Image sensor

Abstract

An imaging element capable of suppressing degradation in pixel signal quality is provided. [Solution] The imaging element includes a first photoelectric conversion unit that converts light into electric charges, a second photoelectric conversion unit that converts light into electric charges, a first transfer unit that transfers the electric charges converted by the first photoelectric conversion unit to a floating diffusion unit, a second transfer unit that transfers the electric charges converted by the second photoelectric conversion unit to the floating diffusion unit, a first discharge unit that discharges the electric charges converted by the first photoelectric conversion unit to a first supply unit that is supplied with a predetermined voltage when the electric charges are being transferred from the second photoelectric conversion unit to the floating diffusion unit by the second transfer unit, and a second discharge unit that discharges the electric charges converted by the second photoelectric conversion unit to a second supply unit that is supplied with a predetermined voltage when the electric charges are being transferred from the first photoelectric conversion unit to the floating diffusion unit by the first transfer unit.

Description

[Technical Field]

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

[0002] Focus detection techniques using focus detection pixels have been known for some time, and there has been a demand for improved focus detection accuracy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-263568 Summary of the Invention

[0004] According to a first aspect, an imaging element includes a first photoelectric conversion unit that converts light into electric charges, a second photoelectric conversion unit that converts light into electric charges, a first transfer unit that transfers the electric charges converted by the first photoelectric conversion unit to a floating diffusion unit, a second transfer unit that transfers the electric charges converted by the second photoelectric conversion unit to the floating diffusion unit, a first discharge unit that discharges the electric charges converted by the first photoelectric conversion unit to a first supply unit that is supplied with a predetermined voltage when the electric charges are being transferred from the second photoelectric conversion unit to the floating diffusion unit by the second transfer unit, and a second discharge unit that discharges the electric charges converted by the second photoelectric conversion unit to a second supply unit that is supplied with a predetermined voltage when the electric charges are being transferred from the first photoelectric conversion unit to the floating diffusion unit by the first transfer unit. [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] FIG. 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 portion of an imaging element according to a first embodiment. [Figure 4] 3A to 3C are diagrams illustrating an example of the operation of the imaging element according to the first embodiment. [Figure 5] 5A to 5C are diagrams illustrating another example of the operation of the imaging element according to the first embodiment. [Figure 6] 6 is a timing chart showing another example of the operation of the imaging element according to the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of the configuration of a portion of an imaging element according to Modification 1. [Figure 8] FIG. 10 is a diagram illustrating an example of the configuration of a portion of an imaging element according to Modification 2. 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 unit 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 image sensor 3 has imaging pixels and AF pixels (focus detection pixels). The imaging pixels output signals used for image generation. The AF pixels output signals used for focus detection. As will be described later, the AF pixels are arranged to replace some of the imaging pixels, and are distributed over almost the entire imaging surface of the image sensor 3. In the following description, when simply referring to pixels, this refers to either or both of the imaging pixels and the AF pixels.

[0009] 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.

[0010] 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 has an imaging control unit 4a, an image data generation unit 4b, and a focus detection unit 4c.

[0011] The imaging control unit 4a supplies signals for controlling the imaging element 3 to the imaging element 3, thereby controlling the operation of the imaging element 3. When displaying a through image (live view image) of a subject on the display unit 6 or when shooting video, the imaging control unit 4a causes the imaging element 3 to repeatedly capture an image of the subject for each frame at a predetermined cycle and output a signal. The imaging control unit 4a performs readout control using a so-called rolling shutter method, in which the pixels of the imaging element 3 are selected row by row in sequence and signals are read out from the selected pixels.

[0012] The imaging control unit 4a controls the image sensor 3 to separately read out signals from pixel rows in which AF pixels are arranged (hereinafter referred to as AF pixel rows) and from pixel rows in which AF pixels are not arranged (hereinafter referred to as imaging pixel rows).The imaging control unit 4a also sequentially selects pixel rows and reads out signals from each pixel, without separately reading out signals from AF pixel rows and imaging pixel rows.

[0013] For example, when displaying a through image on the display unit 6 or when capturing a moving image, the imaging control unit 4a separately reads out the signals of each pixel in the AF pixel row and the signals of each pixel in the imaging pixel row. When capturing a high-resolution still image, the imaging control unit 4a does not separately read out the signals of each pixel in the AF pixel row and the signals of each pixel in the imaging pixel row, but instead selects pixel rows sequentially and performs a process of reading out the signals.

[0014] The image data generation unit 4b generates image data (still image data, moving image data) by performing various image processing on signals output from the imaging pixels of the image sensor 3. Image processing includes image processing such as tone conversion processing and color interpolation processing. Note that the image data generation unit 4b may also generate image data using signals output from the AF pixels.

[0015] The focus detection unit 4c performs focus detection processing required for automatic focusing (AF) of the photographing optical system 2. The focus detection unit 4c detects the in-focus position of the focus lens (the amount of movement of the focus lens to the in-focus position) for the image by the photographing optical system 2 to be focused (formed) on the imaging surface of the image sensor 3. The focus detection unit 4c calculates the defocus amount by a phase difference detection method using first and second signals output from a pair of AF pixels (AF pixel pair) of the image sensor 3.

[0016] The focus detection unit 4c calculates the amount of image shift by performing a correlation calculation between a first signal generated by capturing an image formed by a first light beam that passed through a first region of the exit pupil of the photographing optical system 2 and a second signal generated by capturing an image formed by a second light beam that passed through a second region. The focus detection unit 4c converts this amount of image shift into a defocus amount using a predetermined conversion formula. Based on the calculated defocus amount, the focus detection unit 4c calculates the amount of movement of the focus lens to the in-focus position. The focus lens is driven according to the amount of movement, thereby automatically adjusting the focus. In this way, the control unit 4 controls the position of the focus lens so that the image of the subject formed by the photographing optical system 2 is focused on the image sensor 3.

