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

Abstract

To provide a low power consumption photoelectric conversion device including a photoelectric conversion part for outputting a signal in response to the incidence of a photon, a method for controlling the photoelectric conversion device, and a program.SOLUTION: In the photoelectric conversion device (photoelectric conversion element), a pixel 101 in a sensor chip 11 includes the photoelectric conversion part. A signal processing part 103 in a circuit chip 21 includes a quench element 202, a waveform shaping part 210, a photon counter 211, a time counter 212, and a selection circuit 213. The photon counter 211 measures the number of photons incident on the pixel. The time counter 212 measures a time for reaching a first threshold after the photon counter 211 starts measurement and outputs the time as a pixel value. A threshold change part changes the first threshold on the basis of at least one of environmental information and subject information.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 in response to incident photons, an imaging device, a control method, a computer program, and the like. [Background technology]

[0002] In recent years, imaging devices equipped with CMOS photoelectric conversion devices have become widespread. Meanwhile, a photoelectric conversion device has been proposed that digitally counts the number of photons incident on an avalanche photodiode and outputs the counted value as a photoelectrically converted digital signal from a pixel.

[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 counting until the number of photons reaches a predetermined value, and calculates the pixel value from the measured time. Because the time for measuring photons varies for each pixel, it becomes possible to obtain images with a wide dynamic range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Publication No. 2015 / 0163429 Summary of the Invention [Problem to be solved by the invention]

[0005] However, a photoelectric conversion device using an avalanche photodiode has a problem in that when many photons are incident per unit time, the number of avalanche multiplication events increases, resulting in increased power consumption. In Patent Document 1, many pixels allow photons to be incident up to the first threshold, which causes an issue in that the power consumption of the photoelectric conversion device becomes higher than necessary. An object of the present invention is to provide a photoelectric conversion device that can alleviate the above problems, has a photoelectric conversion unit that outputs a signal in response to incident photons, and consumes less power. [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 incident photons; 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 measurement until when the photon counter reaches a first threshold value and outputs the measured time as a pixel value; a first threshold value changing unit that changes the first threshold value; a temperature detection unit that detects temperature as environmental information, When the temperature detected by the temperature detection unit is higher than a predetermined threshold, the first threshold change unit sets the first threshold lower than when the temperature is equal to or lower than the predetermined threshold. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, it is possible to realize a low-power consumption photoelectric conversion device having a photoelectric conversion section that outputs a signal in response to the incidence of a photon. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a photoelectric conversion device according to a first embodiment. [Figure 2] 1 is a diagram for explaining a configuration example of a sensor chip according to the first embodiment. FIG. [Figure 3] 1 is a block diagram showing an example of the configuration of a circuit chip according to a first embodiment. [Figure 4] 1 is an equivalent circuit diagram of a pixel 101 and a signal processing unit 103 according to the first embodiment. [Figure 5] 4 is a timing chart showing the operation of the photoelectric conversion device according to the first embodiment. [Figure 6] 4 is a graph showing the relationship between temperature and a first threshold value in a first threshold value changing unit according to the first embodiment. [Figure 7] 1 is a block diagram of an imaging device according to a first embodiment. [Figure 8] FIG. 10 is a block diagram of an imaging device according to a second embodiment. [Figure 9] 10A and 10B are diagrams illustrating an example of an image captured by an imaging device 800 according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 designated by the same reference numerals, and duplicated descriptions will be omitted or simplified.

[0010] (Embodiment 1) FIG. 1 is a diagram illustrating the configuration of a photoelectric conversion device according to the first embodiment. The photoelectric conversion device (photoelectric conversion element) 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 pixel circuit regions 22 that process signals detected 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 101 arranged two-dimensionally. That is, the pixel region 12 includes a plurality of pixels 101, and these plurality of pixels are arranged in a plurality of rows and a plurality of columns. Each pixel 101 includes a photoelectric conversion unit 102 including an avalanche photodiode (hereinafter referred to as APD) that outputs a signal in response to incident photons.

