JP2001285819A - Signal branching device for cable network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal branching device for a cable network capable of preventing signal distortion caused by magnetization generated by the surge current of an incorporated magnetic core. SOLUTION: In the signal branching device for a cable network, a trunk line including a DC line and a signal line is formed between an input/output terminals IN-OUT and a signal branching circuit DC connected to at least one branching terminal B is provided at the signal line, DC currents and a signal are transmitted between the input/output terminals, and a signal is supplied toward the branching terminals from the signal branching circuit. The signal branching circuit has at least three lines connected respectively and separately to the input/output terminals and the branching terminals and each of these lines is connected through a capacitor C to the respective terminals and connected to the ground through a choke coil SL.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal branching device for a cable network, and more particularly, to a measure against signal distortion caused by a surge current in the signal branching device.

[0002]

2. Description of the Related Art Cable television (CATV) and T
In the V-sharing facility, a wideband high-frequency signal of, for example, 5-1,000 MHz and a multi-channel is supplied to each home from a so-called head end using a coaxial cable.
A broadband splitter is provided for signal distribution to each home. In this case, a broadband amplifier is provided to compensate for a decrease in signal level.

An amplifier needs to be supplied with power. In order to avoid providing a power cable separately from the signal coaxial cable, a power-pass type branching device in which power is superimposed on the coaxial cable is used. A distributor is used.

[0004] In recent years, there has been a movement to utilize the thus-configured CATV network not only for TV signal transmission services but also for data transmission services such as the Internet. And, for example, the data signal is 5-55 MH
The z and TV signals are operated in respective frequency bands of 70 to 1000 MHz.

[0005] Here, the data signal includes a signal transmitted from the head end and a data signal transmitted from the subscriber's house to the head end (reverse transmission signal). The reverse feed signal is obtained when data from the computer enters the RF modem once and reaches the head end through a coaxial cable as a high frequency signal. During this time, it passes through all the branch distributors existing between the head end and the subscriber.

FIG. 7 shows an example of the branch distributor. This branch distributor includes an input terminal IN, an output terminal OUT, and branch terminals B1-B4 connected to a shield case SC.
Is provided, and between the input terminal IN and the output terminal OUT, not only a high-frequency signal but also power supply power is supplied.

[0007] The power of the power supply is a DC blocking capacitor C1,
The output terminal O is blocked by C2 and passes through the choke coil L.
Flow to UT. On the other hand, the high-frequency signal
At the output terminal OUT via the capacitor C2, the branch distribution circuit DC, and the capacitor C2. In this case, in the branch distribution circuit DC, the branch terminal B1-
The high frequency signal branched to B4 is transferred to capacitors C11-C1.
Feed via 4.

As a result, the branch distribution circuit DC is DC-separated from the input / output terminals IN and OUT and the branch terminals B1 to B4.
The branch distribution circuit DC is not affected by this.

FIG. 8 to FIG. 10 show the transmission characteristics of the branch distributor shown in FIG. That is, as shown in FIG. 8, between input terminal IN and output terminal OUT, 5-10
While the attenuation is less than 2.0 dB in the range of 00 MHz, the input terminal IN and the branch terminal B1-
B4, and about 30 dB between the output terminal OUT and the branch terminals B1-B4, as shown in FIG.
It shows attenuation characteristics of dB or more.

[0010]

Here, the signal splitter / distributor DC has a configuration using a transformer, and when a surge current acts on a magnetic core incorporated in the transformer, signal distortion occurs.

That is, in the circuit of FIG. 7, when a surge current enters from the input terminal IN, the capacitor C1, the primary winding l1 of the transformer T1 in the branch distribution circuit DC,
Whether it flows to the ground via the secondary winding 14 of the transformer T2,
Alternatively, the input terminal IN, the choke L, the capacitor C2,
It flows to the ground via the secondary winding 14 of the transformer T2. As a result, the transformer T used in the branch distribution circuit DC
1. The ferrite core of T2 is magnetized, and then the residual magnetism influences the high frequency operation region of the transformer out of linearity.

Therefore, both the TV signal and the data signal
In some cases, a problem in transmission operation accompanied by signal distortion may occur.

The present invention has been made in view of the above points, and has as its object to provide a signal branching device for a cable network which can effectively prevent signal distortion caused by magnetization of a built-in magnetic core due to a surge current. Aim.

[0014]

According to the present invention, a trunk line including a DC line and a signal line is formed between input and output terminals, and the signal line is connected to one or more branch terminals. A signal branch circuit is provided, a direct current and a signal are transmitted between the input and output terminals, and a signal is supplied from the signal branch circuit to the branch terminal. The signal branch circuit has at least three lines respectively connected to the input / output terminal and the branch terminal, and each of these lines is connected to the respective terminal via a capacitor. And a signal branching device for a cable network, wherein the signal branching device is connected to a ground via a choke coil.

[0015]

FIG. 1 is an explanatory diagram showing a basic configuration of a first embodiment of the present invention. This configuration is different from the configuration of the conventional device shown in FIG. 7 in that the input terminal and the output terminal of the branch distribution circuit DC are connected to the ground by the choke coils SL1 and SL2.
Are connected to the ground by choke coils SL1, SL2, SL3 and SL4, respectively.

