WO2013187511A1 - 光信号検出回路、光量検出装置、および荷電粒子線装置 - Google Patents
光信号検出回路、光量検出装置、および荷電粒子線装置 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/244—Detectors; Associated components or circuits therefor
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
- H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2443—Scintillation detectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2445—Photon detectors for X-rays, light, e.g. photomultipliers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/24495—Signal processing, e.g. mixing of two or more signals
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2201/00—Indexing scheme relating to details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements covered by H03F1/00
- H03F2201/32—Indexing scheme relating to modifications of amplifiers to reduce non-linear distortion
- H03F2201/3215—To increase the output power or efficiency
Definitions
- the present invention relates to an optical signal detection circuit that detects light emitted from a sample, a light amount detection device, and a charged particle beam device.
- Photomultiplier tubes are used in various fields because they can extract very weak light as an electrical signal. For example, a photometer irradiates a sample with light, detects fluorescence generated from the sample by transmitted light, scattered light, or the like with a photomultiplier tube, and analyzes a small amount of contained components in the sample.
- the sample surface is irradiated with an electron beam, and weak secondary electrons generated from the sample surface are detected by a combination of a scintillator and a photomultiplier tube so that the sample surface can be observed in detail. I have to.
- Patent Document 1 discloses a technique for detecting an electrical signal from a photomultiplier tube using a small amount of light.
- the light detection circuit is connected to the anode of a PMT (photomultiplier tube).
- the photodetection circuit includes an I / V conversion circuit that converts an output current from the anode into a voltage signal V1, a dark current removal circuit that removes a dark current (dark count) from the voltage signal V1 and generates a voltage signal V2.
- a first-order lag filter circuit for shaping the voltage signal V2
- an A / D conversion circuit for converting the voltage signal V3 that has passed through the first-order lag filter circuit into digital data, and integrating the digital data according to the amount of light incident on the PMT.
- an arithmetic processing unit (CPU) for generating light quantity data. The arithmetic processing unit sets the integration time to a longer time as the value of the digital data decreases.
- Patent Document 1 describes that noise caused by dark current is removed by offset adjustment of an amplifier circuit included in the dark current removal circuit, a specific example of the offset adjustment is described. This method is not described.
- Patent Document 1 since the noise characteristics due to dark current vary with temperature, the conventional technique described in Patent Document 1 requires that the measurer adjust the offset of the amplifier circuit each time to cope with this. In general, the offset adjustment of an amplifier circuit that handles analog signals has a problem that it requires fine adjustment compared to the case of handling digital signals, which is troublesome.
- the present invention has been made in view of the above problems, and an optical signal detection circuit capable of discriminating a small amount of light signal components from noise signal components caused by dark current with a simple operation, and a light quantity It is an object to provide a detection device and a charged particle beam device.
- An optical signal detection circuit includes an amplifying unit that amplifies an analog detection signal corresponding to the amount of light detected by the photodetecting unit, and an analog / digital conversion unit that converts the analog detection signal amplified by the amplifying unit into a digital detection signal. And detecting the pulse from the digital detection signal converted by the analog-to-digital conversion means, repeating the process of detecting the energy of the detected pulse, obtaining the frequency of appearance of the pulse for each detected energy, and determining the pulse for each obtained energy.
- Threshold detection means for determining a pulse determination threshold based on the appearance frequency of the signal, and a digital detection signal including a pulse of energy equal to or higher than the pulse determination threshold determined by the threshold determination means is output as a detection signal And a threshold processing means.
- an optical signal detection circuit capable of discriminating a signal component of a minute amount of light from a signal component of noise caused by dark current with a simple operation. be able to.
- FIG. 3 is a flowchart illustrating a procedure for measuring a sample using the light amount detection device according to the first embodiment. It is a flowchart for demonstrating the operation
- FIG. 3A is a diagram illustrating an output of the optical signal detection circuit according to the first embodiment
- FIG. 4A illustrates the frequency number at the peak value H2 serving as a boundary between the floor noise region and the dark current noise region A illustrated in FIG.
- (b) is the dark current noise area
- (A) is a figure which shows the relationship between the crest value and frequency when predetermined time passes after a measurement start, Comprising:
- the frequency (line G31) of the crest value used as a pulse determination threshold is frequency lower limit TH1. Is larger than the frequency lower limit value TH1, it is preferable that the frequency of the crest value serving as the pulse determination threshold is adjusted to be smaller than the frequency lower limit value TH1 (line G32).
- (B) is a figure which shows the pulse number detected for every unit time in the case of (a).
- (C) is a diagram showing the relationship between the crest value and the frequency when a predetermined time has elapsed after the start of measurement, and the crest value frequency (line G33) serving as a pulse determination threshold is the frequency lower limit value TH1.
- the frequency value of the crest value distributed around the crest value determined by the multiplication characteristic of the photomultiplier tube is also smaller than the frequency lower limit value TH1, the crest value determined by the multiplication characteristic of the photomultiplier tube
- (D) is a figure which shows the pulse number detected for every unit time in the case of (c).
- FIG. 1 is a diagram showing a pulse wave height distribution of an output pulse of a photomultiplier tube and a pulse wave height distribution of a noise pulse when a small amount of light of a sample irradiated by a light source is input.
- the horizontal axis indicates the peak value that is the maximum voltage value of the pulse
- the vertical axis indicates the frequency (number of appearances) of the peak value within the measurement time.
- G2 the dotted line G2 in FIG.
- the frequency of occurrence of the crest value of the noise pulse is concentrated and distributed in a small value of the crest value, and the frequency abruptly increases between the crest value H1 and the crest value H2. Decrease.
- the frequency of occurrence of the crest value of the noise pulse decreases more slowly between the crest value H2 and the crest value H3 than in the crest value H1 to the crest value H2.
- the frequency of appearance of the peak value of the noise pulse decreases more gradually than between the peak value H2 and the peak value H3.
- the peak value of the output pulse of the photomultiplier tube is influenced by the noise pulse between the peak value H1 and the peak value H3, as shown by the line G1 in FIG. Although it decreases rapidly, the peak value larger than the peak value H3 is distributed around the peak value H4 determined by the multiplication characteristic of the photomultiplier tube.
- the peak value of the output pulse of the photomultiplier tube is measured because the output of the photomultiplier tube is weak, so the output of the photomultiplier tube is amplified by a preamplifier, and the amplified signal is sent to an A / D converter. In general, it is converted into a digital signal and processed. Therefore, the noise pulse is generated when a photomultiplier tube such as a preamplifier or the like is not operating, and a noise pulse caused by dark current (dark current noise pulse) generated when there is no input light in the photomultiplier tube. There is a noise pulse (floor noise pulse) caused by floor noise.
- Floor noise is a collection of waveforms with various frequency characteristics.
- the amplitude of the floor noise is generally smaller than the average peak value of noise caused by dark current. Therefore, the section (floor noise region) from the peak value H1 to the peak value H2 in FIG. 1 is more greatly affected by floor noise than noise due to dark current.
- the section from the peak value H2 to the peak value H3 dark current noise region A
- the influence of floor noise is almost eliminated, but the peak value of the output pulse of the photomultiplier tube by the original light and the wave of the dark current noise pulse Since the high value is comparable, it is greatly affected by noise caused by dark current.
- the peak value of the output pulse of the photomultiplier tube is larger than the peak value of the dark current noise pulse, and the influence of noise due to the dark current is almost eliminated.
- the distribution of output pulses of the photomultiplier tube is distributed around a peak value H4 determined by the multiplication characteristic of the photomultiplier tube. Therefore, it is desirable to detect only the peak value in the dark current noise region B as the optical signal detection.
- the distribution of the output pulse of the photomultiplier tube is centered on the peak value H4 determined by the multiplication characteristic of the photomultiplier tube. Therefore, until the boundary between the dark current noise region A and the dark current noise region B, where the influence of dark current noise is large, the frequency of appearance rapidly decreases from a low peak value to a high peak value, and gradually appears from the boundary. Increases frequency.
- the pulse determination threshold value for detecting the pulse is determined. Specifically, at the start of light measurement, the frequency number associated with the peak value is stored, the peak value where the appearance frequency is equal to or lower than the preset frequency lower limit value TH1 is set as a pulse determination threshold value, and pulse determination is performed. A pulse (only) having a peak value greater than the threshold value is detected and output as a pulse.
- FIG. 2 is a diagram illustrating changes in the pulse height distribution of noise pulses due to temperature.
- the horizontal axis indicates the peak value
- the vertical axis indicates the frequency of appearance of the peak value within the measurement time.
- a line G21 indicates a characteristic at the start of light quantity detection
- a line G22 for example, a time elapses from the start of light quantity detection and the temperature or pressure of the photomultiplier tube is higher than that at the start of light detection. The characteristic when the power supply voltage rises is shown. As shown in FIG.
