Solid-state image sensor and imaging device including the solid-state image sensor

Abstract

The pixel includes a pixel having a photoelectric conversion element, a floating node unit, and a reset unit, a first circuit connected to the pixel, and a second circuit connected to the first circuit, wherein the amount of charge that the floating node unit can handle is smaller than the amount of charge that the photoelectric conversion element can handle, and the first circuit controls the pixel so that a set of resetting the floating node unit, transferring a signal charge to the floating node unit, and reading out a voltage signal corresponding to the amount of signal charge in the floating node unit is performed multiple times, and the second circuit combines a signal corresponding to the voltage signal read out from the pixel for each set.

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, solid-state imaging elements such as charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS) image sensors have been used in imaging devices equipped with an imaging function, such as digital cameras, digital video cameras, and smartphones.

[0003] In this solid-state imaging element, input light is photoelectrically converted in a photoelectric conversion element such as a photodiode, and the signal charge is transferred to a floating node, and a voltage signal (pixel signal) is output from the pixel via a source follower according to the amount of charge.

[0004] In recent years, due to the demand for capturing images of a variety of scenes, there has been a demand to increase the amount of signal charge that a pixel can handle with one input (i.e., the incidence of light) (full well capacity) by increasing the amount of saturation signal charge of a photoelectric conversion element in the pixel of a solid-state imaging device and the amount of charge that can be handled at the floating node to which the signal charge accumulated in the photoelectric conversion element is transferred.

[0005] However, increasing the amount of signal charge that a pixel can handle in one input also increases noise (such as input-converted noise) in the voltage signal output from the pixel, resulting in a decrease in the quality of the captured image. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,075,049 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a solid-state imaging element that can increase the amount of signal charge that a pixel can handle while suppressing an increase in noise in a signal read out from the pixel, and an imaging device including this solid-state imaging element. [Means for solving the problem]

[0008] The solid-state imaging device according to the present invention comprises: a pixel including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, a floating node unit to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset unit that resets the signal charge of the floating node unit; a first circuit connected to the pixel; a second circuit connected to the first circuit, a first charge amount, which is a charge amount that can be handled by one input in the floating node unit, is smaller than a second charge amount, which is a charge amount that can be handled by one input in the at least one photoelectric conversion element; the first circuit controls the pixel so that a first set operation, which is a set of resetting the signal charge of the floating node section, transferring the signal charge from the at least one photoelectric conversion element to the floating node section, and reading out from the pixel a voltage signal corresponding to the amount of charge of the signal charge transferred to the floating node section, is performed a plurality of times in response to one input to the at least one photoelectric conversion element; The second circuit combines, for one input to the at least one photoelectric conversion element, a signal corresponding to the voltage signal read out from the pixel for each of the first set operations.

[0009] In the solid-state imaging device, the first circuit controls the pixel so that, for each first set operation, a reset signal is read as the voltage signal when the floating node unit is in the reset state, and a transferred charge amount signal is read as the voltage signal when the floating node unit has had the signal charge transferred from the at least one photoelectric conversion element to it after the reset signal is read; The second circuit may generate, for each of the first set operations, a difference signal between the transferred charge amount signal and the reset signal as a signal corresponding to the voltage signal.

[0010] In addition, in the solid-state imaging device, The pixel includes a plurality of the photoelectric conversion elements, The first charge amount may be an amount corresponding to the number of the photoelectric conversion elements.

[0011] In addition, in the solid-state imaging device, The pixel may have a gain switching unit that switches a conversion gain of the charge amount of the signal charge transferred to the floating node portion to the voltage signal between a first conversion gain and a second conversion gain lower than the first conversion gain by changing the first charge amount.

[0012] In addition, in the solid-state imaging device, the first circuit controls the pixel so that the reset, the transfer, and the readout in each first set operation are performed in the second conversion gain state, and a second set operation, which is a set in which the reset, the transfer, and the readout are performed in the first conversion gain state, is performed between the reset and the readout in a first set of the first set operations; The second circuit may output a signal corresponding to the voltage signal read out in the second set operation depending on the amount of signal charge generated in the at least one photoelectric conversion element by a single input, or may combine and output signals corresponding to the voltage signals read out for each of the first set operations.

[0013] Moreover, the imaging device according to the present invention comprises: An optical system; Any one of the above solid-state imaging elements is provided, the solid-state imaging device has a pixel array in which the pixels are arranged in a matrix; The optical system images an object onto the pixel array.

[0014] Moreover, the imaging device according to the present invention comprises: a solid-state imaging device in which a plurality of pixels are arranged in a matrix, the pixels including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, and a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element; a first circuit connected to each pixel of the solid-state imaging device; a second circuit connected to the first circuit; an optical system for forming an image of an object to be imaged on the solid-state image sensor; an output unit that outputs the captured image to an outside, an amount of charge that can be handled by the floating node unit of each pixel at one input is smaller than an amount of charge that can be handled by the at least one photoelectric conversion element of the pixel at one input; the first circuit controls the pixel so that a first set operation, which is a set of a transfer of the signal charge from the at least one photoelectric conversion element to the floating node unit and a readout of a voltage signal from the pixel according to an amount of charge of the signal charge transferred to the floating node unit, is performed a plurality of times in response to a single input to the at least one photoelectric conversion element through the optical system; The second circuit combines, for each pixel, a signal corresponding to the voltage signal read out from each pixel for each of the first set operations in response to a single input to the at least one photoelectric conversion element, The output section outputs the captured image generated based on the combined signal to an outside.

[0015] Moreover, the imaging device A mode switching unit capable of switching an imaging mode is provided, The mode switching unit may be switchable between a first mode in which the first set operation is performed a plurality of times and a second mode in which the first set operation is performed one set. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a functional block diagram of the imaging device according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing the configuration of a solid-state imaging element included in the imaging device. [Diagram 3] FIG. 3 is a circuit diagram of a pixel included in the solid-state imaging device. [Figure 4] FIG. 4 is a conceptual diagram for explaining signal processing in the pixel. [Diagram 5] FIG. 5 is a conceptual diagram showing the configuration of a pixel according to the second embodiment. [Figure 6] FIG. 6 is a circuit diagram of the pixel. [Figure 7] FIG. 7 is a conceptual diagram for explaining the amount of charge that can be handled in each of the pixel configurations. [Figure 8] FIG. 8 is a conceptual diagram for explaining the signal processing in the pixel. [Figure 9] FIG. 9 is a conceptual diagram showing the configuration of a pixel according to the third embodiment. [Figure 10] FIG. 10 is a circuit diagram of the pixel. [Figure 11] FIG. 11 is a conceptual diagram for explaining the amount of charge that can be handled in each of the pixel configurations. [Figure 12] FIG. 12 is a conceptual diagram for explaining the signal processing in the pixel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The solid-state imaging device according to this embodiment is a pixel including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, a floating node unit to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset unit that resets the signal charge of the floating node unit; a first circuit connected to the pixel; a second circuit connected to the first circuit, a first charge amount, which is a charge amount that can be handled by one input in the floating node unit, is smaller than a second charge amount, which is a charge amount that can be handled by one input in the at least one photoelectric conversion element; the first circuit controls the pixel so that a first set operation, which is a set of resetting the signal charge of the floating node section, transferring the signal charge from the at least one photoelectric conversion element to the floating node section, and reading out from the pixel a voltage signal corresponding to the amount of charge of the signal charge transferred to the floating node section, is performed a plurality of times in response to one input to the at least one photoelectric conversion element; The second circuit combines, for one input to the at least one photoelectric conversion element, a signal corresponding to the voltage signal read out from the pixel for each of the first set operations.

[0018] In this way, by making the first charge amount smaller than the second charge amount and configuring the first set operation to be performed multiple times in one input to the photoelectric conversion element, it is possible to suppress an increase in noise generated in the floating node portion, etc., even if the second charge amount (i.e., the amount of signal charge that the pixel can handle in one input) is increased. In other words, with the above configuration, it is possible to increase the amount of signal charge that the pixel can handle while suppressing an increase in noise in the signal read out from the pixel.

