JP2002217661A - Relay amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a relay amplifier for changing the output into a prescribed level easily. SOLUTION: A pilot signal is branched at a branching unit 12, and on the basis of the signal, an amplifier 10 is operated under feed-back control by an AGC circuit 20 in a relay amplifier in a network system. An attenuator 14 and a switch unit 15 are provided between the branching unit of the feed back circuit and the AGC circuit 20. When the output should be changed, the switch unit is shifted into variable paths with different attenuation ratios. The amplifier 10 is controlled by the AGC circuit so that the pilot voltage doesn't vary. Then, the output of the relay amplifier is adjusted according to the control. As an example, when the pilot voltage is decreased through a prescribed attenuation path, the output of the amplifier is increased. On the contrary when changing to the branching path 13, the output is decreased. In this case the attenuation ratio (resistance value) of the attenuator 14 is set corresponding to variable output levels previously. Only by changing the switch unit 15, the prescribed level can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay amplifier for a network system which enables easy output change. In particular, the present invention relates to a relay amplifier capable of adjusting the output of an amplifier by simply inserting an attenuator and a switch device into a feedback circuit and switching the switch device. Also, when the signal level in the system is raised as a whole, or when the signal level in a range downstream of a certain relay amplifier is raised as a whole, the adjustment by the relay amplifier is facilitated. INDUSTRIAL APPLICABILITY The present invention is applicable to a CATV relay amplifier that amplifies and transmits a TV signal and a data signal.

[0002]

2. Description of the Related Art Conventionally, there is a relay amplifier for amplifying and transmitting a signal. For example, there is a CATV relay amplifier that amplifies and transmits a TV signal and a data signal. Conventional CATV
The relay amplifier is shown in FIG. The relay amplifier includes an amplifier 10 capable of controlling the amplification factor, a splitter 12, a detector 17, a changeover switch 18, and a manual amplification factor adjustment circuit (MGC) 1.
9, an automatic gain adjustment circuit (AGC circuit) 20. There are two procedures for adjusting the amplification factor. First, the changeover switch 18 is set to the MGC 19 side. Next, a pilot signal having a frequency of 451.25 MHz is input to the amplifier 10, and the output of the pilot signal is split by the splitter 12. Then, the branch signal is input to the detector 17 via the branch path 13 to obtain a pilot voltage. Then, the volume of the MGC circuit 19 is adjusted so that the pilot voltage becomes a predetermined value (for example, 90 dBμ). That is, the gain control voltage V _GC of the amplifier 10 is adjusted. This is the next AGC circuit 2
This is to prepare for a failure of 0, for example. That is, when the AGC circuit 20 fails, the switching is switched to this so that the relay amplifier does not stop.

Next, the changeover switch 18 is set to the AGC circuit 20 side. Then, similarly, a pilot signal having a frequency of 451.25 MHz is input to the amplifier 10, and the output thereof is split by the splitter 12. Then, the branch path 13 from the branch terminal is input to the detector 17, a pilot voltage is similarly obtained, and the pilot voltage is input to the AGC circuit 20. Similarly, the setting value of the AGC circuit 20 is determined so that the signal level at the branch terminal becomes a predetermined value (for example, 90 dBμ). This set value is, for example, a voltage value obtained by adjusting the volume. This is a configuration in which the AGC circuit 20 feeds back to the amplifier 10 so that the branch signal level becomes a predetermined set value. Thus, a stable output can be obtained from the relay amplifier even if the input signal fluctuates. The relay amplifier was set in this way, and was finally switched to the AGC circuit before being shipped.

