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

Abstract

To provide technique materializing suppression of an increase in circuit scale and furthermore materializing suitable reading out of a pixel.SOLUTION: A photovoltaic device has: a pixel including a photovoltaic unit that outputs a signal in accordance with an incident photon. The photovoltaic device has first measuring means, second measuring means, selection means, and control means. The first measuring means measures the number of photons incident on the pixel. The second measuring means measures a time elapsing from the start of the measurement performed by the first measuring means until the time when the measured value of the first measuring means reaches a first threshold value. The selection means switches the first measuring means to be connected to the second measuring means among the plurality of first measuring means. The control means controls the timing at which the connection of the second measuring means is switched by the selection means.SELECTED DRAWING: Figure 4a

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] A 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 incident photons, the photoelectric conversion device comprising: a first measurement means that measures the number of photons incident on the pixel; a second measurement means that measures the time from when the first measurement means starts the measurement until the measurement value of the first measurement means reaches a first threshold; and a plurality of first measurement means: A first measuring means whose measurement value reaches a second threshold value smaller than the first threshold value the fastest is selected and connected to the second measuring means. The device includes a selection means and a control means for controlling the timing at which the selection means switches the connection of the second measurement means. [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] FIG. 1 is a diagram showing an example of a circuit chip of a photoelectric conversion device. [Figure 4a] 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 4b] 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 diagram showing an example of measurement using a photoelectric conversion device. [Figure 6] FIG. 1 is a block diagram illustrating an example of the functional configuration of an imaging device including 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 examples for realizing the present invention, and should be modified or changed as appropriate 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. Furthermore, parts having the same functions in all figures are designated by the same numerals, and repeated explanations thereof are omitted.

[0010] <Embodiment 1: Basic form> 1 is a diagram showing an example of the configuration of a photoelectric conversion device according to this embodiment. 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.

[0011] <Pixel substrate> FIG. 2 is a diagram showing an example of the configuration of the sensor chip 11. 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 from row 0 to row 5 and eight columns from column 0 to column 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.

[0012] <Circuit board> 3 is a diagram showing an example of the configuration of the circuit chip 21. The circuit chip 21 includes a pixel circuit region 22 and a peripheral circuit region .

[0013] <Pixel circuit area> The pixel circuit region 22 includes a plurality of signal processing units 301 arranged two-dimensionally across multiple rows and columns, each corresponding to a pixel 201 of the sensor chip. 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. The signal processing unit includes a photon counter 403 that counts the number of photons and a time counter 406 that measures time. In the photoelectric conversion device of this embodiment, photon counters 403a to 403d are provided for each pixel, but the time counter 406 is shared by multiple pixels. That is, a group of multiple pixels in the pixel region 12 is regarded as one partial pixel region, and photon counters 403a, b, c, and d are arranged for each pixel, while a time counter 406 is arranged for each partial pixel region. By adopting such a configuration, it is possible to reduce the circuit scale. Details will be described later.

[0014] <Peripheral circuit area> 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, a signal restoring 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. Note that in FIG. 3, the control line VSEL is shown together with a symbol indicating the row number. For example, the control 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 vertical selection signals for selectively driving the signal processing units 301 to the signal processing units 301 via vertical selection lines 311VSEL. In this embodiment, the vertical selection lines 311 are divided into readout vertical selection lines for reading out signals from the plurality of signal processing units 301 in each row and reset vertical selection lines for resetting signals from the plurality of signal processing units 301 in each row.

[0015] 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 vertical signal line 310 in the third column is labeled "POUT[3]." The vertical signal line 310 in each column includes n signal lines for outputting an n-bit digital signal.

[0016] 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 control signals to the column circuits 303 of each column via horizontal selection lines 313HSEL. Upon receiving the horizontal selection signals from the horizontal scanning circuit 304, the column circuits 303 sequentially output the retained signals to the horizontal output circuit 307 via signal lines 312HSIG and the signal restoration unit 306. 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 denoted by the symbol "HSEL[3]."

[0017] 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 signal restoration unit 306 calculates pixel values ​​from the measurement value of the time counter 406 and outputs them to the horizontal output circuit 307. The horizontal output circuit 307 outputs a signal corresponding to the pixel value restored by the signal restoration unit 306 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.

