JP7834101B2 - Solid-state image sensor, and imaging device equipped with a solid-state image sensor - Google Patents

Description

This invention relates to a solid-state image sensor and an imaging device equipped with a solid-state image sensor.

Conventionally, imaging devices equipped with imaging functions, such as digital cameras, digital video cameras, and smartphones, have used solid-state image sensors, such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) image sensors.

In this solid-state image sensor, the signal charge obtained by photoelectric conversion of input light in a photoelectric conversion element such as a photodiode 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.

In recent years, driven by the desire to image a variety of scenes, there has been a need to increase the amount of signal charge that a pixel can handle with a single input (i.e., incident light) by increasing the saturation signal charge amount of the photoelectric conversion element in the pixels of solid-state image sensors, and the amount of charge that can be handled by the floating node to which the signal charge accumulated in the photoelectric conversion element is transferred. This requires increasing the signal charge amount (Full Well Capacity) that a pixel can handle with a single input (i.e., incident light).

However, increasing the amount of signal charge that a pixel can handle with a single input also increases the noise (such as input-referred noise) in the voltage signal output from the pixel, resulting in a decrease in the image quality of the resulting captured image.

U.S. Patent Publication No. 7075049

Therefore, the object of the present invention is to provide a solid-state image sensor that can increase the amount of signal charge that a pixel can handle while suppressing the increase in noise in the signal read from the pixel, and an imaging device equipped with this solid-state image sensor.

The solid-state image sensor according to the present invention is
A pixel having at least one photoelectric conversion element that converts input light into photoelectric energy to generate a signal charge, a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset portion for resetting the signal charge in the floating node portion,
A first circuit connected to the aforementioned pixel,
The circuit comprises a second circuit connected to the first circuit,
The first charge amount, which is the amount of charge that can be handled in a single input at the floating node portion, is smaller than the second charge amount, which is the amount of charge that can be handled in a single input at the at least one photoelectric conversion element.
The first circuit controls the pixel such that, for each input to the at least one photoelectric conversion element, a first set operation is performed multiple times, which is a set of operations consisting of resetting the signal charge of the floating node, transferring the signal charge from the at least one photoelectric conversion element to the floating node, and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit combines a single input to the at least one photoelectric conversion element with a signal corresponding to the voltage signal read from the pixel for each of the first set operations.

In the aforementioned solid-state image sensor,
The first circuit controls the pixel such that, for each first set operation, the floating node unit reads out the reset signal as a voltage signal when it is in the reset state, and after the reading of the reset signal, the floating node unit reads out the transferred charge amount signal as a voltage signal when it has received the signal charge from at least one photoelectric conversion element.
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.

Furthermore, in the solid-state image sensor,
The aforementioned pixel has a plurality of photoelectric conversion elements,
The first charge amount may be an amount corresponding to the number of photoelectric conversion elements.

Furthermore, in the solid-state image sensor,
The pixel may have a gain switching unit that changes the first charge amount to switch the conversion gain of the charge amount of the signal charge transferred to the floating node unit to the voltage signal between a first conversion gain and a second conversion gain lower than the first conversion gain.

Furthermore, in the solid-state image sensor,
The first circuit controls the pixels such that the reset, transfer, and read operation in each first set operation are performed in the state of the second conversion gain, and the second set operation, which is a set in which the reset, transfer, and read operation are performed in the state of the first conversion gain, is performed between the reset and read operation in the first set of the first set operation.
The second circuit may output a signal corresponding to the voltage signal read out in the second set operation, depending on the amount of charge of the signal charge generated in the at least one photoelectric conversion element by a single input, or it may output a combined signal corresponding to the voltage signal read out each time the first set operation is performed.

Furthermore, the imaging device according to the present invention is
Optical system and
A solid-state image sensor comprising any of the above,
The solid-state image sensor has a pixel array in which the pixels are arranged in a matrix,
The optical system forms an image of the object to be imaged on the pixel array.

Furthermore, the imaging device according to the present invention is
A solid-state image sensor having a plurality of pixels arranged in a matrix, each having at least one photoelectric conversion element that converts input light into photoelectric energy 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 image sensor,
A second circuit connected to the first circuit,
An optical system for forming an image of the object to be imaged on the solid-state image sensor,
It includes an output unit that outputs the captured image to an external device,
The amount of charge that can be handled in a single input at the floating node portion of each pixel is smaller than the amount of charge that can be handled in a single input at at least one photoelectric conversion element of the pixel.
The first circuit controls the pixels such that, for each input to the at least one photoelectric conversion element through the optical system, a first set operation is performed multiple times, which consists of transferring the signal charge from the at least one photoelectric conversion element to the floating node and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit, in response to a single input to at least one photoelectric conversion element, combines a signal corresponding to the voltage signal read from each pixel for each of the first set operations, for each pixel.
The output unit outputs the captured image generated based on the combined signal to the outside.

Furthermore, the imaging device is
It is equipped with a mode switching section that allows switching between imaging modes.
The mode switching unit may be able to switch between a first mode in which the first set operation is performed multiple times and a second mode in which the first set operation is performed once.

Figure 1 is a functional block diagram of the imaging device according to the first embodiment. Figure 2 shows the configuration of the solid-state image sensor provided in the imaging device. Figure 3 is a circuit diagram of the pixels of the solid-state image sensor. Figure 4 is a conceptual diagram illustrating the signal processing at the aforementioned pixel. Figure 5 is a conceptual diagram showing the pixel configuration according to the second embodiment. Figure 6 is a circuit diagram of the aforementioned pixel. Figure 7 is a conceptual diagram illustrating the amount of charge that can be handled in each of the pixel configurations. Figure 8 is a conceptual diagram illustrating the signal processing at the aforementioned pixel. Figure 9 is a conceptual diagram showing the pixel configuration according to the third embodiment. Figure 10 is a circuit diagram of the aforementioned pixel. Figure 11 is a conceptual diagram illustrating the amount of charge that can be handled in each of the pixel configurations. Figure 12 is a conceptual diagram illustrating the signal processing at the aforementioned pixel.

The solid-state image sensor according to this embodiment is
A pixel having at least one photoelectric conversion element that converts input light into photoelectric energy to generate a signal charge, a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset portion for resetting the signal charge in the floating node portion,
A first circuit connected to the aforementioned pixel,
The circuit comprises a second circuit connected to the first circuit,
The first charge amount, which is the amount of charge that can be handled in a single input at the floating node portion, is smaller than the second charge amount, which is the amount of charge that can be handled in a single input at the at least one photoelectric conversion element.
The first circuit controls the pixel such that, for each input to the at least one photoelectric conversion element, a first set operation is performed multiple times, which is a set of operations consisting of resetting the signal charge of the floating node, transferring the signal charge from the at least one photoelectric conversion element to the floating node, and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit combines a single input to the at least one photoelectric conversion element with a signal corresponding to the voltage signal read from the pixel for each of the first set operations.

