control unit controls the potential barrier of the third transfer unit with respect to the signal charges by a voltage supplied to a gate of a transistor forming the third transfer unit.

26. The photoelectric conversion device according to claim 22, wherein

the exposure period includes a period which starts at a first time point when both the first and third transfer units become in an off state on at least one of the first and third transfer units turning off and ends at a second time point when the first transfer unit turns on for a first time after the first time point,

the control unit changes the potential barrier from the first level to the second level within the period.

30. An imaging system comprising:

the photoelectric conversion device according to claim 22; and

a signal processing unit that processes signals output from the plurality of pixels of the photoelectric conversion device.

31. The imaging system according to claim 30, wherein, when an image acquired from the photoelectric conversion device includes a region in which an output is at a saturation level in a frame and an output is at an intermediate level in a next frame, the signal processing unit corrects an output of the region of the next frame to a saturation level.

32. A movable object comprising:

the photoelectric conversion device according to claim 22;

a distance information acquisition unit adapted to acquire distance information of a distance to an object based on signals from the photoelectric conversion device; and

a controlling unit adapted to control the movable object based on the distance information.