Photoelectric conversion device, imaging device, control method, and computer program

Abstract

To provide a technique for suitably performing pixel readout processing while suppressing an increase in circuit scale.SOLUTION: A photovoltaic device according to the present invention has pixels each of which comprises a photoelectric conversion unit outputting a signal in accordance with incident photons. The photovoltaic device has first measuring means, adding means, and second measuring means. The first measuring means measures the number of photons incident on the pixel. The adding means adds measured values of the plurality of first measuring means. The second measuring means measures a time when the first measuring means starts the measurement until a time when the measured value by the adding means reaches a first threshold value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion device having a photoelectric conversion unit that outputs a signal according to incident photons, an imaging device, a control method, a computer program, and the like. [Background technology]

[0002] In recent years, a photoelectric conversion device has been proposed that digitally counts the number of photons incident on an avalanche photodiode and outputs the counted value from a pixel as a photoelectrically converted digital signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Publication No. 2015 / 0163429 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 proposes a structure that includes a photon counter that counts photons and a time counter that measures time. The time counter measures the time from when the photon counter starts measuring until the number of photons reaches a predetermined value, and calculates the pixel value from the measured time. However, Patent Document 1 requires a photon counter and a time counter for each pixel, which increases the circuit size.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a technique for performing pixel readout processing in an appropriate manner while suppressing an increase in circuit scale. [Means for solving the problem]

[0006] The photoelectric conversion device according to the present invention that solves the above-mentioned problems is a photoelectric conversion device having pixels each equipped with a photoelectric conversion unit that outputs a signal in response to an incident photon, and includes: a first measurement means that measures the number of photons incident on the pixel; an addition means that adds up the measurement values ​​of a plurality of the first measurement means; and a second measurement means that measures the time from when the first measurement means starts the measurement until the measurement value by the addition means reaches a first threshold value. the first measuring means is arranged for each of the plurality of pixels, and the second measuring means is arranged for each of the partial pixel regions including the plurality of pixels having different spectral sensitivities. . [Effects of the Invention]

[0007] The present invention provides a technique for performing pixel readout processing in an appropriate manner while suppressing an increase in circuit scale. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of a hardware configuration of a photoelectric conversion device. [Figure 2] FIG. 1 is a diagram showing an example of a sensor chip of a photoelectric conversion device. [Figure 3] 1 is a diagram showing an example of a circuit chip of a photoelectric conversion device; [Figure 4] FIG. 1 is a diagram showing an example of an equivalent circuit of a pixel and a signal processing unit in a photoelectric conversion device. [Figure 5] FIG. 1 is a block diagram illustrating an example of the functional configuration of an imaging device including a photoelectric conversion device. [Figure 6] FIG. 1 is a diagram showing an example of an equivalent circuit of a pixel and a signal processing unit in a photoelectric conversion device. [Figure 7] 1 is a flowchart illustrating an example of the operation of a photoelectric conversion device. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes in detail embodiments of the present invention. Note that the embodiments described below are merely examples for realizing the present invention, and should be appropriately modified or changed depending on the configuration of the device to which the present invention is applied and various conditions, and the present invention is not limited to the following embodiments.

[0010] (First embodiment) FIG. 1 is a diagram showing an example of the configuration of a photoelectric conversion device according to the first embodiment.

[0011] The photoelectric conversion device 100 is configured by stacking and electrically connecting two chips: a sensor chip 11 and a circuit chip 21. The sensor chip 11 includes a pixel region 12. The circuit chip 21 includes a pixel circuit region 22 that processes signals detected by each pixel in the pixel region 12 in parallel, and a peripheral circuit region 23 that reads signals from the pixel circuit region 22 and controls the pixel circuit region 22.

[0012] FIG. 2 is a diagram showing an example of the configuration of the sensor chip 11 according to the first embodiment.

