Imaging device and method of driving imaging device
An imaging device includes a pixel that outputs a signal based on charges generated by photoelectric conversion, a comparator that compares a pixel signal output from the pixel with a reference signal and outputs a signal in accordance with a comparison result, a buffer circuit that buffers a signal output from the comparator, a switch provided at least one of a part between the buffer circuit and a first node supplied with a first power source voltage and a part between the buffer circuit and a second node supplied with a second power source voltage, and a control circuit that controls the switch to a non-conductive state in a period in which the comparator performs a comparison operation to compare the pixel signal with the reference signal.
1. An imaging device comprising:
a pixel that outputs a signal based on charges generated by photoelectric conversion;
a comparator that compares a pixel signal output from the pixel with a reference signal and outputs a signal in accordance with a comparison result;
a buffer circuit that buffers a signal output from the comparator;
a first switch provided at a part between the buffer circuit and a first node supplied with a first power source voltage;
a control circuit that controls the first switch to a non-conductive state in a period in which the comparator performs a comparison operation to compare the pixel signal with the reference signal; and
a second switch provided at a part between the buffer circuit and a second node supplied with a second power source voltage,
wherein the control circuit controls,
when the output of the comparator is at a high level before the comparison operation, the first switch to a non-conductive state and the second switch to a conductive state in a period in which the comparison operation is performed, and
when the output of the comparator is at a low level before the comparison operation, the first switch to a conductive state and the second switch to a non-conductive state in a period in which the comparison operation is performed.
2. The imaging device according to claim 1 , wherein the control circuit controls the first switch to a conductive state before the comparison operation and sets an output of the buffer circuit to a level opposite to an output of the comparator obtained before the comparison operation.
3. The imaging device according to claim 1 ,
wherein the first switch is provided between the buffer circuit and the first node, and
wherein the comparator outputs a low level signal before the comparison operation and, in response to inversion of a magnitude relationship of the pixel signal and the reference signal, outputs a high level signal.
4. The imaging device according to claim 2 ,
wherein the first switch is provided between the buffer circuit and the first node, and
wherein the comparator outputs a low level signal before the comparison operation and, in response to inversion of a magnitude relationship of the pixel signal and the reference signal, outputs a high level signal.
5. The imaging device according to claim 1 ,
wherein the first switch is provided between the buffer circuit and the second node, and
wherein the comparator outputs a high level signal before the comparison operation and, in response to inversion of a magnitude relationship of the pixel signal and the reference signal, outputs a low level signal.
6. The imaging device according to claim 2 ,
wherein the first switch is provided between the buffer circuit and the second node, and
wherein the comparator outputs a high level signal before the comparison operation and, in response to inversion of a magnitude relationship of the pixel signal and the reference signal, outputs a low level signal.
7. The imaging device according to claim 1 , wherein the reference signal is a signal whose level increases or decreases from a predetermined value with time elapsing.
8. The imaging device according to claim 2 , wherein the reference signal is a signal whose level increases or decreases from a predetermined value with time elapsing.
9. The imaging device according to claim 1 , wherein the reference signal is a signal that is an analog signal converted from a reference value supplied from a successive approximation register.
10. The imaging device according to claim 2 , wherein the reference signal is a signal that is an analog signal converted from a reference value supplied from a successive approximation register.
11. The imaging device according to claim 1 , wherein the buffer circuit includes a NAND circuit.
12. The imaging device according to claim 2 , wherein the buffer circuit includes a NAND circuit.
13. An imaging system comprising:
an imaging device including:
a pixel that outputs a signal based on charges generated by photoelectric conversion;
a comparator that compares a pixel signal output from the pixel with a reference signal and outputs a signal in accordance with a comparison result;
a buffer circuit that buffers a signal output from the comparator;
a first switch provided at a part between the buffer circuit and a first node supplied with a first power source voltage;
a control circuit that controls the first switch to a non-conductive state in a period in which the comparator performs a comparison operation to compare the pixel signal with the reference signal; and
a second switch provided at a part between the buffer circuit and a second node supplied with a second power source voltage,
wherein the control circuit controls,
when the output of the comparator is at a high level before the comparison operation, the first switch to a non-conductive state and the second switch to a conductive state in a period in which the comparison operation is performed, and
when the output of the comparator is at a low level before the comparison operation, the first switch to a conductive state and the second switch to a non-conductive state in a period in which the comparison operation is performed; and
a signal processing unit that processes a signal output from the pixel of the imaging device.
14. A movable object comprising:
an imaging device including:
a pixel that outputs a signal based on charges generated by photoelectric conversion;
a comparator that compares a pixel signal output from the pixel with a reference signal and outputs a signal in accordance with a comparison result;
a buffer circuit that buffers a signal output from the comparator;
a first switch provided at a part between the buffer circuit and a first node supplied with a first power source voltage;
a control circuit that controls the first switch to a non-conductive state in a period in which the comparator performs a comparison operation to compare the pixel signal with the reference signal;
a second switch provided at a part between the buffer circuit and a second node supplied with a second power source voltage,
wherein the control circuit controls,
when the output of the comparator is at a high level before the comparison operation, the first switch to a non-conductive state and the second switch to a conductive state in a period in which the comparison operation is performed, and
when the output of the comparator is at a low level before the comparison operation, the first switch to a conductive state and the second switch to a non-conductive state in a period in which the comparison operation is performed;
a distance information acquisition unit that acquires distance information on a distance to an object, from parallax images based on a signal from the imaging device; and
a control unit that controls the movable object based on the distance information.