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

Abstract

To provide a photoelectric conversion device for suppressing decrease in gradation, when the luminance of a subject is high, an imaging apparatus, a control method, and a computer program.SOLUTION: In the photoelectric conversion device, a pixel 201 includes a photoelectric conversion part 202 for outputting a signal in response to an incident photon. A signal processing part includes a quench element 401, a waveform shaping part 402, a photon counter 403, a time counter 404, a determination circuit 405, a selection circuit 406, a pulse generation circuit 407, and a switch element 408. The photon counter 403 measures the number of photons incident on the pixel. The time counter 404 measures a time period from when the photon counter 403 starts measurement to when a measurement value reaches a first threshold. The pulse generation circuit restricts the number of pulses counted by the photon counter 403, to change the sensitivity of the pixel.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.

[0003] Patent Document 1 proposes a configuration that includes a time counter that measures time in addition to a photon counter that counts photons. The time counter measures the time from when the photon counter starts measuring until the number of photons reaches a predetermined value, and calculates a pixel value from the measured time. Since the time to measure photons differs for each pixel, it becomes possible to obtain an image with a high dynamic range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Publication 2015 / 0163429 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of the configuration of Patent Document 1, when the luminance of the subject is high, the time it takes for the number of photons to reach a predetermined value becomes short, resulting in coarse gradation when the pixel value is calculated. Therefore, an object of the present invention is to provide a photoelectric conversion device or the like capable of suppressing a decrease in gradation. [Means for solving the problem]

[0006] A photoelectric conversion device according to one aspect of the present invention comprises: A pixel including a photoelectric conversion unit that outputs a signal in response to an incident photon; a photon counter that measures the number of photons incident on the pixel; a time counter that measures the time from when the photon counter starts the measurement until the measurement value of the photon counter reaches a first threshold; and a sensitivity adjustment means for changing the sensitivity of the pixel during the period from when the photon counter starts the measurement until the measured value of the photon counter reaches the first threshold value. death, The sensitivity adjustment means changes the sensitivity of the pixel after the first time point in accordance with the measurement value of the photon counter at the first time point. Effect of the Invention

[0007] According to the present invention, it is possible to realize a photoelectric conversion device or the like capable of suppressing a decrease in gradation. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram for explaining the configuration of a photoelectric conversion device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining a configuration example of the sensor chip according to the first embodiment. [Diagram 3] 1 is a block diagram showing an example of the configuration of a circuit chip 21 according to a first embodiment. [Figure 4] 2 is an equivalent circuit diagram of a pixel 201 and a signal processing unit 301 according to the first embodiment. FIG. [Diagram 5] 5A to 5C are diagrams illustrating the operation of sensitivity adjustment by the pulse generating circuit of the first embodiment. [Figure 6] 5A to 5C are diagrams illustrating an example of sensitivity adjustment in the first embodiment. [Figure 7] 13A to 13C are diagrams illustrating an example of sensitivity adjustment in the second embodiment. [Figure 8] FIG. 1 is a block diagram of an imaging device 500 using the photoelectric conversion device 100 of the first or second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, the same members or elements are given the same reference numerals, and duplicated descriptions will be omitted or simplified. <Embodiment 1>

[0010] FIG. 1 is a diagram illustrating the configuration of a photoelectric conversion device according to the first 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 operation of the pixel circuit region 22.

[0011] FIG. 2 is a diagram showing an example of the configuration of the sensor chip 11 according to the first embodiment. The pixel region 12 of the sensor chip 11 includes a plurality of pixels 201 arranged two-dimensionally. That is, the pixel region 12 includes a plurality of pixels 201, and the plurality of pixels are arranged in a plurality of rows and a plurality of columns. Each pixel 201 includes a photoelectric conversion unit 202 including an avalanche photodiode (hereinafter, APD) that outputs a signal in response to incident photons.

