Patent Description:
Conventionally, an imaging element having a storage unit that stores a digital value corresponding to the amount of light received by a pixel and a storage unit that temporarily stores a digital value for signal processing and horizontal transfer control is known (for example, refer to Patent Literature <NUM>).

<CIT> discloses a solid-state image capturing device and an electronic instrument which enable a reduction in power consumption. In an AD converter for each unit pixel or each shared pixel unit, a pixel signal is compared with a reference signal temporally changing. In addition, a magnitude of a pixel signal of a pixel of interest is compared with a magnitude of each of pixel signals of neighboring pixels located in a neighborhood of the pixel of interest using the reference signal, and a result of comparison of the magnitudes is held in a data storage section.

<CIT> discloses a solid state imaging device which includes a pixel array unit that has a plurality of pixels <NUM>-dimensionally arranged in a matrix and a plurality of signal lines arranged along a column direction; A/D conversion units that are provided corresponding to the respective signal lines and convert an analog signal output from a pixel through the signal line into a digital signal; and a switching unit that switches or converts the analog signal output through each signal line into a digital signal using any of an A/D conversion unit provided corresponding to the signal line through which the analog signal is transmitted, and an A/D conversion unit provided corresponding to a signal line other than the signal line through which the analog signal is transmitted.

<CIT> discloses a solid-state imager which converts analog pixel values to digital form on an arrayed per-column basis. An N-bit counter supplies an N-bit DAC to produce an analog ramp output with a level that varies corresponding to the contents of the counter. A ripple counter or equivalent is associated with each respective column. A clock supplies clock signals to the counter elements. A comparator in each column gates the counter element when the analog ramp equals the pixel value for that column. The contents of the counters are transferred sequentially to a video output bus to produce the digital video signal. Additional black-level readout counter elements can create and store a digital value that corresponds to a dark or black video level. A subtraction element subtracts the black level value from the pixel value to reduce fixed pattern noise. An additional array of buffer counter/latches can be employed. The ripple counters can be configured as counters to capture the digital video level, and then as shift registers to clock out the video levels to an output bus. The clock pulses for the DAC counter and for the ripple counters can be at the same or different rates.

According to a first aspect of the present invention, there is provided an imaging element, in accordance with claim <NUM>.

According to a second aspect of the present invention, there is provided an imaging device, in accordance with claim <NUM>.

<FIG> is a diagram which shows a configuration example of a camera <NUM> that is an example of an imaging device according to a first embodiment. The camera <NUM> includes an image capturing optical system (an image forming optical system) <NUM>, an imaging element <NUM>, a control unit <NUM>, a memory <NUM>, a display unit <NUM>, and an operation unit <NUM>. The image capturing optical system <NUM> has a plurality of lenses including a focus adjusting lens (a focus lens) and an aperture diaphragm, and forms an image of a subject on the imaging element <NUM>. The image capturing optical system <NUM> may also be detached from the camera <NUM>.

The imaging element <NUM> is an imaging element such as a CMOS image sensor or a CCD imaging sensor. The imaging element <NUM> receives a luminous flux that has passed through the image capturing optical system <NUM> and captures a subject image formed by the image capturing optical system <NUM>. In the imaging element <NUM>, a plurality of pixels having a photoelectric conversion unit are arranged in a two-dimensional shape (a row direction and a column direction). The photoelectric conversion element is configured by a photodiode (PD). The imaging element <NUM> generates a signal by performing photoelectric conversion on the received light, and outputs the generated signal to the control unit <NUM>.

The memory <NUM> is a recording medium such as a memory card. Image data, a control program, and the like are recorded in the memory <NUM>. Writing data to the memory <NUM> and reading data from the memory <NUM> are controlled by the control unit <NUM>. The display unit <NUM> displays an image based on the image data, information regarding photographing such as a shutter speed and a diaphragm value, a menu screen, and the like. The operation unit <NUM> includes various setting switches such as a release button, a power switch, and a switch for switching between various modes, and outputs a signal based on each operation to the control unit <NUM>.

The control unit <NUM> is configured by a CPU, a processor such as an FPGA and an ASIC, and a memory such as a ROM or a RAM, and controls each part of the camera <NUM> based on the control program. The control unit <NUM> supplies a signal that controls the imaging element <NUM> to the imaging element <NUM> to control an operation of the imaging element <NUM>. In addition, the control unit <NUM> performs various types of image processing on a signal output from the imaging element <NUM> to generate image data. The control unit <NUM> is also an image generation unit that generates image data, and generates still image data and moving image data on the basis of the signal output from the imaging element <NUM>. The image processing includes image processing such as gradation conversion processing and color interpolation processing.

The control unit <NUM> performs processing of individually reading signals of all the pixels of the imaging element <NUM> and processing of mixing (adding) and reading signals of a plurality of pixels. The control unit <NUM> controls the imaging element <NUM> to select (set) a method of reading the pixel signals. For example, the control unit <NUM> performs processing of mixing and reading the signals of a plurality of pixels when a through image (a live-view image) of a subject is displayed on the display unit <NUM> and moving image photography is performed. Moreover, the control unit <NUM> performs processing of individually reading the signals of all the pixels when still image photography with high resolution is performed.

<FIG> is a block diagram which shows a configuration example of the imaging element according to the first embodiment. The imaging element <NUM> is configured by laminating a first substrate <NUM> on which a plurality of pixels <NUM> are formed and a second substrate <NUM> on which a plurality of analog/digital conversion units (AD conversion units) <NUM> are formed. The first substrate <NUM> and the second substrate <NUM> are respectively configured by using a semiconductor substrate. Circuits provided on the first substrate <NUM> and circuits provided on the second substrate <NUM> are electrically connected by bumps, electrodes, and the like.

