Photon Counting Device and Photon Counting Method

Abstract

The photon counting device includes: a plurality of pixels each including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies the charge converted by the photoelectric conversion element and converts it into voltage; an A / D converter that converts the voltage output from the amplifier of each of the plurality of pixels into a digital value and outputs it; a correction unit that corrects the digital value output from the A / D converter in a manner that suppresses the influence of deviations in gain and bias values between the plurality of pixels; an arithmetic unit that adds the corrected digital values corresponding to at least two pixels and outputs the added value; and a conversion unit that converts the added value output from the arithmetic unit into the number of photons.

Description

[0001] This application is a divisional application of a patent application with an application date of June 18, 2018 and an application number of 201880074983.X and an invention title of Photon counter Device and method for photon counting . Technical Field

[0002] The present invention relates to a photon counting device and a photon counting method. Background Art

[0003] For example, Non-Patent Document 1 describes a technique of photon counting using a CMOS image sensor. In this technique, by increasing the frame rate of the image sensor, shooting is performed under the condition that only one photon is incident on one pixel in one frame.

[0004] Prior Art Documents

[0005] Non-Patent Documents

[0006] Non-Patent Document 1: B Saleh Masoodian, Jiaju Ma, Dakota Starkey, Yuichiro Yamashita, and Eric R. Fossum, “A 1Mjot 1040fps 0.22e-rms Stacked BSI Quanta Image Sensor with Cluster-Parallel Readout”, preprint of the 2017 International Image Sensor Workshop (IISW), May 30 - June 2, 2017, P230 - 233 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] For example, when it is desired to perform photon counting using a CMOS image sensor, it is considered to determine the number of photons based on the digital value output from the A / D converter. However, in a CMOS image sensor, each pixel constituting the sensor has readout noise. In addition, the gain and bias values of multiple pixels have deviations within a certain range. At this time, the digital values when the same number of photons are incident are different for each pixel. Therefore, there is a concern that the counting accuracy of photons may decrease when pixel binning is performed.

[0009] An object of one aspect of the present invention is to provide a photon counting device and a photon counting method capable of suppressing a decrease in the counting accuracy of photons.

[0010] Technical Solutions for Solving the Problems

[0011] A photon counting device according to one aspect includes: a plurality of pixels each including a photoelectric conversion element that converts input light into charge and an amplifier that amplifies the charge converted by the photoelectric conversion element and converts it into a voltage; an A / D converter that converts the voltage output from the amplifiers of the plurality of pixels into a digital value and outputs it; a correction unit that corrects the digital value output from the A / D converter to suppress the influence of variations in gain and bias values between the plurality of pixels; an arithmetic unit that outputs a sum value obtained by adding the corrected digital values corresponding to at least two pixels; and a conversion unit that converts the sum value output from the arithmetic unit into the number of photons.

[0012] In such a photon counting device, a voltage corresponding to the photons input to the photoelectric conversion element is output from the amplifier. This voltage is converted into a digital value by the A / D converter. When combining pixels, the sum value obtained by adding the digital values corrected by the correction unit to each other is converted into the number of photons. In the correction unit, the digital value is corrected to suppress the influence of variations in gain and bias values between the plurality of pixels. That is, when the same number of photons are input, the variations in each pixel can be suppressed in the corrected digital value. As a result, the sum value is less likely to reflect the influence of variations in gain and bias values between pixels and is more likely to reflect only the number of photons. Therefore, a decrease in the counting accuracy of photons can be suppressed.

[0013] Alternatively, the correction unit may have preset parameters common to the plurality of pixels corresponding to the gain and bias values, and correct the digital values of each of the plurality of pixels based on the deviation of the gain and bias values from the parameters. In this configuration, the digital value is corrected according to the deviation of the reference parameters from the gain and bias values. Therefore, for example, a threshold based on the parameters can be used to convert the sum value into the number of photons.

[0014] In addition, the readout noise of the amplifier may be 0.2 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 1% or less. Further, the readout noise of the amplifier may be 0.15 [e-rms] or less. In this case, for example, the false detection rate can be suppressed to 0.1% or less.

