JP2022090600A - Time-interleave a-d converter and laser-type gas analyzer - Google Patents

Abstract

To provide a time-interleave A-D converter which is simplified in constitution and enhanced in accuracy by back-ground correcting a characteristic error between unit A-D converters, and a laser-type gas analyzer.SOLUTION: A time-interleave A-D converter has: a clock signal generation part 10 for generating one of a clock signal for retarding the sampling timings of unit A-D converters ADC1 to ADCM at equal intervals and a clock signal for uniforming the sampling timings; an averaging processing part 20 for calculating an average value of output signals of the unit A-D converters ADC1 to ADCM at averaging processing; correction parts 301 to 30M for correcting output characteristics of the unit A-D converters ADC1 to ADCM with the average value as a reference; and an output part 40 for selecting output signals of the correction parts 301 to 30M at time-interleave processing, and selecting an output signal of the averaging processing part 20 at averaging processing. There is also provided a laser-type gas analyzer having the A-D converter.SELECTED DRAWING: Figure 1

Description

The present invention realizes high-speed conversion by operating a plurality of unit A / D converters having different sampling timings in parallel, and has a time interleaved A / D function for correcting an output characteristic error for each unit A / D converter. The present invention relates to a converter and a laser gas analyzer equipped with this time-interleaved A / D converter.

The A / D converter that converts an analog signal into a digital signal converts an analog input voltage or the like into a discrete digital value by sampling and quantization and outputs the signal. At this time, the resolution of sampling and quantization is limited by the A / D converter used. In particular, when sampling, that is, when the sampling resolution is low, the frequency band of the input voltage that can be normally converted becomes small based on the sampling theorem. A / D converter is required. Further, in other fields as well, high speed is required from the viewpoint of noise reduction by oversampling and relaxation of design conditions of antialiasing filter.

As a countermeasure against this, a time interleaved A / D converter as shown in FIG. 11 has been conventionally known.
In FIG. 11, M units A / D converters ADC ₁ to ADC _M to which an analog voltage is input are connected in parallel. A clock signal whose phase is sequentially delayed by 2π / M from the clock signal generator 10 is input to each of these units A / D converters ADCs ₁ to ADC _M , and A / D conversion in each converter ADCs ₁ to ADC _M. By shifting the sampling timing of, it is possible to realize M times faster conversion than in the case of one A / D converter. Reference numeral 40 denotes an output unit that obtains and outputs one digital signal from the output signals of each of the converters ADC ₁ to ADC _M.
In the above configuration, in theory, it is possible to increase the speed to the ideal sampling speed by increasing the number of parallel units of the unit A / D converter.

As shown in FIG. 11, in the time interleaved A / D converter, one digital signal is output by combining the digital outputs of a plurality of unit A / D converters. At this time, each unit A / D converter has characteristics such as offset, gain, and sampling timing, and if there is an error between these units, the output as a time interleaved A / D converter. It appears as a distortion component in the signal, and the signal performance such as the signal-to-noise ratio (SN ratio) deteriorates. These errors can occur not only due to manufacturing variations in electronic circuits but also due to changes in the operating environment such as ambient temperature, and there is a need for a function to correct the effects in real time.

In order to solve the above problem, in Patent Document 1, a reference A / D converter having the same structure and calibrated accuracy is added in addition to the plurality of unit A / D converters constituting the time interleaved A / D converter. The output of each unit A / D converter is digitally corrected using the output as a teacher signal.
In this prior art, the frequency of the clock signal input to the unit A / D converter and the frequency of the clock signal input to the reference A / D converter are separated, and the sampling timing of the reference A / D converter is set. It is possible to correct the output of each unit A / D converter while performing time interleaved A / D conversion so that it is always at the same time as one of the unit A / D converters.

Further, in Patent Documents 2 and 3, an error is corrected by an LMS (Least Mean Square) algorithm using an A / D converter for reference. In this case, since the high resolution output can be set to the target value by using a device having a lower speed and higher resolution than the unit A / D converter as the reference A / D converter, more accurate correction is possible. Is.
That is, in Patent Document 2, the conversion gain, offset, and sampling timing of each unit A / D converter are referred to by the digital calibration unit provided on the output side of the plurality of unit A / D converters. Techniques have been disclosed for correcting errors using the LMS algorithm so that they are equal to those of the converter.
Further, in Patent Document 3, in view of the fact that the time-interleaved A / D converter requires a large chip area and power consumption, the main A / D converter and its output side are sequentially provided and corrected by the LMS algorithm. It is provided with a linearity correction unit, a skew correction unit, and a reference A / D converter, and compensates for the influence of skew generated between the sampling timings of the main A / D converter and the reference A / D converter. Discloses a technique that enables high sample rate and high resolution A / D conversion without the need for a sample hold circuit or the like.

Further, Patent Document 4 discloses a technique for switching between a high-speed output by time interleaving processing and a high-resolution output by averaging processing according to an output request.
That is, when high-speed output is required, time interleaving processing is performed by correcting the output of the unit A / D converter, and when higher resolution output is required, the same clock is applied to all unit A / D converters. By inputting a signal and calculating the average value of the digital output values sampled at the same time, it is possible to obtain an output with improved resolution even at a low speed.