Thus, by making the first charge amount smaller than the second charge amount and configuring the system so that the first set operation is performed multiple times in a single input to the photoelectric conversion element, it is possible to increase the second charge amount (i.e., the amount of signal charge that the pixel can handle in a single input) while suppressing the increase in noise generated in the floating node and other parts. In other words, with the above configuration, it is possible to increase the amount of signal charge that the pixel can handle while suppressing the increase in noise in the signal read out from the pixel.

In the aforementioned solid-state image sensor,
The first circuit controls the pixel such that, for each first set operation, the floating node unit reads out the reset signal as a voltage signal when it is in the reset state, and after the reading of the reset signal, the floating node unit reads out the transferred charge amount signal as a voltage signal when it has received the signal charge from at least one photoelectric conversion element.
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.

Thus, by configuring the first circuit to generate a difference signal (a 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 (difference signal) coupled in the second circuit is suppressed, resulting in higher-quality captured images.

Furthermore, in the solid-state image sensor,
The aforementioned pixel has a plurality of photoelectric conversion elements,
The first charge amount may be an amount corresponding to the number of photoelectric conversion elements.

With this configuration, when multiple photoelectric conversion elements accumulate signal charge up to the second charge amount with a single input, the difference in charge amounts between the signal charges transferred to the floating node section after each first set operation is suppressed. This makes it possible to suppress input-referred noise (including quantization errors, etc.) in the signal (image signal, etc.) output from the solid-state image sensor.

Furthermore, in the solid-state image sensor,
The pixel may have a gain switching unit that changes the first charge amount to switch the conversion gain of the voltage signal of the charge amount of the signal charge transferred to the floating node unit between a first conversion gain and a second conversion gain lower than the first conversion gain.

With this configuration, it becomes possible to select the voltage signal used for image processing from the voltage signals obtained at each gain, according to the amount of input light, thereby improving the image quality of the captured image.

in this case,
The first circuit controls the pixels such that the reset, transfer, and read operation in each first set operation are performed in the state of the second conversion gain, and the second set operation, which is a set in which the reset, transfer, and read operation are performed in the state of the first conversion gain, is performed between the reset and read operation in the first set of the first set operation.
The second circuit may output a signal corresponding to the voltage signal read out in the second set operation, depending on the amount of charge of the signal charge generated in the at least one photoelectric conversion element by a single input, or it may output a combined signal corresponding to the voltage signal read out each time the first set operation is performed.

With this configuration, for example, when the input light intensity is low and all of the signal charge converted photoelectrically by multiple photoelectric conversion elements is transferred to the floating node in the first conversion gain state in a single pass, the signal output from the signal processing circuit is used for image processing. This allows for the acquisition of high-quality images even when imaging in low-light conditions such as dark scenes.

Furthermore, the imaging device according to this embodiment is
Optical system and
A solid-state image sensor as described in any of the above,
The solid-state image sensor has a pixel array in which the pixels are arranged in a matrix,
The optical system forms an image of the object to be imaged on the pixel array.

This configuration allows for an increase in the amount of signal charge that a pixel can handle while suppressing the increase in noise in the signal read from the pixel, thereby obtaining high-quality images.

Furthermore, the imaging device according to this embodiment is
A solid-state image sensor having a plurality of pixels arranged in a matrix, each having at least one photoelectric conversion element that converts input light into photoelectric energy 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 image sensor,
A second circuit connected to the first circuit,
An optical system for forming an image of the object to be imaged on the solid-state image sensor,
It includes an output unit that outputs the captured image to an external device,
The amount of charge that can be handled in a single input at the floating node portion of each pixel is smaller than the amount of charge that can be handled in a single input at at least one photoelectric conversion element of the pixel.
The first circuit controls the pixels such that, for each input to the at least one photoelectric conversion element through the optical system, a first set operation is performed multiple times, which consists of transferring the signal charge from the at least one photoelectric conversion element to the floating node and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit, in response to a single input to at least one photoelectric conversion element, combines a signal corresponding to the voltage signal read from each pixel for each of the first set operations, for each pixel.
The output unit outputs the captured image generated based on the combined signal to the outside.

This configuration allows for an increase in the amount of signal charge that each pixel can handle while suppressing the increase in noise in the signal read from each pixel. As a result, a high-quality image is output (displayed, etc.) at the output unit.

Furthermore, the imaging device is
It is equipped with a mode switching section that allows switching between imaging modes.
The mode switching unit may be able to switch between a first mode in which the first set operation is performed multiple times and a second mode in which the first set operation is performed once.

This configuration allows for the selection (switching) of the imaging mode depending on the imaging scene. This enables power saving in the solid-state image sensor by reducing the number of initial setup operations, or improving the image quality of images obtained in dark environments by increasing the number of initial setup operations.

As described above, this embodiment provides a solid-state image sensor and an imaging device equipped with a solid-state image sensor that can increase the amount of signal charge that a pixel can handle while suppressing an increase in noise in the signal read from the pixel.

The first embodiment of the present invention will be described below with reference to the accompanying drawings.

The imaging device 100 according to the first embodiment comprises an optical system 101a and a solid-state image sensor 1, as shown in Figures 1 to 3. This solid-state image sensor 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. Each pixel 20 has at least one photoelectric conversion element 21 that converts input light into signal charge, a floating node section F to which the signal charge is transferred from the at least one photoelectric conversion element 21, and a reset section R that resets the signal charge of the floating node section F. This imaging device 100 is capable of imaging objects such as digital cameras, smartphones, and tablet devices. In this embodiment, the imaging device 100 is, for example, a smartphone.

Specifically, as shown in Figure 1, the imaging device 100 comprises 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.

The imaging unit 101, under the control of the control unit 102, converts the image of the object to be imaged, formed by the optical system 101a, into an electrical signal, performs noise reduction processing, and outputs the digital data as image data of the captured 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 image sensor 1 that converts the image of the object to be imaged, formed through the optical system 101a, into an electrical signal (i.e., captures an image).

The solid-state image sensor 1 is, for example, incorporated into a smartphone, digital camera, etc., and is an element for capturing an image of an object. In this embodiment, the solid-state image sensor 1 is, for example, a CMOS image sensor.