The first substrate <NUM> has a plurality of pixels <NUM> arranged in a two-dimensional manner. The pixel <NUM> outputs a photoelectric conversion signal and a dark signal, which will be described below, to the second substrate <NUM>. In <FIG>, <NUM> pixels <NUM> of <NUM> pixels in a row direction and <NUM> pixels in a column direction are shown with a pixel <NUM> at an upper left corner set as a pixel <NUM>(<NUM>,<NUM>) in a first row and a first column, and a pixel <NUM> at a lower right corner set as a pixel <NUM>(<NUM>,<NUM>) in a fourth row and a fourth column. The number and arrangement of pixels arranged in the imaging element are not limited to those in the shown example.

The second substrate <NUM> has a plurality of AD conversion units <NUM>. In the present embodiment, the AD conversion unit <NUM> is provided for each pixel <NUM>. In <FIG>, <NUM> AD conversion units <NUM> from an AD conversion unit <NUM>(<NUM>,<NUM>) to an AD conversion unit <NUM>(<NUM>,<NUM>) are shown. As will be described below, the AD conversion unit <NUM> is configured to include a comparison unit and a storage unit, and converts an input photoelectric conversion signal and a dark signal into digital signals having the predetermined number of bits, respectively.

<FIG> is a circuit diagram which shows a configuration example of a part of the imaging element according to the first embodiment. The imaging element <NUM> includes a plurality of pixels <NUM>, a plurality of AD conversion units <NUM>, a reading control unit <NUM>, a signal processing unit <NUM>, and an input/output unit <NUM>.

A pixel <NUM> has a photoelectric conversion unit <NUM>, a transfer unit <NUM>, a reset unit <NUM>, a floating diffusion (FD) <NUM>, an amplification unit <NUM>, and a current source <NUM>. The photoelectric conversion unit <NUM> is a photodiode PD, which converts incident light into electric charges and accumulates the photoelectrically converted electric charges. The transfer unit <NUM> is configured from a transistor M1 controlled by a signal TX, and transfers the electric charges photoelectrically converted by the photoelectric conversion unit <NUM> to the FD <NUM>. The transistor M1 is a transfer transistor. The FD <NUM> accumulates (holds) the electric charges transferred to the FD <NUM>. The current source <NUM> generates a current for reading a signal from the pixel <NUM>, and supplies the generated current to the signal line <NUM> and the amplification unit <NUM>.

The amplification unit <NUM> is configured from a transistor M3 whose gate (terminal) is connected to the FD <NUM>, amplifies signals of electric charges accumulated in the FD <NUM>, and outputs the signals to the signal line <NUM>. The transistor M3 is an amplification transistor. The reset unit <NUM> is configured from a transistor M2 controlled by a signal RST, discharges the electric charges accumulated in the FD <NUM>, and resets a voltage of the FD <NUM>. The transistor M2 is a reset transistor.

The pixel <NUM> sequentially outputs a signal (a dark signal) when the voltage of the FD <NUM> is reset and a signal (a photoelectric conversion signal) corresponding to an electric charge transferred from the photoelectric conversion unit <NUM> to the FD <NUM> by the transfer unit <NUM> to the signal line <NUM>. The dark signal is an analog signal indicating a reference level for the photoelectric conversion signal. In addition, the photoelectric conversion signal is an analog signal generated on the basis of an electric charge photoelectrically converted by the photoelectric conversion unit <NUM>. The dark signal and the photoelectric conversion signal sequentially output from the pixel <NUM> are input to the AD conversion unit <NUM> via the signal line <NUM>, a bump, and the like.

The AD conversion unit <NUM> has a comparison unit <NUM>, a switch SW1, a storage unit <NUM>, and a selection unit <NUM>. The comparison unit <NUM> is configured to include a comparator circuit. A ramp signal ramp, which is a reference signal that changes with an elapse of time, is input to a first terminal <NUM> of the comparison unit <NUM> from a signal generation circuit (not shown). A signal (a photoelectric conversion signal or a dark signal) output from the pixel <NUM> to the signal line <NUM> is amplified and input to a second terminal <NUM> of the comparison unit <NUM> directly or by an amplifier circuit (not shown). The comparison unit <NUM> compares a signal input from the pixel <NUM> with the reference signal, and outputs an output signal that is a result of the comparison from the output terminal <NUM>.

The comparison unit <NUM> is connected to the storage unit <NUM> via the switch SW1. The switch SW1 is configured by a transistor, and electrically connects or disconnects the comparison unit <NUM> and the storage unit <NUM>. When the switch SW1 is in an ON state, the switch SW1 outputs an output signal of the comparison unit <NUM> to the storage unit <NUM>.

The storage unit <NUM> is configured by a plurality of latch circuits corresponding to the number of bits of a digital signal to be stored. The output signal indicating the result of the comparison by the comparison unit <NUM> is input to one input terminal (a G terminal) of each latch circuit via the switch SW1. A clock signal indicating a count value is input from a counter circuit (not shown) to the other input terminal (a D terminal) of each latch circuit. In the example shown in <FIG>, cnt<<NUM>> to cnt<n> indicating count values are input to the other input terminal (the D terminal) of each latch circuit, and the AD conversion unit <NUM> serves as an n-bit AD conversion circuit.