[0019] In the solid-state imaging device, the first circuit controls the pixel so that, for each first set operation, a reset signal is read as the voltage signal when the floating node unit is in the reset state, and a transferred charge amount signal is read as the voltage signal when the floating node unit has had the signal charge transferred from the at least one photoelectric conversion element to it after the reset signal is read; The second circuit may generate, for each of the first set operations, a difference signal between the transferred charge amount signal and the reset signal as a signal corresponding to the voltage signal.

[0020] In this way, by configuring the first circuit to generate a differential signal (a signal corresponding to a voltage signal) between the transfer charge amount signal and the reset signal for each first set operation, reset noise such as thermal noise in each signal (differential signal) combined in the second circuit is suppressed, thereby obtaining an image of higher image quality.

[0021] In addition, in the solid-state imaging device, The pixel includes a plurality of the photoelectric conversion elements, The first charge amount may be an amount corresponding to the number of the photoelectric conversion elements.

[0022] According to this configuration, when multiple photoelectric conversion elements accumulate signal charge up to the second charge amount in one input, the difference between the charge amounts of the signal charge transferred to the floating node portion for each first set operation is reduced, thereby making it possible to reduce input-equivalent noise (including quantization error, etc.) in the signal (image signal, etc.) output from the solid-state imaging element.

[0023] In addition, in the solid-state imaging device, The pixel may have a gain switching unit that switches a conversion gain of the voltage signal for the charge amount of the signal charge transferred to the floating node portion between a first conversion gain and a second conversion gain lower than the first conversion gain by changing the first charge amount.

[0024] With this configuration, it is possible to select a voltage signal to be used for image processing from the voltage signals obtained at each gain depending on the amount of input light, thereby improving the image quality of the captured image.

[0025] in this case, the first circuit controls the pixel so that the reset, the transfer, and the readout in each first set operation are performed in the second conversion gain state, and a second set operation, which is a set in which the reset, the transfer, and the readout are performed in the first conversion gain state, is performed between the reset and the readout in a first set of the first set operations; The second circuit may output a signal corresponding to the voltage signal read out in the second set operation depending on the amount of signal charge generated in the at least one photoelectric conversion element by a single input, or may combine and output signals corresponding to the voltage signals read out for each of the first set operations.

[0026] According to such a configuration, for example, when the amount of input light is small and all of the signal charges photoelectrically converted by the multiple photoelectric conversion elements are transferred in one go to the floating node section in the first conversion gain state, the signal output from the signal processing circuit is used for image processing, thereby making it possible to obtain a high-quality image even when capturing an image in a state where the amount of input light is small, such as in a dark scene.

[0027] In addition, the imaging device according to this embodiment has An optical system; A solid-state imaging device according to any one of the above, the solid-state imaging device has a pixel array in which the pixels are arranged in a matrix; The optical system images an object onto the pixel array.

[0028] According to this configuration, it is possible to increase the amount of signal charge that the pixel can handle while suppressing an increase in noise in the signal read out from the pixel, thereby obtaining a captured image of high quality.

[0029] In addition, the imaging device according to this embodiment has a solid-state imaging device in which a plurality of pixels are arranged in a matrix, the pixels including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, and a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element; a first circuit connected to each pixel of the solid-state imaging device; a second circuit connected to the first circuit; an optical system for forming an image of an object to be imaged on the solid-state image sensor; an output unit that outputs the captured image to an outside, an amount of charge that can be handled by the floating node unit of each pixel at one input is smaller than an amount of charge that can be handled by the at least one photoelectric conversion element of the pixel at one input; the first circuit controls the pixel so that a first set operation, which is a set of a transfer of the signal charge from the at least one photoelectric conversion element to the floating node unit and a readout of a voltage signal from the pixel according to an amount of charge of the signal charge transferred to the floating node unit, is performed a plurality of times in response to a single input to the at least one photoelectric conversion element through the optical system; The second circuit combines, for each pixel, a signal corresponding to the voltage signal read out from each pixel for each of the first set operations in response to a single input to the at least one photoelectric conversion element, The output section outputs the captured image generated based on the combined signal to an outside.

[0030] With this configuration, it is possible to increase the amount of signal charge that each pixel can handle while suppressing an increase in noise in the signal read out from the pixel, thereby allowing a high-quality captured image to be output (displayed, etc.) at the output section.

[0031] Moreover, the imaging device A mode switching unit capable of switching an imaging mode is provided, The mode switching unit may be switchable between a first mode in which the first set operation is performed a plurality of times and a second mode in which the first set operation is performed one set.

[0032] According to such a configuration, the imaging mode can be selected (switched) depending on the imaging scene, thereby reducing the number of first set operations to save power in solid-state imaging elements, etc., or increasing the number of first set operations to improve the image quality of images obtained by imaging in dark places, etc.

[0033] As described above, according to the present embodiment, it is possible to provide a solid-state imaging element that can increase the amount of signal charge that a pixel can handle while suppressing an increase in noise in a signal read out from the pixel, and an imaging device including the solid-state imaging element.

[0034] Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings.

[0035] 1 to 3, an imaging device 100 according to the first embodiment includes an optical system 101a and a solid-state imaging element 1. The solid-state imaging element 1 includes pixels 20, a scanning circuit (first circuit) 3 connected to the pixels 20, and a signal processing circuit (second circuit) 4 connected to the scanning circuit 3. The pixels 20 include at least one photoelectric conversion element 21 that photoelectrically converts input light to generate a signal charge, a floating node unit F to which the signal charge is transferred from the at least one photoelectric conversion element 21, and a reset unit R that resets the signal charge of the floating node unit F. The imaging device 100 is capable of capturing an image of an object such as a digital camera, a smartphone, or a tablet device, and the imaging device 100 of this embodiment is, for example, a smartphone.

[0036] Specifically, as shown in FIG. 1, the imaging device 100 includes an imaging unit 101, a control unit 102, a non-volatile memory 103, a working memory 104, an operation unit 105, a display unit (output unit) 106, a recording 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.

[0037] The imaging unit 101 converts the image of the object to be imaged formed by the optical system 101a into an electric signal under the control of the control unit 102, and then performs noise reduction processing and the like, and outputs the digital data as image data of the captured image. Specifically, the imaging unit 101 has an optical system 101a constituted by at least one optical element such as a lens, and a solid-state imaging element 1 that converts the image of the object to be imaged formed through the optical system 101a into an electric signal (i.e., captures the image).

[0038] The solid-state imaging device 1 is incorporated in, for example, a smartphone, a digital camera, or the like, and is used to capture an image of an object. The solid-state imaging device 1 of this embodiment is, for example, a CMOS image sensor.

[0039] 2, the solid-state imaging element 1 has a pixel array 2 having a plurality of pixels 20, a scanning circuit 3 connected to each pixel 20 of the pixel array 2, and a signal processing circuit 4 connected to the scanning circuit 3. The pixel array 2, the scanning circuit 3, and the signal processing circuit 4 are arranged on the same semiconductor substrate or on a plurality of semiconductor substrates that are electrically connected to each other.

[0040] The pixel array 2 has a plurality of pixels 20 arranged two-dimensionally in a matrix. The pixel array 2 also has a plurality of row signal lines L1 arranged for each row and each extending in the row direction (left-right direction in FIG. 2) for the plurality of pixels 20 arranged in a matrix, and a plurality of column signal lines L2 arranged for each column and each extending in the column direction (up-down direction in FIG. 2). Each of the plurality of row signal lines L1 is connected to a first scanning circuit 31 of the scanning circuit 3, and each of the plurality of column signal lines L2 is connected to a second scanning circuit 32 of the scanning circuit 3.

[0041] 3, each of the pixels 20 has at least one photoelectric conversion element 21 and a floating node 22 to which a signal charge generated in the at least one photoelectric conversion element 21 is transferred. In the solid-state imaging device 1 of this embodiment, the pixel 20 has one photoelectric conversion element 21, and the photoelectric conversion element 21 is, for example, a photodiode. In the pixel 20 of this embodiment, the floating node 22 constitutes the floating node unit F described above.