By connecting these choke coils SL to the ground, the branch distribution circuit DC is connected to the input / output terminals IN and OUT in an AC or high frequency, and is connected to the ground in a DC or low frequency. Connected.

As a result, the input terminal I is connected to the branch distribution circuit DC.
If a high frequency signal is given from N, this is output to output terminal OU
Output to T and branch to branch terminals B1-B4. On the other hand, if a DC current including a surge current is given from any terminal, the current flows to the ground via the choke coil SL,
It does not flow into the branch distribution circuit DC.

In the embodiment shown in FIG. 1, similarly to the conventional apparatus shown in FIG. 7, the branch distribution circuit DC is housed in a shield case, that is, a metal case SC, and the branch distribution circuit DC is connected to the shield case. Output terminals IN and OUT and branch terminal B1
-B4 is connected AC through a capacitor C,
The input / output terminals IN and OUT are connected in a DC manner by a choke coil L.

Therefore, the AC component (or the high frequency component)
Regardless of whether it is a DC component (or a low-frequency component), a signal, or noise, this branching device has no components that enter from terminals other than each terminal. The pure DC component (or low frequency component) of the entered components is blocked by the capacitor C and does not reach the branch distribution circuit DC, and the pure AC component (or high frequency component) passes through the capacitor C and branches and distributes. The signal reaches the circuit DC and is supplied to each terminal.
On the other hand, the surge component once passes through the capacitor C, but is dropped to the ground by the choke coil SL, and does not reach the branch distribution circuit DC.

The change in signal transmission before and after the application of the surge voltage (DC voltage) in the signal branching device configured as shown in FIG. 1 was verified as follows.

That is, the frequency 313.
When two waves of 25 MHz and 338.25 MHz are given at the same time, a difference frequency 25 MHz appearing at the output terminal OUT
I observed the value of the signal with a spectrum analyzer. According to this, the input levels of the two waves are each 120
At the time of dB, the level of the difference frequency signal did not change before and after the DC voltage was applied, and both were 0 dB.

From this, it was found that the level of the difference frequency signal was lower than the input level by 120 dB, and that the signal splitter for a cable network was free from deterioration of the intermodulation characteristics due to the influence of surge. In an experiment using a conventional signal splitter, the input level was 60 dB.
From this comparison, it can be seen that the signal branching device shown in FIG. 1 has sufficiently improved distortion characteristics.

FIG. 2 shows a detailed circuit configuration of the first embodiment of the present invention whose schematic configuration is shown in FIG. The overall configuration is, as described with reference to FIG.
C, and the branch distribution circuit DC has IN-O
The output of the directional coupler composed of the current transformer T1 and the voltage transformer T2 inserted between the capacitors C1 and C2 of the main line connecting the UTs to the transformer T3.
The signal is distributed to four via the distribution circuit constituted by -T8 and supplied to the branch terminals B1 to B4.

The transformer T3 is an impedance matching transformer configured as an auto transformer.
The output is divided into two by a distribution transformer T4 and supplied to two impedance matching transformers T5 and T6. The outputs of these impedance matching transformers T5 and T6 are:
The signals are respectively supplied to the two-distribution transformers T7 and T8, are divided into two, and are supplied to the branch terminals B1-B4 via the capacitors C11-C14.

Each connection line between the impedance matching transformer T3 and the distribution transformer T4, between the impedance matching transformer T5 and the distribution transformer T7, and between the impedance matching transformer T6 and the distribution transformer T8 is grounded by a capacitor. It is connected.
The secondary windings of the distribution transformers T7 and T8 are connected in series at both ends with a resistor between two inductance elements, and each end of the secondary winding is connected to the ground by a capacitor. I have. Thereby, the frequency-loss characteristics of the branch distribution circuit DC are improved.

FIG. 3 shows a circuit configuration of a second embodiment of the present invention. This circuit corresponds to the DC blocking capacitors C1, C2, C11, C12, C13, C14 of FIG.
Are equivalent to C1a, C2a, C11a, C12
a, C13a and C14a, and a capacitor C1 is provided between the branch distribution circuit DC and each of the choke coils SL1-SL6.
b, C2b, C11b, C12b, C13b, C14b
Is additionally inserted.

With this configuration, the branch distribution circuit DC is also cut off from the path connected to the ground via the choke coil SL, so that the branch distribution circuit DC is more DC-separated from other circuit elements. In addition, it is possible to prevent the transformer core incorporated in the branch distribution circuit DC from being polarized.

FIG. 4 shows a detailed circuit configuration of the second embodiment shown in FIG. This circuit configuration corresponds to the detailed circuit of FIG. 2 relating to the first embodiment.
Are the capacitors C1b, C2b, C11b,
The difference is that C12b, C13b, and C14b are added.

FIGS. 5A to 5D show examples of a choke coil formed by winding a coil on a ferrite core used in each embodiment of the present invention.