The storage unit <NUM> stores a count value according to an elapsed time from a start of comparison by the comparison unit <NUM> to an inversion of a result of the comparison as a digital signal on the basis of an output signal of the comparison unit <NUM> and a clock signal from a counter circuit. In other words, the storage unit <NUM> stores a count value according to a time until a magnitude relationship between a level of a signal output from the pixel <NUM> and a level of the reference signal changes (inverts) as a digital signal on the basis of a signal output from the comparison unit <NUM>.

When a dark signal of a pixel <NUM> is input to the comparison unit <NUM>, the comparison unit <NUM> compares the dark signal with the reference signal and outputs a result of the comparison to the storage unit <NUM>. On the basis of the result of the comparison by the comparison unit <NUM> and a clock signal, the storage unit <NUM> stores the count value according to the elapsed time from the start of the comparison by the comparison unit <NUM> to the inversion of the result of the comparison as a digital signal based on the dark signal. When a photoelectric conversion signal of the pixel <NUM> is input to the comparison unit <NUM>, the comparison unit <NUM> compares the photoelectric conversion signal with the reference signal, and outputs a result of the comparison to the storage unit <NUM>. On the basis of the result of the comparison by the comparison unit <NUM> and the clock signal, the storage unit <NUM> stores the count value according to the elapsed time from the start of the comparison by the comparison unit <NUM> to the inversion of the result of the comparison as the digital signal based on the photoelectric conversion signal. In this manner, the AD conversion unit <NUM> converts the photoelectric conversion signal, which is an analog signal, into a digital signal having the predetermined number of bits, and converts the dark signal, which is an analog signal, into a digital signal having the predetermined number of bits.

The selection unit <NUM> is configured by a multiplexer controlled by a signal SEL, and a pixel signal (an n-bit digital signal in <FIG>) converted into a digital signal is input from the storage unit <NUM>. The selection unit <NUM> outputs the pixel signal input from the storage unit <NUM> to the signal line <NUM> (hereinafter, referred to as a data line). The data line <NUM> is configured by a plurality of signal lines corresponding to the number of bits of the digital signal output from the AD conversion unit <NUM>. In the imaging element <NUM>, data lines <NUM> (n signal lines in <FIG>) are provided for each column of the plurality of AD conversion units <NUM> arranged in a longitudinal direction, that is, in a column direction (a vertical direction).

The signal processing unit <NUM> is configured to include an amplifier circuit, a decoder circuit, and the like. A pixel signal converted into a digital signal (a digital signal based on a dark signal or a digital signal based on a photoelectric conversion signal) is input to the signal processing unit <NUM> via the data line <NUM>. The processing unit <NUM> performs signal processing such as correlation double sampling and code conversion processing on a signal input from the AD conversion unit <NUM> via the data line <NUM>, and outputs the signal to the input/output unit <NUM>. The input/output unit <NUM> has an input/output circuit corresponding to a high-speed interface such as those of SLVS and LVDS. The input/output unit <NUM> outputs (transmits) the signal input from the signal processing unit <NUM> to the control unit <NUM> of the camera <NUM> at a high speed.

The reading control unit <NUM> is commonly provided in the plurality of pixels <NUM> and the plurality of AD conversion units <NUM>. The reading control unit <NUM> is configured by a plurality of circuits including a timing generator, which are arranged dividedly on the first substrate <NUM> and the second substrate <NUM>. The reading control unit <NUM> may be arranged on either one of the first substrate <NUM> and the second substrate <NUM>, or may be arranged on a substrate different from the first substrate <NUM> and the second substrate <NUM>.

The reading control unit <NUM> supplies signals such as the signal TX and the signal RST that are controlled by the control unit <NUM> of the camera <NUM> and described above to each pixel <NUM> to control the operation of each pixel <NUM>. The reading control unit <NUM> supplies a signal to a gate of each transistor of the pixel <NUM>, and turns the transistor on (a connected state, a conducting state, or a short-circuited state) or turns it off (a disconnected state, a non-conducting state, an open state, or a cutoff state).

The reading control unit <NUM> supplies the signal SEL described above to the selection unit <NUM> of each AD conversion unit <NUM> and controls the selection unit <NUM> of each AD conversion unit <NUM>. When the selection unit <NUM> is enabled (an on state) by the reading control unit <NUM>, the pixel signal converted into a digital signal, which is input from the storage unit <NUM>, is output to the signal processing unit <NUM> via the data line <NUM>. The reading control unit <NUM> sequentially turns on the selection unit <NUM> of each AD conversion unit <NUM>, and outputs a pixel signal stored in the storage unit <NUM> connected to the selection unit <NUM> that is turned on to the data line <NUM>. It can be said that the reading control unit <NUM> sequentially selects a plurality of AD conversion units <NUM> and reads a pixel signal converted into a digital signal from the selected AD conversion unit <NUM>. An n-bit pixel signal converted into a digital signal is input to the signal processing unit <NUM> for each data line <NUM>.

<FIG> is a diagram which describes reading processing of the imaging element according to the first embodiment. The imaging element <NUM> is provided with a switch SW2 (a switch SW2a to a switch SW2h in <FIG>) that connects or disconnects the comparison unit <NUM> of the AD conversion unit <NUM> and the storage unit <NUM> of an AD conversion unit <NUM> different from the AD conversion unit <NUM>. In the present embodiment, the switch SW2 connects an output terminal <NUM> of the comparison unit <NUM> of one AD conversion unit <NUM> and an input terminal (a G terminal) of the storage unit <NUM> of the other AD conversion unit <NUM> among two AD conversion units <NUM> adjacent to each other in the row direction.

