JPH07103878A - Method and apparatus for measuring pulse signal - Google Patents

Abstract

PURPOSE:To determine the half width of a waveform conveniently by dividing a pulse signal into two processing systems and feeding one of them to a gate circuit through a differentiation circuit whereas feeding the other directly to the gate circuit and then determining the ratio of peak values between both signals by means of a peak hold circuit and an A/D converting circuit. CONSTITUTION:A pulse signal is amplified and divided into two systems and one of them is fed through a differentiation circuit to a gate circuit whereas the other is fed directly to the gate circuit. The gate circuit passes the signal only when pulses higher than a threshold value occur simultaneously in two systems and removes other signals as noise. A peak hold circuit then generates a waveform where the peak value is held for (t) sec and then it is A/D converted within (t) sec before being stored in respective memories. In this regard, the pulse height P is stored along with the pulse height P' of differentiated signal. Half width t1/2 of pulse is then calculated as follows; t1/2=0.7/4(P/P'). This constitution decreases the number of memories thus simplifying the apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse signal measuring apparatus and a measuring method for detecting a pulse signal such as a particle counter used in a clean room.

[0002]

2. Description of the Related Art Conventionally, in order to measure the pulse width of a pulse signal waveform, the entire pulse signal waveform is recorded, and the pulse width is measured and determined from the observation information of the entire waveform itself.

[0003]

In order to record the entire pulse signal waveform as in the above-mentioned prior art, it is necessary to record the waveform before the pulse is generated, and the waveform of one pulse is recorded. There were problems such as requiring a large amount of memory for recording.

[0004]

In order to solve the above-mentioned problems, the present invention provides a pulse signal measuring apparatus in which the measurement signal waveform is a pulse waveform, from the pulse height of the signal waveform and the pulse height of the differential waveform of the signal. A means for obtaining each peak value and an arithmetic unit for obtaining the half width of the measurement signal waveform from the peak value are provided. That is, as shown in FIG. 1, the signal processing system of the pulse signal is divided into two,
One of them is led to a gate circuit through a differentiating circuit and the other is led to a gate circuit as it is, and these two signal systems are respectively passed through peak hold circuits, and the ratio of each peak value P ′ and P is obtained by a divider circuit. The value of the ratio is A / D converted and recorded as a digital amount. The half value width of the pulse waveform is obtained by multiplying the ratio between the peak values P and P ′ by a constant of 0.714 or 2. The means performs digitization through the respective A / D conversion circuits after passing through the respective peak hold circuits, and at the half-width display stage, the CP is displayed.
A value obtained by multiplying P / P ′ by a constant may be obtained by the calculation by U.

[0005]

In the pulse signal measuring device of the present invention, one of the two divided pulse signals is led to the gate circuit through the differentiating circuit, the other signal is directly led to the gate circuit, and then the pulse signal is pulsed in the peak hold circuit. The high P and the pulse height P'of the differential waveform are obtained. As shown in FIGS. 5 and 6, the full width at half maximum (t _1/2 ) of the signal pulse having the Gaussian distribution shape and the triangular pulse is equal to the ratio P / P of the pulse heights.
It is obtained by multiplying P'by a constant. Above P / P '
The constant to be multiplied by is 0.7 for a Gaussian distribution waveform.
14 and 2 in the case of a triangular waveform. The calculation of the full width at half maximum can be applied to a waveform having a general shape other than the signal waveform having a Gaussian distribution shape or a triangular shape.
Therefore, in a signal measuring device in which the signal waveform to be measured is a pulse waveform, it is possible to obtain the half width of the signal waveform from the pulse height of the signal waveform and the pulse height of the differential waveform of the signal, and to determine the noise by the half width and the pulse height. It is possible to distinguish between the pulse signal and the signal and to classify the pulse signal by the half width and the pulse height.

