JP3033652B2 - Line frequency characteristic measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measurement frequency and a number of times of measurement when digitally measuring a frequency characteristic of a line.

[0002]

2. Description of the Related Art A measurement configuration diagram for digitally measuring the frequency characteristics of a line will be described with reference to FIG. 1 is a sine wave generator, 2 is a circuit to be measured, and 3 is an instantaneous voltage measuring device. The instantaneous voltage measuring device 3 samples a voltage at a predetermined sampling frequency and measures an instantaneous voltage value at each sampling time, and obtains one sample value by one measurement. The number of measurements is determined separately, and sampling is continuously performed for the determined number of measurements, and sample values for the number of measurements are obtained.

A sine wave of a certain frequency is input from a sine wave generator 1 to a circuit under test 2, and its output is sampled by an instantaneous voltmeter 3 to measure the instantaneous value of the voltage. And 1
With respect to one measurement frequency, a predetermined number of instantaneous values of all measured voltages, that is, sums of squares of all sampled values are obtained, a ratio with respect to a reference value is obtained, and a frequency characteristic of the line at that frequency is obtained. Here, the reference value is the sum of squares of all sample values when the line under test 2 has no loss or gain at the measurement frequency.

[0004] At each frequency less than one half of the sampling frequency, measurement is performed according to FIG. 1 to determine the frequency characteristic of the circuit under test 2. When digitally measuring the frequency characteristics of a line, if the measurement frequency is an integer fraction of the sampling frequency, a measurement error increases due to a synchronization phenomenon described below.

Next, the synchronization phenomenon will be described with reference to FIG. Fig. 2 shows the case where the measurement frequency is 1/4 of the sampling frequency, and the sample points are at 4 points, 0 °, 90 °, 180 °, and 270 ° during 360 ° of one cycle of the measurement waveform. Is shown. For example, as shown in FIG. 2, when the noise / distortion is near the point of 90 °, the sampling frequency and the measurement frequency are synchronized 4: 1, so that the noise / distortion near the point of 90 ° is sampled every time. That is, even if the measurement is performed over a long period and over many periods, the measurement error does not decrease.

In order to avoid the synchronization phenomenon shown in FIG. 2, a frequency slightly higher (or lower) than an integer fraction of the sampling frequency is conventionally selected as the measurement frequency. For example, if the sampling frequency is 8 kHz and the band from about 300 Hz to 3000 Hz is 100
When measuring in Hz steps, the measurement frequency is 310, 410,
510, ..., 2910, 3010Hz, etc. When measurement is performed at a frequency slightly different from an integer fraction of the sampling frequency as in this series, as shown in FIG. 3, the period of the sample point is slightly different from the period of the measured waveform, and the sample phase shifts with time. Therefore, even if there is noise or distortion at a certain position on the measurement waveform, it is not sampled every time, and measurement is performed over several cycles to disperse the effects of noise and distortion and reduce measurement errors. be able to.

When measuring the frequency characteristics of a line by digital measurement, the output waveform of the circuit under test 2 is sampled by an instantaneous voltage measuring device 3 to measure the instantaneous value of the voltage, and the sum of squares of all sampled values is obtained. In addition to the problem of the synchronization phenomenon described above, there is a problem of duplication and truncation errors based on the relationship between the sampling frequency and the measurement frequency. The overlap / truncation error occurs when the frequency of the measured waveform does not become an integer.

Next, the duplication and truncation errors will be described with reference to FIGS. In FIG. 2, since the sampling frequency and the measurement frequency are synchronized in a four-to-one correspondence, there are four sample points in one cycle of the measurement waveform. Number becomes an integer and overlaps
No truncation error occurs. On the other hand, in FIG. 3, if the sampling frequency is 8 kHz and the measurement frequency is 2010 Hz, there are 800 sample points in 201 cycles of the measurement waveform. In this case, the measurement is performed by making the total number of samples a multiple of 800. The number of cycles of the waveform becomes an integer, and no duplication or truncation error occurs. Conversely, if the number of samples whose measured cycle number does not become an integer is measured, a fractional part of the cycle will appear, and this will be an overlap / truncation error.