[0004]

However, there is a case where the AGC circuit 20 needs to be readjusted when the relay amplifier is attached. For example, a case where the transmission path is extended downstream of the relay amplifier. In this case, an output higher than a predetermined output level is required of the relay amplifier. For example, an output level of 95 dBμ is required for a normal level of 90 dBμ. In such a case, it is necessary to finely adjust the amplification factor of the relay amplifier on the pillar. That is, even if a pilot signal of 95 dBμ is detected, the output level of 95 dBμ is notified to the center as a status monitor signal, and
The amplification factor of the amplifier was adjusted so that an output of Bμ was obtained. Further, in order to increase the number of branches in the system, there is a case where it is desired to raise the operation level of the whole system or a system downstream of a certain relay amplifier by 5 dBμ. However, simply set the transmission level at the head end to 5
If the output level of a certain relay amplifier is increased only by 5 dBμ or the AGC function of the subsequent relay amplifier operates, negative feedback is applied so that the output level becomes constant. Level rise will not be realized. Therefore, in that case, it is necessary to adjust the amplification factor of all the relay amplifiers or all the relay amplifiers within the range of increasing the output level. or,
Since the detected pilot signal level also changes, it is necessary to change the settings relating to the status monitor information. These adjustment operations are detailed manual operations using a measuring instrument, require a great deal of labor, and are not efficient adjustment methods for the operator.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an attenuator and a switch device in a feedback circuit of a relay amplifier of a network system to facilitate output adjustment. It is to provide a relay amplifier.

[0006]

In order to solve the above problems, the relay amplifier according to the first aspect of the present invention has
A relay amplifier of a network system in which a branched pilot signal is detected and an automatic amplification factor adjustment circuit controls the amplifier based on the detected pilot voltage, and an attenuator provided in parallel on a branch path below the branch unit. And a switch device for switching the branch path and a path before or after the attenuator, and the output of the amplifier is adjusted by switching the switch apparatus.

According to a conventional relay amplifier having a splitter, a detector, and an automatic amplification factor adjusting circuit, the splitter is provided at a stage subsequent to the amplifier. A part of the pilot signal output from the amplifier is branched to a branch path via the branch terminal by the branch unit. A detector is provided on the branch path to detect a pilot signal. Then, the pilot voltage obtained by the detection is supplied to the automatic amplification factor adjusting circuit. Since the pilot signal has a constant amplitude, the pilot voltage is a constant voltage. Then, the automatic amplification factor adjustment circuit performs feedback control of the amplifier so that the pilot voltage becomes a predetermined value. Conventional relay amplifiers operate in this manner.

According to the present invention, an attenuator is provided in parallel with a branch path after the above-mentioned splitter or a branch path after the detector, and a switch device is provided after the attenuator. Then, the path of the pilot signal is changed by switching the switch device. That is, the branch path and the attenuation path having the attenuator are switched. The switch device is, for example, a mechanical switch, an electric switch, or the like. Either is acceptable. Including both. The attenuator is an electric element for attenuating a high-frequency signal such as a coil and a resistor. Either is acceptable.

Normally, the switch device is set to a predetermined route. The predetermined path is, for example, a branch path without attenuation. When an increase in the output of the relay amplifier is required, the branch path is switched to the attenuation path by the switch device. As a result, the pilot signal is attenuated. That is, the pilot voltage is reduced. The automatic amplification factor adjusting circuit controls the amplifier to return the pilot voltage to a predetermined value. That is, control is performed so as to increase the amplification factor. As a result, the output of the relay amplifier is increased. When the output of the relay amplifier is required to be reduced, the predetermined path (normal path) is set in advance as the attenuation path. Then, the switch device switches the path from the attenuation path to the branch path. Thereby, the output of the relay amplifier is reduced.

At this time, the amount of attenuation by the attenuator can be set to a predetermined value in advance. For example, 20dB in output
If you want to increase, the pilot signal is 20dB with attenuator
Set the resistance value so that it attenuates. The automatic amplification factor adjustment circuit controls the amplifier to return to the set value when the pilot signal decreases by 20 dB. That is, the output of the amplifier is set to 2
Increase by 0 dB. That is, for example, the operator can increase the output to a predetermined value only by switching the switch device. That is,
There is no need to adjust the automatic gain adjustment circuit each time an output increase request is made. Therefore, the relay amplifier is excellent in convenience. The order of the attenuator and the switch device is not limited. An attenuator may be provided after the switch device.