[0013] The pixel region 12 of the sensor chip 11 includes a plurality of pixels 201 arranged two-dimensionally across multiple rows and columns. Each pixel 201 has a photoelectric conversion unit 202 including an avalanche photodiode (hereinafter referred to as APD) that outputs a signal in response to incident photons. FIG. 2 shows 48 pixels 201 arranged in six rows (rows 0 to 5) and eight columns (columns 0 to 7) along with reference symbols indicating the row and column numbers. For example, the unit pixel 11 arranged in the first row and fourth column is labeled "P14." The number of rows and columns of the pixel array constituting the pixel region 12 is not particularly limited.

[0014] 3 is a diagram showing an example of the configuration of the circuit chip 21 according to the first embodiment. The circuit chip 21 includes a pixel circuit region 22 and a peripheral circuit region 23.

[0015] The pixel circuit region 22 includes multiple signal processing units 301 arranged two-dimensionally across multiple rows and columns. FIG. 3 shows 12 signal processing units 301 arranged in three rows (rows 0 to 2) and four columns (columns 0 to 3), with reference numerals indicating the row and column numbers. For example, the signal processing unit 301 arranged in the second row and second column is designated by the reference numeral "S22." The number of rows and columns of the signal processing unit array constituting the pixel circuit region 22 is not particularly limited. Each signal processing unit 301 is connected to four pixels 201. However, the number of pixels 201 connected to the signal processing unit 301 is not particularly limited. The signal processing unit also includes a photon counter 403 (first measurement means) that counts the number of electrons and a time counter 407 (second measurement means) that measures time. In the photoelectric conversion device of this embodiment, a photon counter 403 is provided for each pixel, but a time counter 407 is configured to be shared by multiple pixels. That is, a group of multiple pixels in the pixel region 12 is considered to be one partial pixel region, and a photon counter 403 is provided for each pixel, while a time counter 407 is provided for each partial pixel region. This configuration makes it possible to reduce the circuit scale. Details will be described later.

[0016] The peripheral circuit region 23 includes a vertical scanning circuit 302, a column circuit 303, a horizontal scanning circuit 304, a control pulse generating unit 305, an image restoration unit 306, and a signal output circuit 307. A vertical selection line 311VSEL is arranged in each row of the signal processing unit array in the pixel circuit region 22, extending in a first direction (the horizontal direction in FIG. 3). The vertical selection line 311VSEL is connected to each of the signal processing units 301 arranged in the first direction and forms a signal line. The first direction in which the vertical selection line 311VSEL extends may be referred to as the row direction or the horizontal direction. In this embodiment, the vertical selection line 311 is divided into a readout vertical selection line for reading out signals from the multiple signal processing units 301 in each row and a reset vertical selection line for resetting signals from the multiple signal processing units 301 in each row. In FIG. 3, the vertical selection line VSEL is shown together with a symbol indicating the row number. For example, the vertical selection line in the first row is labeled "VSEL[1]." The vertical selection line 311VSEL in each row is connected to the vertical scanning circuit 302. The vertical scanning circuit 302 supplies a vertical selection signal for selectively driving the signal processing unit 301 to the signal processing unit 301 via the vertical selection line 311VSEL.

[0017] In each column of the signal processing unit array in the pixel circuit region 22, a vertical signal line 310 is arranged, extending in a second direction (the vertical direction in FIG. 3) intersecting the first direction. The vertical signal line 310 is connected to each of the signal processing units 301 arranged in the second direction and forms a common signal line. The second direction in which the vertical signal lines 310 extend may be referred to as the column direction or the vertical direction. Note that in FIG. 3, the vertical signal lines 310 are shown together with a symbol indicating the column number. For example, the signal line 312 in the third column is labeled "POUT[3]." Each of the vertical signal lines 310 in each column includes n signal lines for outputting an n-bit digital signal.

[0018] The horizontal scanning circuit 304 supplies horizontal selection signals to the column circuits 303 for reading out signals from the column circuits 303. The horizontal scanning circuit 304 supplies the horizontal selection signals to the column circuits 303 of each column via the horizontal selection line 117HSEL. The column circuits 303 that receive control signals from the horizontal scanning circuit 304 output the signals they hold to the pixel restoration unit 306 via the horizontal output line 312HSIG. Note that in FIG. 3, the horizontal selection lines HSEL are shown together with symbols indicating the column numbers. For example, the horizontal selection line for the third column is assigned the symbol "HSEL[3]".