[0042] The first charge amount C1 (see FIG. 4), which is the charge amount that can be handled by one input to the floating node 22, is smaller than the second charge amount C2 (see FIG. 4), which is the charge amount that can be handled by one input to the photoelectric conversion element 21. Here, one input to the floating node 22 means one transfer of signal charge from the photoelectric conversion element 21, and one input to the photoelectric conversion element 21 means one exposure at the time of imaging. In this embodiment, the "handleable charge amount" is the maximum charge amount that can ensure the quality of the obtained captured image (image data), and is a value defined by the input dynamic range of each component downstream of the signal processing circuit 4, and may differ from the "maximum charge amount" which is the maximum charge amount that can be accumulated or stored in the component without considering the quality (noise, etc.) of the obtained captured image.

[0043] Each pixel 20 also includes a transfer transistor 23 connecting the photoelectric conversion element 21 and the floating node 22, a reset transistor 24 connecting the floating node 22 and a reset power supply (reset potential) VDD1, an amplification transistor 25 converting the amount of signal charge of the floating node 22 into a voltage signal, and a selection transistor 26 connecting the amplification transistor 25 and a column signal line L2. Various driving signals φRES, φTX, and φSEL are input to the transfer transistor 23, the reset transistor 24, and the selection transistor 26 from a first scanning circuit 31 of the scanning circuit 3 via a row signal line L1.

[0044] In this pixel 20, the reset transistor 24 constitutes the above-mentioned reset section R. The amplifier transistor 25 has a gate electrode connected to the floating node 22 and a drain electrode connected to a power supply VDD2. This amplifier transistor 25 serves as an input section of a readout circuit (a so-called source follower (intra-sensor amplifier) ​​SF) that converts the amount of signal charge accumulated in the floating node 22 into a voltage signal with a predetermined gain and reads (outputs) it. That is, the amplifier transistor 25 has a source electrode connected to a column signal line L2 via a selection transistor 26, thereby constituting a constant current source and source follower SF connected to one end of the column signal line L2.

[0045] Each of the row signal lines L1 transmits a reset instruction signal φRES, a charge transfer signal φTX, and a select signal φSEL output from the first scanning circuit 31 to each of the pixels 20 connected thereto.

[0046] Here, the reset instruction signal φRES is a signal for turning ON / OFF the reset transistor 24 in order to reset the charge (signal charge) of each pixel 20 (more specifically, the floating node 22), the charge transfer signal φTX is a signal for turning ON / OFF the transfer transistor 23 in order to transfer the signal charge of the photoelectric conversion element 21 to the floating node 22, and the select signal φSEL is a signal for turning ON / OFF the selection transistor 26 in order to convert the amount of signal charge of the floating node 22 into a voltage signal by the amplification transistor 25 and read it out to the column signal line L2.

[0047] Each of the column signal lines L2 is connected to each pixel 20 in the corresponding column, and transmits a voltage signal output from the pixel 20 to the second scanning circuit 32.

[0048] The scanning circuit 3 has a first scanning circuit 31 and a second scanning circuit 32. The first scanning circuit 31 controls each pixel 20 of the pixel array 2 by outputting a reset instruction signal φRES, a charge transfer signal φTX, a select signal φSEL, and the like to each pixel 20, and the second scanning circuit 32 performs signal processing such as noise removal of voltage signals read out from each pixel 20, A / D (Analog / Digital) conversion of the read out voltage signals, and operation of sequentially transmitting the converted signals to the signal processing circuit 4.

[0049] The signal processing circuit 4 is a component that performs various processes on each signal output from the second scanning circuit 32, and the signal processing circuit 4 in this embodiment is, for example, an ISP (Image Signal Processor) within the sensor.

[0050] In the above solid-state imaging device 1, the scanning circuit 3 controls the pixel 20 so that, for one input to the photoelectric conversion element 21, a first set operation is performed multiple times, which is a set of resetting the signal charge of the floating node 22, transferring the signal charge from the photoelectric conversion element 21 to the floating node 22, and reading out from the pixel 20 a voltage signal corresponding to the amount of signal charge transferred to the floating node 22. Then, for one input to the photoelectric conversion element 21, the signal processing circuit 4 combines a signal corresponding to the voltage signal read out from the pixel 20 for each first set operation, and outputs this combined signal.

[0051] Furthermore, in reading out the voltage signal from the pixel 20, the scanning circuit 3 controls the pixel 20 so that, for each first set operation, a reset signal is read out as a voltage signal when the floating node 22 is in a reset state, and a transferred charge amount signal is read out as a voltage signal when the floating node 22 has had signal charge transferred from the photoelectric conversion element 21 after the reset signal has been read out. Then, for each first set operation, the signal processing circuit 4 generates a difference signal between the transferred charge amount signal and the reset signal as a signal corresponding to the voltage signal. That is, in the solid-state imaging element 1, so-called correlated double sampling (CDS) is performed in reading out the voltage signal from each pixel 20.

[0052] A more specific description will be given below with reference to Fig. 4. In the example shown in Fig. 4, the first charge amount C1 of the photoelectric conversion element 21 is Q1, and the first charge amount C1 of the floating node 22 is Q2.

[0053] In Step 1, when imaging is performed by the imaging device 100, an image of an object to be imaged is formed on the pixel array 2, i.e., light (input light) is input to the photoelectric conversion element 21 of each pixel 20. As a result, the input light is photoelectrically converted in the photoelectric conversion element 21, and a signal charge of an amount according to the amount of the input light (in the example shown in FIG. 4, a signal charge of an amount of charge Q1 (an amount of charge equal to the first amount of charge C1)) is accumulated in the photoelectric conversion element 21. In this state, the reset transistor 24 is turned ON / OFF, so that the floating node 22 is reset to a reset potential (the potential of the reset power supply VDD1), and a reset signal RL1, which is a voltage signal at that time, is read out from the pixel 20 and recorded in the second scanning circuit 32.

[0054] Next, in Step 2, the transfer transistor 23 is turned ON / OFF, and the signal charge accumulated in the photoelectric conversion element 21 (in the example shown in FIG. 4, a signal charge of charge amount Q1) is transferred to the floating node 22. At this time, since the second charge amount C2 of the floating node 22 is smaller than the first charge amount C1 of the photoelectric conversion element 21, not all of the signal charge accumulated in the photoelectric conversion element 21 is transferred to the floating node 22, and a part of it (a signal charge of charge amount Q3 in the example shown in FIG. 4) remains in the photoelectric conversion element 21. Here, the charge amount of the signal charge transferred from the photoelectric conversion element 21 to the floating node 22 is Q2, and Q3=Q1-Q2.

[0055] In this state, when the selection transistor 26 is turned ON / OFF, the charge amount Q2 of the signal charge at the floating node 22 at this time is converted by the source follower SF into a transfer charge amount signal (voltage signal) SL1, output to the column signal line L2, and recorded in the second scanning circuit 32.

[0056] Next, in Step 3, the reset transistor 24 is turned ON / OFF to reset the signal charge accumulated in the floating node 22, and the reset signal RL2, which is a voltage signal at that time, is read out from the pixel 20 and recorded in the second scanning circuit 32.

[0057] Furthermore, in Step 4, the signal charge of charge amount Q3 remaining in the photoelectric conversion element 21 is transferred to the floating node 22 in the same manner as in Step 2, and the transferred charge amount signal (voltage signal) SL2 into which the charge amount Q3 of the signal charge accumulated in the floating node 22 at that time is converted is read out from the pixel and recorded in the second scanning circuit 32.

[0058] In each of these steps, the resetting of the floating node 22 in Steps 1 and 3, the transfer of signal charge from the photoelectric conversion element 21 to the floating node 22 in Steps 2 and 4, and the reading out of a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge transferred and accumulated in the floating node 22 constitute the above-mentioned first set operation, and in each pixel 20 of this embodiment, two sets of the first set operation are performed for one input (imaging).

[0059] 4, two sets of the first set operation are performed, so that all the signal charges accumulated in the photoelectric conversion element 21 are transferred to the floating node 22 in one input, and the photoelectric conversion element 21 becomes empty, but this configuration is not limited to this. If the photoelectric conversion element 21 is not empty after two transfers, Step 3 and Step 4 may be repeated a predetermined number of times (a number of times set according to the second charge amount C2 of the photoelectric conversion element 21, i.e., a number of times set so that all the signal charges accumulated in the photoelectric conversion element 21 are transferred). In other words, three or more sets of the first set operation may be performed.