[0012] 2 shows 36 pixels 101 arranged in six rows (rows 0 to 5) and six columns (columns 0 to 5) with reference symbols indicating the row and column numbers. For example, the pixel 101 arranged in the first row and fourth column is given the reference symbol "P14." Note that the number of rows and columns of the pixels 101 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 103 arranged two-dimensionally, consisting of a plurality of rows and a plurality of columns. FIG. 3 shows 36 signal processing units 103 arranged in six rows from row 0 to row 5 and six columns from column 0 to column 5, along with reference symbols indicating the row and column numbers. For example, the signal processing unit 103 arranged in the first row and fourth column is assigned the reference symbol "S14."

[0014] Each signal processing unit 103 is electrically connected to the pixels 101 of the corresponding row number and column number of the sensor chip 11. The number of rows and columns of the signal processing units 103 constituting the pixel circuit region 22 is not limited to the example in FIG. 3, and may be any number that corresponds to the number of rows and columns of the pixels 101 of the sensor chip 11. The peripheral circuit region 23 includes a vertical scanning circuit 110 , a horizontal scanning circuit 111 , a column circuit 112 , a horizontal output circuit 114 , a control pulse generating unit 115 , a horizontal output line 118 , a temperature detecting unit 119 , and a first threshold changing unit 121 .

[0015] Vertical selection lines 116 are wired in a first direction (the horizontal direction in FIG. 3) to the signal processing units 103 in each row of the pixel circuit region 22. The vertical selection lines 116 are connected to the signal processing units 103 lined up in the first direction. The first direction may also be referred to as the row direction or the horizontal direction.

[0016] 3, the vertical selection lines 116 are indicated with symbols indicating row numbers. For example, the vertical selection line 116 of the first row is denoted by the symbol "VSEL[1]." The vertical selection lines 116 of each row are connected to the vertical scanning circuit 110, and the vertical scanning circuit 110 supplies a vertical selection signal VSEL to the signal processing units 103 via the vertical selection lines 116 to selectively drive the signal processing units 103 of a predetermined row.

[0017] Vertical signal lines 113 are wired in a second direction (the vertical direction in FIG. 3) perpendicular to the first direction to the signal processing units 103 in each column of the pixel circuit region 22. The vertical signal lines 113 are connected to the signal processing units 103 arranged in the second direction. The second direction may be referred to as the column direction or the vertical direction. 3, the vertical signal lines 113 are indicated with a symbol indicating the column number. For example, the vertical signal line 113 of the fourth column is assigned the symbol "POUT[4]." The vertical signal lines 113 of each column include n signal lines for outputting n-bit digital signals.

[0018] A control line 122 for controlling the first threshold value is wired from the first threshold value changing unit 121 to each row of the signal processing units 103 in the pixel circuit region 22, and the control line 122 is connected to each of the signal processing units 103 arranged in the first direction. In FIG. 3, the control lines 122 are shown together with a reference symbol indicating the row number. For example, the control line 122 in the first row is labeled "VCON[1]." This embodiment is characterized in that it includes a first threshold value changing unit 121 that changes the first threshold value. Another characteristic is that the first threshold value changing unit 121 is able to change the first threshold value using a predetermined control signal.

[0019] The horizontal scanning circuit 111 supplies a horizontal selection signal for reading out a signal from the column circuit 112 to the column circuit 112 via a horizontal selection line 117. Upon receiving the horizontal selection signal from the horizontal scanning circuit 111, the column circuit 112 outputs the output signal that it has temporarily held to the horizontal output circuit 114 via a horizontal output line 118. 3, the horizontal selection lines 117 are shown together with symbols indicating the column numbers. For example, the horizontal selection line 117 of the fourth column is given the symbol "HSEL[4]." The horizontal output line 118 includes n signal lines for outputting n-bit digital signals.