- the frequency of appearance of the peak value of the dark current noise pulse increases as compared with the case where the temperature or the high-voltage power supply voltage is low. That is, the peak value that is equal to or lower than the lower frequency limit TH1 is equal to or higher than the peak value H5 in the line G21 indicating a low temperature or high voltage power supply voltage characteristic, whereas the peak value is in the line G22 having a high temperature or high voltage power supply voltage characteristic. H6 (H5 ⁇ H6). Therefore, when the temperature or the high-voltage power supply voltage rises and the characteristics of the noise pulse change from the line G21 to the line G22, it is desirable to detect a peak value greater than the peak value H6 as an optical signal.
- the peak value H6 is used as a pulse determination threshold value, a pulse having a peak value equal to or higher than the peak value H6 is detected as an optical signal, and the peak value H5 is obtained after the characteristic changes to the noise pulse characteristic line G21. It is desirable to detect a pulse having a peak value equal to or higher than the peak value H5 as an optical signal by using it as a pulse determination threshold value.
- FIG. 3 is a diagram showing a case where the pulse wave height distribution, which is the output of the photomultiplier tube, changes when the voltage of the high-voltage power supply of the photomultiplier tube rises due to a change in the surrounding environment.
- the horizontal axis indicates the peak value
- the vertical axis indicates the frequency of appearance of the peak value within the measurement time.
- a line G11 indicates the characteristic of the output pulse of the photomultiplier tube based on the line G21 having the characteristic of the noise pulse at the start of light quantity detection shown in FIG.
- the characteristic of the output pulse of the photomultiplier tube based on G22 having the characteristic of the noise pulse at the start of light quantity detection shown in FIG. As shown in FIG.
- the line G12 has a peak value in the line G12 rather than the line G11 because, for example, time has elapsed since the start of light quantity detection, and the high voltage power supply voltage of the photomultiplier tube has increased compared to the start of light detection. Is shifted to the larger side. That is, since the boundary between the dark current noise region A and the dark current noise region B shown in FIG. 1 is shifted to the larger peak value, the distribution of the boundary between the dark current noise region A and the dark current noise region B is changed. The valley is also off. This deviation is caused by a change in the characteristics of the noise pulse shown in FIG.
- the line G11 caused by the characteristic of the noise pulse indicated by the line G21 has a peak value H5
- FIG. 4 is a diagram showing a case where the self-temperature of the photomultiplier tube and the ambient environment temperature rise and the pulse wave height distribution, which is the output of the photomultiplier tube, changes.
- the horizontal axis indicates the peak value
- the vertical axis indicates the frequency of occurrence of the peak value within the measurement time.
- a line G31 indicates the characteristic of the output pulse of the photomultiplier tube based on the line G21 having the characteristic of the noise pulse at the start of light quantity detection shown in FIG.
- the characteristic of the output pulse of the photomultiplier tube based on G22 having the characteristic of the noise pulse at the start of light quantity detection shown in FIG. As shown in FIG.
- the line G32 is caused by dark current in the line G32 rather than the line G31 because, for example, time has elapsed since the start of light quantity detection and the temperature of the photomultiplier tube has risen more than at the start of light detection.
- the frequency of the peak value of the noise pulse that has been changed changes as the whole increases. In particular, this is the case where the peak value frequency in the dark current noise region A shown in FIG. 1 is significantly increased, and the peak value frequency in the dark current noise region B increases relatively slightly.
- the increase in the crest frequency is caused by a change in the characteristics of the noise pulse shown in FIG. 2 due to the temperature rise, and the valley of the distribution of the boundary between the dark current noise region A and the dark current noise region B has a crest value. It changes from H5 to the peak value H7.
- the frequency of appearance decreases rapidly from a low peak value to a high peak value
- the frequency number associated with the peak value is stored, and the peak value at which the appearance frequency is less than or equal to the preset frequency lower limit value TH1 is determined as a pulse.
- Threshold value a pulse (only) larger than the pulse determination threshold is output as a detection pulse, and the pulse determination threshold is compared by comparing the appearance frequency associated with the peak value with the frequency lower limit value TH1 even during optical measurement. The value is adjusted.
- the frequency of appearance rapidly decreases from a low peak value to a high peak value up to the boundary between the dark current noise region A and the dark current noise region B, where the influence of dark current noise is large
- the minimum value of the number is detected, and the peak value with the detected frequency number having the minimum value is set as the pulse determination threshold value.
- a pulse (only) larger than the pulse determination threshold value is output as a detection pulse.
- FIG. Embodiment 1 of the present invention will be described with reference to FIGS.
- FIG. 5 is a block diagram illustrating a configuration of a light amount detection apparatus using the optical signal detection circuit according to the first embodiment of the present invention.
- the light amount detection apparatus includes a light source 1, a photomultiplier tube 3, an optical signal detection circuit 4, and a personal computer (hereinafter referred to as PC) 5, and emits light from the sample 2. Detected.
- the photomultiplier tube 3 is a light detection means
- the personal computer 5 is a control means.
- the light source 1 irradiates the sample 2 to be measured with light.
- the photomultiplier tube 3 is a fluorescent light from the sample 2 that is generated by irradiation of light transmitted from the light source 1 through the sample 2 that has been irradiated with light from the light source 1 or reflected from the light source 1 (collectively, the light from the sample 2 Called).
- the photomultiplier tube 3 outputs an electrical signal (hereinafter referred to as an analog voltage signal) corresponding to the light from the sample 2 to the optical signal detection circuit 4.
- the analog voltage signal is an analog detection signal.
- the optical signal detection circuit 4 detects the light quantity of the sample 2 from the analog voltage signal input from the photomultiplier tube 3 and outputs it to the PC 5.
- the optical signal detection circuit 4 includes an amplifier 41, an analog-digital conversion unit (hereinafter referred to as an A / D conversion unit) 42, a threshold processing unit 43, a data processing unit 441, and a data analysis unit 442. 44, a storage unit 45 having a frequency number storage area 451, and a gain control unit 46.
- the amplifier 41 amplifies the analog voltage signal input from the photomultiplier tube 3 and outputs the amplified voltage signal to the A / D converter 42.
- the A / D converter 42 samples the analog voltage signal input from the amplifier 41 with a predetermined clock and converts it to a digital voltage signal.
- the converted digital voltage signal is sent to the data processor 441 and the threshold processor 43. Output.
- the digital voltage signal is a digital detection signal.
- the storage unit 45 is configured by a RAM (Random Access Memory) or the like, and has a frequency number storage area 451 for storing the number of appearances in association with the peak value of the pulse in the light amount detection.
- RAM Random Access Memory
- the data processing unit 441 detects a pulse from the digital voltage signal input from the A / D conversion unit 42 based on various settings from the PC 5, and stores the frequency number in association with the peak value of the detected pulse. Store in area 451.
- the data analysis unit 442 analyzes the frequency number associated with the crest value stored in the frequency number storage area 451 based on various settings from the PC 5 and performs pulse determination for discriminating between the noise component and the light amount signal component. Determine the threshold (crest value). The data analysis unit 442 outputs the determined pulse determination threshold value to the threshold value processing unit 43.
- the threshold processing unit 43 discriminates the digital voltage signal input from the A / D conversion unit 42 into a noise pulse and a light amount signal pulse based on the pulse determination threshold value input from the data analysis unit 442.
- the signal pulse of the light amount is output to the PC 5.
- the gain control unit 46 controls the light intensity of the light source 1 and the gains of the photomultiplier tube 3 and the amplifier 41 based on various settings from the PC 5.
- the PC 5 has a CPU (Central Processing Unit) and is composed of a general personal computer having input means such as a keyboard and a mouse and display means such as a display.
- the PC 5 sets various setting values input using the input means in the gain control unit 46, the data processing unit 441, and the data analysis unit 442, and the light amount signal input from the threshold processing unit 43.
- the pulse is analyzed, and the analysis result is displayed on a display means such as a display screen 51, for example.
- FIG. 6 is a flowchart showing a procedure for measuring a sample using the light amount detection apparatus of the first embodiment.
- the measurer inputs measurement conditions using the input function of the PC 5.
- the PC 5 sets measurement conditions based on the input measurement conditions (step S100). Specifically, the PC 5 sets the gain control value of the amplifier 41 and the photomultiplier tube 3 and the set value of the light intensity of the light source 1 in the gain control unit 46.
- the light quantity detection device starts measuring floor noise (step S101). Specifically, the measurer turns off the power of the photomultiplier tube 3, turns on the light source 1 and the optical signal detection circuit 4, and inputs an instruction to start measurement using the input means of the PC 5.
- the PC 5 starts the operation of the optical signal detection circuit 4 when an instruction to start measurement is input.
- the floor noise which is a noise component of the amplifier 41 and the A / D converter 42 in the optical signal detection circuit 4 can be measured.
- the sample 2 may or may not be installed in the light amount detection device. Here, it is assumed that the sample 2 is not installed.
- the amplifier 41 amplifies the analog voltage signal input from the photomultiplier tube 3 and outputs the amplified analog voltage signal to the A / D converter 42.
