Solid-state imaging element, and imaging device provided with solid-state imaging element

Abstract

The present invention relates to a solid-state imaging element which is characterized in that a signal of the same exposure is read a plurality of times by different read gains, and in the read at the lowest read gain among the plurality of reads, the correlated multiple sampling is performed.

Description

Solid-state imaging element and imaging device having the same Technical Field

[0001] The present invention relates to a solid-state imaging element and an imaging device including the solid-state imaging element. Background Art

[0002] Conventionally, solid-state imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) image sensors used in digital cameras, digital video cameras, smartphones, and other imaging devices with imaging functions have been known to employ so-called dual conversion gain methods (US7075049B2), which achieve a high dynamic range by reading the same exposure signal at both high and low read gain.

[0003] In recent years, a wider dynamic range (high dynamic range) has been required. Therefore, it is considered to further increase the ratio of high readout gain to low readout gain (gain ratio) in the above-mentioned dual conversion gain type solid-state imaging element.

[0004] However, if the ratio of high read gain to low read gain is further increased, an SNR dip (SNR dip) will occur at the boundary between the signal obtained by reading at high read gain and the signal obtained by reading at low read gain (the boundary of the illumination from the subject) (refer to Figure 5). For example, when photographing a subject with gently changing brightness (colorless wall, sky), the difference in signal dispersion will cause false dividing lines to appear in the area corresponding to the above-mentioned SNR dip in the captured image, thereby degrading the quality of the captured image.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent document 1: US7075049B2.

[0008] Summary of the Invention

[0009] Problems to be solved by the invention

[0010] Therefore, an object of the present invention is to provide a solid-state imaging element and an imaging device having the solid-state imaging element, wherein the solid-state imaging element reads the same exposure signal multiple times with different readout gains, thereby achieving a wider dynamic range while suppressing image degradation.

[0011] Solutions for solving problems

[0012] The solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0013] In the reading at the lowest read gain among the above multiple readings, correlated multi-sampling is performed.

[0014] In addition, in the above-mentioned solid-state imaging element,

[0015] The different read gains include the minimum read gain and a read gain higher than the minimum read gain, namely a high read gain.

[0016] In the reading at the high read gain, the correlated multiple sampling can be performed.

[0017] Furthermore, the solid-state imaging element may be configured as follows:

[0018] The correlated multi-sampling reading can be performed by switching between reading at the lowest read gain and reading at a high read gain, which is a read gain sampling higher than the lowest read gain.

[0019] In addition, in the above-mentioned solid-state imaging element,

[0020] The reading under the same gain includes the reading of reset voltage and signal voltage.

[0021] In the correlated multi-sampling, the number of sampling times for reading the reset voltage and the number of sampling times for reading the signal voltage may be the same.

[0022] In addition, in the above-mentioned solid-state imaging element,

[0023] The reading under the same gain includes the reading of reset voltage and signal voltage.

[0024] In the correlated multi-sampling, the number of sampling times for reading the signal voltage is greater than the number of sampling times for reading the reset voltage.

[0025] Furthermore, the solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0026] In at least one of the plurality of reads except for the read at the highest read gain, correlated multi-sampling is performed.

[0027] In addition, in the above-mentioned solid-state imaging element,

[0028] The correlated multi-sampling may be performed in each of the plurality of reads except for the read at the highest read gain.

[0029] Furthermore, the solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0030] In at least one of the plurality of reads, correlated multi-sampling is performed.

[0031] In addition, the imaging device of the present invention comprises:

[0032] Optical system, and

[0033] any of the above-mentioned solid-state imaging elements arranged at the imaging position of the above-mentioned optical system,

[0034] Furthermore, the imaging device includes an exposure control unit connected to the solid-state imaging element.

[0035] The solid-state imaging element is provided with a plurality of combinations for performing the above-mentioned correlated multi-sampling reading.

[0036] The exposure control unit may instruct the solid-state imaging element, during imaging, to select the optimal combination among the plurality of combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a functional block diagram of an imaging device according to this embodiment.

[0038] FIG. 2 is a diagram showing the configuration of a solid-state imaging element included in the imaging device.

[0039] FIG3 is a circuit diagram of a pixel included in the solid-state imaging element.