[0020] The horizontal output circuit 114 outputs a signal corresponding to the pixel signal as an output signal SOUT of the photoelectric conversion device. The control pulse generation unit 115 supplies control pulse signals that control the operations and timing of the vertical scanning circuit 110, the horizontal scanning circuit 111, and the column circuit 112, and control pulses CTL that control the operation of the signal processing unit 103. Note that at least some of the control pulse signals that control the operations and timing of the vertical scanning circuit 110, the horizontal scanning circuit 111, and the column circuit 112, and the control pulses CTL that control the operation of the signal processing unit 103 may be supplied from outside the photoelectric conversion device 100.

[0021] The temperature detection unit 119 measures temperature information of the photoelectric conversion device 100 using a temperature sensor and outputs the measured temperature to the first threshold change unit 121 as environmental information. The temperature sensor of the temperature detection unit 119 measures the temperature based on the temperature characteristics of a silicon diode, for example. The signal input circuit 120 inputs a signal from outside the photoelectric conversion device 100 to the first threshold change unit 121 and controls the operation of the first threshold change unit 121. The temperature detection unit 119 may use, for example, a dark current level obtained from an optical black as temperature information. Note that the optical black is a light-shielded pixel arranged on the periphery of the two-dimensionally arranged pixels.

[0022] The first threshold changing unit 121 supplies a control signal for changing the first threshold in the signal processing unit 103 to each signal processing unit 103 row by row via a control line 122 in response to a signal input from the temperature detection unit 119 or the signal input circuit 120. Although the control line 122 is shared and connected for each row in Fig. 3, it may be connected for each signal processing unit 103, or may be connected for each predetermined area consisting of a plurality of signal processing units 103.

[0023] FIG. 4 is an equivalent circuit diagram of the pixel 101 and the signal processing unit 103 according to the first embodiment. The pixel 101 in the sensor chip 11 includes an APD 201 which is a photoelectric conversion unit. When a photon is incident on the APD 201, a charge pair is generated by photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 201, and a voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode. That is, a reverse bias voltage is supplied that causes the APD 201 to perform avalanche multiplication. By supplying such a voltage, the charges generated by the incident light undergo avalanche multiplication, generating an avalanche current.

[0024] 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. An APD operating in Geiger mode is called a SPAD (Single Photon Avalanche Diode). In this case, the voltage VL (first voltage) is set to, for example, -30V, and the voltage VH (second voltage) is set to, for example, 1V.

[0025] The signal processing unit 103 in the circuit chip 21 includes a quenching element 202 , a waveform shaping unit 210 , a photon counter 211 , a time counter 212 , and a selection circuit 213 . The quench element 202 is connected to a power supply that supplies a voltage VH and the APD 201. The quench element 202 has a function of converting a change in avalanche current occurring in the APD 201 into a voltage signal.

[0026] The quench element 202 functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, suppressing the voltage supplied to the APD 201 and suppressing avalanche multiplication (quench operation). The quench element can be switched between an ON state and an OFF state by a control signal nodeC from the photon counter 211. When the control signal nodeC is set to a LOW level, the quench element 202 is turned ON, enabling avalanche multiplication by the APD 201. When the quench element 202 is turned OFF, the cathode of the APD is set to a floating state, stopping avalanche multiplication by the APD 201 and reducing power consumption.

[0027] The waveform shaping unit 210 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 210 may be, for example, an inverter circuit or a buffer circuit. Reference numeral 211 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 210 up to a first threshold value. The first threshold value can be changed by a control signal input via a control line 122.

[0028] In this embodiment, the control signal for changing the first threshold is, for example, a predetermined pulse code. The upper limit of the count in the photon counter 211 can be changed by supplying this predetermined pulse code or the like as a control signal to the control line 122. The control signal for changing the first threshold may be, for example, an analog voltage value. In that case, a control signal line for changing the first threshold may be wired separately. Furthermore, when a HIGH level control signal PRES is supplied via the control line 122, the photon counter 211 resets the count value.

