JP2003258636A - Method and device for measurement in d/a converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce measurement waiting time in a D/A converter. <P>SOLUTION: A digital filter 2 is provided in the front stage of the D/A converter 3, and an analog filter 4 is provided in the rear stage of the D/A converter 3, and filter coefficients of the digital filter 2 are determined so that the response delay due to the time constant of the analog filer 4 is compensated. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DA converter measuring method and apparatus, and is particularly suitable for application to a measuring waiting time shortening method.

[0002]

2. Description of the Related Art In a conventional DA converter for voice, a sufficient analog characteristic (THD, SN, SND, etc.) is utilized by effectively utilizing the dynamic range of a digitizer of a measuring device.
In order to obtain, a method of externally attaching a high pass filter and a gain amplifier is used.

FIG. 11 is a block diagram showing a schematic configuration of a conventional DA converter measuring apparatus. In FIG. 11, the measuring device of the DA converter 42 is provided with a signal generating means 41 and a measuring means 45, the measuring means 45 is provided with an AD converter 46 and an analyzer 47, and a high pass filter 43 and a gain amplifier 44. It is attached externally.

The digital signal WD41 generated by the signal generating means 41 is input to the DA converter 42, and the digital signal WD41 is converted into the analog signal WA41.
Is converted to. Then, the analog signal WA41 converted by the DA converter 42 is input to the high-pass filter 43, and the analog signal WA4 in which the low-frequency component is cut off.
2 is output to the gain amplifier 44.

Since the frequency band of the audio DA converter is about 20 Hz to 20 kHz, the cutoff frequency of the high pass filter 43 is set to about 10 Hz. Then, the gain amplifier 44 outputs the analog signal WA.
42 is amplified and the amplified analog signal WA43 is A
It is input to the D converter 46.

Then, the analog signal WA43 is converted into a digital signal WD42 by the AD converter 46, and the digital signal WD42 is measured by the analyzer 47.

[0007]

However, in the conventional DA converter measuring method, since the low frequency component of the analog signal WA41 output from the DA converter 42 is cut, the high pass filter 43 having a cutoff frequency of about 10 Hz is used. Used. Therefore, it takes about 100 ms for the stabilization waiting time of the high-pass filter 43, and DA
There is a problem that the measurement waiting time of the converter increases.

Therefore, an object of the present invention is to provide a DA converter measuring method and apparatus capable of shortening the measurement waiting time.

[0009]

In order to solve the above-mentioned problems, according to the measuring method of the DA converter of the first aspect, the first digital signal is generated by the signal generating means and input to the DA converter. A method of measuring a DA converter, comprising the steps of: and a step of inputting and measuring a first analog signal DA-converted and output from the DA converter into a measuring means provided in a subsequent stage of the DA converter. Inputting a first digital signal to a digital filter provided in the preceding stage of the DA converter and outputting a second digital signal based on a filter coefficient of the digital filter; and outputting the second digital signal to the DA converter. And a first analog signal DA-converted and output from the DA converter, Inputting to an analog filter provided in the latter stage of the converter and filtering to output a second analog signal; and inputting the second analog signal to a measuring means provided in the latter stage of the analog filter to measure. And the filter coefficient of the digital filter is a filter coefficient that compensates for a delay in response due to the time constant of the analog filter.

With this configuration, a delay of the response due to the time constant of the analog filter can be compensated only by providing a digital filter in the preceding stage of the DA converter, and in order to obtain sufficient analog characteristics of the DA converter, the latter stage of the DA converter is obtained. Even when an analog filter is installed in
The measurement waiting time of the DA converter can be shortened.

According to another aspect of the DA converter measuring method of the present invention, the step of generating the first digital signal by the signal generating means and inputting the first digital signal to the DA converter, and the DA converter converting and outputting the first digital signal. A method of inputting a first analog signal to a measuring means provided in a subsequent stage of the DA converter and measuring the same, wherein the first digital signal is provided in a subsequent stage of the signal generating means. Inputting to a provided first digital filter and outputting a second digital signal based on a filter coefficient of the first digital filter;
Inputting the second digital signal to a second digital filter provided in the preceding stage of the DA converter, and outputting a third digital signal based on a filter coefficient of the second digital filter; The step of inputting the digital signal of
Inputting a first analog signal DA-converted and output from the converter to an analog filter provided in a subsequent stage of the DA converter to output a second analog signal; and outputting the second analog signal to the analog signal. Inputting to a measuring means provided at a subsequent stage of the analog filter for measurement, and the filter coefficient of the first digital filter is set so that the third digital signal does not exceed the full scale of the DA converter. It is a filter coefficient for compensation, and the filter coefficient of the second digital filter is a filter coefficient for compensating for a delay in response due to a time constant of the analog filter.