[0040] FIG. 4 is a diagram for explaining the reading of the voltage signal in the above-mentioned pixel.

[0041] FIG. 5 is a diagram showing the relationship between the illuminance from the object and the SN when a voltage signal is read by a solid-state imaging element that does not perform correlated multisampling.

[0042] 6 is a diagram showing the relationship between the illuminance from the object and the SN when a voltage signal is read from a solid-state imaging element using correlated multisampling with a sampling frequency of 2 by reading at the lowest read gain.

[0043] FIG. 7 is a diagram for explaining the reading of the voltage signal in the above-mentioned pixel.

[0044] FIG. 8 is a diagram for explaining reading of a voltage signal under a pixel according to another embodiment.

[0045] 9 is a diagram showing the relationship between the illuminance from the object and the SN when a voltage signal is read from a solid-state imaging element using correlated multisampling with four sampling times by reading at the lowest read gain.

[0046] FIG. 10 is a diagram for explaining the reading of a voltage signal under a pixel according to another embodiment.

[0047] FIG. 11 is a diagram for explaining reading of a voltage signal under a pixel according to another embodiment. DETAILED DESCRIPTION

[0048] The solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0049] In the reading at the lowest read gain among the above multiple readings, correlated multi-sampling is performed.

[0050] According to the above-mentioned configuration, correlated multi-sampling is performed on at least the reading at the lowest reading gain, so that the SNR difference at the boundary (boundary of the illumination from the object) between the signal obtained by reading at the lowest reading gain and the signal obtained by reading at a reading gain one level lower than the lowest reading gain is suppressed (for example, refer to Figures 6 and 9), thereby ensuring a wider dynamic range while suppressing the degradation of the image quality of the captured image.

[0051] In addition, in the above-mentioned solid-state imaging element,

[0052] The different read gains include the minimum read gain and a read gain higher than the minimum read gain, namely a high read gain.

[0053] In the reading at the high read gain, the correlated multiple sampling can be performed.

[0054] According to the above configuration, the influence of noise (random noise, etc.) in the signal read out with a high read gain is suppressed, and the quality of the captured image is improved.

[0055] Furthermore, the solid-state imaging element may be configured as follows:

[0056] The correlated multi-sampling reading can be performed by switching between reading at the lowest read gain and reading at a high read gain, which is a read gain sampling higher than the lowest read gain.

[0057] According to the above configuration, in scenarios where a high dynamic range is required during shooting, the method switches to correlated multiple sampling during reading at the lowest read gain, thereby suppressing the SNR difference at the boundary (boundary of the illumination from the object) between the signal obtained by reading at the lowest read gain and the signal obtained by reading at a high read gain. This makes it possible to suppress degradation of the image quality of the captured image while ensuring a wider dynamic range.

[0058] On the other hand, in scenes where a high dynamic range is not required during shooting, correlated multi-sampling is switched to reading at a high read gain. This suppresses the influence of noise (random noise, etc.) in the signal read at a high read gain, thereby improving the image quality of the captured image (image quality on the low illumination side).

[0059] Moreover, by setting a configuration in which correlated multi-sampling is switched for reading, even if correlated multi-sampling is performed in reading at any gain, the total reading time for reading at the lowest reading gain and reading at a high reading gain is the same or approximately the same, thereby making it possible to make the frame rate during video shooting constant or approximately constant before and after the above-mentioned switching.

[0060] In addition, in the above-mentioned solid-state imaging element,

[0061] The reading under the same gain includes the reading of reset voltage and signal voltage.

[0062] In the correlated multi-sampling, the number of sampling times for reading the reset voltage and the number of sampling times for reading the signal voltage may be the same.

[0063] In this manner, in correlated multi-sampling, the number of sampling times for reading the reset voltage is made equal to the number of sampling times for reading the signal voltage. This appropriately suppresses the influence of noise (random noise, etc.) in the read signal, thereby further improving the quality of the captured image.

[0064] In addition, in the above-mentioned solid-state imaging element,

[0065] The reading under the same gain includes the reading of reset voltage and signal voltage.

[0066] In the correlated multi-sampling, the number of sampling times for reading the signal voltage may be greater than the number of sampling times for reading the reset voltage.

