Image sensor

Abstract

The present invention provides an image sensor that shortens the readout time of pixel signals, enables high-speed readout processing of pixel signals, and improves the frame rate during imaging. [Solution] The image sensor comprises: a first pixel having a first photoelectric conversion unit that converts light into electric charge; a second pixel having a second photoelectric conversion unit that converts light into electric charge and is arranged in the row direction alongside the first photoelectric conversion unit; a first comparison unit having a first signal line electrically connected to the first pixel, a second signal line electrically connected to the second pixel, a first input terminal electrically connected to the first signal line, and a first output terminal; a first storage unit electrically connected to the first output terminal; a second comparison unit having a second input terminal electrically connected to the second signal line, and a second output terminal; and a second storage unit electrically connected to the first output terminal and the second output terminal.

Description

Technical Field

[0004] , , [Figure 1] ,

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

Background Art

[0002] Conventionally, an imaging device 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 has been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] According to a first aspect of the invention, an imaging device includes: a first pixel having a first photoelectric conversion unit that converts light into charge; a second pixel having a photoelectric conversion unit that converts light into charge and is arranged side by side with the first photoelectric conversion unit in a row direction; a first signal line electrically connected to the first pixel; a second signal line electrically connected to the second pixel; a first comparison unit having a first input terminal electrically connected to the first signal line and a first output terminal; a first storage unit electrically connected to the first output terminal; a second comparison unit having a second input terminal electrically connected to the second signal line and a second output terminal; and a second storage unit electrically connected to the first output terminal and the second output terminal.

Brief Description of the Drawings

[0005] [Figure 1] It is a diagram showing a configuration example of an imaging device according to a first embodiment. [Figure 2] It is a block diagram showing a configuration example of an imaging device according to a first embodiment. [Figure 3] It is a circuit diagram showing a configuration example of a part of an imaging device according to a first embodiment. [Figure 4] This figure illustrates the readout process of the image sensor according to the first embodiment. [Figure 5] This figure illustrates an example of a method for adding pixel signals in an image sensor according to the first embodiment. [Figure 6] This figure illustrates another readout process for the image sensor according to the first embodiment. [Figure 7] This figure illustrates another readout process for the image sensor according to the first embodiment. [Figure 8] This figure illustrates another readout process for the image sensor according to the first embodiment. [Figure 9] This figure illustrates another readout process for the image sensor according to the first embodiment. [Figure 10] This figure compares the readout process of the image sensor according to the first embodiment. [Modes for carrying out the invention]

[0006] (First Embodiment) Figure 1 shows an example configuration of a camera 1, which is an example of an imaging device according to the first embodiment. The camera 1 comprises an imaging 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 imaging optical system 2 has a plurality of lenses, including a focus adjustment lens (focus lens), and an aperture diaphragm, and forms an image of the subject on the image sensor 3. The imaging optical system 2 may be detachable from the camera 1.

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

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

[0009] The control unit 4 is composed of a processor such as a CPU, FPGA, or ASIC, and memory such as ROM or RAM, and controls each part of the camera 1 based on a control program. The control unit 4 supplies signals to the image sensor 3 to control its operation. The control unit 4 also performs various image processing on the signals output from the image sensor 3 to generate image data. The control unit 4 is also an image generation unit that generates image data, generating still image data and moving image data based on the signals output from the image sensor 3. Image processing includes image processing such as grayscale conversion and color interpolation.

[0010] The control unit 4 performs two processes: reading the signals of all pixels of the image sensor 3 individually, and reading the signals of multiple pixels mixed (added). The control unit 4 controls the image sensor 3 to select (set) the method of reading the pixel signals. For example, when displaying a live view image of a subject on the display unit 6, or when shooting video, the control unit 4 performs the process of mixing and reading the signals of multiple pixels. Also, when shooting high-resolution still images, the control unit 4 performs the process of reading the signals of all pixels individually.

[0011] Figure 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 constructed by stacking a first substrate 111 on which a plurality of pixels 10 are formed and a second substrate 112 on which a plurality of analog / digital conversion units (AD conversion units) 40 are formed. The first substrate 111 and the second substrate 112 are each made of semiconductor substrates. The circuits provided on the first substrate 111 and the circuits 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 in two dimensions. The pixels 10 output photoelectric conversion signals and dark signals, which will be described later, to the second substrate 112. In Figure 2, the pixel 10 in the upper left corner is designated as pixel 10(1,1) in the first row and first column, and the pixel 10 in the lower right corner is designated as pixel 10(4,4) in the fourth row and fourth column, illustrating 16 pixels 10 arranged in a 4x4 grid. Note that the number and arrangement of pixels on the image sensor are not limited to the example shown.

[0013] The second substrate 112 has a plurality of AD conversion units 40. In this embodiment, an AD conversion unit 40 is provided for each pixel 10. Figure 2 shows 16 AD conversion units 40, from AD conversion unit 40(1,1) to AD conversion unit 40(4,4). As will be described later, the AD conversion unit 40 is composed of a comparison unit and a storage unit, and converts the input photoelectric conversion signal and dark signal into digital signals of a predetermined number of bits, respectively.

[0014] Figure 3 is a circuit diagram showing a partial configuration example of an image sensor according to the first embodiment. The image sensor 3 has a plurality of pixels 10, a plurality of AD conversion units 40, a readout control unit 60, a signal processing unit 70, and an input / output unit 80.

