Imaging device and distance measurement system
Provided is an imaging device capable of suppressing a decrease in a frame rate while improving charge transfer efficiency. An imaging device according to an embodiment of the present disclosure includes: a photoelectric conversion element; a signal converter that is boosted when charge transferred from the photoelectric conversion element is converted into a pixel signal; a selection transistor that interrupts a signal line of the pixel signal during a boosting period of the signal converter; a comparator including a non-inverting input terminal to which the pixel signal is input via the selection transistor, an inverting input terminal to which a ramp signal is input, and an output terminal which outputs a comparison result between the pixel signal and the ramp signal; and a correction circuit that holds a potential of the non-inverting input terminal in the boosting period at a potential of the non-inverting input terminal before the boosting period.
1. An imaging device, comprising:
a photoelectric conversion element;
a signal converter that is boosted when charge transferred from the photoelectric conversion element is converted into a pixel signal;
a selection transistor that interrupts a signal line of the pixel signal during a boosting period of the signal converter;
a comparator including a non-inverting input terminal to which the pixel signal is input via the selection transistor, an inverting input terminal to which a ramp signal is input, and an output terminal which outputs a comparison result between the pixel signal and the ramp signal; and
a correction circuit that holds a potential of the non-inverting input terminal in the boosting period at a potential of the non-inverting input terminal before the boosting period.
2. The imaging device according to claim 1 , wherein
the correction circuit includes:
a first transistor arranged between the selection transistor and the non-inverting input terminal;
a second transistor paired with the first transistor;
a first switch arranged between a gate of the first transistor and a gate of the second transistor;
a second switch arranged between a source of the first transistor and a source of the second transistor; and
a capacitor connected to the gate of the second transistor, and
the first switch is in an off-state and the second switch is in an on-state in the boosting period.
3. The imaging device according to claim 2 , wherein a threshold voltage between the gate and the source of the first transistor is equal to a threshold voltage between the gate and the source of the second transistor.
4. The imaging device according to claim 2 , wherein the first switch is switched from an on-state to the off-state, and the second switch is switched from an off-state to the on-state immediately before the boosting period.
5. The imaging device according to claim 2 , wherein the selection transistor is switched from an on-state to an off-state, the first switch is switched from an on-state to the off-state, and the second switch is switched from an off-state to the on-state in an auto-zero period of the comparator before the boosting period.
6. The imaging device according to claim 5 , wherein the first switch is an N-channel MOSFET.
7. The imaging device according to claim 1 , wherein the photoelectric conversion element, the signal converter, and the selection transistor are arranged on a first semiconductor substrate, and the comparator and the correction circuit are arranged on a second semiconductor substrate stacked on the first semiconductor substrate.
8. The imaging device according to claim 1 , wherein the photoelectric conversion element, the signal converter, the selection transistor, the comparator, and the correction circuit are arranged on one semiconductor substrate.
9. The imaging device according to claim 1 , wherein
a plurality of the photoelectric conversion elements including the photoelectric conversion element is two-dimensionally arranged, and
the comparator and the correction circuit are provided for each of the plurality of photoelectric conversion elements.
10. The imaging device according to claim 9 adopting a global shutter system in which the plurality of photoelectric conversion elements accumulates the charge at a same timing.
11. The imaging device according to claim 9 adopting a rolling shutter system in which the plurality of photoelectric conversion elements accumulates the charge at different timings.
12. A distance measurement system, comprising:
an illumination device that emits distance measurement light; and
an imaging device that receives reflected light of the distance measurement light,
wherein the imaging device includes:
a photoelectric conversion element that photoelectrically converts the reflected light;
a signal converter that is boosted when charge transferred from the photoelectric conversion element is converted into a pixel signal;
a selection transistor that interrupts a signal line of the pixel signal during a boosting period of the signal converter;
a comparator including a non-inverting input terminal to which the pixel signal is input via the selection transistor, an inverting input terminal to which a ramp signal is input, and an output terminal which outputs a comparison result between the pixel signal and the ramp signal; and
a correction circuit that holds a potential of the non-inverting input terminal in the boosting period at a potential of the non-inverting input terminal before the boosting period.
13. The distance measurement system according to claim 12 , wherein
the correction circuit includes:
a first transistor arranged between the selection transistor and the non-inverting input terminal;
a second transistor paired with the first transistor;
a first switch arranged between a gate of the first transistor and a gate of the second transistor;
a second switch arranged between a source of the first transistor and a source of the second transistor; and
a capacitor connected to the gate of the second transistor, wherein the first switch is in an off-state and the second switch is in an on-state in the boosting period.
14. The distance measurement system according to claim 13 , wherein a threshold voltage between the gate and the source of the first transistor is equal to a threshold voltage between the gate and the source of the second transistor.
15. The distance measurement system according to claim 13 , wherein the first switch is switched from an on-state to the off-state, and the second switch is switched from an off-state to the on-state immediately before the boosting period.
16. The distance measurement system according to claim 12 , wherein the photoelectric conversion element, the signal converter, and the selection transistor are arranged on a first semiconductor substrate, and the comparator and the correction circuit are arranged on a second semiconductor substrate stacked on the first semiconductor substrate.
17. The distance measurement system according to claim 12 , wherein the photoelectric conversion element, the signal converter, the selection transistor, the comparator, and the correction circuit are arranged on one semiconductor substrate.