JPH04372874A - Apparatus for measuring distortion rate - Google Patents

Abstract

PURPOSE:To achieve a decrease in cost and to enhance measuring accuracy without requiring high accuracy in the attenuation quantity of a variable attenuator and the gain of a variable gain amplifier in a distortion rate measuring apparatus used in the measurement of acoustic machinery. CONSTITUTION:An A/D converter 10 alternately converting the output corresponding to an input signal level and the output corresponding to a distortion signal level to digital values is provided and a D/A converter 13 controlling the reference voltage terminal of the A/D converter 10 is provided. An electrically erasable read only memory 12 for storing the correction data to the error caused by an input range and a measuring range is provided. By applying the correction data stored in the read only memory 12 to the D/A converter 13 when a distortion rate is measured to be displayed by subjecting the digital values converted by the A/D converter 10 to comparative operational processing by an operational processing display apparatus 11, the scaling of the A/D converter 10 is corrected.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a distortion rate measuring device used to measure the distortion rate, which is one of the indicators of fidelity in the amplification and transmission systems of audio equipment and radio equipment. It is.

0002

[Background Art] In recent years, digitalization has progressed in the field of audio equipment, making it possible to perform high-fidelity recording, playback, and transmission, and higher measurement accuracy is also required for distortion measurement devices that measure this. .

A conventional distortion rate measuring device will be explained below. FIG. 2 shows the configuration of a conventional distortion rate measuring device.

As shown in FIG. 2, a signal under test inputted to an input terminal 201 passes through a first variable attenuator 202 for setting the input range and a first variable gain amplifier 203, and is then subjected to detection for detecting the input signal level. 207 and the fundamental wave removal filter 204. The fundamental wave removal filter 204 is composed of a Wien bridge circuit, a twin T-type circuit, etc.
Removes only the fundamental frequency component of the signal under test and removes the distortion component,
That is, it outputs harmonic components and noise components included in the signal under test. The output of this distortion component passes through a second variable attenuator 205 for setting a measurement range and a second variable gain amplifier 206, and is input to a detector 208 for detecting the distortion signal level. The switch 209 connects the output of the detector 207 for detecting the input signal level and the detector 20 for detecting the distorted signal level.
8 are alternately selected and input to the A/D converter 210. The A/D converter 210 alternately converts the output of the input signal level detection detector 207 and the output of the distorted signal level detection detector 208, which are analog signals, into digital values and outputs the digital values. Note that the power supply Vref, which is a reference for scaling during conversion, is fixed. Arithmetic processing/display device 2
Reference numeral 11 has a function of comparing the two digital value data outputted from the A/D converter 210 and displaying the result of the calculation.

The configuration of the above conventional example will be explained in more detail below along with its operation. Input a signal to the input terminal 201, set the first variable attenuator 202 and the first variable gain amplifier 203 to have an appropriate input range,
Further, the second variable attenuator 205 and the second variable gain amplifier 206 are set to have an appropriate measurement range. As a result, the detector 20 for detecting the input signal level passes through the first variable attenuator 202 and the first variable gain amplifier 203.
7, an output corresponding to the input signal level is obtained, and the distorted signal level is output from the detector 208 for detecting the distorted signal level via the fundamental wave removal filter 204, the second variable attenuator 205, and the second variable gain amplifier 206. You can get output according to the By selecting these two outputs with the switch 209, they are alternately input to the A/D converter 210 and converted into digital values, the arithmetic processing/display device 211 calculates the ratio of the two outputs, and calculates the distortion factor. Displayed as a measured value. The distortion rate A measured here is expressed by (Equation 1).

[0006]

[Math 1]

[0007] Here, E0: Effective value of input signal D: Effective value of harmonics and noise e2 to eN: Effective value of second, third, ... Nth harmonic en:
Effective value of included noise

[0008]

SUMMARY OF THE INVENTION However, the conventional strain rate measuring device described above has the following problems.