[0015] Pixel 10 includes a photoelectric conversion unit 11, a transfer unit 12, a reset unit 13, a floating diffusion (FD) 14, an amplification unit 15, and a current source 16. The photoelectric conversion unit 11 is a photodiode PD that converts incident light into charge and accumulates the photoelectrically converted charge. The transfer unit 12 is composed of a transistor M1 controlled by a signal TX and transfers the charge 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 charge transferred to it. The current source 16 generates a current for reading a signal from the pixel 10 and supplies the generated current to the signal line 18 and the amplification unit 15.

[0016] The amplification unit 15 is composed of a transistor M3 whose gate (terminal) is connected to the FD 14, amplifies the signal due to the charge accumulated in the FD 14, and outputs it to the signal line 18. The transistor M3 is an amplification transistor. The reset unit 13 is composed of a transistor M2 controlled by a signal RST, discharges the charge accumulated in the FD 14, and resets the voltage of the FD 14. The transistor M2 is a reset transistor.

[0017] 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 with respect to the photoelectric conversion signal. Also, 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 the photoelectric conversion signal sequentially output from the pixel 10 are input to the AD conversion unit 40 via the signal line 18 and bumps or the like.

[0018] The AD conversion unit 40 includes a comparison unit 20, a switch SW1, a storage unit 25, and a selection unit 30. The comparison unit 20 is configured to include a comparator circuit. A ramp signal, which is a reference signal that changes over time, is input to the first terminal 21 of the comparison unit 20 from a signal generation circuit (not shown). The signal (photoelectric conversion signal, dark signal) output from the pixel 10 to the signal line 18 is input to the second terminal 22 of the comparison unit 20, either directly or amplified by an amplification circuit (not shown). The comparison unit 20 compares the signal input from the pixel 10 with the reference signal and outputs the output signal, which is the comparison result, from the output terminal 23.

[0019] The comparison unit 20 is connected to the storage unit 25 via switch SW1. Switch SW1 is made up of a transistor and electrically connects or disconnects the comparison unit 20 and the storage unit 25. When switch SW1 is ON, it outputs the output signal of the comparison unit 20 to the storage unit 25.

[0020] The memory unit 25 is composed of multiple latch circuits corresponding to the number of bits of the digital signal to be stored. An output signal indicating the comparison result from the comparison unit 20 is input to one input terminal (G terminal) of each latch circuit via switch SW1. A clock signal indicating the count value is input to the other input terminal (D terminal) of each latch circuit from a counter circuit (not shown). In the example shown in Figure 3, the other input terminal (D terminal) of each latch circuit is input to the cnt signal indicating the count value. <0> ~cnt <n>is input, and the AD conversion unit 40 becomes an n-bit AD conversion circuit.

[0021] Based on the output signal of the comparison unit 20 and the clock signal from the counter circuit, the storage unit 25 stores, as a digital signal, a count value corresponding to the elapsed time from the start of comparison by the comparison unit 20 until the comparison result is inverted. In other words, based on the signal output from the comparison unit 20, the storage unit 25 stores, as a digital signal, a count value corresponding 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 (inverts).

[0022] When the dark signal of the pixel 10 is input to the comparison unit 20, the comparison unit 20 compares the dark signal with the reference signal and outputs the comparison result to the storage unit 25. Based on the comparison result by the comparison unit 20 and the clock signal, the storage unit 25 stores, as a digital signal based on the dark signal, a count value corresponding to the elapsed time from the start of comparison by the comparison unit 20 until the comparison result is inverted. Also, when the photoelectric conversion signal of the pixel 10 is input to the comparison unit 20, the comparison unit 20 compares the photoelectric conversion signal with the reference signal and outputs the comparison result to the storage unit 25. Based on the comparison result by the comparison unit 20 and the clock signal, the storage unit 25 stores, as a digital signal based on the photoelectric conversion signal, a count value corresponding to the elapsed time from the start of comparison by the comparison unit 20 until the comparison result is inverted. Thus, the AD conversion unit 40 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.

[0023] The selection unit 30 is composed of a multiplexer controlled by the signal SEL, and receives the pixel signal (an n-bit digital signal in Figure 3) converted into a digital signal from the storage unit 25. The selection unit 30 outputs the pixel signal input from the storage unit 25 to the signal line 50 (hereinafter referred to as the data line). The data line 50 is composed of multiple signal lines corresponding to the number of bits of the digital signal output from the AD conversion unit 40. In the image sensor 3, data lines 50 (n signal lines in Figure 3) are provided for each row of multiple AD conversion units 40 arranged vertically, i.e., in the column direction (vertical direction).

[0024] The signal processing unit 70 is composed of an amplifier circuit, a decoder circuit, and the like. The signal processing unit 70 receives the pixel signals converted into digital signals (digital signals based on dark signals, digital signals based on photoelectric conversion signals) via the data line 50. The processing unit 70 performs signal processing on the signals input from the AD conversion unit 40 via the data line 50, such as correlated double sampling and code conversion, and outputs them to the input / output unit 80. The input / output unit 80 has input / output circuits that support high-speed interfaces such as SLVS and LVDS. The input / output unit 80 outputs (transmits) the signals input from the signal processing unit 70 to the control unit 4 of the camera 1 at high speed.

[0025] The read control unit 60 is provided in common to multiple pixels 10 and multiple AD conversion units 40. The read control unit 60 is composed of multiple circuits including a timing generator and is arranged separately on the first board 111 and the second board 112. The read control unit 60 may be placed on either the first board 111 or the second board 112, or it may be placed on different boards from the first board 112 and the second board 112.

[0026] The readout control unit 60 is controlled by the control unit 4 of the camera 1 and supplies signals such as the above-mentioned signal TX and signal RST to each pixel 10 to control the operation of each pixel 10. The readout control unit 60 supplies signals to the gates of each transistor of the pixel 10 to set the transistors to an ON state (connected state, conducting state, short circuit state) or an OFF state (disconnected state, non-conductive state, open state, interrupted state).