Conventionally, for example, a laser gas analyzer that irradiates a flue with a laser beam to measure the presence or absence of toxic gas and its concentration has been known, and a signal processing system that measures the gas concentration based on the received signal. An A / D converter is used for.
Since each gaseous gas molecule has its own light absorption spectrum, the laser gas analyzer makes measurements based on the principle that the amount of absorption of laser light at a specific wavelength is proportional to the concentration of the gas to be measured. The concentration of the gas to be measured existing in the measurement space is measured by arithmetically processing the digital signal obtained by A / D converting the laser beam transmitted through the gas in the space.

FIG. 12 is a block diagram showing the main parts of this type of laser gas analyzer.
In FIG. 12, the laser drive signal generation unit 111 in the light source unit 110 emits the laser beam L while sweeping the laser wavelength within the range including the absorption wavelength of the gas to be measured by current control. The laser beam L is absorbed by the gas in the measurement space and is incident on the light receiving element 220.
The signal photoelectrically converted by the light receiving element 220 is converted into a digital signal by the operation of the IV (current-voltage) converter 211, the filter 212, and the A / D converter 213 in the signal processing circuit 210 and given to the arithmetic unit 214. .. The calculation unit 214 measures the concentration of the measurement target gas based on the amplitude of the signal (gas absorption signal) that has absorbed the measurement target gas, and generates a trigger signal for laser drive control to the laser drive signal generation unit 111. Output.
This type of laser gas analyzer is described in, for example, Patent Document 5.

Here, since the amplitude of the gas absorption signal is proportional to the gas concentration, the amplitude becomes small when the gas concentration is low. Therefore, when measuring a low-concentration gas, the resolution of the signal after A / D conversion is lowered, and the SN ratio is lowered. That is, the stability of the gas concentration is impaired because the signal component changes under the influence of noise components such as thermal noise and optical interference noise. Therefore, it is necessary to be able to detect the gas absorption signal with high resolution even if the gas concentration is low.

As a solution to the above problem, it is conceivable to limit the measurement concentration range. For example, at the time of circuit design, the absorption signal when the concentration of the gas to be measured is 100 [ppm] is amplified according to the voltage range of A / D conversion and then converted to be in the range of 0 to 100 [ppm]. A model that can measure the gas concentration can be obtained. Similarly, if the absorption signal when the concentration of the gas to be measured is 200 [ppm] is amplified according to the voltage range of A / D conversion and then converted, the gas concentration is measured in the range of 0 to 200 [ppm]. You can get a possible model.

Therefore, even when A / D converters with the same resolution are used, there is a difference in apparent resolution for signals of the same concentration, and models that can measure in the range of 0 to 100 [ppm] are 0 to 0. It will have twice the resolution of a model that can measure in the range of 200 [ppm]. Therefore, when measuring low-concentration gas with high resolution, it is possible to handle it by selecting a model with a narrower concentration range.
However, in this case, the number of models and manufacturing processes of the A / D converter increases, and the manufacturing cost increases. Further, since such measures cannot be taken in an environment where the change in gas concentration is large, it becomes impossible to measure low-concentration gas with high resolution.
Therefore, in order to deal with these problems, it is required to provide an A / D converter having a wide dynamic range.

On the other hand, for example, Patent Document 6 describes a conventional technique for expanding the dynamic range by switching between laser drive control and light receiving signal processing according to the measured gas concentration.
According to this conventional technique, a wide dynamic range can be realized by switching between the direct absorption method effective for measuring the high concentration of gas and the 2f method effective for measuring the low concentration according to the gas concentration, and the measured concentration. By expanding the range, it becomes possible to unify (decrease) the models of A / D converters and the manufacturing process. On the other hand, since the resolution depends on the performance of the A / D converter, it is fundamentally important to improve the resolution of the A / D converter itself in order to improve the accuracy of the measurement.
In general, there is a trade-off relationship between the resolution of the A / D converter and the sampling frequency, so the higher the resolution of the A / D converter, the slower the sampling. Therefore, since the A / D converter having the required sampling frequency or higher is usually selected with the highest resolution possible, it must be said that the resolution is limited.

Japanese Unexamined Patent Publication No. 2011-97215 ([0014] to [0023], FIGS. 1, 2, etc.) Republished 2010-9532 ([0012]-[0014], FIG. 2, etc.) Republished Publication No. 2011-39859 ([0023]-[0032], Fig. 1, Fig. 3, Fig. 4, etc.) Japanese Unexamined Patent Publication No. 2000-341123 ([0031] to [0045], FIGS. 4 to 6, etc.) Japanese Patent No. 5176535 ([0034] to [0038], FIGS. 1 to 5, etc.) Japanese Patent No. 5359832 ([0023]-[0029], FIG. 2, etc.)

In the prior art described in Patent Documents 1 and 2 described above, (M + 1) A / D converters are used for M times faster speed, and one of them is used for reference A / D conversion. It is necessary to use it as a device, and the conventional technique described in Patent Document 3 also requires a reference A / D converter in addition to the main A / D converter. Therefore, in any case, the entire circuit becomes large, and there are problems such as an increase in cost and an increase in power consumption.