[0012] 2 shows 12 pixels 201 arranged in three rows from row 0 to row 2 and four columns from column 0 to column 3, along with reference numbers indicating row and column numbers. For example, the pixel 201 arranged in row 2 and column 2 is given the reference number "P22." Note that the number of rows and columns of the pixels 201 constituting the pixel region 12 is not limited to the example in FIG. 2.

[0013] FIG. 3 is a block 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 . The pixel circuit region 22 includes a plurality of signal processing units 301 arranged two-dimensionally in a plurality of rows and columns, and each signal processing unit 301 is electrically connected to a corresponding pixel 201 of the sensor chip.

[0014] 3 shows 12 signal processing units 301 arranged in three rows from row 0 to row 2 and four columns from column 0 to column 3, together with reference numbers indicating row and column numbers. For example, the signal processing unit 301 arranged in row 2 and column 2 is given the reference number "S22". Note that the number of rows and columns of the signal processing units 301 constituting the pixel circuit region 22 is not limited to the example in FIG. 3, and may be any number corresponding to the number of rows and columns of the pixels 201 of the sensor chip 11. As will be described later, each signal processing unit 301 is provided with a photon counter 403 that measures the number of photons incident on a pixel, and a time counter 404 that measures time.

[0015] The peripheral circuit region 23 includes a vertical scanning circuit 302, a column circuit 303, a horizontal scanning circuit 304, a control pulse generating section 305, a signal restoring section 306, a horizontal output circuit 307, and the like. A vertical selection line 311 is wired in a first direction (horizontal direction in FIG. 3) to the signal processing units 301 in each row of the pixel circuit region 22. The vertical selection line 311 is commonly connected to each of the signal processing units 301 arranged in the first direction. The first direction may be referred to as the row direction or the horizontal direction.

[0016] 3, the vertical selection lines 311 are shown together with symbols indicating row numbers. For example, the vertical selection line 311 in the first row is given the symbol "VSEL[1]". The vertical selection lines 311 in each row are connected to the vertical scanning circuit 302, and the vertical scanning circuit 302 supplies a vertical selection signal VSEL for selectively driving the signal processing unit 301 in a predetermined row to the signal processing unit 301 via the vertical selection line 311. In this embodiment, the vertical selection line 311 is divided into a readout vertical selection line for reading out signals of the multiple signal processing units 301 in each row and a reset vertical selection line for resetting signals of the multiple signal processing units 301 in each row.

[0017] A vertical signal line 310 is wired in a second direction (vertical direction in FIG. 3) perpendicular to the first direction to a plurality of signal processing units 301 in each column of the pixel circuit region 22. The vertical signal line 310 is commonly connected to a plurality of signal processing units 301 arranged in the second direction. The second direction may be referred to as a column direction or a vertical direction. 3, the vertical signal lines 310 are shown with reference characters indicating the column numbers. For example, the vertical signal line 310 in the third column is given the reference character "POUT[3]." The vertical signal lines 310 in each column include n signal lines for outputting n-bit digital signals.

[0018] The horizontal scanning circuit 304 supplies a horizontal selection signal for reading out a signal from the column circuit 303 to the column circuit 303 via a horizontal selection line 313. The column circuit 303 that has received the horizontal selection signal from the horizontal scanning circuit 304 sequentially outputs the temporarily held output signal to the horizontal output circuit 307 via a signal line 312 and a signal restoration unit 306. The signal line 312 includes n signal lines for outputting an n-bit digital signal. 3, the horizontal selection lines 313 are shown together with a reference symbol indicating a column number. For example, the horizontal selection line 313 in the third column is given the reference symbol "HSEL[3]."

[0019] The control pulse generating unit 305 supplies control pulse signals and the like that control the operations and timings of the vertical scanning circuit 302, the horizontal scanning circuit 304, and the column circuit 303. Note that at least some of the pulse signals and the like that control the operations and timings 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 100.