In the example shown in <FIG>, the switch SW2 is provided between the comparison unit <NUM> of each of AD conversion units <NUM> in an odd-numbered column and the storage unit <NUM> of each of AD conversion units <NUM> in an even-numbered column. The switch SW2 is configured by a transistor. For example, a switch SW2a is a connection unit 2a, and connects the comparison unit <NUM> of an AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of an AD conversion unit <NUM>(<NUM>,<NUM>) among AD conversion units <NUM> in a first row. A switch SW2e is a connection unit 2e, and connects the comparison unit <NUM> of an AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of an AD conversion unit <NUM>(<NUM>,<NUM>) among AD conversion units <NUM> in a third row. The reading control unit <NUM> (refer to <FIG>) supplies signals to each of the switches SW2a to SW2h to control on and off of each switch.

The reading control unit <NUM> performs processing of individually reading a signal of each pixel of the imaging element <NUM> (individual reading processing) and processing of adding and reading signals of a plurality of pixels (addition reading processing). In the individual reading processing, the reading control unit <NUM> sequentially selects an AD conversion unit <NUM> of the imaging element <NUM> from a first row to a fourth row in units of rows, and reads a pixel signal from the selected AD conversion unit <NUM> in <FIG>.

In the addition reading processing, the reading control unit <NUM> controls a plurality of switches SW as shown in <FIG> and connects the FD <NUM> of each of the plurality of pixels <NUM> to each other to add the signals of the plurality of pixels. The reading control unit <NUM> may control a plurality of switch SWs as shown in <FIG>, and connect the amplification unit <NUM> of a plurality of pixels <NUM> to the same signal line <NUM> to add the signals of the plurality of pixels. The reading control unit <NUM> performs processing of selecting some AD conversion units <NUM> to which a signal generated by adding the signals of a plurality of pixels is input (hereinafter, referred to as first AD conversion units) for each row or plural rows among the plurality of AD conversion units <NUM> of the imaging element <NUM> and reading the signals of pixels.

In the present embodiment, the addition reading processing has a first reading method, a second reading method, and a third reading method. The first reading method is a method in which the first AD conversion unit <NUM> is sequentially selected for each row, and a pixel signal converted into a digital signal is read. The first AD conversion unit <NUM> is an AD conversion unit <NUM> that is selected by thinning out AD conversion units <NUM> of a specific row or column among all the AD conversion units <NUM>. In the first AD conversion unit <NUM>, an added pixel signal is input, and the added pixel signal is converted into a digital signal.

The second reading method is a method in which the first AD conversion unit <NUM> is sequentially selected for each of a plurality of rows, and a pixel signal that is converted into a digital signal is read.

The third reading method is a method in which AD conversion of a pixel signal (for example, a photoelectric conversion signal) and reading of a pixel signal converted to a digital signal (for example, a digital signal based on a dark signal) are performed at the same time (in parallel). The control unit <NUM> of the camera <NUM> controls the reading control unit <NUM> to switch a reading method of a pixel signal.

In the individual reading processing, the reading control unit <NUM> turns on the switch SW1 of the plurality of AD conversion units <NUM> of the imaging element <NUM>, and causes each AD conversion unit <NUM> to perform AD conversion. The reading control unit <NUM> sequentially selects the plurality of these AD conversion units <NUM> in units of rows, and causes a pixel signal converted into a digital signal to be output from the selected AD conversion units <NUM> to the data line <NUM>.

In the first reading method, the reading control unit <NUM> turns on the switches SW1 of the plurality of first AD conversion units <NUM>, and causes each of the plurality of first AD conversion units <NUM> to perform AD conversion. The reading control unit <NUM> sequentially selects the plurality of these first AD conversion units <NUM> in units of rows, and causes a pixel signal converted into a digital signal to be output from the selected first AD conversion units <NUM> to the data line <NUM>. As described above, in the case of the first reading method, the reading control unit <NUM> uses only the first AD conversion unit <NUM> among all the AD conversion units <NUM>. Other AD conversion units <NUM> (hereinafter, referred to as second AD conversion units) different from the first AD conversion units <NUM> and the data line <NUM> to which these second AD conversion units <NUM> are connected are not used in the case of the first reading method, and are brought into a pause state.

In the second reading method, the reading control unit <NUM> controls the switch SW1 and the switch SW2 to use the storage unit <NUM> and the selection unit <NUM> of the second AD conversion unit <NUM>, and the data line <NUM> connected to the second AD conversion unit <NUM> in addition to the first AD conversion unit <NUM>. In the second reading method, by using the data lines <NUM> provided for different columns, it is possible to simultaneously read a pixel signal converted into a digital signal from the AD conversion unit <NUM> of a plurality of rows. The imaging element <NUM> can read a pixel signal in a shorter time than in a case where the first AD conversion unit <NUM> is selected in units of rows and a pixel signal is sequentially read by the data line <NUM>.

Also in the case of the third reading method, the reading control unit <NUM> uses the storage unit <NUM> and selection unit <NUM> of the second AD conversion unit <NUM> and the data line <NUM> connected to the second AD conversion unit <NUM> in addition to the first AD conversion unit <NUM>. The reading control unit <NUM> controls the switch SW1 and the switch SW2 and control whether an output signal of the comparison unit <NUM> of the first AD conversion unit <NUM> is output to the storage unit <NUM> of the first AD conversion unit <NUM> or the storage unit <NUM> of the second AD conversion unit <NUM>. It can be said that the reading control unit <NUM> switches the storage unit <NUM> which is an output destination of a result of the comparison by the comparison unit <NUM> of the first AD conversion unit <NUM>.