Furthermore, although it is possible to eliminate the effects of mismatches in conversion gain, offset, and sampling timing between each unit A / D converter by correction, all unit A / D converters are referred to as A / D converter characteristics. Therefore, it is necessary to individually calibrate using a known signal so that the output characteristics of the reference A / D converter become ideal in advance. In this case, the time-interleaved A / D converter built into the system will be calibrated as the initial setting, but the output characteristics may change depending on the operating environment of the system (changes in ambient temperature, etc.), so the system It is desirable to perform calibration in real time even during the actual operation of the system, and the actual operation must be stopped in order to input a known signal.

Further, in the prior art described in Patent Document 4, in order to correct the characteristics of the other unit A / D converter with one of the unit A / D converters as a reference, the reference unit A / D conversion is performed. The output characteristics of the device are reflected in the A / D converter for all units. In order to solve this problem, it is necessary to input a known signal and calibrate the output characteristics of the reference unit A / D converter in advance, but the operation of the system must be stopped.

Further, in the laser type gas analyzer described in Patent Documents 5 and 6, in order to measure the concentration of low concentration gas with high resolution, the A / D converter is made high resolution and the dynamic range is expanded as described above. For that purpose, it has been required to correct the error between the unit A / D converters in real time by using a time interleaved A / D converter or the like.

Therefore, the problem to be solved by the present invention is to simplify the configuration by eliminating the need for the reference A / D converter added to the plurality of unit A / D converters and to improve the output characteristics between the unit A / D converters. It is an object of the present invention to provide a time interleaved A / D converter capable of high-precision output by correcting an error in the background.
Further, another problem of the present invention is that in a laser type gas analyzer that measures various gas concentrations using laser light, the received signal of the laser light transmitted through the gas to be measured is converted into the time interleaved A / D converter. By A / D conversion and arithmetic processing of the output signal, it is possible to measure the gas concentration with high resolution and a wide dynamic range.

In order to solve the above problem, the time interleaved A / D converter according to claim 1 is a time interleaved A / D converter that performs A / D conversion using a plurality of unit A / D converters connected in parallel. In
Multiple units One of the time interleaving processing clock signal that sequentially delays the sampling timing of the A / D converter at equal intervals and the averaging processing clock signal that has the same sampling timing is the plurality of units. The clock signal generator supplied to the A / D converter,
An averaging processing unit that calculates the average value of the output signals of the plurality of unit A / D converters during the averaging process.
A correction unit that corrects and outputs the output characteristics of the plurality of unit A / D converters based on the average value, and a correction unit.
An output unit that selects and outputs the output signal of the correction unit during time interleaving processing and selects and outputs the output signal of the averaging processing unit during averaging processing.
It is characterized by being equipped with.

The time interleaved A / D converter according to claim 2 is claimed in claim 1.
The averaging processing unit is
Deviations between the simple average value of the output signals of the plurality of unit A / D converters and the output signals of the plurality of unit A / D converters with respect to the simple average value were calculated and set based on the deviations. It is characterized in that the weighted average value of the output signals of the plurality of unit A / D converters is calculated as the average value by using the weight.

The time interleaved A / D converter according to claim 3 is claimed in claim 1 or 2.
The correction unit
The average value is used as a teacher signal, and the output characteristics of the plurality of unit A / D converters are corrected by the LMS algorithm.

The time interleaved A / D converter according to claim 4 is the item according to any one of claims 1 to 3.
The output characteristic includes the conversion gain, offset, and sampling timing of the plurality of unit A / D converters.
The correction unit is characterized in that at least one of the output characteristics is corrected so that the outputs of all the unit A / D converters are equal to each other.

The time interleaved A / D converter according to claim 5 is the item of any one of claims 1 to 4.
The correction unit
It is characterized in that a correction coefficient for correcting the output characteristics of the plurality of unit A / D converters is calculated at the time of the averaging process, and the output characteristics are corrected at the time interleave processing using the calculated correction coefficient. do.

The time interleaved A / D converter according to claim 6 is claimed in claim 5.
The output unit is characterized in that the output signal of the correction unit or the averaging unit can be selected by switching between the time interleaving process and the averaging process at a predetermined timing.

The laser gas analyzer according to claim 7 includes a laser element that emits laser light and a laser element.
A light receiving element that receives the laser beam propagated through the measurement space in which the gas to be measured exists, and a light receiving element.
A signal processing circuit that converts the output signal of the light receiving element into a digital signal by a time interleaved A / D converter and measures the concentration of the gas to be measured from the gas absorption signal contained in the digital signal.
Equipped with
The time interleaved A / D converter is
A plurality of unit A / D converters connected in parallel and to which the output signal of the light receiving element is input, and
A plurality of units A clock signal for time interleaving processing in which the sampling timings of the A / D converters are sequentially delayed at equal intervals and a clock signal for averaging processing in which the sampling timings are the same are used in a plurality of units. The clock signal generator supplied to the A / D converter,
An averaging processing unit that calculates the average value of the output signals of the plurality of unit A / D converters during the averaging process.
A correction unit that corrects and outputs the output characteristics of the plurality of unit A / D converters based on the average value, and a correction unit.
Equipped with
At the time of time interleaving processing, the concentration of the gas to be measured is measured by using the output signal of the correction unit.

The laser gas analyzer according to claim 8 is claimed in claim 7.
The averaging processing unit is
Deviations between the simple average value of the output signals of the plurality of unit A / D converters and the output signals of the plurality of unit A / D converters with respect to the simple average value were calculated and set based on the deviations. It is characterized in that the weighted average value of the output signals of the plurality of unit A / D converters is calculated as the average value by using the weight.