[0020] As described below, the signal restoration unit 306 calculates a pixel value from the value of the time counter 404, and outputs the pixel value 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 of the photoelectric conversion device 100. The signal restoration unit 306 may be provided outside the photoelectric conversion device 100 .

[0021] FIG. 4 is an equivalent circuit diagram of the pixel 201 and the signal processing unit 301 according to the first embodiment. The 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, and a voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode via a switch element 408.

[0022] A reverse bias voltage that causes the APD 202 to perform avalanche multiplication is supplied to the anode and cathode of the APD 202. By supplying such a reverse bias voltage, the charge generated by the incident light undergoes avalanche multiplication, generating an avalanche current.

[0023] In addition, the APD 202 has a Geiger mode in which the potential difference between the anode and cathode is greater than the breakdown voltage when a reverse bias voltage is supplied. Also, the APD 202 has a linear mode in which the potential difference between the anode and cathode is close to or less than the breakdown voltage. An APD operated in the Geiger mode is called a SPAD (Single Photon Avalanche Diode). In this case, the voltage VL (first voltage) is, for example, -30V, and the voltage VH (second voltage) is, for example, 1V.

[0024] The signal processing unit 301 in the circuit chip 21 includes a quench element 401, a waveform shaping unit 402, a photon counter 403, a time counter 404, a decision circuit 405, a selection circuit 406, a pulse generation circuit 407, a switch element 408, etc. The pulse generation circuit 407 supplies a pulse for switching the bias potential of the APD 202 between ON and OFF by the switch element 408.

[0025] The quench element 401 is connected to a power supply that supplies a voltage VH and the APD 202 via a switch element 408. The quench element 401 has a function of converting a change in avalanche current occurring 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 a function of suppressing avalanche multiplication by suppressing the voltage supplied to the APD 202 (quench operation).

[0026] The waveform shaping unit 402 shapes the potential change of the cathode of the APD 202 obtained upon photon detection, and outputs a pulse signal. The waveform shaping unit 402 may be, for example, an inverter circuit or a buffer circuit. Reference numeral 403 denotes a photon counter that measures 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 value Cx. Furthermore, the photon counter 403 resets the count value when a predetermined control signal is supplied via the vertical selection line 311.

[0027] The decision circuit 405 decides whether the count value of the photon counter 403 has reached a first threshold value Cx. The time counter 404 measures the time from when the photon counter 403 starts measurement until the count value (measured value) reaches the first threshold value Cx by the decision circuit 405, and outputs the measured time as a pixel value. That is, when the decision circuit 405 decides that the count value of the photon counter 403 has reached the first threshold value Cx, the time counter 404 immediately stops counting time and holds the time count value at that time as the pixel value.

[0028] Therefore, the shorter the time to reach the first threshold Cx, the greater the amount of light incident on the pixel per unit time (the brighter the pixel is). In other words, by measuring the time until saturation, the brightness information of each pixel can be obtained as a pixel value from the count value of the time counter 404. The details of the process of restoring the pixel signal from the count value of the time counter 404 will be described later.

[0029] The selection circuit 406 electrically switches between ON and OFF between the time counter 404 and the vertical signal line 310 in response to a vertical selection signal VSEL for reading out the n-th row, which is supplied from the vertical scanning circuit 302 in Fig. 3 via a vertical selection line 311. When the selection circuit 406 is ON, the time count value is sent to the column circuit 303 via the vertical signal line 310 and output to the outside of the photoelectric conversion device 100 via the signal restoration unit 306 and the horizontal output circuit 307.

[0030] After the time count value is read out by the selection circuit 406 in response to a readout selection signal supplied from the vertical selection line 311, the photon counter 403 and the time counter 404 are reset by a reset signal supplied via the vertical selection line 311. Each counter restarts counting immediately after being reset.

[0031] The pulse generating circuit 407 can adjust the sensitivity of the pixel by limiting the number of pulses counted by the photon counter 403 out of the pulse signals generated by avalanche multiplication.