As a concrete application example of the above-mentioned measuring device,
The following pulse signal measurement can be considered. That is, in a device for detecting fine particles in a fluid by light scattering, the pulse height of the signal waveform of scattered light generated from the fine particles and the pulse height of the differential waveform of the signal are obtained, and the half-value width of the signal waveform is obtained from them. , A device for distinguishing noise from a signal by using the above half width, classifying fine particles, or measuring fine particles in a crystal or on a crystal surface, a pulse height of a signal waveform and differentiation of the signal The full width at half maximum of the signal waveform can be obtained from the pulse height of the waveform, and the full width at half maximum can be used to measure the structure in the crystal or on the crystal surface to classify the detected defects or microscopic objects, or noise.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram showing a signal processing system in a first embodiment of a pulse signal measuring device according to the present invention, FIG. 2 is a diagram showing a pulse signal measuring method of a second embodiment of the present invention, and FIG. 3 is a pulse of an optical detection signal. FIG. 4 is a diagram showing classification by height and pulse width, FIG. 4 is an actual measurement diagram of a signal pulse half-width, and FIG. 5 is a diagram showing a pulse signal measuring method according to a third embodiment of the present invention.

First Embodiment FIG. 1 shows a signal processing system for measuring the pulse half width in the pulse signal measuring apparatus according to the present invention. A pulse signal to be measured is amplified by an appropriate value through an amplifier. Next, the signal system is divided into two, one of which is put into a gate circuit through a differentiating circuit, and the other is directly led to the gate circuit. In the gate circuit, the signal is conducted only when the pulse heights equal to or higher than a certain threshold are simultaneously generated in the two systems. Therefore, the signals generated in the two systems and having different timings are removed as noise. After that, the peak hold circuit generates a waveform that holds the maximum value of the pulse height for a certain period of time (t seconds), digitizes the peak value within t seconds by the A / D converter, and records it in the memory. To do. In this case, two values of the pulse height P and the pulse height P'of the differential signal are recorded for each signal pulse. From P and P'recorded in the above memory, the pulse width for each pulse is defined as a half value width t _1/2 , and calculation is performed by the equation t _1/2 = 0.714 (P / P ').

In the present embodiment, the pulse signal is digitized and recorded as a numerical value, and then the half width is calculated. However, the following method is also possible. That is, this is a method in which a division circuit is installed in the subsequent stage of the peak hold circuit, and the result is digitized by an A / D conversion circuit and recorded. The division circuit may be a combination of a logarithmic amplification circuit and a subtraction circuit.

Second Embodiment FIG. 2 shows a second embodiment of a pulse signal measuring method in which the half width measuring method shown in the first embodiment is applied to the measurement of fine particles by light scattering. For example, laser light is irradiated to a portion where fine particles such as a gas absorption tube flow, scattered light generated from the fine particles is condensed by a lens and detected by a photodetector such as a photomultiplier tube, and the concentration and size of the fine particles are determined. The measurement is made. The fine particle detection signal is a detection signal of a scattered light pulse generated when the fine particles pass through the irradiation region of the laser light, and since the light intensity distribution in the irradiation region is a Gaussian distribution in the case of a single mode laser, In this case, the scattered light detection signal has a Gaussian distribution.

FIG. 3A shows a time pulse waveform.
(B) shows a comparison between two-dimensional maps of pulse height and pulse half width. Note that FIG. 4 is an actual measurement diagram showing the distribution of the half width of the signal pulse in this embodiment. The noise generated by the photodetector includes shot noise and noise caused by cosmic rays, and these noises usually have a half width shorter than the signal pulse, as shown in FIG. For example,
The half-width of shot noise is determined by the response time of the detector, but the half-width of the signal is determined by the irradiation area size and the particle flow velocity. Therefore, it is possible to discriminate between the signal and the noise by regarding the pulse whose half width differs from the width expected by the flow velocity and the irradiation region size by a certain value or more as the noise.

