Solid-state imaging element, imaging device, and method for controlling solid-state imaging element

The computation time in a solid-state imaging element that performs a convolution operation on image data is shortened and the power consumption is reduced. A plurality of pixels are arranged in a two-dimensional lattice pattern in a pixel array unit. A coefficient holding unit holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest. A scanning circuit performs control so that the adjacent pixel generates an amount of charge corresponding to the weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest and performs control so that the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International Patent Application No. PCT/JP2020/007303 filed on Feb. 25, 2020, which claims priority benefit of Japanese Patent Application No. JP 2019-107768 filed in the Japan Patent Office on Jun. 10, 2019. Each of the above-referenced applications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present technology relates to a solid-state imaging element. More specifically, the present invention relates to a solid-state imaging element that performs image processing, an imaging device, and a control method for the solid-state imaging element.

BACKGROUND ART

Conventionally, a convolutional neural network (CNN) has been used for the purpose of improving recognition accuracy in image recognition and voice recognition. CNN is a process of executing a convolutional operation on input data using a matrix in which weighting coefficients of N rows×N columns (N is an integer) called kernels (or filters) are arranged for each of a predetermined number of stages of layers. In image recognition, CNN is mainly performed using a kernel having a minimum size of 3 rows×3 columns (see, for example, NPL 1). This is because the receptive fields of kernels having a size larger than 3 rows×3 columns can be covered by increasing the number of layers, and in neural networks, non-linear operations are performed in each layer, so it is more expressive to repeat convolution with the minimum number of parameters.

CITATION LIST

Non Patent Literature

SUMMARY

Technical Problem

In the above-mentioned conventional technique, the image recognition accuracy is improved using the result of the convolution operation performed in a large number of layers as a feature amount. However, since the convolution operation is executed in order for respective pixels, there is a problem that if a certain number of layers are required to obtain sufficient image recognition accuracy, the amount of computation increases as the number of pixels increases under the certain number of layers, the computation time increases, and the power required for the calculation increases.

The present technology has been made in view of such the above-described problem and an object thereof is to shorten the computation time and reduce the power consumption in a solid-state imaging element that performs a convolution operation on image data.

Solution to Problem

The present technology has been made to solve the above-described problems, and a first aspect thereof provides a solid-state imaging element and a method of controlling the same, the solid-state imaging element including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; and a scanning circuit that performs control so that the adjacent pixel generates an amount of charge corresponding to the weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest and performs control so that the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge. This has the effect that a signal in which the amounts of charge corresponding to the weighting coefficients of the pixel of interest and the adjacent pixels are added is generated.

Further, in the first aspect, the plurality of pixels may be arranged in a two-dimensional lattice pattern. This has the effect that a signal in which the amounts of charge corresponding to the weighting coefficients of nine pixels are added is generated.

Further, in the first aspect, the plurality of pixels may be arranged in a honeycomb pattern. This has the effect that a signal in which the amounts of charge corresponding to the weighting coefficients of seven pixels are added is generated.

Further, in the first aspect, each of the plurality of pixels may include: a photoelectric conversion element that generates the charge by photoelectric conversion; a charge holding portion that holds the charge; an internal transfer transistor that internally transfers the charge from the photoelectric conversion element to the charge holding portion; and the predetermined number of external transfer transistors that externally transfer the charge from the photoelectric conversion element to surrounding pixels among the plurality of pixels. This has the effect that a signal in which the externally transferred charge is added to the internally transferred charge is generated.

Further, in the first aspect, the charge holding portion may be a capacitor. This has the effect that a signal corresponding to the potential of the capacitor is generated.

Further, in the first aspect, the charge holding portion may be a floating diffusion layer. This has the effect that a signal corresponding to the potential of the floating diffusion layer is generated.

Further, in the first aspect, the scanning circuit may cause the predetermined number of adjacent pixels and the pixel of interest to start generating of the charge at different timings. This has the effect that the pixel signal is generated by the pixel of interest and the adjacent pixels whose exposure is started at different timings.

Further, in the first aspect, the scanning circuit may cause the predetermined number of adjacent pixels and the pixel of interest to start generating of the charge at the same timing. This has the effect that a pixel signal is generated by the pixel of interest and the adjacent pixels whose exposure is started at the same time.

Further, in the first aspect, the pixel array unit may be divided into a plurality of windows having a predetermined size, and each of the plurality of windows outputs a pixel signal corresponding to the statistic of the amount of the charge accumulated in each of the pixels in the window. This has the effect that the number of pieces of data is reduced.

Further, on the first aspect, the solid-state imaging element may further include an image processing unit that performs a predetermined convolution operation on the image data output by the pixel array unit. This has the effect that CNN is realized.

A second aspect of the present technology provides an imaging device including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; a scanning circuit that performs control so that the adjacent pixel generates an amount of charge corresponding to the weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest and performs control so that the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge; and an image processing unit that performs predetermined processing on the image data output by the pixel array unit. This has the effect that predetermined processing is executed on the image data composed of the pixel signal in which the amounts of charge corresponding to the weighting coefficients are added.

A third aspect of the present technology provides an imaging device including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; an actuator that changes positions of the plurality of pixels to positions different from predetermined initial positions in pixels units; and a scanning circuit that performs control so that each of the plurality of pixels at the initial positions generates an amount of charge corresponding to the weighting coefficient corresponding to the pixel of interest and performs control so that, each time the position of the pixel array unit is changed, an amount of charge corresponding to the weighting coefficient corresponding to the adjacent pixel related to the changed position is generated. This has the effect that by changing the positions in pixel units, a signal in which the amounts of charge corresponding to the weighting coefficients of the pixel of interest and the adjacent pixels are added is generated.

DESCRIPTION OF EMBODIMENTS

Hereinafter, modes for carrying out the present technique (hereinafter referred to as embodiments) will be described. The description will be made in the following order.1. First Embodiment (Example in which pixel generates amount of charge corresponding to weighting coefficient)2. Second Embodiment (Example in which pixels arranged in honeycomb form generate amount of charge corresponding to weighting coefficient)3. Third Embodiment (Example in which pixel generates amount of charge corresponding to weighting coefficient each time position is changed in pixel units)4. Application Example to Moving Body

1. First Embodiment

FIG.1is a block diagram illustrating a configuration example of an imaging device100according to a first embodiment of the present technology. The imaging device100is a device for capturing image data, and includes an optical unit110, a solid-state imaging element200, and a DSP (Digital Signal Processing) circuit120. The imaging device100further includes a display unit130, an operating unit140, a bus150, a frame memory160, a storage unit170, and a power supply unit180. As the imaging device100, for example, in addition to a digital camera such as a digital still camera, a smartphone, a wearable device, a personal computer, an in-vehicle camera, or the like may be used.

The optical unit110collects the light from a subject and guides the light to the solid-state imaging element200. The solid-state imaging element200generates image data by photoelectric conversion in synchronization with a vertical synchronization signal VSYNC. The vertical synchronization signal VSYNC is a periodic signal having a predetermined frequency indicating the imaging timing. The solid-state imaging element200supplies the generated image data to the DSP circuit120via a signal line209. The solid-state imaging element executes image processing such as image recognition on the image data as necessary, and supplies the processed data to the DSP circuit120.

The DSP circuit120executes predetermined signal processing on the image data from the solid-state imaging element200. The DSP circuit120outputs the processed image data to the frame memory160or the like via the bus150.

The display unit130displays image data. As the display unit130, for example, a liquid crystal panel or an organic EL (Electro Luminescence) panel may be used. The operating unit140generates an operation signal according to the operation of the user.

The bus150is a common route for the optical unit110, the solid-state imaging element200, the DSP circuit120, the display unit130, the operating unit140, the frame memory160, the storage unit170, and the power supply unit180to exchange data with each other.

The frame memory160holds image data. The storage unit170stores various kinds of data such as image data. The power supply unit180supplies power to the solid-state imaging element200, the DSP circuit120, the display unit130, and the like.