[0032] FIG. 5 is a diagram for explaining the operation of sensitivity adjustment by the pulse generating circuit according to the first embodiment. 5 correspond to the signals shown in Fig. 4, where Pctl is a gate control signal supplied from the pulse generating circuit 407 to the gate of the switch element 408, and Vcath is the cathode voltage of the switch element 408 as an input to the waveform shaping unit 402. Also, the timing at which photons are incident is indicated by an arrow.

[0033] Before time t1, the gate control signal Pctrl is at H (High) level, so that the cathode of the APD 202 is in a floating state. Also, the recharge of the APD 202 is completed, and the APD 202 is in a standby state in which avalanche multiplication is possible.

[0034] In this state, when a photon is incident at time t1, avalanche multiplication occurs, the cathode voltage Vcath transitions from H to L (Low), and the count value of photon counter 403 increases by one count via waveform shaping unit 402. However, since the cathode of APD 202 remains in a floating state, no recharge occurs after the count, and the number of counts in photon counter 403 does not change until time t2.

[0035] At time t2, the pulse generating circuit 407 changes the gate control signal Pctrl to the L level. This switches the cathode of the APD 202 from a floating state to a state connected to VH, causing a recharge, and the APD 202 returns to a standby state in which avalanche multiplication is possible. After that, when a photon is incident at time t3, avalanche multiplication occurs, and the count value of the photon counter 403 increases by one via the waveform shaping unit 402.

[0036] In this way, no matter how many photons are incident within one pulse period of the gate control signal Pctrl from the pulse generating circuit 407, the count value of the photon counter 403 is limited to 1. Therefore, the number of counts of the photon counter 403 per unit time, i.e., the sensitivity of the pixel, can be adjusted by the pulse period of the gate control signal Pctrl from the pulse generating circuit 407. That is, by using the pulse generating circuit 407 to lengthen the pulse period of the gate control signal Pctrl, low sensitivity can be achieved, and by shortening it, high sensitivity can be achieved. In this way, it is possible to change the sensitivity by changing the period of the pulse for switching the bias potential of the APD 202.

[0037] 3 restores the time count value counted by the time counter 404 as an output signal of a pixel representing brightness information of the object. When the time from when the photon counter 403 starts counting until the count value reaches a first threshold value Cx is defined as T, the pixel signal value C can be calculated by the following formula 1.

[0038] C=K / T...Formula 1 K is a natural number, and is preferably determined to be a value that does not cause C to become less than 1 LSB. Specifically, K may be set to the maximum value (upper limit) of the time count value. The photoelectric conversion device 100 of this embodiment controls the pulse period of the gate control signal Pctrl output from the pulse generating circuit 407 to suppress the decrease in gray scale.

[0039] First, a problem that arises when the pulse period is not controlled in terms of time, as in the photoelectric conversion device disclosed in Patent Document 1, will be described. As can be seen from the above-mentioned formula 1, the smaller T is, the larger the change in C becomes when T changes by one count.

[0040] Therefore, the gradation of the restored pixel signal decreases as T becomes smaller. T becomes smaller when there are many photons incident on a pixel per unit time, that is, when the brightness of the subject is high. That is, when the luminance of the subject is high, the time T from when the photon counter 403 starts counting until the count value reaches the first threshold value Cx becomes short, and the gradation of the restored pixel signal decreases.

[0041] FIG. 6 is a diagram for explaining an example of sensitivity adjustment in the first embodiment, and explains the relationship between the count number of the time counter 404 and the count number of the photon counter 403. In FIG. Fig. 6(A) is a diagram for explaining an example of driving a conventional photoelectric conversion device shown for comparison, and Fig. 6(B) is a diagram for explaining an example of sensitivity adjustment in the photoelectric conversion device of this embodiment. In each diagram, a curve 601 when the subject brightness is high, a curve 602 when the subject brightness is appropriate, and a curve 603 when the subject brightness is low are shown.