In the third reading method, the reading control unit <NUM> switches a connection destination of the comparison unit <NUM> of the first AD conversion unit <NUM> to the storage unit <NUM> of the first AD conversion unit <NUM> or the storage unit <NUM> of the second AD conversion unit <NUM> when a dark signal is input to the comparison unit <NUM> of the first AD conversion unit <NUM> and when a photoelectric conversion signal is input to the comparison unit <NUM> of the first AD conversion unit <NUM>. For example, when a dark signal is input to the comparison unit <NUM> of the first AD conversion unit <NUM>, the reading control unit <NUM> connects the comparison unit <NUM> of the first AD conversion unit <NUM> and the storage unit <NUM> of the first AD conversion unit <NUM>. The comparison unit <NUM> of the first AD conversion unit <NUM> outputs an output signal indicating a result of comparing the dark signal and the reference signal to the storage unit <NUM> of the first AD conversion unit <NUM> via the switch SW1. The storage unit <NUM> of the first AD conversion unit <NUM> stores a digital signal based on the dark signal on the basis of the output signal of the comparison unit <NUM>.

After the AD conversion of the dark signal is completed, the reading control unit <NUM> starts reading the digital signal based on the dark signal from the storage unit <NUM> of the first AD conversion unit <NUM> to the data line <NUM>. Moreover, the reading control unit <NUM> connects the comparison unit <NUM> of the first AD conversion unit <NUM> and the storage unit <NUM> of the second AD conversion unit <NUM>. At this time, when a photoelectric conversion signal is input to the comparison unit <NUM> of the first AD conversion unit <NUM>, the comparison unit <NUM> of the first AD conversion unit <NUM> outputs an output signal indicating a result of comparing the photoelectric conversion signal and the reference signal to the storage unit <NUM> of the second AD conversion unit <NUM> via the switch SW2. The storage unit <NUM> of the second AD conversion unit <NUM> stores a digital signal based on the photoelectric conversion signal on the basis of the output signal of the comparison unit <NUM> of the first AD conversion unit <NUM>.

In this manner, in the third reading method, AD conversion is performed using different storage units <NUM> depending on whether AD conversion of a dark signal is performed or AD conversion of a photoelectric conversion signal is performed. As a result, reading of a digital signal based on a dark signal and AD conversion of a photoelectric conversion signal can be performed in parallel. Similarly, reading of a digital signal based on a photoelectric conversion signal and AD conversion of a dark signal can be performed in parallel. For this reason, the imaging element <NUM> does not need to wait for a completion of the processing of reading a pixel signal to the data line <NUM> to start next AD conversion processing, and can read a pixel signal in a short time. In the following description, the individual reading processing and the first to third reading methods of the addition reading processing will be further described with reference to <FIG>.

When the individual reading processing is instructed by the control unit <NUM>, the reading control unit <NUM> turns on each switch SW1 of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) as shown in <FIG>, and turns off the switches SW2a to SW2h.

The reading control unit <NUM> turns on each of the reset units <NUM> of the pixel <NUM>(<NUM>,<NUM>) to the pixel <NUM>(<NUM>,<NUM>). As a result, a voltage of each FD <NUM> is reset at each pixel <NUM>. Each dark signal of the pixel <NUM>(<NUM>,<NUM>) to the pixel <NUM>(<NUM>,<NUM>) is output to each of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) via a signal line <NUM> connected to each pixel <NUM>. The AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) convert the input dark signal into a digital signal. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) store a digital signal based on a dark signal of the pixel <NUM>(<NUM>,<NUM>) to pixel <NUM>(<NUM>,<NUM>), respectively.

The reading control unit <NUM> turns on each of the selection units <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) to an AD conversion unit <NUM>(<NUM>,<NUM>), which are AD conversion units <NUM> in a first row, and turns off each of selection units <NUM> of AD conversion units <NUM> in the rows other than the first row. As a result, digital signals based on dark signals of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) are output to each of the data lines 50a to 50d via each of the selection unit <NUM> of the AD conversion units <NUM>.

After reading the digital signal based on a dark signal from each of the AD conversion units <NUM> in the first row, the reading control unit <NUM> turns on each of the selection units <NUM> of an AD conversion unit <NUM>(<NUM>,<NUM>) to an AD conversion unit <NUM>(<NUM>,<NUM>), which are AD conversion units <NUM> in a second row, and turns off each of the selection units <NUM> of AD conversion units <NUM> in the rows other than the second row. As a result, digital signals based on dark signals of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) are output to each of the data lines 50a to 50d via each of the selection units <NUM> of the AD conversion units <NUM>. In addition, similarly, the reading control unit <NUM> sequentially selects AD conversion units <NUM> of a third row and subsequent rows for each row in an order of the third row, a fourth row, and a fifth row, and reads a digital signal based on a dark signal from each of the selected AD conversion units <NUM>.

The reading control unit <NUM> turns on each of the transfer units <NUM> of the pixel <NUM>(<NUM>,<NUM>) to the pixel <NUM>(<NUM>,<NUM>). As a result, at each pixel <NUM>, electric charges photoelectrically converted by each PD <NUM> are transferred to the FD <NUM>. Photoelectric conversion signals of each of the pixel <NUM>(<NUM>,<NUM>) to the pixel <NUM>(<NUM>,<NUM>) are output to the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) via the signal line <NUM> connected to each pixel <NUM>, respectively. The AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) convert the input photoelectric conversion signals into digital signals. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) to the AD conversion unit <NUM>(<NUM>,<NUM>) store digital signals based on photoelectric conversion signals of the pixel <NUM>(<NUM>,<NUM>) to the pixel <NUM>(<NUM>,<NUM>), respectively.

