Image pickup device

Abstract

To reduce power consumption of an imaging element.SOLUTION: The image sensor 3 includes a first photoelectric conversion unit and a second photoelectric conversion unit that are included in the pixels 10 of the pixel blocks 20a and 20b and generate charges by photoelectric conversion, a first signal line 25a to which a first signal based on the charges generated by the first photoelectric conversion unit is output, a second signal line 25b to which a second signal based on the charges generated by the second photoelectric conversion unit is output, an AD conversion unit that is connected to the first signal line and the second signal line and converts the first signal and the second signal from analog signals to digital signals, and supplies currents to the first signal line and the second signal line. And a supply unit 30 that supplies a current smaller than that when the second signal is output to the second signal line or does not supply the current to the second signal line while the AD conversion unit converts the first signal into the digital signal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an imaging device. [Background technology]

[0002] An image sensor is known in which two vertical signal lines and one column processing unit are provided for one column of pixels (Patent Document 1). Conventionally, there has been a demand for reducing power consumption. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-12903 Summary of the Invention

[0004] According to a first aspect of the invention, an imaging element includes a first photoelectric conversion unit and a second photoelectric conversion unit that generate electric charges by photoelectric conversion, a first signal line that outputs a first signal based on the electric charges generated by the first photoelectric conversion unit, a second signal line that outputs a second signal based on the electric charges generated by the second photoelectric conversion unit, an AD conversion unit connected to the first signal line and the second signal line and that converts the first signal and the second signal from analog signals to digital signals, and a supply unit that supplies current to the first signal line and the second signal line, and while the first signal is being converted into a digital signal by the AD conversion unit, supplies a current to the second signal line that is smaller than when the second signal is output, or does not supply current to the second signal line. [Brief explanation of the drawings]

[0005] [Figure 1] 1 is a diagram illustrating an example of the configuration of an imaging device according to a first embodiment. [Figure 2] 1 is a diagram illustrating an example of the configuration of an imaging element according to a first embodiment. [Figure 3] 1 is a diagram illustrating an example of the configuration of a pixel of an imaging element according to a first embodiment. [Figure 4] 1 is a diagram illustrating an example of the configuration of a portion of an imaging element according to a first embodiment. [Figure 5] 3A to 3C are diagrams illustrating an example of the operation of the imaging element according to the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of the configuration of a portion of an imaging element according to a modified example. [Figure 7] FIG. 10 is a diagram showing an example of the arrangement of a part of an imaging element according to a modified example. [Figure 8] 10A and 10B are diagrams illustrating an example of the operation of an imaging element according to a modified example. [Figure 9] FIG. 10 is a diagram showing an example of the arrangement of a part of an imaging element according to a modified example. [Figure 10] FIG. 10 is a diagram showing an example of the arrangement of a part of an imaging element according to a modified example. [Figure 11] FIG. 10 is a diagram illustrating an example of the configuration of a part of a supply unit of an imaging element. DETAILED DESCRIPTION OF THE INVENTION

[0006] (First embodiment) 1 is a diagram showing an example of the configuration of a camera 1, which is an example of an imaging device according to a first embodiment. The camera 1 includes a photographing optical system (imaging optical system) 2, an image sensor 3, a control unit 4, a memory 5, a display unit 6, and an operation unit 7. The photographing optical system 2 has multiple lenses, including a focus adjustment lens (focus lens), and an aperture stop, and forms a subject image on the image sensor 3. The photographing optical system 2 may be detachable from the camera 1.

[0007] The imaging element 3 is an imaging element such as a CMOS image sensor or a CCD image sensor. The imaging element 3 receives a light beam that has passed through the photographing optical system 2 and captures an image of a subject formed by the photographing optical system 2. The imaging element 3 has a plurality of pixels, each having a photoelectric conversion unit, arranged two-dimensionally (in the row and column directions). The photoelectric conversion element is composed of a photodiode (PD). The imaging element 3 photoelectrically converts the received light to generate a signal and outputs the generated signal to the control unit 4.

[0008] The memory 5 is a recording medium such as a memory card. Image data, control programs, etc. are recorded in the memory 5. Writing data to the memory 5 and reading data from the memory 5 are controlled by the control unit 4. The display unit 6 displays an image based on the image data, information related to shooting such as the shutter speed and aperture value, and a menu screen, etc. The operation unit 7 includes various setting switches such as a release button, a power switch, and switches for switching between various modes, and outputs signals to the control unit 4 based on the respective operations.