Specifically, as shown in Figure 2, this solid-state image sensor 1 includes 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. These pixel array 2, scanning circuit 3, and signal processing circuit 4 are arranged on the same semiconductor substrate or on multiple electrically connected semiconductor substrates.

The pixel array 2 has a plurality of pixels 20 arranged in a matrix in two dimensions. Furthermore, the pixel array 2 has a plurality of row signal lines L1 arranged row by row and extending in the row direction (left-right direction in Figure 2), and a plurality of column signal lines L2 arranged column by column and extending in the column direction (up-down direction in Figure 2). Each of these row signal lines L1 is connected to the first scanning circuit 31 of the scanning circuit 3, and each of the column signal lines L2 is connected to the second scanning circuit 32 of the scanning circuit 3.

Each of the multiple pixels 20, as shown in Figure 3, has at least one photoelectric conversion element 21 and a floating node 22 to which the signal charge generated by at least one photoelectric conversion element 21 is transferred. In the solid-state image sensor 1 of this embodiment, each pixel 20 has one photoelectric conversion element 21, which is, for example, a photodiode. In the pixel 20 of this embodiment, the floating node 22 constitutes the floating node section F described above.

The first charge amount C1 (see Figure 4), which is the amount of charge that can be handled in a single input at the floating node 22, is smaller than the second charge amount C2 (see Figure 4), which is the amount of charge that can be handled in a single input at the photoelectric conversion element 21. Here, a single input at the floating node 22 refers to a single transfer of signal charge from the photoelectric conversion element 21, and a single input at the photoelectric conversion element 21 refers to a single exposure during imaging. In this embodiment, the "handlable charge amount" is the maximum amount of charge that can ensure the quality of the obtained image (image data), and is a value defined by the input dynamic range of the scanning circuit 3, signal processing circuit 4, and each configuration after the signal processing circuit 4. It may differ from the "maximum charge amount," which is the maximum amount of charge that can be accumulated or stored in the configuration without considering the quality of the obtained image (noise, etc.).

Furthermore, each pixel 20 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 the reset power supply (reset potential) VDD1, an amplification transistor 25 that converts 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 the row signal line L2. These transfer transistors 23, reset transistor 24, and selection transistor 26 receive various drive signals φRES, φTX, and φSEL from the first scanning circuit 31 of the scanning circuit 3 via the row signal line L1.

In this pixel 20, the reset transistor 24 constitutes the reset section R described above. The amplifying transistor 25 has its gate electrode connected to the floating node 22 and its drain electrode connected to the power supply VDD2. This amplifying transistor 25 serves as the input to a readout circuit (a so-called source follower (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 it out (outputs it). Specifically, the source electrode of the amplifying transistor 25 is connected to the column signal line L2 via the selection transistor 26, thereby forming a source follower SF with a constant current source connected to one end of the column signal line L2.

Each of the multiple row signal lines L1 transmits a reset instruction signal φRES, a charge transfer signal φTX, and a select signal φSEL, respectively, to each connected pixel 20, which are output from the first scanning circuit 31.

Here, the reset instruction signal φRES is a signal to turn the reset transistor 24 ON/OFF to reset the charge (signal charge) of each pixel 20 (more specifically, the floating node 22); the charge transfer signal φTX is a signal to turn the transfer transistor 23 ON/OFF to transfer the signal charge of the photoelectric conversion element 21 to the floating node 22; and the select signal φSEL is a signal to turn the select transistor 26 ON/OFF to convert the charge amount of the 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.

Each of the multiple column signal lines L2 is connected to each pixel 20 in the corresponding column, and the voltage signal output from the pixel 20 is transmitted to the second scanning circuit 32.

The scanning circuit 3 comprises 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, and a select signal φSEL to each pixel 20. The second scanning circuit 32 performs signal processing such as noise reduction of the voltage signals read from each pixel 20, A/D (Analog/Digital) conversion of the read voltage signals, and sequentially transmits the converted signals to the signal processing circuit 4.

The signal processing circuit 4 is the part that performs various processing on each signal output from the second scanning circuit 32. In this embodiment, the signal processing circuit 4 is, for example, an in-sensor ISP (Image Signal Processor).

In the solid-state image sensor 1 described above, the scanning circuit 3 controls the pixel 20 so that, for each input to the photoelectric conversion element 21, a first set operation is performed multiple times. This first set operation consists 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 a voltage signal from the pixel 20 corresponding to the amount of signal charge transferred to the floating node 22. The signal processing circuit 4 then combines a signal corresponding to the voltage signal read from the pixel 20 for each first set operation for each input to the photoelectric conversion element 21, and outputs this combined signal.

Furthermore, during the readout of the voltage signal from the pixel 20, the scanning circuit 3 controls the pixel 20 so that, with each first set operation, it reads out the reset signal as a voltage signal with the floating node 22 reset, and then reads out the transferred charge amount signal as a voltage signal with the floating node 22 having received signal charge from the photoelectric conversion element 21 after the readout of the reset signal. The signal processing circuit 4 then generates the difference signal between the transferred charge amount signal and the reset signal as signals corresponding to the voltage signal with each first set operation. In other words, in the solid-state image sensor 1, so-called correlated double sampling (CDS) is performed during the readout of the voltage signal from each pixel 20.

The following explanation will be more detailed, referring to Figure 4. In the example shown in Figure 4, the first charge quantity C1 of the photoelectric conversion element 21 is Q1, and the first charge quantity C1 of the floating node 22 is Q2.

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

Next, in Step 2, the transfer transistor 23 is switched ON and OFF, transferring the signal charge accumulated in the photoelectric conversion element 21 (in the example shown in Figure 4, the signal charge with charge amount Q1) to the floating node 22. At this time, because 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; a portion (in the example shown in Figure 4, the signal charge with charge amount Q3) remains in the photoelectric conversion element 21. Here, the amount of signal charge transferred from the photoelectric conversion element 21 to the floating node 22 is Q2, and Q3 = Q1 - Q2.

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

Next, in Step 3, the reset transistor 24 is switched ON and OFF, resetting the signal charge accumulated in the floating node 22. The reset signal RL2, which is the voltage signal at that time, is read from the pixel 20 and recorded in the second scanning circuit 32.

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

In each of these steps, the reset 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 first set operation described above. In this embodiment, each pixel 20 performs two sets of the first set operation with a single input (imaging).