[0018] <Pixel circuit> Figure 4 shows an example of an equivalent circuit and block diagram of the pixel 201 in Figure 2 and the signal processing unit 301 in Figure 3. Figure 4 shows one signal processing unit 301 and four corresponding pixels 201a, 201b, 201c, and 201d. Here, a collection of multiple pixels is considered to be one partial pixel region, and photon counters 403a, b, c, and d are provided for each pixel, while a time counter 406 is provided for each partial pixel region. Note that, below, when it is necessary to distinguish between the four pixels, the symbols a, b, c, and d are assigned, and when it is not necessary to distinguish between them, the symbols are omitted.

[0019] Each pixel 201 in the sensor chip 11 includes an APD 202, which is a photoelectric conversion unit. When a photon is incident on the APD 202, a charge pair is generated by photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 202. A voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode of the APD 202 via a switch element 408. A reverse bias voltage is supplied to the anode and cathode so that the APD 202 performs avalanche multiplication. With such a voltage supplied, charges generated by incident light undergo avalanche multiplication, generating an avalanche current.

[0020] When a reverse bias voltage is supplied, there are two modes: Geiger mode, in which the anode and cathode operate at a potential difference greater than the breakdown voltage, and linear mode, in which the anode and cathode operate at a potential difference close to or less than the breakdown voltage. APDs operating in Geiger mode are called SPADs (Single Photon Avalanche Diodes). For example, the voltage VL (first voltage) is -30V, and the voltage VH (second voltage) is 1V.

[0021] The signal processing unit 301 in the circuit chip 21 includes a quenching element 401 , a waveform shaping unit 402 , a photon counter 403 , a switch 404 , a decision circuit 405 , a time counter 406 , a selection circuit 407 and a timing control circuit 410 .

[0022] The quench element 401 is connected to a power supply that supplies a voltage VH and the APD 202. The quench element 401 has a function of converting a change in avalanche current generated in the APD 202 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 202 (quench operation).

[0023] The waveform shaping unit 402 shapes the potential change of the cathode of the APD 202 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.

[0024] The photon counter 403 is a photon counter that measures the number of photons that have entered a pixel, and counts the pulse signal output from the waveform shaping unit 402 up to, for example, a first threshold value Cx. Furthermore, the photon counter 403 resets the measurement value when a predetermined control signal is supplied via the vertical selection line 311.

[0025] The APD 202, quench element 401, waveform shaping unit 402, and photon counter 403 described above are provided for each pixel. Meanwhile, the OR circuit 404, decision circuit 405, and time counter 406 described below are provided one for four pixels (i.e., one partial pixel area). Furthermore, one selection circuit 407 is provided for each photon counter 403, and one selection circuit 407 is provided for the time counter 406.

[0026] The switch 404, decision circuit 405, and timing control circuit 410 have the role of connecting the counter with the largest measurement value among the four photon counters 403a, 403b, 403c, and 403d to the time counter 406. For example, at the start of counting, the photon counter 403a and the time counter 406 are connected by the switch 404. Then, in the middle of counting photons, the switch 404 is switched so that the photon counter 403 with the largest count number among the photon counters 403a, 403b, 403c, and 403d is connected to the time counter 406. Details will be described later.

[0027] The determination circuit 405 also determines whether the measurement value of the photon counter 403, to which the time counter 406 is connected, has reached a first threshold Cx. The time counter 406 measures the time from when the photon counter 403 starts measurement until the measurement value reaches the first threshold Cx, and outputs the measured time as a pixel value. That is, when the determination circuit 405 determines that the measurement value of the photon counter 403 has reached the first threshold Cx, the determination circuit 405 outputs "1." In response, the time counter 406 holds the time measurement value at that time as a pixel value. Then, when a request signal is received from a request circuit (not shown), the measurement value of the time counter 406 that has been held is sent to a peripheral circuit. Also, The output of the decision circuit 405 is also connected to four photon counters 403a, 403b, 403c, and 403d, and when the decision circuit 405 outputs "1", photon counting stops in all four photon counters and each photon measurement value is held.