[0009] The control unit 4 is configured with a processor such as a CPU, FPGA, or ASIC, and memories such as a ROM or RAM, and controls each unit of the camera 1 based on a control program. The control unit 4 supplies a signal that controls the image sensor 3 to the image sensor 3, thereby controlling the operation of the image sensor 3. When taking a still image, taking a video, or displaying a through image (live view image) of the subject on the display unit 6, the control unit 4 causes the image sensor 3 to capture an image of the subject and output a signal.

[0010] The control unit 4 generates image data by performing various types of image processing on the signal output from the imaging element 3. The control unit 4 also functions as a generation unit 4 that generates image data, and generates still image data and moving image data based on the signal output from the imaging element 3. The image processing includes image processing such as tone conversion processing and color interpolation processing.

[0011] 2 is a block diagram showing an example of the configuration of an image sensor according to the first embodiment. The image sensor 3 is configured by stacking a first substrate 111 on which a plurality of pixels 10 are provided and a second substrate 112 on which a plurality of processing units 60, each including an analog-to-digital conversion unit (AD conversion unit) 40, are provided. The first substrate 111 and the second substrate 112 are each configured using a semiconductor substrate. The circuit provided on the first substrate 111 and the circuit provided on the second substrate 112 are electrically connected by bumps, electrodes, etc.

[0012] The first substrate 111 has a plurality of pixels 10 arranged two-dimensionally. The pixels 10 output photoelectric conversion signals and dark signals, which will be described later, to the second substrate 112. In Fig. 2, 72 pixels 10 are shown, 6 pixels in the row direction x 12 pixels in the column direction. Note that the number and arrangement of pixels arranged in the imaging element 3 are not limited to the example shown in the figure.

[0013] The first substrate 111 has multiple regions 20, each of which has multiple pixels 10 arranged therein. In the example shown in FIG. 2, the first substrate 111 has eight regions 20, from region 20(1,1) to region 20(4,2). Each of these eight regions 20 represents one region when the region of the first substrate 111 where the pixels 10 are arranged is divided into regions including nine pixels, i.e., 3 pixels x 3 pixels. Regions 20(1,1) to 20(4,2) each have nine pixels, i.e., 3 pixels x 3 pixels. The regions 20 may or may not overlap partially. The number of pixels in each region 20 may be four, i.e., 2 pixels x 2 pixels, or 16, i.e., 4 pixels x 4 pixels, or any other number. Hereinafter, the regions 20 will be referred to as pixel blocks 20.

[0014] Each pixel block 20 has a signal line 18 (signal lines 18a to 18c in FIG. 2) and a switch SW1 (switches SW1a to SW1c in FIG. 2) for each column of pixels 10 arranged in the vertical direction, i.e., the column direction (vertical direction). Signal line 18a is connected to the first pixel column, signal line 18b is connected to the second pixel column, and signal line 18c is connected to the third pixel column.

[0015] The switch SW1a electrically connects or disconnects the signal line 18a and the signal line 25. When the switch SW1a is in the on state, it outputs the pixel signal output to the signal line 18a to the signal line 25. The switch SW1b electrically connects or disconnects the signal line 18b and the signal line 25. When the switch SW1b is in the on state, it outputs the pixel signal output to the signal line 18b to the signal line 25. The switch SW1c electrically connects or disconnects the signal line 18c and the signal line 25. When the switch SW1c is in the on state, it outputs the pixel signal output to the signal line 18c to the signal line 25. Each of the switches SW1a to SW1c is formed by a transistor.

[0016] 3 is a diagram showing an example of the configuration of a pixel of the image sensor according to the first embodiment. A pixel 10 has a photoelectric conversion unit 11, a transfer unit 12, a reset unit 13, a floating diffusion (FD) 14, an amplifier unit 15, and a selection unit 16. The photoelectric conversion unit 11 is a photodiode PD, which converts incident light into electric charges and accumulates the photoelectrically converted electric charges.

[0017] The transfer unit 12 is composed of a transistor M1 controlled by a signal TX, and transfers the charges photoelectrically converted by the photoelectric conversion unit 11 to the FD 14. The transistor M1 is a transfer transistor. The FD 14 accumulates (holds) the charges transferred to the FD 14.

[0018] The amplifier 15 is composed of a transistor M3 whose gate (terminal) is connected to the FD 14, and amplifies and outputs a signal based on the charge accumulated in the FD 14. The amplifier 15 is connected to a signal line 18 via a selector 16. The transistor M3 is an amplifying transistor. The amplifier 15 and selector 16 constitute an output unit that generates and outputs a signal based on the charge generated by the photoelectric conversion unit 11.