Here, the ferrite core is made of, for example, MnZ.
The n-type sintered ferrite is crushed into powder having an average particle diameter of 100 μm, and molded using a material dispersed in epoxy resin at a weight ratio of epoxy resin 1 to ferrite powder 12.

First, the coil shown in FIG. 5A is configured by winding an insulated wire around a ring-shaped core M several turns. Since the ring-shaped core M constitutes a closed magnetic circuit, it is necessary to select a core material having a low effective magnetic permeability that does not cause magnetic saturation. Next, what is shown in FIG. 5 (b) is a magnetic gap G in the ring-shaped core M of FIG. 5 (a).
Are provided at four locations to reduce the effective magnetic permeability. Therefore,
A core having a relatively high magnetic permeability can be used.

FIG. 5 (c) shows that the magnetic path is open because the rod-shaped core is used, and even if the magnetic permeability of the core material is high, the effective magnetic permeability is lower than that of the closed magnetic circuit configuration. FIG. 5D shows the rod-shaped core of FIG. 5C in which three magnetic gaps are provided to reduce the effective magnetic permeability. In this configuration example, a hollow, round bar-shaped ferrite core 1 is divided into four sections in the longitudinal direction, and a plastic spacer 2 is interposed between the sections. Then, a tube 3 made of a heat-shrinkable material as an insulating coating is hung so as to cover the entire rod. The winding 4 is wound around the outer periphery of the bar-shaped ferrite core 1 thus configured. Then, a locking process 5 such as a silicon bond (registered trademark) is performed so that the plastic spacer 2, the tube 3 and the winding 4 provided on the ferrite core 1 do not fall off.
Is applied.

[0033]

As described above, the present invention relates to a signal branching device for a cable network in which a DC current and a signal are transmitted between an input / output terminal and a signal is supplied from a signal branching circuit to the branching terminal. The signal branch circuit, each of the lines connecting the input / output terminal and the branch terminal separately are connected to each terminal via a capacitor, and connected to the ground via a choke coil. Therefore, the intrusion of the surge is reliably prevented, and the high-frequency operation region of the transformer in the signal branch circuit does not deviate from the range having the linearity, so that the intermodulation characteristics important as a transmission device can be maintained well. As a result, a signal splitter suitable for use in a cable network can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a circuit configuration of one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a detailed circuit configuration of the embodiment shown in FIG. 1;

FIG. 3 is an explanatory diagram showing a circuit configuration of another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a detailed circuit configuration of the embodiment shown in FIG. 3;

FIGS. 5A to 5D are explanatory views showing examples of the configuration of a choke coil used in each embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a circuit configuration of a conventional signal splitter for a cable network.

FIG. 7 is a circuit diagram showing a detailed circuit configuration of the signal splitter shown in FIG. 6;

FIG. 8 is a diagram showing frequency-loss characteristics between input and output terminals in the conventional network signal splitter shown in FIGS. 6 and 7;

FIG. 9 is a diagram illustrating frequency-loss characteristics between an input and a branch terminal in the conventional network signal splitter illustrated in FIGS. 6 and 7;

FIG. 10 is a diagram showing frequency-loss characteristics between an output and a branch terminal in the conventional network signal branch shown in FIGS. 6 and 7;

[Explanation of Symbols] SC housing IN input terminal OUT output terminal B branch terminal TT line transformer FC ferrite core W1, W2 primary winding, secondary winding L choke DC branch circuit T1 current transformer T2 voltage transformer R resistance C Capacitors

Claims (8)

[Claims] A main line including a DC line and a signal line is formed between input and output terminals, and the signal line is provided with a signal branch circuit connected to one or more branch terminals. A direct current and a signal are transmitted between output terminals, and a signal branching device for a cable network in which a signal is supplied from the signal branching circuit toward the branching terminal, wherein the signal branching circuit includes the input / output terminal and the It has at least three lines each separately connected to a branch terminal, each of these lines being respectively connected to each said terminal via a capacitor, and being connected to ground via a choke coil. A signal splitter for a cable network, comprising: 2. A signal branching device for a cable network according to claim 1, wherein said capacitor in each of said lines comprises two capacitors connected in series, and an interconnection point of these capacitors is grounded by said choke coil. A signal splitter for a cable network that is connected. 3. The signal splitter for a cable network according to claim 1, wherein the choke coil is formed by winding an insulated wire around a ring-shaped core. 4. The signal splitter for a cable network according to claim 3, wherein the ring-shaped core is constituted by a plurality of portions having an insulator interposed therebetween. 5. The signal branching device for a cable network according to claim 1, wherein the choke coil is configured by winding an insulated wire around a rod-shaped core. 6. The signal branching device for a cable network according to claim 5, wherein the rod-shaped core is constituted by a plurality of portions having an insulator interposed therebetween. 7. The signal branching device for a cable network according to claim 1, wherein the choke coil is connected to a ferrite core, a coil wound on the ferrite core, and at least a part of the coil. Signal splitter for cable networks, comprising: a damping element; 8. The signal splitter for a cable network according to claim 7, wherein the damping element includes at least one of a resistor and a capacitor.