- the A / D converter 42 samples the analog voltage signal input from the amplifier 41 with a predetermined clock and converts it to a digital voltage signal.
- the converted digital voltage signal is sent to the data processor 441 and the threshold processor 43. Output.
- the floor noise is often inherent to the circuit, and the circuit noise of the optical signal detection circuit 4 has a voltage value (usually 0 V) when there is no signal (the photomultiplier tube 3 is OFF). Shows characteristics close to Gaussian distribution as a reference.
- the floor noise measurement in step S101 is for confirming the characteristics. Therefore, in this floor noise measurement, the threshold value determination unit 44 need not be operated.
- the pulse determination threshold value output from the data analysis unit 442 to the threshold value processing unit 43 is set in advance by the PC 5 to a predetermined value, for example, “0” in step S100.
- a predetermined value for example, “0” in step S100.
- the digital voltage signal that is the output of the A / D converter 42 is directly output to the PC 5 through the threshold processing unit 43 and can be confirmed by the display means of the PC 5.
- the PC 5 may display the input digital voltage signal as it is, or may display it by performing a predetermined process.
- the PC 5 sets a peak value measurement start voltage value in the data processing unit 441 (step S102).
- the peak value measurement start voltage value is used to determine whether or not to count the appearance frequency of the peak value, that is, whether to set the target peak value to store the frequency distribution in the threshold value determination process described later. This is the voltage value of the criterion.
- the peak value in the floor noise region is smaller than the peak value in the dark current noise region A. Therefore, if the frequency distribution (only) of the crest value larger than the crest value measurement start voltage value is stored, the frequency number storage area 451 can be reduced and the amount of data to be processed thereafter is small. Therefore, the processing time can be shortened.
- the measurer determines the peak value measurement start voltage value from the floor noise measurement result, and inputs the determined peak value measurement start voltage value using the input means of the PC 5.
- the PC 5 notifies the data processing unit 441 of the input peak value measurement start voltage value.
- the data processing unit 441 stores the notified peak value measurement start voltage value.
- the light quantity detection device starts measurement of the noise pulse in the non-light state (step S103).
- the measurer turns off the light source 1, turns on the power of the photomultiplier tube 3 and the power of the optical signal detection circuit 4, and inputs a measurement start instruction using the input means of the PC 5.
- the measurement start instruction includes a sampling time for pulse detection, a measurement time of the frequency of appearance of pulses, a time for determining a pulse determination threshold, a frequency lower limit value TH1 for determining a pulse determination threshold, and the like.
- the sampling time is a unit of time for sampling the analog voltage signal in order to detect one pulse from the analog voltage signal from the A / D converter 42.
- the measurement time is a time for executing a process of detecting an appearance frequency for each peak value that is a maximum voltage value of a pulse in order to determine a pulse determination threshold value.
- the PC 5 When the measurement start instruction is input, the PC 5 notifies the data processing unit 441 of the sampling time and the pulse appearance frequency measurement time, and the data processing unit 441 uses a time measuring function (not shown) to perform the sampling time. And the measurement of appearance frequency measurement time is started. Further, the PC 5 notifies the data analysis unit 442 of the pulse determination threshold value determination time for determining the pulse determination threshold value and the frequency lower limit value TH1. The data analysis unit 442 starts measurement of the pulse determination threshold value determination time using a timing function (not shown) and stores the frequency lower limit value TH1. Then, the amplifier 41 amplifies the analog voltage signal input from the photomultiplier tube 3 and outputs the amplified voltage signal to the A / D converter 42. The A / D converter 42 samples the analog voltage signal input from the amplifier 41 with a predetermined clock and converts it to a digital voltage signal. The converted digital voltage signal is sent to the data processor 441 and the threshold processor 43. Output.
- the threshold value determination unit 44 configured by the data processing unit 441 and the data analysis unit 442 executes the threshold value determination process to determine and determine the pulse determination threshold value.
- the pulse determination threshold value is output to the threshold value processing unit 43 (step S104). Step S105 will be described later.
- Threshold determination processing is divided into data processing executed by the data processing unit 441 and first data analysis processing executed by the data analysis unit 442.
- FIG. 7 is a flowchart for explaining the data processing operation. The operation of data processing executed by the data processing unit 441 will be described with reference to FIG.
- the data processing unit 441 displays the digital voltage value indicated by the digital voltage signal input from the A / D conversion unit 42 and the peak value set from the PC 5.
- the measurement start voltage value is compared (step S201).
- the data processing unit 441 determines whether or not the sampling time is a section in which a pulse is detected (pulse section). For example, the data processing unit 441 indicates whether the current sampling time is a pulse interval by using a pulse interval flag indicating that it is a pulse interval if ON, and not a pulse interval if OFF. Determine whether.
- Step S202 If it is not the pulse interval (No at Step S202), the data processing unit 441 returns to Step S200 and stops the process until the next sampling time is reached. Even when the sampling time is not set from the PC 5 (No in step S200), the data processing unit 441 stops the processing until the next sampling time is reached.
- the data processing unit 441 determines whether the sampling time is a pulse interval (step S203). If it is not a pulse interval (step S203, No), the data processing unit 441 turns on the pulse interval flag and stores the start of the pulse interval (step S204).
- the data processing unit 441 After the pulse section flag is turned ON or when it is determined that the pulse section is in progress (step S203, Yes), the data processing unit 441 stores the digital voltage value input from the A / D conversion unit 42 and the maximum stored value. The voltage value is compared (step S205). When the digital voltage value is larger than the maximum voltage value (Yes at Step S205), the data processing unit 441 holds the digital voltage value as the maximum voltage value and updates the maximum voltage value (Step S206). After updating the maximum voltage value or when the digital voltage value is equal to or less than the maximum voltage value (No in step S205), the data processing unit 441 returns to step S200 and stops the process until the next sampling time is reached.
- step S202 determines whether the sampling time is a pulse interval (step S202, Yes).
- the data processing unit 441 turns off the pulse interval flag and stores the end of the pulse interval (step S207).
- the data processing unit 441 increments the value of the frequency count storage area 451 associated with the maximum voltage value (step S208). Specifically, the data processing unit 441 reads the value of the maximum voltage value, and reads the value of the frequency number storage area 451 associated with the read value. Then, the data processing unit 441 adds “1” to the read value, and stores the added value in the frequency number storage area 451 associated with the maximum voltage value. As a result, the number of appearances of the crest value that is the maximum voltage value of the detected pulse is updated.
- the data processing unit 441 initializes the maximum voltage value (here, “0”) (step S209).
- the data processing unit 441 detects the peak value of the pulse in the pulse section in which the digital voltage value larger than the peak value measurement start voltage value is detected, and the value of the frequency number storage area 451 associated with the detected peak value.
- the data processing (steps S200 to S209) for incrementing and storing the frequency number for each peak value is repeated until the measurement end time is reached (step S210).
- the data processing unit 441 ends the measurement when the measurement end time is reached (step S210, Yes), and returns to step S200 when the measurement end time is not reached (step S210, No). Stop processing until the sampling time is reached.
- FIG. 8 is a diagram for explaining an operation of data processing for detecting one pulse and storing the frequency number.
- the horizontal axis indicates time
- the vertical axis indicates voltage.
- the digital voltage value input from the A / D converter 42 is equal to or lower than the peak value measurement start voltage value, so the data processor 441 sets the pulse interval flag to OFF. ing.
- the digital voltage value becomes larger than the peak value measurement start voltage value, and the data processing unit 441 turns on the pulse section flag and stores the digital voltage value “10” as the maximum voltage value.
- the digital voltage value becomes “20”. Therefore, the data processing unit 441 updates the maximum voltage value to “20”.
- the digital voltage value is “13”, and at the sampling time T7, the digital voltage value is “5”.
- the data processing unit 441 stores the maximum voltage value “20” at the sampling time T5. Therefore, the maximum voltage value is not updated.
- the digital voltage value becomes equal to or lower than the peak value measurement start voltage value, and the data processing unit 441 turns off the pulse interval flag. That is, the data processing unit 441 determines that the detection of one pulse has ended, and recognizes that the maximum voltage value of the detected pulse is “20”. The maximum voltage value of the detected pulse is a peak value. Therefore, in FIG. 8A, the peak value of the detected pulse is “20”.
- the address is defined in association with the peak value.
- the address “0” is the peak value “0”
- the address “20” is associated with the peak value “20”. Since “20” is stored as the maximum voltage value, in the case of FIG. 8B, the data processing unit 441 reads and increments the data “B” at the address “20”, and as data at the address “20”. “B + 1” is stored in the storage unit 45.
- the number of appearances (appearance frequency) of each pulse peak value detected within a predetermined time from the start of measurement to the end of measurement by data processing is stored in the frequency number storage area 451.
- FIG. 9 is a flowchart for explaining the operation of the first data analysis process.
- the operation of the first data analysis process executed by the data analysis unit 442 will be described with reference to FIG.
- the first data analysis process is a threshold value determination process as described above, and is a process executed after the data process described with reference to the flowchart of FIG.