Further, the attenuator and the switch device may be provided at a subsequent stage of the detector. At this time, an attenuator is provided in parallel with the branch path from the output terminal of the detector. The pilot voltage obtained by the detector is attenuated by this attenuator and input to the automatic amplification factor adjusting circuit. This has the same effect. Also in this case, the order of the attenuator and the switch device does not matter. As described above, in the present invention, the signal level of the pilot signal input to the automatic amplification factor adjustment circuit does not change at all before and after the adjustment. Therefore, there is no need to change the status monitor information. Further, in the relay amplifier in the range where the input level is changed, since the level of the pilot signal input to the automatic gain adjustment circuit does not change, the amplification factor of the relay amplifier does not change. The frequency characteristics are kept constant. Therefore, it is possible to obtain an output level that changes linearly with respect to a change in the input level. In a relay amplifier that changes only the output level without changing the input level, the operation of the automatic gain adjustment circuit changes the gain so that the level of the pilot signal input to the automatic gain adjustment circuit does not change. , A desired output level is obtained. Also in this case, since the level of the detected pilot signal does not change, there is no need to change the status monitor information. At the headend, since the relay amplifier whose output level has been changed is known, if this amplifier is specified, the actual output level of the relay amplifier can be known.

According to a second aspect of the present invention, the attenuator is an attenuator in which a plurality of resistors are connected in parallel, and the switch device is a multi-stage switch. The resistors have different resistance values. Therefore, the pilot voltage is changed in multiple stages by the switch device. Therefore, by switching the switch device. The output of the relay amplifier can be adjusted in multiple stages. In particular, if the normal state is set and set at the center of the multi-stage, the output of the switch can be increased and decreased stepwise by operating the switch. That is, adjustment in both directions is possible.

According to a third aspect of the present invention, the input section of the automatic amplification factor adjusting circuit has a capacitor and a resistor having one end grounded in parallel. According to the present invention, the signal path is changed by the switch device. Therefore, the pilot signal changes abruptly at the time of the change. According to the present invention, a capacitor and a resistor are provided in parallel at the input terminal of the automatic gain adjustment circuit. Therefore, if the pilot voltage changes abruptly due to the switching of the switch device, this is alleviated by the capacitor and the resistor.

That is, when the pilot voltage drops abruptly, the charge charged in this capacitor is gradually discharged via the resistor to a new predetermined voltage. When the pilot voltage rises sharply, the capacitor is charged with a new charge and becomes a new predetermined voltage. Therefore, there is no sudden voltage change at the input terminal of the automatic amplification factor adjusting circuit. A continuous pilot voltage is supplied to the input terminal of the automatic amplification factor adjusting circuit. Therefore, the automatic amplification factor adjusting circuit stably controls the amplifier. That is, the gain of the relay amplifier can be switched even during signal transmission from the center side, for example.

Further, according to the relay amplifier of the fourth aspect, the switch device is constituted by a semiconductor element. The semiconductor element is, for example, an analog switch, a bipolar transistor element, an FET transistor element, or the like. Since it is a semiconductor element, it is possible to quickly switch signals. Also, there is no chattering found in mechanical switches and relays. Therefore, the relay amplifier operates stably at a high switching speed.

According to the relay amplifier of the present invention, the network system is a CATV network system. The output level of this relay amplifier can be easily changed only by switching the switch device. In other words, if this relay amplifier is used, the transmission path of the system can be easily expanded. Therefore, if this is applied to a CATV system, a CATV system that can easily transmit a TV signal and a data signal to more consumers will be provided.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following examples. (Embodiment) FIG. 1 shows a relay amplifier according to the present invention. The figure is a circuit diagram. The relay amplifier of the present invention is used, for example, in a CATV network system. The relay amplifier according to the present invention includes a controllable amplifier 10, a splitter 12, an attenuator 14, a switch device 15, a detector 17, a changeover switch 18, a manual gain adjustment circuit (MGC circuit) 19, an automatic gain adjustment. Circuit (AGC circuit) 20, capacitor 20
a, and a resistor 20b. Note that the changeover switch 18 and the MGC circuit 19 are circuits for maintenance and are not normally used, so that description thereof will be omitted.

