Solid-state imaging apparatus and method of driving the same
A solid-state imaging apparatus includes a plurality of pixels arranged two-dimensionally in a matrix, a reference signal generating circuit adapted to generate a ramp signal, a counter circuit adapted to perform a counting operation according to output of the ramp signal, comparators arranged on a column by column basis and adapted to compare signals read out of the pixels with the ramp signal, and memories arranged on a column by column basis and adapted to store digital data, wherein if output of the comparator is not changed during an AD conversion period, digital data of a predetermined value is stored in the memory. The solid-state imaging apparatus implements overflow handling using a simplified circuit configuration.
1. A solid-state imaging apparatus, comprising:
a plurality of pixels arranged two-dimensionally in a matrix, and each outputting a pixel signal;
a reference signal generating circuit configured to generate a reference signal that changes a signal level monotonously with time;
a plurality of comparators each arranged corresponding to each of columns of the plurality of pixels, and configured to compare the pixel signal with the reference signal;
a plurality of memories arranged each correspondingly to each of the plurality of comparators;
a counter starting a counting operation according to an output of the reference signal from the reference signal generating circuit, configured to count clock pulses to generate a count signal and configured to supply the count signal to the plurality of memories; and
a data supplying unit configured to supply digital data of a predetermined value to the plurality of memories before the comparing, the predetermined value being a value indicating a saturation level of the pixel signal, configured to not renew the digital data from the predetermined value when an output of the comparator does not change as a result of the comparing, and configured to renew the digital data from the predetermined value into a signal value of the count signal when an output of the comparator changes as a result of the comparing.
2. The solid-state imaging apparatus according to claim 1 , further comprising a selecting circuit configured to supply to the plurality of memories either of the digital data of the predetermined value and the signal value of the count signal.
3. The solid-state imaging apparatus according to claim 1 , wherein each of the plurality of the memories comprises a first memory element configured to store digital data derived by analog-to-digital conversion of a reset level signal of the pixel, and a second memory element configured to store digital data derived by analog-to-digital conversion of a signal generated by photoelectric conversion of a light incident in the pixel and outputted from the pixel.
4. The solid-state imaging apparatus according to claim 3 , wherein the data supplying unit is configured to supply the digital data to the first memory, and configured to supply the digital data of the predetermined value different from the predetermined value of the digital data supplied to the first memory.
5. The solid-state imaging apparatus according to claim 1 , wherein the predetermined value of the digital data supplied by the data supplying unit is variable.
6. The solid-state imaging apparatus according to claim 1 , wherein the predetermined value of the digital data supplied by the data supplying unit is larger than or equal to a maximum value in an output range of the digital data derived by analog-to-digital conversion of the pixel signal.
7. A method of driving a solid-state imaging apparatus, comprising:
a plurality of pixels arranged two-dimensionally in a matrix, and each pixel configured to output a pixel signal;
a reference signal generating circuit configured to generate a reference signal that changes a signal level monotonously with time;
a plurality of comparators each arranged corresponding to each of columns of the plurality of pixels, and configured to compare the pixel signal with the reference signal;
a plurality of memories arranged each correspondingly to each of the plurality of comparators; and
a counter starting a counting operation according to an output of the reference signal from the reference signal generating circuit, configured to count clock pulses to generate a count signal and configured to supply the count signal to the plurality of memories, the method comprising steps of:
writing digital data of the predetermined value to the plurality of memories before the comparing, the predetermined value being a value indicating a saturation level of the pixel signal, and
renewing the digital data from the predetermined value into a signal value of the count signal when an output of the comparator changes as a result of the comparing, and not renewing the digital data from the predetermined value when an output of the comparator does not change as a result of the comparing.
8. The method according to claim 7 , wherein
each of the plurality of the memories comprises a first memory element configured to store digital data derived by analog-to-digital conversion of a reset level signal of the pixel, and a second memory element configured to store digital data derived by analog-to-digital conversion of a signal generated by photoelectric conversion of a light incident in the pixel and outputted from the pixel,
the method further comprising steps of:
supplying the digital data of the predetermined value to the first memory element; and
supplying the digital data of the predetermined value different from the predetermined value of the digital data supplied to the first memory element.
9. The solid-state imaging apparatus according to claim 1 , wherein the predetermined value of the digital data supplied by the data supplying unit is a value of the count signal at a timing of finishing the reference signal changes the signal level monotonously with time.
10. The method according to claim 7 , wherein the predetermined value is larger than or equal to a maximum value in an output range of the digital data derived by analog-to-digital conversion of the pixel signal.
11. The method according to claim 7 , wherein the predetermined value is a value of the count signal at a timing of finishing the reference signal changes the signal level monotonously with time.