[0027] The read control unit 60 supplies the aforementioned signal SEL to the selection unit 30 of each AD conversion unit 40, thereby controlling the selection unit 30 of each AD conversion unit 40. When the selection unit 30 is enabled (turned on) by the read control unit 60, it outputs the pixel signal, which has been converted into a digital signal from the storage unit 25, to the signal processing unit 70 via the data line 50. The read control unit 60 sequentially turns on the selection unit 30 of each AD conversion unit 40, and causes the pixel signal stored in the storage unit 25 connected to the turned-on selection unit 30 to output to the data line 50. It can also be said that the read control unit 60 sequentially selects a plurality of AD conversion units 40 and reads out the pixel signal converted into a digital signal from the selected AD conversion unit 40. The signal processing unit 70 receives the n-bit pixel signal, which has been converted into a digital signal, for each data line 50.

[0028] Figure 4 is a diagram illustrating the readout process of the image sensor according to the first embodiment. The image sensor 3 is provided with switches SW2 (switches SW2a to SW2h in Figure 4) that connect or disconnect the comparison unit 20 of the AD conversion unit 40 and the storage unit 25 of a different AD conversion unit 40. In this embodiment, the switches SW2 connect the output terminal 23 of the comparison unit 20 of one of two AD conversion units 40 adjacent in the row direction to the input terminal (G terminal) of the storage unit 25 of the other AD conversion unit 40.

[0029] In the example shown in Figure 4, a switch SW2 is provided between each comparison unit 20 of the odd-numbered AD conversion unit 40 and each storage unit 25 of the even-numbered AD conversion unit 40. The switch SW2 is made up of transistors. For example, switch SW2a is a connection unit 2a, which connects the comparison unit 20 of AD conversion unit 40(1,1) and the storage unit 25 of AD conversion unit 40(1,2) in the first row of AD conversion unit 40. Switch SW2e is a connection unit 2e, which connects the comparison unit 20 of AD conversion unit 40(3,1) and the storage unit 25 of AD conversion unit 40(3,2) in the third row of AD conversion unit 40. The read control unit 60 (see Figure 3) supplies signals to each switch SW2a to SW2h to control each switch on and off.

[0030] The readout control unit 60 performs two processes: reading out the signal from each pixel of the image sensor 3 individually (individual readout process) and reading out the signals from multiple pixels added together (additional readout process). In the individual readout process, the readout control unit 60 sequentially selects the AD conversion units 40 of the image sensor 3 row by row, from the first row to the fourth row in Figure 4, and reads out the pixel signals from the selected AD conversion units 40.

[0031] In the addition readout process, the readout control unit 60 controls multiple switches SW as shown in Figure 5(a) to connect the FD14 of each of the multiple pixels 10 to each other, thereby adding the signals of the multiple pixels. Alternatively, the readout control unit 60 may also control multiple switches SW as shown in Figure 5(b) to connect the amplification units 15 of the multiple pixels 10 to the same signal line 18, thereby adding the signals of the multiple pixels. The readout control unit 60 selects one or more rows at a time from among the multiple AD conversion units 40 of the image sensor 3 that receive the signal generated by adding the signals of the multiple pixels (hereinafter referred to as the first AD conversion unit) and reads out the pixel signals.

[0032] In this embodiment, the addition readout process includes a first readout method, a second readout method, and a third readout method. The first readout method is a method in which the first AD conversion unit 40 is sequentially selected row by row and the signal of the pixel converted into a digital signal is read out. The first AD conversion unit 40 is an AD conversion unit 40 that is selected by thinning out the AD conversion units 40 of a specific row or column from all the AD conversion units 40. The first AD conversion unit 40 receives the signal of the added pixels as input and converts the signal of the added pixels into a digital signal.

[0033] The second reading method involves sequentially selecting the first AD conversion unit 40 every few rows and reading out the pixel signals that have been converted into digital signals. The third readout method is a method in which the AD conversion of the pixel signal (e.g., photoelectric conversion signal) and the readout of the pixel signal converted to a digital signal (e.g., a digital signal based on the dark signal) are performed simultaneously (in parallel). The control unit 4 of the camera 1 controls the readout control unit 60 to switch the method of reading out the pixel signal.

[0034] (Individual read processing) In the individual readout process, the readout control unit 60 turns on the switches SW1 of the multiple AD conversion units 40 of the image sensor 3, causing each AD conversion unit 40 to perform AD conversion. The readout control unit 60 sequentially selects these multiple AD conversion units 40 one row at a time, and sequentially outputs the pixel signals converted to digital signals from the selected AD conversion units 40 to the data lines 50.

[0035] (First reading method for addition reading process) In the first readout method, the readout control unit 60 turns on the switches SW1 of each of the multiple first AD conversion units 40, causing each of the multiple first AD conversion units 40 to perform AD conversion. The readout control unit 60 sequentially selects these multiple first AD conversion units 40 one row at a time, and outputs the pixel signals converted to digital signals from the selected first AD conversion unit 40 to the data line 50. Thus, in the first readout method, the readout control unit 60 uses only the first AD conversion unit 40 out of all the AD conversion units 40. Other AD conversion units 40 different from the first AD conversion unit 40 (hereinafter referred to as second AD conversion units) and the data line 50 to which these second AD conversion units 40 are connected are not used in the first readout method and remain in a dormant state.

