Solid-state imaging device, and camera system using same
A solid-state imaging device includes a first A/D converter circuit and a second A/D converter circuit per column. The first A/D converter circuit performs a first A/D conversion that (i) refines, using a first comparator, a range including a potential of an analog signal through a binary search, and (ii) generates, based on a result of the binary search, a first digital signal being a high-order portion of the digital signal. The second A/D converter circuit performs a second A/D conversion that generates a second digital signal being a low-order portion that is a remainder of the digital signal by measuring a time required for an output of the second comparator to be inverted, the second comparator comparing a quantitative relationship between the analog signal refined and a ramp signal.
1. A solid-state imaging device, comprising:
a plurality of pixel cells arranged in an X-direction and a Y-direction, the plurality of pixels cells each including a photoelectric converter that converts an optical signal to an electrical signal;
a plurality of vertical signal lines arranged in the X-direction that are connected to the plurality of pixel cells and transmit the electrical signal as an analog signal; and
a plurality of analog-to-digital (A/D) converters arranged in the X-direction that are respectively connected to the plurality of vertical signal lines and convert the analog signal to a digital signal, wherein
the plurality of A/D converters each include:
a first A/D converter circuit having a first comparator; and
a second A/D converter circuit having a second comparator,
the first A/D converter circuit performs a first A/D conversion that (i) refines, using the first comparator, a range including a potential of the analog signal through a binary search, and (ii) generates, based on a result of the binary search, a first digital signal being a high-order portion of the digital signal, and
the second A/D converter circuit performs is a second A/D conversion that generates a second digital signal being a low-order portion that is a remainder of the digital signal by measuring a time required for an output of the second comparator to be inverted, the second comparator comparing a quantitative relationship between the analog signal refined and a ramp signal.
2. The solid-state imaging device according to claim 1 , wherein
the first comparator is faster than the second comparator, and
the second comparator is more resistant to noise contamination than the first comparator.
3. The solid-state imaging device according to claim 1 , wherein
the first A/D converter circuit includes a first control circuit that performs a control to (i) refine, based on an output of the first comparator, the range including the potential of the analog signal through the binary search, and (ii) generate, based on the result of the binary search, the first digital signal, and
the second A/D converter circuit includes a second control circuit that perfou is a control to (i) measure the time necessary for the output of the second comparator to be inverted, and (ii) generate the second digital signal corresponding to the time measured.
4. The solid-state imaging device according to claim 1 , wherein
the first A/D converter circuit includes:
a plurality of capacitors coupled to a first node;
a first switch disposed between the plurality of vertical signal lines and the first node;
a first signal line having a first potential;
a second signal line having a second potential;
a plurality of second switches that are respectively connected to the plurality of capacitors, the plurality of second switches selectively connecting a corresponding one of the plurality of capacitors to the first signal line or the second signal line;
the first comparator connected to the first node;
a reference signal line connected to the first comparator; and
a first control circuit connected to an output of the first comparator,
the second A/D converter circuit includes:
the second comparator connected to the first node;
a ramp signal line connected to the second comparator; and
a second control circuit connected to the output of the second comparator, and
the plurality of capacitors retain the potential corresponding to the analog signal via the first switch.
5. The solid-state imaging device according to claim 4 , comprising:
a buffer circuit disposed between the first node and the second comparator.
6. The solid-state imaging device according to claim 1 , wherein
the first A/D converter circuit includes:
a plurality of capacitors coupled to a first node;
a first switch disposed between the plurality of vertical signal lines and the first node;
a first signal line having a first potential;
a second signal line having a second potential;
a plurality of second switches that are respectively connected to the plurality of capacitors, the plurality of second switches selectively connecting a corresponding one of the plurality of capacitors to the first signal line or the second signal line;
the first comparator connected to the first node;
a reference signal line having a reference potential and being connected to the first comparator; and
a first control circuit connected to an output of the first comparator,
the second A/D converter circuit includes:
the second comparator connected to the first node via a third switch;
a ramp signal line connected to the second comparator; and
a second control circuit connected to the output of the second comparator, and
the first node retains the potential corresponding to the analog signal via the first switch.
7. The solid-state imaging device according to claim 6 , wherein
the third switch electrically disconnects the first node and the second comparator during the first A/D conversion.
8. The solid-state imaging device according to claim 7 , comprising:
a buffer circuit disposed between the first node and the third switch.
9. The solid-state imaging device according to claim 5 , wherein
the buffer circuit is a source follower circuit.
10. The solid-state imaging device according to claim 1 , wherein
the second A/D conversion is performed after the first A/D conversion.
11. The solid-state imaging device according to claim 1 , wherein
the first comparator and the second comparator have a different configuration.
12. The solid-state imaging device according to claim 1 , wherein
the first comparator is a latch comparator circuit.
13. The solid-state imaging device according to claim 1 , wherein
the first comparator is a chopper comparator circuit.
14. The solid-state imaging device according to claim 1 , wherein
the second comparator is a differential amplifier comparator circuit.
15. The solid-state imaging device according to claim 1 , wherein
the photoelectric converter includes a photoelectric conversion film.
16. A camera system, comprising:
the solid-state imaging device according to claim 1 .