[0019] The reset unit 13 is composed of a transistor M2 controlled by a signal RST, and discharges the charge accumulated in the FD 14 and resets the voltage of the FD 14. The transistor M2 is a reset transistor. The selection unit 16 is composed of a transistor M4 controlled by a signal SEL, and electrically connects or disconnects the amplifier unit 15 and a signal line 18. When the transistor M4 of the selection unit 16 is in the on state, it outputs a signal from the amplifier unit 15 to the signal line 18. The transistor M4 is a selection transistor.

[0020] The pixel 10 sequentially outputs to the signal line 18 a signal (dark signal) when the voltage of the FD 14 is reset and a signal (photoelectric conversion signal) corresponding to the charge transferred from the photoelectric conversion unit 11 to the FD 14 by the transfer unit 12. The dark signal is an analog signal indicating a reference level for the photoelectric conversion signal and is used to correct the photoelectric conversion signal. The photoelectric conversion signal is an analog signal generated based on the charge photoelectrically converted by the photoelectric conversion unit 11. The dark signal and photoelectric conversion signal sequentially output from the pixel 10 are input to the processing unit 60 via the signal line 18, the switch SW1, and the signal line 25.

[0021] In FIG. 2, the second substrate 112 has a processing unit 60 and a readout control unit 70, each provided for a plurality of pixel blocks 20. In this embodiment, a processing unit 60 is provided for every two adjacent pixel blocks 20. FIG. 2 illustrates four processing units 60. A processing unit 60(1,1) is provided for pixel block 20(1,1) and pixel block 20(2,1). A processing unit 60(1,2) is provided for pixel block 20(1,2) and pixel block 20(2,2). A processing unit 60(2,1) is provided for pixel block 20(3,1) and pixel block 20(4,1), and a processing unit 60(2,2) is provided for pixel block 20(3,2) and pixel block 20(4,2).

[0022] Of the two pixel blocks 20 connected to the processing unit 60, the signal line 25 (referred to as signal line 25a) of one pixel block 20 serves as the signal line connecting that pixel block 20 to the processing unit 60, and the signal line 25 (referred to as signal line 25b) of the other pixel block 20 serves as the signal line connecting the other pixel block 20 to the processing unit 60. The signal lines 25a and 25b are signal lines using bumps, electrodes, etc.

[0023] The readout control unit 70 is provided in common to the multiple pixels 10 and the multiple processing units 60. The readout control unit 70 is composed of multiple circuits including a timing generator, and is arranged on the second substrate 112. The readout control unit 70 may be divided and arranged on the first substrate 111 and the second substrate 112, or may be arranged on the first substrate 111. The readout control unit 70 may also be arranged on a substrate different from the first substrate 112 and the second substrate 113.

[0024] The readout control unit 70 is controlled by the control unit 4 of the camera 1, and supplies signals such as the above-mentioned signal TX, signal RST, and signal SEL to each pixel 10 to control the operation of each pixel 10. The readout control unit 70 supplies signals to the gates of each transistor in the pixels 10 to turn the transistor on (connected state, conductive state, short-circuited state) or off (disconnected state, non-conductive state, open state, blocked state).

[0025] The readout control unit 70 controls the on / off of the switches SW1a to SW1c and the selection unit 16 of each pixel 10 to select (set) the pixel 10 to be electrically connected to the signal line 25. This allows the readout control unit 70 to read out a signal (photoelectric conversion signal, dark signal) from any pixel 10 in the pixel block 20 to the signal line 25.

[0026] The processing unit 60 has a switch SW2a, a switch SW2b, and an AD conversion unit 50, and is provided in common for every two pixel blocks 20. The switch SW2a electrically connects or disconnects the signal line 25a and the AD conversion unit 50. The switch SW2b electrically connects or disconnects the signal line 25b and the AD conversion unit 50. The switches SW2a and SW2b are each configured with a transistor, and are on / off controlled by the readout control unit 70. In this embodiment, the switches SW2a of the processing units 60(1,1) to 60(2,2) are controlled by the same signal output from the readout control unit 70. The switches SW2b of the processing units 60(1,1) to 60(2,2) are also controlled by the same signal output from the readout control unit 70. As will be described later with reference to FIG. 4, the image sensor 3 is provided with a supply unit that supplies a current to the signal line 25.

