Image sensor, camera, surveillance system, and method for driving the image sensor

• US 9,131,171 B2
• Filed: 02/21/2013
• Issued: 09/08/2015
• Est. Priority Date: 02/29/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Aoki, Takeshi, Ikeda, Takayuki, Sato, Yurika, Dairiki, Koji
• Primary Examiner(s): Velez, Roberto
• Assistant Examiner(s): LE, TUAN H
• Application Number:
  US13/772,663
• Publication Number:
  US 20130222584A1
• Time in Patent Office: 929 Days
• US Class Current: 1/1
• CPC Class Codes: H04N 23/6811 based on the image signal
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 7/18 Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast

Abstract

Provided is an image sensor having a pixel includes a photoelectric conversion element; a capacitor which is connected between the photoelectric conversion element; a reset circuit which resets a potential of a node between the photoelectric conversion element and the capacitor; an amplifier circuit which outputs a signal corresponding to the potential of the node; and a switch which controls electrical conduction between the amplifier circuit and a vertical signal line. When the node is brought into an electrically floating state, the potential of the optical signal is stored in the node in a state of being inverted. When an optical signal is detected while the potential is stored in the node, the potential of the node increases in accordance with an output potential of the photoelectric conversion element, and thus the potential of the node corresponds to a difference in potential between the optical signals in different light-receiving periods.

Claims

1. An image sensor comprising:

a vertical signal line;

a pixel electrically connected to the vertical signal line; and

an analog-digital conversion device electrically connected to the vertical signal line,

wherein the pixel includes a photodiode, a first capacitor, a first transistor, a second transistor, a third transistor, a first wiring, a second wiring, a third wiring, and a fourth wiring,

wherein one electrode of the first capacitor is electrically connected to an anode of the photodiode,

wherein the other electrode of the first capacitor is electrically connected to a gate of the second transistor,

wherein a node between the other electrode of the first capacitor and the gate of the second transistor is configured to store a potential corresponding to an amount of electric charge generated in the photodiode,

wherein a gate of the first transistor is electrically connected to the first wiring,

wherein one of a source and a drain of the first transistor is electrically connected to the node, and the other of the source and the drain of the first transistor is electrically connected to the third wiring,

wherein one of a source and a drain of the second transistor is electrically connected to one of a source and a drain of the third transistor,

wherein a gate of the third transistor is electrically connected to the second wiring,

wherein the analog-digital conversion device includes a comparator to which a first or second reference potential is input and which compares the first or second reference potential with an analog signal input through the vertical signal line; and

a counter which measures a period during which comparison operation is performed by the comparator and holds a measurement result thereof as a digital value,

wherein, the counter is configured to hold an N-bit digital value (N is an integer of 3 or more) as the measurement result when the comparator performs comparison operation using the first reference potential, and

wherein the counter is configured to hold an M-bit digital value (M is an integer of 2 or more and less than N) as the measurement result when the comparator performs comparison operation using the second reference potential.

2. The image sensor according to claim 1, wherein the other of the source and the drain of the second transistor is electrically connected to the fourth wiring, and the other of the source and the drain of the third transistor is electrically connected to the vertical signal line.

3. The image sensor according to claim 2, wherein the pixel further includes a second capacitor one electrode of which is connected to the node and the other electrode of which is set to a constant potential.

4. The image sensor according to claim 2, wherein the first transistor includes an oxide semi conductor layer.

5. The image sensor according to claim 2, wherein the pixel further includes a fourth transistor which controls electrical conduction between the anode of the photodiode and the one electrode of the first capacitor.

6. A camera comprising the image sensor according to claim 2.

7. A camera comprising:

the image sensor according to claim 2; and

a motion determination portion which determines whether an image taken by the image sensor has motion or not based on the M-bit digital value.

8. A surveillance system comprising:

the camera according to claim 7;

a memory device which stores an output of the camera;

a display device which displays the output of the camera; and

a management device which manages the camera, the memory device, and the display device.

9. The image sensor according to claim 1, wherein the other of the source and the drain of the second transistor is electrically connected to the vertical signal line, and the other of the source and the drain of the third transistor is electrically connected to the fourth wiring.

10. The image sensor according to claim 9, wherein the pixel includes a second capacitor one electrode of which is connected to the node and the other electrode of which is set to a constant potential.