[0060] After Steps 1 to 4 are performed as described above (i.e., the first set operation is performed twice), the signal processing circuit 4 generates a differential signal (SL1-RL1) between the transferred charge amount signal SL1 in Step 2 and the reset signal RL1 in Step 1, and also generates a differential signal (SL2-RL2) between the transferred charge amount signal SL2 in Step 4 and the reset signal RL2 in Step 3, and combines these differential signals.Then, the signal processing circuit 4 outputs this combined signal (Signal=(SL1-RL1)+(SL2-RL2): see FIG. 4) to the subsequent configuration (such as the control unit 102).

[0061] In this embodiment, it is preferable to set the input dynamic range of the source follower SF and the downstream signal processing circuit 4 so that they can handle the maximum amplitude of the voltage on the floating node 22 generated by the transfer of the signal charge in the first first set operation, in order to ensure the linearity of the combined signal.

[0062] The control unit 102 controls each unit of the imaging device 100 according to the input signals and programs. The control unit 102 also generates a captured image (image data) from a signal (a signal obtained by combining the above-mentioned differential signals) output from the solid-state imaging element 1, and outputs the captured image to the display unit 106. Note that the configuration is not limited to one in which the control unit 102 controls the entire imaging device 100. A configuration in which the entire imaging device 100 is controlled by multiple hardware devices sharing the processing may also be used.

[0063] The non-volatile memory 103 is an electrically erasable and recordable non-volatile memory. In this embodiment, the non-volatile memory 103 stores an OS (operating system) which is basic software executed by the control unit 102, and applications which cooperate with the OS to realize applied functions.

[0064] The work memory 104 is used as an image display memory for the display unit 106, a work area for the control unit 102, and the like.

[0065] 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 has a power button for instructing ON / OFF of the power supply of the imaging device 100, a touch panel formed on the display unit 106, and the like.

[0066] The display unit 106 displays (outputs to the outside) captured images (image data) and displays characters for operation.

[0067] The recording medium 107 records the image data output from the imaging unit 101 .

[0068] The connection unit 108 is an interface for connecting to an external device, and the imaging device 100 exchanges data with the external device via the connection unit 108.

[0069] The short-distance wireless communication unit 109 is a communication unit for performing short-distance wireless communication. The short-distance wireless communication unit 109 is configured with an antenna for wireless communication, a modulation / demodulation circuit for processing wireless signals, and a communication controller.

[0070] The public network connection unit 110 is an interface for performing public wireless communication. The imaging device 100 communicates with other devices via this public network connection unit 110 to make a call. At this time, the control unit 102 realizes the call by inputting and outputting an audio signal via a microphone 111 and a speaker 112. The public network connection unit 110 in this embodiment is an antenna, and the control unit 102 connects to the public network via this antenna.

[0071] The solid-state imaging element 1 of the imaging device 100 described above includes a pixel 20 having a photoelectric conversion element 21 that photoelectrically converts input light to generate a signal charge, a floating node unit F (floating node 22 in this embodiment) to which the signal charge is transferred from the photoelectric conversion element 21, and a reset unit R (reset transistor 24 in this embodiment) that resets the signal charge of the floating node unit F, a scanning circuit (first circuit) 3 connected to the pixel 20, and a signal processing circuit (second circuit) 4 connected to the scanning circuit 3. A first charge amount C1, which is the charge amount that the floating node unit F can handle in one input, is smaller than a second charge amount C2, which is the charge amount that the photoelectric conversion element 21 can handle in one input. Furthermore, the scanning circuit 3 controls the pixel 20 so that a first set operation, which is a set of resetting the signal charge of the floating node unit F, transferring the signal charge from the photoelectric conversion element 21 to the floating node unit F, and reading out from the pixel 20 a voltage signal (SL1, SL2) corresponding to the amount of the signal charge transferred to the floating node unit F, is performed multiple times for one input to the photoelectric conversion element 21. Then, the signal processing circuit 4 combines a signal corresponding to the voltage signal read out from the pixel 20 for each first set operation for one input to the photoelectric conversion element 21 (see Signal=(SL1-RL1)+(SL2-RL2) in FIG. 4).

[0072] In this manner, by making the first charge amount C1 smaller than the second charge amount C2 and configuring the first set operation to be performed multiple times in one input to the photoelectric conversion element 21, it is possible to suppress an increase in noise generated in the floating node unit F, etc., even if the second charge amount (i.e., the amount of signal charge that the pixel 20 can handle in one input) C2 is increased. That is, according to the above configuration, it is possible to increase the amount of signal charge that the pixel 20 can handle while suppressing an increase in noise in the signal read out from the pixel 20. As a result, in the imaging device 100 including the solid-state imaging element 1, a high-quality captured image is output (displayed, etc.) on the display unit (output unit) 106.

[0073] Moreover, in the solid-state imaging device 1 of this embodiment, the scanning circuit (first circuit) 3 controls the pixel 20 so that, for each first set operation, the reset signal (RL1, RL2) is read as a voltage signal when the floating node section F (in the example of this embodiment, the floating node 22) is reset, and the transferred charge amount signal (SL1, SL2) is read as a voltage signal when the floating node section F has transferred the signal charge from the photoelectric conversion element 21 after the reset signal is read. Furthermore, the signal processing circuit (second circuit) 4 generates, for each first set operation, differential signals ((SL1-RL1), (SL2-RL2)) between the transferred charge amount signal and the reset signal as signals corresponding to the voltage signal. In this way, by configuring the scanning circuit 3 to generate a differential signal (signal corresponding to the voltage signal) between the transferred charge amount signal and the reset signal for each first set operation, reset noise such as thermal noise in each signal (differential signal) combined in the signal processing circuit 4 is suppressed, and thus a captured image with higher image quality can be obtained.

[0074] Next, a second embodiment of the present invention will be described with reference to Figs. 5 to 8. The same components as those in the first embodiment are designated by the same reference numerals, and components different from the first embodiment will be described in detail.

[0075] In the imaging device 100 of this embodiment, as shown in Fig. 5, each pixel 20A of the solid-state imaging element 1 has a plurality of photoelectric conversion elements 21 (four in the example of this embodiment). In this pixel 20A, when the first photoelectric conversion element 21 is represented as PD0, the second photoelectric conversion element 21 is represented as PD1, the third photoelectric conversion element 21 is represented as PD2, and the fourth photoelectric conversion element 21 is represented as PD3, these first to fourth photoelectric conversion elements PD0 to PD3 are arranged in a matrix, and each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 is connected to a floating node 22 via a transfer transistor 23, as shown in Fig. 6. Note that in the pixel 20A of this embodiment as well, the floating node 22 constitutes a floating node section F, and the reset transistor 24 constitutes a reset section R.

[0076] In the above solid-state imaging device 1, the photoelectric conversion elements PD0 to PD3 of each pixel 20A are divided into a plurality of groups g1 and g2 (two in this embodiment), and signals of each group g1 and g2 are processed, as shown in Fig. 5. Note that in Fig. 5, the groups g1 and g2 of the photoelectric conversion elements PD0, PD1, PD2, and PD3 are represented by the type of smoke.

[0077] In this embodiment, the first photoelectric conversion element PD0 and the second photoelectric conversion element PD1 are grouped as a first group g1, and the third photoelectric conversion element PD2 and the fourth photoelectric conversion element PD3 are grouped as a second group g2. In this example, as shown in FIG. 7, the total charge amount (third charge amount) C3 of the charge amount of the first photoelectric conversion element PD0 and the charge amount of the second photoelectric conversion element PD1 is Q11, the total charge amount (fourth charge amount) C4 of the charge amount of the third photoelectric conversion element PD2 and the charge amount of the fourth photoelectric conversion element PD3 is Q12, and the first charge amount C1 of the floating node 22 is Q13. At this time, the second charge amount C2 of the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 is the sum (Q11+Q12) of the third charge amount C3 and the fourth charge amount C4. That is, when one pixel 20A has multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, the second charge amount C2 is the sum (total value) of the handleable charge amounts of each photoelectric conversion element PD0, PD1, PD2, and PD3.

