JPH0579914A - Detecting circuit in fourier spectrometry - Google Patents

Abstract

PURPOSE:To provide a detecting circuit in Fourier spectrometry resistant to noise by using a rapid scan interferometer having a gate circuit and a low-pass filter succeeding it. CONSTITUTION:A periodically sampling gate circuit and a low-pass filter succeeding it are provided in a detecting circuit, the low-frequency component passing through the low-pass filter is Fourier-converted as it is or after being applied with signal processing to determine the spectrum distribution in a rapid scan interferometer. A circuit directly connected with a sample hold circuit (S/H circuit) to the gate circuit is used in place of the gate circuit in a detecting circuit in the Fourier spectrometry using the rapid scan interferometer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection circuit for Fourier spectroscopy using a rapid scan interferometer, and more particularly to improvement of a detection circuit using a gate circuit and a low pass filter following the gate circuit.

[0002]

2. Description of the Related Art The applicant of the present invention is a Fourier spectroscopy method using a rapid scan interferometer, in which a gate circuit and a low pass filter following it are provided in a detection circuit, and the low frequency component passing through the low pass filter is directly or Many methods have been proposed for investigating various spectral characteristics of a sample by performing a Fourier transform after performing signal processing such as frequency conversion (Japanese Patent Application Nos. 1-230209 and 2-82126-7).
No. 2, No. 2-259355, No. 3-2379, No. 3-
No. 64623, No. 3-64624, No. 3-95115
No. 3-158330, 3-165655, 3-243436).

To briefly describe these, Japanese Patent Application No.
-230209, 2-259355, 3-23
No. 79 and No. 3-158330 have an interferogram with respect to a constant delay time from a stimulus from a detector output using a rapid scan interferometer, which stimulus is periodically generated by a stimulus generation means and repeatedly applied to a measurement target. Is a time-resolved spectroscopic method for measuring the reaction state of a measurement target that repeatedly shows the same response to a stimulus by obtaining a spectrum by Fourier transform, and the detector output is a constant delay time after the stimulus. In the sample of the delay time, the sampled signal is sampled by the gate circuit, only the low frequency component of the sampled signal is taken out by the low pass filter, and the low frequency component is subjected to signal processing such as phase correction or phase correction and then Fourier transform. Was to measure the spectral characteristics of.

Japanese Patent Application Nos. 3-64623 and 3-6.
No. 4624 gives a stimulus to a measurement object that shows the same response repeatedly to the stimulus periodically, and samples the output of a detector using a rapid scan interferometer to obtain an interferogram for a certain delay time from the stimulus. Then
A time-resolved spectroscopic measurement method in which the reaction state is measured by Fourier transform and the spectrum, and the measurement target
A stimulus is repeatedly applied at a cycle longer than twice, and the detector output is sampled by a gate circuit by controlling the delay time from the stimulus at a cycle of half the stimulus repetition cycle.
Only the low-frequency component of the sampled signal is extracted by a low-pass filter, and the low-frequency component is subjected to signal processing such as phase correction, and then Fourier-transformed, so that the measurement target and the normal state at the controlled delay time are It was to obtain the difference spectrum with the measurement target in.

Further, Japanese Patent Application No. 2-82126 discloses a Fourier spectrum or a time-resolved Fourier spectrum in which a pulsed light source which emits light at a constant period or a pulsed laser for Raman excitation is used as a light source. Only the component is taken out by a low-pass filter, and the low frequency component is subjected to signal processing as it is or after it is subjected to Fourier transform to measure the spectral characteristic of the measurement object.

In Japanese Patent Application No. 3-165655, the heat generated in the measurement sample is diffused and transmitted to the surrounding gas by irradiating the measurement sample with the light modulated by the rapid scan interferometer. , Depth analysis using photoacoustic spectroscopy and Fourier spectroscopy to detect the density change of the gas based on it, convert it to an electrical signal, and obtain the information in the depth direction of the measurement sample by Fourier transforming the signal In the method, a pulsed light source that emits light at a predetermined cycle is used as a light source, a detection signal is sampled by a gate circuit at a constant delay time after the pulsed light source is emitted, and only a low-frequency component of the sampled signal is extracted by a low-pass filter, The low frequency component is processed as it is or after it is subjected to signal processing such as phase correction, and then Fourier transformed, depending on the irradiation light wave number. It was to obtain a thermal distribution information of a particular depth of the sample.