[0067] In this manner, by making the number of sampling times for reading the signal voltage greater than the number of sampling times for reading the reset voltage in correlated multi-sampling, it is possible to improve the quality of captured images while suppressing the reading time.

[0068] Furthermore, the solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0069] In at least one of the plurality of reads except for the read at the highest read gain, correlated multi-sampling is performed.

[0070] According to the above configuration, the difference in SNR level at at least one point is suppressed, thereby making it possible to suppress degradation in the quality of a captured image while ensuring a wider dynamic range.

[0071] Furthermore, the solid-state imaging element of the present invention reads the same exposure signal multiple times using different readout gains.

[0072] In at least one of the plurality of reads, correlated multi-sampling is performed.

[0073] According to the above configuration, the difference in SNR level at at least one point is suppressed, or the influence of noise (random noise, etc.) in the signal read by the highest read gain is suppressed, thereby suppressing degradation of the captured image quality while ensuring a wider dynamic range.

[0074] In addition, the imaging device of the present invention comprises:

[0075] Optical system, and

[0076] Any of the above-mentioned solid-state imaging elements is arranged at the imaging position of the above-mentioned optical system.

[0077] According to the above configuration, it is possible to suppress degradation of image quality while ensuring a wider dynamic range in the obtained captured image.

[0078] Furthermore, the imaging device includes an exposure control unit connected to the solid-state imaging element.

[0079] The solid-state imaging element is provided with a plurality of combinations for performing the above-mentioned correlated multi-sampling reading.

[0080] The exposure control unit may instruct the solid-state imaging element, during imaging, to select the optimal combination among the plurality of combinations.

[0081] According to the above configuration, the exposure control unit automatically selects the correlated multi-sampling reading.

[0082] According to the above-described solid-state imaging element and imaging device including the solid-state imaging element, it is possible to suppress image degradation while achieving a wider dynamic range in a solid-state imaging element that reads the same exposure signal multiple times with different readout gains.

[0083] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0084] As shown in FIG1 , the imaging device includes an optical system 101 a and a solid-state imaging element 1 arranged at an imaging position of the optical system 101 a . The imaging device can capture images of objects such as digital cameras, smartphones, and tablet devices. The imaging device 100 of this embodiment is, for example, a smartphone.

[0085] The imaging device 100 includes an imaging unit 101 and a control unit 102. Furthermore, the imaging device 100 includes a nonvolatile memory 103, an operation memory 104, an operation unit 105, a display unit 106, a storage medium 107, a connection unit 108, a short-range wireless communication unit 109, a public network connection unit 110, a microphone 111, and a speaker 112.

[0086] Under the control of the control unit 102, the imaging unit 101 converts an image of a subject formed by the optical system 101a of the imaging unit 101 into an electrical signal, performs noise reduction processing, and outputs the digital data as image data of an output image. Specifically, the imaging unit 101 includes an optical system 101a composed of at least one optical element such as a lens, and a solid-state imaging device 1 that converts the image of the subject (photographing object) formed by the optical system 101a into an electrical signal.

[0087] Solid-state imaging element 1 is a device used to capture images of objects, such as those embedded in smartphones and digital cameras. In this embodiment, solid-state imaging element 1 is, for example, a CMOS image sensor. In this solid-state imaging element 1, the same exposure signal is read multiple times using different read gains (voltage conversion gains). Correlated multi-sampling (CMS) is performed during the readings performed at the lowest read gain among these multiple readings.

[0088] The above-mentioned different read gains include a minimum read gain and a high read gain which is a read gain higher than the minimum read gain. The solid-state imaging element 1 of this embodiment is configured to be able to switch between reading at the minimum read gain and reading at the high read gain to perform correlated multi-sampling reading.

[0089] Specifically, as shown in Figure 2, the solid-state imaging element 1 has: a plurality of pixels (pixels) 2 arranged in a matrix, a plurality of row signal lines 3 arranged in each row relative to the matrix-shaped pixel group and extending in the row direction (left-right direction in Figure 2), a plurality of column signal lines 4 arranged in each column and extending in the column direction (up-down direction in Figure 2), and a signal processing unit 5 connecting these plurality of row signal lines 3 with the plurality of column signal lines 4.