[0029] The time counter 212 measures the time from when the photon counter starts counting until it reaches a first threshold, and outputs the measured time as a pixel value. The time counter 212 resets its count value in response to a HIGH-level control signal PRES supplied from the control line 122, and starts counting when the control signal PRES becomes LOW and the reset is released. On the other hand, the end of the count is controlled by a control signal node D from the photon counter 211.

[0030] When an end timing control signal nodeD is input from the photon counter 211, the value counted by the time counter 212 is output to the selection circuit 213. On the other hand, when an end timing signal is not input even when the time measured by the time counter 212 reaches the second threshold, the number of photons measured by the photon counter 211 (count value) is output to the selection circuit 213 as a pixel value.

[0031] The selection circuit 213 switches between electrical connection and disconnection between the photon counter 211 and the time counter 212 and the vertical signal line 113, in response to a vertical selection signal VSEL supplied from the vertical scanning circuit 110 in Fig. 3 via the vertical selection line 116. The selection circuit 213 includes, for example, a buffer circuit for outputting a signal.

[0032] In this embodiment, the second threshold is fixed. However, for example, a pulse code or an analog voltage value different from the predetermined pulse code for changing the first threshold may be supplied as a control signal to the control line 122. This may make it possible to change the upper limit of the count (second threshold β) in the time counter 212. For example, when photographing a fast-moving subject, the upper limit of the count (second threshold β) in the time counter 212 may be controlled to be lowered in order to suppress subject blur.

[0033] 5 is a timing chart showing the operation of the photoelectric conversion device according to the first embodiment. Here, the operation of pixel P00 among the multiple pixels 101 will be described. To simplify the explanation, it is assumed that the shooting environment and camera parameters related to image capture are constant, and that the amount of light transmitted through the lens and received by the sensor is always constant. Furthermore, it is assumed that the second threshold value β of the time counter is constant and does not depend on the first threshold value.

[0034] 5 shows a timing chart corresponding to two frames among the multiple frames constituting a video signal. The period from timing t500 to timing t510 corresponds to the t-th frame FRAME(t). The period from timing t510 to timing t513 corresponds to the t+1-th frame FRAME(t+1).

[0035] Furthermore, in FRAME(t), photon counter 211 reaches the pre-change first threshold A within the frame, and outputs count value B of the time counter to selection circuit 213. In FRAME(t+1), photon counter 211 reaches the post-change first threshold C within the frame, and outputs count value B' of the time counter to selection circuit 213. Here, if the first threshold is A>C, the relationship between the time counter values ​​in each frame is (β>)B>B'. Note that, although not explained here, if photon counter 211 does not reach the first threshold in FRAME(t+n), the count value of the photon counter at the time when the time counter reached second threshold β is output to selection circuit 213.

[0036] First, at timing t500, the control signal nodeC is set to a low level, and the quench element 202 is turned on, thereby causing the APD 201 to transition to the Geiger mode. At timing t501, with the transition of APD 201 to Geiger mode completed, the control signal PREST is set to LOW level via control line 122. This releases the reset of photon counter 211 and time counter 212, causing photon counter 211 and time counter 212 to start counting.

[0037] At timing t503, the photon counter 211 reaches the first threshold A, causing the photon counter 211 to transition the control signal nodeD to High. This causes the photon counter 211 and the time counter 212 to stop counting. Also, at this time, the photon counter 211 sets the control signal nodeC to High, turning the quench element 202 to the OFF state. This stops the avalanche multiplication operation of the APD 201 and reduces power consumption.

[0038] At timing t504, the vertical selection signal VSEL is set to High via the vertical selection line 116, and the n-1 bit value B counted by the time counter 212 is output as the n-1 bit signal to POUT[0] of the vertical signal line 113. In addition, the nth bit is set to 0 and output as the nth bit signal to POUT[0] of the vertical signal line 113. This nth bit value functions as an additional signal and indicates whether or not the photon counter 211 has reached the first threshold, with 0 indicating that the first threshold has been reached and 1 indicating that the first threshold has not been reached.