[0027] The AD conversion unit 50 has a comparison unit 40 and a storage unit 45. The comparison unit 40 is configured to include a comparator circuit. A pixel signal (photoelectric conversion signal, dark signal) from the switch SW2a or switch SW2b is input to a first terminal 41 of the comparison unit 40, either directly or after being amplified by an amplifier circuit (not shown). A ramp signal RAMP, which is a reference signal that changes over time, is input to a second terminal 42 of the comparison unit 40 from a signal generation circuit (not shown). The comparison unit 40 compares the pixel signal with the reference signal and outputs an output signal, which is the comparison result, from an output terminal 43.

[0028] The storage unit 45 is composed of a plurality of latch circuits corresponding to the number of bits of the digital signal to be stored. An output signal indicating the comparison result by the comparison unit 40 is input to one input terminal of each latch circuit. A clock signal CLK indicating a count value from a counter circuit (not shown) is input to the other input terminal of each latch circuit.

[0029] Based on the output signal of the comparing unit 40 and the clock signal from the counter circuit, the storage unit 45 stores, as a digital signal, a count value that corresponds to the elapsed time from when the comparing unit 40 starts comparison until the comparison result is inverted. In other words, based on the signal output from the comparing unit 40, the storage unit 45 stores, as a digital signal, a count value that corresponds to the time until the magnitude relationship between the level of the signal output from the pixel 10 and the level of the reference signal changes (is inverted).

[0030] When the dark signal of pixel 10 is input to the comparison unit 40, the comparison unit 40 compares the dark signal with the reference signal and outputs the comparison result to the storage unit 45. The storage unit 45 stores a count value corresponding to the elapsed time from when the comparison unit 40 starts comparison to when the comparison result is inverted as a digital signal based on the dark signal, based on the comparison result of the comparison unit 40 and the clock signal. Furthermore, when the photoelectric conversion signal of pixel 10 is input to the comparison unit 40, the comparison unit 40 compares the photoelectric conversion signal with the reference signal and outputs the comparison result to the storage unit 45. The storage unit 45 stores a count value corresponding to the elapsed time from when the comparison unit 40 starts comparison to when the comparison result is inverted as a digital signal based on the photoelectric conversion signal, based on the comparison result of the comparison unit 40 and the clock signal. In this way, the AD conversion unit 50 converts the photoelectric conversion signal, which is an analog signal, into a digital signal with a predetermined number of bits, and converts the dark signal, which is an analog signal, into a digital signal with a predetermined number of bits.

[0031] The processing unit 60 outputs the pixel signals converted into digital signals by the AD conversion unit 50 to a signal processing unit (not shown). The pixel signals converted into digital signals (digital signals based on dark signals and digital signals based on photoelectric conversion signals) are input to the signal processing unit. The signal processing unit performs signal processing such as correlated double sampling, which corrects the photoelectric conversion signal by subtracting the digital signal based on the photoelectric conversion signal from the digital signal based on the dark signal, and code conversion processing. The processing unit 60 outputs the signal of each pixel 10 after signal processing to the control unit 4 of the camera 1.

[0032] Fig. 4 is a diagram showing an example of the configuration of a portion of the image sensor according to the first embodiment. Fig. 4 shows two pixel blocks 20 (referred to as pixel block 20a and pixel block 20b) out of the multiple pixel blocks 20 provided in the image sensor 3, one processing unit 60, and a readout control unit 70. The processing unit 60 has switches SW3a and SW3b, a supply unit 30, the above-mentioned switches SW2a and SW2b, and an AD conversion unit 50.

[0033] In the image sensor 3, a switch SW3a is provided for the signal line 25a of the pixel block 20a, and a switch SW3b is provided for the signal line 25b of the pixel block 20b. The switch SW3a electrically connects or disconnects the signal line 25a to or from the supply unit 30. The switch SW3b electrically connects or disconnects the signal line 25b to or from the supply unit 30. The switches SW3a and SW3b are each configured by a transistor, and are on / off controlled by the readout control unit 70. In this embodiment, the switches SW3a of the processing units 60(1,1) to 60(2,2) are controlled by the same signal output from the readout control unit 70. The switches SW3b of the processing units 60(1,1) to 60(2,2) are also controlled by the same signal output from the readout control unit 70.