As a result, the second stage is provided before the DA converter.
The delay of the response due to the time constant of the analog filter can be compensated for only by installing the digital filter of
Even if an analog filter is provided in the subsequent stage of the DA converter in order to obtain sufficient analog characteristics of the converter, the measurement waiting time of the DA converter can be shortened. Furthermore, by providing the first digital filter, it is possible to reduce the possibility that the digital signal output from the second digital filter will exceed the full scale of the DA converter.

According to a third aspect of the DA converter measuring apparatus of the present invention, the signal generating means for generating the first digital signal input to the DA converter and the first analog signal output from the DA converter are provided. A measuring device for a DA converter, which comprises a measuring means for inputting and measuring, and a digital filter for inputting and filtering the first digital signal and outputting a second digital signal input to the DA converter. An analog filter for inputting and filtering a first analog signal output from the DA converter and outputting a second analog signal; and a measuring unit for inputting and measuring the second analog signal, The filter coefficient of the digital filter is a filter that compensates for a delay in response due to the time constant of the analog filter. Characterized in that it is a data coefficients.

With this configuration, the delay of the response due to the time constant of the analog filter can be compensated only by providing the digital filter in the preceding stage of the DA converter, and the measurement waiting time of the DA converter can be shortened and the digitizer of the measuring means can be shortened. By effectively utilizing the dynamic range, it is possible to obtain sufficient analog characteristics of the DA converter. Further, according to the DA converter measuring device of the fourth aspect, a comparing means for setting the filter coefficient based on a comparison result of the AD conversion value of the first digital signal and the AD conversion value of the second analog signal is provided. It is characterized by further comprising.

Thus, the filter coefficient of the digital filter can be set so that the delay of the response due to the time constant of the analog filter can be compensated by only providing the measuring device with the comparing means, which complicates the structure of the measuring device. It is possible to shorten the measurement waiting time of the DA converter without changing. Further, according to the DA converter measuring device of the fifth aspect, the comparing means includes a first digital signal,
The filter coefficient is set such that the difference between the AD conversion value of the second analog signal and the value obtained by multiplying the filter coefficient is equal to or less than a predetermined value.

As a result, the filter coefficient of the digital filter can be calculated so that the delay of the response due to the time constant of the analog filter can be compensated only by performing a simple calculation process, and the load required for the calculation of the filter coefficient. It is possible to reduce the measurement waiting time of the DA converter while suppressing the above. According to the DA converter measuring device of the sixth aspect, the signal generating means for generating the first digital signal to be inputted to the DA converter and the first analog signal outputted from the DA converter are inputted. A measuring device for a DA converter, comprising: a measuring unit for measuring; a first digital filter for inputting and filtering the first digital signal and outputting a second digital signal; and the second digital signal. A second digital filter for inputting and filtering and outputting a third digital signal input to the DA converter;
An analog filter for inputting and filtering a first analog signal output from the converter to output a second analog signal; and a measuring unit for inputting and measuring the second analog signal, The filter coefficient of the digital filter is a filter coefficient for compensating the third digital signal so as not to exceed the full scale of the DA converter, and the filter coefficient of the second digital filter is the filter coefficient of the analog filter. It is characterized in that it is a filter coefficient that compensates for a delay in response due to a time constant.

As a result, the second stage is provided before the DA converter.
The delay of the response due to the time constant of the analog filter can be compensated for only by installing the digital filter of
It is possible to obtain sufficient analog characteristics of the DA converter by effectively utilizing the dynamic range of the digitizer of the measuring means while shortening the measurement waiting time of the converter. Furthermore, by providing the first digital filter, it is possible to reduce the possibility that the digital signal output from the second digital filter will exceed the full scale of the DA converter.

According to a seventh aspect of the DA converter measuring apparatus of the present invention, the second digital filter is based on a comparison result between the second digital signal and the AD conversion value of the second analog signal. It is characterized by further comprising first comparing means for setting the filter coefficient of. Thereby, only by providing the measuring device with the first comparing means,
The filter coefficient of the second digital filter can be set so that the response delay due to the time constant of the analog filter can be compensated, and the measurement waiting time of the DA converter can be shortened without complicating the configuration of the measuring device. can do.

Here, the first comparing means is, for example, the second comparing means.
It may be a subtracter that subtracts the AD conversion value of the second analog signal from the digital signal of 1 and outputs the difference, or may be a full-scale comparator, a window comparator, or other comparator. According to the DA converter measuring device of claim 8, the first comparing means converts the AD conversion values of the second digital signal and the second analog signal into those of the second digital filter. It is characterized in that the filter coefficient of the second digital filter is set so that the difference from the value multiplied by the filter coefficient becomes a predetermined value or less.