[0015] In addition, the gain may be 10 [DN / e] or more. By increasing the gain, the analog value output from the amplifier can be reproduced with high accuracy.

[0016] In addition, a photon counting method according to one aspect includes: a step of converting light input to a photoelectric conversion element that respectively constitutes a plurality of pixels into charges; a step of amplifying the converted charges by an amplifier that constitutes a plurality of pixels and converting them into voltages; a step of converting the voltages output from each amplifier into digital values by an A / D converter and outputting them; a step of correcting the digital values output from the A / D converter to suppress the influence of the deviation of the gain and bias values between the plurality of pixels; a step of adding the corrected digital values corresponding to at least two pixels and outputting an added value; and a step of converting the added value into the number of photons.

[0017] In such a photon counting method, the voltage output from the amplifier according to the input photons is converted into a digital value. When performing pixel merging, the added value obtained by adding the digital values to each other is converted into the number of photons. The digital value is corrected in a manner that suppresses the influence of the deviation of the gain and bias values between the plurality of pixels. That is, when the same number of photons is input, the deviation of each pixel can be suppressed in the corrected digital value. Therefore, the influence of the deviation of the gain and bias values between the pixels can also be suppressed in the added value. Thus, a decrease in the counting accuracy of photons can be suppressed.

[0018] In addition, it may also be that, in the step of correcting the digital value, each of the digital values of the plurality of pixels is corrected based on the deviation of the gain and bias values from a parameter, and the parameter corresponds to the gain and bias values and is preset in a manner common to the plurality of pixels. In this structure, the digital value is corrected based on the deviation of the reference parameter from the gain and bias values. Therefore, for example, a threshold based on the parameter can be used to convert the added value into the number of photons.

[0019] Advantages of the Invention

[0020] According to the photon counting device and photon counting method of one aspect, a decrease in the counting accuracy of photons can be suppressed. Description of the Drawings

[0021] Figure 1 is a diagram showing the structure of a photon counting device according to an embodiment.

[0022] Figure 2 is a graph showing the relationship between the number of electrons and the probability density.

[0023] Figure 3 is a graph showing the relationship between the readout noise and the false detection rate.

[0024] Figure 4 in Figure 4 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 4 (b) is based on Figure 4 (a) is a graph showing the result of the simulation.

[0025] Figure 5 in Figure 5 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 5 (b) is a graph obtained by converting the result of the simulation based on Figure 5 (a) into a numerical value.

[0026] Figure 6 in Figure 6 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 6 (b) is a graph obtained by converting the result of the simulation based on Figure 6 (a) into a numerical value.

[0027] Figure 7 in Figure 7 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 7 (b) is a graph obtained by converting the result of the simulation based on Figure 7 (a) into a numerical value.

[0028] Figure 8 is a diagram schematically showing the process of converting the measured numerical value into the number of photons.

[0029] Figure 9 is a diagram schematically showing the process of converting the measured numerical value into the number of photons.

[0030] Figure 10 is a diagram schematically showing the process of deriving the bias value.

[0031] Figure 11 is a diagram schematically showing the process of deriving the gain.

[0032] Figure 12 is a diagram showing the correspondence between the measured numerical value and the corrected numerical value.

[0033] Figure 13 is a flowchart showing the operation of the photon counting device. Detailed implementation mode

[0034] Hereinafter, the implementation mode will be specifically described with reference to the accompanying drawings. For convenience, there are cases where substantially the same elements are denoted by the same reference numerals and their description is omitted. In addition, the photon counting in the implementation mode includes both the counting of the number of photoelectrons generated by the image sensor and the counting of the number of photons considering the quantum efficiency (QE: Quantum Efficiency) of the image sensor.