[0042] As shown by the curve 601 in Fig. 6A, when a conventional photoelectric conversion device is used, if the brightness of the subject is high, the time from when the photon counter 403 starts counting until the count value reaches the first threshold value Cx becomes short. Therefore, the gradation of the restored pixel signal decreases. In other words, the gradation difference becomes coarse.

[0043] On the other hand, in the photoelectric conversion device of this embodiment, the pulse period before the first time T0 is lengthened to reduce the sensitivity. As a result, as shown by the curve 601' in FIG. 6B, when the luminance is high, the time from when the photon counter 403 starts counting until the count value reaches the first threshold value Cx is lengthened, suppressing the deterioration of the gradation of the restored pixel signal. As a result, the accumulation time is effectively extended when the luminance of the subject is high, and the effect of reducing the influence of the flicker of the light source is also obtained. In addition, the count timing of the high sensitivity pixels is shifted backward, which has the effect of equalizing the power.

[0044] In addition, the pulse generating circuit 407 shortens the pulse period after the first time T0 from when the photon counter 403 starts measuring until the measurement value of the photon counter reaches the first threshold value Cx. This increases the sensitivity of the pixel over time, for example, as shown by curves 602' and 603' in Fig. 6(B). Note that the curves 601', 602', and 603' in Fig. 6(B) correspond to the curves 601, 602, and 603 in Fig. 6(A), respectively.

[0045] In this way, in the photoelectric conversion device of this embodiment, by changing the sensitivity of the pixel to be higher over time midway, it is possible to obtain the effect of improving the S / N ratio when the luminance of the subject is low (curve 603' in FIG. 6(B)). That is, compared to the curve 603 in FIG. 6(A), the curve 603' in FIG. 6(B) can increase the count value of the photon counter 403 when the count value of the time counter 404 reaches the maximum value (upper limit) K. In this way, the pulse generation circuit 407 functions as a sensitivity adjustment means for changing the sensitivity of the pixel at least once from when the photon counter starts measurement until the measurement value of the photon counter reaches the first threshold value Cx.

[0046] In the example of Fig. 6(B), the pulse period is switched only once at the first time T0 until the maximum time count K is reached, but it may be switched multiple times until the maximum time count K is reached, or the period may be changed continuously and gradually. Changing the period multiple times or changing the period gradually continuously is preferable because it allows fine control of the change in sensitivity over time. Even when sensitivity adjustment is performed multiple times, it is preferable to gradually increase the sensitivity of the pixel over time. <Embodiment 2>

[0047] In the first embodiment, the pulse period is switched to a shorter fixed period after the first time T0, but the pulse period may be adaptively changed. That is, in the second embodiment, the period of the pulses after the first time T0 is controlled according to the count value of the photon counter 403 at the first time T0, for example.

[0048] FIG. 7 is a diagram illustrating an example of sensitivity adjustment in the second embodiment. 7, at the first time T0=K / 2, it is determined whether the count value of photon counter 403 is less than half the first threshold value Cx. If the count value is equal to or greater than half the first threshold value Cx (curve 701 in FIG. 7), the pulse period is not changed. Note that the timing of sensitivity change and the threshold value of the count value of photon counter 403 at that time are not limited to the above.

[0049] On the other hand, when the count value of the photon counter 403 is equal to or less than half the first threshold value Cx at the first time T0=K / 2 (curve 702 in FIG. 7), the pulse period is changed so that the count value of the photon counter 403 reaches the first threshold value Cx at the time K. In other words, the sensitivity adjustment means adaptively changes the sensitivity of the pixel after the first time according to the measurement value of the photon counter at the first time.

[0050] Moreover, the sensitivity of the pixel is changed after the first time point so that the measurement value of the photon counter reaches the first threshold value Cx when the time measured by the time counter reaches the maximum value K as the second threshold value. That is, the time when the count value of photon counter 403 reaches the first threshold value Cx can be made to approach the maximum time count value K, and the count value of photon counter 403 when it reaches the maximum time count value K can be made to approach the first threshold value Cx. As a result, the gradation is improved and the S / N ratio is improved.

