JPH06303454A - Multi-tap branching circuit - Google Patents

Abstract

PURPOSE:To provide a branching circuit which can keep the balance of its overall impedance despite a large number of branching terminals. CONSTITUTION:A branching circuit contains four 1-branching circuits cascade connected between an input terminal IN and an output terminal OUT and forms the branching terminals TAP1-TAP4. Then the branching circuit is provided with an impedance matching transformer which is cascade connected between the terminal IN and a 1-branching circuit, two 1-branching circuits which have the terminals TAP1 and TAP2, are cascade connected to each other, and one is connected to an impedance matching transformer T0 and the other to a subsequent circuit element respectively, a tilt attenuating circuit which is connected to the output sides of both 1-branching circuits and compensates the input-output attenuation loss of each 1-branching circuit, and two 1-branching circuits which have the terminals TAP3 and TAP4, are cascade connected to each other, and are connected to the tilt attenuating circuit and to the terminal OUT respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal branch circuit, and more particularly to a circuit suitable for constructing a branch circuit having a large number of branch ends.

[0002]

2. Description of the Related Art For example, a branch circuit for a television signal used in Europe or the like uses a branching device having a large coupling loss between the branching terminals in order to prevent mutual interference between the branching terminals.

FIG. 5 shows a concrete example of a conventional multi-terminal branch circuit. This branch circuit has 12 branch terminals.
It is configured as individual circuits, and TAP1 to T
It has branch terminals up to AP12. This circuit uses twelve 1-branch circuits composed of two cross-connected transformers T1, T2, resistors, and capacitors.

The overall circuit configuration is such that a plurality of one-branch circuits are connected in number and outputs are connected in series. As shown in FIG. 6, the coupling loss between the branch terminals is one branch. The size is the sum of the circuit coupling loss (IN-TAP loss), the reverse coupling loss, and the (OUT-TAP loss).

However, the insertion loss of the entire branch circuit is the insertion loss of one branch circuit multiplied by the number of branch terminals, and the drop is particularly large in the high frequency range. Moreover, when the input and output impedances of the individual one branch circuits have values deviating from the characteristic impedance of the transmission line (for example, 75Ω), the larger the number of branch terminals, the more unbalanced the input and output impedances of the entire branch circuit.

Therefore, as a measure for flattening the high-frequency attenuation of the insertion loss, there is a method of inserting a tilt attenuation circuit composed of a resistor and a capacitor connected in parallel in the middle of the branch circuit. Since this tilt attenuation circuit is arranged in a narrow space between the branch terminals arranged at regular intervals, generally, a simple circuit as shown in FIG. 7 is simply formed by connecting one resistor and one capacitor in parallel. used.

Further, a capacitor, a transformer and the like for impedance correction are provided as needed.

[0008]

This tilt attenuation circuit is
Since it is inserted in series in the main circuit of the branch circuit, it acts to increase the input and output impedance of the entire branch circuit. As a result, when a branch circuit having a large number of branch terminals is configured, a large impedance shift occurs.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a branch circuit having a structure in which the impedance balance of the entire circuit can be maintained even if the number of branch terminals is large.

[0010]

To achieve the above object, in the present invention, in a branch circuit in which four one-branch circuits are vertically connected to form four branch terminals between an input terminal and an output terminal, An impedance matching transformer that is vertically connected between the input terminal and the one branch circuit, and each has a branch terminal and is vertically connected to each other, one of which is connected to the impedance matching transformer and the other of which is a subsequent circuit. Two 1-branch circuits connected to the element and connected to the output side of the 2 1-branch circuits, and configured so that the frequency-to-attenuation loss characteristic compensates for the attenuation loss between the input and the output of the 1-branch circuit. And a tilt attenuation circuit that is connected to the tilt attenuation circuit, each of which has a branch terminal and is vertically connected to each other, one of which is connected to the tilt attenuation circuit and the other of which is connected to an output terminal.
The present invention provides a branch circuit including a branch circuit.

[0011]

The branch circuit composed of four one branch circuits, one impedance matching transformer and the tilt attenuation circuit becomes one unit branch circuit having four branch terminals. Therefore, two units are used to form eight branch terminals, and three units are used to form twelve branch terminals.

The impedance matching transformer inserted in each unit raises the impedance seen from the input terminal side and lowers the impedance seen from the output terminal side. And the input and output impedance of the one branch circuit is
Select the output side equal to the characteristic impedance of the transmission line and the input side lower than that. As a result, even if the tilt attenuation circuit is inserted, the input / output impedance of the entire branch circuit becomes a predetermined value.

[0013]

As described above, the present invention is a unit type in which an impedance matching transformer and a tilt attenuating circuit are combined with four one-branch circuits divided into two groups, two each between the input terminal and the output terminal as described above. Since the branch circuit of 1 is configured, a branch circuit having a large number of terminals can be easily provided by using a required number of the branch circuits. Further, since it is easy to properly adjust the impedance of this unit-type circuit, the impedance can be properly maintained even if the cascade connection is made in a plurality of stages.