In these Fourier spectroscopy methods, FIG.
As shown in, the signal input to the gate circuit includes the interferogram signal F (t) to be obtained,
An analog signal F obtained by a low-pass filter is obtained by converting this into a discrete signal by a gate circuit.
It is a process to return to (t).

[0008]

However, in the Fourier spectroscopy detection circuit using the rapid scan interferometer using the gate circuit and the subsequent low-pass filter as described above, the discrete signal sampled by the gate circuit is , Since it contains very high frequency, noise is likely to be superimposed, and to obtain an accurate signal,
Needs countermeasures against noise.

The present invention has been made in view of such a situation, and an object thereof is to make a detection circuit of Fourier spectroscopy using a rapid scan interferometer using a gate circuit and a low pass filter subsequent thereto a circuit resistant to noise. Is to

[0010]

The Fourier spectroscopy detection circuit of the present invention which achieves the above object is provided with a gate circuit for periodically sampling and a low pass filter following the gate circuit in the detection circuit. In the detection circuit in Fourier spectroscopy using a rapid scan interferometer to obtain the spectral distribution by Fourier transforming the frequency component as it is or after performing signal processing on it,
Instead of the gate circuit, a circuit in which a sample hold circuit is directly connected to the gate circuit is used.

[0011]

In the present invention, since a circuit in which a sample hold circuit is directly connected to the gate circuit is used instead of the gate circuit, the spectral component of the signal converted into the analog signal through the low pass filter is Even though it is almost the same as the spectrum component of the signal obtained by using only the circuit and the low-pass filter, there is almost no period of a discrete signal, so the circuit is strong against noise, and compared to the conventional case. It is possible to obtain a more accurate spectrum that is resistant to noise.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the detection circuit of the present invention will be described with reference to the drawings. According to the present invention, in a circuit including a conventional gate circuit and a low-pass filter following the conventional gate circuit as shown in FIG. 3, a sample hold circuit (S / H circuit) is used instead of the gate circuit as shown in FIG. ) Is directly connected to the circuit, for example, a boxcar integrator is used. As will be described later, even if a circuit in which a sample hold circuit is directly connected to the gate circuit is used instead of the gate circuit, the spectral component of the signal converted into the analog signal by passing through the low pass filter is Is almost the same as the spectral component of the signal obtained by using only the low pass filter, and can be processed after the Fourier transform so that they are exactly the same. On the other hand, the sample hold circuit is directly connected to the gate circuit. When the circuit is used, there is almost no period of a discrete signal, so that the circuit is strong against noise. Therefore, by using the detection circuit of the present invention, it is possible to obtain a more accurate spectrum that is resistant to noise as compared with the conventional case.

Now, returning to FIG. 1, the interferogram signal F (t) contained in the signal input to the gate circuit is sampled by the gate circuit and becomes F (t) Φ (t).
However, here Шτ (t) is a comb function that represents a repetitive operation in which the deluxe functions δ (t) are lined up at regular intervals τ. F (t) Шτ sampled by this gate circuit
When (t) is Fourier-transformed, the spectrum becomes as shown in FIG. 2A, and many harmonics are included in addition to the frequency component of the interferogram signal F (t) to be obtained, which is hatched. When this signal is passed through the sample hold circuit, it becomes {F (t) Φτ (t)} * Rτ (t). Here, Rτ (t) is a box-shaped function of 1 in the range of −τ / 2 to + τ / 2, and 0 otherwise, as shown in FIG. 2B. It becomes a sinc function as shown in the spectrum of 2 (b). In addition, * represents a convolution operation. This signal {F (t) Шτ (t)}
When Fourier transform of * Rτ (t), the Fourier transform of F (t) Шτ (t) is calculated by the convolution theorem (Fig. 2).
(A) spectrum and Rτ (t) Fourier transform (Fig. 2)
(B) spectrum), as shown by the solid line in the spectrum of FIG. 2 (c). When this signal is passed through a low-pass filter having the characteristics shown in FIG. 2D, which passes only the fundamental wave spectrum, its output spectrum is shown in FIG.
And the spectral distribution of the interferogram signal F (t) to be obtained is multiplied by the sinc function. Therefore, the output signal of the low-pass filter has a form of F (t) * Rτ (t) as shown in FIG.