[0039] That is, when the number of photons measured by the photon counter is taken as the pixel value, a predetermined additional signal of 1 is added. Note that the format of the additional signal is not limited to this, and 0 may be used when the first threshold value has not been reached and 1 may be used when the first threshold value has been reached, or the additional signal may be output using a separate signal line.

[0040] At timing t505, PREST is set to High via the control line 122, and the count values ​​of the photon counter 211 and the time counter 212 are reset. Also, at timing t506, the first threshold value changing unit 121 changes the first threshold value from A to C in order to reduce power consumption of the photoelectric conversion device 100.

[0041] At timing t510, the control signal nodeC is set to a low level, and the quench element 202 is turned on, thereby causing the APD 201 to transition to the Geiger mode. At timing t511, with the APD 201 having completed transition to the Geiger mode, the control signal PRES is set to a low level to start counting the photon counter 211 and the time counter 212. At timing t512, the photon counter reaches the first threshold C.

[0042] At this time, as described above, the photon counter 211 causes the control signal nodeD to transition to High. Also, the control signal nodeC is set to High, turning the quench element 202 to the OFF state. At this time, the power consumption before and after changing the first threshold is reduced the longer the period during which the avalanche multiplication operation of the APD 201 is stopped. Specifically, power consumption is reduced during the period T1 (from t503 to t510) in FRAME(t) and the period T2 (from T512 to T513) in FRAME(t+1). However, because T2 > T1, power consumption can be reduced by lowering the first threshold.

[0043] At timing t513, the control signal PREST is set to High, and the photon counter 211 and the time counter 212 are reset. Note that t500, t501, t504, t505, t506, t510, t511, t512, and t513 are timings with a fixed cycle, and t500 to t510, t501 to t511, t504 to t12, and t505 to t513 each correspond to one vertical period. In FRAME(t+n), a case will be described in which the photon counter does not reach the first threshold before the time counter reaches the second threshold β. After the time counter is reset, the vertical selection signal VSEL is set to High by the time counter at the timing of the second threshold β.

[0044] However, up until this point, the count value of the photon counter has not reached the first threshold, so nodeC and nodeD remain LOW. Therefore, the n-1-bit value A' counted by the photon counter 211 is output as the n-1-bit signal to POUT[0] of the vertical signal line 113. Also, the value of the n-th bit is set to 1 and output as the n-th bit signal to POUT[0] of the vertical signal line 113. That is, as described above, when the number of photons measured by the photon counter is used as the pixel value, a predetermined additional signal 1 is added.

[0045] As described above, for each frame, starting from pixel P00, if the photon counter 211 reaches the first threshold, the count value of the time counter is output to the selection circuit 213. If the photon counter 211 does not reach the first threshold, the count value of the photon counter is output to the selection circuit 213. Furthermore, signals from each pixel in the pixel area 12 are read out row by row from row 0 to row 5 in the order P00 to P05, P10 to P15, ... P50 to P55, sequentially from the left side of FIG.

[0046] 6 is a graph showing the relationship between temperature and the first threshold value in the first threshold value changing unit of embodiment 1, where the vertical axis represents the temperature measured by temperature detection unit 119 and the horizontal axis represents the first threshold value. As shown in graph 600, the first threshold value is constant up to temperature 601, and after temperature 601, the first threshold value decreases as the temperature increases.

[0047] As described above, in the first embodiment, the first threshold changing unit 121 changes the first threshold as shown in the graph of Fig. 6 based on the temperature as environmental information detected by the temperature detection unit 119, thereby suppressing power consumption. For example, as shown in Fig. 6, the first threshold is gradually lowered as the temperature detected by the temperature detection unit 119 increases. In other words, when the temperature as environmental information detected by the temperature detection unit 119 is higher than the predetermined threshold, the first threshold changing unit 121 gradually lowers the first threshold. below The first threshold is set lower than in the case of By controlling in this way, it is possible to reduce the power consumption of the photoelectric conversion device 100 and operate it stably for a long period of time even in a high-temperature environment.