In FIG. 3, at least 800 samples are required to avoid duplication / truncation errors. The large number of samples has the advantage that the effects of noise and distortion are dispersed and the measurement error due to the synchronization phenomenon is reduced, but the measurement time is lengthened and the sine wave is generated by storing the sine value in memory and reading it out. When the device 1 is configured, a large memory capacity is required.

If the measurement frequency in FIG. 3 is changed to 2020 Hz,
The number of sample points in the 101 measurement cycles is 400, reducing the required number of samples. However, assuming a measurement frequency sequence of 100 Hz steps, there is 1920 Hz in this sequence. 1920
Hz is not an integer fraction of the sampling frequency, but 6/25. This means that there are 25 sample points in 6 cycles of the measurement waveform, and even if 400 samples are obtained, the degree of reduction of the measurement error is the same as in the case of 25 samples. As described above, the rate at which the measurement error is reduced due to the influence of noise, distortion, and the like differs depending on the measurement frequency.

[0011]

When measuring the frequency characteristics of a line by digital measurement, as described above, the problem of the synchronization phenomenon and the problem of duplication and truncation errors are always common, and a method for unifying both of these problems is unified. Had not been found.

[0012]

In order to solve this problem, according to the present invention, fs is a sampling frequency, m and n.
Is a positive integer, and when k is an integer in the range of 2 ≦ k ≦ 2 ⁿ , the sine wave generator 1 generates a sine wave of the frequency series (2k−1) · fs / 2 ^{n + 2} , The output of the circuit under test 2 to which the output of the generator 1 is input is measured by the instantaneous voltage
Sampling is performed at the frequency fs continuously for ^{n + 2} times, and the instantaneous voltage is measured.

[0013]

Next, a method of measuring line frequency characteristics according to the present invention will be described. In the following description, k ₀ = 2k−1,
Description will be made on the assumption that n _P2 = 2 ^{n + 2} . The measurement frequency sequence according to the present invention has a sampling frequency f
The frequency obtained by dividing s by a power of 2 n _P2 is used as the base frequency f _B
And the frequency that is an odd multiple of the base frequency f _B is determined as the measurement frequency f
k.

When fk is represented by an equation, fk = k ₀ · fs
/ N _P2 = k ₀ · f _B. Since the sampling frequency fs is divided by a power of 2 n _P2 and multiplied by an odd number k ₀ , the measurement frequency fk does not become an integer fraction of the sampling frequency fs except for the base frequency f _B. Does not wake up. The frequency is low for the base frequency f _B ,
Since there are many sampling points between 360 degrees in one cycle of that frequency,
Unlike the case where the number of sample points is small as described in FIG. 2, the measurement error is reduced.

Next, the sample timing diagram further described in Figure 4 when measuring the frequency fk is the base frequency f _B. In FIG. 4, there are many sample points during one cycle of 360 degrees,
For example, there is noise / distortion near the 90-degree point, and even if the nearby sample points are affected, there are many other normal sample points. Therefore, the influence is dispersed as compared with FIG. decrease.

When n _P2 is increased, the base frequency f _B is reduced, and the frequency step of the series of measured frequencies fk is reduced. If the line under test 2 has a characteristic that changes abruptly with a change in frequency, it is necessary to make the frequency step of the series of the measurement frequency fk fine, and increase n _P2 .
The total number of measurements for one measurement frequency fk, ie, the total number of samples, is m times the power of 2 n _P2 that divides the sampling frequency fs. Measurement frequency fk, where k ₀ is an odd number
Is k ₀ · fs / n _P2 , so that k _{0 of the} measurement frequency fk
・ All samples will be included during m periods and will be duplicated.
No truncation error occurs.

M is an integer of 1 or more. By increasing the value of m, it is possible to further disperse the influence of asynchronous noise and distortion at both the sampling frequency fs and the measurement frequency fk.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of measuring the frequency characteristics of a line in a voice frequency band will be described. Audio frequency band is about 300Hz to 3400
Hz band, and the sampling frequency fs = 8 kHz. If n _P2 = 128 (n = 5), the base frequency f _B =
fs / n _P2 = 62.5 Hz.