[0017] FIG. 2 is a diagram showing an example of the configuration of an image sensor according to the first embodiment. The image sensor 3 has a pixel section (pixel region) 100 in which pixels are arranged two-dimensionally (in the row and column directions), a supply section 30, a readout control section 40, and a plurality of processing sections 50. A plurality of image pixels 10 and AF pixels 13 (13a, 13b) are arranged in the pixel section 100 of the image sensor 3. In FIG. 2, the pixel in the upper left corner is image pixel 10(1,1) in the first row and first column, and the pixel in the lower right corner is image pixel 10(16,8) in the 16th row and eighth column, for a total of 128 pixels in 16 rows and 8 columns. Note that the number and arrangement of pixels arranged in the image sensor 3 are not limited to the example shown in the figure.

[0018] Each imaging pixel 10 is provided with one of three color filters 41 having different spectral characteristics of red (R), green (G), or blue (B). The imaging pixels 10 include pixels (hereinafter referred to as R pixels) having color filters 41 with spectral characteristics that separate incident light in a first wavelength range (red (R) light), pixels (hereinafter referred to as G pixels) having color filters 41 with spectral characteristics that separate incident light in a second wavelength range (green (G) light), and pixels (hereinafter referred to as B pixels) having color filters 41 with spectral characteristics that separate incident light in a third wavelength range (blue (B) light). The R pixels 10, G pixels 10, and B pixels 10 are arranged according to a Bayer array.

[0019] The first AF pixel 13a and the second AF pixel 13b are arranged to replace some of the R, G, and B imaging pixels 10 arranged in a Bayer array as described above. The first and second AF pixels 13a and 13b are provided with color filters 41 having spectral characteristics that separate incident light in a second wavelength range (green (G) light). The color filters provided in the first and second AF pixels 13a and 13b may be color filters having spectral characteristics that separate incident light in a first wavelength range (red (R) light) or a third wavelength range (blue (B) light). The first and second AF pixels 13a and 13b may also have filters having spectral characteristics that separate incident light into first, second, and third wavelength ranges. Alternatively, the color filters 41 may not be provided in the first and second AF pixels 13a and 13b.

[0020] The first AF pixel 13a and the second AF pixel 13b each have a light-shielding portion 43 that blocks a portion of light incident on the photoelectric conversion unit. The first AF pixel 13a and the second AF pixel 13b have light-shielding portions 43 located at different positions. The light-shielding portions 43 of the first AF pixel 13a and the second AF pixel 13b are arranged so that light that has passed through different regions of the exit pupil of the photographing optical system 2 enters the photoelectric conversion unit. As a result, the photoelectric conversion unit of the first AF pixel 13a receives a light beam that has passed through a first region of the first and second regions of the exit pupil of the photographing optical system 2. The photoelectric conversion unit of the second AF pixel 13b receives a light beam that has passed through a second region of the first and second regions of the exit pupil of the photographing optical system 2.

[0021] 2, the image sensor 3 has a pixel group (first imaging pixel row) 401 in which G pixels 10 and B pixels 10 are alternately arranged in the left-right direction, i.e., the row direction, and a pixel group (second imaging pixel row) 402 in which R pixels 10 and G pixels 10 are alternately arranged in the row direction. The image sensor 3 also has a pixel group (first AF pixel row) 403a in which G pixels 10 and first AF pixels 13a are alternately arranged in the row direction, and a pixel group (second AF pixel row) 403b in which G pixels 10 and second AF pixels 13b are alternately arranged in the row direction.

[0022] In the image sensor 3, a vertical signal line 20 is provided for each of a plurality of pixels 10 arranged in the horizontal direction (row direction). It can also be said that a vertical signal line 20 is provided for each pixel column, which is a row of a plurality of pixels lined up in the vertical direction (column direction). A current source (current source 25 in FIG. 3 ) and a processing unit 50, which will be described later, are provided for the vertical signal line 20.

[0023] The supply unit 30 is controlled by the imaging control unit 4a of the camera 1 and supplies a predetermined voltage (electric potential) to each pixel. As will be described later, the supply unit 30 supplies a power supply voltage VDD to the imaging pixels 10 and the AF pixels 13 via the supply units 35 (35a, 35b) and 36.

[0024] The readout control unit 40 is composed of multiple circuits including a timing generator. The readout control unit 40 is controlled by the imaging control unit 4a and supplies signals such as a signal TX, a signal RST, and a signal SEL (described later) to each pixel to control the operation of each pixel. The readout control unit 40 supplies signals to the gates of each transistor in the pixel to turn the transistor on (connected, conductive, short-circuited) or off (disconnected, non-conductive, open, or blocked). The signal from each pixel is output to the vertical signal line 20 connected to that pixel.

[0025] The processing unit 50 is configured to include an analog / digital conversion unit (AD conversion unit). The processing unit 50 converts analog pixel signals input from each pixel via the vertical signal line 20 into digital signals. The processing unit 50 may also include an amplifier unit that amplifies the pixel signals input via the vertical signal line 20 by a predetermined gain (amplification factor). In this case, the processing unit 50 converts the pixel signals amplified by the amplifier unit into digital signals.

[0026] The processing unit 50 outputs the pixel signals converted into digital signals by the AD conversion unit to a signal processing unit (not shown). The signal processing unit performs signal processing such as correlated double sampling and signal amount correction on the input pixel signals, and then outputs the processed signals to the control unit 4.