[0090] As shown in Figure 3, a plurality of pixels 2 arranged in a matrix form respectively include: a photoelectric conversion element 21 such as a photodiode, a floating point 22 that transmits the signal charge generated by the photoelectric conversion element 21, a holding capacity 23 that can hold the signal charge, a transfer transistor 24 connecting the photoelectric conversion element 21 and the floating point 22, a holding switch transistor 25 connecting the floating point 22 and the holding capacity 23, a reset transistor 26 connecting the holding capacity 23 and the reset power supply VDD1, a source follower SF having an amplifier transistor 27 and amplifying the voltage signal of the floating point 22, and a selection transistor 28 connecting the amplifier transistor 27 to the column signal line 4.

[0091] The solid-state imaging device 1 of this embodiment is a so-called dual conversion gain (DCG) solid-state imaging device 1 that switches the read gain (voltage conversion gain / conversion gain) between a minimum read gain and a high read gain, or a read gain higher than the minimum read gain, by switching the switching transistor 25 on and off. This read gain is the read gain when the signal charge transferred from the photoelectric conversion element 21 to the floating point 22 in each pixel 2 is read as a voltage signal by the source follower SF. The ratio (gain ratio) of the minimum read gain (Low Conversion Gain: LCG) to the high read gain (High Conversion Gain: HCG) in the solid-state imaging device 1 of this embodiment is, for example, 1:64. Furthermore, "reading" in the solid-state imaging device 1 of this embodiment may be either analog reading or reading after AD conversion.

[0092] This solid-state imaging element 1 performs reading of a reset voltage and reading of a signal voltage separately in reading at the same gain (LCG or HCG).

[0093] Specifically, for a single exposure (image capture) of the solid-state imaging device 1, a reset voltage (a voltage signal indicating a state where the floating point 22 is reset) and a signal voltage (a voltage signal indicating a state where the floating point 22 has transferred signal charge from the photoelectric conversion element 21 after reading the reset voltage) are read from each pixel 2. These signals are read at the same gain (LCG or HCG), and a difference signal between these signal voltages and the reset voltage is generated. In other words, the solid-state imaging device 1 performs so-called correlated double sampling (CDS) when reading from each pixel 2.

[0094] The solid-state imaging device 1 described above reads voltage signals under HCG and LCG for each row of pixels 2 arranged in a matrix. Then, in reading the voltage signals for each row, correlated multiple sampling (CMS) is performed, either under HCG or LCG, based on instructions from the control unit 102. CMS is a signal sampling method that removes correlated noise components and reduces low-frequency noise and random noise caused by averaging by sampling the reset level voltage and signal level voltage multiple times, performing weighted averaging, and taking the difference.

[0095] Specifically, when the control unit 102 performs automatic exposure during capture, and for example, determines that a certain area of ​​the resulting image is missing dark areas or has blown-out highlights, indicating a scene requiring a high dynamic range, the solid-state imaging device 1 switches the correlated multi-sampling to reading under LCG in accordance with an instruction from the control unit (exposure control unit) 102. In this case, the number of samples taken for reading the reset voltage under LCG in correlated multi-sampling in the solid-state imaging device 1 is the same as the number of samples taken for reading the signal voltage under LCG. In the solid-state imaging device 1 of this embodiment, the number of samples taken for reading the reset voltage under LCG and the number of samples taken for reading the signal voltage under LCG in correlated multi-sampling are both two.

[0096] More specifically, for the same exposure signal generated by the photoelectric conversion element 21 of each pixel 2, in the plurality of pixels 2 arranged in a matrix, the reset voltage under LCG is sampled twice (i.e., the reset voltage is sampled twice in correlated multi-sampling) for each row (LCG Ref ADC1, 2 in FIG4 ), the reset voltage under HCG is sampled once (HCG Ref ADC in FIG4 ), the signal voltage under HCG is sampled once (HCG Sig ADC in FIG4 ), and the signal voltage under LCG is sampled twice (i.e., the signal voltage is sampled twice in correlated multi-sampling). FIG4 schematically illustrates the steps for reading each row, and the length in the left-right direction of each step corresponds to the length of the reading time. The same applies to FIG7 , FIG8 , FIG10 , and FIG11 .