[0019] The control pulse generation unit 305 supplies control pulse signals that control the operation and timing of the vertical scanning circuit 302, the horizontal scanning circuit 304, and the column circuit 303. Note that at least some of the control pulse signals that control the operation and timing of the vertical scanning circuit 302, the horizontal scanning circuit 304, and the column circuit 303 may be supplied from outside the photoelectric conversion device. The pixel restoration unit 306 calculates a pixel value by dividing the measurement value of the time counter 407 from the measurement value of the photon counter 403, and outputs the calculated pixel value to the video output circuit 307. The video output circuit 307 outputs a signal corresponding to the pixel signal as an output signal SOUT of the photoelectric conversion device. Note that the signal restoration unit 306 may be configured to output the value of the time counter as is, i.e., may be configured to be provided outside the photoelectric conversion device.

[0020] Fig. 4 shows an example of an equivalent circuit and a block diagram of the pixel 201 of Fig. 2 and the signal processing unit 301 of Fig. 3 according to the first embodiment. Here, a group of multiple pixels is regarded as one partial pixel region, and a photon counter 403 is arranged for each pixel, while a time counter 407 is arranged for each partial pixel region.

[0021] Each pixel 201 in the sensor chip 11 includes an APD 201, which is a photoelectric conversion unit. When light is incident on the APD 201, a charge pair corresponding to the incident light is generated by photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 201. A voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode of the APD 201. A reverse bias voltage is supplied to the anode and cathode so that the APD 201 performs avalanche multiplication. With such a voltage supplied, charges generated by the incident light undergo avalanche multiplication, generating an avalanche current.

[0022] When a reverse bias voltage is supplied, there are two modes: Geiger mode, in which the potential difference between the anode and cathode is greater than the breakdown voltage, and linear mode, in which the potential difference between the anode and cathode is close to or less than the breakdown voltage. APDs operating in Geiger mode are called SPADs. For example, the voltage VL (first voltage) is -30V, and the voltage VH (second voltage) is 1V.

[0023] The signal processing unit 301 in the circuit chip 21 includes a quenching element 401 , a waveform shaping unit 402 , a photon counter unit 403 , a selection circuit unit 404 , an addition circuit unit 405 , a decision circuit 406 , and a time counter 407 .

[0024] The quench element 401 is connected to a power supply that supplies a voltage VH and the APD 201. The quench element 401 has a function of converting a change in avalanche current generated in the APD 201 into a voltage signal. The quench element 401 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, and has the function of suppressing avalanche multiplication by suppressing the voltage supplied to the APD 201 (quench operation).

[0025] The waveform shaping unit 402 shapes the potential change of the cathode of the APD 201 obtained when a photon is detected, and outputs a pulse signal. The waveform shaping unit 402 may be, for example, an inverter circuit or a buffer circuit.

[0026] The photon counter 403 counts the number of photons incident on a pixel and counts the pulse signal output from the waveform shaping unit 402 up to, for example, a first threshold Cx. The photon counter 403 also resets its count value when a predetermined control signal is supplied via a control line 412. The selection circuit 404 electrically connects or disconnects the photon counter 403 from the signal line 410 in response to a vertical selection signal VSEL supplied via a control line 413 from the vertical scanning circuit 302 in FIG. 3. The selection circuit 404 includes, for example, a buffer circuit for outputting signals. The adder circuit 405 adds the measurement values ​​of the four photon counters corresponding to the multiple pixels included in the partial pixel region and outputs the result to the determination circuit. The determination circuit 406 determines whether the sum output from the adder circuit 406 reaches the first threshold. The time counter 407 counts time. The count value is reset by a control signal supplied via a control line 414, and starts counting when the reset is released. If the added value output from the adder circuit unit 406 does not reach the first threshold value even after a predetermined time has elapsed (for example, when the measured value reaches 10 clocks), the time counter 407 is stopped. In this case, the measured value of each photon counter is output. The time counter is also stopped by a control signal supplied from the determination circuit 406. The selection circuit 408 switches between electrical connection and disconnection between the time counter 407 and the signal line 411 by a control signal VSEL supplied from the vertical scanning circuit 302 in FIG. 3 via a control line 415. The selection circuit 408 includes, for example, a buffer circuit for outputting a signal.