[0027] 3 is a diagram showing an example of the configuration of a pixel of the image sensor according to the first embodiment. Each pixel (AF pixel 13 and imaging pixel 10 in FIG. 3) includes a photoelectric conversion unit 11, a connection unit 12, and a connection unit 18. Of two pixels adjacent to each other in the column direction, one pixel (AF pixel 13) has a photoelectric conversion unit 11a, a connection unit 12a, and a connection unit 18a, and the other pixel (imaging pixel 10) has a photoelectric conversion unit 11b, a connection unit 12b, and a connection unit 18b. The photoelectric conversion units 11 (11a, 11b) are photodiodes PD that convert incident light into electric charges and store the photoelectrically converted electric charges.

[0028] As indicated by dashed lines 45 in Fig. 3, the image sensor 3 has a configuration in which two adjacent pixels share a floating diffusion (FD) 14, a connection unit 15, an amplifier unit 16, and a selection unit 17. In this embodiment, the circuit configurations of two adjacent imaging pixels 10 are the same as the circuit configurations of the AF pixel 13 and the imaging pixel 10 shown in Fig. 3. In the example shown in Fig. 3, the connection units 12a, 12b, 18a, 18b, and 15 can each be considered to be switching units (switch units) that switch between connection and disconnection.

[0029] The supply unit 35a is a portion (wiring, electrode, etc.) of the image sensor 3 that supplies (applies) the power supply voltage VDD to the connection unit 18a. The supply unit 35b is a portion of the image sensor 3 that supplies the power supply voltage VDD to the connection unit 18b. The supply unit 36 ​​is a portion of the image sensor 3 that supplies the power supply voltage VDD to the connection unit 15 and the amplifier unit 16. The supply units 35a, 35b, and 36 are supplied with the power supply voltage VDD from the supply unit 30. The supply units 35a, 35b, and 36 may be part of the supply unit 30.

[0030] The connection unit 12a is composed of a transistor M1a controlled by a signal TX1a, and electrically connects or disconnects the photoelectric conversion unit 11a and the FD 14. The connection unit 12a is a transfer unit 12a, and transfers the charges photoelectrically converted by the photoelectric conversion unit 11a to the FD 14.

[0031] The connection unit 12b is composed of a transistor M1b controlled by a signal TX2a, and electrically connects or disconnects the photoelectric conversion unit 11b and the FD14. The connection unit 12b is a transfer unit 12b, and transfers the charges photoelectrically converted by the photoelectric conversion unit 11b to the FD14. The transistors M1a and M1b are each a transfer transistor. The FD14 accumulates (holds) the charges transferred to the FD14 and converts them into a voltage divided by a capacitance value. The FD14 is a storage unit 14, and accumulates the charges generated by the photoelectric conversion unit 11b.

[0032] The amplifier unit 16 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 drain (terminal) and source (terminal) of the transistor M3 are connected to a supply unit 36 ​​that supplies a power supply voltage VDD and a selection unit 17, respectively. The source of the amplifier unit 16 is connected to a vertical signal line 20 via the selection unit 17. The amplifier unit 16 functions as part of a source follower circuit, with a current source 25 as a load current source. The transistor M3 is an amplifying transistor. The amplifier unit 16 and the selection unit 17 constitute an output unit that generates and outputs a signal based on the charge generated by the photoelectric conversion unit 11.

[0033] The connection unit 15 is composed of a transistor M2 controlled by a signal RST, and electrically connects or disconnects the supply unit 36 ​​and the FD14. The connection unit 15 connects the supply unit 36 ​​and the FD14, thereby discharging the charge accumulated by the FD14 to the supply unit 36. The connection unit 15 is a discharge unit (reset unit) 15, which discharges the charge accumulated in the FD14 and resets the voltage of the FD14. The transistor M2 is a reset transistor.

[0034] The selection unit 17 is composed of a transistor M4 controlled by a signal SEL, and electrically connects or disconnects the amplification unit 16 and the vertical signal line 20. When the transistor M4 of the selection unit 17 is in an on state, it outputs a signal from the amplification unit 16 to the vertical signal line 20. The transistor M4 is a selection transistor.

[0035] The connection unit 18a is composed of a transistor M5a controlled by a signal TX1b, and electrically connects or disconnects the supply unit 35a and the photoelectric conversion unit 11a. The connection unit 18a connects the supply unit 35a and the photoelectric conversion unit 11a, thereby discharging the charge accumulated in the photoelectric conversion unit 11a to the supply unit 35a. The connection unit 18a is a discharge unit (reset unit) 18a, which discharges the charge accumulated in the photoelectric conversion unit 11a and resets the voltage of the photoelectric conversion unit 11a. The transistor M5a can also be called a reset transistor.

[0036] The connection unit 18b is composed of a transistor M5b controlled by a signal TX2b, and electrically connects or disconnects the supply unit 35b and the photoelectric conversion unit 11b. The connection unit 18b connects the supply unit 35b and the photoelectric conversion unit 11b, thereby discharging the charge accumulated in the photoelectric conversion unit 11b to the supply unit 35b. The connection unit 18b is a discharge unit (reset unit) 18b, and discharges the charge accumulated in the photoelectric conversion unit 11b and resets the voltage of the photoelectric conversion unit 11b. The transistor M5b can also be called a reset transistor.

[0037] The current source 25 is connected to each pixel via the vertical signal line 20. The current source 25 generates a current for reading out a signal from the pixel, and supplies the generated current to the vertical signal line 20 and the amplifier unit 16 and selector unit 17 of each pixel.

[0038] As described above, the charges photoelectrically converted by the photoelectric conversion unit 11 are transferred to the FD 14 by the transfer unit 12. A signal (pixel signal) corresponding to the charges transferred to the FD 14 is output to the vertical signal line 20. The pixel signal is an analog signal generated based on the charges photoelectrically converted by the photoelectric conversion unit 11. The pixel signals output from the imaging pixels 10 are subjected to signal processing by the processing unit 50 and then output to the control unit 4 of the camera 1. The pixel signals output from the first AF pixel 13a and the second AF pixel 13b are subjected to signal processing by the processing unit 50 and then output to the control unit 4 as a pair of signals (first and second signals).