[0035] [First implementation mode]

[0036] Figure 1This is a diagram showing the structure of a photon counting device. As Figure 1 shown, the photon counting device 1 includes a CMOS image sensor 10 and a computer 20 connected to the CMOS image sensor 10. The CMOS image sensor 10 includes a plurality of pixels 11 and an A / D converter 15. The plurality of pixels 11 are arranged in a two-dimensional shape, arranged in the row direction and the column direction. Each pixel 11 has a photodiode (photoelectric conversion element) 12 and an amplifier 13. The photodiode 12 stores electrons (photoelectrons) generated by the input of photons as charges. The amplifier 13 converts the charges stored in the photodiode 12 into a voltage and amplifies it. The amplified voltage is transmitted to the vertical signal line 16 for each line (each row) by switching the selection switch 14 of each pixel 11. A CDS (correlated double sampling) circuit 17 is arranged in each vertical signal line 16. The CDS circuit 17 removes the noise that varies between pixels and temporarily stores the transmitted voltage.

[0037] The A / D converter 15 converts the voltage output from each amplifier 13 among the plurality of pixels 11 into a digital value. In the present embodiment, the A / D converter 15 converts the voltage stored in the CDS circuit 17 into a digital value. The converted digital values are respectively output to the computer 20. For example, the digital values may also be transmitted to a horizontal signal line (not shown) by switching column selection and then output to the computer 20. In this way, in the CMOS image sensor 10, when photons are input to each pixel 11, digital values corresponding to the number of input photons are output to the computer 20. In addition, the A / D converter 15 may also be provided in each pixel 11.

[0038] When reading out the voltage amplified by the amplifier 13, read noise, which is random noise, is generated in the amplifier 13. Figure 2 This is a graph showing the probability distribution of electrons. The horizontal axis represents the number of electrons, and the vertical axis represents the probability density. As Figure 2 shown, the number of electrons generated by the input photons follows a Poisson distribution. In Figure 2 it shows the probability distribution of electrons when an average of 2 photons are input to 1 pixel for each read noise. As examples of the read noise, 0.12, 0.15, 0.25, 0.35, 0.40, 0.45, and 1.0 [e-rms] can be cited. As Figure 2As shown, the smaller the read noise, the sharper the peak of the waveform of the probability distribution becomes, and the distinction between the distributions of each number of electrons becomes obvious. On the other hand, when the read noise increases, the distributions between adjacent numbers of electrons overlap with each other, and it becomes difficult to distinguish the distribution of each number of electrons. For example, when the read noise is 0.40 [e-rms] or less, it is manifested as being able to recognize the peak of each number of electrons. In contrast, when the read noise is 0.45 [e-rms] or more, it is difficult to recognize the peak of each number of electrons. In the present embodiment, according to whether the peak can be recognized, the magnitude of the read noise capable of distinguishing the number of electrons is obtained. Thus, in the CMOS image sensor 10 of the present embodiment, the read noise is 0.4 [e-rms] or less. Additionally, the magnitude of the read noise capable of distinguishing the number of electrons can also be obtained by performing a second-order differentiation on the probability distribution to detect the inflection point.

[0039] In addition, when a threshold for distinguishing between adjacent numbers of electrons is set, the false detection rate of the detected number of electrons varies according to the read noise. Figure 3 is a graph showing the relationship between the read noise and the false detection rate when, for example, the intermediate value between the numbers of electrons such as 0.5e, 1.5e, 2.5e... is used as the threshold. The false detection rate is the ratio detected as the wrong number of electrons and is caused by the spread of the probability distribution of electrons. As Figure 3 shown, when it is desired to make the false detection rate 1% or less, the read noise needs to be 0.2 [e-rms] or less. In addition, when it is desired to make the false detection rate 0.1% or less, the read noise needs to be 0.15 [e-rms] or less.

[0040] Figure 4 (a) is a graph showing the relationship between the number of electrons and the probability density. Figure 4 (b) is a graph showing the result of the simulation based on Figure 4 (a). In Figure 4 (a), the probability distribution of electrons when the read noise is 0.15 [e-rms] and the average number of photons input to one pixel is 2 is shown. In addition, in Figure 4 (b), the distribution of the number of electrons for each measurement number is shown by the simulated value (analogue value). In the A / D converter 15, the Figure 4 (b) shown simulated value is converted into a digital value and output. The digital value output from each pixel 11 is represented by the following formula.