In the example shown in Figure 4, the first set operation is performed twice, transferring all the signal charge accumulated in the photoelectric conversion element 21 to the floating node 22 with a single input, thus emptying the photoelectric conversion element 21. However, the configuration is not limited to this. If the element is not empty after two transfers, Steps 3 and 4 may be repeated a predetermined number of times (a number set according to the second charge amount C2 of the photoelectric conversion element 21, i.e., a number set so that all the signal charge accumulated in the photoelectric conversion element 21 is transferred). In other words, the first set operation may be performed three or more times.

As described above, Steps 1 to 4 are performed (i.e., the first set operation is performed twice). Subsequently, the signal processing circuit 4 generates a difference signal (SL1 - RL1) between the transfer charge amount signal SL1 from Step 2 and the reset signal RL1 from Step 1, and also creates a difference signal (SL2 - RL2) between the transfer charge amount signal SL2 from Step 4 and the reset signal RL2 from Step 3. These difference signals are then combined. The signal processing circuit 4 then outputs this combined signal (Signal = (SL1 - RL1) + (SL2 - RL2): see Figure 4) to the subsequent configuration (control unit 102, etc.).

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

The control unit 102 controls each part of the imaging device 100 according to the input signals and program. The control unit 102 also generates an image (image data) from the signal output from the solid-state image sensor 1 (a signal obtained by combining the difference signals mentioned above) and outputs it to the display unit 106. Note that the control unit 102 is not limited to controlling the entire imaging device 100. A configuration in which multiple hardware components share the processing to control the entire imaging device 100 is also possible.

The non-volatile memory 103 is a non-volatile memory that can be electrically erased and recorded. In this embodiment, the non-volatile memory 103 stores the operating system (OS), which is the basic software executed by the control unit 102, and applications that work in cooperation with the OS to realize advanced functions.

The working memory 104 is used as the image display memory for the display unit 106 and as the working area for the control unit 102, etc.

The operation unit 105 is used for the user to input instructions for the imaging device 100. In this embodiment, the operation unit 105 includes a power button for instructing the ON/OFF of the imaging device 100, and a touch panel formed on the display unit 106.

The display unit 106 displays the captured image (image data) (outputs it externally) and displays text for operation, etc.

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

The connection section 108 is an interface for connecting to external devices. The imaging device 100 exchanges data with external devices via this connection section 108.

The short-range wireless communication unit 109 is a communication unit for performing short-range wireless communication. The short-range wireless communication unit 109 consists of an antenna for wireless communication, a modulation/demodulation circuit for processing wireless signals, and a communication controller.

The public network connection unit 110 is an interface for performing public wireless communication. Through this public network connection unit 110, the imaging device 100 communicates with other devices for communication. At this time, the control unit 102 realizes the communication by inputting and outputting audio signals via the microphone 111 and speaker 112. In this embodiment, the public network connection unit 110 is an antenna, and the control unit 102 connects to the public network via this antenna.

The solid-state image sensor 1 of the imaging device 100 described above comprises a pixel 20 having a photoelectric conversion element 21 that converts input light into photoelectric energy to generate a signal charge, a floating node section F (floating node 22 in this embodiment) to which the signal charge is transferred from the photoelectric conversion element 21, and a reset section R (reset transistor 24 in this embodiment) that resets the signal charge of the floating node section 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. The first charge amount C1, which is the amount of charge that can be handled in a single input at the floating node section F, is smaller than the second charge amount C2, which is the amount of charge that can be handled in a single input at the photoelectric conversion element 21. Furthermore, the scanning circuit 3 controls the pixel 20 so that, for each input to the photoelectric conversion element 21, the first set operation is performed multiple times. This first set operation consists of resetting the signal charge of the floating node F, transferring the signal charge from the photoelectric conversion element 21 to the floating node F, and reading out voltage signals (SL1, SL2) corresponding to the amount of signal charge transferred to the floating node F from the pixel 20. The signal processing circuit 4 then combines a signal corresponding to the voltage signal read out from the pixel 20 for each first set operation for each input to the photoelectric conversion element 21 (see Signal = (SL1 - RL1) + (SL2 - RL2) in Figure 4).

In this way, by making the first charge amount C1 smaller than the second charge amount C2 and configuring the system so that the first set operation is performed multiple times in a single input to the photoelectric conversion element 21, it is possible to increase the second charge amount (i.e., the amount of signal charge that the pixel 20 can handle in a single input) C2 while suppressing the increase in noise generated in the floating node section F, etc. That is, with the above configuration, it is possible to increase the amount of signal charge that the pixel 20 can handle while suppressing the increase in noise in the signal read from the pixel 20. As a result, in the imaging device 100 equipped with the solid-state image sensor 1, a high-resolution image is output (displayed, etc.) in the display unit (output unit) 106.

Furthermore, in the solid-state image sensor 1 of this embodiment, the scanning circuit (first circuit) 3 controls the pixel 20 so that, for each first set operation, it reads out the reset signals (RL1, RL2) as voltage signals when the floating node F (floating node 22 in this example) is reset, and then reads out the transferred charge amount signals (SL1, SL2) as voltage signals when the floating node F has received signal charge from the photoelectric conversion element 21 after the readout of the reset signals. The signal processing circuit (second circuit) 4 generates difference signals ((SL1-RL1), (SL2-RL2)) between the transferred charge amount signals and the reset signals as signals corresponding to the voltage signals for each first set operation. By configuring the scanning circuit 3 to generate difference signals (signals corresponding to the voltage signals) between the transferred charge amount signals and the reset signals for each first set operation, reset noise such as thermal noise in each signal (difference signal) coupled in the signal processing circuit 4 is suppressed, thereby obtaining higher-quality images.

Next, a second embodiment of the present invention will be described with reference to Figures 5 to 8. The same reference numerals will be used for components similar to those in the first embodiment, and components different from those in the first embodiment will be described in detail.

In the imaging device 100 of this embodiment, as shown in Figure 5, each pixel 20A of the solid-state image sensor 1 has multiple (four in this example) photoelectric conversion elements 21. In this pixel 20A, when the first photoelectric conversion element 21 is represented as PD0, the second as PD1, the third as PD2, and the fourth 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 Figure 6. In this embodiment, the floating node 22 constitutes the floating node section F, and the reset transistor 24 constitutes the reset section R.

In the solid-state image sensor 1 described above, as shown in Figure 5, the multiple photoelectric conversion elements PD0 to PD3 of each pixel 20A are divided into multiple groups (two in this embodiment) g1 and g2, and the signals for each group g1 and g2 are processed. In Figure 5, the type of smoke represents each group g1 and g2 of the photoelectric conversion elements PD0, PD1, PD2, and PD3.