[0036] (Second reading method for the addition reading process) In the second readout method, the readout control unit 60 controls switches SW1 and SW2 to use not only the first AD conversion unit 40, but also the storage unit 25 and selection unit 30 of the second AD conversion unit 40, and the data lines 50 connected to the second AD conversion unit 40. In the second readout method, by using data lines 50 provided for different rows, it becomes possible to simultaneously read out the pixel signals converted to digital signals from multiple rows of AD conversion units 40. The image sensor 3 can read out the pixel signals in a shorter time than when the first AD conversion unit 40 is selected row by row and the pixel signals are sequentially read to the data lines 50.

[0037] (Third reading method for additive reading process) In the third reading method as well, the reading control unit 60 uses the storage unit 25 and selection unit 30 of the second AD conversion unit 40, in addition to the first AD conversion unit 40, and the data line 50 connected to the second AD conversion unit 40. The reading control unit 60 controls switches SW1 and SW2 to control whether the output signal of the comparison unit 20 of the first AD conversion unit 40 is output to the storage unit 25 of the first AD conversion unit 40 or the storage unit 25 of the second AD conversion unit 40. It can also be said that the reading control unit 60 switches the storage unit 25 to which the comparison result from the comparison unit 20 of the first AD conversion unit 40 is output.

[0038] In the third readout method, the readout control unit 60 switches the connection destination of the comparison unit 20 of the first AD conversion unit 40 to either the storage unit 25 of the first AD conversion unit 40 or the storage unit 25 of the second AD conversion unit 40, depending on whether a dark signal is input to the comparison unit 20 of the first AD conversion unit 40 or a photoelectric conversion signal is input to the comparison unit 20 of the first AD conversion unit 40. For example, when a dark signal is input to the comparison unit 20 of the first AD conversion unit 40, the readout control unit 60 connects the comparison unit 20 of the first AD conversion unit 40 to the storage unit 25 of the first AD conversion unit 40. The comparison unit 20 of the first AD conversion unit 40 outputs an output signal indicating the comparison result between the dark signal and the reference signal to the storage unit 25 of the first AD conversion unit 40 via switch SW1. The storage unit 25 of the first AD conversion unit 40 stores the digital signal based on the dark signal based on the output signal of the comparison unit 20.

[0039] After the AD conversion of the dark signal is completed, the readout control unit 60 starts reading the digital signal based on the dark signal from the storage unit 25 of the first AD conversion unit 40 to the data line 50. The readout control unit 60 also connects the comparison unit 20 of the first AD conversion unit 40 to the storage unit 25 of the second AD conversion unit 40. At this time, when the photoelectric conversion signal is input to the comparison unit 20 of the first AD conversion unit 40, the comparison unit 20 of the first AD conversion unit 40 outputs an output signal indicating the comparison result between the photoelectric conversion signal and the reference signal to the storage unit 25 of the second AD conversion unit 40 via switch SW2. The storage unit 25 of the second AD conversion unit 40 stores the digital signal based on the photoelectric conversion signal based on the output signal of the comparison unit 20 of the first AD conversion unit 40.

[0040] Thus, in the third readout method, different memory units 25 are used for AD conversion when performing AD conversion on the dark signal and when performing AD conversion on the photoelectric conversion signal. This allows for parallel readout of the digital signal based on the dark signal and AD conversion of the photoelectric conversion signal. Similarly, it allows for parallel readout of the digital signal based on the photoelectric conversion signal and AD conversion of the dark signal. Therefore, the image sensor 3 does not need to wait for the completion of the readout process of the pixel signal to the data line 50 before starting the next AD conversion process, and the pixel signal can be read out in a short time. The first to third readout methods of individual readout processing and additive readout processing will be further explained below with reference to Figures 4 to 10.

[0041] (Individual read processing) When the control unit 4 instructs the read control unit 60 to perform individual read processing, it turns on switches SW1 of the AD conversion units 40(1,1) to 40(4,4) and turns off switches SW2a to SW2h, as shown in Figure 4.

[0042] The readout control unit 60 turns on the reset units 13 of pixels 10(1,1) to 10(4,4). This resets the voltage of the respective FD14 in each pixel 10. The dark signals of pixels 10(1,1) to 10(4,4) are output to the AD conversion units 40(1,1) to 40(4,4) respectively via the signal lines 18 connected to each pixel 10. The AD conversion units 40(1,1) to 40(4,4) convert the input dark signals into digital signals. The storage units 25 of each AD conversion unit 40(1,1) to 40(4,4) store the digital signals based on the dark signals of pixels 10(1,1) to 10(4,4).

[0043] The read control unit 60 turns on the selection units 30 of the first row's AD conversion unit 40, specifically AD conversion units 40(1,1) to 40(1,4), and turns off the selection units 30 of the other rows' AD conversion units 40. As a result, the digital signals based on the dark signals of each of the AD conversion units 40(1,1) to 40(1,4) are output to the data lines 50a to 50d via the selection units 30 of each AD conversion unit 40.

[0044] After reading out the digital signals based on the dark signals from each AD conversion unit 40 in the first row, the read control unit 60 turns on the selection units 30 of the AD conversion units 40 (2,1) to 40 (2,4) in the second row, and turns off the selection units 30 of the AD conversion units 40 in the other rows. As a result, the digital signals based on the dark signals of each AD conversion unit 40 (2,1) to 40 (2,4) are output to the data lines 50a to 50d via the selection unit 30 of each AD conversion unit 40. Similarly, the read control unit 60 sequentially selects the AD conversion units 40 from the third row onward, one row at a time, in the order of the third row, fourth row, fifth row, and so on, and reads out the digital signals based on the dark signals from each selected AD conversion unit 40.

