Solid-state imaging device, method of driving the same, and electronic apparatus
The present technology relates to a solid-state imaging device, a method of driving the solid-state imaging device, and an electronic apparatus by which pixels can be read effectively. The solid-state imaging device includes a readout unit that performs a common-source operation or a source follower operation with respect to pixels to read a signal for each column. According to a level of illumination, the readout unit performs a common-source readout operation to reset a floating diffusion region and read an electric charge transferred from a photoelectric transducer and held in the floating diffusion region, and performs a source follower readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region. The present technology is applicable to a solid-state imaging device such as a CMOS image sensor.
1. A solid-state imaging device comprising:
a plurality of pixels each including:
a photoelectric transducer that generates an electric charge according to an amount of incident light and accumulates the electric charge inside;
one or a plurality of transfer gates that transfers the electric charge accumulated in the photoelectric transducer; and
a floating diffusion region that holds the electric charge transferred by the transfer gates in order for the electric charge to be read as a signal; and
a readout unit that performs a common-source operation or a source follower operation with respect to the plurality of pixels to read a signal for each column, wherein the readout unit performs, according to a level of illumination:
a common-source readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region; and
a source follower readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region;
an analog/digital (A/D) converter that performs A/D conversion on an analog pixel signal read by the common-source readout operation or the source follower readout operation to obtain a digital signal; and
an inverting amplifier that is provided upstream of the A/D converter and operated at the time of the common-source readout operation, wherein the inverting amplifier is operated to:
shift a voltage range of the common-source readout operation in accordance with a voltage range of the source follower readout operation to align a reset level of the common-source readout operation with a reset level of the source follower readout operation; and
invert output of the common-source readout operation to align a signal of the common-source readout operation and a signal of the source follower readout operation in the same direction, the signals being input to the A/D converter.
2. The solid-state imaging device according to claim 1 , further comprising:
a control unit that switches an operating mode to the common-source readout operation in a case where the level of illumination of a subject is lower than a predetermined illumination, or to the source follower readout operation in a case where the level of illumination of the subject is higher than or equal to the predetermined illumination, on the basis of a frame acquired temporally before a current frame.
3. The solid-state imaging device according to claim 1 , wherein the plurality of pixels is arranged in two dimensions and is read in an operating mode that is switched alternately and successively between the common-source readout operation and the source follower readout operation in a horizontal direction.
4. The solid-state imaging device according to claim 1 , wherein the plurality of pixels is arranged in two dimensions and is read in an operating mode that is switched alternately and successively between the common-source readout operation and the source follower readout operation frame by frame.
5. The solid-state imaging device according to claim 1 , wherein the plurality of pixels is arranged in two dimensions and is read in an operating mode that is switched alternately and successively between the common-source readout operation and the source follower readout operation in horizontal and vertical directions.
6. The solid-state imaging device according to claim 1 , wherein the A/D converter adaptively switches an operating mode to the common-source readout operation in a case where the level of illumination of a subject is lower than a predetermined illumination, or to the source follower readout operation in a case where the level of illumination of the subject is higher than or equal to the predetermined illumination, on the basis of output from the readout unit.
7. The solid-state imaging device according to claim 6 , wherein
the A/D converter switches the operating mode in a way that:
an auto zero (AZ) period is completed first;
a reset level of the common-source readout operation is acquired;
a reset level of the source follower readout operation is acquired;
the electric charge is transferred from the photoelectric transducer to the floating diffusion region by the transfer gates; and
a signal level of the common-source readout operation or a signal level of the source follower readout operation is acquired according to a result of determination on a signal level.
8. The solid-state imaging device according to claim 6 , wherein
the A/D converter switches the operating mode in a way that:
an auto zero (AZ) period is completed first;
a reset level of the common-source readout operation is acquired;
the electric charge is transferred from the photoelectric transducer to the floating diffusion region by the transfer gates;
a signal level of the common-source readout operation or a signal level of the source follower readout operation is acquired according to a result of determination on a signal level; and
a reset level of the source follower readout operation is acquired.
9. The solid-state imaging device according to claim 1 , wherein
each of the plurality of pixels further comprises a lateral overflow integration capacitor that can accumulate the electric charge generated by the photoelectric transducer as well as reduce conversion efficiency, and
the readout unit performs a lateral overflow integration capacitor (LOFIC) readout operation using the lateral overflow integration capacitor on the plurality of pixels to read a signal for each column.