In this embodiment, the first photoelectric conversion element PD0 and the second photoelectric conversion element PD1 are designated as the first group g1, and the third photoelectric conversion element PD2 and the fourth photoelectric conversion element PD3 are designated as the second group g2. In this example, as shown in Figure 7, the total handleable charge amount (third charge amount) C3, which is the sum of the handleable charge amount of the first photoelectric conversion element PD0 and the handleable charge amount of the second photoelectric conversion element PD1, is Q11, the total handleable charge amount (fourth charge amount) C4, which is the sum of the handleable charge amount of the third photoelectric conversion element PD2 and the handleable 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 of the third charge amount C3 and the fourth charge amount C4 (Q11 + Q12). In other words, if a single pixel 20A has multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, the second charge quantity C2 is the sum of the charge quantities that each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 can handle (the total value).

In this solid-state image sensor 1, the signal is processed as follows during imaging.

In Step 1, during imaging by the imaging device 100, an image of the object to be imaged is formed on the pixel array 2. That is, light (input light) is input to each of the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 in each pixel 20A. As a result, the input light is photoelectrically converted by each photoelectric conversion element PD0, PD1, PD2, and PD3, and a signal charge (in the example shown in Figure 8, signal charges of charge amounts Q11 and Q12 (third charge amount C3, fourth charge amount C4)) corresponding to the amount of input light is accumulated. In this state, the reset transistor 24 is switched ON and OFF, resetting the floating node 22 to the reset potential (the potential of the power supply VDD1). The reset signal RL1, which is the voltage signal at that time, is read from the pixel 20A and recorded in the second scanning circuit 32.

Next, in Step 2, the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are turned ON and OFF respectively, transferring the signal charge Q11 stored in the first and second photoelectric conversion elements PD0 and PD1 to the floating node 22. At this time, the signal charge Q12 stored in the third and fourth photoelectric conversion elements PD2 and PD3 has not been transferred to the floating node 22. Therefore, not all of the signal charge stored in the first to fourth photoelectric conversion elements PD0 to PD3 is transferred with a single input to the floating node 22, and a portion (in the example shown in Figure 8, the signal charge Q12 stored in the third and fourth photoelectric conversion elements PD2 and PD3) remains in the photoelectric conversion elements PD2 and PD3. In this state, when the selection transistor 26 is switched ON and OFF, the charge amount Q11 of the signal charge at the floating node 22 at that time is converted into a voltage signal (transferred charge amount signal) SL1 by the source follower SF, output to the column signal line L2, and recorded in the second scanning circuit 32.

Next, in Step 3, the reset transistor 24 is switched ON and OFF, resetting the signal charge accumulated in the floating node 22. The reset signal RL2, which is the voltage signal at that time, is read from the pixel 20A and recorded in the second scanning circuit 32.

Furthermore, in Step 4, the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2 and PD3 are switched ON and OFF, respectively. This transfers the signal charge Q12 that remained in the third and fourth photoelectric conversion elements PD2 and PD3 without being transferred to the floating node 22 in Step 2. As a result, the transferred charge amount signal (voltage signal) SL2, which is the converted signal charge Q12 accumulated in the floating node 22, is read from the pixel 20A and recorded in the second scanning circuit 32.

Here, 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 and PD1 in Step 2. However, in Step 4, 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, allowing these residual signal charges to be read out.

In this embodiment, in each step, the first set operation consists of resetting the floating node 22 in Steps 1 and 3, transferring signal charge from the photoelectric conversion elements PD0, PD1, PD2, and PD3 of groups g1 and g2 to the floating node 22 in Steps 2 and 4, and reading out a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge transferred and accumulated in the floating node 22. In this embodiment, each pixel 20A performs two sets of the first set operation with a single input (imaging).

After Steps 1 through 4 are performed (i.e., two sets of the first set operation are performed), the signal processing circuit 4 generates a difference signal (SL1 - RL1) between the transfer charge amount signal SL1 from Step 2 and the reset signal RL1 from Step 1. It also creates a difference signal (SL2 - RL2) between the transfer charge amount signal SL2 from Step 4 and the reset signal RL2 from Step 3, and combines these difference signals. The signal processing circuit 4 then outputs this combined signal (LCG signal = (SL1 - RL1) + (SL2 - RL2): see Figure 8) to the subsequent configuration (control unit 102, etc.).

According to the solid-state image sensor 1 of the imaging device 100 described above, similar to the first embodiment, by making the first charge amount C1 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 configuring the device so that the first set operation is performed multiple times in a single input to the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, it is possible to increase the second charge amount (i.e., the amount of signal charge that the pixel 20A can handle in a single input) C2, while suppressing the increase in noise generated in the floating node section (in this embodiment, the floating node 22), etc. In other words, according to the solid-state image sensor 1 of this embodiment, it is possible to increase the amount of signal charge that the pixel 20A can handle while suppressing the increase in noise in the signal read from the pixel 20A. As a result, in the imaging device 100 equipped with the solid-state image sensor 1, a high-quality image is output (displayed, etc.) in the display unit (output unit) 106.

Furthermore, in the solid-state image sensor 1 of this embodiment, each 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, amounts corresponding to the handleable charge amounts C3 and C4 for each group g1 and g2 of the photoelectric conversion elements 21).

With this configuration, when multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 accumulate signal charge up to the second charge amount C2 with a single input, the difference in charge amounts between the signal charges transferred to the floating node section F (floating node 22 in this embodiment) for each first set operation is suppressed. This makes it possible to suppress input-referred noise (including quantization errors, etc.) in the signal (image signal, etc.) output from the solid-state image sensor 1. Further details are as follows.

As in the first embodiment, if 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 (A/D converter, etc.) must be set to match the first set operation with the larger charge amount. In this case, the input dynamic range becomes larger, and as a result, the input-referred noise (including the quantization error of the A/D conversion) increases.

Therefore, in the solid-state image sensor 1 of this embodiment, the number of photoelectric conversion elements PD0, PD1, PD2, and PD3 that are transferred simultaneously is controlled to suppress the difference in charge amounts between the signal charges transferred to the floating node 22 for each first set operation.

Specifically, in each pixel 20A of this embodiment, the four photoelectric conversion elements PD0, PD1, PD2, and PD3 are divided into two groups, a first group g1 and a second group g2. For each input to the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, signal charge is transferred to the floating node 22 for each group g1 and g2 (75,000 electrons are transferred at a time). This allows for suppressing (reducing) the input dynamic range of the subsequent readout system (A/D converter, etc.), thereby suppressing input-referred noise (including quantization errors, etc.), and consequently obtaining high-quality captured images.

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 components similar to those in the first and second embodiments, while components different from those in the first and second embodiments will be described in detail.