The reading control unit <NUM> selects AD conversion units for each row in the order of the first row, the second row, the third row, the fourth row, and the fifth row, and read a digital signal based on a photoelectric conversion signal from each selected AD conversion unit <NUM> in the same manner as when it reads a digital signal based on a dark signal from each AD conversion unit <NUM>.

In this manner, in the individual reading processing, the reading control unit <NUM> individually reads the signals of pixels of the imaging element <NUM>. The digital signal based on a dark signal and the digital signal based on a photoelectric conversion signal that are sequentially output to the data lines 50a to 50d are subjected to signal processing such as correlation double sampling performed by the signal processing unit <NUM> (refer to <FIG>), and then are output to the control unit <NUM> via the input/output unit <NUM>.

In the first to third reading methods of the addition reading processing, the reading control unit <NUM> adds the signals of a plurality of pixels for each of the plurality of pixels. In the following description, an example will be described in which, for every four pixels of <NUM> pixels×<NUM> pixels, the signals of these four pixels are added. A signal obtained by adding a signal of the pixel <NUM>(<NUM>,<NUM>), a signal of the pixel <NUM>(<NUM>,<NUM>), a signal of the pixel <NUM>(<NUM>,<NUM>), a signal of the pixel <NUM>(<NUM>,<NUM>) is input to the AD conversion unit <NUM>(<NUM>,<NUM>). A signal obtained by adding signals of each of a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), and a pixel <NUM>(<NUM>,<NUM>) is input to the AD conversion unit <NUM>(<NUM>,<NUM>). In addition, a signal obtained by adding signals of each of a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), and a pixel <NUM>(<NUM>,<NUM>) is input to the AD conversion unit <NUM>(<NUM>,<NUM>), and a signal obtained by adding signals of each of a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), a pixel <NUM>(<NUM>,<NUM>), and a pixel <NUM>(<NUM>,<NUM>) is input to the AD conversion unit <NUM>(<NUM>,<NUM>).

The AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) function as the first AD conversion unit described above. In <FIG>, these AD conversion units <NUM> surrounded by thick lines are examples of AD conversion units used in the case of the first reading method. The AD conversion units <NUM> surrounded by thick lines in <FIG> are examples of AD conversion units used in the case of the second reading method, and the AD conversion units <NUM> surrounded by thick lines in <FIG> and <FIG> are examples of AD conversion units used in the case of the third reading method.

When the first reading method is instructed by the control unit <NUM>, the reading control unit <NUM> turns on the switch SW1 of each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>), as shown in <FIG>, and turns off the switches SW2a to SW2h. When an added dark signal is input, the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) convert the dark signal into a digital signal. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) store a digital signal based on the added dark signal, respectively.

The reading control unit <NUM> turns on the selection units <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) in the first row, respectively, and turns off the selection units <NUM> of other AD conversion units <NUM> different from the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>). As a result, a digital signal based on an added dark signal of the AD conversion unit <NUM>(<NUM>,<NUM>) is output to the data line 50a via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Moreover, a digital signal based on an added dark signal of the AD conversion unit <NUM>(<NUM>,<NUM>) is output to the data line 50c via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

After the digital signals based on the dark signals from the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) in the first row are read, the reading control unit <NUM> turns on the selection units <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) in the third row, respectively. Moreover, the reading control unit <NUM> turns off the selection units <NUM> of other AD conversion units <NUM> different from the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>), respectively. As a result, a digital signal based on an added dark signal of the AD conversion unit <NUM>(<NUM>,<NUM>) is output to the data line 50a via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Furthermore, a digital signal based on an added dark signal of the AD conversion unit <NUM>(<NUM>,<NUM>) is output to the data line 50c via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). After that, in the same manner, the reading control unit <NUM> sequentially selects AD conversion units <NUM> for each row, and reads a digital signal based on a dark signal from each of the selected AD conversion units <NUM>.

When an added photoelectric conversion signal is input, the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) convert the photoelectric conversion signal to a digital signal. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) store a digital signal based on an added photoelectric conversion signal, respectively. The reading control unit <NUM> sequentially selects AD conversion units <NUM> for each row and reads a digital signal based on a photoelectric conversion signal from each of the selected AD conversion units <NUM> in the same manner as when a digital signal based on a dark signal is read from each AD conversion unit <NUM>.

In this manner, in the first reading method, the reading control unit <NUM> sequentially selects some AD conversion units <NUM> among all the AD conversion units <NUM> of the imaging element <NUM> for each row, and reads a pixel signal converted into a digital signal. The digital signal based on a dark signal and the digital signal based on a photoelectric conversion signal sequentially output to the data lines 50a and 50c are output to the control unit <NUM> by the input/output unit <NUM> after being subjected to signal processing by the signal processing unit <NUM>.

When the second reading method is instructed by the control unit <NUM>, the reading control unit <NUM> turns on each switch SW1 of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) as shown in <FIG>. In addition, the reading control unit <NUM> turns on the switch SW2e and the switch SW2f. When the switch SW2e is turned on, the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) are electrically connected. Furthermore, when the switch SW2f is turned on, the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) are electrically connected. The AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) function as the second AD conversion unit described above.

When an added dark signal is input, the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) convert the dark signal into a digital signal. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) store a digital signal based on an added dark signal, respectively.

When an added dark signal is input, the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) outputs an output signal indicating a result of comparing the added dark signal and the reference signal to the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) via the switch SW2e. The storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) stores a digital signal based on the added dark signal on the basis of the output signal of the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). In this manner, the added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

When an added dark signal is input, the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) outputs an output signal indicating a result of comparing the dark signal and the reference signal to the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) via the switch SW2f. The storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) stores a digital signal based on the added dark signal on the basis of the output signal of the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). In this manner, the added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

The reading control unit <NUM> turns on the selection units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) in the first row, and the selection units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) in the third row, respectively. Moreover, the reading control unit <NUM> turns off the selection units <NUM> of other AD conversion units <NUM> different from the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>).