[0039] In this embodiment, the imaging control unit 4a performs rolling shutter readout control. The imaging pixel rows and AF pixel rows of the image sensor 3 are sequentially selected by the readout control unit 40. In the image sensor 3, discharge of charges accumulated in the pixels (reset operation) and operation of reading signals based on the charges accumulated in the pixels from the pixels (readout operation) are performed while scanning row by row, for example, from the top row to the bottom row. The imaging control unit 4a controls the readout control unit 40 to perform a first readout process in which all pixel rows are sequentially selected and signals of each pixel are read out, and a second readout process in which signals of each pixel in the AF pixel rows and signals of each pixel in the imaging pixel rows are read out separately.

[0040] When the imaging control unit 4a instructs the first readout process, the readout control unit 40 sequentially selects multiple pixel rows and causes each pixel to output a signal. In FIG. 2, the readout control unit 40 sequentially selects pixel rows from the first row to the sixteenth row. The readout control unit 40 causes each pixel in the selected pixel row to output a signal to the vertical signal line 20. An example of a signal readout method for the first readout process will be described below.

[0041] The readout control unit 40 turns on the connection units 15 of the G pixels 10(1,1) to B pixels 10(1,8), which are pixels in the first imaging pixel row 401 in the first row. As a result, the charges in the FDs 14 of the G pixels 10(1,1) to B pixels 10(1,8) in the first row are discharged to the supply unit 36, and the voltages of the FDs 14 are reset. Thereafter, the readout control unit 40 turns on the connection units 12a of the G pixels 10(1,1) to B pixels 10(1,8) in the first row. The readout control unit 40 also turns off the connection units 12 (connections 12a and 12b) of pixels in rows other than the first row. As a result, the charges photoelectrically converted by the photoelectric conversion units 11a of the G pixels 10(1,1) to B pixels 10(1,8) in the first row are transferred to the FDs 14. The pixel signals of the G pixel 10(1,1) to B pixel 10(1,8) in the first row are output to the vertical signal lines 20a to 20h, respectively, via the selection units 17 of the respective pixels.

[0042] Next, the readout control unit 40 turns on the connection units 15 of the R pixels 10(2,1) to G pixels 10(2,8), which are pixels in the second imaging pixel row 402 in the second row, to cause the charge in the FDs 14 of the R pixels 10(2,1) to G pixels 10(2,8) to be discharged to the supply unit 36. After that, the readout control unit 40 turns on the connection units 12b of the R pixels 10(2,1) to G pixels 10(2,8) in the second row. The readout control unit 40 also turns off the connection units 12 (connections 12a and 12b) of pixels in rows other than the second row. As a result, the charge photoelectrically converted by the photoelectric conversion units 11b of the R pixels 10(2,1) to G pixels 10(2,8) in the second row is transferred to the FDs 14. The pixel signals of the R pixel 10(2,1) to G pixel 10(2,8) in the second row are output to the vertical signal lines 20a to 20h, respectively, via the selection units 17 of the respective pixels.

[0043] Next, the readout control unit 40 turns on the connection units 15 of the G pixel 10(3,1) to the first AF pixel 13a(3,8), which are pixels in the first AF pixel row 403a in the third row, and causes the charge in the FDs 14 of the G pixel 10(3,1) to the first AF pixel 13a(3,8) to be discharged to the supply unit 36. After that, the readout control unit 40 turns on the connection units 12a of the G pixel 10(3,1) to the first AF pixel 13a(3,8). The readout control unit 40 also turns off the connection units 12 (connections 12a and 12b) of pixels in rows other than the third row. As a result, the charge photoelectrically converted by the photoelectric conversion units 11a of the G pixel 10(3,1) to the first AF pixel 13a(3,8) in the third row is transferred to the FDs 14. The pixel signals of the G pixel 10(3,1) to the first AF pixel 13a(3,8) in the third row are output to the vertical signal lines 20a to 20h, respectively, via the selection units 17 of the respective pixels. Similarly, the readout control unit 40 sequentially selects the pixels in the fourth row and beyond, row by row, starting with the fourth row, fifth row, sixth row, and seventh row, and reads out pixel signals from each selected pixel.

[0044] In this way, in the first readout process, the readout control unit 40 sequentially selects all pixel rows and reads out pixel signals from each pixel. The pixel signals read out from each pixel are subjected to signal processing by the processing unit 50 and then output to the control unit 4.

[0045] When the imaging control unit 4a instructs the second readout process, the readout control unit 40 separately reads out signals from each pixel in the AF pixel row and signals from each pixel in the imaging pixel row. When reading out signals from the AF pixel rows (first AF pixel row 403a, second AF pixel row 403b), the readout control unit 40 sequentially selects the multiple AF pixel rows of the image sensor 3 from the top row to the bottom row and reads out signals from each pixel. When reading out signals from the imaging pixel rows (first imaging pixel row 401, second imaging pixel row 402), the readout control unit 40 sequentially selects the multiple imaging pixel rows of the image sensor 3 from the top row to the bottom row and reads out signals from each pixel.

[0046] In this way, in the second readout process, signals from each pixel in the AF pixel row are read out separately from signals from each pixel in the imaging pixel row, so signals used for focus detection can be obtained efficiently and the burden of signal processing for AF can be reduced. When the second readout process is instructed, the readout control unit 40 may read signals from each pixel in the AF pixel row before reading signals from the imaging pixel row. In this case, the first and second signals of the AF pixel pair can be read out quickly, thereby shortening the time required for focus adjustment. Furthermore, the readout control unit 40 may read signals from each pixel in the imaging pixel row before reading signals from the AF pixel row.

