JP2001304965A - Fourier spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Fourier spectroscope of high S/N by providing a plurality of processing channels to optimize a method or synthesizing an interface program. SOLUTION: An interferometer is made to scan for measuring the interference light of measured light, and the measuring result is Fourier-transformed with a calculation controlling circuit for the spectrum of the measured light. Here, there are provided a light receiving means for detecting an interference light, a low-gain processing channel, a medium-gain processing channel, and a high- gain processing channel where the output of the light receiving means is converted into a digital signal and is held; and a calculation control circuit where the saturation range of the high-gain processing channel is replaced with the output of medium-gain processing channel which is reduced for the output of the high-gain processing channel; while the saturation range of the replaced output of the medium-gain processing channel is replaced with the output of low-gain processing channel which is reduced for the output of high- gain processing channel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fourier spectrometer, and more particularly to a Fourier spectrometer in which the noise of an A / D converter is reduced.

[0002]

2. Description of the Related Art A conventional Fourier spectrometer scans an interferometer to measure interference light of measurement light, and obtains a spectrum of the measurement light by performing a Fourier transform on the measurement result by an arithmetic control means such as a computer.

[0003] A steep peak called a center burst exists in the center of the interferogram as a measurement result. For this reason, in the conventional Fourier spectrometer, since the full span of the A / D converter is set so as not to saturate the center burst, the quantization voltage increases and S / S
There was a problem that N decreased.

[0004] To solve such a problem, there is Japanese Patent Application No. 11-126761 filed by the present applicant.
In the above-mentioned application, two processing channels, a high gain processing channel and a low gain processing channel, are provided, and a saturated portion of the measurement result in the high gain processing channel is replaced with the measurement result in the low gain processing channel, thereby obtaining a high S signal. / N Fourier spectrometer is realized.

FIG. 5 is a block diagram showing an example of such a conventional Fourier spectroscope. In FIG. 5, 1 is a light receiving means comprising a photodiode serving as a light receiving element and a current-voltage conversion circuit, 2 is a filter circuit for attenuating a high-frequency signal of 1/2 or more of the sampling frequency, and 3 is a center burst portion not saturated. Low gain amplifiers whose gains are set as described above, 4 and 7 are A / D converters,
5 and 8 are storage circuits, 6 is a high gain amplifier whose gain is set so that the center burst portion is saturated, 9 is an operation control circuit, and 100 is interference light from an interferometer (not shown).

[0006] Also, 3 to 5 are low gain processing channels 50.
6 to 8 constitute the high gain processing channel 51, and 1 to 8 constitute the processing means 52, respectively.

[0007] The interference light 100 detected by the light receiving means 1 is converted into an electric signal, and a high frequency signal having a frequency equal to or more than の of the sampling frequency is attenuated by the filter circuit 2. The output signal of the filter circuit 2 is amplified by the low-gain amplifier 3 and the high-gain amplifier 6, respectively, converted into digital signals by the A / D converters 4 and 7, and stored in the storage circuits 5 and 8.

The arithmetic and control circuit 9 performs a synthesizing process of the respective interferograms stored in the storage circuits 5 and 8.
The combined interferogram is subjected to Fourier transform to determine the spectrum of the measurement light.

The operation of the conventional example shown in FIG. 5 will now be described with reference to FIGS. FIG. 6 is a flowchart illustrating the operation of the arithmetic and control circuit 9, and FIG. 7 is an explanatory diagram illustrating generation of an interferogram.

FIG. 7A shows an example of low-gain data obtained in the low-gain processing channel 50, and FIG. 7B shows an example of high-gain data obtained in the high-gain processing channel 51. c) is a characteristic curve showing the error voltage in the conventional case. However, the characteristic curve shown in FIG. 7 (b) is divided by the set gain of the high gain amplifier 6, and the voltage value is converted to the characteristic curve of FIG. 7 (a).

In "S001" in FIG. 6, the arithmetic and control circuit 9 detects a saturation start point, a saturation end point and a saturation range from the high gain data stored in the storage circuit 8. "S0" in FIG.
If the arithmetic and control circuit 9 cannot detect saturation in "02", the process of "S007" in FIG. 6 is performed without replacing the low gain data in "S003" in FIG.

For example, the saturation level is set to "SV11" in FIG.
And “SV12”, the arithmetic control circuit 9
The saturation start point and the saturation end point as shown in “SP11” and “EP11” are detected, and “S” in FIG.
The saturation range indicated by R11 ″ is obtained.

On the other hand, when the arithmetic and control circuit 9 detects saturation in "S002" in FIG. 6, "S004" in FIG.
A range that includes both the detected saturation range and the preset setting range is determined, and this range is defined as the low gain data use range.