[0078] In this solid-state imaging device 1, when an image is captured, signals are processed as follows.

[0079] In Step 1, when the imaging device 100 captures an image of an object to be imaged, an image is formed on the pixel array 2. That is, light (input light) is input to each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 in each pixel 20A. As a result, the input light is photoelectrically converted in each of the photoelectric conversion elements PD0, PD1, PD2, and PD3, and a signal charge in an amount corresponding to the amount of the input light (in the example shown in FIG. 8, signal charges of charges Q11 and Q12 (third charge amount C3 and fourth charge amount C4) are accumulated in the first and second groups g1 and g2, respectively) is stored. In this state, the reset transistor 24 is turned ON / OFF to reset the floating node 22 to a reset potential (potential of the power supply VDD1), and a reset signal RL1, which is a voltage signal at that time, is read out from the pixel 20A and recorded in the second scanning circuit 32.

[0080] Next, in Step 2, the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are turned ON / OFF, respectively, so that the signal charge of the charge amount Q11 accumulated in the first and second photoelectric conversion elements PD0 and PD1 is transferred to the floating node 22. At this time, the signal charge of the charge amount Q12 accumulated in the third and fourth photoelectric conversion elements PD2 and PD3 is not transferred to the floating node 22, so that not all of the signal charges accumulated in the first to fourth photoelectric conversion elements PD0 to PD3 are transferred by one input to the floating node 22, and a part of the signal charges (the signal charge of the charge amount Q12 accumulated in the third and fourth photoelectric conversion elements PD2 and PD3 in the example shown in FIG. 8) remains in the photoelectric conversion elements PD2 and PD3. In this state, the selection transistor 26 is turned ON / OFF, so that the charge amount Q11 of the signal charge at the floating node 22 at this time is converted into a voltage signal (transfer charge amount signal) SL1 by the source follower SF, output to the column signal line L2, and recorded in the second scanning circuit 32.

[0081] Next, in Step 3, the reset transistor 24 is turned ON / OFF to reset the signal charge accumulated in the floating node 22, and the reset signal RL2, which is a voltage signal at that time, is read out from the pixel 20A and recorded in the second scanning circuit 32.

[0082] Furthermore, in Step 4, the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2, PD3 are turned ON / OFF, respectively, so that the signal charge of the charge amount Q12 that was not transferred to the floating node 22 in Step 2 and remained in the third and fourth photoelectric conversion elements PD2, PD3 is transferred to the floating node 22, and a transferred charge amount signal (voltage signal) SL2 into which the charge amount Q12 of the signal charge accumulated in the floating node 22 is converted is read out from the pixel 20A and recorded in the second scanning circuit 32.

[0083] Depending on the design of each photoelectric conversion element PD0, PD1, PD2, PD3 and the floating node 22, signal charges may remain in the first and second photoelectric conversion elements PD0, PD1 in Step 2. In Step 4, when the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2, PD3 are turned ON / OFF, the transfer transistors 23 of the first and second photoelectric conversion elements PD0, PD1 are also turned ON / OFF, so that this remaining signal charge can also be read out.

[0084] In this embodiment, in each step, the reset of the floating node 22 in Steps 1 and 3, the transfer of signal charges from the photoelectric conversion elements PD0, PD1, PD2, and PD3 of each group g1 and g2 to the floating node 22 in Steps 2 and 4, and the readout of a voltage signal (transferred charge amount signal) corresponding to the amount of charge of the signal charge transferred and accumulated in the floating node 22 constitute a first set operation, and in each pixel 20A of this embodiment, two sets of the first set operation are performed with one input (imaging).

[0085] After Steps 1 to 4 are performed (i.e., two sets of the first set operation are performed), the signal processing circuit 4 generates a differential signal (SL1-RL1) between the transferred charge amount signal SL1 of Step 2 and the reset signal RL1 of Step 1, and also generates a differential signal (SL2-RL2) between the transferred charge amount signal SL2 of Step 4 and the reset signal RL2 of Step 3, and combines these differential signals.Then, the signal processing circuit 4 outputs this combined signal (LCG signal=(SL1-RL1)+(SL2-RL2): see FIG. 8) to the subsequent configuration (such as the control unit 102).

[0086] According to the solid-state imaging element 1 of the imaging device 100, as in the first embodiment, the first charge amount C1 is made smaller than the second charge amount C2 (in this embodiment, the sum of the third charge amount C3 and the fourth charge amount C4) and the first set operation is performed multiple times in one input to the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, so that even if the second charge amount (i.e., the signal charge amount that the pixel 20A can handle in one input) C2 is increased, the increase in noise generated in the floating node portion (in this embodiment, the floating node 22) and the like can be suppressed. That is, according to the solid-state imaging element 1 of this embodiment, the signal charge amount that the pixel 20A can handle can be increased while suppressing the increase in noise in the signal read out from the pixel 20A. As a result, in the imaging device 100 including the solid-state imaging element 1, a high-quality captured image is output (displayed, etc.) in the display unit (output unit) 106.

[0087] Furthermore, in the solid-state imaging element 1 of this embodiment, the pixel 20A has multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, and the first charge amount C1 is an amount corresponding to the number of photoelectric conversion elements PD0, PD1, PD2, and PD3 (specifically, an amount corresponding to the handleable charge amounts C3 and C4 for each group g1 and g2 of the photoelectric conversion elements 21).

[0088] According to this configuration, when the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 accumulate signal charges up to the second charge amount C2 in one input, the difference between the charge amounts of the signal charges transferred to the floating node unit F (in this embodiment, the floating node 22) for each first set operation is suppressed, and this makes it possible to suppress input conversion noise (including quantization error, etc.) in the signal (image signal, etc.) output from the solid-state imaging device 1. The details are as follows.

[0089] As in the first embodiment, when there is a large difference between the amount of signal charge transferred to the floating node unit F in the first set operation of the first set and the amount of signal charge transferred to the floating node unit F in the first set operation of the second set, the input dynamic range of the subsequent readout system (such as an A / D converter) must be set to match the first set operation having the larger amount of charge.In this case, the input dynamic range becomes large, and as a result, the input conversion noise (including the quantization error of the A / D conversion) increases.

[0090] Therefore, in the solid-state imaging element 1 of this embodiment, the number of photoelectric conversion elements PD0, PD1, PD2, and PD3 that are transferred simultaneously is controlled to reduce the difference in the amount of signal charge transferred to the floating node 22 for each first set operation.

[0091] Specifically, in each pixel 20A of this embodiment, four photoelectric conversion elements PD0, PD1, PD2, and PD3 are divided into a first group g1 and a second group g2, and for one input to the photoelectric conversion elements PD0, PD1, PD2, and PD3, signal charges are transferred for each group g1 and g2 to the floating node 22 (75,000 electrons are transferred each time). Therefore, the input dynamic range of the subsequent readout system (A / D converter, etc.) can be suppressed (reduced), and thus input conversion noise (including quantization error, etc.) can be suppressed, resulting in a captured image with high image quality.

[0092] Next, a third embodiment of the present invention will be described with reference to Figures 9 to 12. The same reference numerals will be used for configurations similar to those of the first and second embodiments, and configurations different from those of the first and second embodiments will be described in detail.

[0093] In the imaging device 100 of this embodiment, similarly to the second embodiment, each pixel 20B of the solid-state imaging element 1 has a plurality of (four in this embodiment) photoelectric conversion elements PD0, PD1, PD2, and PD3 (see FIG. 9). Also, as shown in FIG. 10, this pixel 20B has a storage capacitance 27 and a switch transistor 28. This storage capacitance 27 is a capacitor, and is connected to the floating node 22 via the switch transistor 28, and is also connected to a reset power supply VDD1 via the reset transistor 24.