Thus, the filter coefficient of the second digital filter can be calculated so that the delay of the response due to the time constant of the analog filter can be compensated by only performing a simple calculation process. It is possible to reduce the measurement waiting time of the DA converter while suppressing the load on the DA converter. According to the DA converter measuring device of claim 9, the filter coefficient of the first digital filter is set based on a comparison result between the third digital signal and a full-scale value of the DA converter. It is characterized by further comprising a second comparing means for

With this arrangement, the filter coefficient of the digital filter is set so that the digital signal output from the second digital filter does not exceed the full scale of the DA converter simply by providing the measuring device with the second comparing means. The digital signal output from the second digital filter can be D, without complicating the configuration of the measuring device.
The possibility of exceeding the full scale of the A converter can be reduced.

Here, the second comparing means is, for example, the third comparing means.
It may be a subtracter that subtracts the full-scale value of the DA converter from the digital signal and outputs the difference, or it may be a full-scale comparator, a window comparator, or another comparator. According to the DA converter measuring device of claim 10, the second comparing means sets the difference between the third digital signal and the full-scale value of the DA converter to a predetermined value or less. The filter coefficient of the first digital filter is set.

As a result, the digital signal output from the second digital filter does not exceed the full scale of the DA converter by performing a simple arithmetic process.
The filter coefficient of the digital filter can be calculated, and the digital signal output from the second digital filter is D while suppressing the load on the calculation of the filter coefficient.
The possibility of exceeding the full scale of the A converter can be reduced.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION D according to an embodiment of the present invention
A measurement method and apparatus of the A converter will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a DA converter measuring device according to a first embodiment of the present invention.

In FIG. 1, the measuring device of the DA converter 3 is provided with a signal generating means 1 and a measuring means 5,
The digital filter 2 is provided in the front stage of the DA converter 3, and the analog filter 4 is provided in the rear stage of the DA converter 3.
Is provided. Here, the digital filter 2 is F
IR (Finite Impulse Responses)
e: Finite impulse response) type, IIR (Inf
Init Impulse Response) type, and the filter coefficient of the digital filter 2 is determined so as to compensate the delay of the response due to the time constant of the analog filter 4.

The analog filter 4 improves the analog characteristics (THD, SN, SND, etc.) of the DA converter 3, and either a high-pass filter, a low-pass filter, or a band-pass filter is used alone or these are used. May be used in combination. Then, the digital signal WD1 generated by the signal generating means 1 is input to the digital filter 2, and the digital signal WD1 is converted into the digital signal WD2 so as to compensate the delay of the response due to the time constant of the analog filter 4.

Then, the digital signal WD2 converted by the digital filter 2 is input to the DA converter 3, and this digital signal WD2 is converted into the analog signal WA1. Then, the analog signal WA1 converted by the DA converter 3 is input to the analog filter 4, and the waveform-shaped analog signal WA2 is output to the measuring means 5.

Here, since the digital signal WD2 input to the DA converter 3 is converted so as to compensate for the delay in response due to the time constant of the analog filter 4, D
Even when the analog signal WA1 output from the A converter 3 is input to the analog filter 4, the stabilization waiting period of the analog signal WA2 output from the analog filter 4 can be reduced.

Therefore, the stabilization waiting period of the analog filter 4, which occupies most of the measurement time, can be reduced,
The measurement time of the DA converter 3 can be reduced, and the dynamic range of the digitizer of the measuring means 5 can be effectively used. FIG. 2 is a block diagram showing a schematic configuration of a DA converter measuring device according to a second embodiment of the present invention.

In FIG. 2, the measuring device of the DA converter 13 is provided with the signal generating means 11 and the measuring means 15, and the FIR filter 1 is provided in the preceding stage of the DA converter 13.
2 is provided, and a high-pass filter 14 is provided at the subsequent stage of the DA converter 13. The measuring means 15 is provided with a comparing means 19 in addition to the buffer 16, the AD converter 17 and the analyzer 18. In addition,
The buffer 16 may be omitted.

Here, the digital signal WD11 output from the signal generation means 11 and the digital signal WD13 output from the AD converter 17 are input to the comparison means 19. Then, the comparison means 19
The filter coefficient h of the FIR filter 12 is set to the digital signal W
Generate a value multiplied by D13, and use this value and the digital signal WD
The difference from 11 is calculated.

Then, a filter coefficient h for which this difference is equal to or less than a predetermined value is obtained, and the filter coefficient h is output to the FIR filter 12. The calculation of the filter coefficient h is D
It may be performed every time the A converter 13 is measured,
The filter coefficient h may be calculated only once at the beginning, and the value may be fixed and used. Also, comparison means 1
9 may be, for example, a subtractor, or may be a full-scale comparator, a window comparator, or another comparator.

The digital signal WD11 generated by the signal generating means 11 is input to the FIR filter 12, and the filter coefficient h output from the comparing means 19 is multiplied by the digital signal WD11, whereby the digital signal WD12 is obtained. Is generated. Then, the digital signal WD12 generated by the FIR filter 12 is input to the DA converter 13, and the digital signal WD12 is converted into the analog signal WA11.