[0028] Timing control circuit 410 teeth The timing for switching the connection of the time counter 406 is controlled based on predetermined conditions. For example, the connection may be switched at regular intervals, or the timing may be determined based on the measurement value of the photon counter. Detailed operation will be described later. By switching the connection of the time counter shared by multiple photon counters according to the timing, photons can be measured efficiently. Note that while FIG. 4 shows an example in which a timing control circuit is arranged for each partial pixel region, a timing control circuit may also be arranged for each pixel.

[0029] <Explanation of effect> As described above, time counter 406 is connected to photon counter 403 with the largest count among photon counters 403a, 403b, 403c, and 403d. Therefore, time counter 406 measures the time from when light starts to be incident on the pixel to when the pixel is saturated, for the pixel with the largest amount of light incident per unit time among pixels 201a, 201b, 201c, and 201d.

[0030] The shorter the time until saturation, the greater the amount of light (brighter) that enters the pixel per unit time. Therefore, by measuring the time until saturation, the brightness information of the brightest pixel among the four pixels can be obtained from the measurement value of the time counter 406.

[0031] Of the four photon counters, the measurement value of the brightest pixel is always the first threshold, while the other three photon counters each measure the photon values ​​at the point when the measurement value of the brightest pixel reaches the first threshold. Therefore, from the measurement value of the photon counter 403, it is possible to obtain brightness information of the other three pixels relative to the brightest pixel from the measurement value of the photon counter 403. Therefore, by combining the measurement value of the time counter 406 and the measurement value of the photon counters, it is possible to obtain brightness information of all four pixels. Specific pixel signal restoration processing will be described later.

[0032] <Selection circuit> 3 via a vertical selection line 311 for reading out the nth row, the selection circuit 407 switches between electrical connection and disconnection between the photon counter 403 and the time counter 406 and the vertical signal line 310. The pixel measurement values ​​and time measurement values ​​that are read out sequentially are sent to the column circuit 303 and output to the outside of the photoelectric conversion device 100 via the signal restoration unit 306 and the horizontal output circuit 307. After the pixel measurement values ​​and time measurement values ​​are read out by the selection circuit 407 in response to a readout selection signal supplied from the vertical selection line 311, the photon counter and time counter are reset by a reset signal supplied via the vertical selection line 311 and each restart their counting.

[0033] In addition, in FIG. 4, a vertical signal line 310 for the time counter is provided in addition to the vertical signal line 310 for the photon counter of each column. It may also be .

[0034] For example, since the photon measurement value of the brightest pixel among the four pixels should always match the first threshold, the time measurement value may be read out instead of the photon measurement value of the brightest pixel. Specifically, the time measurement value can be read out when a control signal for reading out the photon measurement value of the pixel connected to the time counter is received by the vertical selection signal VSEL. This configuration is preferable because it reduces the amount of signal to be read out and reduces power consumption.

[0035] In addition, a flag signal for identifying which of the four pixels has reached the first threshold, the time measurement value of the pixel that has reached the first threshold, and the photon measurement values ​​of the three pixels that have not reached the first threshold may be output together on a single signal line using a multiplexer circuit or the like.

[0036] <Photon counter switching: Variation 1> Here, we will explain a method for switching the photon counter to which the time counter is connected using switch 404 during photon counting. First, we will explain the first method, which uses a peripheral scanning circuit to switch the switches of each pixel sequentially. In this method, the timing control circuit 410 that controls the timing for selecting the pixel for time measurement is located in the peripheral scanning circuit section, as shown in Figure 4a.

[0037] As described above, the time counter 406 counts the time until the measurement value of any of the photon counters 403a, 403b, 403c, and 403d reaches the first threshold Cx. Therefore, the switch 404 needs to compare the measurement values ​​of the photon counters 403a, 403b, 403c, and 403d before the measurement value of the photon counter reaches a specific threshold and before the time counter reaches a threshold (first predetermined time).

[0038] Therefore, the photoelectric conversion device 100 sends a request signal at regular intervals (a second predetermined time shorter than the first predetermined time) from a request signal sending circuit in the vertical scanning circuit 110 in Fig. 3 to the signal processing unit 301 of each pixel via the vertical selection line 311. When the signal processing unit 301 receives a request signal from the request signal sending circuit, the determination circuit 405 determines whether any of the four photon counters 403a, 403b, 403c, and 403d has reached a second threshold value that is smaller than the first threshold value, and sends the determination result to the vertical scanning circuit 110. In response to the determination result, the vertical scanning circuit 110 switches the connection destination of the time counter to the photon counter that has reached the second threshold value.