[0094] Moreover, the pixel 20B of this embodiment has a gain switching section G that switches the conversion gain of the charge amount of the signal charge transferred to the floating node section F to a voltage signal between a high gain (first conversion gain) and a low gain (second conversion gain lower than the first conversion gain) by changing the first charge amount C1. The floating node section F of this embodiment is composed of a floating node 22 and a holding capacitor 27, and the gain switching section G is composed of a switch transistor 28. Moreover, the reset section R is composed of a reset transistor 24.

[0095] In pixel 20B having this floating node section F and gain switching section G, when switch transistor 28 is turned OFF, the charge amount (first charge amount) C1 that can be handled in floating node section F becomes equal to the charge amount that can be handled in floating node 22, and the conversion gain when the charge amount of the signal charge accumulated in floating node section F is converted into a voltage signal by source follower SF becomes a high gain.

[0096] On the other hand, when the switch transistor 28 is turned ON, the charge amount (first charge amount) C1 that can be handled at the floating node section F becomes equal to the sum of the charge amount that can be handled at the floating node 22 and the charge amount that can be handled by the storage capacitance 27 (i.e., the capacitance of the storage capacitance 27), and the conversion gain when the charge amount of the signal charge accumulated in the floating node section F is converted into a voltage signal by the source follower SF becomes a low gain.

[0097] In the above pixel 20B, the first scanning circuit 31 of the scanning circuit 3 controls pixel 20B so as to perform the reset of the floating node portion F in each first set operation, the transfer of signal charge to the floating node portion F, and the reading of the amount of charge of the signal charge accumulated in the floating node portion F (conversion of the amount of charge into a voltage signal) in a low gain state, and to perform a second set operation, which is a set in which the reset, the transfer, and the readout are performed in a high gain state, between the reset and the readout in the first set of first set operations.

[0098] In addition, the second scanning circuit 32 outputs a signal corresponding to the voltage signal read out in the second set operation depending on the amount of signal charge generated in each photoelectric conversion element PD0, PD1, PD2, and PD3 by a single input, or combines and outputs signals corresponding to the voltage signals read out for each first set operation.

[0099] In the solid-state imaging device 1 described above, similarly to the second embodiment, the photoelectric conversion elements PD0, PD1, PD2, and PD3 of each pixel 20B are divided into a plurality of groups g1 and g2 (two in this embodiment), and signals for each group g1 and g2 are processed (see FIG. 9). Note that in FIG. 9, the groups g1 and g2 of the photoelectric conversion elements PD0, PD1, PD2, and PD3 are represented by the type of smoke.

[0100] In this embodiment, as in the second embodiment, the first photoelectric conversion element PD0 and the second photoelectric conversion element PD1 are grouped as a first group g1, and the third photoelectric conversion element PD2 and the fourth photoelectric conversion element PD3 are grouped as a second group g2. In this example, as shown in FIG. 11, the total amount of charge (third charge) C3 of the charge that can be handled by the first photoelectric conversion element PD0 and the charge that can be handled by the second photoelectric conversion element PD1 is Q21, and the total amount of charge (fourth charge) C4 of the charge that can be handled by the third photoelectric conversion element PD2 and the charge that can be handled by the fourth photoelectric conversion element PD3 is Q22. At this time, the second charge C2 is the sum (Q21+Q22) of the third charge C3 and the fourth charge C4, as in the second embodiment. In other words, when one pixel 20B has multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, the second charge amount C2 is the sum (total value) of the handleable charge amounts of each photoelectric conversion element PD0, PD1, PD2, and PD3.

[0101] Also, the first charge amount C1(HCG) in the high gain state (i.e., when the switch transistor 28 is OFF) of the floating node unit F is Q(HCG), and the first charge amount C1(LCG) in the low gain state (i.e., when the switch transistor 28 is ON) is Q(LCG) (see FIG. 11). In the case of a configuration in which the conversion gain when the charge amount of the signal charge of the floating node unit F is converted into a voltage signal (transfer charge amount signal) can be switched like the solid-state imaging device 1 of this embodiment, when the charge amount of the signal charge transferred from the photoelectric conversion element 21 to the floating node unit F in the high gain state is sufficiently larger than the first charge amount C1(HCG), the maximum charge amount (maximum charge amount) of the transferred signal charge is Qmax. However, C1(LCG)>Qmax>C1(HCG). In addition, the maximum charge amount refers to the maximum amount of charge that can be accumulated or stored in the configuration without considering the quality of the captured image obtained (the input dynamic range of the subsequent circuit, etc.).

[0102] In this solid-state imaging device 1, when an image is captured, signals are processed as follows.

[0103] In Step 1, an image of an object to be imaged is formed on the pixel array 2 when the imaging device 100 captures an image. That is, light (input light) is input to each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 in each pixel 20B. As a result, the input light is photoelectrically converted in each of the photoelectric conversion elements PD0, PD1, PD2, and PD3, and a signal charge in an amount corresponding to the amount of light of the input light (in the example shown in FIG. 12, signal charges of charges Q21 and Q22 (third charge amount C3 and fourth charge amount C4) are accumulated in the first and second groups g1 and g2, respectively) is stored. At this time, the floating node section F (floating node 22 and holding capacitor 27) in a low gain state is reset to a reset potential by turning on and off the reset transistor 24 with the switch transistor 28 turned on. The reset signal RL1, which is a voltage signal at that time, is read out from the pixel 20B and recorded in the second scanning circuit 32.

[0104] Next, in Step 2, while each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 retains its accumulated signal charge, the switch transistor 28 is turned OFF and the reset transistor 24 is turned ON / OFF, whereby the floating node unit F (floating node 22) in the high gain state is reset to a reset potential, and the reset signal RH, which is the voltage signal at that time, is read out from the pixel 20B and recorded in the second scanning circuit 32.

[0105] Next, in Step 3, the floating node section F is in a high gain state, and the transfer transistors 23 are turned ON / OFF, so that the signal charges accumulated in the photoelectric conversion elements PD0, PD1, PD2, and PD3 are transferred to the floating node section F.

[0106] At this time, when the charge amount (total of signal charges of each photoelectric conversion element PD0, PD1, PD2, PD3) of the signal charges accumulated in all the photoelectric conversion elements PD0, PD1, PD2, PD3 is sufficiently larger than the first charge amount C1 (Q(HCG) in the example shown in FIG. 11) of the floating node section F in the high gain state (when it is larger than the maximum charge amount Qmax in the example shown in FIG. 11), all the signal charges (signal charges of charge amount (Q21+Q22)) accumulated in each photoelectric conversion element PD0, PD1, PD2, PD3 are not transferred to the floating node section F, and a part of them remains in each photoelectric conversion element PD0, PD1, PD2, PD3 (in the example shown in FIG. 12, a signal charge of charge amount Q23 remains in the first group g1, and a signal charge of charge amount Q24 remains in the second group g2). Here, Q23=Q21-(Qmax / 2), and Q24=Q22-(Qmax / 2).

[0107] On the other hand, when the charge amount (total charge amount) of the signal charges accumulated in all the photoelectric conversion elements PD0, PD1, PD2, and PD3 is less than or equal to the maximum charge amount Qmax of the floating node section F in the high gain state, all of the signal charges accumulated in each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 are transferred to the floating node section F.

[0108] In the example shown in Fig. 12, all the signal charges accumulated in each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 are transferred to the floating node section F until the charge amount (total charge amount) of the signal charges accumulated in all the photoelectric conversion elements PD0, PD1, PD2, and PD3 reaches the maximum charge amount Qmax (see Step 3 in Fig. 12). However, since the obtained voltage signal is larger than the input dynamic range of the subsequent circuit, when the charge amount of the signal charge transferred to the floating node section F is larger than the charge amount Q(HCG) which is the first charge amount C1(HCG), the voltage signal read out in the high gain state is not used to generate the captured image, and the voltage signal read out after switching to the low gain state is used to generate the captured image. On the other hand, when the charge amount of the signal charge transferred to the floating node section F is equal to or smaller than the charge amount Q(HCG) which is the first charge amount C1, the voltage signal read out in the high gain state is used to generate the captured image.

[0109] Next, when the selection transistor 26 is turned ON / OFF, the amount of signal charge in the floating node portion F at this time is converted by the source follower SF into a voltage signal (transferred charge amount signal) SH, output to the column signal line L2, and recorded in the second scanning circuit 32.