The analog signal WA11 converted by the DA converter 13 is input to the high-pass filter 14 and the low-frequency component is cut off from the analog signal WA12.
Is output to the measuring means 15. Where the analog signal W
When A12 is input to the measuring means 15, this analog signal WA12 is passed through the buffer 16 to the AD converter 17
Entered in.

Then, the analog signal WA12 is converted into a digital signal WD13 by the AD converter 17,
The digital signal WD13 is measured by the analyzer 18. The digital signal WD13 output from the AD converter 17 is also output to the comparison means 19, and
The digital signal WD11 output from the signal generating means 11 is also input to the comparing means 19.

Then, the comparison means 19 generates a value obtained by multiplying the digital signal WD13 by the filter coefficient h of the FIR filter 12, and the filter coefficient is adjusted so that the difference between this value and the digital signal WD11 becomes a predetermined value or less. h is calculated, and the filter coefficient h is output to the FIR filter 12. As a result, the response delay due to the time constant of the high-pass filter 14 can be compensated, the stabilization waiting period of the high-pass filter 14 which occupies most of the measurement time can be reduced, and the measurement time of the DA converter 13 can be reduced. AD which is possible and is provided in the measuring means 15.
The dynamic range of the converter 17 can be effectively used.

FIG. 3 is a flowchart showing a measuring method of the DA converter according to the embodiment of the present invention. Figure 3
In, the signal generating means 11 generates the digital signal WD11 and outputs it to the FIR filter 12 (step S).
1). Next, the FIR filter 12 produces | generates the digital signal WD12 by multiplying the filter coefficient h by the digital signal WD11, and outputs it to the DA converter 13 (step S2).

Next, the DA converter 13 converts the digital signal WD12 into an analog signal WA11 and outputs it to the high pass filter 14 (step S3). Next, the high pass filter 14 filters the analog signal WA11 to generate the analog signal WA12 (step S4) and outputs it to the measuring means 15 (step S5).

FIG. 4 is a flowchart showing a method of calculating filter coefficients according to an embodiment of the present invention. In FIG. 4, the measuring means 15 fetches the digital signal WD11 generated by the signal generating means 11 into the comparing means 19 (step S11). Next, the measuring means 15 fetches the analog signal WA12 output from the high pass filter 14 into the AD converter 17 via the buffer 16 (step S12).

Next, the AD converter 17 AD-converts the analog signal WA12 to obtain the digital signal W.
D13 is generated (step S13) and output to the analyzer 18 and the comparing means 19. Next, the comparison unit 19 multiplies the digital signal WD13 by the filter coefficient h of the FIR filter 12 and the digital signal WD.
The filter coefficient h is calculated so that the difference from 11 is less than or equal to a predetermined value (step S14).

FIG. 5 is a flowchart showing an example of a filter coefficient optimizing method according to an embodiment of the present invention. In FIG. 5, the comparison means 19 is a digital signal WD.
The number of points of 13 is set to N, and the order of the FIR filter 12 is set to M (step S21).

Next, the comparison means 19 is the FIR filter 1
The filter coefficient h of 2 is set to the initial value (step S22), and the point j is set to 1 (step S22).
23). Next, it is determined whether the point j is less number of points N (step S24), and if the point j is less than the number of points _{N, WD13 j + M-1} -i · h i a i = 0 to M-1
The value added up to is subtracted from WD11 _j , and err _j
(Step S25).

Next, according to the following equation, the filter coefficient h
Is updated (step S26). h _i = h _i −β · err
_j · WD13 _{j + M-1-i} where β is the feedback rate. next,
1 is added to the point j (step S27), and steps S24 to S2 are performed until the point j exceeds the number N of points.
The process of 7 is repeated.

When the point j exceeds the number N of points, it is determined whether or not the difference between the value obtained by multiplying the digital signal WD13 by the filter coefficient h of the FIR filter 12 and the digital signal WD11 is less than a predetermined value (step). S2
8). Then, if this difference is not less than or equal to the predetermined value, the process returns to step S23, and if this difference is less than or equal to the predetermined value, the filter coefficient h obtained in step S26 is set to the FIR filter 1
Output to 2.

FIG. 6A is a diagram showing the input waveform of the DA converter according to the embodiment of the present invention in comparison with the conventional example,
FIG. 6B is a diagram showing a time change of the SND of the DA converter according to the embodiment of the present invention in comparison with the conventional example. Here, IN1 is before the time reduction (the FIR filter 1
The waveform of the input to the DA converter 13 (when there is no 2) (when the digital signal WD11 is directly input to the DA converter 13), IN2 is after the time is shortened (the FIR filter 12).
The input waveform (digital signal WD12) to the DA converter 13 (when present) is shown.

