JPS627283A - Link amplifier - Google Patents

Abstract

PURPOSE:To reduce distortion trouble by taking out cross modulation components from a TV signal to a pilot signal through a filter which allows the above components to pass a horizontal scanning frequency of the TV signal and integer multiple of the above frequency and also lowering the amplification degree at levels. CONSTITUTION:Signals included by the TV signal and non-modulated pilot signal enter in an input terminal 1 and is amplified by a line amplifier 8. The pilot signal receiving cross modulation is extracted by the first filter 18 and is amplified by a pilot signal amplifier 19 then envelope lines can be taken out after being detected by a detector 20. An output of the detector 20 permits one or plural components among frequency components of the horizontal scanning frequency and integer multiple of the frequency to pass the second filter 9 then develops detecting signals. The second filter 9 allows S/N of the detecting signals to improve. The detected signals are amplified by a detection amplifier 10 and detected signal levels are detected by a level detector 11. If the detecting signal levels go to abnormally hi the distortion is lightened by lowering amplification degree of the line amplifier 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a repeater amplifier used in a transmission system including a television signal, such as a CATV transmission system.

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, especially relay amplifiers, 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 problems 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 faults.

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 5 is configured as described above.

The operation of the relay amplifier configured as above will be described below. A downlink signal consisting of a downlink video signal and a pilot signal of a specific frequency added to check 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 amplifier 3. It is amplified by 3. The pilot signal amplified together with the downlink video signal is extracted by the first filter 18, detected by the DC detector 402, and the output level of the downlink 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. 56-33723, etc.) Problems to be Solved by the Invention However, in the above configuration, problems occur because the input to the line amplifier partially becomes excessive within the band due to disturbances in the in-band characteristics. distortion 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 relay amplifier of the present invention includes an unmodulated pilot signal in the transmission signal and controls one or more amplification degrees in the relay 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 second wave 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. This device includes a filter and a level detector that detects the level of the detection signal that has passed through the second filter.

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 it, it becomes possible to reduce distortion disturbances.

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, 10 is a detection signal amplifier, and 11 is a level detector, and these and the pilot signal amplification/detection section 21 constitute a distortion generation detection section 22. Further, 1 is an input terminal, 7 is an output terminal, and 8 is a line amplifier, thus configuring a unidirectional 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 = Ac
os at + B cos bt ・
The component corresponding to the so-called third-order distortion of "-■x3" is expressed by the following equation using the 0 equation.

x” = (Acos at+Bcos bt) '=
1/4 (A3cos 3at+B”cos
3bt) + 3/4 (A” B cos (2a
±b) t+AB2 cos (2b±a) t)+
3/4 (A3cos at+ B″cos
bt) + 3/2 (AB” cos at+
BA” cos bt)・・・・・・■ ■In the equation, the first term is the third harmonic component, the second term is the intermodulation component, the third term is the fundamental wave nonlinear component, and the fourth term is This 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, the video signal is s (t), and B -1+ s (t
) ・・・・・・■ A, a, and b are constants. Therefore, focusing on AB''cosat, which is a cross-modulation component, the formula 0 is expressed as follows.This indicates that the video signal component and its second-order distortion component appear in the pilot signal envelope of the line amplifier output. On the other hand, the video signal s(t) has very strong components at the horizontal scanning frequency and its integral multiples.Therefore, by detecting the pilot signal of the line amplifier output, we detect the horizontal scanning frequency and frequency components at its integral multiples. It is possible to detect the occurrence of distortion in the amplifier by detecting an increase in the level of the line amplifier.This also applies to the case where a plurality of television signals are input to the line amplifier.

In FIG. 1, a signal containing a television signal and an unmodulated pilot signal is input to an input terminal 1, and is amplified by a line amplifier 8. 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 20 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 mentioned above, the output of the detector 20 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 total increase detection operation.