[0039] By sending the request signal multiple times before one frame is completed, the connection of the time counter can be switched when the largest measurement value among the four photon counters 403a, 403b, 403c, and 403d reaches the second threshold. In other words, the connection of the time counter can be switched to the brightest pixel among the four pixels before the measurement value of the brightest pixel reaches the first threshold. With this configuration, brightness information of the brightest pixel among the four pixels can be obtained from the measurement value of the time counter 406.

[0040] In other words, the photoelectric conversion device of this embodiment reduces the circuit size by sharing a time counter among multiple pixels. The issues that arise from sharing a time counter among multiple pixels are resolved by switching the connection destination of the time counter midway. The following describes these issues.

[0041] Figure 5 is a diagram illustrating the relationship between time and photon count values. Figure 5(a) shows a case where, among multiple pixels that share a time counter, the pixel to which the time counter is connected has the highest sensitivity. On the other hand, Figure 5(b) shows a case where, among multiple pixels that share a time counter, there is another pixel that has a higher sensitivity than the pixel to which the time counter is connected.

[0042] As shown in Figure 5(a), when the photon counter connected to the time counter has the highest pixel sensitivity, brightness information for multiple pixels can be obtained by measuring the time until the photon counter connected to the time counter saturates. On the other hand, as shown in Figure 5(b), when there are other pixels with higher pixel sensitivity than the photon counter connected to the time counter, the photon counters not connected to the time counter will saturate before the photon counter connected to the time counter saturates. In this case, even if the time until the photon counter connected to the time counter saturates is measured, it is not possible to obtain brightness information for pixels that have already saturated. As such, when a time counter is shared by multiple pixels, brightness information may not be obtained correctly depending on the subject.

[0043] To solve this problem, the photoelectric conversion device of this embodiment switches the connection destination of the time counter to the pixel with the highest pixel sensitivity, thereby preventing photon counters that are not connected to a time counter from becoming saturated.

[0044] <Counter Switching: Variation 2> Next, we will explain the second method, in which a switching circuit is placed in each pixel. In this method, the timing control circuit 410 that controls the timing of selecting the pixel for time measurement is located in the signal processing section of each pixel, as shown in Figure 4b.

[0045] As described above, the time counter 406 counts the time until the measurement value of the photon counter with the largest count among the photon counters 403a, 403b, 403c, and 403d reaches the first threshold. Therefore, the switch 404 needs to compare the measurement values ​​of the photon counters 403a, 403b, 403c, and 403d before the measurement value of the photon counter reaches a specific threshold.

[0046] Therefore, the decision circuit 405 determines whether any of the photon counters 403a, 403b, 403c, and 403d has reached a second threshold value that is smaller than the first threshold value. Then, the connection of the time counter is switched to the photon counter that has reached the second threshold value. For example, if the first threshold value is the saturation level and the second threshold value is half the saturation level, the decision circuit 405 can be provided with an OR circuit for the most significant two bits of the measurement values ​​of the four photon counters, and when the output of the OR circuit becomes 1, the connection of the time counter can be switched. With this configuration, brightness information of the brightest pixel among the four pixels can be obtained from the measurement value of the time counter 406.

[0047] <Performing the switching operation multiple times: Variation 3> Note that counter switching may be controlled multiple times within one frame. For example, if the difference in measurement values ​​between multiple photon counters is small, it may be impossible to predict which photon counter will saturate first due to the effects of photon shot noise. Therefore, when one of the multiple photon counters reaches the second threshold, if the difference in measurement values ​​between photon counter A, which has the largest measurement value, and photon counter B, which has the second largest measurement value, is smaller than the third threshold, it is better to switch the counter again. The third threshold can be determined by photon shot noise, and may be, for example, the square root of the second threshold or approximately twice that value.