[0034] The supply unit 30 includes a current source 31a and a current source 31b, and supplies current to the signal line 25a and the signal line 25b. The current source 31a is connected to each pixel 10 in the pixel block 20a via a switch SW3a, a signal line 25a, and a switch SW1 (see FIGS. 2 and 3). The current source 31b is connected to each pixel 10 in the pixel block 20b via a switch SW3b, a signal line 25b, and a switch SW1. The current sources 31a and 31b each generate a current for reading a signal from each pixel 10. The current source 31a supplies the generated current to the signal line 25a and the selection unit 16 and the amplifier unit 15 of each pixel 10 in the pixel block 20a. Similarly, the current source 31b supplies the generated current to the signal line 25b and the selection unit 16 and the amplifier unit 15 of each pixel 10 in the pixel block 20b.

[0035] The readout control unit 70 controls the switch SW2a and the switch SW2b to electrically connect the signal line 25a or the signal line 25b to the AD conversion unit 50. When the switch SW2a is on and the switch SW2b is off, the signal from the pixel 10 in the pixel block 20a output to the signal line 25a is input to the AD conversion unit 50. When the switch SW2a is off and the switch SW2b is on, the signal from the pixel 10 in the pixel block 20b output to the signal line 25b is input to the AD conversion unit 50. This makes it possible for a single AD conversion unit 50 to perform AD conversion on the signals of the pixels in the pixel block 20a and the signals of the pixels in the pixel block 20b. The image sensor 3 according to this embodiment does not need to provide an AD conversion unit 50 for each pixel block 20, and two pixel blocks 20 share a single AD conversion unit 50. Therefore, compared to when an AD conversion unit is provided for each pixel block 20, the number of AD conversion units can be halved, and the power consumption of the AD conversion units of the image sensor 3 can be halved. Furthermore, it is possible to prevent an increase in the area of ​​the image sensor and an increase in manufacturing costs.

[0036] The readout control unit 70 controls each pixel 10 and the switches SW2a and SW2b to cause the AD conversion unit 50 to perform AD conversion of the pixel signal output to one of the signal lines 25a and 25b, and to read out the signal from the pixel 10 to the other signal line. When the AD conversion unit 50 performs AD conversion of the pixel signal input from the pixel block 20a via the signal line 25a and the switch SW2a, the readout control unit 70 reads out the pixel signal from the pixel block 20b to the signal line 25b. When the AD conversion unit 50 performs AD conversion of the pixel signal input from the pixel block 20b via the signal line 25b and the switch SW2b, the readout control unit 70 reads out the pixel signal from the pixel block 20a to the signal line 25a. In this way, in the image sensor 3, AD conversion of the pixel signal output from one of the two pixel blocks 20 by the AD conversion unit 50 and readout of the signal from the other pixel block 20 are performed simultaneously (in parallel).

[0037] Generally, when the length of the signal line 25 is short or when the number of pixels 10 connected to the signal line 25 is small, the time required to read out the pixel signals to the signal line 25 is shorter than the time required for AD conversion of the pixel signals. It can also be said that the settling time of the pixel signals is shorter than the AD conversion time for the pixel signals. Therefore, if current is constantly supplied from the supply unit 30 to the signal line 25 connected to the pixels 10 in one pixel block 20 while AD conversion of the pixel signals in the other pixel block 20 is being performed, an extra time will be required for the pixel signals to be held in that signal line 25.

[0038] Therefore, the image sensor 3 according to this embodiment performs processing to prevent current from being supplied to the signal line 25 connected to one pixel block 20 during part of the period in which the AD conversion unit 50 converts the pixel signals of the other pixel block 20 into digital signals. Note that while the AD conversion unit 50 converts the pixel signals of one pixel block 20 into digital signals, the image sensor 3 may supply a current to the signal line 25 connected to the other pixel block 20 that is smaller than the current supplied when reading out the pixel signals from the other pixel block 20. In this case, the magnitude (current value) of the current to the signal line 25 connected to the other pixel block 20 may be zero, and the above-mentioned small current also includes "0".

[0039] The readout control unit 70 stops supplying current to the signal line 25 connected to one pixel block 20 for a predetermined time after starting AD conversion processing of the pixel signals of the other pixel block 20. The image sensor 3 starts supplying current to the signal line 25 connected to the other pixel block 20 after a predetermined time has elapsed since starting AD conversion processing of the pixel signals of one pixel block 20. This makes it possible to reduce the time that pixel signals are unnecessarily held in the signal line 25 connected to the other pixel block 20, thereby reducing the power consumption of the image sensor 3.

