JPS6225595A - Repeating amplifier - Google Patents

Abstract

PURPOSE:To detect a distortion fault of a repeating amplifier, and to reduce the distortion fault by lowering an amplification degree of a line amplifier by fetching a cross modulation component to a pilot signal from a television signal which is being transmitted, and monitoring its level. CONSTITUTION:To an input terminal 1, a signal containing a pilot signal of non-modulation is inputted as a transmission signal together with a television signal, and amplified by a down-line amplifier 3. The first filter 18 for extracting the pilot signal which is brought to a cross modulation by a distortion of the down-line amplifier 3, a detector 20 for fetching an envelope of this pilot signal, the second filter 9 for making one or plural components in a horizontal scanning frequency and a frequency component of its integer multiple pass through, and a level detector 11 are provided, by which a distortion fault is detected exactly by detecting a level increase of a cross modulation component to the pilot signal from the television signal, the distortion fault is reduced by lowering an amplification degree of the down-line amplifier 3, an abnormality informing signal is sent back to a head end, and in which repeating amplifier the distortion has been generated is recognized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a technique for reducing failures occurring in repeater amplifiers used in transmission systems including television signals such as CATV transmission systems.

Conventional CATV has a tendency to become multichannel in order to provide not only simple retransmission but also a variety of services such as independent broadcasting and paid program service (Pay TV).

Accordingly, transmission lines and relay amplifiers that separate the transmission line are required to have particularly high performance. Many of the major factors that reduce the reliability of such transmission systems are related to repeater amplifiers that include active elements.

One of the faults associated with relay amplifiers is the occurrence of distortion due to excessive signal levels. It is very useful to detect the occurrence of such distortion faults and to alleviate the fault.

Conventionally, the method for detecting such distortion disturbances is to simultaneously transmit a pilot signal of a specific frequency and detect the distortion disturbance indirectly by knowing the level of this pilot signal at the input or output of a relay amplifier. It had been taken.

An example of such a conventional repeater amplifier will be described below with reference to the drawings.

FIG. 4 shows a configuration diagram of a conventional repeater amplifier.

In Fig. 4, 1 is an input terminal, 2 is an upper and lower signal separation filter, 3 is a down line amplifier, 4 is an up line amplifier, 6 is an upper and lower signal separation filter, 7 is an output terminal, 18 is a first filter, and 402 is a DC Detector, 17 is a modulation signal generator,
16 is a modulator, 15 is a carrier wave oscillator, 14 is a multiplexer,
The relay amplifier 6 is configured as described above.

The operation of the relay amplifier configured as above will be described below. A lower signal consisting of a downlink video signal and a pilot signal of a specific frequency added to the device for checking the operating state of the downlink amplifier 3 enters from the input terminal 1, is separated by the upper and lower signal separation filter 2, and is sent to the downlink. It is amplified by amplifier 3. The pilot signal amplified together with the lower line video signal is extracted by the first filter 18, detected by the DC detector 402, and the output level of the lower line amplifier 3 is measured. Therefore, if the level of this test signal appears to be abnormally high, it can be predicted that distortion has occurred. In this example, the return carrier wave obtained from the carrier wave oscillator 15 is transmitted to the modulator 1 using a signal obtained from the modulation signal generator 17 whose frequency etc. can be changed according to this level value.
6 and returns it to the head end as an upstream signal, it is possible to monitor the generation of distortion due to an excessive input level of the relay amplifier at the head end.

(Japanese Unexamined Patent Publication No. 50-33723, etc.) Problems to be Solved by the Invention However, in the above configuration, the input to the line amplifier becomes partially excessive within the band due to the disturbance K of the in-band characteristics. The distortion that occurs may not be detected. This is because only the frequency of the pilot signal is monitored.

In view of the above-mentioned problems, the present invention aims to directly and accurately detect the occurrence of distortion during actual video transmission services, and to reduce distortion disturbances, instead of using indirect methods such as level monitoring. The present invention provides a repeater amplifier that can be used.

Means for Solving the Problems In order to solve the above problems, the repeater amplifier of the present invention includes an unmodulated pilot signal in the transmission signal, and controls one or more amplification degrees in the repeater amplifier. A first pilot signal connected to the output of a line amplifier capable of
a filter, a detector capable of extracting the envelope of the pilot signal, and a detector capable of passing one or more frequency components of the horizontal scanning frequency of the transmitted television signal and frequencies that are integral multiples thereof. The apparatus is equipped with a second filter, a level detector that detects the level of the detection signal that has passed through the second filter, and means for returning a signal indicating the state of occurrence of distortion as an upstream transmission signal.