The amplifier 10 is an amplifier that amplifies a signal input from the main line 5 according to the gain control voltage V _GC . The branching unit 12 is a branching unit that branches a part of the output of the amplifier 10 from the branch terminal to the AGC circuit 20 via the branch path 13. Attenuator 14 connected to branch path 13
Is an attenuator for attenuating a signal, for example, a resistor is connected in parallel. The switch device 15 is a device that switches the signal path in multiple stages, and switches between a branch path 13 that does not attenuate the signal and an attenuation path that variously attenuates the signal. Normally, the switch device 15 is set on the branch path 13 side.

The detector 17 is, for example, an AM detector comprising a filter, a diode, and a capacitor. The filter is a band-pass filter that allows a specific frequency to pass. In this case, only a pilot signal having a frequency of 451.25 MHz is passed. Since the pilot signal has a constant signal amplitude, a constant voltage (pilot voltage) is obtained by AM detection. The AGC circuit 20 is a circuit that compares the pilot voltage with a set value set from the outside and controls the amplifier so that the values become the same.

Usually, the pilot signal is a transmission signal 70 MHz to 77 MHz from the center side of the CATV network.
It is included at 0 MHz. Therefore, the pilot voltage is always detected by the detector 17, and the AGC circuit 20 controls the amplifier 10 based on the detected pilot voltage. This allows
Even if the input signal in the 70 to 770 MHz band fluctuates, the relay amplifier amplifies so as to compensate for the fluctuation. That is, a signal is always output at a predetermined level such as 95 dBμ. Normally, this relay amplifier operates in this manner.

However, this relay amplifier may be required to have an output higher than a predetermined value. For example, a case where the transmission path is extended downstream of the relay amplifier. For example, an output of 95 dBμ is required for a predetermined level of 90 dBμ. In such a case, conventionally, for example, a signal level monitor is attached to a branch terminal and adjusted by the volume of the AGC circuit 20. In this embodiment, the switch device 15 is connected to the attenuator 1.
Switch to 5 side. That is, the signal path is switched to one of the attenuation paths.

Thus, the pilot signal is attenuated. That is, the pilot voltage input to the AGC circuit 20 is reduced. When the pilot voltage decreases, the AGC circuit 20 controls the amplifier 10 to return the pilot voltage to a predetermined value. That is, control is performed so as to increase the amplification factor. That is, the output of the amplifier 10 is increased only by switching the switch device 15 without changing the set value of the AGC circuit 20.

At this time, each resistance value of the attenuator 14 is set to a predetermined value in advance. For example, in output, 5dB, 10dB,
When it is desired to increase the pilot signal by 20 dB, the attenuator 14 selects and sets the resistance value so that the pilot signal is attenuated by 5 dB, 10 dB and 20 dB, respectively.
By setting in advance in this way, it is not necessary for the operator to adjust the set value of the AGC circuit 20 using the level detector each time even when a request for increasing the output is made. It is only necessary to switch the switch device 15 to a predetermined attenuation path. That is, the relay amplifier has excellent work efficiency. If there is no change in the relay span of the relay amplifier whose amplification factor has increased, the signal level generally increases in the system downstream of the relay amplifier. In this case, it is necessary to adjust the output signal level of the relay amplifier in the range in which the signal level is improved so that the output signal level becomes the changed value. Also in this case, the attenuation factor (for example, 5 dB) of the attenuator 14 of each relay amplifier may be selected. By this adjustment, the amplification factor of the relay amplifier is not converted, so that the output signal level changes linearly according to the change of the input signal level. Further, the signal level of the pilot signal input to the automatic gain adjustment circuit of these relay amplifiers does not change before and after the adjustment. Therefore, since it is not necessary to change the status monitor information, it is possible to adjust the signal level of the entire system by adjusting only the attenuator 14, and the adjustment becomes extremely easy. Also, when the level of the transmission signal at the head end is increased, it is necessary to adjust all the relay amplifiers.
Only the setting of the decay rate of, no other adjustment is required.