The laser gas analyzer according to claim 9 is the present invention according to claim 7 or 8.
The correction unit
Using the average value as a teacher signal, the output characteristics of the plurality of unit A / D converters are corrected by an LMS (Least Mean Square) algorithm.

The laser gas analyzer according to claim 10 is the one according to any one of claims 7 to 9.
The output characteristic includes the conversion gain, offset, and sampling timing of the plurality of unit A / D converters.
The correction unit is characterized in that at least one of the output characteristics is corrected so that the outputs of all the unit A / D converters are equal to each other.

The laser gas analyzer according to claim 11 is the one according to any one of claims 7 to 10.
The correction unit
It is characterized in that a correction coefficient for correcting the output characteristics of the plurality of unit A / D converters is calculated at the time of the averaging process, and the output characteristics are corrected at the time interleave processing using the calculated correction coefficient. do.

The laser gas analyzer according to claim 12 is the one according to any one of claims 7 to 11.
It is characterized in that the time interleaving process and the averaging process are switched according to the timing of controlling the laser element.

According to the time-interleaved A / D converter of the present invention, since it has a simple configuration without using an additional reference A / D converter, there are problems such as an increase in circuit size, cost increase, and power consumption increase. Can be avoided. In addition, by correcting the error in the output characteristics between the unit A / D converters using the average value with a small error as the teacher signal ideally, the actual operation of the system including the time interleaved A / D converter is not stopped. It is also possible to correct the effects of characteristic changes caused by the operating environment such as changes in ambient temperature.
Further, according to the laser gas analyzer of the present invention, the concentration of the gas to be measured is measured by correcting the error of the output characteristic between a plurality of unit A / D converters by using the time interleaved A / D converter. The resolution of the measurement can be increased and the dynamic range can be expanded. In addition, by alternately executing the time interleaving process and the averaging process for correction, the operating environment such as changes in the ambient temperature without stopping the actual operation of the laser gas analyzer including the time interleaving A / D conversion. The effect of the characteristic change due to the above can also be corrected in real time.

It is a block diagram of the time interleaved A / D converter which concerns on embodiment of this invention. FIG. 3 is a waveform diagram of a clock signal when time interleaving processing is performed in the embodiment of the present invention. In the embodiment of the present invention, it is a waveform diagram of the clock signal when the averaging process is performed. It is a block diagram of the averaging processing part in FIG. It is sectional drawing which shows the main part of the laser type gas analyzer which concerns on embodiment of this invention. It is a block diagram of the light source part and the like in FIG. It is a waveform diagram which shows the operation of the laser drive signal generation part in FIG. It is a block diagram of the signal processing circuit and the like in FIG. It is a block diagram of the time interleaved A / D converter in FIG. It is a waveform diagram which shows the operation of the clock signal generation part in FIG. It is a block diagram of the conventional time interleaving A / D converter. It is a block diagram which shows the main part of the conventional laser type gas analyzer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a time interleaved A / D converter according to the present embodiment. In FIG. 1, M units (multiple Ms) to which analog voltages are input are connected in parallel to the units A / D converters ADC ₁ to ADC _M , and these units A / D converters ADC ₁ to ADC M are connected to the units A / D converters ADC 1 to ADC _M. , Clock signals CLK ₁ to CLK _M , which are reference for sampling timing, are input from the clock signal generation unit 10.
The output signals D ₁ to _DM after A / D conversion by the unit A / D converters ADC ₁ to ADC _M are input to the output unit 40 via the corresponding correction units 30 ₁ to 30 _M , respectively.

Further, the output signals D ₁ to _DM of the units A / D converters ADC ₁ to ADC _M are input to the averaging processing unit 20, and the average value of these signals is calculated, and the average value is the correction unit 30 ₁ to. It is input to 30 _M and the output unit 40.
In the present embodiment, the digital signal subjected to time interleaving processing by the unit A / D converters ADC ₁ to ADC _M and the correction units 30 ₁ to 30 _M and the digital signal subjected to averaging processing by the averaging processing unit 20 are used. One of them can be selected and output by the output unit 40. Then, at the time of time interleaving processing, the correction units 30 ₁ to 30 _M use the average value output from the averaging processing unit 20 to correct the error in the output characteristics of each unit A / D converter ADC ₁ to ADC _M. Is selected by the output unit 40, and at the time of averaging processing, the output unit 40 selects and outputs the output signal of the averaging processing unit 20.

The clock signal generation unit ₁₀ outputs the clock signals CLK1 to _CLKM for time interleaving processing shown in FIG. 2 when performing time interleaving processing, and for averaging processing shown in FIG. 3 when performing averaging processing. Clock signals CLK ₁ to CLK _M are output. In FIGS. 2 and 3, CLK _S is a reference clock signal.
2 and 3 show clock signals CLK ₁ to CLK ₄ when there are four unit A / D converters (M = 4), but the number of clock signals is the unit A / D converter. It becomes any plurality of M according to the number.