FIG.2is a block diagram illustrating a configuration example of the solid-state imaging element200according to the first embodiment of the present technology. The solid-state imaging element200includes a row scanning circuit210, a pixel array unit220, a coefficient holding unit230, a DAC (Digital to Analog Converter)250, a signal processing unit260, a timing control unit270, a column scanning circuit280, and an image processing unit290.

A plurality of pixels are arranged in a two-dimensional lattice pattern in the pixel array unit220. The coefficient holding unit230holds a weighting coefficient that constitutes a kernel of a predetermined size. The size of the kernel is, for example, 3 rows×3 columns.

The row scanning circuit210sequentially drives the rows in the pixel array unit220according to a mode signal MODE to generate a pixel signal. Here, the mode signal MODE is a signal indicating one of a plurality of modes including an image recognition mode in which image recognition is executed and a normal mode in which image recognition is not performed. The mode signal MODE is generated by, for example, the DSP circuit120.

In the image recognition mode, the row scanning circuit210reads the weighting coefficient from the coefficient holding unit230. Then, the row scanning circuit210simultaneously generates an amount of charge corresponding to the weighting coefficient for all the pixels in the pixel array unit220, and externally transfers the charge to the adjacent pixels. Here, “external transfer” means transferring charge between pixels. The row scanning circuit210simultaneously generates an amount of charge corresponding to the weighting coefficient for all the pixels and accumulates the charge together with the externally transferred charge. Next, the row scanning circuit210drives the rows in order to output a pixel signal corresponding to the amount of accumulated charge to the signal processing unit260.

On the other hand, in the normal mode, the row scanning circuit210generates and accumulates charge for all the pixels over the exposure period without using the weighting coefficient. Then, the row scanning circuit210drives the rows in order to output a pixel signal corresponding to the amount of accumulated charge to the signal processing unit260.

The row scanning circuit210is an example of a scanning circuit described in the claims.

The timing control unit270controls the operation timings of the row scanning circuit210, the DAC250, the signal processing unit260, and the column scanning circuit280in synchronization with the vertical synchronization signal VSYNC.

The DAC250generates a predetermined reference signal that changes in a slope with the passage of time by DA (Digital to Analog) conversion. The DAC250supplies the generated reference signal to the pixel array unit220.

The signal processing unit260performs predetermined signal processing including AD (Analog to Digital) conversion on the pixel signal from the pixel array unit220for each column. The signal processing unit260supplies the processed pixel data to the image processing unit290.

The column scanning circuit280drives the signal processing unit260under the control of the timing control unit270to sequentially output pixel data.

The image processing unit290executes predetermined image processing on the image data composed of the pixel data. In the image recognition mode, the image processing unit290executes a predetermined convolution operation on the image data, and executes image recognition processing using the calculated data. On the other hand, in the normal mode, the image processing unit290executes various kinds of image processing such as demosaic processing and white balance processing. Then, the image processing unit290supplies the processed data to the DSP circuit120.

The DSP circuit120may execute at least a part of the processing of the image processing unit290.

FIG.3is a diagram illustrating an example of a kernel according to the first embodiment of the present technology. The number of rows in the pixel array unit220is I (I is an integer), and the number of columns is J (J is an integer). When focusing on a pixel in a certain i-th (i is an integer of 0 to I−1) row and j-th (j is an integer of 0 to J−1) column in the pixel array unit220, a predetermined weighting coefficient to be applied is set to each of the pixel of interest and a predetermined number of adjacent pixels adjacent to the pixel of interest. For example, a weighting coefficient is set to each of nine pixels at the addresses of (i−1, j−1), (i−1, j), (i−1, j+1), (i, j−1), (i, j), (i, j+1), (i+1, j−1), (i+1, j) and (i+1, j+1). These weighting coefficients are w0to w8. The coefficient holding unit230holds the weighting coefficients w0to w8.

The set of weighting coefficients illustrated in the drawing is generally called a kernel (or filter). The number of weighting coefficients in the kernel, in other words, the number of pixels to which the kernel is applied, corresponds to the size of the kernel.

[Configuration Example of Pixel Array Unit]

FIG.4is a diagram illustrating a configuration example of the pixel array unit220according to the first embodiment of the present technology. In the pixel array unit220, a plurality of pixels such as pixels300,310,320,330,340,350,360,370, and380are arranged in a two-dimensional lattice pattern.

The kernel is applied to nine pixels including a pixel of interest and eight adjacent pixels therearound using each of all the pixels in the pixel array unit220as the pixel of interest. For example, focusing on the pixel340, the pixels300,310,320,330,350,360,370and380are adjacent to the pixel340. Here, “adjacent” means that the Euclidean distance from the pixel of interest is within a certain value. The kernel is applied to a pixel block505of nine pixels of 3 rows×3 columns including the pixel of interest and eight adjacent pixels therearound.

Further, when focusing on the pixel350, the kernel is applied to the pixel350and eight pixels (the pixel340or the like) adjacent to the pixel350. The same applies to other pixels.

The adjacent pixel (the pixel300or the like) generates an amount of charge corresponding to the weighting coefficient corresponding to the adjacent pixel under the control of the row scanning circuit210and transfers the charge to the pixel of interest externally. The pixel of interest (the pixel340or the like) generates an amount of charge corresponding to the weighting coefficient corresponding to the pixel of interest under the control of the row scanning circuit210, and accumulates the charge together with the externally transferred charge. For example, when the weighting coefficient w0of the adjacent pixel is 1.5 times the weighting coefficient w4of the pixel of interest, the row scanning circuit210sets the exposure time of the pixel300to 1.5 times the pixel340, and the pixels are exposed in order. By setting the exposure time to a time proportional to the weighting coefficient in this way, an amount of charge corresponding to the weighting coefficient is generated. By integrating these charges, a convolutional operation of the 0-th layer in CNN is performed. The convolution operation after the first and subsequently layers is executed by the image processing unit290.

[Configuration Example of Pixel Circuit]

FIG.5is a circuit diagram illustrating a configuration example of the pixel340according to the first embodiment of the present technology. The pixel340includes a photoelectric conversion element341, a transfer transistor342, a capacitor343, an operational amplifier344and a reset switch345, and transfer transistors410,411,412,413,415,416,417and418.

The photoelectric conversion element341generates charge by photoelectric conversion. As the photoelectric conversion element341, for example, a photodiode is used.

The transfer transistor342internally transfers the charge from the photoelectric conversion element341to the capacitor343according to the transfer signal SW4from the row scanning circuit210. Here, “internal transfer” means transferring charge between elements in a pixel.

The transfer transistor410externally transfers the charge from the photoelectric conversion element341to the adjacent pixel300according to a transfer signal SW0from the row scanning circuit210. The transfer transistor411externally transfers the charge from the photoelectric conversion element341to the adjacent pixel310according to a transfer signal SW1from the row scanning circuit210. The transfer transistor412externally transfers the charge from the photoelectric conversion element341to the adjacent pixel320according to a transfer signal SW2from the row scanning circuit210. The transfer transistor413externally transfers the charge from the photoelectric conversion element341to the adjacent pixel330according to a transfer signal SW3from the row scanning circuit210.

The transfer transistor415externally transfers the charge from the photoelectric conversion element341to the adjacent pixel350according to a transfer signal SW5from the row scanning circuit210. The transfer transistor416externally transfers the charge from the photoelectric conversion element341to the adjacent pixel360according to a transfer signal SW6from the row scanning circuit210. The transfer transistor417externally transfers the charge from the photoelectric conversion element341to the adjacent pixel370according to a transfer signal SW7from the row scanning circuit210. The transfer transistor418externally transfers the charge from the photoelectric conversion element341to the adjacent pixel380according to a transfer signal SW8from the row scanning circuit210.