[0045] The readout control unit 60 turns on the transfer units 12 of pixels 10(1,1) to 10(4,4). As a result, the charge photoelectrically converted by each PD11 in each pixel 10 is transferred to the FD14. The respective photoelectric conversion signals of pixels 10(1,1) to 10(4,4) are output to the AD conversion units 40(1,1) to 40(4,4) via the signal lines 18 connected to each pixel 10. The AD conversion units 40(1,1) to 40(4,4) convert the input photoelectric conversion signals into digital signals. The respective storage units 25 of the AD conversion units 40(1,1) to 40(4,4) store the digital signals based on the photoelectric conversion signals of pixels 10(1,1) to 10(4,4).

[0046] The readout control unit 60 sequentially selects the first row, second row, third row, fourth row, and fifth row in the same manner as when reading out the digital signal based on the dark signal from each AD conversion unit 40, and reads out the digital signal based on the photoelectric conversion signal from each selected AD conversion unit 40.

[0047] In this way, during the individual readout process, the readout control unit 60 reads out the signals of each pixel of the image sensor 3 individually. The digital signals based on the dark signals and the digital signals based on the photoelectric conversion signals, which are sequentially output to the data lines 50a to 50d, are subjected to signal processing such as correlated double sampling by the signal processing unit 70 (see Figure 3) and then output to the control unit 4 via the input / output unit 80.

[0048] (First to third reading methods for the addition reading process) In the first to third readout methods of the add-and-read process, the readout control unit 60 adds the signals of multiple pixels for each set of pixels. Below, we will describe an example in which the signals of four pixels are added for each set of four pixels in a 2x2 pixel arrangement. The signal obtained by adding the signals of pixel 10(1,1), pixel 10(1,2), pixel 10(2,1), and pixel 10(2,2) is input to the AD conversion unit 40(1,1). The signal obtained by adding the signals of pixel 10(1,3), pixel 10(1,4), pixel 10(2,3), and pixel 10(2,4) is input to the AD conversion unit 40(1,3). Furthermore, the signal obtained by adding the signals of pixels 10(3,1), 10(3,2), 10(4,1), and 10(4,2) is input to the AD conversion unit 40(3,1), and the signal obtained by adding the signals of pixels 10(3,3), 10(3,4), 10(4,3), and 10(4,4) is input to the AD conversion unit 40(3,3).

[0049] The AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3) function as the first AD conversion units described above. In Figure 6, these AD conversion units 40 enclosed by thick lines are examples of AD conversion units used in the first reading method. Note that the AD conversion units 40 enclosed by thick lines in Figure 7 are examples of AD conversion units used in the second reading method, and the AD conversion units 40 enclosed by thick lines in Figures 8 and 9 are examples of AD conversion units used in the third reading method.

[0050] (First reading method for addition reading process) When the control unit 4 instructs the first readout method, the readout control unit 60 turns on the respective switches SW1 of the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3), and turns off the switches SW2a to SW2h, as shown in Figure 6. When the added dark signals are input to the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3), they convert the dark signals into digital signals. The storage units 25 of each of the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3) store the digital signals based on the added dark signals.

[0051] The read control unit 60 turns on the selection units 30 of the first row's AD conversion unit 40(1,1) and AD conversion unit 40(1,3), respectively, and turns off the selection units 30 of the other AD conversion units 40 that are different from AD conversion unit 40(1,1) and AD conversion unit 40(1,3). As a result, the digital signal based on the summed dark signals of AD conversion unit 40(1,1) is output to data line 50a via the selection unit 30 of AD conversion unit 40(1,1). In addition, the digital signal based on the summed dark signals of AD conversion unit 40(1,3) is output to data line 50c via the selection unit 30 of AD conversion unit 40(1,3).

[0052] After reading the digital signals based on the dark signals from the first row's AD conversion unit 40(1,1) and AD conversion unit 40(1,3), the read control unit 60 turns on the selection units 30 of the third row's AD conversion unit 40(3,1) and AD conversion unit 40(3,3). The read control unit 60 also turns off the selection units 30 of other AD conversion units 40 that are different from AD conversion unit 40(3,1) and AD conversion unit 40(3,3). As a result, the digital signal based on the added dark signals from AD conversion unit 40(3,1) is output to data line 50a via the selection unit 30 of AD conversion unit 40(3,1). The digital signal based on the added dark signals from AD conversion unit 40(3,3) is output to data line 50c via the selection unit 30 of AD conversion unit 40(3,3). Subsequently, the readout control unit 60 sequentially selects an AD conversion unit 40 every other row and reads out a digital signal based on the dark signal from each selected AD conversion unit 40.

[0053] The AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3) convert the summed photoelectric conversion signals into digital signals when they are input. The storage units 25 of each of the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3) each store the digital signals based on the summed photoelectric conversion signals. The readout control unit 60 sequentially selects the AD conversion units 40 every other row, in the same manner as when reading out the digital signals based on the dark signals from each AD conversion unit 40, and reads out the digital signals based on the photoelectric conversion signals from each selected AD conversion unit 40.

[0054] Thus, in the first readout method, the readout control unit 60 sequentially selects some of the AD conversion units 40 of the image sensor 3 one row at a time and reads out the pixel signals that have been converted to digital signals. The digital signals based on the dark signals and the digital signals based on the photoelectric conversion signals, which are sequentially output to the data lines 50a and 50c, are processed by the signal processing unit 70 and then output to the control unit 4 by the input / output unit 80.