In this embodiment, a capacitor 20a and a resistor 20b are added in parallel to the input terminal of the AGC circuit 20. This is because the pilot voltage changes abruptly when the signal path is changed in the switch device 15, and there is a possibility that noise is mixed into the transmission signal. This is alleviated by the capacitor 20a and the resistor 20b. For example, when the pilot voltage suddenly drops due to a switch operation, the charge charged in the capacitor 20a is gradually discharged via the resistor 20b. Then, the voltage becomes a new predetermined voltage. Conversely, when the pilot voltage rises sharply, the capacitor 20a is newly charged with electric charge, for example, spikes are removed. Therefore, there is no sudden voltage change such as a spike at the input terminal of the AGC circuit 20. A continuous pilot voltage is supplied to the input terminal of the AGC circuit 20. Therefore, the AGC circuit 20 controls the amplifier 10 stably. That is, according to this configuration, the amplification factor of the relay amplifier can be switched even during signal transmission, for example.

(Modifications) Although one embodiment of the present invention has been described, various other modifications are conceivable. For example, although the switch device 15 and the attenuator 14 are provided at the branch terminal of the branching device 12 in the above embodiment, they may be provided at the subsequent stage of the detector 17 as shown in FIG. That is, the attenuator 14 may be provided in the branch path 13 from the detector 17, and the switch device 15 may be arranged at the subsequent stage. In this case, first, the detector 17
, And the pilot voltage is attenuated by the attenuator 14. Since the attenuated pilot voltage is input to the AGC circuit 20, the effect is the same. The arrangement of the switch device 15 and the attenuator 17 may be changed. As a result, if the pilot voltage input to the input terminal of the AGC circuit 20 is reduced,
The arrangement does not matter.

Although the switch device 15 of the above embodiment has been described as a mechanical switch device, it may be an electric switch using a transistor or an analog switch. For example, as shown in FIG. 3, the switch device 15 may be configured by an analog switch 15a, an inverter 15b, and a decoder 15c. When a numerical value (binary) is electrically input to the decoder 15c, a predetermined analog switch 15a is selected and a predetermined attenuation is achieved. That is, by inputting a predetermined numerical value from a numerical input device (not shown), a predetermined output is obtained. With such an electric switch, the path can be switched instantaneously. Therefore, the relay amplifier has excellent switching response. The switch device 15 may be configured as described above. Further, in the above embodiment, the amplifier has been described as a unidirectional amplifier, but may be a bidirectional amplifier. The present invention can be applied to a bidirectional relay amplifier.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a relay amplifier according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a relay amplifier according to a modification of the present invention.

FIG. 3 illustrates a switch device according to a modification of the present invention;
Example circuit diagram.

FIG. 4 is a circuit diagram showing a configuration of a relay amplifier according to a conventional example.

[Explanation of symbols]

 Reference Signs List 5 Main line 10 Amplifier 12 Branch device 13 Branch path 14 Attenuator 15 Switch device 17 Detector 18 Changeover switch 19 Manual gain adjustment circuit 20 Automatic gain adjustment circuit 20a Capacitor

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5C056 FA02 FA03 FA05 FA09 GA01 GA02 GA14 HA01 HA14 HA15 5C064 BA01 BB05 BC12 BC13 BC14 BD09 5J100 AA03 AA09 AA12 BA01 BB09 BB15 BC05 CA06 CA11 DA06 EA02 FA01 JA01 5K072 GG22

Claims (5)

[Claims] 1. A relay amplifier for a network system in which a branched pilot signal is detected, and an automatic gain adjustment circuit controls the amplifier based on the detected pilot voltage, wherein the relay amplifier is in parallel with a branch path below the branch unit. A relay amplifier, comprising: an attenuator provided; and a switch device for switching a path between the branch path and a preceding or subsequent stage of the attenuator, wherein an output of the amplifier is adjusted by switching the switching device. 2. The relay amplifier according to claim 1, wherein the attenuator is an attenuator in which a plurality of resistors are connected in parallel, and the switch device is a multi-stage switch. 3. The relay amplifier according to claim 1, wherein the input section of the automatic amplification factor adjusting circuit has a capacitor and a resistor having one end grounded in parallel. 4. The relay amplifier according to claim 1, wherein said switch device is formed of a semiconductor element. 5. The relay amplifier according to claim 1, wherein the network system is a CATV network system.