FIGS. 2(a) to 2(C) show examples of frequency characteristics of such a second filter 9. However, in FIG. 2, fH indicates the horizontal scanning frequency.

The detection signal obtained in this way is sent 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, distortion is reduced by lowering the amplification degree of the line amplifier 8. It is desirable that the portion of the line amplifier 8 where the amplification degree can be varied is closer to the input side. The degree of amplification can be controlled by continuously decreasing the degree of amplification when the detected signal level exceeds a certain threshold value, or by controlling the degree of amplification to maintain the detected signal level at this threshold value. The amplification degree may be lowered stepwise so as not to exceed the threshold value.

As described above, according to this embodiment, the first filter 18 extracts the pilot signal cross-modulated by the distortion of the line amplifier 8, the detector 20 extracts the envelope of this pilot signal, and the horizontal scanning frequency and its integer. A second filter that passes one or more of the doubled frequency components.
By providing the filter 9 and the level detector 11, distortion disturbances can be accurately detected by detecting an increase in the level of cross-modulation components from the television signal to the pilot signal, and distortion can be detected by lowering the amplification degree of the line amplifier 8. Obstacles can be reduced.

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 occurrence detection section 22 similar to the configuration shown in FIG. Further, 1 is an input terminal, and 7 is an output terminal, which is the same as the configuration shown in FIG. 1st
The difference from the configuration shown in the figure is the pilot signal amplification and detection section 21.
A third filter 23 is connected to the output of the line amplifier 8, and this output and the output of the level detector 11 are combined in a control signal synthesizer 28 according to a suitable algorithm to control the amplification degree of the line amplifier 8. Note that the unidirectional relay amplifier 5 is configured as described above.

The operation of the relay amplifier configured as described above will be described below. The distortion reduction method is exactly the same as in the first embodiment, and when the distortion of the line amplifier 8 increases, the output of the level detector 11 increases and the amplification degree of the line amplifier 8 is reduced, thereby reducing the distortion. 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 line amplifier 8
The 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 generation reduction operation. For example, level detector 11
If the output 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 line amplifier 8 can be maintained at an appropriate level.

As described above, the third filter 23 and the control signal synthesizer 28
By providing a controller and controlling the amplification degree of the line amplifier 8, the pilot signal and the noloft signal amplification/detection section 21 can be used in common to perform the distortion generation reduction operation and the output level optimization operation.

In addition, in the first and second embodiments, if there are two or more line amplifiers such as bidirectional relay amplifiers, such as up and down lines, the line amplifier 8 may correspond to any one.
The distortion reduction and output level optimization operations may be performed on a plurality of line amplifiers as in these embodiments.

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 components of the line and monitoring their levels, it is possible to accurately detect distortion disturbances in the relay amplifier, and reduce the distortion disturbances by lowering the amplification degree of the line amplifier.

[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, 5...Relay amplifier,
7...Output terminal, 8...Line amplifier,
9... Second filter, 10... Detection signal amplifier, 11... Level detector, 18...
...First filter, 19...Pilot signal amplifier, 20...Detector, 21...Pilot signal amplification and detection section, 22...Distortion generation Detection section, 23...Third filter, 28...
Control signal synthesizer. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) In a relay amplifier for a transmission system that includes television signals, the transmission signal includes an unmodulated pilot signal and is connected to the output of a line amplifier that can control one or more amplification levels in the relay amplifier. a first filter that extracts the pilot signal cross-modulated due to the nonlinearity of the line amplifier; and a detector that can extract the envelope of the pilot signal that has passed through the first filter;
a second filter capable of passing one or more frequency components of the horizontal scanning frequency of the television signal being transmitted from the detector output signal and frequencies that are integral multiples thereof;
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 lowered to reduce the occurrence of distortion. Features: Relay amplifier. (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 3. The repeater amplifier according to claim 1, wherein the amplification degree of the line amplifier is controlled so that the DC component of the output is constant.