OUT1A has the input waveform IN1 as D
Output waveform from the DA converter 13 when input to the A converter 13, OUT1B is an output waveform from the high pass filter 14 when the input waveform IN1 is input to the DA converter 13, and OUT2A is an input waveform IN2 to the DA converter 13. An output waveform from the DA converter 13 when input, OUT2B, shows an output waveform from the high-pass filter 14 when the input waveform IN2 is input to the DA converter 13.

A sine wave changing from DC to 1.0 KHz was used as the DAC input waveform, and the sampling frequency fs was 32.0 KHz. The time constant of the high pass filter 14 is set to 1/100 Hz. In FIG. 6, it can be seen that the output waveform OUT2B from the high-pass filter 14 after the time reduction has a shorter stabilization waiting time than the output waveform OUT1B from the high-pass filter 14 before the time reduction.

Therefore, by inputting the input waveform IN2 after the time reduction to the DA converter 13, the measurement time of the DA converter 13 can be shortened. Figure 7
It is a block diagram which shows schematic structure of the measuring device of the DA converter which concerns on 3rd Embodiment of this invention. In FIG. 7, D
The measuring device of the A converter 23 is provided with the signal generating means 21 and the measuring means 25, the FIR filter 22 is provided in the front stage of the DA converter 23, and the high pass filter 24 is provided in the rear stage of the DA converter 23. .

The measuring means 25 includes a buffer 26,
DA in addition to AD converter 27 and analyzer 28
A converter 29 and comparison means 30 are provided.
The buffer 26 may be omitted. Here, the comparing means 30 receives the analog signal WA23 obtained by DA converting the digital signal WD21 output from the signal generating means 21 by the DA converter 29, and the buffer 26.
The analog signal WA22 output via the is input.

Then, the comparison means 30 calculates the difference between the analog signal WA22 multiplied by the filter coefficient h of the FIR filter 22 and the analog signal WA23. Then, a filter coefficient h for which this difference is equal to or less than a predetermined value is obtained, and the filter coefficient h is output to the FIR filter 22. The comparison unit 30 may be, for example, a subtracter, or a full-scale comparator, a window comparator, or another comparator.

The digital signal WD21 generated by the signal generating means 21 is input to the FIR filter 22, and the filter coefficient h output from the comparing means 30 is multiplied by the digital signal WD21, whereby the digital signal WD22 is obtained. Is generated. Then, the digital signal WD22 generated by the FIR filter 22 is input to the DA converter 23, and this digital signal WD22 is converted into the analog signal WA21.

Then, the analog signal WA21 converted by the DA converter 23 is input to the high-pass filter 24, and the analog signal WA22 from which the low frequency component is cut off.
Is output to the measuring means 25. Where the analog signal W
When A22 is input to the measuring means 25, this analog signal WA22 is passed through the buffer 26 to the AD converter 27.
Entered in.

Then, the analog signal WA22 is converted into a digital signal WD23 by the AD converter 27,
This digital signal WD23 is measured by the analyzer 28. Further, the analog signal WA22 output from the high pass filter 24 is output to the comparison means 30 via the buffer 26, and the digital signal WD21 output from the signal generation means 21 is supplied to the comparison means 30 by the DA converter 29. The analog signal WA23 that has been DA converted is input.

Then, the comparing means 30 generates a value obtained by multiplying the analog signal WA22 by the filter coefficient h of the FIR filter 22, and the filter coefficient is adjusted so that the difference between this value and the analog signal WA23 becomes a predetermined value or less. h is calculated, and the filter coefficient h is output to the FIR filter 22. As a result, the response delay due to the time constant of the high pass filter 24 can be compensated, and the DA converter 23 can be compensated.
It is possible to reduce the measurement time of (1) and to effectively utilize the dynamic range of the AD converter 27 provided in the measuring means 25, and it is possible to obtain sufficient analog characteristics of the DA converter 23.

Next, a fourth embodiment of the present invention will be described with reference to the drawings. In the second embodiment, when the digital signal WD12 input to the DA converter 13 is calculated by the filter coefficient h calculated in the FIR filter 12, the digital signal WD12 may exceed the full scale of the DA converter 13. Therefore, in the present embodiment, an FIR filter is provided in the preceding stage of the FIR filter 12 to prevent the digital signal input to the DA converter 13 from exceeding its full scale.

FIG. 8 shows a DA according to the fourth embodiment of the present invention.
It is a block diagram which shows schematic structure of the measuring device of a converter. In FIG. 8, the measuring device of the DA converter 34 is provided with a signal generating means 31 and a measuring means 36,
The FIR filter 33 is provided before the DA converter 34,
Further, the FIR filter 32 is provided in the preceding stage. Further, a high pass filter 35 is provided at the subsequent stage of the DA converter 34.

The measuring means 36 has a buffer 37,
In addition to the AD converter 38 and the analyzer 39, comparison means 40, comparison means 41, and storage means 42 are provided. The buffer 37 may be omitted. here,
The digital signal WD32 obtained by filtering the digital signal WD31 output from the signal generating means 31 by the FIR filter 32 is input to the comparison means 40, and the digital signal W output from the AD converter 38 is input.
D34 is input.