During the time interleaving process, as shown in FIG. 2, the sampling frequency for the time interleaving process is _set to M times, that is, 4 times the sampling frequency F _s of the units A / D converters ADC ₁ to ADC ₄ . Time interleaving clock signals CLK ₁ to CLK ₄ are generated by delaying the reference clock signal CLK _S of frequency F _s by phase (2π / 4), and are input to the units A / D converters ADC ₁ to ADC ₄ , respectively. ..
On the other hand, during the averaging process, as shown in FIG. 3, all the units A / D converters ADC ₁ to ADC ₄ are sampled at the same timing, so that the phase is aligned at the frequency F _s for the averaging process. Clock signals CLK ₁ to CLK ₄ are generated and input to the unit A / D converters ADC ₁ to ADC ₄ , respectively.
The clock signal generation unit 10 may switch and output the clock signals CLK ₁ to CLK ₄ of FIG. 2 or 3 according to the trigger signal according to the switching timing of the operation between the time interleaving process and the averaging process. The clock signal generation unit 10 can be configured by using an oscillator or an FPGA (Field Programmable Gate Array).

Next, FIG. 4 shows a specific example of the averaging processing unit 20 in FIG. The configuration of the averaging processing unit 20 is not limited to FIG.
The averaging processing unit 20 shown in FIG. 4 operates only during the averaging process. The output signals D ₁ to D ₄ of the unit A / D converters ADC ₁ to ADC ₄ are input to the simple average calculation unit 21, the deviation calculation unit 22, the weighted average calculation unit 24, and the correction units 30 ₁ to 30 ₄ . The simple average calculation unit 21 calculates the simple average values of the output signals D ₁ to D ₄ of the units A / D converters ADC ₁ to ADC ₄ and outputs them to the deviation calculation unit 22. In the deviation calculation unit 22, the output signals D 1 to D 4 of the output signals D _{1 to D 4 are obtained from the output signals D 1 to D 4 of each} unit A / D converter ADC ₁ to ADC ₄ and the simple average value output from the simple average calculation unit 21. Deviations x ₁ to x ₄ are calculated and output to the weight calculation unit 23.

In the weight calculation unit 23, the weights w ₁ to w ₄ for obtaining the weighted average of the output signals D ₁ to D ₄ of the units A / D converters ADC ₁ to ADC ₄ are used by the above deviations x ₁ to x ₄ . Is calculated by the following formula 1.

In Equation 1, i = ₁ to 4, that is, M = ₄ , and the weights w1 to w4 are large for the unit A / D converter with a small deviation and are used for the unit A / D converter with a large deviation. On the other hand, it is set to be small. In Equation 1, the weight is calculated using the square of the deviation, but Equation 1 is just an example, and the method is not limited to this method, for example, using the absolute value of the deviation.

The calculated weights w ₁ to w ₄ are output to the weighted average calculation unit 24. In the weighted average calculation unit 24, the weighted average value x (in the text, in the text, from the output signals D ₁ to D ₄ of the input units A / D converters ADC ₁ to ADC ₄ and the respective weights w ₁ to w ₄ ). Due to the format described, "￣" indicating the average value is omitted) is calculated by the following formula 2. The weighted average value x is output to the correction units 30 ₁ to 304 and the output unit ₄₀ for correcting the error in the output characteristics of the units A / D converters ADC ₁ to ADC ₄ .

As described above, instead of calculating the weighted average value of the output signals D1 to _D4 of the units _A / D converters ADC ₁ to ADC ₄ , the simple average value may be used for the correction.
By simply averaging the output signals D ₁ to D ₄ of the unit A / D converters ADC ₁ to ADC ₄ , the resolution of the digital output value is improved with respect to the unit A / D converter alone, so that the resolution is increased. The effect of is obtained. Further, in general, the characteristic error depending on the manufacturing variation of the A / D conversion element can be considered to have a normal distribution centered on the error ± 0. As the number of A / D conversion elements used for time-interleaved A / D conversion increases, the error distribution of the elements becomes closer to the normal distribution, and the simple average value of the output is a highly accurate output when the error is ± 0. Approaching.
Therefore, even if a reference A / D converter whose output characteristics have been calibrated in advance is not prepared, correction can be performed with high accuracy by using the simple average value for reference during the time interleaving process.

On the other hand, if the number of elements used is small, or if some of the elements used have a large error, the simple average value of those outputs may become a value that is greatly affected by the error due to the dispersion of the error values. .. Therefore, by calculating the weighted average value as shown in FIG. 4, the influence of the output of the unit A / D converter having an error deviating from the set of error distributions can be reduced, so that the accuracy is higher. A digital output can be obtained.

As shown in FIGS. 1 and 4, the correction units 30 ₁ to 30 ₄ have the output signals D ₁ to D ₄ of the units A / D converters ADC ₁ to ADC ₄ and the weighted average value from the averaging processing unit 20. x is input.
At the time of averaging processing, the weighted average value x is used as a teacher signal, and the output signals D ₁ to D ₄ of each unit A / D converter ADC ₁ to ADC ₄ are corrected to correct the units A / D converters ADC ₁ to ADC ₄ . Reduces the effects of errors in the output characteristics of. At this time, the latest correction coefficient is stored in the correction coefficient used for the correction.
On the other hand, during the time interleaving process, the correction units 30 ₁ to 30 ₄ use the correction coefficients calculated and stored during the averaging process to output the output signals D ₁ to D ₄ of the unit A / D converters ADC ₁ to ADC ₄ . It is corrected and given to the output unit 40.
The weighted average value x by the averaging processing unit 20 and the corrected output signals from the correction units 30 ₁ to 304 are input to the output unit ₄₀ , and the averaging processing unit 20 outputs the corrected output signals. The input value, that is, the weighted average value x is switched so as to output the input value from the correction units 30 ₁ to ₃₀₄ during the time interleaving process.