[0047] 4 is a diagram showing an example of the operation of the image sensor according to the first embodiment, illustrating an example of the operation when performing a second readout process to read out pixel signals. The vertical axis indicates pixel rows, and the horizontal axis indicates the timing (time t) at which the reset operation and readout operation of each pixel row are performed. FIG. 4 schematically illustrates the transition of pixel rows at which the reset operation and readout operation are performed.

[0048] As shown in Fig. 4, the readout control unit 40 performs reset operations and readout operations on the imaging pixel rows, and also performs reset operations and readout operations on the AF pixel rows. In this embodiment, the number of AF pixel rows is smaller than the number of imaging pixel rows, as schematically shown in Fig. 2. In the example shown in Fig. 4, the total number of AF pixel rows on which reset operations and readout operations are performed is smaller than the total number of imaging pixel rows on which reset operations and readout operations are performed, and the time required for scanning the AF pixel rows is shorter than that for scanning the imaging pixel rows.

[0049] 4, within dotted-line frame G1, there are cases where the readout operation of an imaging pixel row and the reset operation of an AF pixel row adjacent to that imaging pixel row are performed simultaneously. Also, within dotted-line frame G2, there are cases where the readout operation of an AF pixel row and the reset operation of an imaging pixel row adjacent to that AF pixel row are performed simultaneously.

[0050] During the period indicated by the dotted line in the frame G1, the readout control unit 40 turns on the connection units 12b of each pixel in the imaging pixel row to be read out and turns off the connection units 12a of each pixel in the AF pixel row adjacent to that imaging pixel row. The readout control unit 40 also turns on the selection unit 17 shared by the pixels in that imaging pixel row and the pixels in the AF pixel row. Charges photoelectrically converted by the respective photoelectric conversion units 11b in each pixel in the imaging pixel row to be read out are transferred to the FD 14. The pixel signals of each pixel in the imaging pixel row are output to the respective vertical signal lines 20a to 20h via the selection units 17 of each pixel.

[0051] When discharging charges accumulated in pixels in an AF pixel row adjacent to an imaging pixel row for which a readout operation is being performed, the readout control unit 40 turns on the connection units 18a of each pixel in the AF pixel row. Turning on the connection units 18a electrically connects the photoelectric conversion units 11a and the supply units 35a. As a result, in each pixel in the AF pixel row, the charges accumulated in the photoelectric conversion units 11a are discharged to the supply units 35a, and the voltage of the photoelectric conversion units 11a is reset. In this manner, the readout control unit 40 controls the connection units 12b to connect the photoelectric conversion units 11b of the pixels in the imaging pixel row to the FDs 14, and the connection units 18a to connect the photoelectric conversion units 11a of the pixels in the AF pixel row to the supply units 35a. By controlling the connection units 18a, the image sensor 3 according to this embodiment can discharge charges accumulated in each pixel in the AF pixel row adjacent to the imaging pixel row, even when a readout operation for the imaging pixel row is being performed.

[0052] During the period within the dotted-line frame G2, the readout control unit 40 turns on the connection units 12a of each pixel in the AF pixel row to be read out and turns off the connection units 12b of each pixel in the imaging pixel row adjacent to that AF pixel row. The readout control unit 40 also turns on the selection unit 17 shared by the pixels in that AF pixel row and the pixels in the imaging pixel row. Charges photoelectrically converted by the respective photoelectric conversion units 11a in each pixel in the AF pixel row to be read out are transferred to the FD 14. Pixel signals from each pixel in the AF pixel row are output to the respective vertical signal lines 20a to 20h via the selection units 17 of each pixel.

[0053] When discharging charges accumulated in pixels in an imaging pixel row adjacent to an AF pixel row for which a readout operation is being performed, the readout control unit 40 turns on the connection units 18b of each pixel in that imaging pixel row. Turning on the connection units 18b electrically connects the photoelectric conversion units 11b and the supply unit 35b. As a result, in each pixel in the imaging pixel row, the charges accumulated in the photoelectric conversion units 11b are discharged to the supply unit 35b, and the voltage of the photoelectric conversion units 11b is reset. In this manner, the readout control unit 40 controls the connection units 12a to connect the photoelectric conversion units 11a of the pixels in the AF pixel row to the FD 14, and the connection units 18b to connect the photoelectric conversion units 11b of the pixels in the imaging pixel row to the supply unit 35b. By controlling the connection units 18b, the image sensor 3 can discharge charges accumulated in each pixel in the imaging pixel row adjacent to the AF pixel row, even when a readout operation for the AF pixel row is being performed.

[0054] In the present embodiment, even if the timing of the readout operation of one pixel and the timing of the reset operation of the other pixel among adjacent pixels that share the FD 14 are simultaneous, it is possible to suppress degradation of the pixel signal quality. Below, the ability to suppress degradation of the pixel signal quality will be described in comparison with a comparative example.

[0055] The comparative example is a case where the AF pixel 13 and the imaging pixel 10 in FIG. 3 do not have the connection portion 18a and the connection portion 18b. In the comparative example, when discharging the charge accumulated in the photoelectric conversion unit 11a (or 11b), the charge accumulated in the photoelectric conversion unit 11a (or 11b) needs to be discharged to the supply unit 36 ​​via the connection portion 12a (or 12b), the FD 14, and the connection portion 15. When reading out a pixel signal, the charge photoelectrically converted by the photoelectric conversion unit 11b (or 11a) is transferred to the FD 14 via the connection portion 12b (or 12a). For this reason, if a reset operation of one of two adjacent pixels sharing the FD 14 and a readout operation of the other pixel are simultaneously performed, the charges generated in the photoelectric conversion units 11a and 11b may be mixed together, or the charge transferred from the photoelectric conversion unit 11 of the pixel to be read out to the FD 14 may be discharged to the supply unit 36. In other words, a collision occurs between the read operation and the reset operation. In this case, it becomes impossible to properly read out a pixel signal corresponding to the charge photoelectrically converted by the photoelectric conversion unit 11 of the pixel to be read out.