- the data analysis unit 442 selects a processing target peak value (step S301). In the first case of processing, the data analysis unit 442 selects the smallest peak value among the pulse peak values detected by the data processing unit 441 as the processing target peak value. This is because, as described above with reference to FIG. 1, the smaller the peak value, the greater the appearance frequency. In addition, when it is not the pulse determination threshold value determination time (step S300, No), the data analysis unit 442 stops the process until the pulse determination threshold value determination time is reached.
- the data analysis unit 442 acquires the frequency number corresponding to the processing target peak value (step S302). Specifically, the data analysis unit 442 acquires data of the frequency number storage area 451 associated with the processing target peak value. The data analysis unit 442 compares the acquired data (frequency number) with the frequency lower limit value TH1 set by the PC 5 and stored in itself (step S303).
- the data analysis unit 442 selects the next processing target peak value (Step S304). Specifically, the data analysis unit 442 selects a peak value that is one larger than the current processing target peak value as a new processing target peak value. Then, the data analysis unit 442 acquires the frequency number corresponding to the processing target peak value until the frequency number corresponding to the processing target peak value is equal to or lower than the frequency lower limit value TH1, and the acquired frequency number and the frequency lower limit value TH1. Are repeated (steps S302 to S304).
- the data analysis unit 442 When the acquired frequency number is equal to or less than the frequency lower limit value TH1 (Yes in step S303), the data analysis unit 442 outputs the value of the processing target peak value to the threshold processing unit 43 as a pulse determination threshold value (step S305). ), The first data analysis process is terminated.
- the light amount detection device starts measuring the light amount of the sample 2 (step S105). Specifically, the measurer turns on the power of the light source 1, the photomultiplier tube 3, and the optical signal detection circuit 4, installs the sample 2 in the light amount detection device, and uses the input means of the PC 5 to sample 2. Input an instruction to start light quantity measurement. When the PC 5 receives an instruction to start light quantity measurement, the PC 5 notifies the optical signal detection circuit 4 to that effect and starts measurement.
- the amplifier 41 amplifies the analog voltage signal input from the photomultiplier tube 3 and outputs the amplified voltage signal to the A / D converter 42.
- the A / D converter 42 samples the analog voltage signal input from the amplifier 41 with a predetermined clock and converts it to a digital voltage signal.
- the converted digital voltage signal is sent to the data processor 441 and the threshold processor 43. Output.
- the threshold processing unit 43 compares the voltage value indicated by the digital voltage signal with the pulse determination threshold value indicating the voltage value notified from the data analysis unit 442. When the voltage value is equal to or higher than the pulse determination threshold value, the threshold value processing unit 43 outputs the digital voltage signal input from the A / D conversion unit 42 to the PC 5 as it is. When the voltage value is smaller than the pulse determination threshold value, the threshold value processing unit 43 sets the digital voltage signal to “0” and outputs it to the PC 5.
- the frequency lower limit value TH1 is larger than the boundary line between the floor noise region and the dark current noise region A shown in FIG. 1 based on the actual measurement values such as the measurement result of the floor noise measurement in step S101 shown in FIG. Set the value. For example, a frequency value satisfying a predetermined performance of the light quantity detection device is set as a frequency lower limit value TH1. Further, since the dark current noise varies due to the temperature of the photomultiplier tube 3, it is often influenced by the installation location of the light quantity detection device. Therefore, since it is often unique to the installation location, an experimentally obtained value may be set as the frequency lower limit value TH1.
- FIG. 10 is a diagram showing the output of the optical signal detection circuit of the first embodiment.
- the frequency number at the peak value H2 that is the boundary between the floor noise region and the dark current noise region A shown in FIG. 1 is set as the frequency lower limit value TH1
- the threshold value is the voltage value of the peak value H2. Therefore, the pulse P1 resulting from dark current noise is output together with the optical signal pulse.
- the pulse determination threshold value is the voltage value of the peak value H3. Therefore, it is possible to remove the pulse P1 caused by dark current noise and output an optical signal pulse (only).
- the data processing unit 441 detects a pulse from the digital voltage signal corresponding to the light amount converted by the amplifier 41 and the A / D conversion unit 42, and the maximum of the detected pulses.
- the crest value which is a voltage value, is obtained, and the appearance frequency for each obtained crest value is stored in the frequency number storage area 451.
- the data analysis unit 442 predetermines the number of occurrences of the peak value in order from the smallest value of the peak value associated with the peak value stored in the frequency number storage area 451. Are compared with the frequency lower limit value, and the peak value whose number of appearances is equal to or lower than the frequency lower limit value is determined as the pulse determination threshold value.
- the threshold processing unit 43 outputs a digital voltage signal (only) equal to or higher than the pulse determination threshold as a detection signal. Thereby, it is possible to discriminate between a small amount of light signal components and noise signal components caused by dark current by a simple operation of setting the frequency lower limit value TH1.
- the optical signal detection circuit 4 since the optical signal detection circuit 4 removes noise signals caused by dark current, S / N (Signal-Noise) ratio) can be increased, and a light amount detection device capable of detecting a weak light amount can be obtained.
- the pulse determination threshold value is obtained by performing the noise pulse measurement in the non-lighting state in step S103 of FIG. 6 and the threshold value determination process in step S104. Can be changed. This makes it possible to determine an appropriate pulse determination threshold even when the frequency of appearing pulses changes due to a temperature change, resulting from a small amount of light signal components and dark current corresponding to the temperature change. The signal component of noise can be discriminated.
- a threshold value determination process may be executed every predetermined time to obtain a pulse determination threshold value every predetermined time.
- the data analysis unit 442 notifies the PC 5 so that the PC 5 displays on the output means that the pulse determination threshold has been changed and the value of the pulse determination threshold. It may be. As a result, the measurer can recognize that the pulse determination threshold has been changed and the pulse determination threshold.
- the pulse determination threshold value is determined by the threshold value determination process in step S104 of FIG. 6, the relationship between the determined pulse determination threshold value and the temperature is previously functioned, and the light quantity measurement of the sample 2 is performed.
- the pulse determination threshold value may be dynamically changed.
- the function of the relationship between the pulse determination threshold value and the temperature is stored in the data analysis unit 442 in advance by the PC 5.
- the light quantity detection device is provided with a sensor for detecting the temperature, and the detected temperature is notified to the data analysis unit 442 of the optical signal detection circuit 4.
- the data analysis unit 442 may determine the pulse determination threshold based on the temperature notified from the sensor and the stored relationship between the pulse determination threshold and the temperature.
- FIG. 11 is a block diagram illustrating a configuration of a light amount detection apparatus using the optical signal detection circuit according to the second embodiment of the present invention.
- the light amount detection device of the second embodiment shown in FIG. 11 is substantially the same as the light amount detection device of the first embodiment shown in FIG. 5 except for the threshold value determination unit 44 of the optical signal detection circuit 4.
- a data analysis unit 442a is provided. Constituent elements having the same functions as those of the light quantity detection device of Embodiment 1 are denoted by the same reference numerals, and redundant description is omitted.
- the data analysis unit 442a has a function of analyzing the appearance frequency stored in association with the peak value and determining a value having the lowest appearance frequency as the pulse determination threshold value.
- the operation of the light quantity detection device of the second embodiment is almost the same as the operation of the light quantity detection device of the first embodiment. The difference is that the second data analysis process performed by the data analysis unit 442a during the light quantity detection is performed. Only the operation of the second data analysis process will be described here because it is added.
- the operation of the second data analysis process is performed at the time of measuring the light quantity in step S105 shown in FIG. Further, it is assumed that the data processing unit 441 performs the data processing operation described with reference to the flowchart of FIG.
- FIG. 12 is a flowchart for explaining the operation of the second data analysis process.
- the data analysis unit 442a selects a processing target peak value (step S400). Specifically, the data analysis unit 442a selects the peak value of the smallest value among the pulse peak values detected by the data processing unit 441 as the processing target peak value.
- the data analysis unit 442a selects a comparison target peak value (step S401). Specifically, the data analysis unit 442a selects a peak value next to the processing target peak value as a comparison target peak value.
- the data analysis unit 442a acquires the frequency numbers of the processing target peak value and the comparison target peak value (step S402). Specifically, the data analysis unit 442a obtains data (frequency number) in the frequency number storage area 451 associated with the processing target peak value and the comparison target peak value, respectively. The data analysis unit 442a compares the frequency number of the acquired processing target peak value with the frequency number of the comparison target peak value (step S403).
- the data analysis unit 442a selects a new processing target peak value and a comparison target peak value (step S404). Specifically, the current comparison target peak value is selected as a new processing target peak value, and the peak value next to the new processing target peak value is selected as a new comparison target peak value. Then, returning to step S402, the frequency numbers of the processing target peak value and the comparison target peak value are acquired from the frequency number storage area 451, and the frequency number of the acquired processing target peak value and the frequency number of the comparison target peak value are compared. To do.