[0041] Digital value [DN] = gain [DN / e] × number of electrons [e] + offset value [DN]

[0042] Figure 5 (b), Figure 6 (b) andFigure 7 (b) respectively are the graphs when converting the analog values of Figure 4 (b) into digital values. In Figure 5 (a), Figure 6 (a) and Figure 7 (a), the probability distributions of electrons when the readout noise is 0.15 [e-rms] and the average number of photons input per pixel is 2 are shown in the same way as Figure 4 (a). In Figures 5 to 7 , thresholds for distinguishing between electron numbers are set with the intermediate values between electron numbers as the reference, such as 0.5e, 1.5e, 2.5e... In the drawings, the thresholds are represented by dashed lines. In Figure 5 (b), the gain is 2 [DN / e] and the bias value is 100 [DN]. As shown in Figure 5 (b), when the gain is 2 [DN / e], it is difficult to reflect the deviation of the measured values observed with analog values in the graph. In addition, the proportion of digital values representing the same value as the threshold becomes higher.

[0043] In Figure 6 (b), the gain is 10 [DN / e] and the bias value is 100 [DN]. As shown in Figure 6 (b), when the gain is 10 [DN / e], the distribution of digital values is approximated to the distribution of analog values. On the other hand, since the gain is an even number, as shown in the drawings, there are also cases where digital values corresponding to the thresholds are taken. In Figure 7 (b), the gain is 11 [DN / e] and the bias value is 100 [DN]. As shown in Figure 7 (b), when the gain is 11 [DN / e], the distribution of digital values is more approximated to the analog values. Further, since the gain is an odd number, the cases of taking digital values corresponding to the thresholds can be suppressed. In this way, by increasing the value of the gain, the output digital values can be approximated to the analog values. In this embodiment, the CMOS image sensor 10 may also have a gain of, for example, 10 [DN / e] or more.

[0044] Refer to again Figure 1The computer 20 physically includes storage devices such as RAM and ROM, processors (arithmetic circuits) such as CPUs, communication interfaces, etc. As such a computer 20, for example, a personal computer, a cloud server, an intelligent device (such as a smart phone, a tablet terminal, etc.), a microcomputer, an FPGA (field-programmable gate array), etc. can be cited. The computer 20 functions as a storage unit 21, a correction unit 22, an arithmetic unit 23, a conversion unit 24, a data processing unit 25, and a control unit 26, for example, by a CPU of the computer system executing a program stored in the storage device. The computer 20 can be arranged either inside the camera including the CMOS image sensor 10 or outside the camera. The computer 20 can be connected to a display device 27 and an input device 28. The display device 27 is, for example, a display that can display the photon counting result obtained by the computer 20. The input device 28 is a keyboard, a mouse, etc. for a user to input measurement conditions. In addition, a common touch screen can also be used as the display device 27 and the input device 28.

[0045] The storage unit 21 stores reference data for converting the digital values output from the CMOS image sensor 10 into the number of photons. The reference data includes, for example, the gain and bias values of each of the plurality of pixels 11. In addition, the reference data includes threshold data for converting the digital values into the number of photons. The threshold data can also be prepared for each binning size. In addition, the binning size can be, for example, the number of pixels to be binned. When binning 3×3 pixels, the binning size is "9".

[0046] The correction unit 22 corrects the digital values corresponding to the respective pixels output from the A / D converter 15. In the present embodiment, the digital values are corrected to suppress the influence of the deviation of the gain and bias values among the plurality of pixels 11.

[0047] The arithmetic unit 23 outputs an added value obtained by adding the corrected digital values of at least two pixels 11 to each other. The plurality of pixels whose digital values are added to each other can have the same number of pixels in the row direction and the column direction, such as 2×2 pixels or 3×3 pixels. In addition, the plurality of pixels whose digital values are added to each other can have different numbers of pixels in the row direction and the column direction, such as 1×2 pixels or 2×5 pixels. In addition, the corrected digital values of all the pixels constituting the CMOS image sensor 10 can be added to each other.