For example, if the set range is a range shown by "CR11" in FIG. 3, "CR11" in FIG. 6 includes both the saturation range shown by "SR11" in FIG. 6 and the set range.
11 "is the low-gain data use range. However, when the saturation range" SR11 "is in a relationship including the set range" CR11 ", the saturation range" SR11 "becomes the low-gain data use range. .

Further, in "S005" in FIG. 6, the arithmetic and control circuit 9 expands the low gain data use range by a predetermined value.

For example, "AR11" and "AR1" in FIG.
The range of use of low-gain data is enlarged by the amount shown in FIG.
The part indicated by the middle “LD11” is a new low-gain data use range.

As described above, the reason why the low-gain data use range is expanded by a predetermined value is that the saturation range is lower when the saturation range has a relationship that encompasses the set range as described above. This is because the gain data is used and a large error existing at the boundary of the saturation range remains without being removed.

For example, in FIG.
When the saturation range indicated by SR11 "becomes the low-gain data use range, the low-gain data use range (saturation range) is expanded by" AR11 "and" AR12 "in FIG. A large error existing at the boundary of the saturation range as shown in the middle "ER11" and "ER12" is removed.

In "S006" in FIG. 6, the arithmetic and control circuit 9 replaces the high gain data in the previously set low gain data use range with the low gain data whose value has been converted, and synthesizes an interferogram.

Finally, in "S007" in FIG. 6, the arithmetic and control circuit 9 Fourier-transforms the synthesized interferogram to obtain a spectrum of the measurement light.

That is, in the case shown in FIG. 7, "L" in FIG.
Since the error in the low gain data use range indicated by D11 is “0”, for example, “ER11” or “ER12” in FIG.
The S / N is improved by removing the error as shown in FIG.

[0022]

However, in the conventional example shown in FIG. 5, since the low gain processing channel 50 and the high gain processing channel 51 are composed of two channels, the center burst portion is saturated in the low gain processing channel 50. In such a case, there is a problem in that the data cannot be replaced as described above. Therefore, an object of the present invention is to realize a high S / N Fourier spectrometer by providing a plurality of processing channels and optimizing an interferogram synthesizing method.

[0023]

In order to achieve the above object, according to the first aspect of the present invention, the interferometer is scanned to measure the interference light of the measurement light, and the measurement result is obtained. In a Fourier spectroscope for obtaining a spectrum of the measurement light by performing a Fourier transform by an arithmetic control circuit, a light receiving means for receiving the interference light, a low gain processing channel for converting an output of the light receiving means into a digital signal and holding the digital signal, A gain processing channel and a high gain processing channel, and replacing a saturation range of an output of the high gain processing channel with an output of the medium gain processing channel converted with respect to an output of the high gain processing channel; Replace the saturation range of the output of the medium gain processing channel with the output of the low gain processing channel converted to the output of the high gain processing channel By having a that calculation control circuit, a Fourier spectrometer high S / N can be achieved.

According to a second aspect of the present invention, there is provided a Fourier spectrometer for measuring an interference light of a measuring light by scanning an interferometer, and performing a Fourier transform on the measurement result by an arithmetic and control circuit to obtain a spectrum of the measuring light. A light receiving means for receiving the interference light; a low gain processing channel, a medium gain processing channel, and a high gain processing channel for converting and holding the output of the light receiving means to a digital signal; The converted saturation range of the output of the high gain processing channel is replaced with the output of the medium gain processing channel, and the replaced saturation range of the output of the medium gain processing channel is changed with respect to the output of the medium gain processing channel. And an arithmetic control circuit for replacing the output of the low gain processing channel with a converted value,
An N Fourier spectrometer can be realized.

According to a third aspect of the present invention, there is provided a Fourier spectroscope which scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. A light receiving means for receiving the interference light; a low gain processing channel, a medium gain processing channel and a high gain processing channel for converting an output of the light receiving means into a digital signal and holding the digital signal; The converted saturation range of the output of the high gain processing channel is replaced with the output of the medium gain processing channel converted with respect to the output of the low gain processing channel, and the output of the replaced medium gain processing channel is replaced. And an arithmetic control circuit that replaces the saturation range with the output of the low gain processing channel.
An N Fourier spectrometer can be realized.

According to a fourth aspect of the present invention, in the Fourier spectrometer according to the first to third aspects of the present invention, the saturation range is expanded by a predetermined value.
A large error existing at the boundary of the saturation range is removed, and the S / N is further improved.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing one embodiment of a Fourier spectrometer according to the present invention. In FIG. 1, 1 to 8,
50, 51 and 100 have the same reference numerals as in FIG.
9a is an arithmetic control circuit, 10 is a medium gain amplifier having an intermediate gain between the low gain amplifier 3 and the high gain amplifier 6, and 11 is A
The / D converter 12 is a storage circuit.