[0048] Specifically, after switching the counter once, it is determined whether any of the multiple photon counters has reached a fourth threshold, which is greater than the second threshold and less than the first threshold. Then, the connection destination of the time counter is switched to the photon counter that has reached the fourth threshold. By switching the connection destination of the time counter multiple times in this way, the probability that the connection destination of the time counter is the pixel with the highest pixel sensitivity is increased. Note that at this time, only photon counter A and photon counter B are required to determine whether the fourth threshold has been reached. This is because photon counters other than photon counters A and B are less likely to saturate before photon counters A and B, even when considering the effect of photon shot noise.

[0049] <Signal restoration section> The signal restoration unit 306 restores the time measurement value counted by the time counter 406 and the photon measurement value counted by the photon counter 403 into pixel signals representing brightness information of the subject. When the time measurement value is T0 and the photon measurement values ​​of the four pixels 201a, 201b, 201c, and 201d are P1, P2, P3, and P4, respectively, the pixel signal values ​​C1, C2, C3, and C4 can be calculated using the following equations. C1=K×P1 / T0, C2=K×P2 / T0 C3 = K × P3 / T0, C4 = K × P4 / T0 K is a natural number, and is preferably determined to be a value that prevents C1, C2, C3, and C4 from becoming less than 1 LSB. Specifically, K may be set to the maximum value of the time measurement value.

[0050] <Output of photon measurement value after a certain time: Variation 4> Note that the determination circuit 405 may be configured to stop the time counter 406 and output the photon count value at that time if the count value of the photon counter connected to the time counter does not reach the first threshold value even after a predetermined time (first predetermined time) has elapsed. This configuration can solve the problem of the frame rate slowing down when the brightness of the subject is very low. It is preferable to set the predetermined time to the maximum value of the time count.

[0051] <Spectral sensitivity, Bayer array> 3 and 4 show an example in which one signal processing unit 301 is connected to four pixels 201, but the circuit scale can be reduced if two or more pixels are connected to one signal processing unit 301. Specifically, a photon counter may be provided for each pixel, and a time counter may be shared by multiple pixels.

[0052] Each pixel 201 may have an on-chip color filter and be configured to be able to acquire spectral information. For example, assuming a Bayer array color filter, a configuration in which one signal processing unit 301 is provided for four 2x2 pixels is preferable, since this makes it possible to acquire brightness information for each Bayer pixel. In other words, it is preferable that at least some of the pixels that share a time counter have different spectral sensitivities.

[0053] If the spectral sensitivities of the pixels are not different, the pixel count values ​​of multiple pixels may reach the first threshold Cx simultaneously. In this case, the time measurement value at the time when the multiple pixels reach the first threshold Cx is held as the pixel value. Then, when a request signal is received from a request circuit (not shown), the held measurement value of the time counter 406 is sent to the peripheral circuit. The time counter is then connected to one of the pixels that has not yet reached the first threshold Cx. Thereafter, the same operation is repeated each time the pixel count value of the pixel connected to the time counter reaches the first threshold Cx.

[0054] In the case of a Bayer array, since green pixels have the highest sensitivity in a typical subject, it is preferable to initially connect the time counter to a green pixel. Furthermore, when capturing a video with multiple frames, it is even more preferable to compare the values ​​of the red, green, and blue pixels in the previous frame and, in the next frame, initially connect the time counter to the pixel with the highest sensitivity in the previous frame.

[0055] <Imaging device> FIG. 6 is a block diagram of an imaging device 500 using the photoelectric conversion device 100.

[0056] The imaging device 500 is, for example, a digital camera, and is an imaging device that includes the photoelectric conversion device 100, and includes a lens 501, an image processing unit 502, an optical control unit 503, a memory unit 504, and a wireless I / F (Interface) unit 505 as a communication unit.

[0057] 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 lens 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.

[0058] <Flowchart> 7 is a flowchart illustrating the operation performed by the photoelectric conversion device of the present invention. In the following description, each process (step) is represented by prefixing it with S, and the process (step) is notated in detail. In S700, switch 404 initially connects time counter 406 to one of four photon counters 403a, 403b, 403c, and 403d. The initial connection destination may be selected arbitrarily, or information from the previous frame may be used.

[0059] In S701, it is determined whether any of the measurement values ​​of the four photon counters has reached the second threshold. If the measurement value has not reached the second threshold, the connection destination of the time counter remains the initial connection and photon counting and time counting continue. If the measurement value has reached the second threshold, the process proceeds to S702, where the connection destination of the time counter is switched to the photon counter that has reached the second threshold.