[0056] In this embodiment, when the readout control unit 40 is performing a readout operation on one of two adjacent pixels, it can discharge the charge from the photoelectric conversion unit 11 of the other pixel without going through the FD 14 by controlling the connection unit 18 as described above. A reset operation is performed via a path separate from the path used for reading out pixel signals.

[0057] When a readout operation of an imaging pixel row is being performed, the readout control unit 40 can discharge the charges accumulated in the photoelectric conversion units 11a of the pixels in the AF pixel row to the supply unit 35a by turning on the connection unit 18a. Because the charges from the photoelectric conversion units 11a are discharged without passing through the FD 14, it is possible to prevent the charges generated in the photoelectric conversion units 11b of the pixels in the imaging pixel row from being affected. This makes it possible to prevent a decrease in the quality of the signals from each pixel in the imaging pixel row. Furthermore, when a readout operation of an AF pixel row is being performed, the readout control unit 40 can discharge the charges accumulated in the photoelectric conversion units 11b of the pixels in the imaging pixel row to the supply unit 35b by turning on the connection unit 18b. Because the charges from the photoelectric conversion units 11b are discharged without passing through the FD 14, it is possible to prevent the charges generated in the photoelectric conversion units 11a of the pixels in the AF pixel row from being affected. This makes it possible to prevent a decrease in the quality of the signals from each pixel in the AF pixel row. This makes it possible to prevent a decrease in the accuracy of focus detection using pixel signals.

[0058] In this way, the image sensor 3 according to this embodiment can avoid a collision between the readout operation and the reset operation. The image sensor 3 can appropriately read out pixel signals corresponding to the charges photoelectrically converted by the photoelectric conversion unit 11 of the pixel to be read out.

[0059] FIG. 5 is a diagram showing an example of the operation of the image sensor according to the first embodiment, illustrating another example of the operation when pixel signals are read out by performing a second readout process. The imaging control unit 4a performs a reset operation and a readout operation for an AF pixel row, and a reset operation and a readout operation for an imaging pixel row, for each frame at a predetermined interval. In the example shown in FIG. 5, the readout control unit 40 is controlled by the imaging control unit 4a and reads signals from each pixel in the AF pixel row before the imaging pixel row, for each frame. Also, in the example shown in FIG. 5, within a frame G2 indicated by a dotted line, there are cases in which the readout operation for an AF pixel row and the reset operation for an imaging pixel row adjacent to that AF pixel row are performed simultaneously.

[0060] FIG. 6 is a timing chart showing an example of the operation of the image sensor during the period enclosed by the dotted line frame G2 in FIG. 5. FIG. 6 shows control signals input to each pixel in an AF pixel row to be read and to each pixel in an imaging pixel row adjacent to that AF pixel row. In the timing chart shown in FIG. 6, the vertical axis represents the signal voltage level, and the horizontal axis represents time. In FIG. 6, transistors receiving a high-level (e.g., power supply voltage VDD) control signal (signal SEL, signal RST, signal TX) are turned on, and transistors receiving a low-level (e.g., ground voltage) control signal are turned off. Below, an example of the operation of the image sensor during the period enclosed by the dotted line frame G2 in FIG. 5 will be described using the AF pixel 13 in the AF pixel row and the imaging pixel 10 in the imaging pixel row shown in FIG. 3 as examples.

[0061] 6, signal RST goes high. When signal RST goes high, transistor M2 of connection unit 15 shared by AF pixels 13 in the AF pixel row to be read and imaging pixels 10 in the imaging pixel row adjacent to that AF pixel row is turned on, electrically connecting FD 14 to supply unit 36. This resets the charge in FD 14 shared by AF pixels 13 and imaging pixels 10, and the voltage of FD 14 becomes the reset voltage.

[0062] Also, at time t1, the signal SEL goes high. When the signal SEL goes high, the transistor M4 of the selection unit 17, which is shared by the AF pixel 13 and the imaging pixel 10, goes into the on state. As a result, a signal based on the reset voltage of the AF pixel 13, i.e., a signal after the charge of the FD 14 of the AF pixel 13 has been reset, is output to the vertical signal line 20 by the amplifier unit 16 and the selection unit 17. The signal based on the reset voltage of the AF pixel 13 is input as a dark signal to the processing unit 50 via the vertical signal line 20 and converted into a digital signal.

[0063] At time t2, the signal TX1a goes high. When the signal TX1a goes high, the transistor M1a of the connection unit 12a in the AF pixel 13 is turned on, and the photoelectric conversion unit 11a and the FD 14 are electrically connected. As a result, the charge photoelectrically converted by the photoelectric conversion unit 11a is transferred to the FD 14. Also, because the signal SEL is high, a pixel signal based on the charge generated by the photoelectric conversion unit 11a of the AF pixel 13 is output to the vertical signal line 20 by the amplifier 16 and the selector 17. The pixel signal of the AF pixel 13 is input to the processing unit 50 via the vertical signal line 20 and converted into a digital signal.

[0064] Also, at time t2, signal TX2b goes high. When signal TX2b goes high, transistor M5b of connection unit 18b in imaging pixel 10 goes on, electrically connecting photoelectric conversion unit 11b and supply unit 35b. This causes the charge in photoelectric conversion unit 11b of imaging pixel 10 to be discharged to supply unit 35b, resetting the voltage of photoelectric conversion unit 11b. At time t3, signal SEL goes low, turning transistor M4 of selection unit 17 off.