[0040] 5A to 5C are diagrams showing an example of the operation of the image sensor according to the first embodiment. Figures 5A to 5C respectively show the driving states of the signal line 25A connected to the pixel block 20A, the signal line 25B connected to the pixel block 20B, and the AD conversion unit 50. Figures 5A to 5C show the case where pixel signals are read out alternately from the pixel block 20A and the pixel block 20B on the same time axis.

[0041] At time t1 shown in FIG. 5, the signal RST supplied to the pixel 10 in the pixel block 20a goes high. When the signal RST goes high, the transistor M2 in the reset unit 13 of the pixel 10 in the pixel block 20a is turned on. This causes the charge in the FD 14 of the pixel 10 in the pixel block 20a to be discharged, and the voltage of the FD 14 becomes the reset voltage. Furthermore, the switch SW3a is turned on, and the switch SW3b is turned off. This causes a current to be supplied to the signal line 25a from the current source 31a of the supply unit 30 via the switch SW3a.

[0042] Also, at time t1, the signal SEL supplied to the pixels 10 in the pixel block 20a goes high. When the signal SEL goes high, a dark signal based on the reset voltage of the pixels 10 in the pixel block 20a is output by the amplifier unit 15 and the selector unit 16 to the signal line 25a via the signal line 18 and the switch SW1. That is, a signal (dark signal) obtained after the charge in the FD 14 of the pixel 10 in the pixel block 20a has been discharged is output to the signal line 25a.

[0043] At time t2, switch SW2a is turned on and switch SW2b is turned off. With switch SW2a turned on, the dark signal from the pixel 10 in pixel block 20a is input to the AD conversion unit 50 via signal line 25a. During the period from time t2 to time t4, switch SW3a remains on, and current is supplied to signal line 25a from current source 31a. As a result, the dark signal from the pixel 10 in pixel block 20a is held in signal line 25a. During the period from time t2 to time t4, the AD conversion unit 50 converts the dark signal input from pixel block 20a via signal line 25a into a digital signal.

[0044] At time t3, the signal RST supplied to the pixels 10 in the pixel block 20b goes high. When the signal RST goes high, the charge in the FD 14 of the pixels 10 in the pixel block 20b is discharged, and the voltage of the FD 14 becomes the reset voltage. Also at time t3, the switch SW3b is turned on. When the switch SW3b goes on, a current is supplied to the signal line 25b from the current source 31b of the supply unit 30 via the switch SW3b.

[0045] At time t3, the signal SEL supplied to the pixel 10 in the pixel block 20b goes high. When the signal SEL goes high, the dark signal of the pixel 10 in the pixel block 20b is output by the amplifier 15 and the selector 16 to the signal line 25b via the signal line 18 and the switch SW1.

[0046] At time t4, the switch SW3a is turned off. With the switch SW3a turned off, the supply of current from the current source 31a of the supply unit 30 is suspended (stopped). From time t4 to time t5, the switch SW3a remains off, and no current is supplied to the signal line 25a from the current source 31a of the supply unit 30, resulting in a suspended state.

[0047] Also, at time t4, switch SW2a is turned off and switch SW2b is turned on. With switch SW2b turned on, the dark signal from pixel 10 in pixel block 20b is input to the AD conversion unit 50 via signal line 25b. From time t4 to time t6, switch SW3b remains on, and current is supplied to signal line 25b from current source 31b. As a result, the dark signal from pixel 10 in pixel block 20b is held in signal line 25b. From time t4 to time t6, the AD conversion unit 50 converts the dark signal input from pixel block 20b via signal line 25b into a digital signal.

[0048] At time t5, the signal TX supplied to the pixel 10 in the pixel block 20a goes high, turning on the transistor M1 in the transfer unit 12 of the pixel 10, and the charge photoelectrically converted in the photoelectric conversion unit 11 is transferred to the FD 14. Also, at time t5, the signal SEL supplied to the pixel 10 in the pixel block 20a is high, so the photoelectric conversion signal based on the charge generated in the photoelectric conversion unit 11 is output by the amplifier 15 and selector 16 to the signal line 25a via the signal line 18 and the switch SW1.

[0049] At time t6, the switch SW3b is turned off, halting the supply of current from the current source 31b of the supply unit 30. During the period from time t6 to time t7, the switch SW3b remains off, and the signal line 25b is in a halt state.

[0050] Also, at time t6, switch SW2a is turned on and switch SW2b is turned off. With switch SW2a turned on, the photoelectric conversion signal of pixel 10 in pixel block 20a is input to the AD conversion unit 50 via signal line 25a. From time t6 to time t8, switch SW3a remains on, and current is supplied to signal line 25a from current source 31a. As a result, the photoelectric conversion signal of pixel 10 in pixel block 20a is held in signal line 25a. From time t6 to time t8, the AD conversion unit 50 converts the photoelectric conversion signal input from pixel block 20a via signal line 25a into a digital signal.