[0027] In Fig. 4, four photon counters are connected to one time counter. This makes it possible to reduce the circuit size compared to when one photon counter is connected to one time counter. Note that in this embodiment, four photon counters are connected to one time counter, but this is not limited to this. However, if the number of photon counters connected to one time counter increases, the possibility of saturating the pixel 201 increases.

[0028] FIG. 5 is a block diagram of an imaging device 500 according to the first embodiment.

[0029] The imaging device 500 is an imaging device including the photoelectric conversion device 100, and includes a lens 501, an image processing unit 502, an optical control unit 503, a storage unit 504, and a wireless I / F (Interface) unit 505 as a communication unit.

[0030] The lens 501 forms an optical image of a subject and transmits the formed optical image to the imaging surface of the photoelectric conversion device 100, which is equipped with a focus lens, a zoom lens, an aperture, and the like. The photoelectric conversion device 100 captures the optical image formed by the optical system 501. Signals read from the photoelectric conversion device 100 are output to an image processing unit 502. The image processing unit 502 performs processing on the signals output from the photoelectric conversion device 100, such as signal rearrangement, defective pixel correction, noise reduction, color conversion, white balance correction, gamma correction, and data compression, to generate an image. The image processing unit 502 incorporates a CPU as a computer and functions as a control unit that controls the operation of each component of the entire imaging device 500 based on a computer program stored in a memory as a storage medium. The optical control unit 503 controls the focus lens, zoom lens, aperture, and the like provided in the lens 501. A recording medium (not shown) is attached to the recording unit 504, which stores the image output from the image processing unit in the storage medium. Such a recording medium may be, for example, a memory card. Alternatively, a hard disk may be used as the recording medium. A wireless I / F (Interface) unit 505 serving as a communication unit outputs the image signal generated by the image processing unit 502 to the outside of the imaging device 500. Reference numeral 506 denotes a network, which is composed of, for example, a plurality of routers, switches, cables, etc. that satisfy a communication standard such as Ethernet (registered trademark), and a client controls the imaging device 500 via the network 506.

[0031] (Second embodiment) Next, a description will be given of a second embodiment. In the second embodiment, the configuration of the signal processing unit 301 is different from that of the second embodiment, but the other components are the same.

[0032] FIG. 6 is an example of an equivalent circuit and a block diagram of the pixel 201 in FIG. 2 and the signal processing unit 301 in FIG. 3 according to the second embodiment.

[0033] Each pixel 201 in the sensor chip 11 includes an APD 201, which is a photoelectric conversion unit. When light is incident on the APD 201, a charge pair corresponding to the incident light is generated by photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 201. A voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode of the APD 201. A reverse bias voltage is supplied to the anode and cathode so that the APD 201 performs avalanche multiplication. With such a voltage supplied, charges generated by the incident light undergo avalanche multiplication, generating an avalanche current.

[0034] When a reverse bias voltage is supplied, there are two modes: Geiger mode, in which the potential difference between the anode and cathode is greater than the breakdown voltage, and linear mode, in which the potential difference between the anode and cathode is close to or less than the breakdown voltage. APDs operating in Geiger mode are called SPADs. For example, the voltage VL (first voltage) is -30V, and the voltage VH (second voltage) is 1V.

[0035] The signal processing unit 301 in the sensor chip 21 includes a quenching element 601 , a waveform shaping unit 602 , a photon counter unit 603 , a selection circuit unit 604 , an addition circuit unit 605 , a decision circuit 606 , and a time counter 607 .

[0036] The quench element 601 is connected to a power supply that supplies a voltage VH and the APD 201. The quench element 601 has a function of converting a change in avalanche current generated in the APD 201 into a voltage signal. The quench element 601 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, and has the function of suppressing avalanche multiplication by suppressing the voltage supplied to the APD 201 (quench operation).