The capacitor343accumulates and holds the charge internally transferred by the transfer transistor342and the charge externally transferred by the adjacent pixels300,310,320,330,350,360,370and380. The capacitor343is inserted between the inverting input terminal (−) and the output terminal of the operational amplifier344. The capacitor343generates a voltage corresponding to the amount of accumulated charge.

The operational amplifier344outputs a voltage corresponding to the amount of charge accumulated in the inverting input terminal (−) to the output terminal as a pixel signal. The inverting input terminal (−) of the operational amplifier344is connected to the transfer transistor342, the capacitor343and the reset switch345, and the pixels300,310,320,330,350,360,370and380. The non-inverting input terminal (+) of the operational amplifier344is connected to a predetermined power source. The output terminal of the operational amplifier344is connected to a vertical signal line VSL.

The reset switch345short-circuits the inverting input terminal (−) and the output terminal of the operational amplifier344according to a reset signal Cint_rstfrom the row scanning circuit210. This short-circuiting initializes the amount of charge of the capacitor343.

The vertical signal line VSL is wired along the vertical direction for each row. A load MOS (Metal-Oxide-Semiconductor) transistor420is inserted in the vertical signal line VSL. Then, an analog pixel signal Vin is output to the signal processing unit260via the vertical signal line VSL.

The configuration of pixels (the pixel300and the like) other than the pixel340is the same as that of the pixel340. However, the number of adjacent pixels at the outermost circumference of the pixel array unit220is less than 8. Here, the “outermost circumference” means that the row address is either I or 0 or the column address is either J or 0. For example, the pixel at the address (0,0) does not have adjacent pixels at the upper left, upper, upper right, left, and lower left side thereof. In such pixels, a reset power source is connected to a transfer transistor having no transfer destination adjacent pixel. In this way, zero-padding is realized. It is also possible to reduce the number of transfer transistors having no transfer destination.

The transfer transistor342is an example of an internal transfer transistor described in the claims. Transfer transistors410,411,412,413,415,416,417and418are examples of an external transfer transistor described in the claims. The capacitor343is an example of a charge accumulation unit described in the claims.

The size of the kernel is set to 3 rows×3 columns, and nine transfer transistors (the transfer transistors410and the like) are arranged according to the size, but the size of the kernel is not limited to 3 rows×3 columns. For example, the size of the kernel may be 5 rows×5 columns. In this case, twenty-five transfer transistors may be arranged for each pixel, and the number of exposures may be 25.

FIG.6is a circuit diagram illustrating a configuration example of the pixel block505according to the first embodiment of the present technology. In this pixel block505, pixels300,310,320,330,340,350,360,370and380of 3 rows×3 columns are arranged.

In the pixel block505, photoelectric conversion elements301,311,321,331,341,351,361,371and381are arranged. Further, the transfer transistors302,312,322,332,342,352,362,372and382, the capacitor343, the operational amplifier344and the reset switch345are arranged.

The photoelectric conversion element301and the transfer transistor302are arranged in the pixel300, and the photoelectric conversion element311and the transfer transistor312are arranged in the pixel310. The photoelectric conversion element321and the transfer transistor322are arranged in the pixel320, and the photoelectric conversion element331and the transfer transistor332are arranged in the pixel330. The photoelectric conversion element351and the transfer transistor352are arranged in the pixel350, and the photoelectric conversion element361and the transfer transistor362are arranged in the pixel360. The photoelectric conversion element371and the transfer transistor372are arranged in the pixel370, and the photoelectric conversion element381and the transfer transistor382are arranged in the pixel380.

In the drawing, the capacitors, operational amplifiers, and reset switches in the pixels other than the pixel340are omitted. The transfer transistors410,411,412,413,415,416,417and418in the pixel340are omitted.

In the image recognition mode, the pixel of interest is the pixel340, and the transfer transistor302and the like of the pixels adjacent to the pixel of interest externally transfer an amount of charge corresponding to the corresponding weighting coefficient from the corresponding photoelectric conversion element301and the like to the capacitor343of the pixel of interest.

The transfer transistor342in the pixel of interest (the pixel340) internally transfers an amount of charge corresponding to the corresponding weighting coefficient from the corresponding photoelectric conversion element341to the capacitor343. The capacitor343accumulates these charges. In this way, the charges generated by the nine pixels in the pixel block505are added. Since each of the transferred charge amounts is the amount corresponding to the weighting coefficient, the amount of accumulated charge of the capacitor343is the amount corresponding to the result of a product-sum operation convoluted using the kernel of 3 rows×3 columns.

On the other hand, in the normal mode, the transfer transistor (the transfer transistor342or the like) of each pixel performs only internal transfer of charge. In this way, the image data when the kernel is not applied is generated.

FIG.7is a diagram illustrating an example of the layout of the elements in the pixel array unit220according to the first embodiment of the present technology. The transfer transistors302,312,322,332,352,362,372and382are arranged between the signal line501and the eight photoelectric conversion elements301,311,321,331,351,361,371and381around the photoelectric conversion element341. Further, the transfer transistor342is arranged between the photoelectric conversion element341and the signal line501.

The signal line501is wired so as to surround the photoelectric conversion element341and is connected to the input terminal of the operational amplifier344. The capacitor343and the reset switch345are omitted in the drawing.

[Configuration Example of Signal Processing Unit]

FIG.8is a block diagram illustrating a configuration example of the signal processing unit260according to the first embodiment of the present technology. A plurality of comparators261and a plurality of counters262and a plurality of latches263are arranged in the signal processing unit260.

The comparator261and the counter262and the latch263are provided for each row. Assuming that the number of columns is J, J comparators261and J counters262and J latches263are provided.

The comparator261compares a reference signal RMP from the DAC250with a pixel signal Vin from the corresponding column. The comparator261supplies the comparison result to the counter262.

The counter262counts the count value over a period until the comparison result COMP is reversed. The counter262outputs a digital signal indicating the count value to the latch263so that the digital signal is held therein. Further, a counter control signal for controlling the counting operation is input to the counter262.

The latch263holds the digital signal of the corresponding row. The latch263outputs a digital signal to the image processing unit290as pixel data under the control of the column scanning circuit280.

The above-mentioned comparator261and counter262convert an analog pixel signal into digital pixel data. That is, the comparator261and the counter262function as an ADC. An ADC having a simple structure including a comparator and a counter in this way is called a single-slope ADC.

Further, in addition to the AD conversion, the signal processing unit260performs CDS (Correlated Double Sampling) processing for obtaining the difference between a reset level and a signal level for each column. Here, the reset level is the level of the pixel signal at the time of pixel initialization, and the signal level is the level of the pixel signal at the end of exposure. For example, the CDS processing is realized by the counter262performing one of the down-counting and the up-counting at the time of converting the reset level, and the counter262performing the other of the down-counting and the up-counting at the time of converting the signal level. It should be noted that the counter262may be configured to perform only up-counting, and a circuit for performing CDS processing may be added in the subsequent stage.

FIG.9is a timing chart illustrating an example of the operation of the solid-state imaging element200according to the first embodiment of the present technology. When the image recognition mode is set, the row scanning circuit210supplies a high-level reset signal Cint_rstto all pixels at timings T0to T1to initialize the amount of charge of the capacitors (the capacitor343and the like) of all pixels.

Next, over the period of timings T1to T2, the row scanning circuit210supplies the high-level transfer signal SW0to all pixels. In this way, exposure is performed on all the pixels over the period of timings T1and T2, and each pixel transfers the charge to, for example, the pixel on the lower-right corner thereof. The exposure time t0is a time corresponding to the weighting coefficient w0.

Then, over the period of timings T2to T3, the row scanning circuit210supplies the high-level transfer signal SW1to all the pixels. In this way, exposure is performed on all the pixels over the period of timings T2to T3, and each pixel transfers a charge to, for example, a pixel on the lower side thereof. The exposure time t1is a time corresponding to the weighting coefficient w1.