[0048] The conversion unit 24 refers to the threshold data stored in the storage unit 21 and converts the added value output from the arithmetic unit 23 into the number of photons. The data processing unit 25 creates a two-dimensional image representing the number of photons of each pixel 11 based on the number of photons output from the conversion unit 24. In addition, the data processing unit 25 may also create a histogram or the like that is a layout (plot) of the number of pixels with respect to the number of photons. The created two-dimensional image or the like can be output to the display device 27. The control unit 26 can uniformly control each function of the computer 20 and the CMOS image sensor 10. For example, the control unit 26 controls the photon counting device 1 based on the setting conditions input by the input device 28.

[0049] Next, centering on the processing of the correction unit 22, the arithmetic unit 23, and the conversion unit 24, the details of the photon counting device 1 will be described while showing a specific example. Hereinafter, for simplicity of explanation, an example will be described in which it is assumed that the CMOS image sensor 10 of the photon counting device has a plurality (nine) of pixels 11 arranged in 3 rows × 3 columns and performs binning of 3 × 3 pixels. In addition, the number of pixels in the row direction and the column direction for binning can be specified according to the measurement conditions input to the input device 28.

[0050] First, a method of converting a digital value into the number of photons will be described assuming that there is no deviation in the gain and bias values. Figure 8 Schematically shows the process of converting the measured digital value into the number of electrons. In Figure 8 's example, it is assumed that in each pixel, the offset value is 100 [DN] and the gain is 11 [DN / e]. In addition, it is assumed that the readout noise is 0.15 [e-rms].

[0051] As Figure 8 shown, in such a CMOS image sensor 10, when photons are input to each pixel 11, charges are stored in each pixel 11 according to the number of photons. In the illustrated example, a case where 5 electrons are stored in all pixels 11 is shown. That is, 45 electrons are stored in 9 pixels. The stored charge is converted into a voltage by the amplifier 13 and converted into a digital value by the A / D converter 15. In Figure 8 's example, the digital value of each pixel is shown inside the pixel.

[0052] The digital value of each pixel is obtained by adding the pixels to be binned to each other. In Figure 8 's example, the digital values (155, 153, 155, 156, 154, 156, 156, 157, 153) of 9 pixels arranged in 3 rows × 3 columns are added to each other. Thus, as shown in the figure, the added value of the digital value of the binned pixel 31 is 1395.

[0053] The added value is converted into the number of electrons. At this time, for example, the added value is converted into the number of electrons using a threshold range. When the upper and lower limits of the threshold range are the intermediate values of the number of electrons, the thresholds representing the lower limit of each number of electrons and the thresholds representing the upper limit are shown by the following equations respectively. The range from the threshold of the lower limit to the threshold of the upper limit is the threshold range corresponding to the number of electrons.

[0054] Threshold (lower limit) = (number of electrons - 0.5) × gain + bias value × binning size

[0055] Threshold (upper limit) = (number of electrons + 0.5) × gain + bias value × binning size

[0056] In Figure 8 's example, as described above, it is assumed that the gain and bias value are 11 [DN / e] and 100 [DN] respectively, and there is no deviation in the gain and bias value between pixels. Therefore, for example, the lower limit of the threshold range corresponding to 45 electrons is 1390 [DN], and the upper limit is 1400 [DN]. Referring to this threshold range, when converting the Figure 8 illustrated digital value into the number of electrons, 1395 [DN], which is the added value of the merged pixel 31, is converted into 45 electrons. The number of electrons generated by the input photons follows a Poisson distribution. Therefore, the number of photons can be obtained by dividing the converted number of electrons by the quantum efficiency. For example, when the quantum efficiency is 100%, the number of electrons and the number of photons are the same.