- the data analysis unit 442a uses the value of the processing target peak value as a pulse determination threshold value to perform the threshold processing unit 43 (Step S405), and the second data analysis process is terminated.
- the data processing unit 441 detects a pulse from the digital voltage signal corresponding to the detected light amount converted by the amplifier 41 and the A / D conversion unit 42, and the detected pulse
- the peak value which is the maximum voltage value is obtained, and the appearance frequency for each obtained peak value is stored in the frequency number storage area 451.
- the data analysis unit 442a compares the frequency number for each peak value in order from the smallest peak value among the frequency values of the peak value associated with the peak value stored in the frequency number storage area 451.
- the minimum value of the frequency number is obtained, and the peak value indicating the minimum value of the frequency number is set as the pulse determination threshold value.
- the threshold value processing unit 43 outputs a digital voltage signal (only) equal to or higher than the pulse determination threshold value as a detection signal, even when the frequency number of appearance pulses changes due to a temperature change, it is appropriate. It is possible to determine a simple pulse determination threshold value, and it is possible to discriminate between a minute amount of a light signal component and a noise signal component caused by a dark current in response to a temperature change.
- the optical signal detection circuit 4 since the optical signal detection circuit 4 removes a noise signal caused by dark current, S / N (Signal-Noise) ratio) can be increased, and a light amount detection device capable of detecting a weak light amount can be obtained.
- the peak value having the smallest frequency number is used as the pulse determination threshold value.
- the peak value having a larger or smaller peak value is set by a predetermined amount than the peak value having the smallest frequency number. May be used as a pulse determination threshold value.
- a value indicating how much the peak value is to be increased or decreased is set in advance in the data analysis unit 442a from the PC 5, and a value obtained by subtracting a predetermined value from the minimum peak value or the minimum peak value A value obtained by adding a predetermined value to the value may be used as the pulse determination threshold value.
- the data processing unit 441 acquires the number of appearance frequencies for each peak value by data processing, and the data analysis unit 442a performs the second processing. Since the pulse determination threshold value is determined from the number of appearance frequencies for each peak value by the data analysis processing, the sample 2 is executed without executing the procedure for measuring the sample of the light quantity detection device of the first embodiment.
- the pulse determination threshold value may be determined by executing the light quantity measurement. Thereby, it is possible to determine the pulse determination threshold without setting the frequency lower limit value TH1.
- the data analysis unit 442a notifies the PC 5, and the PC 5 displays on the output means that the pulse determination threshold has been changed and the value of the pulse determination threshold. It may be.
- the measurer can recognize that the pulse determination threshold has been changed and the pulse determination threshold.
- FIG. A third embodiment of the present invention will be described with reference to FIGS.
- gain adjustment of the light source 1, the photomultiplier tube 3, and the amplifier 41 may be necessary.
- gain adjustment of the light source 1, the photomultiplier tube 3, and the amplifier 41 will be described.
- FIG. 13 is a diagram for explaining conditions for gain adjustment.
- a horizontal axis shows the crest value and the vertical axis
- shaft has shown frequency.
- the horizontal axis represents time
- the vertical axis represents the number of pulses detected per unit time.
- a line G31 in FIG. 13A shows the relationship between the peak value and the frequency when a predetermined time has elapsed after the start of measurement.
- the peak value of the boundary where the frequency decreases and increases again that is, the frequency of the peak value serving as the pulse determination threshold is greater than the frequency lower limit value TH1.
- the frequency of the peak value serving as the pulse determination threshold is larger than the frequency lower limit value TH1
- the number of pulses detected per unit time is appropriate as shown in FIG. It is distributed within an appropriate frequency between the lower limit value TH6 and the appropriate upper limit value TH7, and is in a stable state. This indicates that the quantization efficiency is stable and means that the voltage amplification degree of the amplifier 41 is insufficient.
- the frequency of the peak value serving as the pulse determination threshold is greater than the frequency lower limit value TH1, and the number of pulses detected per unit time is distributed within the appropriate frequency between the appropriate lower limit value TH6 and the appropriate upper limit value TH7. If so, the gain of the amplifier 41 is adjusted so that the frequency of the crest value serving as the pulse determination threshold becomes smaller than the frequency lower limit value TH1 as indicated by a line G32 in FIG. It is preferable to adjust to.
- a line G33 in FIG. 13C shows the relationship between the crest value and the frequency when a predetermined time has elapsed after the start of measurement.
- the frequency of the crest value serving as the pulse determination threshold is smaller than the frequency lower limit value TH1 and the crest value is distributed around the crest value determined by the multiplication characteristic of the photomultiplier tube 3. Is smaller than the lower frequency limit TH1.
- the number of pulses detected per unit time is not distributed within an appropriate frequency between the appropriate lower limit value TH6 and the appropriate upper limit value TH7, and the appropriate lower limit value TH6. It becomes the following. This indicates that the voltage of the photomultiplier tube 3 is insufficient.
- the voltage determined by the multiplication characteristic of the photomultiplier tube 3 is adjusted by adjusting the voltage of the photomultiplier tube 3 (gain adjustment is performed). It is preferable that the frequency number of the crest values distributed around the high value is also larger than the frequency lower limit value TH1.
- the number of pulses detected per unit time is counted, and the gains of the light source 1, the photomultiplier tube 3, and the amplifier 41 are calculated based on the counted result and the pulse determination threshold value. Make adjustments.
- FIG. 14 is a block diagram illustrating a configuration of a light amount detection apparatus using the optical signal detection circuit according to the third embodiment of the present invention.
- the light quantity detection device using the optical signal detection circuit according to the third embodiment of the present invention shown in FIG. 14 is the same as the light quantity detection device using the optical signal detection circuit according to the second embodiment shown in FIG.
- a pulse number storage area 452 is added to the storage unit 45 of the circuit 4, and a pulse measurement control unit 47 is added.
- a data processing unit 441 a is provided instead of the data processing unit 441, a data analysis unit 442 b is provided instead of the data analysis unit 442 a, and a gain control unit 46 a is provided instead of the gain control unit 46.
- Constituent elements having the same functions as those of the light quantity detection device of Embodiment 1 are denoted by the same reference numerals, and redundant description is omitted.
- the data processing unit 441a outputs a pulse detection notification for notifying that a pulse has been detected to the pulse measurement control unit 47 when the frequency number in the frequency number storage area 451 is updated.
- the pulse measurement control unit 47 controls the unit time of pulse measurement set by the PC 5 and the timing of gain adjustment determination. Further, the pulse measurement control unit 47 counts the pulse detection notification received within the unit time, and stores the count value in the pulse number storage area 452.
- the data analysis unit 442b determines whether to perform gain adjustment based on a notification from the pulse measurement control unit 47. Such determination will be described later with reference to FIG.
- the data analysis unit 442b outputs a gain adjustment notification to the gain control unit 46a.
- the gain control unit 46a adjusts the gains of the light source 1, the photomultiplier tube 3, and the amplifier 41.
- the operation of determining the pulse determination threshold value of the light amount detection device of the third embodiment is the same as the threshold value determination process of the first embodiment or the second embodiment.
- the operation of the gain adjustment determination process described below is performed. Therefore, only operations related to gain adjustment performed during light amount detection will be described here.
- step S206 of the data processing described with reference to the flowchart of FIG. 7 the data processing unit 441a outputs a pulse detection notification for notifying that a pulse has been detected to the pulse measurement control unit 47 after updating the maximum voltage value.
- the pulse measurement control unit 47 repeats the operation of counting up the value of a pulse counter (not shown) until a preset unit time is completed.
- the pulse measurement control unit 47 stores the value of the pulse counter in the pulse number storage area 452.
- the pulse measurement control unit 47 initializes the value of the pulse counter (sets it to “0”), and counts up the value of the pulse counter for the next unit time.
- the pulse number storage area 452 is associated with an address for each unit time, and stores the value (number of pulses) of the pulse counter for each unit time.
- the pulse measurement control unit 47 notifies the data analysis unit 442b of the gain adjustment determination time.
- the data analysis unit 442b executes a gain adjustment determination process.
- FIG. 15 is a flowchart for explaining the operation of the gain adjustment determination process.
- the operation of the gain adjustment determination process will be described in detail with reference to the flowchart of FIG. Note that the processing for obtaining the minimum value of the peak value frequency is the same as steps S400 to S404 described in the flowchart of FIG. 12, and therefore, the same reference numerals are given and detailed description thereof is omitted.
- the data analysis unit 442b selects a processing target peak value and a comparison target peak value (steps S400 and S401).
- the data analysis unit 442b acquires the frequency numbers of the processing target peak value and the comparison target peak value (step S402).
- the data analysis unit 442b compares the frequency number of the acquired processing target peak value with the frequency number of the comparison target peak value (step S403). When the frequency number of the processing target peak value is larger than the frequency number of the comparison target peak value (step S403, Yes), the data analysis unit 442b selects a new processing target peak value and a comparison target peak value (step S404). .