[0097] However, the solid-state imaging element 1 averages the reset voltage and signal voltage of the LCG that have been correlated multi-sampled, i.e., sampled multiple times (twice in the example of this embodiment), and then generates a difference signal between the average reset voltage and the average signal voltage (i.e., correlated double sampling), and also generates a difference signal between the reset voltage and the signal voltage of the HCG (correlated double sampling).

[0098] At this time, in reading under LCG, the reading gain is low, so the influence of random noise, etc., becomes greater. However, by generating an image signal using a signal that has been sampled multiple times and averaged using correlated multisampling, the influence of noise such as random noise in reading under LCG is suppressed compared to a case where correlated multisampling is not performed. As a result, the SNR dip (SNR dip) α at the boundary (the boundary of illumination from the subject) between the signal obtained by reading under LCG and the signal obtained by reading under HCG can be reduced (see Figure 6). In addition, in Figure 6, the graph to the right of the SNR dip α shows the read signal under LCG, and the graph to the left of the SNR dip α shows the read signal under HCG.

[0099] For example, the solid-state imaging element 1 of this embodiment (where the reset voltage and signal voltage are sampled twice each under LCG conditions; see Figure 6 ) reduces the SNR difference α from 6 dB to 4 dB compared to the case without correlated multisampling (see Figure 5 ). Figures 5 and 6 are graphs with the vertical axis representing SNR [dB] and the horizontal axis representing illuminance [lux] from the subject. The same applies to Figure 9 .

[0100] On the other hand, when the control unit 102 determines during imaging that a high dynamic range scene is not required, the solid-state imaging device 1 switches the correlated multi-sampling to reading under HCG in response to an instruction from the control unit (exposure control unit) 102. In this case, the solid-state imaging device 1 performs correlated multi-sampling similar to when reading under LCG, and the number of sampling times for reading the reset voltage under HCG in correlated multi-sampling is the same as the number of sampling times for reading the signal voltage under HCG. In the solid-state imaging device 1 of this embodiment, the number of sampling times for reading the reset voltage under HCG and the number of sampling times for reading the signal voltage under HCG in correlated multi-sampling are both two.

[0101] More specifically, for the same exposure signal generated by the photoelectric conversion element 21 of each pixel 2, in the multiple pixels 2 arranged in a matrix, the reset voltage under LCG is read once for each row, the reset voltage under HCG is read and sampled twice (i.e., the reset voltage is sampled twice in the correlated multiple sampling), the signal voltage under HCG is read and sampled twice (i.e., the signal voltage is sampled twice in the correlated multiple sampling), and the signal voltage under LCG is read once (refer to Figure 7).

[0102] Then, the solid-state imaging element 1 performs correlated double sampling of the reset voltage and signal voltage of the LCG, averages the reset voltage and signal voltage of the HCG that have been correlated multi-sampled, that is, sampled multiple times (twice in the example of this embodiment), and then performs correlated double sampling of the averaged reset voltage and the averaged signal voltage.

[0103] At this time, in the reading under HCG, the image signal is generated using the signal obtained by multiple sampling and averaging through correlated multi-sampling. Therefore, in the reading under HCG, the influence of noise such as random noise in the reading under HCG is suppressed compared with the case where correlated multi-sampling is not performed. As a result, the image quality on the side with lower illumination in the reading signal under HCG in Figure 6 is improved.

[0104] Returning to Figure 1 , the control unit 102 controls each unit of the imaging device 100 according to input signals and programs. Furthermore, the control unit 102 generates a captured image (image data) based on the signal output from the solid-state imaging element 1 and outputs it to the display unit 106. Furthermore, the control unit 102 of this embodiment includes an exposure control unit 102A that instructs the solid-state imaging element 1 on whether to perform correlated multisampling, either by reading under LCG or reading under HCG.

[0105] The nonvolatile memory 103 is an electrically erasable and storable nonvolatile memory. The nonvolatile memory 103 of this embodiment stores an OS (Operating System) as basic software executed by the control unit 102 and an application program that realizes application functions in cooperation with the OS.

[0106] The operation memory 104 is used as an image display memory for the display unit 106 , an operation area for the control unit 102 , and the like.