(1) In the arithmetic processing/display device 211, when performing the ratio arithmetic processing of the above (Equation 1), the proportional coefficient when giving the effective value E0 of the input signal is set in the first variable attenuator 202. Ideal values are given as the attenuation amount and the gain set to the first variable gain amplifier 203, respectively. In addition, the proportional coefficient when giving the effective value D of harmonics and noise, which is distortion, is determined by the second variable attenuator 205.
the attenuation amount set to and the second variable gain amplifier 20
As the gain set to 6, each ideal value is given. Therefore, errors in the respective attenuation amounts and gains are compounded by various combinations of the attenuation amounts and gains, resulting in deterioration of measurement accuracy.

(2) The problem in item (1) above is that the variable attenuator 2
Although this problem can be solved by increasing the precision of the elements used in the variable gain amplifiers 203 and 206, it becomes very expensive. Also,
Adjustment using variable elements and the like also involves a lot of work.

The present invention solves these conventional problems, and improves measurement accuracy at low cost without requiring high precision in the attenuation amount of a variable attenuator and the gain of a variable gain amplifier. It is an object of the present invention to provide a distortion rate measuring device that can perform the following.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first variable means capable of manipulating attenuation and amplification according to the level of an input signal; a first wave detector for detecting the input signal level from the output of the first variable means; a fundamental wave removal filter for removing the fundamental wave component of the input signal to extract a distorted signal from the output of the first variable means; a second variable means that receives the output of the filter and can manipulate the amount of attenuation and amplification according to the level of the distorted signal; and a second detector that receives the output of the second variable means and detects the level of the distorted signal. a switch for selecting the outputs of the first and second detectors, an A/D converter for converting the outputs of the first and second detectors selected by the switch into digital values; A D/A converter that varies the reference voltage of the A/D converter, and an arithmetic process for comparing the distortion signal level digitized by the A/D converter and the input signal level to obtain a distortion factor. and a correction means for providing correction data to the D/A converter.

[0013]

[Operation] Therefore, according to the present invention, the input signal level is obtained from the detector for detecting the input signal level through the first variable means by inputting the signal under test, and the fundamental wave removal filter and the second variable means Outputs corresponding to the distortion signal level are obtained through the means, and these outputs are selected by the switch and converted into digital values by the A/D converter, and subjected to comparative calculation processing by the arithmetic processing means to measure the distortion factor. Ru. At this time, A
The scaling value during /D conversion is not fixed, that is,
Since the reference voltage of the A/D converter is not fixed, the correction data is given to the D/A converter from the correction means to correct the reference voltage for each range, and the attenuation amount of each variable attenuator and the variable gain amplifier are adjusted. Remove the gain error.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing a distortion rate measuring device according to an embodiment of the present invention. As shown in Figure 1,
The signal under test inputted to the input terminal 1 is passed through a first variable attenuator 2 and a first variable gain amplifier 3, which set the input range.
The signal is then input to a detector 7 for detecting the input signal level and a fundamental wave removal filter 4. The fundamental wave removal filter 4 removes only the fundamental frequency component of the signal under test and outputs distortion components, that is, harmonic components and noise components contained in the signal under test. The output of this distortion component passes through a second variable attenuator 5 for setting a measurement range and a second variable gain amplifier 6, and is input to a detector 8 for detecting the distortion signal level. The switch 9 alternately selects the output of the wave detector 7 for detecting the input signal level and the output of the wave detector 8 for detecting the distorted signal level and inputs them to the A/D converter 10. The A/D converter 10 alternately converts the output of the input signal level detecting detector 7 and the output of the distorted signal level detecting detector 8, which are analog signals, into digital values and outputs them, and outputs the digital values. 11. A reference voltage input terminal, which is a scaling terminal of the A/D converter 10, is connected to the output of the D/A converter 13,
The scaling value is configured to be voltage controlled. The arithmetic processing/display device 11 has a function of calculating a ratio between two input digital value data, displaying the calculation result as a measured value, and also has a function of creating correction data. The arithmetic processing/display device 11 includes an electrically erasable read-only memory 12 and a read/write control line (R/W).
, connected by an address bus and a data bus. Further, the data bus of the electrically erasable read-only memory 12 is connected to a data input terminal of the D/A converter 13.