[0014]

1 is a block diagram showing a circuit configuration of an embodiment of the present invention. The circuit of FIG. 1 is
1 is a unit circuit for forming a branch circuit according to the present invention. Then, this unit is configured to have four branch terminals. For this purpose, there are four 1-branch circuits, and these 4 1-branch circuits are each divided into 2 groups, and an impedance matching transformer is provided between the input terminal and the 1-branch of the 1st group. The tilt attenuation circuit is inserted between the first group branching device and the second group branching device. The output terminal of the second group of branching devices is connected to the output terminal. Further, when forming a multi-terminal branch circuit, a plurality of illustrated units are vertically connected to form a branch circuit.

The one-branch circuit used in this unit is
It is customary to use a directional coupler having a branch loss of about -12 dB, that is, a branch transformer. In this branch transformer, the core material, shape, number of windings, etc. are selected so that the output side impedance is set to 75Ω and the input side impedance is set to be lower than 75Ω.

When such branch transformers are vertically connected, the total output impedance is 75Ω.
The input impedance is further reduced. The larger the number of cascade connections, the lower the input impedance.

On the other hand, since the tilt attenuation circuit is serially inserted in the vertical connection circuit of the branching device, both the input impedance and the output impedance are increased.

When a circuit in which four 1-branch circuits and a tilt attenuating circuit are vertically connected is viewed from the input terminal side, branch transformers each having an input impedance lower than a predetermined value, that is, 75Ω are vertically connected. Although it is considerably lower than 75Ω, it is somewhat lower than 75Ω because the impedance component of the tilt attenuation circuit is added.

On the other hand, when a circuit in which four branching devices and a tilt attenuating circuit are vertically connected is viewed from the output terminal side, the branch transformer itself has an output impedance of 75Ω, but the impedance component of the tilt attenuating circuit is 7 to join
It will be somewhat higher than 5Ω.

The impedance matching transformer inserted at the input terminal has a function of increasing the impedance when the output terminal side is viewed from the input terminal side and lowering the impedance when the input terminal side is viewed from the output terminal side. Looking from the terminal side to the output terminal side, the function of the branching device works to raise the impedance that is lower than the specified value to close to the specified value, and conversely when you look at the input terminal side from the output terminal side, the effect of the tilt attenuation circuit The impedance that is higher than the predetermined value by working is returned to almost the predetermined value.

As a result, the circuit of FIG. 1 has a predetermined impedance when viewed from the input terminal side or the output terminal side. Therefore, even if the units shown in FIG. 1 are cascade-connected, the overall impedance does not deviate from the predetermined value, and there is no problem when the units are cascade-connected in two or more stages.

FIG. 2 shows a specific circuit configuration of the circuit shown in FIG. That is, a circuit configuration similar to one branch circuit of the branch terminal TAP1 formed by the two cross-connected transformers T1 and T2, the resistor R1 and the capacitor C1 is adopted for each of the branch terminals TAP2, TAP3 and TAP4.

Then, the branch terminals TAP2 and TAP3
A tilt attenuation circuit composed of a resistor R3 and a capacitor C3 is directly inserted between the one-branch circuit for use in the. Further, an impedance matching transformer T0 is connected between the one branch circuit for the branch terminal TAP1 and the input terminal IN. The output of the branching device for the branching terminal TAP4 is connected to the output terminal OUT.

FIG. 3 shows the configuration of a branch circuit having 12 branch terminals constructed according to the present invention. This branch circuit is a three-stage cascade connection of the units shown in FIG. 1 or FIG. 2, but is partially modified.

FIG. 4 shows the structure of a print substrate which constitutes the branch circuit of FIG. As can be seen from this figure, twelve one branch circuits for each branch terminal are arranged, and a tilt attenuation circuit is inserted between them. Since the one-branch circuit and the tilt attenuating circuit are assembled in the limited space as described above, there are dimensional restrictions on each element.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing the configuration of FIG.

FIG. 3 is a circuit diagram showing a branch circuit having 12 branch terminals configured according to the present invention.

4 is a perspective view of a printed circuit board used in the branch circuit of FIG.

FIG. 5 is a circuit diagram showing a conventional branch circuit.

FIG. 6 is an explanatory diagram of inter-terminal coupling loss of the branching device.

7 is a perspective view of a printed circuit board used in the branch circuit of FIG.

[Explanation of symbols]

 T transformer C capacitor R resistance

Claims (1)

[Claims] 1. A branch circuit in which four one-branch circuits are vertically connected between an input terminal and an output terminal to form four branch terminals, and the one-branch circuit is vertically connected between the input terminal and the one-branch circuit. An impedance matching transformer connected to the impedance matching transformer, and two one-branch circuits each having a branch terminal and connected in tandem, one of which is connected to the impedance matching transformer and the other of which is connected to a subsequent circuit element; A tilt attenuation circuit connected to the output side of one one-branch circuit and having a frequency-to-attenuation loss characteristic configured to compensate for the attenuation loss between the input and output of the one-branch circuit; And a single branch circuit connected to each other in cascade connection, one of which is connected to the tilt attenuation circuit and the other of which is connected to an output terminal.