The measurement frequency fk is an odd multiple of the base frequency 62.5 Hz, since the band is in the range of about 300Hz to 3400 Hz, in fk = k ₀ · f _B, if _{5 ≦ k 0 ≦ 55 (3} ≦ k ≦ 28), fk = 312.5, 437.5,..., 3312.5,
Obtain a measurement frequency sequence of 3437.5Hz. In this case, the step of the measurement frequency fk is 125 Hz. The number of measurements is an integer multiple of 128, which is about 1280.

The case where the sine wave generator 1 used in this example is constituted by a sine value table reference system will be described. The sine value table reference method uses a sine value in the range of 0 to 360 degrees as R
This is a method in which sine values are sequentially read from this table, registered as a table in an OM memory, and D / A converted to generate a sine wave. In some cases, only sine values in the range of 0 to 90 degrees are registered in a table to save memory capacity.

In this embodiment, the number of measurements is an integer multiple of 128, and at a base frequency f _B = 62.5 Hz, there are 128 sampling points during one cycle of 360 °. So the table
357.875 in steps from 0 degrees to 360 degrees / 128 = 2.8125 degrees
Prepare a sine value up to degrees. This table from 0 degrees to 1
Increasing the angle step by step, sampling frequency 8k
When read 128 points in Hz timing, sinusoidal wave of the base frequency f _B is obtained one cycle.

In order to obtain a frequency k ₀ times the base frequency f _B , the angle is sequentially increased from 0 degree in steps of k ₀ to 8 k
Read 128 points at Hz timing. As a result, a sine wave having a frequency k ₀ times the base frequency f _B is obtained for k ₀ periods. At this time, all the 128 sine values prepared in the table are read once. From this, it can be seen that when measuring the voltage by sampling in the instantaneous voltage measuring device 3 on the receiving side, the sample phase when sampling the measured waveform becomes the same every 128 samples.

Although FIG. 3 shows that the sample phase shifts with time, according to this embodiment, the phase returns to the original every 128 samples. This is every 128 samples when measuring at any measurement frequency fk, so by measuring over several cycles, the effect of dispersing the effects of noise, distortion, etc. will be the same when measuring at any measurement frequency. Become.

[0024]

According to the present invention, at all measurement frequencies except the base frequency, the measurement frequency does not become an integer fraction of the sampling frequency, so that the synchronization phenomenon can be avoided, and an overlap / truncation error occurs. Since the measurement is performed with the number of measurements not performed, the frequency characteristics of the line can be measured with a smaller measurement error.

[Brief description of the drawings]

FIG. 1 is a measurement configuration diagram for digitally measuring a frequency characteristic of a line.

FIG. 2 is a sample timing diagram in which a sampling frequency and a measurement frequency are synchronized.

FIG. 3 is a sample timing chart in which a sampling frequency and a measurement frequency are asynchronous.

FIG. 4 is a sample timing chart when a measurement frequency is a base frequency.

[Explanation of symbols]

 1 Sine wave generator 2 Circuit under test 3 Instantaneous voltage measuring instrument

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiichi Shibata 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Kazuhide Tokumaru 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo No. Within Nippon Telegraph and Telephone Corporation (72) Inventor Ronde Honest 5-10-27 Minamiazabu, Minato-ku, Tokyo Inside Anritsu Corporation (72) Inventor Eikichi Tanaka 4--19-19 Mejiro, Toshima-ku, Tokyo ( 72) Inventor Toshihiro Tamura 4-19-7 Kamata, Ota-ku, Tokyo Inside Ando Electric Co., Ltd. (72) Inventor Isao Ishikura 4-19-7 Kamata, Ota-ku, Tokyo Inside Ando Electric Co., Ltd. (56) References JP-A-1-235863 (JP, A) JP-A-63-247665 (JP, A) JP-B-60-10262 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 27/28 G01R 13/34 G01R 19/00 G01R 31/316

Claims (1)

(57) [Claims] When fs is a sampling frequency, m and n are positive integers, and k is an integer in the range of 2 ≦ k ≦ 2 ⁿ , the frequency series (2k−1) · fs / 2 ^{n + 2} A sine wave is generated from the sine wave generator (1), and the output of the circuit under test (2), to which the output of the sine wave generator (1) is input, is m · 2 ^{n + 2} by the instantaneous voltage measurement device (3). A line frequency characteristic measuring method in which sampling is performed at a frequency fs successively and an instantaneous voltage is measured.