Imaging device and imaging method

Abstract

[Problem] To suppress a decrease in measurement accuracy dependent on a degree of overexposure. [Solution] This imaging device comprises: a pixel that can convert an amount of charge corresponding to an amount of incident light into a voltage and output the voltage to a signal line as a voltage signal; and a detecting circuit that detects that overexposure has occurred when an amount of change in the potential of the voltage signal over a predetermined time range is larger than the amount of change in the potential of a reference signal that has been subjected continuously to a predetermined displacement over the time range. The potential of the reference signal increases or decreases monotonically over time. The detecting circuit detects that overexposure has occurred if there is a predetermined magnitude relationship between the potential of the voltage signal and the voltage of the reference signal at the end point of the time range.

Claims

1. An imaging device comprising: a pixel capable of converting an amount of charge corresponding to the amount of incident light into a voltage and outputting it as a voltage signal on a signal line; and a detection circuit that detects that an overexposure has occurred when the amount of change in the potential of the voltage signal in a predetermined time range is greater than the amount of change in the potential of a reference signal that has been continuously displaced in a predetermined time range.

2. The imaging apparatus according to claim 1, wherein the reference signal has a potential that monotonically increases or decreases over time from a reference potential within the time range.

3. The imaging apparatus according to claim 2, wherein the detection circuit detects that an overexposure has occurred when there is a predetermined magnitude relationship between the potential of the voltage signal and the voltage of the reference signal at the end of the time range.

4. The imaging apparatus according to claim 3, wherein the pixel comprises a photoelectric conversion element that generates and stores an electric charge corresponding to incident light; a charge-voltage conversion unit that stores the charge generated by the photoelectric conversion element as the amount of charge and converts it into a voltage; and a transfer transistor that controls the potential barrier between the photoelectric conversion element and the charge-voltage conversion unit, and the voltage signal is a signal when the potential barrier exceeds a predetermined size.

5. The imaging apparatus according to claim 3, further comprising an analog-to-digital conversion unit connected to the signal line and converting the voltage signal into a digital value.

6. The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit is connected to the signal line via a first switch, and the detection circuit changes the first switch from a connected state to a disconnected state when it detects that an overexposure has occurred.

7. The imaging apparatus according to claim 6, wherein the detection circuit, when it detects that the amount of light overexposure has occurred, sets the input potential to the analog-to-digital conversion unit to a predetermined potential.

8. The imaging apparatus according to claim 7, wherein the detection circuit is connected to the input terminal of the analog-to-digital conversion unit and to the ground potential via a second switch, and when the detection circuit detects that the amount of light overexposure has occurred, it changes the first switch to the disconnected state and then changes the second switch from the disconnected state to the connected state.

9. The imaging apparatus according to claim 8, wherein the detection circuit is connected to the signal line via a buffer unit.

10. The imaging apparatus according to claim 9, wherein the buffer unit has a first amplification transistor for amplifying the voltage signal, and the detection circuit is connected to the signal line via the first amplification transistor.

11. The imaging apparatus according to claim 10, wherein the buffer unit has a second amplification transistor for amplifying the reference signal, and the detection circuit is connected to the reference signal via the second amplification transistor.

12. The imaging apparatus according to claim 11, wherein the first amplification transistor and the second amplification transistor are connected to a common constant current source or to different constant current sources.

13. The imaging apparatus according to claim 12, wherein the detection circuit comprises: a differential amplifier that amplifies the voltage signal and the reference signal; a dynamic comparator that outputs a determination signal indicating that the amount of overexposure has occurred when the voltage signal amplified by the differential amplifier and the reference signal have a predetermined magnitude relationship at the end of the time range; and a logic control unit that controls the first switch and the second switch based on the determination signal.

14. The imaging apparatus according to claim 13, wherein the amplified signal of the first amplification transistor is input to the first terminal of the differential amplifier via the first capacitor, and the amplified signal of the second amplification transistor is input to the second terminal of the differential amplifier via the second capacitor.

15. The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit outputs a predetermined value when the detection circuit detects that the amount of light overexposure has occurred.

16. The imaging apparatus according to claim 5, further comprising a signal processing unit for signal processing of the output value of the analog-to-digital conversion unit, wherein the signal processing unit outputs a predetermined value when the detection circuit detects that the amount of light overexposure has occurred.

17. The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit comprises a comparator for detecting the timing at which the voltage signal and the second reference signal coincide, and a counter for counting the elapsed time until the timing of the coincidence, and the counter outputs a predetermined value when the detection circuit detects that the amount of overexposure has occurred.

18. The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit comprises: a comparator that, upon detecting the timing at which the voltage signal and the second reference signal coincide, changes a first logic value to a second logic value and outputs it; a logic gate that outputs the output value of the comparator according to the output value of the detection circuit; and a counter that counts the elapsed time until the timing at which the signals coincide based on the second logic value, and the logic gate outputs the first logic value when the detection circuit detects that the amount of light overexposure has occurred.

19. The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit comprises a comparator that, upon detecting the timing at which the voltage signal and the second reference signal coincide, changes the first logical value to the second logical value and outputs it, and a counter that, based on the second logical value, counts the elapsed time until the timing at which the signals coincide, and the comparator outputs the first logical value when the detection circuit detects that the amount of light overexposure has occurred.

20. An imaging method comprising: a step of converting an amount of charge corresponding to the amount of incident light into a voltage and outputting it as a voltage signal to a signal line; and a detection step of detecting that an overexposure has occurred when the amount of change in the potential of the voltage signal in a predetermined time range is greater than the amount of change in the potential of a reference signal that has been continuously displaced for a predetermined time range.

Images