The added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 90a, and then is output to the data line 50a via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Moreover, the added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is, as schematically shown by an arrow 90b, converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), and then is output to the data line 50b via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

The added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 90c, and then is output to the data line 50c via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Moreover, the added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 90d, and then is output to the data line 50d via the selection unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). After that, in the same manner, the reading control unit <NUM> sequentially selects AD conversion units <NUM> for each two rows, and reads a digital signal based on a dark signal from each of the selected AD conversion units <NUM>.

When an added photoelectric conversion signal is input, the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) convert the photoelectric conversion signal into a digital signal. The storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>) and the AD conversion unit <NUM>(<NUM>,<NUM>) store a digital signal based on an added photoelectric conversion signal, respectively. The added photoelectric conversion signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). In addition, the added photoelectric conversion signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

The reading control unit <NUM> sequentially selects AD conversion units <NUM> for each two rows, and reads a digital signal based on a photoelectric conversion signal from each of the selected AD conversion units <NUM> in the same manner as when the digital signal based on a dark signal from each AD conversion unit <NUM> is read.

In this manner, in the second reading method, the reading control unit <NUM> controls the switch SW1 and the switch SW2 such that an AD conversion unit <NUM> that is in the pause state in the case of the first reading method and the data lines 50b and 50d connected to the AD conversion unit <NUM> are also used. For this reason, the reading control unit <NUM> can sequentially select AD conversion units <NUM> for each two rows and read a pixel signal converted into a digital signal. As a result, a pixel signal can be read in a shorter time than when AD conversion units <NUM> are sequentially selected for each row to read a pixel signal. The digital signal based on a dark signal and the digital signal based on a photoelectric conversion signal sequentially output to the data lines 50a to 50d are output to the control unit <NUM> by the input/output unit <NUM> after being subjected to signal processing by the signal processing unit <NUM>.

<FIG> and <FIG> are diagrams which describe the reading processing of an imaging element when the third reading method is instructed by the control unit <NUM>. <FIG> shows a connection state of the switch SW1 and the switch SW2 when an added dark signal is input to the comparison unit <NUM> of the AD conversion unit <NUM>. <FIG> shows the connection state of the switch SW1 and the switch SW2 when an added photoelectric conversion signal is input to the comparison unit <NUM> of the AD conversion unit <NUM>. In the examples shown in <FIG> and <FIG>, the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) function as the second AD conversion unit described above.

When an added dark signal is input to the comparison unit <NUM> of the AD conversion unit <NUM>, the reading control unit <NUM> turns on each switch SW1 of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) as shown in <FIG>. Moreover, the reading control unit <NUM> turns off the switches SW2a to SW2h.

The reading control unit <NUM> causes each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) to perform AD conversion on an added dark signal. For example, an added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 91a, and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Moreover, an added dark signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 91c, and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

At the same time as the AD conversion of a dark signal, the reading control unit <NUM> reads a digital signal based on a photoelectric conversion signal stored at the time of AD conversion of a previous photoelectric conversion signal from the storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>). For example, as schematically shown by an arrow 92b, a digital signal based on an added photoelectric conversion signal is output to the data line 50b from the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Furthermore, as schematically shown by an arrow 92d, a digital signal based on an added photoelectric conversion signal is output to the data line 50d from the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). After that, in the same manner, the reading control unit <NUM> sequentially selects AD conversion units <NUM> for each row, and reads a digital signal based on a photoelectric conversion signal from each of the selected AD conversion units <NUM>.

When an added photoelectric conversion signal is input to the comparison unit <NUM> of the AD conversion unit <NUM>, the reading control unit <NUM> turns off each switch SW1 of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>) as shown in <FIG>. Furthermore, the reading control unit <NUM> turns on the switch SW2a, the switch SW2b, the switch SW2e, and the switch SW2f.

The reading control unit <NUM> causes each of the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>), and the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) to perform AD conversion on an added photoelectric conversion signal. For example, an added photoelectric conversion signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 91b, and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Moreover, an added photoelectric conversion signal input to the comparison unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) is converted into a digital signal by the comparison unit <NUM> and the AD conversion unit <NUM>(<NUM>,<NUM>) and the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>) as schematically shown by an arrow 91d, and stored in the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>).

At the same time as AD conversion of a photoelectric conversion signal, the reading control unit <NUM> reads a digital signal based on a dark signal stored at the time of the AD conversion of a previous dark signal from the storage units <NUM> of each of the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), the AD conversion unit <NUM>(<NUM>,<NUM>), and the AD conversion unit <NUM>(<NUM>,<NUM>). For example, as schematically shown by an arrow 92a, a digital signal based on an added dark signal is output to the data line 50a from the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). Furthermore, as schematically shown by an arrow 92c, a digital signal based on an added dark signal is output to the data line 50c from the storage unit <NUM> of the AD conversion unit <NUM>(<NUM>,<NUM>). After that, in the same manner, the reading control unit <NUM> sequentially selects AD conversion units <NUM> for each row, and reads a digital signal based on a photoelectric conversion signal from each of the selected AD conversion units <NUM>.

In this manner, in the third reading method, the reading control unit <NUM> controls the switch SW1 and the switch SW2 to perform AD conversion using different storage units <NUM> depending on whether AD conversion of a dark signal is performed or AD conversion of a photoelectric conversion signal is performed. As a result, the imaging element <NUM> can perform AD conversion of a pixel signal and reading of a pixel signal converted into a digital signal to the data line <NUM> in parallel. For this reason, a pixel signal can be read in a short time.