[0107] The operation unit 105 is used by a user or the like to input instructions to the imaging device 100. The operation unit 105 of this embodiment includes a power button for turning on / off the power of the imaging device 100, a touch panel formed on the display unit 106, and the like.

[0108] The display unit 106 displays (outputs to the outside) a captured image (image data), displays characters for operation, and the like.

[0109] The storage medium 107 stores image data output from the imaging unit 101 .

[0110] The connection unit 108 is an interface for connecting to an external device. The imaging device 100 exchanges data with the external device via the connection unit 108 .

[0111] The NFC unit 109 is a communication unit for performing NFC wireless communication and is composed of an antenna for wireless communication, a modulation and demodulation circuit for processing wireless signals, and a communication controller.

[0112] The public network connection unit 110 is an interface for public wireless communications. The camera 100 communicates with other devices via this public network connection unit 110 for the purpose of making calls. The control unit 102 inputs and outputs audio signals via the microphone 111 and speaker 112, thereby enabling these calls. In this embodiment, the public network connection unit 110 is an antenna, through which the control unit 102 connects to the public network.

[0113] The solid-state imaging element 1 of the above-described imaging device 100 reads the same exposure signal multiple times using different readout gains, and performs correlated multi-sampling (CMS) during reading at the lowest readout gain (LCG) among the multiple readings.

[0114] In this way, correlated multisampling is performed on at least the readings under the LCG. Therefore, the SNR difference α at the boundary (the boundary of illumination from the subject) between the signal obtained by reading under the LCG and the signal obtained by reading under a lower reading gain (HCG in this embodiment) is suppressed (for example, see symbol α in Figures 5 and 6). This ensures a wider dynamic range (HDR) while suppressing degradation in captured image quality.

[0115] In the solid-state imaging element 1 of this embodiment, the different read gains include a lowest read gain (LCG) and a high read gain (HCG) higher than the LCG. Correlated multi-sampling (CMS) is performed in reading under the HCG.

[0116] According to the above configuration, the influence of noise (random noise, etc.) in the signal read out under HCG is suppressed, and the image quality is improved.

[0117] Furthermore, the solid-state imaging element 1 of this embodiment is configured to be able to switch between reading at the lowest read gain (LCG) and reading at a high read gain (HCG) having a higher read gain than LCG and perform correlated multi-sampling (CMS) reading.

[0118] According to the above configuration, in scenes requiring a high dynamic range during shooting, the method switches to correlated multiple sampling during reading under LCG, thereby suppressing the SNR difference α at the boundary between the signal obtained by reading under LCG and the signal obtained by reading under HCG (the boundary of the illumination from the object being photographed), thereby ensuring a wider dynamic range while suppressing the degradation of the image quality of the captured image.

[0119] On the other hand, in scenes where high dynamic range is not required during shooting, correlated multisampling is performed during reading under HCG, thereby suppressing the influence of noise (random noise, etc.) in the signal read under HCG, thereby improving the image quality of the captured image (the image quality on the side with lower illumination).

[0120] Moreover, by setting a configuration in which correlated multi-sampling is switched for reading, even when correlated multi-sampling is performed in reading at an arbitrary reading gain (voltage conversion gain), the total reading time of the reading under LCG and the reading under HCG is the same or approximately the same, and therefore, the frame rate during video shooting before and after the above-mentioned switching can be made constant or approximately constant.

[0121] In addition, in the solid-state imaging element 1 of this embodiment, reading under the same gain (same read gain) includes reading the reset voltage and reading the signal voltage. In correlated multi-sampling (CMS), the number of sampling times for reading the reset voltage is the same as the number of sampling times for reading the signal voltage.

[0122] In this manner, in correlated multi-sampling, the number of sampling times for reading the reset voltage is made equal to the number of sampling times for reading the signal voltage. This appropriately suppresses the influence of noise (random noise, etc.) in the read signal, thereby further improving the quality of the captured image.

[0123] Furthermore, the imaging device 100 of this embodiment includes an optical system 101 a and the solid-state imaging element 1 arranged at an imaging position of the optical system 101 a .

[0124] According to the imaging device 100 , it is possible to suppress degradation in the image quality of the obtained captured image while ensuring a wider dynamic range.

