Solid-state image sensing device
There is provided a solid-state image sensing device that can prevent the occurrence of vertical line noise with a simple circuit. A timing adjustment circuit generates a first clock supplied to a ramp generator and a second clock supplied to a counter so that a phase difference between the first clock and the second clock is within a predetermined range and differs according to lines in an image sensor.
1. A solid-state image sensing device comprising:
an image sensor in which a plurality of unit pixels for photoelectrically converting incident light into an analog pixel signal are arranged in a matrix;
a ramp generator for generating and outputting a ramp signal in accordance with a first clock having a period T;
a counter for updating a count value in accordance with a second clock having a period that is identical to or an integral multiple of the period of the first clock and having a different phase from that of the first clock;
a plurality of comparators which each compare an analog pixel signal from a corresponding column in the image sensor and a ramp signal from the ramp generator;
a plurality of counter latches which each latch a count value outputted from the counter at timing when the pixel signal matches the ramp signal at a corresponding comparator, and output it as a digital value of the pixel signal; and
a timing adjustment circuit for generating the first clock and the second clock so that a phase difference between the first clock and the second clock is within a predetermined range and differs according to lines in the image sensor,
wherein if an error range of the digital value is 1/a of 1LSB (Least Significant Bit) of the digital value, the predetermined range is (1−1/a)×T.
2. The solid-state image sensing device according to claim 1 , wherein the timing adjustment circuit generates the first clock and the second clock so that the phase difference between the first clock and the second clock becomes a random value within the predetermined range, for each line of the image sensor.
3. The solid-state image sensing device according to claim 2 , wherein the timing adjustment circuit passes a reference clock as the first clock and generates the second clock by delaying the reference clock by ΔT in a random manner, and the maximum value of ΔT is (1−1/a)×T.
4. The solid-state image sensing device according to claim 2 , wherein the timing adjustment circuit generates a reference clock as the second clock and generates the first clock by delaying the reference clock by ΔT in a random manner, and the maximum value of ΔT is (1−1/a)×T.
5. The solid-state image sensing device according to claim 2 , wherein the timing adjustment circuit generates the first clock by delaying a reference clock by ΔT 1 in a random manner and generates the second clock by delaying the reference clock by ΔT 2 in a random manner, and the maximum difference between ΔT 2 and ΔT 1 is (1−1/a)×T.
6. The solid-state image sensing device according to claim 5 , wherein the timing adjustment circuit generates the first clock and the second clock so that (ΔT 1 +ΔT 2 )/2=(MAX+MIN)/2, where MIN denotes the minimum value of ΔT 1 and ΔT 2 , and MAX denotes the maximum value of ΔT 1 and ΔT 2 .