[0048] FIG. 7 is a block diagram of an imaging device 700 according to the first embodiment. The imaging device 700 is an imaging device such as a digital camera that includes the photoelectric conversion device 100, and includes a lens 701, an image processing unit 702, a temperature detection unit 703, an optical control unit 704, a memory unit 705, and an I / F unit 706 as a communication unit. The lens 701 includes a focus lens, a zoom lens, an aperture, and the like, and forms an optical image of a subject, and makes the formed optical image incident on the imaging surface of the photoelectric conversion device 100 .

[0049] The photoelectric conversion device 100 captures an optical image formed by a lens 701. Signals read from the pixel region 12 of the photoelectric conversion device 100 are processed in an image processing unit 702, including signal rearrangement, defective pixel correction, noise reduction, color conversion, white balance correction, gamma correction, and data compression, to generate an image signal. The image processing unit 702 has a built-in CPU as a computer, which functions as control means for controlling the operation of each unit of the entire imaging device 700 based on a computer program stored in a memory as a storage medium.

[0050] Furthermore, in this embodiment, different image processing is performed on pixel values ​​to which the predetermined additional signal has been added and pixel values ​​to which the additional signal has not been added in the image processing unit 702. Specifically, stronger noise reduction is applied to pixel values ​​to which 1, the predetermined additional signal, has been added as the value of the n-th bit than to pixel values ​​to which the additional signal has not been added.

[0051] The temperature detection unit 703 includes a semiconductor temperature sensor such as a thermistor or a silicon diode for detecting temperature information as environmental information, and is arranged near the photoelectric conversion device 100. Note that while the temperature detection unit 119 in Fig. 3 is provided on the circuit chip 21 in the photoelectric conversion device 100, the temperature detection unit 703 in Fig. 7 is provided near the photoelectric conversion device 100, at a position separate from the photoelectric conversion device 100.

[0052] Temperature information as environmental information detected by the temperature detection unit 703 is output to the photoelectric conversion device 100. Based on the temperature information detected by the temperature detection unit 703, the photoelectric conversion device 100 changes the first threshold value according to the characteristics shown in the graph of Fig. 6, for example. The optical control unit 704 controls the focus lens, zoom lens, aperture, etc. provided in the lens 701.

[0053] The storage unit 705 includes a recording medium such as a memory card, a hard disk, etc. An I / F (Interface) unit 706 serving as a communication unit transmits image signals generated by the image processing unit 702 to the outside of the imaging device 700 via, for example, a network 707, and receives signals from the outside. The I / F unit 706 includes, for example, a plurality of routers, switches, cables, etc. that comply with communication standards such as Ethernet (registered trademark), and enables a client to control the imaging device 700 via the network 707.

[0054] As described above, the first embodiment reduces power consumption by including a first threshold value changing step of changing the first threshold value in the photoelectric conversion device 100 based on temperature information serving as environmental information detected by a temperature detection unit 703 provided near the photoelectric conversion device 100. For example, as shown in FIG. 6, when the temperature detected by the temperature detection unit 604 is high, the first threshold value is lowered, thereby reducing power consumption of the photoelectric conversion device 100.

[0055] This allows the imaging device 700 to continue capturing images even in a high-temperature environment. The first threshold value changing step is performed by a CPU serving as a computer in the image processing unit 702 executing a computer program stored in a memory serving as a storage medium.

[0056] (Embodiment 2) Fig. 8 is a block diagram of an imaging device 800 according to embodiment 2. In Fig. 8, the imaging device 800, such as a digital camera, differs from the configuration in Fig. 7 in that a subject detection unit 803 is added, and the same members or elements as those in Fig. 7 are assigned the same reference numerals, and duplicated descriptions will be omitted or simplified.