[0055] (Second reading method for the addition reading process) When the control unit 4 instructs the read control unit 60 to use the second read method, it turns on the switches SW1 of the AD conversion unit 40(1,1) and AD conversion unit 40(1,3), as shown in Figure 7. The read control unit 60 also turns on switches SW2e and SW2f. When switch SW2e is turned on, the comparison unit 20 of the AD conversion unit 40(3,1) and the storage unit 25 of the AD conversion unit 40(3,2) are electrically connected. When switch SW2f is turned on, the comparison unit 20 of the AD conversion unit 40(3,3) and the storage unit 25 of the AD conversion unit 40(3,4) are electrically connected. The AD conversion units 40(3,2) and AD conversion units 40(3,4) function as the second AD conversion units described above.

[0056] When an added dark signal is input to the AD conversion unit 40(1,1) and the AD conversion unit 40(1,3), the dark signal is converted into a digital signal. The respective storage units 25 of the AD conversion unit 40(1,1) and the AD conversion unit 40(1,3) each store the digital signal based on the added dark signal.

[0057] When the comparison unit 20 of the AD conversion unit 40(3,1) receives an added dark signal, it outputs an output signal indicating the comparison result between the dark signal and the reference signal to the storage unit 25 of the AD conversion unit 40(3,2) via switch SW2e. The storage unit 25 of the AD conversion unit 40(3,2) stores the digital signal based on the added dark signal, based on the output signal of the comparison unit 20 of the AD conversion unit 40(3,1). In this way, the added dark signal input to the comparison unit 20 of the AD conversion unit 40(3,1) is converted into a digital signal by the comparison unit 20 of the AD conversion unit 40(3,1) and the storage unit 25 of the AD conversion unit 40(3,2).

[0058] When the comparison unit 20 of the AD conversion unit 40(3,3) receives an added dark signal, it outputs an output signal indicating the comparison result between the dark signal and the reference signal to the storage unit 25 of the AD conversion unit 40(3,4) via switch SW2f. The storage unit 25 of the AD conversion unit 40(3,4) stores the digital signal based on the added dark signal based on the output signal of the comparison unit 20 of the AD conversion unit 40(3,3). In this way, the added dark signal input to the comparison unit 20 of the AD conversion unit 40(3,3) is converted into a digital signal by the comparison unit 20 of the AD conversion unit 40(3,3) and the storage unit 25 of the AD conversion unit 40(3,4).

[0059] The read control unit 60 turns on the selection units 30 of the first row's AD conversion units 40(1,1) and 40(1,3), and the selection units 30 of the third row's AD conversion units 40(3,2) and 40(3,4). The read control unit 60 also turns off the selection units 30 of other AD conversion units 40 that are different from AD conversion units 40(1,1), 40(1,3), 40(3,2), and 40(3,4).

[0060] The summed dark signals input to the comparison unit 20 of the AD conversion unit 40(1,1) are converted into digital signals by the AD conversion unit 40(1,1) as schematically shown by arrow 90a, and then output to the data line 50a via the selection unit 30 of the AD conversion unit 40(1,1). Similarly, the summed dark signals input to the comparison unit 20 of the AD conversion unit 40(3,1) are converted into digital signals by the comparison unit 20 of the AD conversion unit 40(3,1) and the storage unit 25 of the AD conversion unit 40(3,2), as schematically shown by arrow 90b, and then output to the data line 50b via the selection unit 30 of the AD conversion unit 40(3,2).

[0061] The summed dark signals input to the comparison unit 20 of the AD conversion unit 40(1,3) are converted into digital signals by the AD conversion unit 40(1,3) as schematically shown by arrow 90c, and then output to the data line 50c via the selection unit 30 of the AD conversion unit 40(1,3). Similarly, the summed dark signals input to the comparison unit 20 of the AD conversion unit 40(3,3) are converted into digital signals by the comparison unit 20 of the AD conversion unit 40(3,3) and the storage unit 25 of the AD conversion unit 40(3,4), as schematically shown by arrow 90d, and then output to the data line 50d via the selection unit 30 of the AD conversion unit 40(3,4). Thereafter, the readout control unit 60 sequentially selects two rows of the AD conversion units 40 at a time and reads out digital signals based on the dark signals from each selected AD conversion unit 40.

[0062] When the AD conversion unit 40(1,1) and the AD conversion unit 40(1,3) receive an added photoelectric conversion signal, they convert the photoelectric conversion signal into a digital signal. The respective storage units 25 of the AD conversion unit 40(1,1) and the AD conversion unit 40(1,3) each store the digital signal based on the added photoelectric conversion signal. The added photoelectric conversion signal input to the comparison unit 20 of the AD conversion unit 40(3,1) is converted into a digital signal by the comparison unit 20 of the AD conversion unit 40(3,1) and the storage unit 25 of the AD conversion unit 40(3,2), and stored in the storage unit 25 of the AD conversion unit 40(3,2). Furthermore, the summed photoelectric conversion signals input to the comparison unit 20 of the AD conversion unit 40(3,3) are converted into digital signals by the comparison unit 20 of the AD conversion unit 40(3,3) and the storage unit 25 of the AD conversion unit 40(3,4), and stored in the storage unit 25 of the AD conversion unit 40(3,4).

[0063] The readout control unit 60 sequentially selects the AD conversion units 40 two rows at a time, in the same manner as when reading out digital signals based on dark signals from each AD conversion unit 40, and reads out digital signals based on photoelectric conversion signals from each selected AD conversion unit 40.

[0064] Thus, in the second readout method, the readout control unit 60 controls switches SW1 and SW2 to utilize the AD conversion unit 40, which is in a dormant state in the first readout method, and the data lines 50b and 50d connected to it. Therefore, the readout control unit 60 can sequentially select two rows at a time from the AD conversion unit 40 and read out the pixel signals that have been converted to digital signals. This allows the pixel signals to be read out in a shorter time than when sequentially selecting one row at a time from the AD conversion unit 40 to read out the pixel signals. The digital signals based on the dark signals and the digital signals based on the photoelectric conversion signals, which are sequentially output to the data lines 50a to 50d, are processed by the signal processing unit 70 and then output to the control unit 4 by the input / output unit 80.

