JPH0343590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention measures the amplitude-frequency characteristics of a system under test, such as a television line, using a waveform such as a multi-burst waveform in which n different frequencies are amplitude-modulated. The present invention relates to an amplitude frequency characteristic measuring device for use in the present invention.

Conventionally, when measuring the amplitude-frequency characteristics of a television line or the like (system under test) using a waveform in which n different frequencies are amplitude-modulated, such as the multi-burst waveform shown in FIG. 2a, for example, A multi-burst waveform with constant amplitude of each waveform is output to the system under test, and the multi-burst waveform output from the system under test is directly observed with an oscilloscope, and the amplitude frequency is determined by relative comparison of the amplitude of each burst waveform. I was looking for characteristics.

Additionally, in order to further improve measurement accuracy, the multiburst waveform was enlarged and the upper or lower peaks of each frequency waveform were compared relative to each other.

However, due to the influence of non-linear distortion of the multi-burst waveform via a television line etc., the average value of the superimposed sine wave of the multi-burst waveform fluctuates, compared to the average value of the regular superimposed sine wave. The amplitude of the waveform is often asymmetric;
This is particularly noticeable at high frequencies of several MHz or more. In such cases, the method of enlarging the waveforms and relatively comparing the peaks of each waveform in order to improve measurement accuracy has not been able to measure the amplitude frequency characteristics of the actual transmission line with high measurement accuracy.

Therefore, when observing such multi-burst waveforms with an oscilloscope, it is necessary to perform a relative comparison of all amplitudes of the waveforms, making it difficult to measure with high precision. In addition, when measuring automatically without direct observation, there is a method of envelope detection for each frequency, A-D conversion, and digital processing, but a detector with a different detection time constant for each frequency is used. , the circuit configuration becomes large-scale. Additionally, since the detector uses many active elements, it is susceptible to temperature changes.

This invention was made in view of the above problems, and involves receiving n burst waveforms having constant amplitudes and different frequencies through a system under test, and Convert the burst waveform into a full-wave rectified wave so that the frequency thereof is doubled, and detect n average value components proportional to the average value component of the amplitude of each of the full-wave rectified waves. The present invention provides an amplitude frequency characteristic measuring device that detects the amplitude frequency characteristic of the system under test from the level of the average value component. In addition,
The full-wave rectified wave has a waveform as shown by the solid line in FIG.

This invention will be explained below. FIG. 1 shows a block diagram of a first embodiment of the invention. In this figure, the waveform converter 1 receives a signal from the system under test, for example, a multi-burst waveform consisting of six different frequencies, and converts it into a full-wave rectified wave with twice the frequency of each waveform. It consists of separators 1a, 1b and waveform synthesizer 1c.

The waveform separators 1a and 1b each include a first clip circuit that detects a positive half-wave rectified wave from the multiburst waveform, and a second clip circuit that detects a negative half-wave rectified wave from the multiburst waveform. It is composed of.

The waveform synthesizer 1c is composed of a differential amplifier, etc., and receives and synthesizes each of the half-wave rectified waves separated into positive and negative by the waveform separators 1a and 1b, and generates frequency components twice the frequency, respectively. outputs a full-wave rectified wave with

The detector 2 is composed of a low-pass filter and the like, and detects six average value components proportional to the amplitude of each full-wave rectified wave from the output waveform of the waveform synthesizer 1c. The sampling holder 3 samples and holds the levels of the six average value components output from the detector 2, respectively.

The A/D converter 4 converts the signal held by the sampling holder 3 into a digital signal. The calculation device 5 receives the output of the A-D converter 4 and calculates the amplitude value of each of the multi-burst waveforms, thereby outputting the amplitude frequency characteristics of the system under test. The display 6 digitally displays the value of the amplitude frequency characteristic output from the arithmetic device 5.

Next, its operation will be explained.

A multi-burst waveform as shown in FIG. 2a is applied to the input terminal 7 from the system under test. The multiburst waveform has six different frequencies, each of which is amplitude modulated as shown in Figure 2b. This multi-burst waveform is transferred to a waveform separator 1a,
1b, the first clip circuit 1a and the second
The clip circuit 1b separates the polarity into positive polarity (FIG. 2c) and negative polarity (FIG. 2e) based on the average value A. FIG. 2d shows a separated one-frequency positive polarity half-wave rectified wave, and FIG. 2f shows a negative polarity half-wave rectified wave. The half-wave rectified waves (FIG. 2 c, e) separated into positive and negative waves by the waveform separators 1a and 1b are combined by the waveform synthesizer 1c, and are shown in FIG. 2g, each having a frequency component twice the frequency mentioned above. A full-wave rectified wave is output. FIG. 2h shows a full-wave rectified wave of low frequency l when passing through the low frequency range of the system under test, and the dotted line is the average value component. In addition, Fig. 2 j is different from Fig. 2 a due to the influence of nonlinear distortion in the high frequency range of lines, etc.
This shows the full-wave rectified wave when the waveform amplitude a of the high frequency m shown in Fig. 1 becomes asymmetrical.