- the data analysis unit 442b acquires the frequency numbers of the processing target peak value and the comparison target peak value from the frequency number storage area 451, and the frequency number of the acquired processing target peak value and the comparison target peak value. Compare the frequency number of.
- the data analysis unit 442b compares the frequency number of the processing target peak value with the frequency lower limit value TH1 (step S500). ). When the frequency number of the processing target peak value is larger than the frequency lower limit value TH1 (step S500, Yes), the data analysis unit 442b determines whether the number of pulses is within an appropriate range (step S501).
- the data analysis unit 442b acquires all the pulse numbers detected for each unit time stored in the pulse number storage area 452.
- the data analysis unit 442b determines whether or not the acquired number of pulses per unit time is greater than or equal to a predetermined appropriate lower limit value TH6 and less than or equal to an appropriate upper limit value TH7. In this case, for example, the case where the number of pulses in all time units is not less than the appropriate lower limit value TH6 and not more than the appropriate upper limit value TH7 may be determined to be within the appropriate range.
- the number of unit times in which the number of pulses is equal to or greater than the appropriate lower limit value TH6 and equal to or less than the appropriate upper limit value TH7 may be determined to be within the appropriate range if it is equal to or greater than a predetermined value.
- step S501, Yes When it is determined that the number of pulses is within the appropriate range (step S501, Yes), the data analysis unit 442b outputs a gain adjustment notification for adjusting the amplifier 41 to the gain control unit 46a (step S502). finish.
- step S501, No When it is determined that the number of pulses is out of the appropriate range (step S501, No), the data analysis unit 442b ends the process.
- the data analysis unit 442b determines whether the number of pulses is outside the appropriate range (Step S503). All the pulse numbers detected per unit time stored in the pulse number storage area 452 are acquired. The data analysis unit 442b determines whether the acquired number of pulses is equal to or greater than a predetermined appropriate lower limit value TH6 and equal to or less than a proper upper limit value TH7. In this case, for example, when the number of pulses in all time units is less than or equal to the appropriate lower limit value TH6 or more than the appropriate upper limit value TH7, it may be determined that it is out of the appropriate range. If the number of unit times whose number is not more than the appropriate lower limit value TH6 or not less than the appropriate upper limit value TH7 is not less than a predetermined value, it may be determined that the number is outside the appropriate range.
- step S503 If it is determined that the number of pulses is out of the appropriate range (step S503, Yes), the data analysis unit 442b outputs a gain adjustment notification for adjusting the voltage of the photomultiplier tube 3 to the gain control unit 46a (step S504). ) End the process.
- step S503 No the data analysis unit 442b ends the process.
- the gain control unit 46a When the gain control unit 46a receives the gain adjustment notification by the above gain adjustment determination process, the gain control unit 46a adjusts the amplifier 41 or the photomultiplier tube 3 based on the gain adjustment notification.
- the adjustment amount may be determined in advance by an experiment or the like and set in the gain control unit 46a by the PC 5. Further, not only the photomultiplier tube 3 but also the light source 1 may be adjusted.
- the pulse measurement control unit 47 counts the number of pulses detected by the data processing unit 441a, and stores the counted number of pulses in the pulse number storage area in association with the unit time. .
- the data analysis unit 442b compares the number of appearances for each peak value in order from the smallest peak value among the number of appearances of the peak value associated with the peak value stored in the frequency number storage area 451. The minimum value of the number of appearances is obtained, and the amplifier 41 and the photomultiplier tube are based on the obtained minimum value, the frequency lower limit value TH1, and the number of pulses detected per unit time stored in the pulse number storage area 452. It is determined whether or not the gain of 3 is adjusted.
- the gain control unit 46a adjusts the gains of the amplifier 41 and the photomultiplier tube 3 based on the determination result, the gain control of the amplifier 41 and the photomultiplier tube 3 can be controlled. It is possible to appropriately distinguish a small amount of light signal components from noise signal components caused by dark current.
- FIG. 16 is a block diagram illustrating a configuration of a light amount detection apparatus using the optical signal detection circuit according to the fourth embodiment of the present invention.
- 16 includes an optical signal detection circuit 4a instead of the optical signal detection circuit 4 of the light amount detection apparatus of the first embodiment shown in FIG.
- the threshold value processing unit 43 is deleted from the optical signal detection circuit 4, and a digital / analog conversion unit (hereinafter referred to as a D / A conversion unit) 49, a comparator 48 (CMP in the figure), , And a counter 50 are added.
- a digital / analog conversion unit hereinafter referred to as a D / A conversion unit
- CMP CMP in the figure
- symbol is attached
- the D / A conversion unit 49 converts the pulse determination threshold value input from the data analysis unit 442 from digital data to an analog signal (hereinafter referred to as an analog pulse determination threshold value).
- the comparator 48 compares the analog voltage signal input from the photomultiplier tube 3 with the analog pulse determination threshold value input from the D / A converter 49. When the analog voltage signal is equal to or greater than the analog pulse determination threshold value (only) as a result of the comparison, the comparator 48 outputs a pulse (count instruction signal) instructing the count-up after waveform shaping to the counter 50. When the count instruction signal is input, the counter 50 counts up the count value and outputs the count value to the PC 5.
- the procedure for measuring the sample 2 using the light amount detection device of the fourth embodiment is the same as the procedure described with reference to the flowchart of FIG. 6, and the pulse determination threshold is the flowchart of FIG. And the data analysis process described with reference to the flowchart of FIG. 9 described above.
- the difference is that the data analysis unit 442 outputs the pulse determination threshold value determined by the first data analysis process to the D / A conversion unit 49 instead of outputting it to the threshold value processing unit 43. Therefore, only the differences will be described here.
- the D / A conversion unit 49 converts the pulse determination threshold value from digital data to an analog pulse determination threshold value. Then, the D / A converter 49 outputs the analog pulse determination threshold value to the comparator 48.
- the comparator 48 compares the analog voltage signal input from the photomultiplier tube 3 with the analog pulse determination threshold value.
- the comparator 48 outputs a count instruction signal to the counter 50 when the analog voltage signal is equal to or greater than the analog pulse determination threshold value.
- the count instruction signal is input, the counter 50 counts up the count value and outputs the count value to the PC 5.
- the PC 5 calculates the intensity or number of pulses of light incident on the photomultiplier tube 3 based on the count value from the counter 50.
- the data processing unit 441 detects a pulse from the digital voltage signal corresponding to the light amount converted by the amplifier 41 and the A / D conversion unit 42, and detects the maximum voltage of the detected pulse.
- the peak value which is a value is obtained, and the appearance frequency for each obtained peak value is stored in the frequency number storage area 451.
- the data analysis unit 442 predetermines the number of occurrences of the peak value in order from the smallest value of the peak value associated with the peak value stored in the frequency number storage area 451.
- the frequency lower limit value is compared, and as a result of the comparison, the peak value at which the number of appearances is equal to or lower than the frequency lower limit value TH1 is set as a pulse determination threshold value.
- the D / A converter 49 converts the pulse determination threshold value to an analog signal, and the analog signal pulse determination obtained by converting the analog voltage signal input from the photomultiplier tube 3 by the A / D converter 42 is performed. The number exceeding the threshold value is counted and output to the PC 5.
- Embodiment 4 demonstrated the case where the photomultiplier tube 3 was one, you may make it provide the photomultiplier tube 3 with two or more. In this case, the same number of comparators and counters of the optical signal detection circuit 4a as the photomultiplier tubes 3 may be provided.
- FIG. 17 is a block diagram showing the configuration of the light quantity detection device when two photomultiplier tubes are provided. As shown in FIG. 17, a plurality (two in this case) of photomultiplier tubes 3-1 and 3-2 for detecting fluorescence from the sample 2 are provided. Further, the optical signal detection circuit 4a includes comparators 48-1 and 48-2 and counters 50-1 and 50-2 corresponding to the number of photomultiplier tubes 3 (in this case, two).
- the photomultiplier tube 3-1 and the photomultiplier tube 3-2 are arranged at different positions and detect fluorescence from the sample 2, respectively.
- the photomultiplier 3-1 outputs an analog voltage signal, which is an electrical signal corresponding to the detected fluorescence, to the amplifier 41 and the comparator 48-1.
- the photomultiplier tube 3-2 outputs an analog voltage signal to the comparator 48-2.
- the comparators 48-1 and 48-2 receive the analog voltage signal input from the photomultiplier tubes 3-1 and 3-2 and the D / A converter 49.
- the analog pulse judgment threshold value to be compared is compared.
- the comparators 48-1 and 48-2 receive a pulse (count instruction signal) for instructing count-up after waveform shaping. -1,50-2.
- the count instruction signal is input, the counters 50-1 and 50-2 count up the count value and output the count value to the PC 5.
- the pulse determination threshold value can be determined from the output of one photomultiplier tube 3-1. Therefore, the circuit scale of the optical signal detection circuit 4a can be reduced.