10. The solid-state imaging device according to claim 9 , wherein the plurality of pixels is arranged in two dimensions and is read in an operating mode that is switched alternately and successively among the common-source readout operation, the source follower readout operation, and the LOFIC readout operation in a horizontal direction or frame by frame.
11. The solid-state imaging device according to claim 9 , wherein the A/D converter adaptively switches an operating mode to the common-source readout operation, the source follower readout operation, or the LOFIC readout operation according to the level of illumination of a subject on the basis of output from the readout unit.
12. The solid-state imaging device according to claim 11 , wherein
the A/D converter switches the operating mode in a way that:
an auto zero (AZ) period is completed first;
a reset level of the LOFIC readout operation is acquired;
a reset level of the source follower readout operation is acquired;
a reset level of the common-source readout operation is acquired;
the electric charge is transferred from the photoelectric transducer to the floating diffusion region by the transfer gates; and
a signal level of the common-source readout operation, a signal level of the source follower readout operation, or a signal level of the LOFIC readout operation is acquired according to a result of determination on a signal level.
13. The solid-state imaging device according to claim 11 , wherein
the A/D converter switches the operating mode in a way that:
an auto zero (AZ) period is completed first;
a reset level of the common-source readout operation is acquired;
the electric charge is transferred from the photoelectric transducer to the floating diffusion region by the transfer gates;
a signal level of the common-source readout operation, a signal level of the source follower readout operation, or a signal level of the LOFIC readout operation is acquired according to a result of determination on a signal level; and
a reset level of the source follower readout operation or a reset level of the LOFIC readout operation is acquired according to a result of determination on a signal level.
14. A method of driving a solid-state imaging device comprising:
a plurality of pixels each including:
a photoelectric transducer that generates an electric charge according to an amount of incident light and accumulates the electric charge inside;
one or a plurality of transfer gates that transfers the electric charge accumulated in the photoelectric transducer; and
a floating diffusion region that holds the electric charge transferred by the transfer gates in order for the electric charge to be read as a signal; and
a readout unit that performs a common-source operation or a source follower operation with respect to the plurality of pixels to read a signal for each column, wherein
the method includes a step in which the readout unit performs, according to a level of illumination:
a common-source readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region; and
a source follower readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region; the solid-state imaging device further comprising:
an analog/digital (A/D) converter that performs A/D conversion on an analog pixel signal read by the common-source readout operation or the source follower readout operation to obtain a digital signal; and
an inverting amplifier that is provided upstream of the A/D converter and operated at the time of the common-source readout operation, wherein the inverting amplifier is operated to:
shift a voltage range of the common-source readout operation in accordance with a voltage range of the source follower readout operation to align a reset level of the common-source readout operation with a reset level of the source follower readout operation; and
invert output of the common-source readout operation to align a signal of the common-source readout operation and a signal of the source follower readout operation in the same direction, the signals being input to the A/D converter.
15. An electronic apparatus equipped with a solid-state imaging device comprising:
a plurality of pixels each including:
a photoelectric transducer that generates an electric charge according to an amount of incident light and accumulates the electric charge inside;
one or a plurality of transfer gates that transfers the electric charge accumulated in the photoelectric transducer; and
a floating diffusion region that holds the electric charge transferred by the transfer gates in order for the electric charge to be read as a signal;
a readout unit that performs a common-source operation or a source follower operation with respect to the plurality of pixels to read a signal for each column, wherein the readout unit performs, according to a level of illumination:
a common-source readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region; and
a source follower readout operation to reset the floating diffusion region and read the electric charge transferred from the photoelectric transducer and held in the floating diffusion region;
an analog/digital (A/D) converter that performs A/D conversion on an analog pixel signal read by the common-source readout operation or the source follower readout operation to obtain a digital signal; and
an inverting amplifier that is provided upstream of the A/D converter and operated at the time of the common-source readout operation, wherein the inverting amplifier is operated to:
shift a voltage range of the common-source readout operation in accordance with a voltage range of the source follower readout operation to align a reset level of the common-source readout operation with a reset level of the source follower readout operation; and
invert output of the common-source readout operation to align a signal of the common-source readout operation and a signal of the source follower readout operation in the same direction, the signals being input to the A/D converter.