[0051] 7, the pulse period may be changed multiple times before the time measured by the time counter reaches the maximum value K as the second threshold. Changing the period multiple times is preferable because it further improves the gradation and the S / N ratio. It is preferable that the timing for changing the sensitivity is K / (2 to the power of N), and in this case, it is preferable that the pulse period is 1 / (2 to the power of N), where N is an integer.

[0052] Also, before changing the sensitivity the first time, it may be determined whether the count values ​​of the photon counters 403 of all pixels or a predetermined region have reached a predetermined threshold value, for example. Also, before changing the sensitivity the second time, it is desirable to gradually reduce the number of pixels to be referenced for the determination, for example, by determining whether the count values ​​of the photon counters 403 of pixels that were equal to or greater than the predetermined count value the first time have reached a predetermined threshold value. When changing the sensitivity multiple times, the sensitivity may be changed to a constant or decreased during the process instead of increasing the sensitivity each time. Also, the sensitivity may be gradually decreased in order to widen the dynamic range, for example.

[0053] In the above example, the pulse period of the pulse generating circuit is used as the sensitivity adjustment means for adjusting the sensitivity of the pixel, but other sensitivity adjustment means may be used. For example, an ND filter using liquid crystal or electrochromic material may be provided on the light incident side, and the transmittance of the ND filter may be changed so as to increase over time, or a high-density ND filter may be mechanically switched to a low-density ND filter.

[0054] Alternatively, an aperture may be provided in the imaging optical system, and the aperture opening may be changed over time to gradually increase. Also, any one of these sensitivity adjustment means may be used to control the sensitivity to be increased halfway through, or a plurality of these sensitivity adjustment means may be combined to control the sensitivity adjustment step of increasing the sensitivity halfway through. The sensitivity of the pixels may be varied over time for each pixel, or may be varied uniformly over time for all pixels, or may be varied for each pixel region that includes a predetermined number of pixels (e.g., 2 pixels vertically by 2 pixels horizontally).

[0055] For example, when arranging color filters in a Bayer array in which color filters are arranged in the order of RGRG on pixels in a predetermined row of the photoelectric conversion device and in the order of GBGB on pixels in the next row, the pixel area (2 pixels vertical × 2 pixels horizontal) will have four pixels of R, G, B, and G. In this case, the sensitivity adjustment means changes the sensitivity of the pixels over time for each predetermined pixel area including the above-mentioned multiple pixels (2 pixels vertical × 2 pixels horizontal), thereby suppressing changes in color balance.

[0056] When changing the pulse period for all pixels or pixel regions and reviewing the pulse period midway, it is preferable to change the pulse period so that the largest count value of photon counter 403 at time K reaches first threshold value Cx. Alternatively, the pulse period may be changed based on the average value or histogram of count values ​​of photon counter 403 of multiple pixels. Using the largest count value is preferable because it is possible to restore pixel signals from all pixels, whereas using a histogram has the effect of eliminating the count values ​​of defective pixels that fall outside the histogram, thereby improving the signal-to-noise ratio of the image.

[0057] Even if the count value of the time counter 404 reaches a predetermined second threshold, if the count value of the photon counter 403 connected to the time counter 404 does not reach the first threshold Cx, the decision circuit 405 stops the time counter 404. Then, the measurement value of the photon counter 403 at that time is output. With this configuration, the frame rate does not become slow when the brightness of the subject is very low. The predetermined second threshold is preferably set to the maximum value K of the time count.

[0058] FIG. 8 is a block diagram of an imaging device 500 using the photoelectric conversion device 100 of the first or second embodiment. The imaging device 500 is, for example, a digital camera, and includes the photoelectric conversion device 100, a lens 501, an image processing unit 502, an optical control unit 503, a storage unit 504, and, for example, a wireless I / F (Interface) unit 505 as a communication unit.