[0037] The waveform shaping unit 602 shapes the potential change of the cathode of the APD 201 obtained when a photon is detected, and outputs a pulse signal. The waveform shaping unit 602 may be, for example, an inverter circuit or a buffer circuit.

[0038] The photon counter 603 counts the number of photons incident on a pixel and counts the pulse signal output from the waveform shaping unit 602 up to, for example, a first threshold Cx. The photon counter unit 603 also resets its count value when a predetermined control signal is supplied via the vertical selection line 311. The selection circuit 604 electrically connects or disconnects the photon counter unit 603 from the signal line 610 in response to a vertical selection signal VSEL supplied via a control line 613 from the vertical scanning circuit 302 in FIG. 3. The selection circuit 604 includes, for example, a buffer circuit for outputting signals. The adder circuit 605 adds the outputs of the photon counters connected to pixels P00, P10, and P11 via the waveform shaping unit and outputs the sum of the measured values ​​of each photon counter to a decision circuit. The decision circuit 606 determines whether the sum output from the adder circuit unit 606 reaches the first threshold. This decision circuit 606 can change the first threshold via a signal line 616. For example, lowering the first threshold reduces the possibility that the output of the photon counter 603 will saturate, but increases noise in the image.

[0039] The first threshold can be changed by a control signal 615. When the first threshold is reached, a control signal is output to a time counter. The time counter 607, which is a counter that counts time, resets its count value by a control signal supplied via a control line 614, and starts counting when the reset is released. The time counter is stopped by a control signal supplied from the determination circuit 606. The selection circuit 608 switches between electrical connection and disconnection between the time counter circuit 608 and a signal line 611 by a control signal VSEL supplied via a control line 615 from the vertical scanning circuit 302 in FIG. 3. The selection circuit 608 includes, for example, a buffer circuit for outputting a signal.

[0040] In the first embodiment, the outputs of all photon counters included in the signal processing unit are output to the adder circuit unit 605, but in the second embodiment, some of the photon counters are configured not to output to the adder circuit unit 605. This makes it possible to reduce the circuit scale of the adder circuit unit 605. On the other hand, adopting the configuration of the second embodiment increases the possibility that the output values ​​of the photon counters that are not output to the adder circuit unit 605 will saturate. If saturation occurs, this can be suppressed by increasing the first threshold in the determination circuit 606. Furthermore, saturation can be suppressed by using pixels in the signal processing unit 301 that have the same spectral sensitivity for the photon counters that are not output to the adder circuit unit 605; for example, if there are two green pixels as in a Bayer array, using either one of them.

[0041] <Flowchart> FIG. 7 is a flowchart illustrating the operation of the photoelectric conversion device 100 according to the first or second embodiment. In the following description, each process (step) is prefixed with an S to omit the process (step). In S700, the adder circuit unit 605 is initially connected to two or more or all of the pixels. In S701, the adder circuit 605 and the time counter 407 start measuring photons or time, respectively. In S7020, the determination circuit 606 determines whether the total number of photons measured at each pixel exceeds a first threshold. If the answer is Yes, proceed to S703; if the answer is No, proceed to S7021. In S7021, the determination circuit 606 determines whether the time elapsed since the start of photon measurement exceeds a predetermined time. If the answer is Yes, proceed to S704; if the answer is No, return to S701 to continue measuring photons. In S703, the time counter 407 outputs the time at which the adder circuit 605 reaches the first threshold. In S704, the adding circuit 605 or the photon counter 603 outputs the photon measurement value. In S705, the decision circuit 606 determines whether or not to perform a reset. If there is no end instruction, the process returns to S702 to continue the measurement. If there is an end instruction, the operation ends without resetting.

[0042] <Other embodiments> In the embodiment, the imaging device is described as being a digital camera, but the imaging device also includes electronic devices with imaging capabilities, such as digital movie cameras, smartphones with cameras, tablet computers with cameras, in-vehicle cameras, drone cameras, cameras mounted on robots, and network cameras.

[0043] The present invention has been described in detail above based on its preferred embodiments, but the present invention is not limited to the above-mentioned embodiments, and various modifications are possible based on the gist of the present invention, and these modifications are not excluded from the scope of the present invention.