Subsequently, over the period of timings T3to T4, the row scanning circuit210supplies the high-level transfer signal SW2to all the pixels. In this way, exposure is performed on all the pixels over the period of timings T3to T4, and each pixel transfers the charge to, for example, the pixel on the lower-left corner thereof. The exposure time t2is a time corresponding to the weighting coefficient w2. Hereinafter, similarly, the transfer signals SW4to SW8are supplied in order.

FIG.10is a diagram for explaining the 0-th to third transfer control in the first embodiment of the present technology. First, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w0according to the transfer signal SW0, and transfer (that is, external transfer) the charge to the pixels on the lower-right corner thereof. In the drawing, the arrows indicate the direction of charge transfer.

Next, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w1according to the transfer signal SW1and transfer the charge to the pixels on the lower side thereof. Subsequently, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w2according to the transfer signal SW2and transfer the charge to the pixels on the lower-left corner thereof. Then, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w3according to the transfer signal SW3and transfer the charge to the pixels on the right side thereof.

FIG.11is a diagram for explaining the fourth to seventh transfer control in the first embodiment of the present technology. The row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w4according to the transfer signal SW4and internally transfer the charge to the capacitors.

Next, the row scanning circuit210causes all the pixels to generate a charge in an amount corresponding to the weighting coefficient w5according to the transfer signal SW5and transfer the charge to the pixel on the left side thereof. Subsequently, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w6according to the transfer signal SW6and transfer the charge to the pixels on the upper-right corner thereof. Then, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w7according to the transfer signal SW7and transfer the charge to the pixels on the upper side thereof.

FIG.12is a diagram for explaining the eighth transfer control in the first embodiment of the present technology. The row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w8according to the transfer signal SW8and transfer the charge to the pixels on the upper-left corner thereof.

By the nine exposures and transfers illustrated inFIGS.10to12, the results of convolution operation of the respective charge amounts of the pixel and the eight pixels therearound by the weighting coefficient of the kernel are held in the capacitors of all the pixels. The pixel signal Vin corresponding to the amount of charge is expressed by, for example, the following equation.
Vin=V0×w0+V1×w1+V2×w2+V3×w3+V4×w4+V5×w5+V6×w6+V7×w7+V8×w8

In the above equation, V1to V8are pixel signals of the pixels300to380, respectively, when the kernel is not applied.

The row scanning circuit210supplies the transfer signals in the order of SW0to SW8, but the order of these nine transfers is not limited to the order illustrated inFIGS.9to12.

Here, as a comparative example, a solid-state imaging element is assumed in which image data in which digital pixel data is arranged is subjected to a convolution operation in order for each pixel using the kernel.

FIG.13is a diagram for explaining an example of the operation of the 0-th layer in the comparative example. The solid-state imaging element of this comparative example first focuses on the upper-leftmost pixel, that is, the pixel at the address (0, 0), and performs a convolution operation on the pixel of interest and the eight pixels therearound using the kernel. However, since the upper-left pixel does not have the upper left, upper, upper right, left, or lower-left pixel data, the pixel data having a value of “0” is inserted instead of them. In other words, zero-padding is done.

Next, the solid-state imaging element focuses on the pixel at the address (0, 1), and performs a convolution operation on the pixel of interest and the eight pixels therearound using the kernel. Then, the solid-state imaging element focuses on the pixel at the address (0, 2), and performs a convolution operation on the pixel of interest and the eight pixels therearound using the kernel. Hereinafter, similarly, the convolution operation is executed for each pixel in the 0-th row. Then, the solid-state imaging element focuses on the pixel at the address (1, 0), and performs a convolution operation on the pixel of interest and the eight pixels therearound using the kernel. Hereinafter, similarly, the convolution operation is executed for each pixel in the first row. The same applies to the second and subsequent rows of the 0-th layer and the first and subsequent layers. A CNN is realized by the processing of these layers.

As illustrated in the drawing, in the comparative example, the convolution operation is executed in order for each piece of the digital pixel data. In this configuration, the number of operations increases in proportion to the amount of input data (that is, the number of pixels), so that the increase in the number of pixels results in an increase in power consumption and latency.

On the other hand, in the solid-state imaging element200that transfers an amount of charge corresponding to the weighting coefficient, the analog circuit illustrated inFIG.6executes the convolution operation of the 0-th layer. Therefore, the amount of computation of the convolution operations for the digital pixel data after the first layer is reduced. By reducing the amount of computation, the power consumption of the digital circuit (image processing unit290or the like) that performs computation can be reduced, and the computation time can be shortened.

The convolution operation of the 0-th layer is completed by nine exposures and transfers regardless of the number of pixels as illustrated inFIGS.9to12. Therefore, as compared with the comparative example, the time required for the convolution operation of the entire CNN including the 0-th layer can be shortened. Further, since the number of exposures required for the operation of the 0-th layer does not change even if the number of pixels increases, it is possible to suppress an increase in the computation time and power consumption when the number of pixels is increased.

FIG.14is a diagram for explaining CNN in the first embodiment of the present technology. When the image recognition mode is set, in the 0-th layer, the pixels310,320,330,340,350,360,370, and380generate and transfer an amount of charge corresponding to their respective weighting coefficients, and the pixel340adds and outputs the amounts of charge. Similar processing is executed in parallel for other pixels. In this way, the convolution operation of the 0-th layer is realized. The processing result of the 0-th layer is AD-converted by the signal processing unit260and digital image data is generated.

The image processing unit290performs a convolution operation of the first layer on the digital image data in the same manner as in the comparative example. The processing of the second and subsequent layers is executed in the same manner as in the comparative example with respect to the processing result of the layer in the previous stage.

As illustrated in the drawing, the process of executing the convolution operation using the kernel for each of the plurality of stages of layers corresponds to CNN.

FIG.15is a flowchart illustrating an example of the operation of the solid-state imaging element200according to the first embodiment of the present technology. This operation starts, for example, when a predetermined application for image recognition is executed.

The row scanning circuit210in the solid-state imaging element200supplies the reset signal Cint_rstto initialize the charge amounts of all the pixels (step S901). Then, the row scanning circuit210sets “0” to n (n is an integer) (step S902).

The row scanning circuit210exposes all the pixels for an exposure time corresponding to the weighting coefficient wnaccording to the transfer signal SWnand transfers the charge (step S903). The row scanning circuit210increments n (step S904) and determines whether n is larger than “8” (step S905).

When n is “8” or less (step S905: No), the row scanning circuit210repeats step S903and subsequent steps. On the other hand, when n is larger than “8” (step S905: Yes), the signal processing unit260and the image processing unit290execute signal processing and image processing (step S906), and end the operation for image recognition.

As described above, according to the first embodiment of the present technology, since the row scanning circuit210exposes the pixels300and the like over the exposure period corresponding to the weighting coefficient, each pixel can transfer and accumulate an amount of charge corresponding to the weighting coefficient. Therefore, the solid-state imaging element200can execute the convolution operation by a fixed number of (nine or the like) transfer operation regardless of the number of pixels. In this way, the time required for the convolution operation can be shortened as compared with the case where the convolution operation is performed sequentially for each pixel.

First Modification

In the first embodiment described above, all the pixels output the result of the convolution operation as it is, but in this configuration, the data size of the image data increases as the number of pixels increases. In CNN, in addition to the convolutional operation, a pooling process is generally executed for the purpose of providing translation invariance and reducing the data size of image data. Here, the pooling process is a process of dividing the image data into a plurality of windows and outputting the statistic (average value or maximum value) of the pixel data for each window. The solid-state imaging element200of the first modification of the first embodiment is different from the first embodiment in that the pooling process is further executed.

FIG.16is a diagram illustrating a configuration example of the pixel array unit220in the first modification of the first embodiment of the present technology. The pixel array unit220of the first modification of the first embodiment is divided by a plurality of windows such as windows506to509. Here, the window is an area composed of M (M is an integer) pixels, and for example, the pixel array unit220is divided by a window506having a size of 2 rows×2 columns. Assuming that the number of pixels is I×J, the pixel array unit220is divided into (I×J)/4 windows. Pixels300,310,330and340are arranged in the window506, for example.

