Solid-state imaging element, imaging apparatus, and method of controlling solid-state imaging element
Erroneous detection caused by flicker is suppressed in a solid-state imaging element that detects an address event. solid-state imaging element includes a plurality of pixels, a current detection unit, and a threshold control unit. In the solid-state imaging element, each of the plurality of pixels compares an amount of change in a voltage corresponding to a photocurrent with a predetermined threshold. Further, the current detection unit detects a sum of the photocurrents of the respective plurality of pixels as a total current. Further, the threshold control unit controls the predetermined threshold to a value corresponding to the total current detected by the current detection unit.
1. A solid-state imaging element comprising:
a plurality of pixels, each of which is configured to compare an amount of change in a voltage corresponding to a photocurrent with a predetermined threshold;
current detection circuitry configured to detect a sum of photocurrents of the respective plurality of pixels as a total current; and
threshold control circuitry configured to control the predetermined threshold to a value corresponding to the total current.
2. The solid-state imaging element according to claim 1 , wherein
the threshold control circuitry includes
adjustment circuitry configured to adjust the total current and output the total current as an adjustment current,
an offset current source configured to generate a predetermined offset current, and
conversion circuitry configured to convert a sum or difference between the adjustment current and the predetermined offset current into the predetermined threshold and supply the predetermined threshold to each of the plurality of pixels.
3. The solid-state imaging element according to claim 2 , wherein
the offset current source includes
a reference current source configured to generate a predetermined reference current,
a first distribution circuit configured to distribute the predetermined reference current at a plurality of different ratios to generate a plurality of distribution currents, and
a first decoder configured to control the first distribution circuit and output a sum of a predetermined number of the plurality of distribution currents as the predetermined offset current.
4. The solid-state imaging element according to claim 2 , wherein
the adjustment circuitry includes
a second distribution circuit configured to distribute the total current at a plurality of different ratios to generate a plurality of distribution currents, and
a second decoder configured to control the second distribution circuit and output a sum of a predetermined number of the plurality of distribution currents as the adjustment current.
5. The solid-state imaging element according to claim 2 , wherein
the conversion circuitry includes
resistance elements, and
a third decoder configured to connect a predetermined number of the resistance elements in parallel and output a voltage generated by the adjustment current flowing through a combined resistance of the predetermined number of the resistance elements as the predetermined threshold.
6. The solid-state imaging element according to claim 1 , wherein
the current detection circuitry detects a sum of the photocurrents of some of the plurality of pixels as the total current.
7. The solid-state imaging element according to claim 1 , wherein
the threshold control circuitry controls the predetermined threshold to a higher value as the total current is larger.
8. The solid-state imaging element according to claim 1 , wherein:
the predetermined threshold includes an upper threshold and a lower threshold that are different from each other; and
each of the plurality of pixels
detects that the amount of change exceeds the upper threshold as an on event, and
detects that the amount of change falls below the lower threshold as an off event.
9. An imaging apparatus comprising:
a plurality of pixels, each of which is configured to compare an amount of change in a voltage corresponding to a photocurrent with a predetermined threshold;
current detection circuitry configured to detect a sum of photocurrents of the respective plurality of pixels as a total current;
threshold control circuitry configured to control the predetermined threshold to a value corresponding to the total current; and
a signal processor configured to process a signal including a comparison result of each of the plurality of pixels.
10. A method of controlling a solid-state imaging element, the method comprising:
comparing, for each of a plurality of pixels, an amount of change in a voltage corresponding to a photocurrent with a predetermined threshold;
detecting a sum of photocurrents of the respective plurality of pixels as a total current; and
controlling the predetermined threshold to a value corresponding to the total current.
11. The imaging apparatus according to claim 9 , wherein
the threshold control circuitry includes
adjustment circuitry configured to adjust the total current and output the total current as an adjustment current,
an offset current source configured to generate a predetermined offset current, and
conversion circuitry configured to convert a sum or difference between the adjustment current and the predetermined offset current into the predetermined threshold and supply the predetermined threshold to each of the plurality of pixels.
12. The imaging apparatus according to claim 11 , wherein
the offset current source includes
a reference current source configured to generate a predetermined reference current,
a first distribution circuit configured to distribute the predetermined reference current at a plurality of different ratios to generate a plurality of distribution currents, and
a first decoder configured to control the first distribution circuit and output a sum of a predetermined number of the plurality of distribution currents as the predetermined offset current.
13. The imaging apparatus according to claim 11 , wherein
the adjustment circuitry includes
a second distribution circuit configured to distribute the total current at a plurality of different ratios to generate a plurality of distribution currents, and
a second decoder configured to control the second distribution circuit and output a sum of a predetermined number of the plurality of distribution currents as the adjustment current.
14. The imaging apparatus according to claim 11 , wherein
the conversion circuitry includes
resistance elements, and
a third decoder configured to connect a predetermined number of the resistance elements in parallel and output a voltage generated by the adjustment current flowing through a combined resistance of the predetermined number of the resistance elements as the predetermined threshold.
15. The imaging apparatus according to claim 9 , wherein
the current detection circuitry detects a sum of the photocurrents of some of the plurality of pixels as the total current.
16. The imaging apparatus according to claim 9 , wherein
the threshold control circuitry controls the predetermined threshold to a higher value as the total current is larger.
17. The imaging apparatus according to claim 9 , wherein:
the predetermined threshold includes an upper threshold and a lower threshold that are different from each other; and
each of the plurality of pixels
detects that the amount of change exceeds the upper threshold as an on event, and
detects that the amount of change falls below the lower threshold as an off event.