10 to 12 are medium gain processing channels 53, and 1 to 8, 9a and 10 to 12 are processing means 52a.
Respectively.

The interference light 100 detected by the light receiving means 1 is converted into an electric signal, and a high-frequency signal of 1/2 or more of the sampling frequency is attenuated by the filter circuit 2. The output signal of the filter circuit 2 is amplified by a low gain amplifier 3, a high gain amplifier 6, and a medium gain amplifier 10 and converted into digital signals by A / D converters 4, 7, and 11, and then stored in storage circuits 5, 8. And 12.

The arithmetic and control circuit 9a includes storage circuits 5, 8, and 1
2 is synthesized. The combined interferogram is subjected to Fourier transform to determine the spectrum of the measurement light.

The operation of the embodiment shown in FIG. 1 will be described with reference to FIGS. FIG. 2 is a flowchart illustrating the operation of the arithmetic control circuit 9a, and FIG. 3 is an explanatory diagram illustrating a central portion of a synthesized interferogram. However, the basic circuit operation is the same as that of the conventional example shown in FIG.

In FIG. 3, the gain of the high gain amplifier 6 is "16 times", the gain of the medium gain amplifier 10 is "4 times",
The center part of the combined interferogram when the gain of the low gain amplifier 3 is set to "1" is shown.

At "S101" in FIG. 2, the arithmetic control circuit 9a detects the saturation range from the high gain data stored in the storage circuit 8. If the arithmetic control circuit 9a cannot detect the saturation in "S102" in FIG. 2, "S103" in FIG.
In FIG. 2, the process of "S110" in FIG.

On the other hand, when the arithmetic and control circuit 9a detects saturation in "S102" in FIG. 2, "S10" in FIG.
4 ”, other than the saturation range detected in other words,
The non-saturation range is used as the high-gain data use range.

For example, "SL12" and SL1 in FIG.
If "3" is the saturation level of the high gain channel 51, the high gain data is saturated at the portions "PT11" and "PT12" in FIG. 3, so that "HD11" and "HD1" in FIG.
The range of non-saturation indicated by 2 "is a high-gain data use range.

Further, in "S105" in FIG. 2, the arithmetic and control circuit 9a detects the saturation range from the medium gain data stored in the storage circuit 12. If the operation control circuit 9a cannot detect the saturation in "S106" in FIG.
In S107 ", the process of" S110 "in FIG. 2 is performed with the saturation range of the high gain data as the medium gain data use range.

On the other hand, if the arithmetic and control circuit 9a detects saturation at "S106" in FIG. 2, "S10" in FIG.
8 "is a high gain saturation range and a range other than the medium gain saturation range, in other words, a medium gain non-saturation range is a medium gain data use range.

Further, in "S109" in FIG. 2, the arithmetic and control circuit 9a sets the saturation range of the medium gain to the low gain data use range.

For example, "SL11" and SL1 in FIG.
If "4" is the saturation level of the middle gain channel 53, the middle gain data is saturated at the portions "PT13" and "PT14" in FIG. 3, so that "MD11" and "MD1" in FIG.
The range of non-saturation shown in 2 "is the range for using medium gain data,
The remaining saturated range indicated by “LD11” in FIG. 3 is defined as a low-gain data use range.

Finally, in "S110" in FIG. 2, the arithmetic and control circuit 9a converts the high gain data into the high gain data in the low gain data use range and the medium gain data use range previously set, and converts the high gain data into a low gain data. The interferogram is synthesized by applying the gain data and the medium gain data.

Further, in "S111" in FIG. 2, the arithmetic and control circuit 9a performs a Fourier transform on the synthesized interferogram to obtain a spectrum of the measurement light.

As a result, by providing a plurality of processing channels and applying medium gain data to the range where the high gain data is saturated, and applying low gain data to the range where the medium gain data is saturated, a high S / N ratio is obtained. Can be realized.

FIG. 4 is a characteristic curve diagram showing the S / N increase in the conventional example shown in FIG. 5 and the embodiment shown in FIG. The curve indicated by "CH11" in FIG. 4 shows the characteristics of the conventional example shown in FIG. 5, and is composed of two channels of 1 and the designated gain on the horizontal axis. In addition, “特性” indicates the characteristic of the embodiment shown in FIG. 1 and is configured so that the gain of each channel is increased twice from 1 to the designated gain on the horizontal axis.

For example, the configuration showing the characteristic of "CP11" in FIG. 4 is composed of five channels having gains of 1, 2, 4, 8, and 16 times, respectively.
Configurations exhibiting 2 "characteristics are 1 time, 2 times, 4 times, and 8 times, respectively.
It is composed of 6 channels having double, 16 and 32 gains.