[0057] Next, consider the case of converting the digital value into the number of electrons using the same threshold range as in the Figure 8 example in a state where the gain and bias value have deviations. Figure 9 represents an example of the digital value when the gain and bias value have deviations. In this example, the average gain is 11 [DN / e], and the deviation σ of the gain is 10%. That is, the gain ± σ can take values from 9.9 to 12.1. In addition, the average bias value is 100 [DN], and the deviation σ of the bias value is 3%. That is, the bias value ± σ can take values from 97 to 103. Figure 9 's example is also the same as Figure 8 in that it is a model in which 5 electrons are stored in all pixels. Similar to the Figure 8 example, when adding the digital values of 9 pixels arranged in 3 rows × 3 columns to each other, the added value of the merged pixel 31 is 1435 [DN]. When obtaining the threshold range in the same way as in the Figure 8 example based on the average bias value and average gain, the threshold range containing the added value of 1435 [DN] corresponds to 49 electrons. That is, 1435 [DN] is converted into 49 electrons. In this way, in a state where the gain and bias value have deviations, there are cases where it is difficult to convert the digital value into the correct number of electrons.

[0058] Thus, in the photon counting device 1 of the present embodiment, the correction unit 22 corrects the digital value output from the A / D converter 15 in such a way as to suppress the influence of the deviation of the gain and the bias value among the plurality of pixels 11. In the present embodiment, by correcting the digital value of each pixel 11, the apparent gain and the apparent bias value are the same for each pixel 11. The corrected digital value can be derived based on the deviation of the gain and the bias value of each pixel 11 from the apparent gain and the apparent bias value common to all pixels. For example, the corrected digital value can be derived by the following correction formula. In addition, the apparent gain and the apparent bias value (parameters) are preset and stored in the storage unit 21.

[0059] Corrected digital value = ((Digital value - Bias value) / Gain) × Apparent gain + Apparent bias value

[0060] The bias value and the gain in the above correction formula are included in the reference data stored in the storage unit 21. Here, the process for obtaining the gain and the bias value will be described. Figure 10 It is a schematic diagram showing the process of obtaining the bias value. As described above, the digital value is represented by the following formula. Therefore, the bias value represents the digital value output from the CMOS image sensor 10 in the state without input light. Thus, when obtaining the bias value, first, based on a plurality of dark images obtained by the CMOS image sensor 10 in the state without input light, the digital values output from the plurality of pixels are obtained. Then, the bias value is obtained by averaging the obtained digital values for each pixel.

[0061] Digital value [DN] = Gain [DN / e] × Number of electrons [e] + Bias value [DN]

[0062] Figure 11 It is a schematic diagram showing the process of obtaining the gain. When obtaining the gain of each pixel, under the condition of being given sufficient light amount, the CMOS image sensor 10 obtains multiple frames of images. Then, the average optical signal value S [DN] and the standard deviation N [DN] of the digital values of each pixel are obtained. The gain can be expressed as N 2 / S, so the gain can be obtained through the average optical signal value S and the standard deviation N.

[0063] Figure 12 It is a diagram showing the correspondence between the measured digital value and the corrected digital value. In Figure 12 the example, each pixel 11 constituting the CMOS image sensor 10 has Figure 10 the shown gain and Figure 11 the shown bias value. In Figure 12 the example, it shows that the digital value obtained by Figure 9An example of the digital value measured by the CMOS image sensor 10 in []. In this example, the conversion unit 24 corrects the digital value so that the apparent gain of all pixels becomes 11 [DN / e] and the apparent offset value becomes 100 [DN]. That is, the corrected digital value can be derived using the following correction formula.

[0064] Corrected digital value = ((digital value - offset value) / gain) × 11 + 100

[0065] In the conversion unit 24, the number of electrons is obtained using the threshold data common to each pixel for the corrected digital value. For example, the storage unit 21 may hold the threshold range derived by the following formula in a table. The conversion unit 24 can refer to the threshold data held in the table and convert the corrected digital value into the number of electrons. In addition, in the Figure 12 example, the apparent gain is 11 [DN / e] and the apparent offset value is 100 [DN]. Therefore, in the merging of 3×3 pixels, the merging size is "9", and when the corrected digital value is 1390 to 1400, it is determined to be 45 electrons. The conversion unit 24 can obtain the number of photons by dividing the converted number of electrons by the quantum efficiency.