[0065] The processing unit 50 performs signal processing such as correlated double sampling using the dark signal converted into a digital signal and the pixel signal, and then outputs the processed signal to the control unit 4. As described above, in this embodiment, the image sensor 3 can perform a reset operation on the photoelectric conversion unit 11 by controlling the connection unit 18. The image sensor 3 can perform a reset operation on the photoelectric conversion unit 11 via a path separate from the path used to read out pixel signals, thereby preventing a decrease in the quality of pixel signals read out by the readout operation.

[0066] The above-described embodiment provides the following advantageous effects. (1) The image sensor 3 includes a first photoelectric conversion unit 11a that photoelectrically converts light to generate electric charges, a light-shielding unit 43 that blocks a portion of light incident on the first photoelectric conversion unit 11a, a second photoelectric conversion unit 11b that photoelectrically converts light to generate electric charges, an accumulation unit 14 that accumulates at least one of the electric charges generated by the first photoelectric conversion unit 11a and the electric charges generated by the second photoelectric conversion unit 11b, a supply unit 30 that supplies a predetermined voltage, a first connection unit 15 that can connect the accumulation unit 14 to the supply unit 30, and a second connection unit 18a that can connect the first photoelectric conversion unit 11a to the supply unit 30. As described above, the image sensor 3 according to this embodiment can discharge the electric charges from the photoelectric conversion unit 11a to the supply unit 30 without going through the accumulation unit 14 by controlling the connection unit 18a. The charge of the photoelectric conversion unit 11a can be discharged via a path separate from the path used to read out the pixel signal, thereby preventing the quality of the pixel signal from deteriorating.

[0067] (2) In this embodiment, when reading out a signal based on the charge photoelectrically converted by the photoelectric conversion unit 11a, the readout control unit 40 controls the charge accumulated in the photoelectric conversion unit 11b to be discharged to the supply unit 30 via the connection unit 18b. Furthermore, when reading out a signal based on the charge photoelectrically converted by the photoelectric conversion unit 11b, the readout control unit 40 controls the charge accumulated in the photoelectric conversion unit 11a to be discharged to the supply unit 30 via the connection unit 18a. This makes it possible to prevent a decrease in the quality of the pixel signal read out by the readout operation.

[0068] 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.

[0069] (Variation 1) 7 is a diagram showing an example configuration of a portion of an image sensor according to Modification 1. The imaging pixel 10 has a photoelectric conversion unit 11, a connection unit (transfer unit) 12a, a connection unit (transfer unit) 12b, an FD 14a, an FD 14b, a connection unit (reset unit) 15a, and a connection unit (reset unit) 15b. The imaging pixel 10 further has an amplifier unit 16a, an amplifier unit 16b, a selection unit 17a, and a selection unit 17b. In this modification, as shown in FIG. 7, the imaging pixel 10 and the AF pixel 13 have the same circuit configuration.

[0070] The connection unit (transfer unit) 12a electrically connects or disconnects the photoelectric conversion unit 11 and the FD 14a. The connection unit 12a transfers the charges photoelectrically converted by the photoelectric conversion unit 11 to the FD 14a. The FD 14a accumulates the charges transferred to the FD 14a. The amplifier unit 16a amplifies and outputs a signal based on the charges accumulated in the FD 14a. The connection unit (reset unit) 15a electrically connects or disconnects the supply unit 36a and the FD 14a. By connecting the supply unit 36a and the FD 14a, the connection unit 15a discharges the charges accumulated in the FD 14a to the supply unit 36a and resets the voltage of the FD 14a. The selection unit 17a electrically connects or disconnects the amplification unit 16a and the vertical signal line 21a. The selection unit 17a outputs a signal from the amplification unit 16a to the vertical signal line 21a.

[0071] The connection unit (transfer unit) 12b electrically connects or disconnects the photoelectric conversion unit 11 and the FD 14b. The connection unit 12b transfers the charges photoelectrically converted by the photoelectric conversion unit 11 to the FD 14b. The FD 14b accumulates the charges transferred to the FD 14b. The amplifier unit 16b amplifies and outputs a signal based on the charges accumulated in the FD 14b. The connection unit (reset unit) 15b electrically connects or disconnects the supply unit 36b and the FD 14b. By connecting the supply unit 36b and the FD 14b, the connection unit 15b discharges the charges accumulated in the FD 14b to the supply unit 36b and resets the voltage of the FD 14b. The selection unit 17b electrically connects or disconnects the amplification unit 16b and the vertical signal line 21b. The selection unit 17b outputs a signal from the amplification unit 16b to the vertical signal line 21b.

[0072] Current source 25a is connected to each pixel via vertical signal line 21a. Current source 25b is connected to each pixel via vertical signal line 21b. Current sources 25a and 25b each generate a current for reading out a signal from the pixel and supply the generated current to each pixel.

[0073] The readout control unit 40 can output pixel signals to the vertical signal line 21a by turning on the selection unit 17a. The readout control unit 40 can also output pixel signals to the vertical signal line 21b by turning on the selection unit 17b. The readout control unit 40 can also discharge the charges accumulated in the photoelectric conversion unit 11 to the supply unit 36a via the connection unit 12a, FD 14a, and connection unit 15a. The readout control unit 40 can also discharge the charges accumulated in the photoelectric conversion unit 11 to the supply unit 36b via the connection unit 12b, FD 14b, and connection unit 15b.

[0074] The readout control unit 40 may, for example, transfer charges generated by the photoelectric conversion units 11 of the pixels in the imaging pixel row to the FDs 14a via the connection units 12a, and may also perform control to connect the FDs 14b of the pixels in the AF pixel row to the supply unit 36b via the connection units 15b. This allows the readout control unit 40 to read out signals from the pixels in the imaging pixel row to the vertical signal lines 21a, and to discharge charges photoelectrically converted by the photoelectric conversion units 11 of the pixels in the AF pixel row to the supply unit 36b.