[0051] At time t7, the signal TX supplied to the pixels 10 in the pixel block 20b goes high, causing the charges photoelectrically converted by the photoelectric conversion unit 11 to be transferred to the FD 14. Also at time t7, the signal SEL supplied to the pixels 10 in the pixel block 20b is high, so that a photoelectric conversion signal based on the charges generated by the photoelectric conversion unit 11 is output by the amplifier 15 and the selector 16 to the signal line 25b via the signal line 18 and the switch SW1.

[0052] At time t8, the switch SW3a is turned off, halting the supply of current from the current source 31a of the supply unit 30. During the period from time t8 to time t9, the switch SW3a remains off, and the signal line 25a is in a halt state.

[0053] Also, at time t8, switch SW2a is turned off and switch SW2b is turned on. With switch SW2b turned on, the photoelectric conversion signal of pixel 10 in pixel block 20b is input to the AD conversion unit 50 via signal line 25b. From time t8 to time t10, switch SW3b remains on, and current is supplied to signal line 25b from current source 31b. As a result, the photoelectric conversion signal of pixel 10 in pixel block 20b is held in signal line 25b. From time t8 to time t10, the AD conversion unit 50 converts the photoelectric conversion signal input from pixel block 20b via signal line 25b into a digital signal.

[0054] As described above, in the present embodiment, the readout control unit 70 stops the supply of current to the signal line 25b for a predetermined time (from time t2 to time t3 and from time t6 to time t7 in FIG. 5) after starting AD conversion processing of the pixel signals of the pixel block 20a. The readout control unit 70 also stops the supply of current to the signal line 25a for a predetermined time (from time t4 to time t5 and from time t8 to time t9 in FIG. 5) after starting AD conversion processing of the pixel signals of the pixel block 20b. This reduces the time that the signal line 25b and the signal line 25a hold the pixel signals excessively, thereby reducing the power consumption of the image sensor 3.

[0055] The above-described embodiment provides the following advantageous effects. (1) An image sensor includes a first photoelectric conversion unit and a second photoelectric conversion unit that generate electric charges through photoelectric conversion, a first signal line that outputs a first signal based on the electric charges generated by the first photoelectric conversion unit, a second signal line that outputs a second signal based on the electric charges generated by the second photoelectric conversion unit, an AD conversion unit 50 connected to the first signal line and the second signal line and that converts the first signal and the second signal from analog to digital, and a supply unit 30 that supplies current to the first signal line and the second signal line and, while the first signal is being converted into a digital signal by the AD conversion unit 50, supplies a current to the second signal line that is smaller than the current used when the second signal is output, or does not supply a current to the second signal line. In this embodiment, the image sensor 3 performs processing to not supply current to the signal line 25 connected to one pixel block 20 during a period when the AD conversion unit 50 is converting a pixel signal of the other pixel block 20 into a digital signal. This allows the power consumption of the imaging element 3 to be reduced.

[0056] (2) While the first signal is being converted into a digital signal by the AD conversion unit 50 and before the second signal is output, the supply unit 30 supplies a smaller current to the second signal line than when the second signal is output, or does not supply a current to the second signal line. In this embodiment, the supply unit 30 stops supplying current to the signal line 25 connected to one pixel block 20 for a predetermined time after starting AD conversion processing of the pixel signal of the other pixel block 20. This makes it possible to reduce the time that the signal line 25 connected to the other pixel block 20 holds the pixel signal unnecessarily, thereby reducing the power consumption of the image sensor 3.

[0057] The following modifications are also within the scope of the present invention, and one or more of the modifications may be combined with the above-described embodiment.

[0058] (Variation 1) Fig. 6 is a diagram showing a configuration example of a portion of an imaging element according to Modification 1. Fig. 7 is a diagram showing an arrangement example of a portion of an imaging element according to Modification 1. In this modification, the switches SW2a (SW2a1 to SW2a4), switches SW2b (SW2b1 to SW2b4), switches SW3a (SW3a1 to SW3a4), and switches SW3b (SW3b1 to SW3b4) of each of processing units 60(1,1) to 60(2,2) are on / off controlled by different signals.