[0060] In S703, it is determined whether the measurement value of the photon counter to which the time counter is connected after the switch has reached the first threshold value. Then, in S704, when the measurement value of the photon counter reaches the first threshold value, the time counter stops counting time and outputs the number of photon counts and the number of time counts.

[0061] <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.

[0062] The present invention has been described in detail above based on its preferred embodiments, but the present invention is not limited to the above 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.

[0063] 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]

[0064] 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; a second measuring means for measuring the time from when the first measuring means starts the measurement until the measured value of the first measuring means reaches a first threshold value; a selection means for selecting, from among the plurality of first measurement means, a first measurement means whose measurement value reaches a second threshold value that is smaller than the first threshold value earliest, and connecting the first measurement means to the second measurement means; and control means for controlling the timing of switching the connection of said second measurement means by said selection means.

2. The photoelectric conversion device according to claim 1, characterized in that the control means determines whether or not to switch the connection of the second measurement means by the selection means based on the measurement values ​​of each of the plurality of first measurement means at predetermined time intervals.

3. the control means is arranged for each partial pixel region made up of a plurality of the pixels, and determines whether or not a measurement value measured by the first measurement means corresponding to the pixel included in the partial pixel region is greater than the second threshold value which is smaller than the first threshold value; 3. The photoelectric conversion device according to claim 1, wherein the selection means switches the connection to the first measurement means whose measurement value is greater than the second threshold value.

4. 4. The photoelectric conversion device according to claim 3, wherein the selection means connects the second measurement means to the first measurement means corresponding to the pixel included in the partial pixel area and having the largest measurement value by the first measurement means.

5. the control means is arranged for each pixel, and determines whether or not a measurement value by the first measurement means corresponding to each pixel is greater than the second threshold value, which is smaller than the first threshold value; 3. The photoelectric conversion device according to claim 1, wherein the selection means switches the connection to the first measurement means whose measurement value is greater than the second threshold value.

6. 6. 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.

7. 7. The photoelectric conversion device according to claim 6, wherein the output means outputs, among the measurement values ​​by the first measurement means corresponding to each of the plurality of pixels, the measurement values ​​by the first measurement means other than the first measurement means that has reached the first threshold, and the measurement values ​​by the second measurement means.

8. The photoelectric conversion device according to claim 6 or 7, 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.

9. 9. The photoelectric conversion device according to claim 6, 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 first predetermined time.

10. 9. 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.

11. the first measuring means is arranged for each of the plurality of pixels, 11. The photoelectric conversion device according to claim 1, wherein the second measurement means is arranged for each partial pixel region including a plurality of the pixels having different spectral sensitivities.

12. 12. The photoelectric conversion device according to claim 11, wherein the second measurement means is connected to the first measurement means corresponding to a pixel of the plurality of pixels that had the highest sensitivity in a previous frame.

13. the photoelectric conversion device has red, blue, and green pixels; 12. The photoelectric conversion device according to claim 11, wherein the second measurement means is initially connected to the first measurement means corresponding to the green pixel.

14. the control means determines, based on a request signal, whether the measurement values ​​of the first measurement means corresponding to each of the plurality of pixels have reached the second threshold value, which is smaller than the first threshold value; The photoelectric conversion device according to any one of claims 1 to 13, characterized in that the selection means switches the connection of the second measurement means to the first measurement means whose measurement value has reached the second threshold value based on the judgment result.

15. 15. The photoelectric conversion device according to claim 1, wherein the control means controls the timing of selecting pixels for time measurement a plurality of times within one frame.

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

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

18. 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 the photons that have entered the pixel; a second measurement means for measuring a time from when the first measurement means starts the measurement until when a measurement value of the first measurement means reaches a first threshold value, a selection step of selecting, from among the plurality of first measurement means, a first measurement means whose measurement value reaches a second threshold value that is smaller than the first threshold value earliest, and connecting the first measurement means to the second measurement means; a control step of controlling timing for switching the connection of the second measurement means by the selection step.

19. A computer program for causing a computer to function as each means of the photoelectric conversion device described in any one of claims 1 to 16 or the imaging device described in claim 17.

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