[0065] (Third reading method for additive reading process) Figures 8 and 9 illustrate the image sensor readout process when the control unit 4 instructs a third readout method. Figure 8 shows the connection state of switches SW1 and SW2 when the dark signal added to the comparison unit 20 of the AD conversion unit 40 is input. Figure 9 shows the connection state of switches SW1 and SW2 when the photoelectric conversion signal added to the comparison unit 20 of the AD conversion unit 40 is input. In the example shown in Figures 8 and 9, the AD conversion units 40(1,2), 40(1,4), 40(3,2), and 40(3,4) function as the second AD conversion units described above.

[0066] When the dark signal added to the comparison unit 20 of the AD conversion unit 40 is input, the read control unit 60 turns on the switches SW1 of the AD conversion unit 40(1,1), AD conversion unit 40(1,3), AD conversion unit 40(3,1), and AD conversion unit 40(3,3), as shown in Figure 8. The read control unit 60 also turns off switches SW2a to SW2h.

[0067] The read control unit 60 causes each of the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3) to perform AD conversion of the added dark signals. For example, the added dark signals input to the comparison unit 20 of the AD conversion unit 40(1,1) are converted into digital signals by the AD conversion unit 40(1,1) and stored in the storage unit 25 of the AD conversion unit 40(1,1), as schematically shown by arrow 91a. Similarly, the added dark signals input to the comparison unit 20 of the AD conversion unit 40(1,3) are converted into digital signals by the AD conversion unit 40(1,3) and stored in the storage unit 25 of the AD conversion unit 40(1,3), as schematically shown by arrow 91c.

[0068] Simultaneously with the A / D conversion of the dark signal, the readout control unit 60 reads out digital signals based on the photoelectric conversion signals stored during the previous A / D conversion of the photoelectric conversion signals from the respective storage units 25 of the A / D conversion units 40(1,2), A / D conversion unit 40(1,4), A / D conversion unit 40(3,2), and A / D conversion unit 40(3,4). For example, as schematically shown by arrow 92b, a digital signal based on the added photoelectric conversion signals is output to data line 50b from the storage unit 25 of A / D conversion unit 40(1,2). Also, as schematically shown by arrow 92d, a digital signal based on the added photoelectric conversion signals is output to data line 50d from the storage unit 25 of A / D conversion unit 40(1,4). Thereafter, the readout control unit 60 sequentially selects an A / D conversion unit 40 every other row and reads out digital signals based on the photoelectric conversion signals from each selected A / D conversion unit 40.

[0069] When the photoelectric conversion signal added to the comparison unit 20 of the AD conversion unit 40 is input, the readout control unit 60 turns off the switches SW1 of the AD conversion unit 40(1,1), AD conversion unit 40(1,3), AD conversion unit 40(3,1), and AD conversion unit 40(3,3), as shown in Figure 9. The readout control unit 60 also turns on switches SW2a, SW2b, SW2e, and SW2f.

[0070] The readout control unit 60 causes the comparison unit 20 of the AD conversion unit 40(1,1) and the storage unit 25 of the AD conversion unit 40(1,2), the comparison unit 20 of the AD conversion unit 40(1,3) and the storage unit 25 of the AD conversion unit 40(1,4), the comparison unit 20 of the AD conversion unit 40(3,1) and the storage unit 25 of the AD conversion unit 40(3,2), and the comparison unit 20 of the AD conversion unit 40(3,3) and the storage unit 25 of the AD conversion unit 40(3,4) to perform AD conversion of the added photoelectric conversion signal. For example, the added photoelectric conversion signal input to the comparison unit 20 of the AD conversion unit 40(1,1) is converted into a digital signal by the comparison unit 20 of the AD conversion unit 40(1,1) and the storage unit 25 of the AD conversion unit 40(1,2), as schematically shown by arrow 91b, and stored in the storage unit 25 of the AD conversion unit 40(1,2). Furthermore, the summed photoelectric conversion signals input to the comparison unit 20 of the AD conversion unit 40(1,3) are converted into digital signals by the comparison unit 20 of the AD conversion unit 40(1,3) and the storage unit 25 of the AD conversion unit 40(1,4), as schematically shown by arrow 91d, and stored in the storage unit 25 of the AD conversion unit 40(1,4).

[0071] Simultaneously with the AD conversion of the photoelectric conversion signal, the readout control unit 60 reads out digital signals based on the dark signals stored during the previous AD conversion of the dark signals from the respective storage units 25 of the AD conversion units 40(1,1), 40(1,3), 40(3,1), and 40(3,3). For example, as schematically shown by arrow 92a, a digital signal based on the added dark signals is output to data line 50a from the storage unit 25 of the AD conversion unit 40(1,1). Also, as schematically shown by arrow 92c, a digital signal based on the added dark signals is output to data line 50c from the storage unit 25 of the AD conversion unit 40(1,3). Thereafter, the readout control unit 60 sequentially selects an AD conversion unit 40 every other row and reads out digital signals based on the photoelectric conversion signal from each selected AD conversion unit 40.

[0072] Thus, in the third readout method, the readout control unit 60 controls switches SW1 and SW2 to perform AD conversion using different memory units 25 depending on whether it is performing AD conversion of the dark signal or the photoelectric conversion signal. As a result, the image sensor 3 can perform AD conversion of the pixel signal and read out the pixel signal converted to a digital signal to the data line 50 in parallel. Therefore, the pixel signal can be read out in a short time.