Next, the correction principle in this embodiment will be described.
The time interleaving process and the averaging process may be switched between operations at predetermined timings, and may be switched according to the required performance (speed, resolution) of each system operation. For example, the operation may be switched at regular intervals, or the operation may be switched when environmental information such as ambient temperature is observed and changed. Alternatively, the output signal performance (SN ratio, dynamic range, magnitude of distortion component, etc.) may be measured and the operation may be switched when it changes.
The operation of the time interleaving process and the averaging process may be switched at regular timings or irregular timings.
As the correction algorithm, for example, it is desirable to use the LMS algorithm as in Patent Document 2 and Patent Document 3, but the output of the reference A / D converter is not used as a teacher signal as in these documents, but is a unit. By using the weighted average values x of the A / D converters A / D ₁ to A / D ₄ , it is possible to correct errors due to output characteristics with high accuracy.

As described above, according to the time interleaved A / D converter of the present embodiment, the error caused by the output characteristics, the operating environment, etc. of the plurality of unit A / D converters in the time interleaved A / D conversion is referred to. It is possible to perform background correction with high accuracy without using an A / D converter.

Next, a laser gas analyzer that A / D-converts the received signal of the laser beam using the time-interleaved A / D converter described above and calculates and processes the output signal to measure the presence or absence of the gas to be measured and its concentration. The embodiment of the above will be described.

FIG. 5 shows the laser gas analyzer of this embodiment. In FIG. 5, the flanges 51a and 51b are fixed to the walls 50a and 50b of a pipe such as a flue through which the gas to be measured passes, by welding or the like. A bottomed cylindrical light emitting unit container 130 is attached to the flange 51a on the light emitting unit 100 side via a mounting seat 52a.
A light source unit 110 is arranged inside the light emitting unit container 130, and the laser beam L emitted from the light source unit 110 is collimated to parallel light by an optical system including a collimating lens 120. The collimated parallel light passes through the center of the flange 51a, enters the inside of the walls 50a, 50b, and is absorbed when passing through the gas to be measured inside the walls 50a, 50.

A bottomed cylindrical light-receiving part container 240 is attached to the flange 51b on the light-receiving part 200 side via a mounting seat 52b. The parallel light that has passed through the insides of the walls 50a and 50b is collected by the condenser lens 230 inside the light receiving unit container 240 and received by the light receiving element 220. This light is converted into an electric signal by the light receiving element 220 and input to the signal processing circuit 210A in the subsequent stage. The signal processing circuit 210A and the light source unit 110 are connected by a communication line 60 for transmitting and receiving a trigger signal used for laser drive control.

Next, FIG. 6 shows the configuration of the light source unit 110. In the light source unit 110, the laser drive signal generation unit 111 generates a laser drive signal with reference to the trigger signal transmitted from the calculation unit 214 in the signal processing circuit 210A. This signal is sent to the current control unit 112 to drive the laser element 113 to emit the laser beam L.

FIG. 7 shows the operation of the laser drive signal generation unit 111. The laser drive signal is a signal in which the laser wavelength is swept within a range including the absorption wavelength of the gas to be measured, but when detected by the so-called 2f method, the swept signal may be further modulated. The laser drive signal output from the laser drive signal generation unit 111 is converted into a current by the current control unit 112 and supplied to the laser element 113 made of a semiconductor laser to emit the laser beam L.

Next, FIG. 8 shows the configuration of the signal processing circuit 210A.
In FIG. 8, as the light receiving element 220, a photodiode or the like having sensitivity to the emission wavelength of the laser element 113 is used. The output current of the light receiving element 220 is converted into a voltage by the IV converter 211, and the output signal is supplied to the filter 212 to remove noise components other than the gas absorption signal component, and then the above-mentioned time interleave A / D conversion. It is converted into a digital signal by the device 215.
Since the order of the filter 212 and the time interleaved A / D converter 215 is not limited, a digital filter may be used after the A / D conversion by the time interleaved A / D converter 215.
The output of the time interleaved A / D converter 215 is sent to the arithmetic unit 214 including a CPU or the like. The calculation unit 214 measures and outputs the concentration of the gas to be measured, and also generates a pulse-shaped trigger signal for laser drive control and outputs it to the laser drive signal generation unit 111 and the time interleaved A / D converter 215. do.

Next, a method for measuring the concentration of the gas to be measured will be described.
First, the laser drive signal generation unit 111 of the light source unit 110 has the laser shown in FIG. 7 so that the gas to be measured can be measured in advance within the sweep range of the laser drive signal (so that a predetermined gas absorption signal can be obtained). Generate a drive signal. After that, the laser element 113 is driven to emit the laser light L into the internal space of the walls 50a and 50b where the gas to be measured exists, and the focused laser light L is incident on the light receiving element 220.