In the imaging device 100 of this embodiment, similar to the second embodiment, each pixel 20B of the solid-state image sensor 1 has multiple (four in this example) photoelectric conversion elements PD0, PD1, PD2, and PD3 (see Figure 9). Furthermore, as shown in Figure 10, each pixel 20B has a retaining capacitor 27 and a switch transistor 28. This retaining capacitor 27 is connected to the floating node 22 via the switch transistor 28 and also to the reset power supply VDD1 via the reset transistor 24.

Furthermore, the pixel 20B of this embodiment has a gain switching unit G that switches the conversion gain of the signal charge amount 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. The floating node unit F of this embodiment is composed of a floating node 22 and a holding capacitor 27, and the gain switching unit G is composed of a switch transistor 28. The reset unit R is composed of a reset transistor 24.

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

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

In the above-described pixel 20B, the first scanning circuit 31 of the scanning circuit 3 controls the pixel 20B such that it performs the following actions in each first set operation: resetting the floating node F, transferring signal charge to the floating node F, and reading out the amount of signal charge accumulated in the floating node F (converting the amount of charge into a voltage signal) in a low-gain state, while performing a second set operation, which is a set in which the reset, transfer, and reading are performed in a high-gain state, between the reset and the reading in the first set operation.

Furthermore, the second scanning circuit 32 outputs a signal corresponding to the voltage signal read out in the second set operation, or outputs a combined signal corresponding to the voltage signals read out in each of the first set operations, depending on the amount of signal charge generated in each photoelectric conversion element PD0, PD1, PD2, and PD3 by a single input.

In the solid-state image sensor 1 described above, similar to the second embodiment, the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 of each pixel 20B are divided into multiple groups (two in this embodiment) g1 and g2, and the signals for each group g1 and g2 are processed (see Figure 9). In Figure 9, the type of smoke represents each group g1 and g2 of the photoelectric conversion elements PD0, PD1, PD2, and PD3.

In this embodiment, as in the second embodiment, the first photoelectric conversion element PD0 and the second photoelectric conversion element PD1 are designated as the first group g1, and the third photoelectric conversion element PD2 and the fourth photoelectric conversion element PD3 are designated as the second group g2. In this example, as shown in Figure 11, the total handleable charge amount (third charge amount) C3, which is the sum of the handleable charge amount of the first photoelectric conversion element PD0 and the handleable charge amount of the second photoelectric conversion element PD1, is Q21, and the total handleable charge amount (fourth charge amount) C4, which is the sum of the handleable charge amount of the third photoelectric conversion element PD2 and the handleable charge amount of the fourth photoelectric conversion element PD3, is Q22. At this time, the second charge amount C2 is the sum of the third charge amount C3 and the fourth charge amount C4 (Q21 + Q22), as in the second embodiment. In other words, if a single pixel 20B has multiple photoelectric conversion elements PD0, PD1, PD2, and PD3, the second charge quantity C2 is the sum of the charge quantities that each of the photoelectric conversion elements PD0, PD1, PD2, and PD3 can handle (the total value).

Furthermore, the first charge amount C1(HCG) in the high-gain state of the floating node F (i.e., when the switch transistor 28 is OFF) 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 Figure 11). Note that, as in the solid-state image sensor 1 of this embodiment, in the case where the conversion gain when the charge amount of the signal charge in the floating node F is converted into a voltage signal (transferred charge amount signal) is switchable, the maximum value of the transferred signal charge amount (maximum charge amount) when the charge amount of the signal charge transferred from the photoelectric conversion element 21 to the floating node F in the high-gain state is sufficiently larger than the first charge amount C1(HCG) is Qmax. However, C1(LCG) > Qmax > C1(HCG). Furthermore, 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 resulting image (such as the input dynamic range of subsequent circuits).

In this solid-state image sensor 1, the signal is processed as follows during imaging.

In Step 1, during imaging by the imaging device 100, an image of the object to be imaged is formed on the pixel array 2. That is, light (input light) is input to each of the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 in each pixel 20B. As a result, the input light is photoelectrically converted by each photoelectric conversion element PD0, PD1, PD2, and PD3, and a signal charge (in the example shown in Figure 12, signal charges of charge amounts Q21 and Q22 (third charge amount C3, fourth charge amount C4)) corresponding to the amount of input light is accumulated. At this time, with the switch transistor 28 ON, the reset transistor 24 is turned ON and OFF, resetting the low-gain floating node section F (floating node 22 and holding capacitor 27) to the reset potential. The reset signal RL1, which is the voltage signal at that time, is read from the pixel 20B and recorded in the second scanning circuit 32.

Next, in Step 2, while each photoelectric conversion element PD0, PD1, PD2, and PD3 retains the accumulated signal charge, the reset transistor 24 is switched ON and OFF with the switch transistor 28 OFF. This resets the high-gain floating node section F (floating node 22) to the reset potential, and the reset signal RH, which is the voltage signal at that time, is read from the pixel 20B and recorded in the second scanning circuit 32.

Next, in Step 3, with the floating node F in a high-gain state, the signal charges accumulated in each photoelectric conversion element PD0, PD1, PD2, and PD3 are transferred to the floating node F by switching each transfer transistor 23 ON and OFF.

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

On the other hand, when the total charge amount of the signal charge accumulated in all photoelectric conversion elements PD0, PD1, PD2, and PD3 is less than or equal to the maximum charge amount Qmax of the floating node F in the high-gain state, all the signal charge accumulated in each photoelectric conversion element PD0, PD1, PD2, and PD3 is transferred to the floating node F.

In the example shown in Figure 12, all signal charges accumulated in each photoelectric conversion element PD0, PD1, PD2, and PD3 are transferred to the floating node F until the total charge amount of the signal charges accumulated in each element reaches the maximum charge amount Qmax (see Step 3 in Figure 12). However, because the resulting voltage signal exceeds the input dynamic range of the subsequent circuitry, when the charge amount of the signal charges transferred to the floating node F is greater 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. Instead, 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 charges transferred to the floating node F is less than or equal to 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.

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

Next, in Step 4, after the switch transistor 28 is turned OFF and the floating node F is switched to a low-gain state, the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are turned ON and OFF respectively, transferring the signal charge accumulated in the first and second photoelectric conversion elements PD0 and PD1 to the floating node F. In this transfer, since signal charge (a portion of the signal charge accumulated in each photoelectric conversion element PD0, PD1, PD2, and PD3) is transferred to the floating node F from each photoelectric conversion element PD0, PD1, PD2, and PD3 when in the high-gain state, not all of the signal charge in the first and second photoelectric conversion elements PD0 and PD1 is transferred (in the example shown in Figure 12, a signal charge of charge amount Q26 is transferred), and some signal charge remains (in the example shown in Figure 12, a signal charge of charge amount Q25 remains). Here, Q25 = Q23 - Q26.