- Embodiment 5 FIG. In the first to fourth embodiments, the case where the optical signal detection circuit is applied to the light amount detection device has been described. In the fifth embodiment, a case where the optical signal detection circuit is applied to a scanning electron microscope which is one of charged particle beam apparatuses will be described.
- FIG. 18 is a diagram showing a configuration of a scanning electron microscope using the optical signal detection circuit of the present invention.
- a scanning electron microscope using the optical signal detection circuit of the present invention includes an electron source 601, an extraction electrode 602, an acceleration electrode 603, a first focusing electrode 605, a diaphragm 606, a second focusing electrode 607, Electron beam manipulation deflector 608, ExB deflector 612, objective lens 609, sample stage 611, secondary electron detector 614, preamplifier 615, high voltage controller 620, focusing lens controller 622, deflection controller 623, detection controller 624, an objective lens control unit 625, a stage control unit 626, and a computer 630.
- the high voltage control unit 620 controls the electron source 601, the extraction electrode 602, and the acceleration electrode 603.
- the focusing lens control unit 622 controls the first focusing electrode 605 and the second focusing electrode 607.
- the deflection control unit 623 controls the deflector 608 for operating an electron beam.
- the objective lens control unit 625 controls the objective lens 609.
- the stage control unit 626 controls the sample stage 611.
- the detection control unit 624 detects light from the signal detected by the secondary electron detector 614 and amplified by the preamplifier 615. As the detection control unit 624, the optical signal detection circuit of the first to fourth embodiments is used.
- the computer 630 displays an image of the surface shape of the sample 610 to be inspected based on the signal detected by the detection control unit 624.
- Electrons emitted from the electron source 601 are accelerated by the extraction electrode 602 and the acceleration electrode 603.
- the accelerated electrons 604 pass through the first focusing electrode 605, the diaphragm 606, and the second focusing electrode 607, are focused through the ExB deflector 612, and are converged by the lens action of the objective lens 609 to be sample stage 611. Is scanned one-dimensionally or two-dimensionally.
- the secondary electrons 613 generated from the sample 610 to be inspected reach the secondary electron detector 614 by the ExB deflector 612.
- the secondary electron detector 614 outputs a voltage signal corresponding to the reached secondary electron 614 to the preamplifier 615.
- the preamplifier 615 amplifies the voltage signal and outputs it to the detection control unit 624.
- the detection control unit 624 is the optical signal detection circuit according to any one of the first to fourth embodiments.
- the pulse determination threshold is determined by the operation of any of the first to fourth embodiments, and an output pulse or a count value of the number of output pulses is output to the computer 630 based on the determined pulse determination threshold.
- the computer 630 displays an image of the surface shape of the sample 610 to be inspected on a display unit such as a monitor based on the output pulse input from the detection control unit 624 or the count value of the number of output pulses.
- the optical signal detection circuit of any of the first to fourth embodiments is used for the detection control unit 624. Therefore, a small amount of light signal component and noise signal component caused by dark current are discriminated by a simple operation such as setting the frequency lower limit TH1, and a small amount of light signal component corresponding to the change is determined. It becomes possible to discriminate the noise signal component caused by the dark current, and it is possible to obtain a scanning electron microscope having a higher optical signal detection S / N (Signal-Noise ratio).
- the optical signal detection circuit according to any one of the first to fourth embodiments may be used for detection of an apparatus that detects and analyzes light from a measurement target such as an ion microscope.
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Abstract
Description
図1~図4を用いて、本発明に係る光信号検出回路の概要および特徴を説明する。図1は、光源によって照射された試料の微量の光が入力された際の光電子増倍管の出力パルスのパルス波高分布およびノイズパルスのパルス波高分布を示す図である。図1において、横軸はパルスの最大電圧値である波高値を示し、縦軸は測定時間内における波高値の出現の頻度(出現回数)を示している。ノイズパルスの波高値の出現の頻度は、図1の点線G2に示すように、波高値の小さい値に集中して分布しており、波高値H1から波高値H2の間で急激にその頻度が減少する。そして、ノイズパルスの波高値の出現の頻度は、波高値H2から波高値H3の間では、波高値H1から波高値H2と比較して頻度の減少は緩やかになる。さらに、波高値H3より大きい波高値においては、ノイズパルスの波高値の出現の頻度は、波高値H2から波高値H3の間と比較してさらに緩やかに減少する。
また、図3において、線G11は、図2に示した光量検出開始時におけるノイズパルスの特性を有する線G21の基での光電子増倍管の出力パルスの特性を示し、線G12は、図2に示した光量検出開始時におけるノイズパルスの特性を有するG22の基での光電子増倍管の出力パルスの特性を示している。
図3に示すように、線G12は、たとえば光量検出開始時から時間が経過し、光検出開始時よりも光電子増倍管の高圧電源電圧が上昇したため、線G11より線G12のほうが、波高値が大きいほうにずれている。すなわち、先の図1に示した暗電流ノイズ領域Aと暗電流ノイズ領域Bとの境界が波高値の大きいほうにずれたため、暗電流ノイズ領域Aと暗電流ノイズ領域Bとの境界の分布の谷間もずれている。このずれは、先の図2に示したノイズパルスの特性の高圧電源電圧による変化に起因しており、暗電流ノイズ領域Aと暗電流ノイズ領域Bとの境界の分布の谷間は、図2の線G21で示すノイズパルスの特性に起因している線G11では概ね波高値H5となり、図2の線G22で示すノイズパルスの特性に起因している線G12では概ね波高値H6となる。
また、図4において、線G31は、図2に示した光量検出開始時におけるノイズパルスの特性を有する線G21の基での光電子増倍管の出力パルスの特性を示し、線G32は、図2に示した光量検出開始時におけるノイズパルスの特性を有するG22の基での光電子増倍管の出力パルスの特性を示している。
図4に示すように、線G32は、たとえば光量検出開始時から時間が経過し、光検出開始時よりも光電子増倍管の温度が上昇したため、線G31より線G32のほうが、暗電流に起因したノイズパルスの波高値の頻度が全体的に多くなるほうに変化している。特には、先の図1に示した暗電流ノイズ領域Aの波高値頻度が顕著に多くなるほうにずれ、暗電流ノイズ領域Bの波高値頻度は、比較的少なめに増加した場合である。この波高頻度の増加は、先の図2に示したノイズパルスの特性の温度上昇による変化に起因しており、暗電流ノイズ領域Aと暗電流ノイズ領域Bとの境界の分布の谷間は波高値H5から波高値H7に変化する。