Then, the comparison means 40 generates a value obtained by multiplying the digital signal WD34 by the filter coefficient h of the FIR filter 33, and calculates the difference between this value and the digital signal WD32. Then, a filter coefficient h for which this difference is equal to or less than a predetermined value is obtained, and the filter coefficient h is output to the FIR filter 33.

The storage means 42 is composed of a register and a memory and stores the full scale value of the DA converter 34. Further, in the comparing means 41, the digital signal WD31 output from the signal generating means 31 is filtered by the FIR filters 32 and 33 to obtain the digital signal W.
D33 is input and the full scale value of the storage means 42 is input.

Then, the comparison means 41 outputs the digital signal W
The difference between D33 and the full-scale value is calculated, the filter coefficient h ′ at which this difference is equal to or less than a predetermined value is obtained, and the filter coefficient h ′ is output to the FIR filter 32. The filter coefficients h and h ′ may be calculated each time the DA converter 34 is measured, or the filter coefficients h and h ′ may be calculated.
It is also possible to first calculate the value only once and use that value as a fixed value. Further, the comparison means 40 and 41 may be, for example, subtractors, or full-scale comparators, window comparators, and other comparators.

The digital signal WD31 generated by the signal generating means 31 is input to the FIR filter 32, and the filter coefficient h ′ output from the comparing means 41 is multiplied by the digital signal WD31,
The digital signal WD32 is generated. Then, the digital signal WD32 generated by the FIR filter 32 is FI
The digital signal WD33 is generated by multiplying the digital signal WD32 by the filter coefficient h input to the R filter 33 and output from the comparison means 40.

Then, the digital signal WD33 generated by the FIR filter 33 is input to the DA converter 34, and the digital signal WD33 is converted into the analog signal WA31. Then, the analog signal WA31 converted by the DA converter 34 is input to the high-pass filter 35, and the analog signal WA32 from which the low frequency component is cut is output to the measuring means 36.

When the analog signal WA32 is input to the measuring means 36, the analog signal WA32 is input to the AD converter 38 via the buffer 37. Then, the analog signal WA32 is converted into the digital signal WD34 by the AD converter 38, and the digital signal WD34 is obtained.
Are measured by the analyzer 39. Thus, in the present embodiment, the digital signal WD34 output from the AD converter 38 is also output to the comparison unit 40, and the comparison unit 40 is also input with the digital signal WD32 output from the FIR filter 32. It Then, the comparison means 40 generates a value obtained by multiplying the digital signal WD34 by the filter coefficient h of the FIR filter 33, and calculates the filter coefficient h such that the difference between this value and the digital signal WD32 is equal to or less than a predetermined value. Then, the filter coefficient h is output to the FIR filter 33.

As a result, the response delay due to the time constant of the high-pass filter 35 can be compensated, and the stabilization waiting period of the high-pass filter 35, which occupies most of the measurement time, can be shortened and the measurement time of the DA converter 34 can be reduced. In addition, it is possible to effectively utilize the dynamic range of the AD converter 38 provided in the measuring means 36.

Further, in this embodiment, the digital signal WD33 output from the FIR filter 33 is the comparison means 4
In addition to being output to 1, the full scale value of the storage means 42 is also input to the comparison means 41. Then, the comparison means 41 calculates the difference between the digital signal WD33 and the full scale value, obtains the filter coefficient h ′ at which this difference is less than or equal to a predetermined value, and outputs the filter coefficient h ′ to the FIR filter 32.

As a result, it is possible to prevent the digital signal WD33 output from the FIR filter 33 from exceeding the full scale of the DA converter 34.
FIG. 9 is a block diagram showing a method of calculating filter coefficients according to an embodiment of the present invention. In the present embodiment, in the fourth embodiment, the full scale (F) is obtained by modifying the target signal (referred to as an ideal output signal) near the change point.
Find the fastest convergence signal that does not exceed S).

In FIG. 9, d (= [... d _-1 , d ₀ , d ₁
]] Indicates a digital signal input to the DA converter 34, X (= [... x ₋₁ , x ₀ , x ₁ ...]) indicates a digital signal input to the analyzer 39, and W is FIR
The filter coefficient of the filter 33 is shown. From the input signal x _k of the DA converter 34, the signal Z _k of the following equation (1) is defined.

[0068]

[Equation 1]

Using the FIR filter 32 with the tap coefficient B (the number of taps M _z ), and the signal Z, the error signal ε is expressed by the following equation (2).
Can be calculated by

[0070]

[Equation 2]

Therefore,

[0072]

[Equation 3]

[0073]

[Equation 4]

W that minimizes the error signal ε and satisfies Z = 0
And d can be obtained. At this time, B = 0. Here, P _Z and R _Z are defined by the following equations (5) and (6).