Effect of the Invention With the above-described configuration, the present invention extracts the cross-modulation component from the transmitted television signal to the pilot signal, and by monitoring its level, accurately detects distortion disturbances in the repeater amplifier and adjusts the amplification degree of the line amplifier. By lowering the distortion, it becomes possible to reduce the distortion disturbance and recognize the relay amplifier where the distortion is occurring at the head end.

Embodiment Hereinafter, a relay amplifier according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of a relay amplifier according to a first embodiment of the present invention. In FIG. 1, 18 is a first filter, 19 is a pilot signal amplifier, and 20 is a detector, and these constitute a pilot signal amplification and detection section 21. Further, 9 is a second filter, 1o is a detection signal amplifier, and 11 is a level detector, and these and the pilot signal amplification/detection section 21 constitute a distortion increase detection section 22. Furthermore, 1 is an input terminal, 2 and 6 are upper and lower signal separation filters, 3 is a down line amplifier, 4 is an up line amplifier, 1
4 is a multiplexer, 15 is a carrier wave oscillator, 16 is a modulator, 17
1 is a modulation signal generator, 7 is an output terminal, and the above constitutes a bidirectional relay amplifier 5.

Regarding the relay amplifier configured as above, the following is the first section.
The operation will be explained using the diagram and FIG.

When a signal passes through a line amplifier that is generally not linear, the output contains more than the input signal components.

Now, when the input signal X is expressed by the following formula, X = person cos
at -1-B cos bt ・----
---■ The component corresponding to the so-called third-order distortion of X is expressed by the following formula using the formula (■).

x = (A cos at -4-B cos bt
)'= 1/4 (Acos 3at+B cos
3bt) + 3/4 (person Bcos (2a±b) at
−)−B cos bt )+3/2 (A B2c
os at -) 8 people 2cos bt) ・-
・・・-・■■On the right side of the equation, the first term is the third harmonic component, the second term is the intermodulation component, the third term is the fundamental nonlinear component,
The fourth term is a cross-modulation component. Furthermore, in the equation (2), if the first term is an unmodulated pilot signal and the second term is a television signal, then the video signal is s (t), and B = 1-) s (t)... ...
It can be expressed as ・・・・・・■. Person, a, and b are constants. Therefore, focusing on A B2cos at, which is a cross-modulation component, using equation 0, A B2cos at = M(5(t) + 25(t)+1) cos at
・・・・・・・・・■. This means that the pilot signal envelope of the line amplifier output includes the video signal component and its second component.
This shows that a second-order distortion component appears. On the other hand, the video signal s
(t) has very strong components at the horizontal scanning frequency and frequencies that are integral multiples thereof. Therefore, by detecting the pilot signal output from the line amplifier and detecting an increase in the level of the horizontal scanning frequency and its integral multiple frequency components, it is possible to detect the occurrence of distortion in the amplifier. Note that this also applies when a plurality of television signals are input to the line amplifier.

In FIG. 1, a signal containing an unmodulated pilot signal together with a television signal is input to an input terminal 1 as a down transmission signal, and is amplified by a down line amplifier 3. The pilot signal that has undergone cross modulation in the output signal is extracted by the first filter 18, amplified by the pilot signal amplifier 19, and detected by the detector 20. The detector 2o may be of any type as long as it can extract the envelope, such as a half-wave rectifier type, a full-wave rectifier type, a square law detector, or a synchronous detector using a PLL or the like.

As described above, the output of the detector 2o includes the horizontal scanning frequency and frequency components that are integral multiples thereof, and the second filter 9 passes one or more of these components. . If the output signal of the second filter 9 is called a detection signal, the second filter 9 serves to improve the S/N ratio of the detection signal and stabilize the distortion increase detection operation 6. FIGS. 2(a) to 2(C) show examples of frequency characteristics of such a second filter 9. FIG. However, in Fig. 2, fH indicates the horizontal scanning frequency. The detection signal obtained in this way is transmitted to the detection signal amplifier 1.
After being amplified by 0, the level detector 11 detects the detection signal level. If the detection signal level becomes abnormally high, the distortion is reduced by lowering the amplification degree of the downlink amplifier 3. Note that it is desirable that the portion of the downlink amplifier 3 where the amplification degree can be varied be closer to the input side. The amplification degree may be controlled such that when the detection signal level exceeds a certain threshold, the amplification degree may be continuously lowered to maintain the detection signal level at this threshold;
The amplification degree may be lowered stepwise so as not to exceed this threshold value.