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

Then, in this state, the selection transistor 26 is switched ON and OFF, and the amount of signal charge of the floating node F at this time (in the example shown in Figure 12, the signal charge of charge amount Q27) is converted by the source follower SF into a transferred 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 this embodiment, the charge amount Q27 is slightly larger than the first charge amount C1(LCG) of the floating node F in the low-gain state, which is Q(LCG).

Next, in Step 5, the reset transistor 24 is switched ON and OFF, resetting the signal charge accumulated in the floating node F. The reset signal RL2, which is the voltage signal at that time, is read from pixel 20B and recorded in the second scanning circuit 32.

Furthermore, in Step 6, while the floating node F remains in a low-gain state, the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2 and PD3 are switched ON and OFF respectively, transferring the signal charge remaining in the third and fourth photoelectric conversion elements PD2 and PD3 (in the example shown in Figure 12, the signal charge of charge amount Q24) to the floating node F. Also, in Step 6, when the transfer transistors 23 of the third and fourth photoelectric conversion elements PD2 and PD3 are switched ON and OFF respectively, the transfer transistors 23 of the first and second photoelectric conversion elements PD0 and PD1 are also switched ON and OFF, thereby transferring the signal charge remaining in the first and second photoelectric conversion elements PD0 and PD1 that was not transferred to the floating node F in Step 4 (in the example shown in Figure 12, the signal charge of charge amount Q25) to the floating node F. As a result, the floating node F accumulates a signal charge of charge amount Q28. Here, Q28 = Q24 + Q25.

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

In this embodiment, in each step, the first set operation consists of resetting the floating node F in a low-gain state in Steps 1 and 5, transferring signal charge from the photoelectric conversion elements PD0, PD1, PD2, and PD3 to the floating node F in the low-gain state in Steps 4 and 6, and reading out a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge accumulated in the floating node F in the low-gain state. In this embodiment, each pixel 20B performs two sets of the first set operation with a single input (imaging).

Furthermore, the reset of the floating node F in the high-gain state in Step 2, the transfer of signal charge from each photoelectric conversion element PD0, PD1, PD2, and PD3 to the floating node F in the high-gain state in Step 3, and the reading out of a voltage signal (transferred charge amount signal) corresponding to the amount of signal charge accumulated in the floating node F in the high-gain state constitute the second set operation. The second set operation is performed between the reset and the reading in the first set operation, or more specifically, between the reset and the transfer.

After Steps 1 through 6 are completed, if the transfer charge amount signal SH read in Step 3 (readout of the second set operation) is less than or equal to the voltage signal corresponding to the first charge amount C1 (HCG) of the high-gain floating node section F (floating node 22), the signal processing circuit 4 generates a difference signal (SH - RL) between the transfer charge signal SH from Step 3 and the reset signal RH from Step 2. This generated difference signal (signal corresponding to the transfer charge signal SH read in the second set operation / HCG signal = (SH - RL): see Figure 12) is then output to the subsequent configuration (control unit 102, etc.).

On the other hand, if the transfer charge amount signal SH read out in Step 3 (readout of the second set operation) is greater than the voltage signal corresponding to the first charge amount C1 (HCG) of the floating node section F (floating node 22) in a high-gain state, the signal processing circuit 4 generates a difference signal (SL1-RL1) between the transfer charge amount signal SL1 from Step 4 and the reset signal RL1 from Step 2, and also generates a difference signal (SL2-RL2) between the transfer charge amount signal SL2 from Step 6 and the reset signal RL2 from Step 5. These difference signals are then combined, and this combined signal (LCG signal = (SL1-RL1) + (SL2-RL2): see Figure 12) is output to the subsequent configuration (control unit 102, etc.).

According to the solid-state image sensor 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 this embodiment, the sum of the third charge amount C3 and the fourth charge amount C4), and by configuring the system so that the first set operation is performed multiple times with a single input to the photoelectric conversion elements PD0, PD1, PD2, and PD3, it is possible to suppress the increase in noise generated in the floating node section F, etc., when the first charge amount C1 (LCG) in the low-gain state (i.e., the amount of signal charge that the pixel 20B can handle with a single input) is increased. In other words, according to the solid-state image sensor 1 of this embodiment, it is possible to increase the amount of signal charge that the pixel 20B can handle while suppressing the increase in noise in the signal read out from the pixel 20B. As a result, in the imaging device 100 equipped with the solid-state image sensor 1, a high-quality image is output (displayed, etc.) in the display unit (output unit) 106.

Furthermore, in the solid-state image sensor 1 of this embodiment, the pixel 20B has a gain switching unit G (switch transistor 28) that switches the conversion gain of the signal charge amount 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 becomes possible to select the voltage signal used for image processing according to the amount of input light from the voltage signals obtained at each gain (SH-RH, (SL1-RL1) + (SL2-RL2), etc.), thereby improving the image quality of the captured image.

Furthermore, in the solid-state image sensor 1 of this embodiment, the scanning circuit (first circuit) 3 controls the pixels 20B so that it performs multiple first set operations, in which reset, transfer, and readout are performed in a low-gain (second conversion gain) state, and a second set operation, in which reset, transfer, and readout are performed in a high-gain (first conversion gain) state, is performed between the reset and readout in the first set operation. 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, based on the total charge amount of the signal charge generated in the photoelectric conversion elements PD0, PD1, PD2, and PD3 by a single input, or outputs a combined signal ((SL1-RL1) + (SL2-RL2)) corresponding to the transfer charge amount signals (voltage signals) SL1 and SL2 read out for each first set operation.

With this configuration, for example, when the input light intensity is low and all of the signal charge converted photoelectrically by the multiple photoelectric conversion elements PD0, PD1, PD2, and PD3 is transferred to the high-gain floating node section F in a single pass, the signal output from the signal processing circuit 4 is used for image processing. This allows for the acquisition of high-quality images even when imaging in low-light conditions, such as dark scenes.

Furthermore, the solid-state image sensor 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 spirit of the invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Moreover, a part of the configuration of one embodiment can be deleted.

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

Thus, by equipping the imaging device with a mode switching unit, the imaging mode can be selected (switched) depending on the imaging scene. This allows for power saving in the solid-state image sensor 1 by reducing the number of initial setup operations, or for improving the image quality of images obtained in dark places, etc., by increasing the number of initial setup operations.