[0057] The subject detection unit 803 detects whether a subject exists in the image generated by the image processing unit 802. That is, the subject detection unit 803 detects a subject area where a subject exists as subject information based on the image signal read out from the pixel area 12 of the photoelectric conversion device 100. The subject area is detected by, for example, processing such as temporal difference of the background of the image, motion detection, and object detection.

[0058] Based on the detection result, a first threshold value in the photoelectric conversion device 100 is determined for each pixel region. Furthermore, the first threshold value changing unit 121 sets the first threshold value in the object region higher than the first threshold value outside the object region. Because the first threshold value is lower outside the object region, image noise increases, but power consumption of the imaging device 800 can be reduced.

[0059] The area in which the subject exists set by the subject detection unit 803 may be set by the user via the network 707. In this case, the user can freely set a region of interest (ROI) such as an area in which the subject exists, and the subject information includes whether or not the ROI is such a region of interest set by the user. Furthermore, the photoelectric conversion device 100 changes the first threshold value based on the temperature information detected by the temperature detection unit 703, as in the first embodiment.

[0060] FIG. 9 is a diagram illustrating an example of a video image captured by the imaging device 800 according to the second embodiment. Image 900 is an image captured by imaging device 800, and 901 is an area detected as an object by object detection unit 803. In the photoelectric conversion device 100, the first threshold value of the pixels in the region 901 is set high, and the first threshold value of the pixels in the regions other than the region 901 is set low.

[0061] In this way, in the second embodiment, the first threshold is changed to be lowered when the temperature is high based on temperature information as environmental information, and subject information (e.g., subject area) in the image is detected, and the first threshold is lowered in areas where no subject is detected. This makes it possible to reduce power consumption of the imaging device 800 while maintaining image quality in areas where important subjects are present in surveillance video, etc.

[0062] In the second embodiment, whether or not an object is an object region is used as object information, but for example, when a focus adjustment mechanism is provided, whether or not an object is in focus at a predetermined threshold value or more may be used as object information. That is, the first threshold value for objects in focus at a predetermined threshold value or more may be set higher than the first threshold value for other objects. Alternatively, an object with relatively high contrast may be used as object information.

[0063] That is, the first threshold for an object with a relatively high contrast may be set higher than the first threshold for an object with a relatively low contrast. That is, the object information includes any one of whether or not it is an object region, whether or not the object is in focus by a predetermined threshold or more, and whether or not the object has a relatively high contrast. It should be noted that the first threshold value changing unit 121 may change the first threshold value based on at least one of the temperature information and the subject information as environmental information, rather than based on both of them.

[0064] Furthermore, a voltage measurement unit may be provided to measure the voltage of a power source, such as a battery, for driving the photoelectric conversion device as environmental information, and the first threshold may be lowered when the voltage of the battery serving as the power source drops below a predetermined threshold. That is, a voltage measurement unit may be provided to detect the voltage of the power source of the imaging device as environmental information, and when the power source voltage is lower than a predetermined threshold, the first threshold may be lowered compared to when the power source voltage is equal to or higher than the predetermined threshold. While the embodiments have exemplified temperature and power source voltage as examples of environmental information, this is not limiting. Environmental information may also include, for example, whether the brightness of the subject is lower than a predetermined threshold, whether a lighting device is usable when the brightness is low, the shooting mode of the imaging device, and whether the power consumption of the imaging device is equal to or higher than a predetermined value.

[0065] In the embodiments, the imaging device is described as being, for example, 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.