As can be seen from FIG. 4, it can be seen that the increase in S / N is improved and the S / N is increased by adopting the configuration of six or more channels as compared with the conventional example shown in FIG.

Although the embodiment shown in FIG. 1 exemplifies a configuration of three channels for simplicity of explanation, a plurality of channels may be used as described with reference to FIG.

Further, when synthesizing the interferogram, even if the values of the low gain data and the medium gain data are converted into the values of the high gain data and synthesized, the values of the low gain data and the high gain data are converted to the medium gain data. Even if it is converted to the value of
The value of the medium gain data and the value of the high gain data may be converted to the value of the low gain data and combined, or any of them may be used.

In the description of FIG. 1, low gain data (or medium gain data) is simply based on the saturation range.
Is used, the low gain data (or medium gain data) usage range is expanded by a preset value as in the conventional example, and a large error existing at the boundary of the saturation range is removed. Then, the S / N may be further improved.

[0049]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. According to the first to third aspects of the present invention, a plurality of processing channels are provided, medium gain data is applied to a range where high gain data is saturated, and low gain data is applied to a range where medium gain data is saturated. As a result, a high S / N Fourier spectrometer can be realized.

According to the fourth aspect of the present invention, by expanding the saturation range by a predetermined value, a large error existing at the boundary of the saturation range is removed, and the S is further reduced.
/ N is improved.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing one embodiment of a Fourier spectroscope according to the present invention.

FIG. 2 is a flowchart illustrating an operation of an arithmetic control circuit.

FIG. 3 is an explanatory diagram showing a central portion of a synthesized interferogram.

FIG. 4 is a characteristic curve diagram showing an increase in S / N between a conventional example and an example.

FIG. 5 is a configuration block diagram illustrating an example of a conventional Fourier spectrometer.

FIG. 6 is a flowchart illustrating the operation of the arithmetic control circuit.

FIG. 7 is an explanatory diagram showing generation of an interferogram.

[Explanation of symbols]

 Reference Signs List 1 light receiving means 2 filter circuit 3 low gain amplifier 4, 7, 11 A / D converter 5, 8, 12 storage circuit 6 high gain amplifier 9, 9a operation control circuit 10 medium gain amplifier 50 low gain processing channel 51 high gain processing Channel 52, 52a processing means 53 medium gain processing channel 100 interference light

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Morio Wada 2-9-32 Nakamachi, Musashino-shi, Tokyo F-term in Yokogawa Electric Corporation (reference) 2G020 CA12 CD32 CD35 5J022 AA01 BA02 BA08 CA07 CD02 CF02

Claims (4)

[Claims] 1. A Fourier spectrometer for measuring an interference light of a measurement light by scanning an interferometer and performing a Fourier transform of the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light, wherein the interference light is received. A light-receiving means; a low-gain processing channel, a medium-gain processing channel, and a high-gain processing channel for converting the output of the light-receiving means into a digital signal and holding the digital signal; The output of the medium gain processing channel is replaced with the output of the medium gain processing channel, and the replaced saturation range of the output of the medium gain processing channel is converted into the low gain converted with respect to the output of the high gain processing channel. A Fourier spectrometer, comprising: an arithmetic control circuit for performing replacement with an output of a processing channel. 2. A Fourier spectrometer that scans an interferometer to measure interference light of measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. Light receiving means; a low gain processing channel, a medium gain processing channel, and a high gain processing channel for converting and holding an output of the light receiving means to a digital signal; and the high gain converted with respect to the output of the medium gain processing channel. Replacing the saturation range of the output of the processing channel with the output of the medium gain processing channel, and replacing the saturation range of the output of the replaced medium gain processing channel with the low gain converted to the output of the medium gain processing channel. A Fourier spectrometer, comprising: an arithmetic control circuit for performing replacement with an output of a processing channel. 3. A Fourier spectrometer that scans an interferometer to measure the interference light of the measurement light, and Fourier-transforms the measurement result by an arithmetic and control circuit to obtain a spectrum of the measurement light. Light receiving means; a low gain processing channel, a medium gain processing channel, and a high gain processing channel for converting and holding an output of the light receiving means to a digital signal; and the high gain converted with respect to the output of the low gain processing channel. Replacing the saturation range of the output of the processing channel with the output of the medium gain processing channel converted with respect to the output of the low gain processing channel, and changing the saturation range of the output of the replaced medium gain processing channel to the low gain. A Fourier spectrometer, comprising: an arithmetic control circuit for performing replacement with an output of a processing channel. 4. The Fourier spectroscope according to claim 1, wherein said saturation range is expanded by a predetermined value.