In the signal processing circuit 210A of FIG. 8, when the laser beam is not absorbed by the gas to be measured, the gas absorption signal component is not detected, so that the output signal of the filter 212 becomes a substantially horizontal straight line. On the other hand, when the laser beam is absorbed by the gas to be measured, the gas absorption signal is detected as the output of the filter 212. The maximum or minimum value of this gas absorption signal corresponds to the concentration of the gas to be measured.

Therefore, the calculation unit 214 may measure the maximum value or the minimum value of the gas absorption signal, or integrate a part or all of the gas absorption signal and calculate the concentration of the gas to be measured from the integrated value. Further, there is a certain temporal correlation between the trigger signal output from the calculation unit 214 and the output signal of the filter 212. In other words, the timing at which the gas absorption signal and its maximum and minimum values are generated can be detected almost accurately in advance with respect to the timing of the trigger signal, and high-precision measurement is possible by measuring with the trigger signal as a reference. ..

Next, the configuration and operation of the time interleaved A / D converter 215 will be described.
FIG. 9 is a block diagram of the time interleaved A / D converter in FIG. Since the configuration and operation are basically the same as those described with reference to FIGS. 1, 2, etc., a part thereof is omitted, but the overall operation is as a unit A / D converter ADC ₁ to ADC. An averaging process that calculates a weighted average value by simultaneously performing an A / D conversion operation on ₄ and a time interleaving process that speeds up the overall sampling by giving a phase difference to each A / D conversion operation. , Are alternately performed to correct the error in the output characteristics between the unit A / D converters, thereby enabling higher resolution digital output.

First, as shown in FIG. 10, the clock signal generation unit 10 in FIG. 9 alternately outputs the averaging processing clock signal and the time interleaving processing clock signal with reference to the trigger signal sent from the arithmetic unit 214. do. That is, the clock signal of FIG. 2 and the clock signal of FIG. 3 are alternately switched and output.
As described above, the clock signal for averaging processing is the same clock signal having the same phase in order to simultaneously perform A / D conversion by all the units A / D converters ADC ₁ to ADC ₄ , and is time interleaving processing. The clock signal is a clock signal having a phase difference in order to perform A / D conversion by the units A / D converters ADC ₁ to ADC ₄ at different timings.

The configuration and operation of the averaging processing unit 20 to which the output signals of the unit A / D converters ADC ₁ to ADC ₄ are input are as described with reference to FIG. 4, and the weighted average calculation unit 24 uses the unit A / D conversion. Using the output signals D ₁ to D ₄ of the ADCs ₁ to ADC ₄ and the weights w ₁ to w ₄ calculated by the weight calculation unit 23 by the formula 1, the weighted average value x is calculated by the formula 2 and the unit A / Output to the correction units 31 ₁ to ₃₁₄ corresponding to the D converters ADC ₁ to ADC ₄ , respectively.

The correction units 31 ₁ to 314 include trigger signals from the calculation unit 214, output signals D ₁ to D ₄ of the units A / D converters ADC ₁ to ADC ₄ , and weighted _average values from the weighted average calculation unit 24. x is input, and the correction method is switched based on the trigger signal.
That is, at the time of averaging processing, the weighted average value x is used as a teacher signal, the output signals D1 to _D4 of each unit _A / D converter ADC ₁ to ADC ₄ are corrected, and the correction coefficient is calculated to obtain the latest one. Remember.
The correction algorithm is the same as in Patent Documents 2 and ₃ , but the weighted average value x of the output signals D1 to D4 is used instead of using the output of the additional _A / D converter as the teacher signal. It is possible to perform background correction with high accuracy without the need for an additional A / D converter.

On the other hand, during the time interleaving process, the correction units 31 ₁ to 31 ₄ correct the output signals D ₁ to D ₄ using the correction coefficients calculated and stored during the averaging process, and the corrected signal is output to the calculation unit 214. Will be done. The calculation unit 214 calculates the concentration of the gas to be measured only during the time interleaving process.
Basically, the time interleaving process is executed in a cycle of 1/2 of the trigger signal, but the averaging process is not limited to this, and the cycle of the trigger signal is smaller, such as 1/4 cycle or 1/8 cycle. You may do it. In that case, the frequency of updating the correction coefficient in the averaging process is reduced, but the process can be reduced.

As the unit A / D converters ADC ₁ to ADC ₄ , a low-speed high-resolution A / D converter or a high-speed low-resolution A / D converter may be used. When a low-speed high-resolution A / D converter is used, the speed can be increased to the required sampling frequency by the time-interleaved A / D conversion, and the high resolution can be realized by the above-mentioned correction. When using a high-speed, low-resolution A / D converter, high resolution is achieved by oversampling by time-interleaved A / D conversion and then performing the above-mentioned correction and band limitation by the arithmetic unit 214. can do.
As described above, according to the present embodiment, the error in the output characteristics between the unit A / D converters ADC ₁ to ADC ₄ in the time interleaved A / D converter is background-corrected to increase the resolution, and the laser gas is used. It is possible to realize a wide dynamic range in the analyzer.