<FIG> is a diagram which compares the first to third reading methods of the addition reading processing of the imaging element according to the first embodiment. <FIG> shows the processing in the case of the first reading method, <FIG> shows the processing in the case of the second reading method, and <FIG> shows the processing in the case of the third reading method. Moreover, in <FIG>, reading processing of a dark signal from the pixel <NUM>, AD conversion processing of a dark signal, reading processing of a digital signal based on a dark signal, reading processing of a photoelectric conversion signal from the pixel <NUM>, AD conversion processing of a photoelectric conversion signal, and reading processing of a digital signal based on a photoelectric conversion signal are shown side by side on the same time axis.

In the case of the second reading method of <FIG>, as described above, the reading control unit <NUM> sequentially selects AD conversion units <NUM> for each two rows and reads a digital signal based on a dark signal and a digital signal based on a photoelectric conversion signal. For this reason, the reading control unit <NUM> can read the digital signal based on a dark signal from each AD conversion unit <NUM> in about <NUM>/<NUM> time and can also read the digital signal based on a photoelectric conversion signal from each AD conversion unit <NUM> in about <NUM>/<NUM> time as compared with the case of the first reading method of <FIG>. As a result, the imaging element <NUM> can improve a frame rate at the time of photography.

In the case of the third reading method of <FIG>, as described above, the reading control unit <NUM> performs the AD conversion of a dark signal (or a photoelectric conversion signal) read from a pixel and reading of a photoelectric conversion signal converted into a digital signal (or a dark signal) in parallel. Therefore, the imaging element <NUM> can further improve the frame rate at the time of photography as compared with the case of the second reading method of <FIG>.

It is considered to provide a storage unit for AD conversion and a storage unit for reading a signal to the data line <NUM> separately for each pixel <NUM>, but, in this case, an area of the imaging element will increase. In the present embodiment, it is not necessary to separately provide the storage unit for AD conversion and the storage unit for reading a signal to the data line <NUM>, and thus it is possible to prevent the area of the imaging element from increasing.

According to the embodiment described above, the following effects can be obtained.

The following modifications are also within the scope of the present invention, and one or more of modified examples can be combined with the embodiment described above.

In the embodiment described above, an example in which the reading control unit <NUM> performs addition reading processing by adding signals of a plurality of pixels has been described. The reading control unit <NUM> may perform processing of thinning out pixels of a specific row or column among all the pixels to read a signal (thinning-out reading processing). In the case of thinning-out reading processing, the reading control unit <NUM> may perform the same reading method as the first to third reading methods described above.

In the embodiment described above, an example in which the imaging element <NUM> is configured by laminating the first substrate <NUM> and the second substrate <NUM> has been described. However, the first substrate <NUM> and the second substrate <NUM> may not be laminated.

In the embodiment described above, an example in which the data line <NUM> is configured by a plurality of signal lines corresponding to the number of bits of a digital signal output from the AD conversion unit <NUM> has been described. The data line <NUM> may be one signal line or an arbitrary number of signal lines.

In the embodiment and modified examples described above, an example in which a photodiode is used as a photoelectric conversion unit has been described. However, a photoelectric conversion film (an organic photoelectric film) may be used as the photoelectric conversion unit.

The imaging element and the imaging device described in the embodiments and modified examples described above may be applied for cameras, smartphones, tablets, cameras embedded in PCs, in-vehicle cameras, cameras mounted on unmanned aerial vehicles (drones, radio-controlled vehicles, and the like), and the like.

Claim 1:
An imaging element (<NUM>) comprising:
a first photoelectric conversion unit (<NUM>) and a second photoelectric conversion unit (<NUM>) configured to generate electric charges by photoelectric conversion;
a first comparison unit (<NUM>) configured to output a first signal based on a result of comparing a signal based on electric charges generated by the first photoelectric conversion unit (<NUM>) and a reference signal;
a first storage unit (<NUM>) configured to store a signal based on the first signal that is output by the first comparison unit (<NUM>);
a second comparison unit (<NUM>) configured to output a second signal based on a result of comparing a signal based on electric charges generated by the second photoelectric conversion unit (<NUM>) and the reference signal;
a second storage unit (<NUM>) configured to store a signal based on the second signal that is output from the second comparison unit (<NUM>);
a first connection unit (SW2) configured to connect or disconnect the first comparison unit (<NUM>) and the second storage unit (<NUM>);
a second connection unit (SW1) that connects or disconnects the first comparison unit (<NUM>) and the first storage unit (<NUM>);
a third connection unit (SW1) that connects or disconnects the second comparison unit (<NUM>) and the second storage unit (<NUM>);
a control unit (<NUM>) configured to control the first connection unit (SW2) , the second connection unit, and the third connection unit in order to control whether the first signal is output to the first storage unit (<NUM>) or the second storage unit (<NUM>);
an accumulation unit configured to accumulate electric charges generated by the first photoelectric conversion unit (<NUM>); and
a reset unit (<NUM>) configured to reset electric charges accumulated in the accumulation unit,
wherein the first comparison unit (<NUM>) is configured to output a fourth signal based on a result of comparing a signal after electric charges accumulated in the accumulation unit are reset and the reference signal,
the control unit (<NUM>) is configured to control whether to output the fourth signal to the first storage unit (<NUM>) or the second storage unit (<NUM>), such that the fourth signal is output to a storage unit different from the storage unit to which the first signal is output.