FIG.17is a circuit diagram illustrating a configuration example of the window506in the first modification of the first embodiment of the present technology. In the window506, amplification transistors308,318,338and348are further arranged. The transfer transistor for external transfer is omitted in the drawing.

The amplification transistor308is arranged on the pixel300, and the amplification transistor318is arranged on the pixel310. The amplification transistor338is arranged on the pixel330, and the amplification transistor348is arranged on the pixel340.

The gate of the amplification transistor308is connected to the output of the operational amplifier304to amplify the voltage of the capacitor303. The amplification transistors318,338and348likewise amplify the voltages of the corresponding capacitors. Then, the respective sources of these amplification transistors308,318,338and348are commonly connected to the vertical signal line VSL. With this connection configuration, a pixel signal corresponding to the maximum value of the respective charge amounts of the pixels300,310,330, and340is output from the window506. The circuit illustrated in the drawing is generally called a winner-take-all circuit or the like, and has a simple source follower circuit configuration.

The configuration of other windows, such as the windows507,508and509, is similar to that of the window506.

FIG.18is a diagram for explaining the pooling process in the first modification of the first embodiment of the present technology. It is assumed that the respective charge amounts of the four pixels in the window506are “1”, “1”, “5” and “6”, and the respective charge amounts of the four pixels in the window507are “2” and “4”, “7” and “8”. It is assumed that the respective charge amounts of the four pixels in the window508are “3”, “2”, “1” and “2”, and the respective charge amounts of the four pixels in the window509are “1”, “0”, “3” and “4”.

In this case, each window outputs a pixel signal corresponding to the maximum value of the charge amounts. That is, the window506outputs a pixel signal corresponding to the charge amount “6”, and the window507outputs a pixel signal corresponding to the charge amount “8”. The window508outputs a pixel signal corresponding to the charge amount “3”, and the window509outputs a pixel signal corresponding to the charge amount “4”.

The number of pieces of data can be reduced to ¼ by the process illustrated in the drawing. By reducing the number of pieces of data, the signal processing cost in the subsequent stage can be further reduced. In particular, when the signal processing unit260performs AD conversion, the power and circuit size thereof can be reduced. In general, since the AD conversion cost accounts for a large proportion of the entire system, the power and time can be significantly reduced by reducing the signal processing cost of the signal processing unit260.

The process of selecting and outputting statistics such as the maximum value for each window in this way is called a pooling process. In particular, the pooling process for selecting the maximum value is called max pooling.

In each window, the maximum value is selected as the statistic, but a statistic (average value or the like) other than the maximum value can also be selected. Further, although the size of the window is 2 rows×2 columns, the size of the window is not limited to 2 rows×2 columns.

As described above, according to the first modification of the first embodiment of the present technology, since each of the windows outputs a pixel signal corresponding to the statistic (maximum value or the like) of the amount of charge of each pixel, the number of pieces of data can be reduced as compared with the case where the pixel signal is output for each pixel.

Second Modification

In the first embodiment described above, the row scanning circuit210starts nine exposures at different timings from each other, but in this configuration, the difference in exposure time between the exposures may increase. In this case, shake called blur may occur in the image data due to the difference in the exposure time. The row scanning circuit210of the second modification of the first embodiment is different from the first embodiment in that nine exposures are started at the same timing.

FIG.19is a timing chart illustrating an example of the operation of the solid-state imaging element200in the second modification of the first embodiment of the present technology. In the second modification of the first embodiment, the row scanning circuit210starts generation (in other words, exposure) of charge at the same timing for all pixels by setting the transfer signals SW0to SW9to a high level at the timing T1.

The row scanning circuit210calculates the exposure times t0′ to t9′ in advance before exposure from the exposure times t0to t9according to the weighting coefficients w0to w9by nine simultaneous equations. For the sake of simplicity, the case where the exposure start timings are aligned only for the first three times is considered. In this case, the exposure times t0′ to t2′ are calculated by the following three simultaneous equations.

The signal processing unit260or the image processing unit290in the subsequent stage sets the pixel signals corresponding to the exposure times t0′ to t2′ to Vin0′ to Vin2′, and calculates the pixel signals Vin0to Vin2corresponding to the exposure times t0to t2by solving the following simultaneous equations.

When aligning the nine exposure start timings, the signal processing unit260and the like may calculate the pixel signals corresponding to the exposure time t0′ to t9′ from the pixel signals corresponding to the exposure times t0to t9by solving the nine simultaneous equations.

As described above, by aligning the exposure start timings, it is possible to reduce the difference in exposure time between the nine exposures. In this way, deterioration in image quality of image data due to the difference in exposure time can be suppressed.

The first modification can be applied to the second modification of the first embodiment.

As described above, according to the second modification of the first embodiment of the present technology, the row scanning circuit210starts the exposure at the same timing for all the pixels, so that it is possible to reduce the difference in exposure time between the nine exposures as compared with the case where the exposure is started at different timings. In this way, deterioration in image quality due to the difference in exposure time can be suppressed.

2. Second Embodiment

In the first embodiment described above, the pixels are arranged in a two-dimensional lattice pattern in the pixel array unit220, but in this arrangement, the size of the kernel cannot be made smaller than 3 rows×3 columns. The solid-state imaging element200of the second embodiment is different from the first embodiment in that the size of the kernel is reduced by arranging the pixels in a honeycomb pattern.

FIG.20is a diagram illustrating a configuration example of the pixel array unit220according to the second embodiment of the present technology. In the pixel array unit220, a plurality of pixels such as pixels300,310,320,330,340,350, and360are arranged in a honeycomb pattern.

Further, the kernel is applied to seven pixels including a pixel of interest and six adjacent pixels therearound using each of all the pixels in the pixel array unit220as the pixel of interest. For example, focusing on the pixel330, the pixels300,310,320,340,350and360are adjacent to the pixel330. The kernel is applied to a pixel block505of seven pixels including the pixel of interest and six adjacent pixels therearound. Moreover, the number of weighting coefficients in the kernel is seven.

Similarly, when focusing on the pixel340, the kernel is applied to the pixel340and the six pixels (the pixel330and the like) adjacent to the pixel340. The same applies to other pixels.

The adjacent pixel (the pixel300or the like) generates an amount of charge corresponding to the weighting coefficient corresponding to the adjacent pixel under the control of the row scanning circuit210and transfers the charge to the pixel of interest. The pixel of interest (the pixel330or the like) generates an amount of charge corresponding to the weighting coefficient corresponding to the pixel of interest under the control of the row scanning circuit210, and accumulates the charge together with the transferred charge.

As illustrated in the drawing, by arranging the pixels in a honeycomb pattern and forming a kernel including seven weighting coefficients, it is possible to reduce the number of weighting coefficients from nine to seven while maintaining sufficient spatial information. This facilitates the realization of CNNs in a two-dimensional to three-dimensional structure with respect to circuits, devices, optical calculations, and the like, and as a result, the overall performance of power, size, and speed can be improved.

The honeycomb-shaped arrangement can be applied to when CNN is configured and executed by software implementation using general-purpose computing means such as GPU (Graphics Processing Unit) as a general-purpose CNN kernel with the minimum configuration that replaces the general 3 row×3 column kernel.

FIG.21is a circuit diagram illustrating a configuration example of the pixel330according to the second embodiment of the present technology. The pixel330of the second embodiment includes a photoelectric conversion element331, a transfer transistor332, a reset transistor336, a floating diffusion layer337, an amplification transistor338, and transfer transistors410,411,412,414,415and416.

The photoelectric conversion element331generates charge by photoelectric conversion.

The transfer transistor332internally transfers the charge from the photoelectric conversion element331to the floating diffusion layer337according to the transfer signal SW3from the row scanning circuit210.