10: Clock signal generation unit 20: Average processing unit 21: Simple average calculation unit 22: Deviation calculation unit 23: Weight calculation unit 24: Weighted average calculation unit 30 ₁ to 30 _M , 31 ₁ to 31 _M : Correction unit 40: Output units 50a, 50b: Walls 51a, 51b: Flange 52a, 52b: Mounting seat 60: Communication line 100: Light emitting unit 110: Light source unit 111: Laser drive signal generation unit 112: Current control unit 113: Laser element 120: Collimating lens 130: Light emitting unit container 200: Light receiving unit 210A: Signal processing circuit 211: IV converter 212: Filter 214: Calculation unit 215: Time interleaved A / D converter 220: Light receiving element 230: Condensing lens 240: Light receiving unit container ADC ₁ to ADC _M : Unit A / D converter L: Laser light

Claims (12)

In a time-interleaved A / D converter that performs A / D conversion using a plurality of unit A / D converters connected in parallel.
Multiple units One of the time interleaving processing clock signal that sequentially delays the sampling timing of the A / D converter at equal intervals and the averaging processing clock signal that has the same sampling timing is the plurality of units. The clock signal generator supplied to the A / D converter,
An averaging processing unit that calculates the average value of the output signals of the plurality of unit A / D converters during the averaging process.
A correction unit that corrects and outputs the output characteristics of the plurality of unit A / D converters based on the average value, and a correction unit.
An output unit that selects and outputs the output signal of the correction unit during time interleaving processing and selects and outputs the output signal of the averaging processing unit during averaging processing.
A time interleaved A / D converter characterized by being equipped with. In the time interleaved A / D converter according to claim 1,
The averaging processing unit is
Deviations between the simple average value of the output signals of the plurality of unit A / D converters and the output signals of the plurality of unit A / D converters with respect to the simple average value were calculated and set based on the deviations. A time interleaved A / D converter characterized in that a weighted average value of output signals of the plurality of unit A / D converters is calculated as the average value using weights. In the time interleaved A / D converter according to claim 1 or 2.
The correction unit
A time interleaved A / D converter characterized in that the output characteristics of the plurality of unit A / D converters are corrected by an LMS (Least Mean Square) algorithm using the mean value as a teacher signal. In the time interleaved A / D converter according to any one of claims 1 to 3.
The output characteristic includes the conversion gain, offset, and sampling timing of the plurality of unit A / D converters.
The correction unit is a time interleaved A / D converter characterized in that at least one of the output characteristics is corrected so that the outputs of all the unit A / D converters are equal. In the time interleaved A / D converter according to any one of claims 1 to 4.
The correction unit
It is characterized in that a correction coefficient for correcting the output characteristics of the plurality of unit A / D converters is calculated at the time of the averaging process, and the output characteristics are corrected at the time interleave processing using the calculated correction coefficient. Time interleaved A / D converter. In the time interleaved A / D converter according to claim 5.
The output unit is characterized in that the output signal of the correction unit or the averaging unit can be selected by switching between the time interleaving process and the averaging process at a predetermined timing. vessel. A laser element that emits laser light and
A light receiving element that receives the laser beam propagated through the measurement space in which the gas to be measured exists, and a light receiving element.
A signal processing circuit that converts the output signal of the light receiving element into a digital signal by a time interleaved A / D converter and measures the concentration of the gas to be measured from the gas absorption signal contained in the digital signal.
Equipped with
The time interleaved A / D converter is
A plurality of unit A / D converters connected in parallel and to which the output signal of the light receiving element is input, and
A plurality of units A clock signal for time interleaving processing in which the sampling timings of the A / D converters are sequentially delayed at equal intervals and a clock signal for averaging processing in which the sampling timings are the same are used in a plurality of units. The clock signal generator supplied to the A / D converter,
An averaging processing unit that calculates the average value of the output signals of the plurality of unit A / D converters during the averaging process.
A correction unit that corrects and outputs the output characteristics of the plurality of unit A / D converters based on the average value, and a correction unit.
Equipped with
A laser gas analyzer characterized in that the concentration of the gas to be measured is measured by using the output signal of the correction unit at the time of time interleaving processing. In the laser gas analyzer according to claim 7,
The averaging processing unit is
Deviations between the simple average value of the output signals of the plurality of unit A / D converters and the output signals of the plurality of unit A / D converters with respect to the simple average value were calculated and set based on the deviations. A laser gas analyzer characterized in that a weighted average value of output signals of the plurality of unit A / D converters is calculated as the average value using weights. In the laser gas analyzer according to claim 7 or 8.
The correction unit
A laser gas analyzer characterized in that the output characteristics of the plurality of unit A / D converters are corrected by an LMS (Least Mean Square) algorithm using the average value as a teacher signal. In the laser gas analyzer according to any one of claims 7 to 9, the laser gas analyzer.
The output characteristic includes the conversion gain, offset, and sampling timing of the plurality of unit A / D converters.
The correction unit is a laser gas analyzer characterized in that at least one of the output characteristics is corrected so that the outputs of all the unit A / D converters are equal. In the laser gas analyzer according to any one of claims 7 to 10.
The correction unit
It is characterized in that a correction coefficient for correcting the output characteristics of the plurality of unit A / D converters is calculated at the time of the averaging process, and the output characteristics are corrected at the time interleave processing using the calculated correction coefficient. Laser type gas analyzer. In the laser gas analyzer according to any one of claims 7 to 11.
A laser gas analyzer characterized in that the time interleaving process and the averaging process are switched according to the timing of controlling the laser element.

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