[0059] The lens 501 includes a focus lens, a zoom lens, an aperture, etc., and forms an optical image of a subject, and causes the formed optical image to be incident on the imaging surface of the photoelectric conversion device 100 . In the photoelectric conversion device 100, an optical image formed by a lens 501 is captured. Signals read from a pixel region 12 of the photoelectric conversion device 100 are subjected to processing such as signal rearrangement, defective pixel correction, noise reduction, color conversion, white balance correction, gamma correction, and data compression in an image processing unit 502, and an image signal is generated.

[0060] The image processing unit 502 has a built-in CPU as a computer, and functions as a control unit that controls the operation of each part of the entire image capturing device 500 based on a computer program stored in a memory as a storage medium. The image processing unit 502 also causes the pulse generating circuit 407 to perform control for changing the sensitivity of the pixel 201 during the period from when the photon counter 403 starts measurement until the measurement value of the photon counter 403 reaches a first threshold value Cx. An optical control unit 503 controls the focus lens, zoom lens, aperture, and the like provided in the lens 501 .

[0061] The storage unit 504 includes a recording medium such as a memory card, a hard disk, etc. A wireless I / F (Interface) unit 505 as a communication unit transmits an image signal generated by the image processing unit 502 to the outside of the imaging device 500 via a network 506, for example, and receives a signal from the outside. The I / F unit 505 may be, for example, a plurality of routers, switches, cables, etc. that satisfy a communication standard such as Ethernet (registered trademark), and a client can control the imaging device 500 via the network 506.

[0062] In the above embodiment, the first threshold (threshold for the number of photons) Cx of the photon counter 403 is fixed, but for example, a first threshold changing means may be provided for changing the first threshold Cx based on environmental information, subject information, etc. As environmental information, for example, a detection unit for detecting temperature and battery voltage may be provided, and when the temperature is higher than a predetermined temperature or when the battery voltage is lower than a predetermined voltage value, the first threshold Cx may be lowered.

[0063] Also, the subject information may include, for example, any one of whether or not it is a subject area, whether or not the subject is in focus at a predetermined threshold value or more, and whether or not the subject has a relatively high contrast, and if these conditions are met, the first threshold value Cx may be lowered. By controlling in this way, power consumption can be optimized.

[0064] Furthermore, the operation of changing the sensitivity of the pixel over time as in the first and second embodiments may be combined with the operation of changing the first threshold (threshold of the number of photons) Cx according to environmental information, subject information, etc., as described above. This makes it possible to further optimize the gradation and power consumption of the imaging device 500. As described above, the shorter the time T until the number of photons reaches the first threshold Cx, the coarser the gradation. If the number of photons incident on the photoelectric conversion element is constant, the smaller Cx is, the shorter T is. Therefore, when the first threshold Cx is greater than the third threshold, the sensitivity of the pixel is not changed over time, and when the first threshold Cx is less than the third threshold, the sensitivity of the pixel may be changed over time. The smaller the first threshold Cx is, the more frequently the sensitivity of the pixel is changed over time. In addition, since the more important the object area is, the more gradation information is required, a configuration may be adopted in which the sensitivity of pixels is not changed over time in areas other than the object area, and the sensitivity of pixels is changed over time in the object area. The frequency of the change in the sensitivity of pixels over time may be changed depending on whether the area is an object area or not. In the embodiment, the imaging device is, for example, a digital camera. However, the imaging device may include electronic devices having an imaging function, such as a digital movie camera, a smartphone with a camera, a tablet computer with a camera, an in-vehicle camera, a drone camera, a camera mounted on a robot, and a network camera.