The transfer transistor410externally transfers the charge from the photoelectric conversion element331to the adjacent pixel300according to the transfer signal SW0from the row scanning circuit210. The transfer transistor411externally transfers the charge from the photoelectric conversion element331to the adjacent pixel310according to the transfer signal SW1from the row scanning circuit210. The transfer transistor412externally transfers the charge from the photoelectric conversion element331to the adjacent pixel320according to the transfer signal SW2from the row scanning circuit210. The transfer transistor414externally transfers the charge from the photoelectric conversion element331to the adjacent pixel340according to the transfer signal SW4from the row scanning circuit210.

The transfer transistor415externally transfers the charge from the photoelectric conversion element331to the adjacent pixel350according to the transfer signal SW5from the row scanning circuit210. The transfer transistor416externally transfers the charge from the photoelectric conversion element331to the adjacent pixel360according to the transfer signal SW6from the row scanning circuit210.

The floating diffusion layer337accumulates and holds the charge internally transferred by the transfer transistor332and the charge externally transferred by the pixels300,310,320,340,350and360. The floating diffusion layer337is an example of a charge accumulation unit described in the claims.

The amplification transistor338amplifies the voltage of the floating diffusion layer337and outputs the voltage as a pixel signal to the vertical signal line VSL.

The reset transistor336initializes the charge amount of the floating diffusion layer337according to the reset signal RD from the row scanning circuit210.

The configuration of pixels (the pixel300and the like) other than pixel330is the same as that of the pixel330.

Instead of the floating diffusion layer337, the amplification transistor338, and the reset transistor336, the capacitor343, the operational amplifier344, and the reset switch345may be arranged as in the first embodiment.

As illustrated in the drawing, by arranging the pixels in a honeycomb pattern, the number of transfer destination adjacent pixels is reduced from eight pixels to six pixels, so that the number of transfer transistors can be reduced by 2 for each pixel. When the total number of pixels is I×J, I×J×2 transfer transistors can be reduced.

FIG.22is a circuit diagram illustrating a configuration example of the pixel block505according to the second embodiment of the present technology. Pixels300,310,320,330,340,350and360are arranged in the pixel block505of the second embodiment.

In the pixel block505, photoelectric conversion elements301,311,321,331,341,351and361are arranged. Further, transfer transistors302,312,322,332,342,352and362, a reset transistor336, a floating diffusion layer337and an amplification transistor338are arranged.

In the drawing, the floating diffusion layer, the amplification transistor, and the reset transistor in the pixels other than the pixel340are omitted. The transfer transistors410,411,412,414,415and416in the pixel340are omitted.

In the image recognition mode, using the pixel330as the pixel of interest, the transfer transistor302and the like of the pixels adjacent to the pixel of interest externally transfer an amount of charge corresponding to the corresponding weighting coefficient from the corresponding photoelectric conversion elements301and the like to the floating diffusion layer337of the pixel of interest.

The transfer transistor332in the pixel of interest (the pixel330) internally transfers an amount of charge corresponding to the corresponding weighting coefficient from the corresponding photoelectric conversion element331to the floating diffusion layer337. The floating diffusion layer337accumulates these charges. In this way, the charges generated by the seven pixels in the pixel block505are added. Since each of the transferred charge amounts is the amount corresponding to the weighting coefficient, the amount of accumulated charge of the floating diffusion layer337is the amount corresponding to the result of a product-sum operation convoluted using the kernel including seven weighting coefficients.

FIG.23is a diagram illustrating an example of the layout of the elements in the pixel array unit220according to the second embodiment of the present technology. The transfer transistors302,312,322,342,352and362are arranged between the signal line501and the six photoelectric conversion elements301,311,321,341,351and361around the photoelectric conversion element331. Further, the transfer transistor332is arranged between the photoelectric conversion element331and the signal line501.

The signal line501is wired so as to surround the photoelectric conversion element331and is connected to the floating diffusion layer337. The reset transistor336and the amplification transistor338are omitted in the drawing.

FIG.24is a timing chart illustrating an example of the operation of the solid-state imaging element200according to the second embodiment of the present technology. In the image recognition mode, the row scanning circuit210simultaneously supplies the transfer signals SW0to SW6to all the pixels within the period of the timings T0to T1, and supplies the reset signal RD to all the pixels at the timing T1. In this way, the floating diffusion layers of all pixels are initialized to a desired potential.

Then, the row scanning circuit210supplies the transfer signal SW0at the timing T2when the exposure time to has elapsed from the timing T1. Assuming that the amount of current due to photoelectric conversion when the kernel is not applied is IPD, the amount of charge of IPD×t0is generated in the photoelectric conversion element during the period of timings T1to T2and is accumulated in the floating diffusion layer.

Subsequently, the row scanning circuit210supplies the transfer signal SW1at the timing T3when the exposure time t1has elapsed from the timing T2, and supplies the transfer signal SW2at the timing T4when the exposure time t2has elapsed from the timing T3. Hereinafter, similarly, the transfer signals SW3to SW6are sequentially supplied at the timing when the corresponding exposure time elapses.

By the above-mentioned seven exposures and transfers, the floating diffusion layers of all the pixels hold the results of convolution operation on the respective charge amounts of the pixel and the six pixels therearound according to the weighting coefficient of the kernel.

By arranging the pixels in a honeycomb pattern in this way, the number of pixels to which the kernel is applied is reduced from nine pixels to seven pixels, so that the number of exposures can be reduced from nine times to seven times. In this way, the total exposure time can be shortened.

FIG.25is a diagram for explaining CNN in the second embodiment of the present technology. When the image recognition mode is set, in the 0-th layer, each pixel generates an amount of charge corresponding to the weighting coefficient and transfers the charge to seven pixels including itself. In the drawing, the arrow indicates the transfer direction. In this way, the convolution operation of the 0-th layer is realized. The processing result of the 0-th layer is AD-converted by the signal processing unit260to generate digital image data.

The image processing unit290performs a convolution operation of the first layer on the digital image data in the same manner as in the comparative example. The processing of the second and subsequent layers is executed in the same manner as in the comparative example with respect to the processing result of the layer in the previous stage.

As described above, according to the second embodiment of the present technology, since the pixels are arranged in a honeycomb pattern, the number of adjacent pixels is reduced from eight pixels to six pixels as compared with the case where the pixels are arranged in a two-dimensional lattice pattern. In this way, the circuit scale of the pixels can be reduced and the total exposure time can be shortened.

Modification

In the second embodiment described above, all the pixels output the result of the convolution operation as it is, but in this configuration, the data size of the image data increases as the number of pixels increases. The solid-state imaging element200of the modification of the second embodiment is different from the second embodiment in that the pooling process is further executed.

The pixel array unit220of the modification of the second embodiment is divided by a plurality of windows composed of a predetermined number of (4 or the like) pixels.

FIG.26is a circuit diagram illustrating a configuration example of the window506in the modification of the second embodiment of the present technology. In the window506, the drains of the amplification transistors308,318,338and348are commonly connected to the vertical signal line VSL. With this connection configuration, a pixel signal corresponding to the maximum value of the respective charge amounts of the pixels300,310,330, and340is output from the window506.

It should be noted that the second modification of the first embodiment in which the exposure start timing is aligned can also be applied to the modification of the second embodiment.

According to the modification of the second embodiment of the present technology, each of the windows in the honeycomb-shaped arrangement outputs a pixel signal corresponding to the statistic (maximum value or the like) of the amount of charge of each pixel, so that the number of pieces of data can be reduced as compared with the case where a pixel signal is output for each pixel.

In the first embodiment described above, the transfer transistor is arranged for each pixel to realize the convolution operation, but in this configuration, the circuit scale for each pixel is increased as compared with the case where the convolution operation is not performed. The imaging device100of the third embodiment is different from that of the first embodiment in that the convolution operation is realized by shifting the position of the solid-state imaging element200in pixel units.