[0075] The readout control unit 40 may also control the transfer of charges generated by the photoelectric conversion units 11 of the pixels in the AF pixel row to the FD 14a via the connection unit 12a, and the connection of the FD 14b of the pixels in the imaging pixel row to the supply unit 36b via the connection unit 15b. This allows the readout control unit 40 to read out signals from the pixels in the AF pixel row to the vertical signal line 21a, and to discharge charges photoelectrically converted by the photoelectric conversion units 11 of the pixels in the imaging pixel row to the supply unit 36b. The image sensor according to this modification can perform a reset operation via a path separate from the path used to read out pixel signals, thereby avoiding conflict between the readout operation and the reset operation. This also reduces degradation in pixel signal quality.

[0076] The readout control unit 40 may turn on the selector 17a of each pixel in one of the two rows and the selector 17b of each pixel in the other row. In this case, the signals of the pixels in one of the two rows are output to the vertical signal line 21a, and the signals of the pixels in the other row are output to the vertical signal line 21b. This allows the readout control unit 40 to simultaneously read out signals from pixels in two rows, and to sequentially select pixel rows in pairs to read out pixel signals.

[0077] (Variation 2) An image sensor according to Modification 2 will be described with reference to FIG. 8. In the drawing, parts that are the same as or equivalent to those in Modification 1 are designated by the same reference numerals, and differences from the image sensor according to Modification 1 will be mainly described. FIG. 8 is a diagram showing a partial configuration example of an image sensor according to Modification 2. The AF pixel 13 has a photoelectric conversion unit 11a and connection units (transfer units) 12a and 12b. The imaging pixel 10 has a photoelectric conversion unit 11b and connection units (transfer units) 12c and 12d. The AF pixel 13 and the imaging pixel 10 each have FDs 14a and 14b, connection units (reset units) 15a and 15b, amplifiers 16a and 16b, and selection units 17a and 17b. In this modification, the circuit configurations of two adjacent imaging pixels 10 are the same as those of the AF pixel 13 and the imaging pixel 10 shown in FIG. 8.

[0078] The connection portion 12a electrically connects or disconnects the photoelectric conversion portion 11a and the FD 14a. The connection portion 12b electrically connects or disconnects the photoelectric conversion portion 11a and the FD 14b. The connection portion 12c electrically connects or disconnects the photoelectric conversion portion 11b and the FD 14a. The connection portion 12d electrically connects or disconnects the photoelectric conversion portion 11b and the FD 14b.

[0079] The read control unit 40 can discharge the charges accumulated in the photoelectric conversion unit 11a to the supply unit 36a via the connection unit 12a, the FD 14a, and the connection unit 15a. The read control unit 40 can also discharge the charges accumulated in the photoelectric conversion unit 11a to the supply unit 36b via the connection unit 12b, the FD 14b, and the connection unit 15b. The read control unit 40 can also discharge the charges accumulated in the photoelectric conversion unit 11b to the supply unit 36a via the connection unit 12c, the FD 14a, and the connection unit 15a. The read control unit 40 can also discharge the charges accumulated in the photoelectric conversion unit 11b to the supply unit 36b via the connection unit 12d, the FD 14b, and the connection unit 15b.

[0080] In the case of the image sensor according to this modification, the reset operation can also be performed via a path separate from the path used for reading out pixel signals, thereby preventing conflict between the readout operation and the reset operation. As in the case of modification 1, the readout control unit 40 can simultaneously read out signals from pixels in two rows, and can sequentially select pixel rows in pairs to read out pixel signals.

[0081] (Variation 3) In the above-described embodiment, an example has been described in which the connection portion 18a and the connection portion 18b are provided to two pixels (the AF pixel 13 and the imaging pixel 10 in FIG. 3). However, the two pixels may be configured to have only one of the connection portion 18a and the connection portion 18b.

[0082] (Variation 4) In the above-described embodiment, an example has been described in which two adjacent pixels share the FD 14 and the amplifier 16, but the pixel configuration is not limited to this. Three or more pixels may share the FD 14, etc. For example, four pixels may share the FD 14, etc.

[0083] (Variation 5) In the above-described embodiment, an example has been described in which a photodiode is used as the photoelectric conversion unit, but a photoelectric conversion film (organic photoelectric film) may also be used as the photoelectric conversion unit.

[0084] (Variation 6) In the above embodiment, a case has been described in which primary color (RGB) color filters are used in the imaging element 3, but complementary color (CMY) color filters may also be used.

[0085] (Variation 7) 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.

[0086] 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]

[0087] 1...imaging device, 3...imaging element, 4a...imaging control section, 4b...image data generation section, 10...imaging pixel, 11...photoelectric conversion section, 12, 15, 18...connection section, 13...AF pixel, 14...storage section, 20...vertical signal line, 30, 35, 36...supply section, 43...light shielding section

Claims

[Claim 1] a first photoelectric conversion unit that converts light into electric charges; a second photoelectric conversion unit that converts light into electric charges; a first transfer unit that transfers the charges converted by the first photoelectric conversion unit to a floating diffusion unit; a second transfer unit that transfers the charges converted by the second photoelectric conversion unit to the floating diffusion unit; a first discharge unit that discharges the charges converted by the first photoelectric conversion unit to a first supply unit that is supplied with a predetermined voltage when the charges are transferred from the second photoelectric conversion unit to the floating diffusion unit by the second transfer unit; a second discharge unit that discharges the charges converted by the second photoelectric conversion unit to a second supply unit that is supplied with a predetermined voltage when the charges are transferred from the first photoelectric conversion unit to the floating diffusion unit by the first transfer unit; An imaging element comprising:

Images