The full-wave rectified waves (Fig. 2g) outputted from the waveform synthesizer 1c are sent to a detector 2 composed of a low-pass filter, and as shown in Fig. 2k, the full-wave rectified waves (Fig. Detect the average value components. In other words, if we consider a low-frequency full-wave rectified wave that is not affected by nonlinear distortion as shown in Figure 3, the expansion formula for this waveform is e(ωt)/E=2/π+4/ π [1/3c
os2ωt−1/15cos4ωt+…+(−1) ⁿ⁺¹ /4n ² −1cos
2nωt＋…]. Therefore, when the signal is passed through a low-pass filter with a cutoff of 2ωt, only the 2/π component remains, and the output signal of the low-pass filter becomes e(ωt)=2/πE. This indicates the average of the sine wave, so the low-pass filter only needs to be able to remove the lowest frequency 2ωt component. The same is true for asymmetric full-wave rectified waves in the high range. In this way, the peak values of the six average value components detected by the detector 2 faithfully represent the amplitude frequency characteristics of the system under test. The levels of the six average value components detected by the detector 2 are digitally processed by a sampling holder 3, an A/D converter 4, and an arithmetic unit 5. The amplitude values of the digitally processed multi-burst waveforms, that is, the amplitude frequency characteristics of the system under test are digitally displayed on the display 6.

FIG. 4 shows a block diagram of a second embodiment of the invention, in which numerals 1, 2, and 7 are the same as in FIG. 1.

Six average value components detected by detector 2 (second
The level in Fig. k) is directly observed using a direct observation device 8 such as an oscilloscope, and the relative deviation is measured.

As explained above, the present invention enables n burst waveforms having constant amplitude and different frequencies to be
a waveform converter for converting the n burst waveforms received via the system under test and included in the received signal into full-wave rectified waves so that the frequency thereof is doubled; and the converter and a detector for detecting n average value components proportional to the amplitude of each of the full-wave rectified waves from the output waveform of the full-wave rectified wave. frequency deviation can be read with high precision. Furthermore, when automatically measuring by digital processing, it is only necessary to take in one sampling data for each frequency, which simplifies the circuit configuration. Furthermore, since there are fewer sampling points, it has the advantage of shortening the measurement time.

Note that the waveform converter and the detector are not limited to the above-described embodiments, and can be implemented with various modifications without changing the gist.

[Brief explanation of drawings]

FIG. 1 is a first embodiment of this invention, FIG. 2 is a waveform diagram for explaining an embodiment of this invention, FIG. 3 is a full wave waveform diagram, and FIG. 4 is a second embodiment of this invention. It is. 1 is a waveform converter, 2 is a detector, 3 is a sampling holder, 4 is an AD converter, 5 is an arithmetic unit, and 6 is a display.

Claims (1)

[Claims] 1. n burst waveforms having constant amplitude and different frequencies are received via a system under test, and the frequencies of the n burst waveforms included in the received signal are respectively a waveform converter for converting into a full-wave rectified wave so as to double the amplitude; n average value components proportional to the average value component of the amplitude of each of the full-wave rectified waves from the output waveform of the waveform converter; An amplitude frequency characteristic measuring device comprising: a detector for detecting the n average value components, and detecting the amplitude frequency characteristic of the system to be measured from the level of the n average value components. 2. The waveform converter includes a waveform separator for separating the amplitude of the received signal into positive and negative polarities, and receives each half-wave rectified wave separated into positive and negative polarities by the waveform separator and output. The amplitude frequency characteristic measuring device according to claim 1, further comprising a waveform synthesizer for synthesizing and outputting the full-wave rectified wave. 3. Receive n burst waveforms with constant amplitude and different frequencies through the system under test, and divide the entire waveform so that the frequency of each of the n burst waveforms included in this received signal is doubled. a waveform converter for converting a full-wave rectified wave into a rectified wave; and a detection for detecting n average value components proportional to the average value component of the amplitude of each of the full-wave rectified waves from the output waveform of the waveform converter; a sampling holder for sampling and holding the levels of the n average value components output from the detector; and an A-D conversion for converting the signal held in the holder into a digital signal. With vessel;
An amplitude frequency characteristic measuring device comprising: an arithmetic device for receiving the output of the A-D converter and calculating an amplitude frequency characteristic of the system under test. 4. The waveform converter includes a waveform separator for separating the amplitude of the received signal into positive and negative polarities, and receives each half-wave rectified wave separated into positive and negative polarities by the waveform separator and output. 4. The amplitude frequency characteristic measuring device according to claim 3, further comprising a waveform synthesizer for synthesizing and outputting the full-wave rectified wave.