FIG.27is a block diagram illustrating a configuration example of the imaging device100according to the third embodiment of the present technology. The imaging device100of the third embodiment includes an optical unit110, a solid-state imaging element200, a pixel shift control unit451, a Y-axis actuator452, an X-axis actuator453, and a storage unit170.

The configuration of the optical unit110and the storage unit170of the second embodiment is the same as that of the first embodiment.

The X-axis actuator453changes the horizontal position of the solid-state imaging element200to a position different from the initial position in pixel units under the control of the pixel shift control unit451.

The Y-axis actuator452changes the vertical position of the solid-state imaging element200to a position different from the initial position in pixel units under the control of the pixel shift control unit451. The X-axis actuator453and the Y-axis actuator452are realized by, for example, a piezoelectric element.

The X-axis actuator453and the Y-axis actuator452are examples of an actuator described in the claims.

In the image recognition mode, the pixel shift control unit451controls the X-axis actuator453and the Y-axis actuator452to change the position of the solid-state imaging element200in pixel units. The position of the solid-state imaging element200is changed in pixel units in eight directions about the initial position, for example. At the initial position, the solid-state imaging element200generates an amount of charge for each pixel according to the weighting coefficient of the pixel of interest. Further, each time the position is changed, the solid-state imaging element200generates an amount of charge for each pixel according to the weighting coefficient of the adjacent pixel related to the position.

On the other hand, in the normal mode, the pixel shift control unit451keeps the position of the solid-state imaging element200at the initial position, and the solid-state imaging element200acquires image data in synchronization with the vertical synchronization signal.

FIG.28is a circuit diagram illustrating a configuration example of the pixel300according to the third embodiment of the present technology. The pixel300of the third embodiment is different from that of the first embodiment in that the transfer transistors410,411,412,413,415,416,417and418for transferring charge to surrounding pixels are not arranged.

FIG.29is a diagram for explaining the 0-th and first exposure control in the third embodiment of the present technology. In the drawing, the alternate long and short dash line indicates the outer circumference of the pixel array unit220of the solid-state imaging element200at the initial position.

At the initial position, the row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w4of the pixel of interest. Then, the X-axis actuator453and the Y-axis actuator452shift the solid-state imaging element200to the left by one pixel and upward by one pixel from the initial position. The row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w0corresponding to the adjacent pixel on the upper-left corner.

FIG.30is a diagram for explaining the second and third exposure control in the third embodiment of the present technology. The X-axis actuator453shifts the solid-state imaging element200to the right by one pixel from the state of being shifted to the upper-left corner to move the solid-state imaging element200to an upper position from the initial position. The row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w1corresponding to the adjacent pixel on the upper side.

Then, the X-axis actuator453shifts the solid-state imaging element200to the right by one pixel from the upwardly shifted state to move the solid-state imaging element200to an upper-right position from the initial position. The row scanning circuit210causes all the pixels to generate an amount of charge corresponding to the weighting coefficient w2corresponding to the adjacent pixel on the upper-right corner.

Hereinafter, similarly, the X-axis actuator453and the Y-axis actuator452shift the solid-state imaging element200sequentially to the left side, the right side, the lower-left corner, the lower side, and the lower right corner, and all the pixels generate an amount of charge corresponding to the result of a product-sum operation convoluted using the kernel of 3 rows×3 columns.

In addition, the first modification and the second modification of the first embodiment can be applied to the third embodiment.

As described above, according to the third embodiment of the present technology, each time the position of the solid-state imaging element200is changed in pixel units, the pixel generates an amount of charge corresponding to the weighting coefficient, so that the convolution operation can be realized without transferring charge between pixels. This eliminates the need for the transfer transistor410or the like for transferring charges between pixels, and the circuit scale of the pixels can be reduced accordingly.

4. Application Example to Moving Body

The technology (the present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of mobile body such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a ship, and a robot.

FIG.31is a block diagram illustrating a schematic configuration example of a vehicle control system which is an example of a moving body control system to which the technology according to the present disclosure can be applied.

A vehicle control system12000includes a plurality of electronic control units connected via a communication network12001. In the example illustrated inFIG.31, the vehicle control system12000includes a drive system control unit12010, a body system control unit12020, a vehicle exterior information detection unit12030, a vehicle interior information detection unit12040, and an integrated control unit12050. Furthermore, as a functional configuration of the integrated control unit12050, a microcomputer12051, an audio/image output unit12052, and an in-vehicle network interface (I/F)12053are illustrated.

The drive system control unit12010controls the operation of devices related to the drive system of the vehicle according to various programs. For example, the drive system control unit12010functions as a control device of a driving force generation device for generating a driving force of the vehicle such as an internal combustion engine or a driving motor, a driving force transmission mechanism for transmitting the driving force to wheels, a steering mechanism for adjusting a steering angle of the vehicle, a braking device for generating a braking force of the vehicle, and the like.

The body system control unit12020controls operations of various devices mounted on the vehicle body according to various programs. For example, the body system control unit12020functions as a control device of a keyless entry system, a smart key system, a power window device, or various lamps such as a head lamp, a back lamp, a brake lamp, a turn signal, or a fog lamp. In this case, radio waves transmitted from a portable device that substitutes for a key or signals of various switches can be input to the body system control unit12020. The body system control unit12020receives input of these radio waves or signals, and controls a door lock device, a power window device, a lamp, and the like of the vehicle.

The vehicle exterior information detection unit12030detects information outside the vehicle on which the vehicle control system12000is mounted. For example, an imaging unit12031is connected to the vehicle exterior information detection unit12030. The vehicle exterior information detection unit12030causes the imaging unit12031to capture an image of the outside of the vehicle, and receives the captured image. The vehicle exterior information detection unit12030may perform object detection processing or distance detection processing of a person, a vehicle, an obstacle, a sign, a character on a road surface, or the like on the basis of the received image.

The imaging unit12031is an optical sensor that receives light and outputs an electrical signal corresponding to the amount of received light. The imaging unit12031can output the electrical signal as an image or can output the electrical signal as distance measurement information. Furthermore, the light received by the imaging unit12031may be visible light or invisible light such as infrared rays.

The vehicle interior information detection unit12040detects information on the inside of the vehicle. For example, a driver state detection unit12041that detects a driver's state is connected to the vehicle interior information detection unit12040. The driver state detection unit12041includes, for example, a camera that images the driver, and the vehicle interior information detection unit12040may calculate the degree of fatigue or the degree of concentration of the driver or may determine whether the driver is dozing off on the basis of the detection information input from the driver state detection unit12041.

The microcomputer12051can calculate a control target value of the driving force generation device, the steering mechanism, or the braking device on the basis of the information inside and outside the vehicle acquired by the vehicle exterior information detection unit12030or the vehicle interior information detection unit12040, and output a control command to the drive system control unit12010. For example, the microcomputer12051can perform cooperative control for the purpose of implementing functions of an advanced driver assistance system (ADAS) including collision avoidance or impact mitigation of the vehicle, follow-up traveling based on an inter-vehicle distance, vehicle speed maintenance traveling, vehicle collision warning, vehicle lane departure warning, or the like.

Furthermore, the microcomputer12051can perform cooperative control for the purpose of automatic driving or the like in which the vehicle autonomously travels without depending on the operation of the driver by controlling the driving force generation device, the steering mechanism, the braking device, or the like on the basis of the information around the vehicle acquired by the vehicle exterior information detection unit12030or the vehicle interior information detection unit12040.

Furthermore, the microcomputer12051can output a control command to the body system control unit12020on the basis of the vehicle exterior information acquired by the vehicle exterior information detection unit12030. For example, the microcomputer12051can perform cooperative control for the purpose of preventing glare, such as switching from a high beam to a low beam, by controlling the headlamp according to the position of a preceding vehicle or an oncoming vehicle detected by the vehicle exterior information detection unit12030.