[0044] Note that a computer program that realizes part or all of the control in this embodiment and the functions of the above-described embodiment may be supplied to a photoelectric conversion device, an imaging device, or the like via a network or various storage media. Then, a computer (or a CPU, MPU, or the like) in the photoelectric conversion device, imaging device, or the like may read and execute the program. In this case, the program and the storage medium storing the program constitute the present invention. [Explanation of symbols]

[0045] 100 Photoelectric conversion device 500 Imaging device 501 Lens 502 Image processing unit 503 Optical control unit 504 Storage section 505 I / F section

Claims

1. A photoelectric conversion device having pixels each including a photoelectric conversion unit that outputs a signal in response to an incident photon, a first measuring means for measuring the number of photons incident on the pixel; an adding means for adding the measurement values ​​of the plurality of first measuring means; a second measuring means for measuring the time from when the first measuring means starts the measurement until when the measured value by the adding means reaches a first threshold value; the first measuring means is arranged for each of the plurality of pixels, The photoelectric conversion device is characterized in that the second measuring means is disposed for each partial pixel region including a plurality of the pixels having different spectral sensitivities.

2. 2. The photoelectric conversion device according to claim 1, wherein the second measurement means outputs the measurement value of the first measurement means if the measurement value by the addition means has not reached a first threshold value when a predetermined time has elapsed since the first measurement means started the measurement.

3. 2. The photoelectric conversion device according to claim 1, wherein the adding means adds together the measurement values ​​of the plurality of first measuring means corresponding to at least some of the pixels included in the partial pixel region.

4. 4. The photoelectric conversion device according to claim 3, wherein the adding means adds together the measurement values ​​of the plurality of first measuring means corresponding to all the pixels included in the partial pixel region.

5. 5. The photoelectric conversion device according to claim 2, wherein when the pixels included in the partial pixel region include pixels having the same spectral sensitivity, the measurement values ​​of the first measurement means corresponding to any of the pixels having the same spectral sensitivity are added together.

6. 5. The photoelectric conversion device according to claim 2, wherein when the pixels included in the partial pixel region have different spectral sensitivities, the measurement values ​​of the first measurement means corresponding to the pixel with the highest sensitivity are added together.

7. 7. The photoelectric conversion device according to claim 1, further comprising an output unit that outputs the measurement value obtained by the first measurement unit or the measurement value obtained by the second measurement unit corresponding to the pixel.

8. The photoelectric conversion device according to claim 7, characterized in that the output means outputs the measurement values ​​by the first measurement means corresponding to each of the plurality of pixels, excluding the measurement values ​​by the first measurement means that have reached the first threshold, and the measurement values ​​by the second measurement means.

9. The photoelectric conversion device according to claim 7 or 8, characterized in that the output means outputs a single signal that combines the measurement value of the first measurement means and the measurement value of the second measurement means included in a partial pixel area consisting of a plurality of the pixels.

10. 10. The photoelectric conversion device according to claim 7, wherein the output means outputs the measurement value by the first measurement means corresponding to each pixel when the measurement value by the second measurement means reaches a predetermined time.

11. 11. The photoelectric conversion device according to claim 1, further comprising a signal restoration means for restoring a pixel signal based on a measurement value by the first measurement means corresponding to each pixel or a time measurement value by the second measurement means.

12. 12. The photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit includes an avalanche photodiode for detecting incident photons.

13. An imaging device comprising the photoelectric conversion device according to claim 1 .

14. A control method for controlling a photoelectric conversion device having a pixel including a photoelectric conversion unit that outputs a signal in response to incident photons, and a first measurement means that measures the number of photons incident on the pixel, the method comprising: an adding step of adding together the measurement values ​​of the plurality of first measurement means; a second measuring step of measuring the time from when the first measuring means starts the measurement until when the measured value obtained by the adding step reaches a first threshold value, the first measuring means is arranged for each of the plurality of pixels, a second measuring step for measuring each partial pixel region including a plurality of pixels having different spectral sensitivities;

15. A computer program for controlling each unit of the photoelectric conversion device according to any one of claims 1 to 12 or the imaging device according to claim 13 by a computer.

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