[0110] Next, in Step 4, the switch transistor 28 is turned OFF to switch the floating node section F to a low gain state, and then the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are turned ON and OFF, respectively, so that the signal charges accumulated in the first and second photoelectric conversion elements PD0 and PD1 are transferred to the floating node section F. In this transfer, since the signal charges (part of the signal charges accumulated in the photoelectric conversion elements PD0, PD1, PD2, and PD3) are transferred from the photoelectric conversion elements PD0, PD1, PD2, and PD3 to the floating node section F in the high gain state, not all of the signal charges in the first and second photoelectric conversion elements PD0 and PD1 are transferred (in the example shown in FIG. 12, the signal charge of the charge amount Q26 is transferred), and some of the signal charges remain (in the example shown in FIG. 12, the signal charge of the charge amount Q25 remains). Here, Q25=Q23-Q26.

[0111] At this time, since the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2, PD3 remain OFF, the signal charge accumulated in the third and fourth photoelectric conversion elements PD2, PD3 (in the example shown in Figure 12, the signal charge of charge amount Q24) is not transferred to the floating node section F and remains in the third and fourth photoelectric conversion elements PD2, PD3.

[0112] In this state, the selection transistor 26 is turned ON / OFF, and the charge amount of the signal charge in the floating node section F at this time (in the example shown in FIG. 12, the signal charge of charge amount Q27) is converted by the source follower SF into a transfer charge amount signal (voltage signal) SL1, output to the column signal line L2, and recorded in the second scanning circuit 32. Here, Q27=Qmax+Q26, and Q27≧Q(HCG). In the example of this embodiment, the charge amount Q27 is a value slightly larger than Q(LCG), which is the first charge amount C1(LCG) of the floating node section F in the low gain state.

[0113] Next, in Step 5, the reset transistor 24 is turned ON / OFF to reset the signal charge accumulated in the floating node portion F, and the reset signal RL2, which is the voltage signal at that time, is read out from the pixel 20B and recorded in the second scanning circuit 32.

[0114] Furthermore, in Step 6, the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2 and PD3 are turned ON and OFF while the floating node section F remains in the low gain state, so that the signal charge remaining in the third and fourth photoelectric conversion elements PD2 and PD3 (in the example shown in FIG. 12, the signal charge of the charge amount Q24) is transferred to the floating node section F. Also, in this Step 6, when the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2 and PD3 are turned ON and OFF, the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are also turned ON and OFF, so that the signal charge remaining in the first and second photoelectric conversion elements PD0 and PD1 (in the example shown in FIG. 12, the signal charge of the charge amount Q25) without being transferred to the floating node section F in Step 4 is transferred to the floating node section F. As a result, the signal charge of the charge amount Q28 is accumulated in the floating node section F. Here, Q28=Q24+Q25.

[0115] In this state, by turning the selection transistor 26 ON / OFF, the charge amount Q28 of the signal charge in the floating node portion F is converted into a transfer charge amount signal SL2 by the source follower SF, output to the column signal line L2, and recorded in the second scanning circuit 32.

[0116] In this embodiment, in each step, the resetting of the floating node unit F in the low gain state in Steps 1 and 5, the transfer of signal charges from the photoelectric conversion elements PD0, PD1, PD2, and PD3 to the floating node unit F in the low gain state in Steps 4 and 6, and the reading out of a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge accumulated in the floating node unit F in the low gain state constitute a first set operation, and in each pixel 20B of this embodiment, two sets of the first set operation are performed with one input (imaging).

[0117] In addition, the resetting of the floating node section F in the high gain state in Step 2, the transfer of signal charges from each photoelectric conversion element PD0, PD1, PD2, and PD3 to the floating node section F in the high gain state in Step 3, and the readout of a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge accumulated in the floating node section F in the high gain state constitute a second set operation, and the second set operation is performed between the resetting and readout in the first set operation of the first set, more specifically, between the resetting and transfer.

[0118] After Steps 1 to 6 have been performed, if the transferred charge amount signal SH read out in Step 3 (reading out the second set operation) is equal to or less than the voltage signal corresponding to the first charge amount C1 (HCG) of the floating node section F (floating node 22) in the high gain state, the signal processing circuit 4 generates a differential signal (SH-RL) between the transferred charge signal SH in Step 3 and the reset signal RH in Step 2, and outputs this generated differential signal (a signal corresponding to the transferred charge signal SH read out in the second set operation / HCG signal=(SH-RL): see Figure 12) to a downstream configuration (such as the control section 102).

[0119] On the other hand, when the transferred charge amount signal SH read out in Step 3 (reading out the second set operation) is larger than the voltage signal corresponding to the first charge amount C1 (HCG) of the floating node section F (floating node 22) in the high gain state, the signal processing circuit 4 generates a differential signal (SL1-RL1) between the transferred charge amount signal SL1 in Step 4 and the reset signal RL1 in Step 2, and also generates a differential signal (SL2-RL2) between the transferred charge amount signal SL2 in Step 6 and the reset signal RL2 in Step 5, combines these differential signals, and outputs this combined signal (LCG signal=(SL1-RL1)+(SL2-RL2): see Figure 12) to the downstream configuration (such as the control section 102).

[0120] According to the solid-state imaging element 1 of the imaging device 100 described above, by making the first charge amount C1 (LCG) in the low gain state smaller than the second charge amount C2 (in the example of this embodiment, the total value of the third charge amount C3 and the fourth charge amount C4) and performing the first set operation multiple times in one input to the photoelectric conversion elements PD0, PD1, PD2, and PD3, it is possible to suppress an increase in noise generated in the floating node unit F or the like when increasing the first charge amount C1 (LCG) in the low gain state (i.e., the amount of signal charge that the pixel 20B can handle in one input). That is, according to the solid-state imaging element 1 of this embodiment, it is possible to increase the amount of signal charge that the pixel 20B can handle while suppressing an increase in noise in the signal read out from the pixel 20B. As a result, in the imaging device 100 including the solid-state imaging element 1, a high-quality captured image is output (displayed, etc.) on the display unit (output unit) 106.

[0121] Moreover, in the solid-state imaging device 1 of this embodiment, the pixel 20B has a gain switching unit G (switch transistor 28) that switches the conversion gain of the charge amount of the signal charge transferred to the floating node unit F to a voltage signal between a high gain (first conversion gain) and a low gain (second conversion gain lower than the first conversion gain) by changing the first charge amount C1. Therefore, it is possible to select a voltage signal used for image processing according to the amount of input light from the voltage signals (SH-RH, (SL1-RL1)+(SL2-RL2), etc.) obtained at each gain, thereby improving the image quality of the captured image.

[0122] In addition, in the solid-state imaging device 1 of this embodiment, the scanning circuit (first circuit) 3 controls the pixel 20B to perform a first set operation in which resetting, transferring, and reading out are performed in a low gain (second conversion gain) state multiple times, and to perform a second set operation in which resetting, transferring, and reading out are performed in a high gain (first conversion gain) state between resetting and reading out in the first set operation of the first set. In addition, the signal processing circuit (second circuit) 4 outputs a signal (SH-RH) corresponding to the voltage signal SH read out in the second set operation according to the charge amount (total charge amount) of the signal charge generated in the photoelectric conversion elements PD0, PD1, PD2, and PD3 by one input, or outputs a signal (SL1-RL1, SL2-RL2) corresponding to the transfer charge amount signals (voltage signals) SL1 and SL2 read out for each first set operation by combining them ((SL1-RL1)+(SL2-RL2)).

[0123] According to such a configuration, for example, when the amount of input light is small and all of the signal charges photoelectrically converted by the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 are transferred in one go to the floating node section F in a high gain state, the signal output from the signal processing circuit 4 is used for image processing, so that a high-quality image can be obtained even when imaging a dark scene or other situation in which the amount of input light is small.

[0124] The solid-state imaging element 1 and imaging device 100 of the present invention are not limited to the first to third embodiments described above, and various modifications can be made without departing from the scope of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Furthermore, part of the configuration of one embodiment can be deleted.