When the distortion increase abnormality is detected in this way and the distortion reduction operation is being performed, the modulation signal generator 17 generates a signal indicating that the condition is present, and the carrier wave oscillator 16 generates a carrier wave. is modulated by a modulator 16. The abnormality notification signal thus obtained is sent back to the head end as an upstream transmission signal using the multiplexer 1.4. The abnormality notification signal may be one that changes in phase, amplitude, or frequency, such as one that simply turns on and off depending on whether it is abnormal or normal. Alternatively, the signal generated by the modulation signal generator 17 may be a digital signal constituting a certain code. The frequency of the carrier wave obtained by the carrier wave oscillator 15 differs for each relay amplifier, and the head end can recognize which relay amplifier the abnormality notification signal is from.

As described above, according to this embodiment, the first
A filter 18, a detector 20 for extracting the envelope of this pilot signal, a second filter 9 for passing one or more components of the horizontal scanning frequency and its integral multiples, and a level detector 11 are provided. The system accurately detects distortion disturbances by detecting an increase in the level of cross-modulation components from the television signal to the pilot signal.
Distortion disturbances are reduced by lowering the amplification degree of the downlink amplifier 3, and the abnormality notification signal is sent back to the headend as an uplink transmission signal, thereby recognizing which relay amplifier is causing distortion at the headend. be able to.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of a relay amplifier showing a second embodiment of the present invention. In the figure, 21 is a pilot signal amplification and detection section, 9 is a second filter, 10 is a detection signal amplifier,
Reference numeral 11 denotes a level detector, which constitutes a distortion increase detection section 22 similar to the configuration shown in FIG.

Further, 1 is an input terminal, 7 is an output terminal, 2 and 6 are upper and lower signal separation filters, 3 is a lower 9 line amplifier, 4 is an up line amplifier, 14 is a multiplexer, 16 is a carrier wave oscillator, 16 is a modulator, Reference numeral 17 denotes a modulation signal generator, which has the same structure as that shown in FIG. The difference from the configuration shown in FIG. 1 is that a third filter 23 is provided which is connected to the output of the pilot signal amplification/detection section 21, and this output and the output of the level detector 11 are combined by a control signal synthesizer 28 according to an appropriate algorithm. and to control the amplification degree of the downlink amplifier 3.

Note that the bidirectional relay amplifier 6 is configured as described above.

The operation of the relay amplifier configured as described above will be described below. The method for reducing distortion is exactly the same as in the first embodiment. When the distortion of the downlink amplifier 3 increases, the output of the level detector 11 increases and the amplification degree of the downlink amplifier 3 is reduced, thereby reducing the distortion. do. The difference from the first embodiment is that the DC component of the output of the pilot signal amplification/detection section 21 is extracted by the third filter 23, and when no distortion is detected, the downlink amplifier is used to maintain this level constant. This point is to control the degree of amplification.

The control signal synthesizer 28 has the role of determining whether to perform an output level optimization operation or a distortion reduction operation. For example, if the output of the level detector 11 does not exceed a certain threshold value, it is assumed that no distortion has occurred, and an output level optimization operation is performed; conversely, if the output exceeds a certain threshold value, a distortion reduction operation is performed.

This is realized by the control signal synthesizer 28 determining which output of the third filter 23 or the level detector 11 is used to control the amplification degree of the line amplifier, based on the output of the level detector 11. This function can also be realized by adding together the outputs of the third filter 23 and the level detector 11. In this way, when no distortion occurs, the output level of the downlink amplifier 3 can be maintained at an appropriate level.

The method of returning the abnormality notification signal is the same as in the first embodiment, but it also has an abnormality notification signal corresponding to an abnormality in the output level of the third filter 23 and an abnormality in the output level of the down-line amplifier 3, It may be possible to monitor not only the occurrence of distortion but also output level abnormalities at the head end.

As described above, the third filter 23 and the control signal synthesizer 28
By providing this and being able to control the amplification degree of the downlink amplifier 3, the pilot signal and the pilot signal amplification/detection section 21 can be used in common to perform distortion reduction operations and output level optimization operations.