11. The image sensor according to claim 9, wherein the first transistor includes an oxide semiconductor layer.

12. The image sensor according to claim 9, wherein the pixel includes a fourth transistor which controls electrical conduction between the anode of the photodiode and the one electrode of the first capacitor.

13. A camera comprising the image sensor according to claim 9.

14. A camera comprising:

the image sensor according to claim 9; and

a motion determination portion which determines whether an image taken by the image sensor has motion or not from the M-bit digital value.

15. A surveillance system comprising:

the camera according to claim 14;

a memory device which stores an output of the camera;

a display device which displays the output of the camera; and

a management device which manages the camera, the memory device, and the display device.

16. A method for driving an image sensor:

the image sensor including;

a pixel, a vertical signal line and a signal processing circuit which is configured to convert an analog signal output from the pixel through the vertical signal line into a digital signal,

wherein the pixel includes a capacitor;

a photoelectric conversion element electrically connected to one electrode of the capacitor;

an amplifier circuit electrically connected to the other electrode of the capacitor, the amplifier circuit configured to output an analog signal corresponding to a potential of a node between the other electrode of the capacitor and the amplifier circuit;

a first switch which controls electrical conduction between the amplifier circuit and the vertical signal line; and

a circuit which resets the potential of the node;

the method for driving the image sensor comprising;

a first step of accumulating electric charge in the photoelectric conversion element while the node is an electrically floating state;

a second step of reading the analog signal corresponding to the potential of the node in the first step through the vertical signal line and converting the analog signal into an N-bit digital signal (N is an integer of 3 or more) in the signal processing circuit;

a third step of accumulating electric charge in the photoelectric conversion element while the potential of the node is fixed, and then bringing the node into an electrically floating state;

a fourth step, after the third step, of accumulating electric charge in the photoelectric conversion element while the node is maintained in an electrically floating state; and

a fifth step of reading the analog signal corresponding to the potential of the node in the fourth step through the vertical signal line and converting the analog signal into an M-bit digital signal (M is an integer of 2 or more and less than N) in the signal processing circuit.

17. The method for driving an image sensor according to claim 16, further comprising a sixth step of determining whether an image taken by the image sensor has motion or not based on the M-bit digital signal,

wherein which of the first step and the third step is performed next is determined in accordance with a determination result of the sixth step.

18. A method for driving an image sensor:

the image sensor including;

a pixel, a vertical signal line and a signal processing circuit which is configured to convert an analog signal output from the pixel through the vertical signal line into a digital signal,

wherein the pixel includes a capacitor;

a photoelectric conversion element electrically connected to one electrode of the capacitor;

an amplifier circuit electrically connected to the other electrode of the capacitor, the amplifier circuit configured to output an analog signal corresponding to a potential of a node between the other electrode of the capacitor and the amplifier circuit;

a first switch which controls electrical conduction between the amplifier circuit and the vertical signal line;

a circuit which resets the potential of the node by supplying a constant potential to the node; and

a second switch which controls electrical conduction between the photoelectric conversion element and the other electrode of the capacitor;

the method for driving the image sensor comprising;

a first step of accumulating electric charge in the photoelectric conversion element in a state where the second switch is turned on and then turning off the second switch, while the node is maintained in an electrically floating state;

a second step of reading the analog signal corresponding to the potential of the node in the first step through the vertical signal line and converting the analog signal into an N-bit digital signal (N is an integer of 3 or more) in the signal processing circuit;

a third step of accumulating electric charge in the photoelectric conversion element in the state where the second switch is turned on and then turning off the second switch while the potential of the node is fixed, and then bringing the node into an electrically floating state;

a fourth step, after the third step, of accumulating electric charge in the photoelectric conversion element in the state where the second switch is turned on and then turning off the second switch while the node is maintained in an electrically floating state; and

a fifth step of reading the analog signal corresponding to the potential of the node in the fourth step through the vertical signal line and converting the analog signal into an M-bit digital signal (M is an integer of 2 or more and less than N) in the signal processing circuit.

19. The method for driving an image sensor, according to claim 18, further comprising a sixth step of determining whether an image taken by the image sensor has motion or not based on the M-bit digital signal,

wherein which of the first step and the third step is performed next is determined in accordance with a determination result of the sixth step.