[0059] In FIG. 7, SW2a1 to SW2a4, SW2b1 to SW2b4, SW3a1 to SW3a4, and SW3b1 to SW3b4 indicate control signals input from the read control unit 70 to the switches SW2a1 to SW2a4, SW2b1 to SW2b4, SW3a1 to SW3a4, and SW3b1 to SW3b4, respectively. The signal lines to which these control signals are supplied are individually provided as shown in FIG. 7 and connected to each processing unit 60. This allows the read control unit 70 to individually (independently) control each switch of the processing unit 60(1,1) to processing unit 60(2,2). The read control unit 70 can vary the timing at which each switch of the processing unit 60(1,1) to processing unit 60(2,2) is turned on and off.

[0060] Fig. 8 is a diagram showing an example of the operation of the image sensor according to Modification 1. In Fig. 8, the dark signal is represented as a D signal, and the photoelectric conversion signal is represented as an S signal. As shown in Fig. 8, by shifting the time for which the supply unit 30 stops supplying current for each processing unit 60, it is possible to distribute the peaks in power consumption of the image sensor 3 and reduce noise mixed into pixel signals.

[0061] 9 and 10 are diagrams illustrating other exemplary layouts of a portion of an imaging element according to Modification 1. As in the example illustrated in FIG. 9, a readout control unit 70 may be provided for each processing unit 60. For example, the readout control unit 70 provided for the processing unit 60(1,1) controls the switches SW2a, SW2b, SW3a, and SW3b in the processing unit 60(1,1). The readout control unit 70 provided for the processing unit 60(1,2) controls the switches SW2a, SW2b, SW3a, and SW3b in the processing unit 60(1,2). Alternatively, as in the example illustrated in FIG. 10, a readout control unit 70 may be provided for each of a plurality of processing units 60. The readout control unit 70 may control the on / off timing of the switches SW2a, SW2b, SW3a, and SW3b of each processing unit 60 differently for each processing unit 60, or may control the on / off timing differently for each of a plurality of processing units 60.

[0062] (Variation 2) 11 is a diagram showing a configuration example of a part of a supply unit of an image sensor. The current source 31 (each of the current source 31a and the current source 31b) of the supply unit 30 may be configured by a single transistor, as shown in FIGS. 11(a) and 11(b). Note that the current source 31a and the current source 31b may each be configured by cascode-connecting multiple transistors.

[0063] 11(a), the read control unit 70 may, as in the above-described embodiment, turn off the switch SW3 to electrically disconnect the current source 31 from the signal line 25 and stop the supply of current from the current source 31 to the signal line 25. The read control unit 70 may adjust the magnitude of the current supplied from the current source 31 to the signal line 25 by adjusting the voltage supplied to the gate of the transistor of the current source 31. As in the example shown in FIG. 11(b), the read control unit 70 may turn off the switch SW4 connected to the gate of the transistor of the current source 31 to stop the supply of current from the current source 31 to the signal line 25.

[0064] (Variation 3) In the above-described embodiment, an example has been described in which the imaging element 3 is configured by stacking the first substrate 111 and the second substrate 112. However, the first substrate 111 and the second substrate 112 do not have to be stacked.

[0065] (Variation 4) In the above-described embodiment and modified examples, a photodiode is used as the photoelectric conversion unit, but a photoelectric conversion film (organic photoelectric film) may be used as the photoelectric conversion unit.

[0066] (Variation 5) The imaging elements and imaging devices described in the above-mentioned embodiments and variations may be applied to cameras, smartphones, tablets, cameras built into PCs, in-vehicle cameras, cameras mounted on unmanned aerial vehicles (drones, radio-controlled aircraft, etc.), etc.

[0067] Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments that are conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0068] 1...imaging device, 3...imaging element, 4...control unit, 10...pixel, 11...photoelectric conversion unit, 30...supply unit, 50...AD conversion unit, 60...processing unit, 70...readout control unit

Claims

[Claim 1] a first photoelectric conversion unit and a second photoelectric conversion unit that generate electric charges by photoelectric conversion; a first signal line through which a first signal based on the charge generated by the first photoelectric conversion unit is output; a second signal line through which a second signal based on the charge generated by the second photoelectric conversion unit is output; an AD conversion unit connected to the first signal line and the second signal line, and configured to convert the first signal and the second signal from analog signals to digital signals; a supply unit that supplies current to the first signal line and the second signal line, and that, while the first signal is being converted into a digital signal by the AD conversion unit, supplies a current to the second signal line that is smaller than the current when the second signal is output, or does not supply a current to the second signal line.

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