[0066] 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. 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]

[0067] 100 Photoelectric conversion device 11 Sensor chip 12 pixel area 21 Circuit Chip 101 pixels 102 Photoelectric conversion unit 103 Signal Processing Unit 119 Temperature detection unit 121 First threshold change unit 201 APD

Claims

1. a pixel including a photoelectric conversion unit that outputs a signal in response to incident photons; 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 measurement until when the photon counter reaches a first threshold value and outputs the measured time as a pixel value; a first threshold value changing unit that changes the first threshold value; a temperature detection unit that detects temperature as environmental information, A photoelectric conversion device characterized in that the first threshold change unit lowers the first threshold when the temperature detected by the temperature detection unit is higher than a predetermined threshold compared to when the temperature is below the predetermined threshold.

2. 2. The photoelectric conversion device according to claim 1, wherein the first threshold value changing unit changes the first threshold value using a predetermined control signal.

3. 3. The photoelectric conversion device according to claim 2, wherein the first threshold value changing unit changes the first threshold value in response to the predetermined control signal based on at least one of environmental information other than temperature and subject information.

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

5. A photoelectric conversion device according to any one of claims 1 to 4, characterized in that if the time measured by the time counter reaches a second threshold but the number of photons does not reach the first threshold, the number of photons measured by the photon counter is used as a pixel value.

6. 6. The photoelectric conversion device according to claim 5, wherein a predetermined additional signal is added when the number of photons measured by the photon counter is used as a pixel value.

7. 7. The photoelectric conversion device according to claim 6, wherein different image processing is performed for pixel values ​​to which the predetermined additional signal has been added and pixel values ​​to which the predetermined additional signal has not been added.

8. 8. The photoelectric conversion device according to claim 7, wherein noise reduction for pixel values ​​to which the predetermined additional signal has been added is stronger than that for pixel values ​​to which the predetermined additional signal has not been added.

9. a pixel including a photoelectric conversion unit that outputs a signal in response to incident photons; 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 measurement until when the photon counter reaches a first threshold value and outputs the measured time as a pixel value; a first threshold value changing unit that changes the first threshold value; a pixel region including a plurality of the pixels and arranged two-dimensionally; a subject detection unit that detects a subject area based on an image signal read from the pixel area, The photoelectric conversion device according to claim 1, wherein the first threshold change unit sets the first threshold for the object region detected by the object detection unit to be higher than the first threshold for regions other than the object region.

10. a pixel including a photoelectric conversion unit that outputs a signal in response to incident photons; 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 measurement until when the photon counter reaches a first threshold value and outputs the measured time as a pixel value; a first threshold value changing unit that changes the first threshold value, the first threshold value changing unit changes the first threshold value in response to a predetermined control signal based on at least one of environmental information and subject information, The photoelectric conversion device, wherein the subject information includes one of whether or not the subject is a subject area, whether or not the subject is in focus at or above a predetermined threshold, and whether or not the subject has a relatively high contrast.

11. a voltage measurement unit that detects a voltage of a power supply for driving the photoelectric conversion device, The photoelectric conversion device according to any one of claims 1 to 10, characterized in that when the voltage of the power supply is lower than a predetermined threshold, the first threshold is made lower than when the voltage of the power supply is equal to or higher than the predetermined threshold.

12. The photoelectric conversion device according to any one of claims 1 to 11, an image processing unit that processes an image read from the photoelectric conversion device; a communication unit that transmits the image processed by the image processing unit to an external device.

13. a pixel including a photoelectric conversion unit that outputs a signal in response to incident photons; a photon counter that counts the number of photons incident on the pixel; a time counter that measures the time from when the photon counter starts measurement until when the photon counter reaches a first threshold value and calculates a pixel value from the measured time; a temperature detection unit that detects temperature as environmental information, a first threshold value changing step of changing the first threshold value; A control method for a photoelectric conversion device, characterized in that the first threshold change step lowers the first threshold when the temperature detected by the temperature detection unit is higher than a predetermined threshold compared to when the temperature is equal to or lower than the predetermined threshold.

14. A computer program for causing a computer to function as each part of the photoelectric conversion device according to any one of claims 1 to 11 or the imaging device according to claim 12.

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