JPH01251827A - Circuit monitoring circuit - Google Patents

Abstract

PURPOSE:To realize the stable and accurate circuit monitor with compensation of the influence of the noise level fluctuation by changing the gain of the 2nd DC amplifier of a noise deciding circuit or the noise deciding level based on the output of a pilot signal deciding circuit. CONSTITUTION:The gain of a gain variable DC amplifier 9 or the deciding level of a 2nd deciding circuit 10 is changed by the output of a 1st deciding circuit 5 so that these gain and level can follow even in case of the level fluctuation of a pilot signal or the interruption of this signal. Thus the influence of the noise level fluctuation can be compensated. In other words, the pilot signal level and the noise level are decided by the circuits 5 and 10 respectively. Then the gain of the amplifier 9 is controlled by the output of the circuit 5 so that the fluctuation characteristics of the noise detecting level caused by the pilot signal level can be compensated. As a result, an effective noise level can be detected even when the pilot signal level has fluctuation or is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a line monitoring circuit for detecting the pilot signal and noise level of a communication line.

[Conventional technology]

In monitoring systems for communication lines that transmit TV signals, multiplex telephone signals, etc. as baseband signals, a predetermined pilot signal is usually transmitted, and the receiver detects its level to determine the quality of the communication line. The quality of the communication line is determined by detecting the noise level within the band. Furthermore, the frequency band for noise detection is set to be the same as the frequency of the pilot signal, thereby making effective use of the baseband frequency band and reducing costs.

A block diagram of a conventional line monitoring circuit in such a system is shown in FIG. In Fig. 2, 1 is a bandpass filter;
2 is a first detector, 3 is a first low-pass filter, 4 is a first DC amplifier, 5 is a first judgment circuit, 6 is a high-pass filter, 7
The second detector 28 is a second low-pass filter, and 11 is a second DC amplifier.

10 is a second determination circuit.

In this circuit, a pilot signal transmitted through a communication line is extracted by a bandpass filter 1 and detected by a first detector 2, and the DC component of the detected output is sent to a first low-pass filter 3. The signal is taken out by the first DC amplifier 4 and amplified by the first DC amplifier 4, and the first judgment circuit 5 judges whether the pilot signal level is good or bad. On the other hand, the AC component of the detection output of the first detector 2 is extracted by the high-pass filter 6, further detected by the second detector 7, and the DC component of the detection output is extracted by the second low-pass filter. second DC amplifier 11
The second determination circuit 10 determines whether the line noise level is good or bad.

[Problem to be solved by the invention]

However, in conventional circuits, if the level of the pilot signal fluctuates or is cut off due to some reason (for example, a failure in the transmitting pilot signal oscillator or fluctuation in transmission line gain), an example of this is shown in Figure 3. Thus, the detected noise level varies by several dB, making it impossible to stably and accurately detect the noise level.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a line monitoring circuit that can solve these problems and perform effective noise level detection even when the pilot signal level fluctuates or is interrupted.

[Means to solve the problem]

The line monitoring circuit of the present invention includes a bandpass filter, a first detector,
A first low-pass filter and a first DC amplifier.

A first determination circuit determines the quality of the pilot signal level, and the first detector and the second detector.

A second low-pass filter, a second DC amplifier, and a second determination circuit determine the quality of the noise level, and the output of the first determination circuit determines the gain of the second DC amplifier or the second determination circuit. The configuration is such that the determination level of the second determination circuit is changed.

[Operation] In the above-described configuration, when the gain of the second DC amplifier or the judgment level of the second judgment circuit is changed by the output of the first judgment circuit, and the level of the pilot signal fluctuates or is cut off. This is also followed to compensate for the effects of noise level fluctuations.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, 1 is a bandpass filter, 2 is a first detector, 3 is a first low-pass filter, 4 is a first DC amplifier, 5 is a first judgment circuit, and 6 is a high-frequency filter. 7 is a second wave detector, 8 is a second low-pass filter, and 10 is a second determination circuit, which is the same as that shown in FIG. Also, in Figure 1, 9
is a second DC amplifier whose gain can be changed by a control voltage.

In this circuit, the first determination circuit 5 determines the pilot signal level, and the second determination circuit 10 determines the noise level, but the gain of the second DC amplifier 9 is determined by the output of the first determination circuit 5. Control is thereby performed to compensate for the fluctuation characteristics of the noise detection level due to the pilot signal level shown in FIG.

In the example shown in Figure 3, the pilot signal is at standard level (OdB
), when the pilot signal is cut off (-ωdB), the noise detection level decreases by about 7 dBM. Therefore, in this case, if the first determination circuit 5 determines that the pilot signal is disconnected, by increasing the gain of the second DC amplifier 9 by approximately 7 dB using the output thereof, the noise detection level due to the pilot signal can be reduced. The effects of fluctuations can be compensated for.

It should be noted that, in the present invention, even if the judgment level of the second judgment circuit 10 is changed by the output of the first judgment circuit 5, it is possible to compensate for the influence of fluctuations in the noise level due to the pilot signal in the same way as the circuit shown in FIG. it is obvious.

〔Effect of the invention〕

As explained above, the present invention is capable of detecting when the pilot signal decreases or is cut off by changing the gain of the second DC amplifier of the noise determining circuit or the noise determination level based on the output of the pilot signal determining circuit. However, it can follow this and perform stable and accurate line monitoring that compensates for the effects of noise level fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a line monitoring circuit according to the present invention, and FIG.
The figure is a block diagram of a conventional circuit, and FIG. 3 is a characteristic diagram showing the correlation between the pilot signal level and the noise detection level. 1... Bandpass filter, 2... First detector, 3...
First low-pass filter, 4... First DC amplifier, 5...
・First judgment circuit, 6...High-pass filter, 7...Second
Detector, 8... Second low-pass filter, 9... Second DC amplifier with variable gain, 10... Second judgment circuit, 1
1...Second DC amplifier. All π4 Samurai Mawarishi A'l Le

Claims (1)

[Claims] 1. A bandpass filter that extracts the pilot signal included in the received signal, a first detector that detects this, a first low-pass filter that extracts the DC component of the detected output, and a first DC amplifier for amplification, a first determination circuit for determining the quality of the pilot signal level based on its output, and a high-pass filter for extracting the AC component of the detection output of the first detector; A second wave detector detects this, a second low-pass filter extracts the DC component of the detected output, a second DC amplifier amplifies this, and the bandpass filter uses the output thereof. and a second determination circuit for determining whether the noise level that has passed is good or bad, and the gain of the second DC amplifier or the determination level of the second determination circuit is changed based on the output of the first determination circuit. A line monitoring circuit characterized in that it is configured as follows.