The distortion rate measuring device constructed as described above will be explained in more detail below along with its operation.

The operation of the apparatus of the present invention can be divided into the following two operation modes. (1) Correction data writing operation mode (calibration mode) (2
) Correction data read operation mode (measurement mode) Correction data write operation mode applies voltage and distortion calibration signals to the device of the present invention, checks errors in each range of the device of the present invention, and writes correction data for this to the memory. This is the operating mode. In addition, the correction data read operation mode is an operation mode that measures the actual distortion factor, and reads correction data from the memory.
This is an operation mode in which measurements are performed while correcting the above errors. Each operation mode will be explained below.

(1) Correction data writing operation mode A calibration signal serving as a reference for the input level is input to input terminal 1, and the first
When the variable attenuator 2 and the first variable gain amplifier 3 are set to have an appropriate input range corresponding to the input level, the input signal is transmitted through the first variable attenuator 2 and the first variable gain amplifier 3. An output corresponding to the input signal level is obtained from the level detection detector 7. In addition, the second variable attenuator 5
, when the second variable gain amplifier 6 is set to an appropriate measurement range, the detection for detecting the distortion signal level is performed via the fundamental wave removal filter 4, the second variable attenuator 5, and the second gain amplifier 6. An output corresponding to the distortion signal level is obtained from the device 8. In addition, as the above-mentioned calibration signal, for example, when an input range of 1V and a measurement range of 0.1% exist in the device of the present invention, and this is to be calibrated, a two-signal mixed wave with a fundamental wave level of 1V and a harmonic level of 1mV is used. Use. And first,
By selecting the output of the detector 7 for detecting the input signal level with the switch 9, the output is converted into a digital value by the A/D converter 10 and applied to the arithmetic processing/display device 11. A
Since the reference voltage is controlled by the output voltage of the D/A converter 13, that is, the input data of the D/A converter 13, the output data of the /D converter 10 is controlled by the input calibration signal. It is possible to set the value to be a value corresponding to the input level of . The arithmetic processing/display device 11 sends input correction data to the D/A converter 13 so that the input data of the A/D converter 10 becomes a value corresponding to the input level of the input calibration signal, and The error related to the input range can be known by the operation. Next, by selecting the output of the detector 8 for detecting the distorted signal with the switch 9, the output is converted into a digital value by the A/D converter 10 and applied to the arithmetic processing/display device 11. A/D converter 10
Since the output data of is controlled by the input data of the D/A converter 13 as described above, it is possible to set it to a value corresponding to the distortion signal level of the input calibration signal. The arithmetic processing/display device 11 converts the input data of the A/D converter 10 into a value corresponding to the distortion signal level of the input calibration signal.
By this operation, it is possible to know the error related to the measurement range. The input correction data and distortion correction data thus obtained are each stored in separate addresses of the electrically erasable read-only memory 12.

Hereinafter, all the first variable attenuators 2 are sequentially
, a calibration signal is added to the combination of the first variable gain amplifier 3, the second variable attenuator 5, and the second variable gain amplifier 6 to create input correction data and distortion correction data, respectively, and the read-only memory 12 stored in separate addresses. Due to these operations, all the error information regarding the variable attenuators 2 and 5 and the variable gain amplifiers 3 and 6 is stored in the read-only memory 12. Therefore, by calling this information from the read-only memory 12 and using it, , errors during measurement can be corrected.