[0075]

[Equation 5]

[0076]

[Equation 6]

First, the filter coefficient W is calculated by the following equation (7).
And the input signal to the DA converter 34 is obtained.

[0078]

[Equation 7]

Calculating Z from this input signal, the following equation (8)
Then, B that minimizes E [ε ² ] is similarly obtained.

[0080]

[Equation 8]

Here, d _Zk can be calculated by the following equation (9).

[0082]

[Equation 9]

From the calculated B and Z, d is calculated by the following equation (10).
Update with d _k .

[0084]

[Equation 10]

Β is a feedback ratio for stabilizing the numerical calculation, and normally β <1. The following flow may be repeated until Z becomes sufficiently small. In the above method, R _Z becomes irregular (or close to it) at the solution (and near the solution) (R Z = 0 from _Z = 0), which makes the numerical calculation unstable. Therefore, in practice, the above equation (4) is replaced by the following equation (1
Modify as in 1).

[0086]

[Equation 11]

[0087] However, it is _{R 'Z = R Z + I} . here,
Since B ^T B is smaller than B ^T R ′ _Z B at a position apart from the solution, B can be calculated by the following equation (12) if neglected.

[0088]

[Equation 12]

Further, since B ^T B becomes larger near the solution, it may be better to update B by the following equation (13).

[0090]

[Equation 13]

Next, the effect of obtaining the filter coefficient by this calculation method will be described with reference to FIG. FIG. 10A is a diagram showing an input waveform and an output waveform for the measuring device of FIG. 2, and FIG. 10B is a diagram showing an input waveform and an output waveform for the measuring device of FIG.

Here, IN1 is the target signal and IN2 is
Indicates the input waveform after adaptive equalization, IN3 indicates the excess of the input waveform after adaptive equalization from full scale, and OU1 indicates the output waveform after adaptive equalization. As the measurement conditions in FIG. 10, it is assumed that a low-pass filter (order 1, f _c = 22.05 [KHz]) and a high-pass filter (order 1, f _c = 66.4 [KHz]) are present in the DA converter output. The input impedances of the low-pass filter and the high-pass filter are infinite, and the output impedances of the DA converter, the low-pass filter and the high-pass filter are 0 so that they do not interfere with each other. As the DA converter of the input waveform, a sine wave _{(f s = 44.1 [KHz]} , FS = 8388607 (24bi
t), bin = 11 (/ 511pts.)). Further, the number of taps is M = 49 and M _Z = 12.

In the measuring apparatus of FIG. 2, as shown in FIG. 10A, it can be seen from the waveform IN3 that the input waveform after adaptive equalization exceeds the full scale. On the other hand, FIG.
In the measuring device of No. 1, as shown in FIG.
It can be seen from 3 that the input waveform after adaptive equalization does not exceed the full scale. Therefore, the digital signal WD33 output from the FIR filter 33 is transferred to the DA converter 3
4 can be prevented from exceeding the full scale.

[0094]

As described above, according to the present invention,
By providing a digital filter in the preceding stage of the DA converter, it is possible to compensate for the response delay due to the time constant of the analog filter, shorten the measurement waiting time of the DA converter, and effectively utilize the dynamic range of the digitizer of the measuring means. As a result, sufficient analog characteristics of the DA converter can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a DA converter measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a DA converter measuring apparatus according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a DA converter measuring method according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a method of calculating filter coefficients according to an embodiment of the present invention.

FIG. 5 is a flowchart showing an example of a filter coefficient optimization method according to an embodiment of the present invention.

FIG. 6A is a DA according to an embodiment of the present invention.
FIG. 6 is a diagram showing input waveforms of the converter in comparison with a conventional example.
(B) is a figure showing a time change of the SND of the DA converter according to the embodiment of the present invention in comparison with a conventional example.

FIG. 7 is a block diagram showing a schematic configuration of a DA converter measuring apparatus according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a schematic configuration of a DA converter measuring apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a method of calculating filter coefficients according to an embodiment of the present invention.

10 (a) is a diagram showing an input waveform and an output waveform for the measuring device of FIG. 2, and FIG. 10 (b) is a diagram showing FIG.
FIG. 3 is a diagram showing an input waveform and an output waveform with respect to the measuring device of FIG.

FIG. 11 is a block diagram showing a schematic configuration of a conventional DA converter measuring apparatus.