[0125] The solid-state imaging element 1 and imaging device 100 including the solid-state imaging element 1 of the present invention are not limited to the above-described embodiments. Various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or a portion of the configuration of one embodiment may be replaced with the configuration of another embodiment. Furthermore, a portion of the configuration of one embodiment may be deleted.

[0126] In the solid-state imaging device 1 of the above embodiment, the number of correlated multi-sampling sampling times is two for each of reading the reset voltage and reading the signal voltage. However, the present invention is not limited to this configuration. The number of sampling times for reading the reset voltage under LCG and the number of sampling times for reading the signal voltage under LCG may be three or more.

[0127] The greater the number of sampling times for reading the reset voltage under LCG and the number of sampling times for reading the signal voltage under LCG, the smaller the SNR difference α at the boundary (the boundary of illumination from the subject) between the signal obtained by reading under LCG and the signal obtained by reading under HCG. For example, as shown in FIG8 , when the number of sampling times for reading the reset voltage under LCG and the number of sampling times for reading the signal voltage under LCG are both 4, the SNR difference α at the boundary between the signal obtained by reading under LCG and the signal obtained by reading under HCG is suppressed to 2 dB as shown in FIG9 .

[0128] In the solid-state imaging device 1 of the above embodiment, the number of sampling times for reading the reset voltage and the number of sampling times for reading the signal voltage at the same gain in correlated multi-sampling is the same. However, the present invention is not limited to this configuration. In correlated multi-sampling, the number of sampling times for reading the reset voltage and the number of sampling times for reading the signal voltage at the same gain may also be different.

[0129] In this case, as shown in Figure 10, in correlated multi-sampling, it is preferable that the number of sampling times for reading the signal voltage at the same gain be greater than the number of sampling times for reading the reset voltage. By thus increasing the number of sampling times for reading the signal voltage relative to the number of sampling times for reading the reset voltage in correlated multi-sampling, it is possible to improve the image quality of the captured image (to a certain extent) while also reducing the reading time in the solid-state imaging device 1.

[0130] Furthermore, in the solid-state imaging device 1 of the above embodiment, correlated multisampling is performed during reading at either LCG or HCG gain, but the present invention is not limited to this configuration. Correlated multisampling may also be performed separately during reading at each gain. For example, as shown in FIG11 , correlated multisampling may be performed separately during reading at LCG and reading at HCG.

[0131] In the solid-state imaging device 1 of the above embodiment, correlated multi-sampling reading is performed by switching between readings at different gains, but the present invention is not limited to this configuration. Correlated multi-sampling reading may be fixed to reading at LCG, for example.

[0132] In the solid-state imaging element 1 of the above embodiment, the read gain when reading the voltage signal is two types (LCG and HCG), but it may be three or more types.

[0133] In this case, correlated multi-sampling can be performed during the reading at the lowest read gain among the multiple readings. According to the above configuration, correlated multi-sampling is performed at least during the reading at the lowest read gain. Therefore, the difference in SNR at the boundary (the boundary of illumination from the subject) between the signal obtained by reading at the lowest read gain and the signal obtained by reading at a read gain one step lower than the lowest read gain is suppressed, thereby ensuring a wider dynamic range while suppressing image quality degradation.

[0134] Furthermore, correlated multisampling can be performed in at least one of the multiple readouts, excluding the readout at the highest readout gain. According to the above configuration, the SNR difference at at least one location is suppressed, thereby ensuring a wider dynamic range while suppressing image quality degradation.

[0135] Furthermore, correlated multisampling can be performed in at least one of the multiple readouts. This configuration suppresses the difference in SNR at at least one location, or reduces the influence of noise (random noise, etc.) in the signal readout at the highest readout gain. This allows for a wider dynamic range while minimizing image quality degradation.

[0136] In the solid-state imaging device 1 of the above embodiment, the ratio of LCG to HCG (gain ratio) is, for example, 1:64, but this is not limiting. For example, the gain ratio may be 1:4, 1:8, or other gain ratios. Furthermore, as the gain ratio increases, the SNR peak-to-peak difference α increases. Therefore, correlated multisampling significantly reduces the SNR peak-to-peak difference α.