[0066] Threshold (lower limit) = (number of electrons - 0.5) × apparent gain + apparent offset value × merging size

[0067] Threshold (upper limit) = (number of electrons + 0.5) × apparent gain + apparent offset value × merging size

[0068] Next, the operation of the photon counting device 1 will be described. Figure 13 is a flowchart showing the operation of the photon counting device. In the present embodiment, when the measurement starts in the state where the photon counting device 1 is operating, first, the light incident on the pixels of the CMOS image sensor 10 is converted into charge by the photodiode 12 (step S1). Then, the converted charge is converted into voltage by the amplifier 13 (step S2). This voltage is converted into a digital value by the A / D converter 15 and output to the computer 20 (step S3). The digital value is corrected for each pixel by the correction unit 22 of the computer 20 (step S4). The corrected digital values are merged (step S5). That is, the corrected digital values corresponding to the pixels 11 that make up the merged pixel 31 are added to each other, and the added value is output. The added value, that is, the merged digital value, is compared with the threshold data (step S6), and based on the comparison result, the added value is converted into the number of photons (step S7). Thus, the number of incident photons is measured for each merged pixel. The measurement result can be displayed on the display device 27 as, for example, image data, or output as a numerical value.

[0069] As described above, in the photon counting device 1, a voltage corresponding to the input photons is output from the amplifier 13. This voltage is converted into a digital value by the A / D converter 15. Then, when the pixels 11 are combined, the sum value obtained by adding the digital values corrected by the correction unit 22 to each other is converted into the number of photons. In the correction unit 22, the digital values are corrected to suppress the influence of the deviation of the gain and bias values among the plurality of pixels 11. That is, when the same number of photons are input, the deviation of each pixel 11 can be suppressed in the corrected digital values. Thereby, the influence of the deviation of the gain and bias values between the pixels is not easily reflected in the sum value, and it is easy to reflect only the number of photons. Therefore, a decrease in the counting accuracy of photons can be suppressed.

[0070] The correction unit 22 may also have preset parameters common to a plurality of pixels corresponding to the gain and bias values, and correct the digital values of the respective pixels based on the deviation between the gain and bias values and the parameters. In this structure, since the digital values are corrected according to the deviation between the reference parameter and the gain and bias values, for example, a threshold value based on the parameter can be used to convert the sum value into the number of photons.

[0071] The readout noise of the amplifier 13 may also be 0.2 [e-rms] or less. At this time, for example, the false detection rate can be suppressed to 1% or less. Further, the readout noise of the amplifier 13 may also be 0.15 [e-rms] or less. At this time, the false detection rate can be suppressed to 0.1% or less, for example.

[0072] The gain may also be 10 [DN / e] or more. Since the CMOS image sensor 10 has a high gain, the analog value output from the amplifier 13 can be reproduced as a digital value with high accuracy.

[0073] As described above, the embodiments have been described in detail with reference to the drawings, but the specific structure is not limited to this embodiment.

[0074] For example, in the CMOS image sensor 10 of the present embodiment, an example in which the readout noise of each pixel is 0.4 [e-rms] or less is shown. However, even if the readout noise in the sensor method is 0.4 [e-rms] or less, there are cases where the noise of some pixels is larger than 0.4 [e-rms]. In such a case, the pixels with a readout noise of 0.4 [e-rms] or less can be grasped in advance by measurement or the like, and photon counting can be performed using only the pixels with a readout noise of 0.4 [e-rms] or less.

[0075] In addition, an example of obtaining the corrected digital value by the following formula is shown, but it is not limited thereto.

[0076] Corrected digital value = ((digital value - bias value) / gain) × apparent gain + apparent bias value

[0077] For example, the corrected digital value can also be obtained using the following formula.

[0078] Corrected digital value = ((Digital value - Offset value) / Gain) × Apparent gain

[0079] At this time, for example, the storage unit 21 can also hold the threshold range derived from the following formula as a table. The conversion unit 24 can convert the corrected digital value into the number of electrons with reference to the threshold data held in the table.

[0080] Threshold (lower limit) = (Number of electrons - 0.5) × Apparent gain

[0081] Threshold (upper limit) = (Number of electrons + 0.5) × Apparent gain

[0082] In addition, the corrected digital value can also be obtained using the following formula.