[0125] In the imaging device 100 of the first to third embodiments described above, there is only one imaging mode for the number of times (the number of sets) of the first set operation during imaging (i.e., one input to the pixel array 2), but this configuration is not limited to this. The imaging device 100 may be configured to have a plurality of the imaging modes. That is, the imaging device 100 may include a mode switching unit capable of switching the imaging mode, and the mode switching unit may be capable of switching between a first mode in which the first set operation is performed a plurality of times and a second mode in which the first set operation is performed one set.

[0126] In this way, by providing the imaging device with a mode switching unit, the imaging mode can be selected (switched) depending on the imaging scene, which makes it possible to reduce the number of first set operations to save power in the solid-state imaging element 1, etc., or to increase the number of first set operations to improve the image quality of the captured image obtained by imaging in a dark place, etc.

[0127] Furthermore, a configuration in which the first charge amount C1 of the floating node unit F is made smaller than the second charge amount C2 of at least one photoelectric conversion element 21, and the first set operation (specifically, a set of resetting the signal charge of the floating node unit F, transferring the signal charge from the photoelectric conversion element 21 to the floating node unit F, and reading out from the pixel 20 a voltage signal corresponding to the charge amount of the signal charge of the floating node unit F) is performed multiple times, such as in the solid-state imaging element 1 of the first to third embodiments described above, may be applied to an imaging device of a so-called image plane phase difference detection autofocus type that performs focus determination based on the phase difference of input light to two photoelectric conversion elements 21 included in one pixel 20, and a solid-state imaging element provided in the imaging device.

[0128] In the imaging devices 100 of the first to third embodiments, the solid-state imaging element 1 includes the scanning circuit (first circuit) 3 and the signal processing circuit (second circuit) 4, but is not limited to this configuration. At least one of the first circuit and the second circuit may be disposed at a position in the imaging device other than the solid-state imaging element 1. For example, the imaging device 100 may have a configuration including the solid-state imaging element 1, the first circuit 3, the second circuit 4, the optical system 101a, and the display unit (output unit) 106, or a configuration including the solid-state imaging element 1 having the first circuit 3, the second circuit 4, the optical system 101a, and the display unit (output unit) 106. With these configurations, it is possible to increase the amount of signal charge that each pixel 20 can handle while suppressing an increase in noise in a signal read out from the pixel 20, and thus a high-quality captured image is output (displayed, etc.) on the display unit (output unit) 106.

[0129] In order to express the present invention, the present invention has been described adequately and sufficiently through the embodiments with reference to the drawings in the above description, but it should be recognized that those skilled in the art can easily change and / or improve the above-mentioned embodiments. Therefore, unless the changes or improvements made by those skilled in the art are at a level that departs from the scope of the claims described in the claims, the changes or improvements are interpreted as being included in the scope of the claims. [Explanation of symbols]

[0130] 1...solid-state imaging element, 2...pixel array, 20, 20A, 20B...pixel, 21...photoelectric conversion element, 22...floating node, 23...transfer transistor, 24...reset transistor, 25...amplifying transistor, 26...selection transistor, 27...holding capacitance, 28...switch transistor, 3...scanning circuit (first circuit), 31...first scanning circuit, 32...second scanning circuit, 4...signal processing circuit (second circuit), 100...imaging device, 101...imaging section, 101a...optical system, 102...control section, 103...non-volatile memory, 104...working memory, 105...operation section, 106...display section (output section), 107...recording medium, 108...connection section, 109...near-field wireless communication section, 110...public network connection section, 111...microphone, 11 2...speaker, C1...first charge amount, C2...second charge amount, C3...third charge amount, C4...fourth charge amount, F...floating node section, G...gain switching section, g1...first group, g2...second group, L1...row signal line, L2...column signal line, PD0...first photoelectric conversion element, PD1...second photoelectric conversion element, PD2...third photoelectric conversion element, PD3...fourth photoelectric conversion element, R...reset section, RH, RL1, RL2...reset signal (voltage signal), SF...source follower, SH, SL1, SL2...transfer charge amount signal (voltage signal), VDD1...reset power supply, VDD2...power supply, φRES...reset instruction signal, φSEL...select signal, φTX, φTX1, φTX2, φTX3, φTX4...charge transfer signal

Claims

1. a pixel including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, a floating node unit to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset unit that resets the signal charge of the floating node unit; a first circuit connected to the pixel; a second circuit connected to the first circuit, a first charge amount, which is a charge amount that can be handled by one input in the floating node unit, is smaller than a second charge amount, which is a charge amount that can be handled by one input in the at least one photoelectric conversion element; the first circuit controls the pixel so that a first set operation, which is a set of resetting the signal charge of the floating node section, transferring the signal charge from the at least one photoelectric conversion element to the floating node section, and reading out from the pixel a voltage signal corresponding to the amount of charge of the signal charge transferred to the floating node section, is performed a plurality of times in response to one input to the at least one photoelectric conversion element; The second circuit combines a signal corresponding to the voltage signal read out from the pixel for each of the first set operations with respect to a single input to the at least one photoelectric conversion element, the solid-state imaging element.

2. the first circuit controls the pixel so that, for each first set operation, a reset signal is read as the voltage signal when the floating node unit is in the reset state, and a transferred charge amount signal is read as the voltage signal when the floating node unit has had the signal charge transferred from the at least one photoelectric conversion element to it after the reset signal is read; 2 . The solid-state imaging device according to claim 1 , wherein the second circuit generates, for each of the first set operations, a difference signal between the transfer charge amount signal and the reset signal as a signal corresponding to the voltage signal.

3. The pixel includes a plurality of the photoelectric conversion elements, The solid-state imaging device according to claim 1 , wherein the first charge amount is an amount corresponding to the number of the photoelectric conversion elements.

4. The solid-state imaging element according to any one of claims 1 to 3, wherein the pixel has a gain switching section that switches the conversion gain of the voltage signal for the charge amount of the signal charge transferred to the floating node section between a first conversion gain and a second conversion gain lower than the first conversion gain by changing the first charge amount.

5. the first circuit controls the pixel so that the reset, the transfer, and the readout in each first set operation are performed in the second conversion gain state, and a second set operation, which is a set in which the reset, the transfer, and the readout are performed in the first conversion gain state, is performed between the reset and the readout in a first set of the first set operations; The solid-state imaging element of claim 4, wherein the second circuit outputs a signal corresponding to the voltage signal read out in the second set operation, or combines and outputs signals corresponding to the voltage signals read out for each of the first set operations, depending on the amount of charge of the signal charge generated in the at least one photoelectric conversion element by a single input.

6. An optical system; The solid-state imaging device according to any one of claims 1 to 5, the solid-state imaging device has a pixel array in which the pixels are arranged in a matrix; The optical system forms an image of an object to be imaged on the pixel array.

7. a solid-state imaging device in which a plurality of pixels are arranged in a matrix, the pixels including at least one photoelectric conversion element that performs photoelectric conversion on input light to generate a signal charge, and a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element; a first circuit connected to each pixel of the solid-state imaging device; a second circuit connected to the first circuit; an optical system for forming an image of an object to be imaged on the solid-state image sensor; an output unit that outputs the captured image to an outside, an amount of charge that can be handled by the floating node unit of each pixel at one input is smaller than an amount of charge that can be handled by the at least one photoelectric conversion element of the pixel at one input; the first circuit controls the pixel so that a first set operation, which is a set of a transfer of the signal charge from the at least one photoelectric conversion element to the floating node unit and a readout of a voltage signal from the pixel according to an amount of charge of the signal charge transferred to the floating node unit, is performed a plurality of times in response to a single input to the at least one photoelectric conversion element through the optical system; The second circuit combines, for each pixel, a signal corresponding to the voltage signal read out from each pixel for each of the first set operations in response to a single input to the at least one photoelectric conversion element, The output section outputs the captured image generated based on the combined signal to an outside of the imaging device.

8. A mode switching unit capable of switching an imaging mode is provided, The imaging device according to claim 6 , wherein the mode switching unit is switchable between a first mode in which the first set operation is performed a plurality of times and a second mode in which the first set operation is performed one set.

Images