[0137] In addition, the imaging device 100 can be configured as follows: it has an exposure control unit 102A connected to the solid-state imaging element 1, and the solid-state imaging element 1 is provided with multiple combinations of readings for performing correlated multiple sampling. When shooting, the exposure control unit 102A indicates the best combination among the above multiple combinations to the solid-state imaging element 1.

[0138] As an example of switching the read combinations, under conditions where the SNR difference increases, such as when the absolute value of the LCG gain is small and the gain ratio between LCG and HCG is large (e.g., 1:32 or greater), the following two combinations are switched based on the instruction: a combination in which the number of correlated multisampling of the LCG is increased compared to the HCG; and a combination in which the number of correlated multisampling of the HCG is increased compared to the LCG when performing high dynamic range shooting in a dark scene with a large absolute value of the LCG gain (e.g., 4 times or greater) to improve the SNR in dark areas. That is, exposure control unit 102A selects the combination with the best image quality from among the multiple combinations set as the optimal combination, in order to ensure a wider dynamic range while suppressing degradation in the quality of the captured image.

[0139] According to the above configuration, the exposure control unit 102A automatically selects the correlated multi-sampling reading.

[0140] To illustrate the present invention, the present invention has been appropriately and fully described above through the embodiments with reference to the accompanying drawings. However, those skilled in the art will recognize that modifications and / or improvements to the above-described embodiments are readily achievable. Therefore, as long as modifications or improvements implemented by those skilled in the art do not depart from the scope of the claims as set forth in the claims, such modifications or improvements should be construed as being included within the scope of the claims.

[0141] Explanation of the reference numerals: 1…solid-state imaging element, 2…pixel, 21…photoelectric conversion element, 22…floating point, 23…holding capacity, 24…transmission transistor, 25…holding switch transistor, 26…reset transistor, 27…amplification transistor, 28…selection transistor, 3…row signal line, 4…column signal line, 5…signal processing unit, 100…imaging device, 101…imaging unit, 101a…optical system, 102…control unit, 102A…exposure control unit, 103…non-volatile memory, 104…operation memory, 105…operation unit, 106…display unit, 107…storage medium, 108…connection unit, 109…near-field wireless communication unit, 110…public network connection unit, 111…microphone, 112…speaker, SF…source follower, α…SNR dip.

Claims

1. A solid-state imaging element that reads the same exposure signal multiple times using different readout gains, In a read at the lowest read gain among the multiple reads, correlated multi-sampling is performed.

2. The solid-state imaging element according to claim 1, wherein The different read gains include the lowest read gain and a read gain higher than the lowest read gain, namely, a high read gain. In the reading at the high read gain, the correlated multiple sampling is performed.

3. The solid-state imaging element according to claim 1 or 2, wherein: The correlated multi-sampling reading can be switched between reading at the lowest read gain and reading at a high read gain, the high read gain being a read gain higher than the lowest read gain.

4. The solid-state imaging element according to any one of claims 1 to 3, wherein The reading under the same gain includes the reading of reset voltage and the reading of signal voltage. In the correlated multiple sampling, the number of samplings for reading the reset voltage is the same as the number of samplings for reading the signal voltage.

5. The solid-state imaging element according to any one of claims 1 to 3, wherein The reading under the same gain includes the reading of reset voltage and the reading of signal voltage. In the correlated multiple sampling, the number of samplings for reading the signal voltage is greater than the number of samplings for reading the reset voltage.

6. A solid-state imaging element that reads the same exposure signal multiple times using different read gains, In at least one of the plurality of reads except for a read at a highest read gain, correlated multi-sampling is performed.

7. The solid-state imaging element according to claim 6, wherein: The correlated multi-sampling is performed in each of the plurality of reads except for the read at the highest read gain.

8. A solid-state imaging element that reads the same exposure signal multiple times using different read gains, In at least one of the plurality of reads, correlated multiple sampling is performed.

9. A photographing device comprising: Optical system, and The solid-state imaging element according to any one of claims 1 to 8, arranged at an imaging position of the optical system. 10 . The imaging device according to claim 9 , further comprising an exposure control unit connected to the solid-state imaging element. The solid-state imaging element includes a plurality of combinations for performing the correlated multi-sampling reading. The exposure control unit instructs the solid-state imaging element to select the best combination among the plurality of combinations during imaging.

Images