As described above, in a Fourier spectroscopy detection circuit using a rapid scan interferometer using a gate circuit and a low pass filter following the gate circuit, a gate circuit is used instead of the gate circuit as shown in FIG. When a circuit in which the sample and hold circuit is directly connected is used, the spectral component of the signal that has passed through the low pass filter and converted into an analog signal is sinc to the spectral component of the signal obtained by using only the gate circuit and the low pass filter.
It becomes a form multiplied by a function, and the spectral distribution is somewhat deformed by passing through the sample hold circuit, but this is not a problematic modification in practical use. In this modification, the signal passed through the low-pass filter is subjected to the Fourier transform after being subjected to the necessary signal processing as it is, and then the sin
It can also be removed by dividing by the c function. When a circuit in which the sample hold circuit is directly connected to the gate circuit is used, the circuit is strong against noise because there is almost no period of a discrete signal.
Therefore, by using the detection circuit of the present invention, it is possible to obtain a more accurate spectrum that is resistant to noise as compared with the conventional case.

The present invention relates to the above-mentioned applicants' Japanese Patent Application Nos. 1-230209, 2-82126 to 7, and 2
-259355, 3-2379, 3-6462
No. 3, No. 3-64624, No. 3-95115, No. 3
-158330, 3-165655, 3-24
A Fourier spectroscopy method using the rapid scan interferometer of No. 3436, in which a detection circuit is provided with a gate circuit and a low pass filter following the gate circuit, and low frequency components passing through the low pass filter are directly processed or signal processing such as frequency conversion is performed. After applying, it can be applied to the method of investigating various spectral characteristics of the sample by Fourier transform, but in addition to that, the detection signal is periodically sampled by the gate circuit and the discrete signal is passed through a low pass filter to obtain low frequency components. It is obvious that the present invention can be applied to other detection circuits that take out the signal and Fourier transform the signal to obtain the spectral component. As the circuit in which the sample hold circuit is directly connected to the gate circuit, various circuits other than the above-mentioned boxcar integrator can be used.

[0016]

As described above, according to the detection circuit in the Fourier spectroscopy of the present invention, since the circuit in which the sample hold circuit is directly connected to the gate circuit is used instead of the gate circuit, it passes through the low pass filter. Since the spectral component of the signal converted into an analog signal is almost the same as the spectral component of the signal obtained by using only the gate circuit and the low-pass filter, there is almost no discrete signal period, Since the circuit is strong against noise, the spectrum is strong against noise and more accurate spectrum can be obtained as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a signal waveform in a main part and each part of a detection circuit in Fourier spectroscopy according to the present invention.

FIG. 2 is a diagram showing a signal waveform and its spectrum in each part of FIG.

FIG. 3 is a diagram showing signal waveforms in a main part and each part of a detection circuit in conventional Fourier spectroscopy.

Claims (1)

[Claims] 1. A detection circuit is provided with a gate circuit for periodically sampling and a low-pass filter following the gate circuit, and a low-frequency component passing through the low-pass filter is subjected to Fourier transform as it is or after signal processing to obtain a spectrum distribution. A detection circuit in Fourier spectroscopy using a rapid scan interferometer, wherein a circuit in which a sample hold circuit is directly connected to the gate circuit is used instead of the gate circuit in the detection circuit in Fourier spectroscopy.