[0065] 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. A computer program for implementing all or part of the control in this embodiment may be supplied to a photoelectric conversion device, an imaging device, or the like via a network or various storage media. 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]

[0066] 100: Photoelectric conversion device 11: Sensor chip 12: Pixel area 21: Circuit chip 22: Pixel circuit area 23: Peripheral circuit area 201: Pixel 202: Photoelectric conversion unit 301: Signal processing unit 302: Vertical scanning circuit 303: Column circuit 304: Horizontal scanning circuit 305: Control pulse generation unit 306: Signal restoration section 307: Horizontal output circuit 310: Vertical signal line 311: Vertical selection line 401: Quench element 402: Waveform shaping section 403: Photon Counter 404: Time Counter 405: Judgment circuit 406: Selection circuit 500: Imaging device 501: Lens 502: Image processing unit 503: Optical control unit 504: Storage section 505:I / F section

Claims

1. A pixel including a photoelectric conversion unit that outputs a signal in response to an incident photon; a photon counter that measures the number of photons incident on the pixel; a time counter that measures the time from when the photon counter starts the measurement until the measurement value of the photon counter reaches a first threshold; a sensitivity adjustment means for changing the sensitivity of the pixel during a period from when the photon counter starts the measurement until the measured value of the photon counter reaches the first threshold value, The photoelectric conversion device according to claim 1, wherein the sensitivity adjustment means changes the sensitivity of the pixel after the first time point in response to the measurement value of the photon counter at the first time point.

2. The photoelectric conversion device according to claim 1 , wherein the photoelectric conversion section includes an avalanche photodiode.

3. 3. The photoelectric conversion device according to claim 1, wherein the sensitivity change includes a change to increase the sensitivity of the pixel.

4. 4. The photoelectric conversion device according to claim 1, wherein the sensitivity adjustment means includes a pulse generation circuit that changes a period of a pulse for switching a bias potential of the photoelectric conversion unit.

5. 5. The photoelectric conversion device according to claim 4, wherein the pulse generating circuit shortens the period of the pulse during the period from when the photon counter starts the measurement until when the measured value of the photon counter reaches the first threshold value.

6. 6. The photoelectric conversion device according to claim 1, further comprising a signal restoration section that restores the time measured by the time counter as an output signal of the pixel.

7. A photoelectric conversion device described in any one of claims 1 to 6, characterized in that if the time measured by the time counter reaches a second threshold value but the measurement value of the photon counter does not reach the first threshold value, the measurement value of the photon counter is output.

8. The photoelectric conversion device according to claim 1, characterized in that the sensitivity adjustment means changes the sensitivity of the pixel from the first time onwards so that the measurement value of the photon counter reaches the first threshold when the time measured by the time counter reaches a second threshold.

9. 9. The photoelectric conversion device according to claim 1, wherein the sensitivity adjustment means changes the sensitivity of the pixel for each of a plurality of pixel regions including the pixels.

10. 10. The photoelectric conversion device according to claim 1, further comprising a first threshold value changing means for changing the first threshold value.

11. The photoelectric conversion device according to any one of claims 1 to 10, a control means for causing the sensitivity adjustment means to change the sensitivity of the pixel; An imaging device comprising:

12. A pixel including a photoelectric conversion unit that outputs a signal in response to an incident photon; a photon counter that measures the number of photons incident on the pixel; a time counter that measures the time from when the photon counter starts the measurement until the measurement value of the photon counter reaches a first threshold; A control method for controlling a photoelectric conversion device having a sensitivity adjustment means for changing the sensitivity of the pixel, comprising: a sensitivity adjustment step of changing the sensitivity of the pixel by the sensitivity adjustment means during a period from when the photon counter starts the measurement until the measured value of the photon counter reaches the first threshold value, A control method, characterized in that in the sensitivity adjustment step, the sensitivity of the pixel after the first time point is changed in accordance with the measurement value of the photon counter at the first time point.

13. A computer program for controlling each unit of the photoelectric conversion device according to any one of claims 1 to 10 or the imaging device according to claim 11 by a computer.

Images