Solid-state imaging element and imaging device that detect address event
A high-quality image is taken by a solid-state imaging element that detects an address event. The solid-state imaging element is provided with a pixel array unit and an analog-to-digital conversion unit. In the pixel array unit in the solid-state imaging element, a normal pixel that generates an analog signal by photoelectric conversion of incident light and outputs the analog signal and a detection pixel that detects that an amount of change in incident light becomes larger than a predetermined threshold and outputs a detection result are arranged. Furthermore, the analog-to-digital conversion unit converts the analog signal into a digital signal.
1. A solid-state imaging element, comprising:
a pixel array unit that includes:
a set of normal pixels in two rows by two columns, wherein
a normal pixel of the set of normal pixels is configured to output an analog signal; and
a plurality of detection pixels, wherein
the plurality of detection pixels includes a set of detection pixels in two rows by two columns,
the set of detection pixels is adjacent to the set of normal pixels,
a detection pixel of the plurality of detection pixels is configured to:
detect that an amount of change in incident light becomes larger than a first threshold; and
output a detection result, and
the detection pixel includes:
a pixel circuit configured to generate a voltage signal by photoelectric conversion of the incident light;
a differentiation circuit configured to generate a differentiation signal corresponding to a change in the voltage signal with respect to a reference value, wherein the reference value corresponds to a value of the voltage signal at a time of reset of the differentiation circuit; and
a comparator configured to compare a level of the differentiation signal with the first threshold and a second threshold to output one of a high-level comparison result or a low-level comparison result as the detection result, wherein the first threshold is higher than the second threshold.
2. The solid-state imaging element according to claim 1 , further comprising an analog-to-digital conversion unit configured to convert the analog signal into a digital signal.
3. The solid-state imaging element according to claim 1 , wherein the normal pixel includes:
a photodiode configured to photoelectrically convert the incident light to generate electric charge;
a discharge transistor configured to discharge the electric charge from the photodiode;
a former stage electric charge accumulation unit configured to accumulate the electric charge;
a former stage transfer transistor configured to transfer the electric charge from the photodiode to the former stage electric charge accumulation unit;
a latter stage electric charge accumulation unit configured to accumulate the electric charge and generate a voltage corresponding to an amount of the electric charge;
a reset transistor configured to initialize the latter stage electric charge accumulation unit; and
a latter stage transfer transistor configured to transfer the electric charge from the former stage electric charge accumulation unit to the latter stage electric charge accumulation unit.
4. The solid-state imaging element according to claim 3 , wherein
the discharge transistor is further configured to discharge the electric charge at an exposure starting timing,
the former stage transfer transistor is further configured to transfer the electric charge at an exposure finishing timing,
the reset transistor is further configured to initialize the latter stage electric charge accumulation unit based on transfer of the electric charge to the former stage electric charge accumulation unit, and
the latter stage transfer transistor is further configured to transfer the electric charge based on initialization of the latter stage electric charge accumulation unit.
5. The solid-state imaging element according to claim 1 , wherein the normal pixel includes:
a photodiode configured to photoelectrically convert the incident light to generate electric charge;
an electric charge accumulation unit configured to accumulate the electric charge and generate a voltage corresponding to an amount of the electric charge;
a transfer transistor configured to transfer the electric charge from the photodiode to the electric charge accumulation unit; and
a reset transistor configured to initialize the electric charge accumulation unit.
6. The solid-state imaging element according to claim 5 , wherein
the transfer transistor is further configured to transfer the electric charge at an exposure starting timing,
the reset transistor is further configured to initialize the electric charge accumulation unit at the exposure starting timing,
the transfer transistor is further configured to transfer the electric charge at an exposure finishing timing, and
the reset transistor is further configured to initialize the electric charge accumulation unit based on transfer of the electric charge.
7. The solid-state imaging element according to claim 1 , further comprising an analog-to-digital conversion unit configured to convert the analog signal into a digital signal, wherein
a specific number of columns are in a direction perpendicular to a determined direction in the pixel array unit,
at least one of the normal pixel or the detection pixel is in each of the specific number of columns,
the analog-to-digital conversion unit includes a plurality of analog-to-digital converters of a positive integral multiple of the specific number of columns, and
each of the plurality of analog-to-digital converters is configured to convert the analog signal from a different column out of the specific number of columns into the digital signal.
8. The solid-state imaging element according to claim 1 , wherein the detection pixel is further configured to output the generated voltage signal.
9. The solid-state imaging element according to claim 1 , further comprising:
an analog-to-digital conversion unit configured to convert the analog signal into a digital signal; and
a correlated double sampling unit configured to obtain a difference between a reset level on the digital signal and a signal level on the digital signal, wherein the reset level is a level of the analog signal that is set based on initialization of a latter stage electric charge accumulation unit in the normal pixel.
10. The solid-state imaging element according to claim 9 , wherein the signal level is a level of the analog signal that is set based on an exposure amount.
11. The solid-state imaging element according to claim 1 , wherein
the detection pixel includes a buffer configured to perform impedance conversion of the voltage signal,
the differentiation circuit includes a first capacitance, a second capacitance, a PMOS transistor, and an NMOS transistor,
a first end of the first capacitance is connected to the buffer and a second end of the first capacitance is connected to one end of the second capacitance and a gate of the PMOS transistor,
the PMOS transistor is connected to the NMOS transistor in series between a power supply and a ground terminal,
a bias voltage is applied to a gate of the NMOS transistor on a ground side, and
a connection point of the PMOS transistor and the NMOS transistor is connected to the comparator.
12. An imaging device, comprising:
a pixel array unit that includes:
a set of normal pixels in two rows by two columns, wherein
a normal pixel of the set of normal pixels is configured to output an analog signal; and
a plurality of detection pixels, wherein
the plurality of detection pixels includes a set of detection pixels in two rows by two columns,
the set of detection pixels is adjacent to the set of normal pixels,
a detection pixel of the plurality of detection pixels is configured to:
detect that an amount of change in incident light becomes larger than a first threshold; and
output a detection result, and
the detection pixel includes:
a pixel circuit configured to generate a voltage signal by photoelectric conversion of the incident light;
a differentiation circuit configured to generate a differentiation signal corresponding to a change in the voltage signal with respect to a reference value, wherein the reference value corresponds to a value of the voltage signal at a time of reset of the differentiation circuit; and
a comparator configured to compare a level of the differentiation signal with the first threshold and a second threshold to output one of a high-level comparison result or a low-level comparison result as the detection result, wherein the first threshold is higher than the second threshold; and
an analog-to-digital conversion unit configured to convert the analog signal into a digital signal.