[Explanation of symbols]

1, 11, 21, 31 Signal generating means 2 Digital filter 3, 13, 23, 29, 34 DA converter 4 Analog filter 5, 15, 25, 36 Measuring means 12, 22, 32, 33 FIR filter 14, 24, 35 High-pass filter 16, 26, 37 Buffer 17, 27, 38 AD converter 18, 28, 39 Analyzer 19, 30, 40, 41 Comparison means 42 Storage means WD1, WD2, WD11 to WD13, WD21 to WD
23 digital signals WD31 to WD34 digital signals WA1, WA2, WA11, WA12, WA21 to WA
23 Analog signal WA31, WA32 Analog signal

Claims (10)

[Claims] 1. A step of generating a first digital signal by a signal generating means and inputting it to a DA converter, and a first analog signal DA-converted and output from the DA converter are provided in a subsequent stage of the DA converter. And a step of inputting to the measuring means to perform measurement, wherein the first digital signal is input to a digital filter provided in the preceding stage of the DA converter to obtain a filter coefficient of the digital filter. Outputting a second digital signal based on the DA converter, inputting the second digital signal to the DA converter, and outputting a first analog signal DA-converted and output from the DA converter to the DA converter. Input to the analog filter provided in the latter stage and output the second analog signal after filtering. And a step of inputting and measuring the second analog signal to a measuring unit provided at a subsequent stage of the analog filter, wherein the filter coefficient of the digital filter is a response of a time constant of the analog filter. A method of measuring a DA converter, which is a filter coefficient for compensating for a delay. 2. A step of generating a first digital signal by a signal generating means and inputting it to a DA converter, and a first analog signal DA-converted and output by the DA converter is provided in a subsequent stage of the DA converter. And a step of inputting to the measuring means to perform measurement, wherein the first digital signal is input to a first digital filter provided after the signal generating means, and the first digital signal is input to the first digital filter. Outputting a second digital signal based on a filter coefficient of the digital filter, and inputting the second digital signal to a second digital filter provided before the DA converter to output the second digital filter. Outputting a third digital signal based on the filter coefficient of the DA converter, Inputting the first analog signal output from the DA converter to the DA converter and outputting the second analog signal by inputting the first analog signal to an analog filter provided in a subsequent stage of the DA converter and filtering the first analog signal. Inputting the second analog signal to a measuring unit provided at a stage subsequent to the analog filter to measure, and the filter coefficient of the first digital filter is set such that the third digital signal is the DA signal. It is a filter coefficient for compensating so as not to exceed the full scale of the converter, and the filter coefficient of the second digital filter is a filter coefficient for compensating for a response delay due to a time constant of the analog filter. DA converter measurement method. 3. A measurement of a DA converter comprising a signal generating means for generating a first digital signal input to the DA converter and a measuring means for inputting and measuring the first analog signal output from the DA converter. A device for inputting and filtering the first digital signal,
A digital filter that outputs a second digital signal that is input to the DA converter; an analog filter that inputs and filters the first analog signal that is output from the DA converter and outputs a second analog signal; A measuring means for inputting and measuring the second analog signal, wherein the filter coefficient of the digital filter is a filter coefficient for compensating for a delay in response due to a time constant of the analog filter. Converter measuring device. 4. The comparison means according to claim 3, further comprising a comparison means for setting the filter coefficient based on a comparison result of the AD conversion value of the first digital signal and the AD conversion value of the second analog signal. DA converter measuring device. 5. The comparing means sets a difference between a first digital signal and a value obtained by multiplying the AD conversion value of the second analog signal by the filter coefficient to a predetermined value or less.
5. The filter coefficient is set, and the filter coefficient is set.
The measuring device of the described DA converter. 6. A measurement of a DA converter comprising a signal generating means for generating a first digital signal input to a DA converter and a measuring means for inputting and measuring a first analog signal output from the DA converter. A device for inputting and filtering the first digital signal,
A first digital filter for outputting a second digital signal; and inputting and filtering the second digital signal,
A second digital filter that outputs a third digital signal that is input to the DA converter, and an analog that outputs a second analog signal by inputting and filtering the first analog signal that is output from the DA converter. A filter and a measuring unit that inputs and measures the second analog signal, and the filter coefficient of the first digital filter prevents the third digital signal from exceeding a full scale of the DA converter. A DA converter measuring apparatus, wherein the filter coefficient of the second digital filter is a filter coefficient for compensating for a delay in response due to a time constant of the analog filter. 7. A first comparison means for setting the filter coefficient of the second digital filter based on a comparison result between the AD conversion value of the second digital signal and the AD conversion value of the second analog signal. The DA converter measuring device according to claim 6, further comprising: 8. The first comparing means calculates a difference between the second digital signal and a value obtained by multiplying an AD conversion value of the second analog signal by the filter coefficient of the second digital filter. 8. The DA converter measuring device according to claim 7, wherein the filter coefficient of the second digital filter is set so as to be a predetermined value or less. 9. The apparatus further comprises second comparing means for setting the filter coefficient of the first digital filter based on a comparison result of the third digital signal and a full scale value of the DA converter. The DA converter measuring apparatus according to claim 6, wherein the measuring apparatus is a DA converter. 10. The second comparing means sets the filter coefficient of the first digital filter so that a difference between the third digital signal and a full-scale value of the DA converter becomes a predetermined value or less. The DA converter measuring device according to claim 9, wherein the setting is performed.