In addition, in the first and second embodiments, when a television signal is included in upstream transmission, the upstream line amplifier 4 is subjected to distortion detection, distortion reduction, output level optimization, and similar processes to the downstream line amplifier 3. It may also be one that performs an abnormality notification operation. Further, it is also possible to have a plurality of distortion increase detection sections 22 and perform these operations for a plurality of line amplifiers. Although the multiplexer 14 is located on the output side of the uplink amplifier 4, it may also be located on the input side. In addition, a command is sent from the head end as a downstream transmission signal, and the relay amplifier further has a receiver that can receive this command.
The status of each relay amplifier may be known at the head end by exchanging commands between each relay amplifier and the head end. However, in this case, the carrier wave frequency obtained by the carrier wave oscillator 16 of each relay amplifier may be the same by using a method such as polling, or
The carrier wave frequency of the downlink command from the head end may also be the same.

Effects of the Invention As described above, the present invention provides a transmission signal which includes an unmodulated pilot signal in a transmission signal and which is connected to the output of a line amplifier capable of controlling one or more amplification degrees in a repeater amplifier. a first filter that extracts a pilot signal that has been cross-modulated due to the nonlinearity of the line amplifier; a detector that can extract the envelope of this pilot signal; A second filter capable of passing one or more frequency components among the frequencies, and a level detector that detects the level of the detection signal that has passed the second filter, from the transmitted television signal to the pilot signal. By extracting the cross-modulation component of the signal and monitoring its level, it is possible to accurately detect distortion disturbances in the relay amplifier, reduce distortion disturbances by lowering the amplification degree of the line amplifier, and use the signal as an uplink transmission signal. By having a means for notifying an abnormality, it is possible to recognize a relay amplifier in which distortion is occurring at the head end.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a relay amplifier in a first embodiment of the present invention, FIG. 2 is a diagram showing an example of frequency characteristics of the second filter 9, and FIG. 3 is a diagram of a relay amplifier in a second embodiment of the present invention. FIG. 4 is a circuit diagram of a conventional relay amplifier. 1...Input terminal, 2...Upper and lower signal separation filter, 3...Down line amplifier, 4...
...up line amplifier, 5...relay amplifier, 6.
...Upper and lower signal separation filter, 7...Output terminal, 9...Second filter, 10...
Detection signal amplifier, 11...Level detector, 14
...... Multiplexer, 15... Carrier wave oscillator,
16...Modulator, 17...Modulation signal generator, 18...First filter, 19...
...Pilot signal amplifier, 20...Detector,
21...Pilot signal amplification and detection section, 22...
. . . Distortion increase detection section, 23 . . . Third filter, 28 . . . Control signal synthesizer. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure (fH2chis 3fs 4f
s N wave number (b) fs 2s 3ht
4fH frequency (C)

Claims (4)

[Claims] (1) In a relay amplifier for a two-way transmission system that includes television signals on either or both the upstream and downstream sides, the transmission signal includes an unmodulated pilot signal to control one or more amplification levels within the relay amplifier. a first filter connected to the output of a line amplifier capable of extracting the pilot signal cross-modulated due to nonlinearity of the line amplifier; and extracting an envelope of the pilot signal that has passed through the first filter. a second filter capable of passing one or more frequency components among the horizontal scanning frequency of the television signal being transmitted and frequencies that are integral multiples thereof, from among the output signals of the detector; A level detector is provided to detect the level of the detection signal that has passed through the second filter, and when the level of the detection signal increases, the amplification degree of the line amplifier is reduced to reduce the occurrence of distortion, and A repeater amplifier comprising means for returning a signal indicating an increase in the level of the detection signal as an upstream transmission signal, and capable of recognizing a repeater amplifier in which distortion is occurring at the head end. (2) The repeater amplifier according to claim (1), wherein the transmission system is a CATV transmission system. (3) Furthermore, it has a third filter connected to the output of the detector that can pass only the DC component of the signal after passing through the detector, and when no distortion is detected, the third filter The repeater amplifier according to claim 1 or 2, wherein the amplification degree of the line amplifier is controlled so that the DC component of the output is constant. (4) Furthermore, even if the DC component of the output of the third filter is below or above the specified value as an upstream transmission signal, the head The repeater amplifier according to claim 3, wherein a repeater amplifier having an abnormal output level can be recognized at the end.