Third Embodiment A third embodiment of the present invention applies the signal processing system of the pulse waveform half width measurement shown in the first embodiment to a measuring device for detecting crystal defects in a solid by light scattering. It was done. In the case of this embodiment, in order to detect crystal defects in a semiconductor wafer such as a silicon wafer, a wavelength of 1.064 μm is used.
The YAG laser is used as a light source to illuminate the inside of the wafer, and the scattered light from crystal defects in the wafer or foreign matter on the wafer surface is measured while scanning the semiconductor wafer by moving the stage in each of XYZ directions. The scattered light detection signal from the defect smaller than the irradiation area size becomes a pulse signal having a half width that allows the irradiation area size in the moving speed and moving direction of the stage. Also in the case of the measurement of the present embodiment, the noise generated in the photodetector includes shot noise and noise due to cosmic rays, and these noises have a half width shorter than the signal pulse. Therefore, in order to determine whether it is a signal or noise based on the above-mentioned half-value width, it is sufficient to regard a pulse that differs by a certain value or more as noise from the half-value width expected by the moving speed of the stage and the irradiation area size. The full width at half maximum of the scattered light signal due to a defect larger than the irradiation area size is determined by the defect size and the stage moving speed. In this measurement, the advantage that occurs when the full width at half maximum in addition to the signal pulse height is known is that, in addition to the above noise removal, the defect size is larger than the irradiation area size, but the scattering cross section is small (refractive index of the defect such as stacking fault Is a defect with a small difference between the refractive index of the surroundings and the surrounding, and is judged by a signal with a large pulse width / pulse height), and a defect with a small defect size but a large scattering cross section (refractive index of the defect such as a precipitate). It is a defect that has a large difference from the refractive index of the surroundings, and is determined by a signal having a small pulse width / pulse height).

[0013]

As described above, the pulse signal measuring device and the measuring method according to the present invention are, in a pulse signal measuring device in which the measuring signal waveform is a pulse waveform, the pulse height of the signal waveform and the pulse height of the differential waveform of the signal. By providing a means for obtaining each peak value from the above and an arithmetic unit for obtaining the half width of the measurement signal waveform from the peak value, the half width of the pulse signal waveform can be measured easily and at high speed. Therefore, for example, it becomes possible to realize the half-width measurement in the measurement of a large number of nonuniform fine particles, and it becomes possible to perform detailed classification of fine particles. Further, since noise can be removed by the half width, the detection sensitivity can be improved.

An example in which the method for measuring the half-value width is applied to the measurement of fine particles in a fluid and the measurement of defects in crystals has been shown in the examples, but the above-mentioned half-value width measuring method is a general method, and The field of application is not limited to the application example, and as a field in which simple measurement of a pulse signal has a great advantage, it can be applied to, for example, removing noise from a digital signal in communication.

[Brief description of drawings]

FIG. 1 is a diagram showing a signal processing system in a first embodiment of a pulse signal measuring device according to the present invention.

FIG. 2 is a diagram showing a pulse signal measuring method according to a second embodiment of the present invention.

FIG. 3 is a diagram showing signal classification according to pulse height and pulse width of a light detection signal, FIG. 3A is a diagram showing a time pulse waveform,
(B) is a diagram showing a two-dimensional map of the pulse height and the pulse full width at half maximum.

FIG. 4 is an actual measurement diagram of a signal pulse half width in the above embodiment.

FIG. 5 is a diagram showing a pulse signal measuring method according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a half width of a Gaussian distribution waveform pulse.

FIG. 7 is a diagram showing a half width of a triangular waveform pulse.

Front Page Continuation (72) Inventor Atsushi Hiraiwa 1-280 Higashi Koigokubo, Kokubunji, Tokyo Metropolitan Research Center

Claims (6)

[Claims] 1. A pulse signal measuring device in which the measurement signal waveform is a pulse waveform, means for obtaining respective peak values from the pulse height of the signal waveform and the pulse height of the differential waveform of the signal, and the measurement signal from the peak value. A pulse signal measuring device comprising: an arithmetic device for obtaining a half-width of a waveform. 2. The pulse signal measuring device according to claim 1, wherein noise and a signal are distinguished from each other based on a half-value width of the signal waveform and a pulse height of the signal waveform. 3. The pulse signal measuring device according to claim 1, wherein the measurement signals are classified according to a half-value width of the signal waveform and a pulse height of the signal waveform. 4. A pulse signal measuring method for detecting fine particles in a fluid by light scattering, wherein a half value width of the signal waveform is determined from a pulse height of a signal waveform emitted from each individual fine particle and a pulse height of a differential waveform of the signal. A method for measuring a pulse signal, which comprises obtaining and classifying fine particles in a fluid by using the half-width. 5. A pulse signal measuring method for detecting defects or minute objects in a crystal or surface by light scattering, the pulse height of a signal waveform generated from each of the defects or minute objects and the pulse height of a differential waveform of the signal. The pulse signal measuring method is characterized in that the full width at half maximum of the signal waveform is obtained from the above, and noise, defects or minute objects are classified using the full width at half maximum. 6. The pulse signal measuring method according to claim 5, wherein the detected defects are stacking faults and precipitates.