The audio/image output unit12052transmits an output signal of at least one of a sound or an image to an output device capable of visually or audibly notifying an occupant of the vehicle or the outside of the vehicle of information. In the example ofFIG.31, an audio speaker12061, a display unit12062, and an instrument panel12063are illustrated as the output device. The display unit12062may include, for example, at least one of an on-board display and a head-up display.

FIG.32is a diagram illustrating an example of positions at which the imaging unit12031is installed.

InFIG.32, imaging units12101,12102,12103,12104, and12105are provided as the imaging unit12031.

The imaging units12101,12102,12103,12104, and12105are provided, for example, at positions such as a front nose, a side mirror, a rear bumper, a back door, and an upper portion of a windshield in a vehicle interior of the vehicle12100. The imaging unit12101provided at the front nose and the imaging unit12105provided at the upper portion of the windshield in the vehicle interior mainly acquire images in front of the vehicle12100. The imaging units12102and12103provided at the side mirrors mainly acquire images of the sides of the vehicle12100. The imaging unit12104provided on the rear bumper or the back door mainly acquires an image behind the vehicle12100. The front images acquired by the imaging unit12105is mainly used for detecting a preceding vehicle, a pedestrian, an obstacle, a traffic light, a traffic sign, a lane, or the like.

FIG.32illustrates an example of imaging ranges of the imaging units12101to12104. An imaging range12111indicates an imaging range of the imaging unit12101provided at the front nose, imaging ranges12112and12113indicate imaging ranges of the imaging units12102and12103provided at the side mirrors, respectively, and an imaging range12114indicates an imaging range of the imaging unit12104provided at the rear bumper or the back door. For example, by superimposing image data captured by the imaging units12101to12104, an overhead view image of the vehicle12100viewed from above is obtained.

For example, the microcomputer12051obtains a distance to each three-dimensional object in the imaging ranges12111to12114and a temporal change of the distance (relative speed with respect to the vehicle12100) on the basis of the distance information obtained from the imaging units12101to12104, thereby extracting, as a preceding vehicle, a three-dimensional object traveling at a predetermined speed (for example, 0 km/h or more) in substantially the same direction as the vehicle12100, in particular, the closest three-dimensional object on a traveling path of the vehicle12100. The microcomputer12051can set an inter-vehicle distance to be secured in advance in front of the preceding vehicle, and can perform automatic brake control (including follow-up stop control), automatic acceleration control (including follow-up start control), and the like. As described above, it is possible to perform cooperative control for the purpose of automatic driving or the like in which the vehicle autonomously travels without depending on the operation of the driver.

For example, on the basis of the distance information obtained from the imaging units12101to12104, the microcomputer12051can classify and extract three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, and other three-dimensional objects such as utility poles, and use the three-dimensional object data for automatic avoidance of obstacles. For example, the microcomputer12051identifies obstacles around the vehicle12100as obstacles that can be visually recognized by the driver of the vehicle12100and obstacles that are difficult to visually recognize. The microcomputer12051determines a collision risk indicating a risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and there is a possibility of collision, the microcomputer12051can perform driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker12061or the display unit12062or performing forced deceleration or avoidance steering via the drive system control unit12010.

At least one of the imaging units12101to12104may be an infrared camera that detects infrared light. For example, the microcomputer12051can recognize pedestrians by determining whether there are the pedestrians in images captured by the imaging units12101to12104. The pedestrians are recognized, for example, in an order in which feature points in the images captured by the imaging units12101to12104serving as infrared cameras are extracted and an order in which a pattern matching process is performed on a series of feature points indicating the contour of an object to determine whether there is a pedestrian. When the microcomputer12051determines that there is the pedestrian in the images captured by the imaging units12101to12104and recognizes the pedestrian, the audio/image output unit12052controls the display unit12062such that a rectangular contour line for emphasizing the recognized pedestrian is superimposed and displayed. The audio/image output unit12052may control the display unit12062such that an icon or the like indicating the pedestrian is displayed at a desired position.

The example of the vehicle control system to which the technology according to the present disclosure is applied has been described above. The technology of the present disclosure can be applied to the imaging unit12031and the like in the above-described configuration. Specifically, the imaging device100inFIG.1can be applied to the imaging unit12031. By applying the technology according to the present disclosure to the imaging unit12031, it is possible to shorten the computation time of image recognition, so that the image recognition can be performed at a high speed, and the stability of the vehicle control system can be improved.

The above-described embodiments show examples for embodying the present technique, and matters in the embodiments and matters specifying the invention in the claims have a corresponding relationship with each other. Similarly, the matters specifying the invention in the claims and the matters in the embodiments of the present technique having the same name have a corresponding relationship with each other. However, the present technique is not limited to the embodiments and can be embodied by applying various modifications to the embodiments without departing from the gist thereof.

In addition, the effects described in the present specification are merely examples and are not intended as limiting, and other effects may be obtained.

The present technology can also be configured as described below.(1) A solid-state imaging element including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; and a scanning circuit that performs control so that the adjacent pixel generates an amount of charge corresponding to the weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest and performs control so that the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge.(2) The solid-state imaging element according to (1), wherein the plurality of pixels are arranged in a two-dimensional lattice pattern.(3) The solid-state imaging element according to (1), wherein the plurality of pixels are arranged in a honeycomb pattern.(4) The solid-state imaging element according to any one of (1) to (3), wherein each of the plurality of pixels includes: a photoelectric conversion element that generates the charge by photoelectric conversion; a charge holding portion that holds the charge; an internal transfer transistor that internally transfers the charge from the photoelectric conversion element to the charge holding portion; and the predetermined number of external transfer transistors that externally transfer the charge from the photoelectric conversion element to surrounding pixels among the plurality of pixels.(5) The solid-state imaging element according to (4), wherein the charge holding portion is a capacitor.(6) The solid-state imaging element according to (4), wherein the charge holding portion is a floating diffusion layer.(7) The solid-state imaging element according to any one of (1) to (6), wherein the scanning circuit causes the predetermined number of adjacent pixels and the pixel of interest to start generating of the charge at different timings.(8) The solid-state imaging element according to any one of (1) to (6), wherein the scanning circuit causes the predetermined number of adjacent pixels and the pixel of interest to start generating of the charge at the same timing.(9) The solid-state imaging element according to any one of (1) to (8), wherein the pixel array unit is divided into a plurality of windows having a predetermined size, and each of the plurality of windows outputs a pixel signal corresponding to the statistic of the amount of the charge accumulated in each of the pixels in the window.(10) The solid-state imaging element according to any one of (1) to (9), further including an image processing unit that performs a predetermined convolution operation on the image data output by the pixel array unit.(11) An imaging device including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; a scanning circuit that performs control so that the adjacent pixel generates an amount of charge corresponding to the weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest and performs control so that the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge.(12) An imaging device including: a pixel array unit in which a plurality of pixels are arranged in a two-dimensional lattice pattern; a coefficient holding unit that holds a predetermined weighting coefficient correlated with each of a pixel of interest among the plurality of pixels and a predetermined number of adjacent pixels adjacent to the pixel of interest; an actuator that changes positions of the plurality of pixels to positions different from predetermined initial positions in pixels units; and a scanning circuit that performs control so that each of the plurality of pixels at the initial positions generates an amount of charge corresponding to the weighting coefficient corresponding to the pixel of interest and performs control so that, each time the position of the pixel array unit is changed, an amount of charge corresponding to the weighting coefficient corresponding to the adjacent pixel related to the changed position is generated.(13) A method for controlling a solid-state imaging element, including: a transfer procedure in which an adjacent pixel adjacent to a pixel of interest generates an amount of charge corresponding to a weighting coefficient correlated with the adjacent pixel and transfers the charge to the pixel of interest; and an accumulation procedure in which the pixel of interest generates an amount of charge corresponding to the weighting coefficient correlated with the pixel of interest and accumulates the charge together with the transferred charge.

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