Successive approximation analog-to-digital converter, imaging device, imaging system, and moving body

1. A successive approximation analog-to-digital converter that converts an analog signal into an N-bit (N is an integer of 2 or more) digital signal, the successive approximation analog-to-digital converter comprising:

a comparator that receives as inputs, the analog signal and a comparison signal;

a first digital-to-analog converter that converts the comparison signal into a voltage corresponding to each bit of the N bits;

a second digital-to-analog converter that includes an offsetting unit that applies an offset corresponding to lower n bits of the N bit to the comparison signal; and

a controller that causes the comparator to perform a plurality of comparisons between the analog signal and the comparison signal that the first digital-to-analog converter converts into the voltage with the offset applied to the comparison signal,

wherein an amount of the offset applied to the comparison signal by the offsetting unit is a same amount in each of the plurality of comparisons.

2. The successive approximation analog-to-digital converter according to claim 1 ,

wherein the first digital-to-analog converter and the second digital-to-analog converter each include a capacitor element and a switch that is connected to the capacitor element, and

wherein a common voltage is applied to the capacitor element of the first digital-to-analog converter and the capacitor element of the second digital-to-analog converter.

3. The successive approximation analog-to-digital converter according to claim 1 ,

wherein a digital signal value corresponding to a noise component contained in the analog signal is obtained, and the offset is a voltage corresponding to a digital signal larger than the digital signal value.

4. The successive approximation analog-to-digital converter according to claim 1 , further comprising:

an amplifier that amplifies an inputted signal with a gain value that is selected from different gain values and outputs the amplified signal as the analog signal to the successive approximation analog-to-digital converter,

wherein the offset is a voltage corresponding to a first bit number when the amplifier amplifies the inputted signal with a first gain value of the gain values, and

wherein the offset is a voltage corresponding to a second bit number larger than the first bit number when the amplifier amplifies the inputted signal with a second gain value of the gain values that is larger than the first gain value.

5. An imaging device comprising:

the successive approximation analog-to-digital converter according to claim 1 ; and

pixels each of which outputs a pixel signal,

wherein the successive approximation analog-to-digital converter uses the pixel signal as the analog signal for AD conversion.

6. The imaging device according to claim 5 ,

wherein each of the pixels outputs a first signal based on electric charges of some of the photoelectric converters and a second signal based on electric charges of all of the photoelectric converters,

wherein the successive approximation analog-to-digital converter converts the first signal into a digital signal at least two times and converts the second signal into a digital signal at least two times, and

wherein a bit number when the first signal is converted at a second time is lower than a bit number when the second signal is converted at a second time.

7. The imaging device according to claim 6 ,

wherein each of the pixels outputs a noise signal that is a signal at a noise level,

wherein the successive approximation analog-to-digital converter converts the noise signal into a digital signal at least two times, and

wherein a bit number when the noise signal is converted at a second time is lower than the bit number when the first signal is converted at the second time.

8. The imaging device according to claim 5 ,

wherein a first chip includes the pixels, a second chip includes the successive approximation analog-to-digital converter, and the first chip and the second chip are stacked.

9. The imaging device according to claim 8 ,

wherein the first chip further includes a light-shielded pixel that includes a light-shielded photoelectric converter, and

wherein the light-shielded pixel and the successive approximation analog-to-digital converter overlap in a plan view.

10. An imaging system comprising:

the imaging device according to claim 5 ; and

a signal processing unit that processes a signal that is outputted from the imaging device to generate an image.

11. A moving body comprising:

the imaging device according to claim 5 ;

a distance-information-obtaining unit that obtains information about a distance from a parallax image based on a signal from the imaging device to an object; and

a control unit that controls the moving body on a basis of the information about the distance.

12. An imaging device comprising:

pixels each of which includes photoelectric converters; and

a successive approximation analog-to-digital converter,

wherein each of the pixels outputs a first signal based on electric charges of some of the photoelectric converters and a second signal based on electric charges of all of the photoelectric converters,

wherein the successive approximation analog-to-digital converter converts the first signal into a digital signal at least two times and converts the second signal into a digital signal at least two times, and

wherein a bit number when the first signal is converted at a second time is lower than a bit number when the second signal is converted at a second time.

13. The imaging device according to claim 12 ,

wherein each of the pixels outputs a noise signal that is a signal at a noise level,

wherein the successive approximation analog-to-digital converter converts the noise signal into a digital signal at least two times, and

wherein a bit number when the noise signal is converted at a second time is lower than the bit number when the first signal is converted at the second time.

14. The imaging device according to claim 12 ,

wherein a first chip includes the pixels, a second chip includes the successive approximation analog-to-digital converter, and the first chip and the second chip are stacked.

15. The imaging device according to claim 14 ,

wherein the first chip further includes a light-shielded pixel that includes a light-shielded photoelectric converter, and

wherein the light-shielded pixel and the successive approximation analog-to-digital converter overlap in a plan view.

16. An imaging system comprising:

the imaging device according to claim 12 ; and

a signal processing unit that processes a signal that is outputted from the imaging device to generate an image.

17. A moving body comprising:

the imaging device according to claim 12 ; and

a distance-information-obtaining unit that obtains information about a distance from a parallax image based on a signal from the imaging device to an object; and

a control unit that controls the moving body on a basis of the information about the distance.