図5~図9を用いて、本発明の実施形態1を説明する。図5は、本発明の実施形態1の光信号検出回路を用いた光量検出装置の構成を示すブロック図である。図5に示すように、光量検出装置は、光源1と、光電子増倍管3と、光信号検出回路4と、パーソナルコンピュータ(以下、PCと呼ぶ)5とを備えて試料2からの光を検出対象とする。なお、光電子増倍管3は、光検出手段であり、パーソナルコンピュータ5は、制御手段である。
図11および図12を用いて、本発明の実施形態2を説明する。図11は、本発明の実施形態2の光信号検出回路を用いた光量検出装置の構成を示すブロック図である。図11に示した実施形態2の光量検出装置は、先の図5に示した実施形態1の光量検出装置とほぼ同じであるが、相違点は光信号検出回路4のしきい値決定部44のデータ解析部442の代わりに、データ解析部442aを備えることである。実施形態1の光量検出装置と同じ機能を有する構成要素には、同一符号を付し、重複する説明を省略する。
図13~図15を用いて、本発明の実施形態3を説明する。先の実施形態1および実施形態2において光量を検出する際に、光源1や光電子増倍管3、アンプ41のゲイン調整が必要となる場合がある。この実施形態3では、光源1や光電子増倍管3、アンプ41のゲイン調整について説明する。
パルス数記憶領域452は、単位時間ごとにアドレスが対応付けられ、それぞれの単位時間ごとのパルスカウンタの値(パルス数)を記憶する。
図16および図17を用いて、本発明の実施形態4を説明する。図16は、本発明の実施形態4の光信号検出回路を用いた光量検出装置の構成を示すブロック図である。図16に示した実施形態4の光量検出装置は、先の図5で示した実施形態1の光量検出装置の光信号検出回路4の代わりに、光信号検出回路4aを備えている。光信号検出回路4aは、光信号検出回路4からしきい値処理部43が削除され、デジタルアナログ変換部(以下、D/A変換部と呼ぶ)49と、コンパレータ48(図中ではCMP)と、カウンタ50とが追加されている。なお、実施形態1の光量検出装置と同じ機能を有する構成要素には、同一符号を付し、重複する説明を省略する。
先の実施形態1~4では、光信号検出回路を光量検出装置に適応した場合について説明した。この実施形態5では、光信号検出回路を荷電粒子線装置の1つである走査型電子顕微鏡に適用した場合について説明する。
2 試料
3 光電子増倍管(光検出手段)
4 光信号検出回路
5 パーソナルコンピュータ(制御手段)
41 アンプ(増幅手段)
42 A/D変換部(アナログデジタル変換手段)
43 しきい値処理部(しきい値処理手段)
44 しきい値決定部(しきい値決定手段)
46,46a ゲイン制御部(ゲイン制御手段)
47 パルス測定制御部(パルス測定制御手段)
48 コンパレータ(比較手段)
49 D/A変換部(デジタルアナログ変換手段)
50 カウンタ(カウント手段)
441 データ処理部(データ処理手段)
442,442a データ解析部(データ解析手段)
451 頻度数記憶領域(頻度数記憶手段)
452 パルス数記憶領域(パルス数記憶手段)
Claims (14)
- 光検出手段により検出される光量に応じたアナログ検出信号を増幅する増幅手段と、
前記増幅手段によって増幅されたアナログ検出信号をデジタル検出信号に変換するアナログデジタル変換手段と、
前記アナログデジタル変換手段によって変換されたデジタル検出信号からパルスを検出するとともに、検出したパルスのエネルギを検出する処理を繰り返し、検出したエネルギごとのパルスの出現頻度を求め、求めたエネルギごとのパルスの出現頻度に基づいてパルス判定しきい値を決定するしきい値決定手段と、
前記しきい値決定手段によって決定されたパルス判定しきい値以上のエネルギのパルスを含む前記デジタル検出信号を検出信号として出力するしきい値処理手段と、
を備えることを特徴とする光信号検出回路。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順に当該エネルギのパルスの出現頻度と予め定められた頻度下限値とを比較し、比較の結果、パルスの出現頻度が前記頻度下限値以下となったエネルギの値をパルス判定しきい値に決定するデータ解析手段と、
を備えることを特徴とする請求項1に記載の光信号検出回路。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順にエネルギごとのパルスの出現頻度を比較してパルスの出現頻度の最小値を求め、パルスの出現頻度が最小値を示すエネルギの値をパルス判定しきい値に決定するデータ解析手段と
を備えることを特徴とする請求項1に記載の光信号検出回路。 - 光検出手段により検出される光量に応じたアナログ検出信号を増幅する増幅手段と、
前記増幅手段によって増幅されたアナログ検出信号をデジタル検出信号に変換するアナログデジタル変換手段と、
前記アナログデジタル変換手段によって変換されたデジタル検出信号からパルスを検出するとともに、検出したパルスのエネルギを検出する処理を繰り返し、検出したエネルギごとのパルスの出現頻度を求め、求めたエネルギごとのパルスの出現頻度に基づいてパルス判定しきい値を決定するしきい値決定手段と、
前記しきい値決定手段によって決定されたパルス判定しきい値をデジタル信号からアナログ信号に変換するデジタルアナログ変換手段と、
前記検出した光量に応じたアナログ検出信号が、前記デジタルアナログ変換手段によって変換されたアナログ信号のパルス判定しきい値以上であるか否かを判定する比較手段と、
前記比較手段によって前記検出した光量に応じたアナログ検出信号が、前記デジタルアナログ変換手段によって変換されたアナログ信号のパルス判定しきい値以上であると判定された数をカウントして出力するカウント手段と、
を備えることを特徴とする光信号検出回路。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順に当該エネルギのパルスの出現頻度と予め定められた頻度下限値とを比較し、比較の結果、パルスの出現頻度が前記頻度下限値以下となったエネルギの値をパルス判定しきい値に決定するデータ解析手段と、
を備えることを特徴とする請求項4に記載の光信号検出回路。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順にエネルギごとのパルスの出現頻度を比較してパルスの出現頻度の最小値を求め、パルスの出現頻度が最小値を示すエネルギの値をパルス判定しきい値に決定するデータ解析手段と
を備えることを特徴とする請求項4に記載の光信号検出回路。 - 光量を検出し、検出した光量に応じたアナログ検出信号を出力する光検出手段と、
前記光検出手段によって検出されたアナログ検出信号を増幅する増幅手段と、
前記増幅手段によって増幅されたアナログ検出信号をデジタル検出信号に変換するアナログデジタル変換手段と、
前記アナログデジタル変換手段によって変換されたデジタル検出信号からパルスを検出するとともに、検出したパルスのエネルギを検出する処理を繰り返し、検出したエネルギごとのパルスの出現頻度を求め、求めたエネルギごとのパルスの出現頻度に基づいてパルス判定しきい値を決定するしきい値決定手段と、
前記しきい値決定手段によって決定されたパルス判定しきい値以上のエネルギのパルスを含む前記デジタル検出信号を検出信号として出力するしきい値処理手段と、
前記しきい値決定手段から出力される検出信号に基づいて、前記光検出手段に入射された光の強度またはパルス数を算出して前記光量を解析する制御手段と、
を備えることを特徴とする光量検出装置。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順に当該エネルギのパルスの出現頻度と予め定められた頻度下限値とを比較し、比較の結果、パルスの出現頻度が前記頻度下限値以下となったエネルギの値をパルス判定しきい値に決定するデータ解析手段と、
を備えることを特徴とする請求項7に記載の光量検出装置。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順にエネルギごとのパルスの出現頻度を比較してパルスの出現頻度の最小値を求め、パルスの出現頻度が最小値を示すエネルギの値をパルス判定しきい値に決定するデータ解析手段と
を備えることを特徴とする請求項7に記載の光量検出装置。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段と、
所定の単位時間に対応付けて当該単位時間に検出したパルス数を記憶するパルス数記憶手段と、
前記所定の単位時間ごとに、前記しきい値決定手段が検出したパルス数をカウントし、カウントしたパルス数を前記所定の単位時間に対応付けて前記パルス数記憶手段に記憶させるパルス測定制御手段と、
ゲイン調整通知に基づいて、前記光検出手段および前記増幅手段のゲインを調整するゲイン制御手段と、
をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順に当該エネルギのパルスの出現頻度と予め定められた頻度下限値とを比較し、比較の結果、パルスの出現頻度が前記頻度下限値以下となったエネルギの値をパルス判定しきい値に決定するとともに、前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順にエネルギごとのパルスの出現頻度を比較してパルスの出現頻度の最小値を求め、求めた最小値と、前記頻度下限値と、前記パルス数記憶手段に記憶された単位時間ごとに検出された各パルス数とに基づいて、前記光検出手段および前記増幅手段のゲインを調整するか否かを判定し、ゲインを調整すると判定した場合には、前記ゲイン調整通知を前記ゲイン制御手段に出力するデータ解析手段と、
を備えることを特徴とする請求項7に記載の光量検出装置。 - 光量を検出し、検出した光量に応じたアナログ検出信号を出力する光検出手段と、
前記光検出手段によって検出されたアナログ検出信号を増幅する増幅手段と、
前記増幅手段によって増幅されたアナログ検出信号をデジタル検出信号に変換するアナログデジタル変換手段と、
前記アナログデジタル変換手段によって変換されたデジタル検出信号からパルスを検出するとともに、検出したパルスのエネルギを検出する処理を繰り返し、検出したエネルギごとのパルスの出現頻度を求め、求めたエネルギごとのパルスの出現頻度に基づいてパルス判定しきい値を決定するしきい値決定手段と、
前記しきい値決定手段によって決定されたパルス判定しきい値をデジタル信号からアナログ信号に変換するデジタルアナログ変換手段と、
前記検出した光量に応じたアナログ検出信号が、前記デジタルアナログ変換手段によって変換されたアナログ信号のパルス判定しきい値以上であるか否かを判定する比較手段と、
前記比較手段によって前記検出した光量に応じたアナログ検出信号が、前記デジタルアナログ変換手段によって変換されたアナログ信号のパルス判定しきい値以上であると判定された数をカウントして出力するカウント手段と、
前記カウント手段から出力されるカウント数に基づいて、前記光検出手段に入力された光の強度またはパルス数を算出して前記光量を解析する制御手段と、
を備えることを特徴とする光量検出装置。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順に当該エネルギのパルスの出現頻度と予め定められた頻度下限値とを比較し、比較の結果、パルスの出現頻度が前記頻度下限値以下となったエネルギの値をパルス判定しきい値に決定するデータ解析手段と、
を備えることを特徴とする請求項11に記載の光量検出装置。 - 前記検出されたパルスのエネルギに対応付けて当該エネルギのパルスの出現頻度を記憶する頻度数記憶手段をさらに備え、
前記しきい値決定手段は、
前記エネルギごとのパルスの出現頻度を前記頻度数記憶手段に記憶させる処理を行うデータ処理手段と、
前記頻度数記憶手段に記憶されたエネルギごとのパルスの出現頻度のうち、エネルギの値が小さいものから順にエネルギごとのパルスの出現頻度を比較してパルスの出現頻度の最小値を求め、パルスの出現頻度が最小値を示すエネルギの値をパルス判定しきい値に決定するデータ解析手段と
を備えることを特徴とする請求項11に記載の光量検出装置。 - 請求項1に記載の光信号検出回路を備えることを特徴とする荷電粒子線装置。
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