[0083] Corrected digital value = ((Digital value - Offset value) / Gain)

[0084] At this time, for example, the storage unit 21 can also hold the threshold range derived from the following formula as a table. The conversion unit 24 can convert the corrected digital value into the number of electrons with reference to the threshold data held in the table.

[0085] Threshold (lower limit) = (Number of electrons - 0.5)

[0086] Threshold (upper limit) = (Number of electrons + 0.5)

[0087] Explanation of reference numerals

[0088] 1... Photon counting device, 11... Pixel, 12... Photodiode (photoelectric conversion element), 13... Amplifier, 15... A / D converter, 21... Storage unit, 22... Correction unit, 23... Arithmetic unit, 24... Conversion unit.

Claims

1. A photon counting device, characterized in that, Comprising: A plurality of pixels, which include a photoelectric conversion element that converts input light into charge and an amplifier that amplifies the charge converted by the photoelectric conversion element and converts it into voltage; An A / D converter that converts the voltage output from the amplifier of each of the plurality of pixels into a digital value and outputs it; An arithmetic unit that outputs an added value obtained by adding the digital values of at least two of the pixels to each other; And A conversion unit that converts the added value output from the arithmetic unit into the number of photons by referring to threshold data for differentiating between adjacent numbers of electrons.

2. The photon counting device according to claim 1, characterized in that: The threshold data is prepared respectively according to the number of at least two of the pixels whose digital values are added to each other.

3. The photon counting device according to claim 1 or 2, characterized in that: Further comprising an input device for inputting measurement conditions, the measurement conditions specifying the number of pixels in the row direction and the column direction among at least two of the pixels whose digital values are added to each other.

4. The photon counting device according to claim 1 or 2, characterized in that: Among at least two of the pixels whose digital values are added to each other, the number of pixels in the row direction and the number of pixels in the column direction are the same number.

5. The photon counting device according to claim 1 or 2, characterized in that: Among at least two of the pixels whose digital values are added to each other, the number of pixels in the row direction and the number of pixels in the column direction are different from each other.

6. The photon counting device according to claim 1 or 2, characterized in that: Further comprising a data processing unit that creates a two-dimensional image representing the number of photons of each pixel based on the number of photons converted by the conversion unit.

7. The photon counting device according to claim 1 or 2, characterized in that: Further comprising a data processing unit that creates a layout diagram of the number of pixels with respect to the number of photons based on the number of photons converted by the conversion unit.

8. A photon counting method, characterized in that, Comprising: A step of converting the light input to the photoelectric conversion elements respectively constituting a plurality of pixels into charge; A step of amplifying the converted charge by the amplifiers constituting the plurality of pixels and converting it into voltage; A step of converting the voltage output from each of the amplifiers into a digital value by an A / D converter and outputting it; A step of adding the digital values corresponding to at least two of the pixels and outputting an added value; And A step of converting the added value into the number of photons by referring to threshold data for differentiating between adjacent numbers of electrons.

9. The photon counting method according to claim 8, characterized in that: The threshold data is prepared respectively according to the number of at least two of the pixels whose digital values are added to each other.

10. The photon counting method according to claim 8 or 9, characterized in that: Further comprising an input step of inputting measurement conditions, the measurement conditions specifying the number of pixels in the row direction and the column direction among at least two of the pixels whose digital values are added to each other.

11. The photon counting method according to claim 8 or 9, characterized in that: Among at least two of the pixels whose digital values are added to each other, the number of pixels in the row direction and the number of pixels in the column direction are the same number.

12. The photon counting method according to claim 8 or 9, characterized in that: Among at least two of the pixels whose digital values are added to each other, the number of pixels in the row direction and the number of pixels in the column direction are different from each other.

13. The photon counting method according to claim 8 or 9, characterized in that: Further comprising a data processing step of creating a two-dimensional image representing the number of photons of each pixel based on the number of photons converted by the conversion step.

14. The photon counting method according to claim 8 or 9, characterized in that: Further comprising a data processing step of creating a layout diagram of the number of pixels with respect to the number of photons based on the number of photons converted by the conversion step.

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