(2) Correction data read operation mode Input the signal under test to the input terminal 1, and select the first variable attenuator 2, the first
The variable gain amplifier 3 is set to have an appropriate input range, and the second variable attenuator 5 and second variable gain amplifier 6 are set to have an appropriate measurement range. As a result, an output corresponding to the input signal level is obtained from the detector 7 for detecting the input signal level via the first variable attenuator 2 and the first variable gain amplifier 3, and the fundamental wave removal filter 4
, a second variable attenuator 5, and a second variable gain amplifier 6, an output corresponding to the distorted signal level is obtained from the detector 8 for detecting the distorted signal level. By selecting these two outputs with the switch 9, they are alternately input to the A/D converter 10 and converted into digital values, and the arithmetic processing/display device 11 outputs the two outputs.
Find the ratio of the two outputs and display this as a measured value of distortion factor. Then, when performing A/D conversion alternately as described above,
The input correction data and distortion correction data of the input range and measurement range addresses stored in the electrically erasable read-only memory 12 in which the correction data is registered are read out alternately, and the input data of the D/A converter 13 is read out. By giving as follows, it is possible to manipulate the reference voltage of the A/D converter 10 and remove errors in each of the variable attenuators 2 and 5 and the variable gain amplifiers 3 and 6.

As described above, according to the above embodiment, by applying a calibration signal to the input terminal 1, the error of each input range and the error of each measurement range can be known, and the data for correcting the error for each range can be obtained. It can be stored in an electrically erasable read-only memory 12. Further, the scaling value at the time of A/D conversion is not fixed, that is, the reference voltage of the A/D converter 10 is not fixed, and the reference voltage is corrected for each range based on the correction data. Can be done. Therefore, individual correction data can be stored for each distortion measurement device, and the data can be rewritten by the distortion measurement device itself as necessary, without using special data rewriting equipment. It is. Furthermore, data will not be lost even if power is not supplied to the distortion factor measuring device.

[0022]

As explained above, according to the present invention, the input signal level is obtained from the detector for detecting the input signal level via the first variable means upon input of the signal under test, and the fundamental wave removal filter , outputs corresponding to the distortion signal level are obtained through the second variable means, these outputs are selected by a switch and converted into digital values by an A/D converter,
A comparison calculation process is performed by the calculation processing means, and the distortion rate is measured. At this time, the scaling value during A/D conversion is not fixed, that is, the reference voltage of the A/D converter is not fixed, and the
Correction data is supplied from the correction means to the /A converter to correct the reference voltage for each range, thereby making it possible to eliminate errors in the attenuation amount of each variable attenuator and the gain of the variable gain amplifier. Therefore, there is no need to improve the attenuation amount of the variable attenuator or the gain accuracy of the variable gain amplifier, and measurement accuracy can be improved at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing a distortion rate measuring device in an embodiment of the present invention.

[Figure 2] Schematic block diagram showing a conventional distortion rate measuring device

[Explanation of symbols]

1 Input terminal 2 First variable attenuator 3 First variable gain amplifier 4 Fundamental wave removal filter 5 Second variable attenuator 6 Second variable gain amplifier 7 Detector for input signal level detection 8 Distorted signal level detection Detector 9 Switch 10 A/D converter 11 Arithmetic processing/display device 12 Electrically erasable read-only memory 13
D/A converter

Claims (1)

[Claims] 1. A first variable means capable of manipulating attenuation and amplification according to the level of an input signal; and a first detector that detects the input signal level from the output of the first variable means. , a fundamental wave removal filter that removes the fundamental wave component of the input signal from the output of the first variable means to extract a distorted signal; and a fundamental wave removal filter that receives the output of the fundamental wave removal filter and adjusts the amount of attenuation and amplification according to the level of the distorted signal. a second variable means capable of manipulating the degree of distortion; a second detector that receives the output of the second variable means to detect the distortion signal level; and selects the outputs of the first and second detectors. a switch, an A/D converter that converts the outputs of the first and second detectors selected by the switch into digital values, and a D/A converter that varies the reference voltage of the A/D converter. a computation processing means for performing a computation process of comparing the distortion signal level digitized by the A/D converter and the input signal level to obtain a distortion rate; and a computation processing means for providing correction data to the D/A converter. Distortion rate measuring device equipped with.