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

Furthermore, in the imaging device 100 of the first to third embodiments described above, the solid-state image sensor 1 is equipped with a scanning circuit (first circuit) 3 and a signal processing circuit (second circuit) 4, but the configuration is not limited to this.
At least one of the first and second circuits may be located in a position separate from the solid-state image sensor 1 in the imaging device. For example, the imaging device 100 may have a configuration comprising a solid-state image sensor 1, a first circuit 3, a second circuit 4, an optical system 101a, and a display unit (output unit) 106, or a configuration comprising a solid-state image sensor 1 having a first circuit 3, a second circuit 4, an optical system 101a, and a display unit (output unit) 106. With these configurations as well, it is possible to increase the amount of signal charge that each pixel 20 can handle while suppressing the increase in noise in the signal read out from each pixel 20, thereby enabling the display unit (output unit) 106 to output (display, etc.) a high-quality image.

To illustrate the present invention, the embodiments have been adequately and fully described above with reference to the drawings. However, those skilled in the art should recognize that modifying and/or improving the above-described embodiments is easily achievable. Therefore, unless such modifications or improvements implemented by those skilled in the art deviate from the scope of the claims, they shall be considered to be included within the scope of those claims.

1...Solid-state image sensor, 2...Pixel array, 20, 20A, 20B...Pixel, 21...Photoelectric conversion element, 22...Floating node, 23...Transfer transistor, 24...Reset transistor, 25...Amplification transistor, 26...Selection transistor, 27...Holding capacitor, 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 unit, 101a...Optical system, 102...Control unit, 103...Non-volatile memory, 104...Working memory, 105...Operation unit, 106...Display unit (Output unit), 107...Recording medium, 108...Connection unit, 109...Short-range wireless communication unit, 110...Public network connection unit, 111...Microphone, 11 2…Speaker, C1…First charge quantity, C2…Second charge quantity, C3…Third charge quantity, C4…Fourth charge quantity, 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 quantity 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 (6)

A pixel having at least one photoelectric conversion element that converts input light into photoelectric energy to generate a signal charge, a floating node portion to which the signal charge is transferred from the at least one photoelectric conversion element, and a reset portion for resetting the signal charge in the floating node portion,
A first circuit connected to the aforementioned pixel,
The circuit comprises a second circuit connected to the first circuit,
The first charge amount, which is the amount of charge that can be handled in a single input at the floating node portion, is smaller than the second charge amount, which is the amount of charge that can be handled in a single input at the at least one photoelectric conversion element.
The first circuit controls the pixel such that, for each input to the at least one photoelectric conversion element, a first set operation is performed multiple times, which is a set of operations consisting of resetting the signal charge of the floating node, transferring the signal charge from the at least one photoelectric conversion element to the floating node, and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit combines a signal corresponding to the voltage signal read from the pixel for each of the first set operations with a single input to the at least one photoelectric conversion element.
The pixel has a gain switching unit that changes the first charge amount to switch the conversion gain of the charge amount of the signal charge transferred to the floating node unit to the voltage signal between a first conversion gain and a second conversion gain lower than the first conversion gain .
The first circuit controls the pixels such that the reset, transfer, and read operation in each first set operation are performed in the state of the second conversion gain, and the second set operation, which is a set in which the reset, transfer, and read operation are performed in the state of the first conversion gain, is performed between the reset and read operation in the first set of the first set operation.
The second circuit is a solid-state image sensor that outputs a signal corresponding to the voltage signal read out in the second set operation, or outputs a combined signal corresponding to the voltage signal read out each time the first set operation is performed, depending on the amount of charge of the signal charge generated in the at least one photoelectric conversion element by a single input . The first circuit controls the pixel such that, for each first set operation, the floating node unit reads out the reset signal as a voltage signal when it is in the reset state, and after the reading of the reset signal, the floating node unit reads out the transferred charge amount signal as a voltage signal when it has received the signal charge from at least one photoelectric conversion element.
The solid-state image sensor according to claim 1, wherein the second circuit generates a difference signal between the transferred charge amount signal and the reset signal as a signal corresponding to the voltage signal for each of the first set operations. The aforementioned pixel has a plurality of photoelectric conversion elements,
The solid-state image sensor according to claim 1 or 2, wherein the first charge amount is an amount corresponding to the number of photoelectric conversion elements. Optical system and
A solid-state image sensor according to claim 1 or 2, comprising:
The solid-state image sensor has a pixel array in which the pixels are arranged in a matrix,
The optical system is an imaging device that forms an image of an object to be imaged on the pixel array. A solid-state image sensor having a plurality of pixels arranged in a matrix, each having at least one photoelectric conversion element that converts input light into photoelectric energy 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 image sensor,
A second circuit connected to the first circuit,
An optical system for forming an image of the object to be imaged on the solid-state image sensor,
It includes an output unit that outputs the captured image to an external device,
The amount of charge that can be handled in a single input at the floating node portion of each pixel is smaller than the amount of charge that can be handled in a single input at at least one photoelectric conversion element of the pixel.
The first circuit controls the pixels such that, for each input to the at least one photoelectric conversion element through the optical system, a first set operation is performed multiple times, which consists of transferring the signal charge from the at least one photoelectric conversion element to the floating node and reading out a voltage signal from the pixel corresponding to the amount of the signal charge transferred to the floating node.
The second circuit, in response to a single input to at least one photoelectric conversion element, combines a signal corresponding to the voltage signal read from each pixel for each of the first set operations, for each pixel.
The output unit outputs the captured image generated based on the combined signal to the outside.
The pixel has a gain switching unit that changes the first charge amount to switch the conversion gain of the charge amount of the signal charge transferred to the floating node unit to the voltage signal between a first conversion gain and a second conversion gain lower than the first conversion gain .
The first circuit controls the pixels such that the reset, transfer, and read operation in each first set operation are performed in the state of the second conversion gain, and the second set operation, which is a set in which the reset, transfer, and read operation are performed in the state of the first conversion gain, is performed between the reset and read operation in the first set of the first set operation.
The imaging device wherein the second circuit outputs a signal corresponding to the voltage signal read out in the second set operation, or outputs a combined signal corresponding to the voltage signal read out each time the first set operation is performed, depending on the amount of charge of the signal charge generated in the at least one photoelectric conversion element by a single input . It is equipped with a mode switching section that allows switching between imaging modes.
The imaging apparatus according to claim 4 , wherein the mode switching unit can switch between a first mode in which the first set operation is performed multiple times and a second mode in which the first set operation is performed once.