[0073] (Comparison of the first to third reading methods for the addition reading process) Figure 10 is a diagram comparing the first to third readout methods for the summation readout process of the image sensor according to the first embodiment. Figure 10(a) shows the process for the first readout method, Figure 10(b) shows the process for the second readout method, and Figure 10(c) shows the process for the third readout method. In addition, Figures 10(a) to 10(c) show the readout process of the dark signal from pixel 10, the AD conversion process of the dark signal, the readout process of the digital signal based on the dark signal, the readout process of the photoelectric conversion signal from pixel 10, the AD conversion process of the photoelectric conversion signal, and the readout process of the digital signal based on the photoelectric conversion signal side by side on the same time axis.

[0074] In the second readout method shown in Figure 10(b), the readout control unit 60 sequentially selects two rows of the AD conversion unit 40 at a time, as described above, and reads out the digital signal based on the dark signal and the digital signal based on the photoelectric conversion signal. Therefore, compared to the first readout method shown in Figure 10(a), the readout control unit 60 can read out the digital signal based on the dark signal from each AD conversion unit 40 in about half the time, and can also read out the digital signal based on the photoelectric conversion signal from each AD conversion unit 40 in about half the time. As a result, the image sensor 3 can improve the frame rate during shooting.

[0075] In the third readout method shown in Figure 10(c), the readout control unit 60 performs the AD conversion of the dark signal (or photoelectric conversion signal) read out from the pixel and the readout of the photoelectric conversion signal (or dark signal) converted to a digital signal in parallel, as described above. As a result, the image sensor 3 can further improve the frame rate during shooting compared to the second readout method shown in Figure 10(b).

[0076] It is also conceivable to provide a separate memory unit for AD conversion and a separate memory unit for reading signals to the data line 50 for each pixel 10, but in this case, the area of ​​the image sensor would increase. In this embodiment, it is not necessary to provide a separate memory unit for AD conversion and a separate memory unit for reading signals to the data line 50, and an increase in the area of ​​the image sensor can be prevented.

[0077] According to the above-described embodiment, the following effects and advantages can be obtained. (1) The image sensor 3 includes a first photoelectric conversion unit 11 and a second photoelectric conversion unit 11 that generate electric charge by photoelectric conversion; a first comparison unit 20 that outputs a first signal based on the result of comparing a signal based on the charge generated by the first photoelectric conversion unit 11 with a reference signal; a first storage unit 25 that receives the first signal from the first comparison unit 20 and stores a signal based on the first signal; a second comparison unit 20 that outputs a second signal based on the result of comparing a signal based on the charge generated by the second photoelectric conversion unit 11 with a reference signal; a second storage unit 25 that receives the second signal from the second comparison unit 20 and stores a signal based on the second signal; a first connection unit (switch SW2) that can connect or disconnect the first comparison unit 20 and the second storage unit 25; and a control unit (read control unit) that controls the first connection unit to control whether to output the first signal to the first storage unit or the second storage unit. In this manner, the readout control unit 60 according to this embodiment can shorten the pixel signal readout time by controlling the switch SW2 to perform the pixel signal readout process.

[0078] (2) In this embodiment, the image sensor 3 performs the second and third readout methods by controlling switches SW1 and SW2. This enables high-speed readout processing of pixel signals. It also improves the frame rate during imaging.

[0079] The following modifications are also within the scope of the present invention, and it is possible to combine one or more of these modifications with the embodiments described above.

[0080] (Variation 1) In the above-described embodiment, an example was given in which the read control unit 60 performs an additive read operation by adding the signals of multiple pixels. The read control unit 60 may also perform a process of reading out the signal by decimating pixels in a specific row or column from all pixels (decimal read operation). In the case of decimal read operation, the read control unit 60 may also perform a read operation similar to the first to third read operations described above.

[0081] (Modification 2) In the embodiment described above, an example was described in which the image sensor 3 is constructed by stacking a first substrate 111 and a second substrate 112. However, the first substrate 111 and the second substrate 112 do not necessarily have to be stacked.

[0082] (Variation 3) In the embodiment described above, an example was described in which the data line 50 is composed of multiple signal lines corresponding to the number of bits of the digital signal output from the AD conversion unit 40. The data line 50 may be a single signal line or any number of signal lines.

[0083] (Modification 4) In the embodiments and modifications described above, examples were given in which a photodiode was used as the photoelectric conversion unit. However, a photoelectric conversion film (organic photoelectric film) may also be used as the photoelectric conversion unit.

[0084] (Variation 5) The image sensor and imaging device described in the above embodiments and modifications 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.).

[0085] Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0086] The disclosures of the following priority application are incorporated herein by reference. Japanese Patent Application No. 2019-69145 (filed March 29, 2019) [Explanation of Symbols]

[0087] 1...Imaging device, 3...Image sensor, 4...Control unit, 10...Pixel, 11...Photoelectric conversion unit, 20...Comparison unit, 25...Storage unit, 40...AD conversion unit, 60...Readout control unit< / n>

Claims

[Claim 1] A first pixel having a first photoelectric conversion unit that converts light into electric charge, A second pixel having a photoelectric conversion unit that converts light into electric charge and is arranged in the row direction alongside the first photoelectric conversion unit, A first signal line electrically connected to the first pixel, A second signal line electrically connected to the second pixel, A first comparison unit having a first input terminal electrically connected to the first signal line and a first output terminal, A first storage unit electrically connected to the first output terminal, A second comparison unit having a second input terminal electrically connected to the second signal line and a second output terminal, A second storage unit electrically connected to the first output terminal and the second output terminal, An image sensor equipped with the following features.

Images