JPS59175225A - In-phase noise elimination system - Google Patents

Abstract

PURPOSE:To realize size reduction and economization by allowing a hybrid transformer to function as a two-wire/four-wire converting circuit and an eliminating means for an in-phase noise generated between both lines of a two-wire commuication circuit and the ground. CONSTITUTION:The two-wire/four-wire converting circuit consists of the hybrid transformer 7; and a balanced connection network 8 is connected to the neutral point of a four-wire side winding 7-2, and a two-wire side winding 7-1 is divided into two at the neutral point. Those windings have the same number of turns; the winding 7-1a starts its turn at the neutral-point side terminal and is connected to a DC power source through a capacitor 4, and the winding 7-1b ends its turn at the neutral-point side terminal and is grounded through a capacitor 4. This hybrid transformer 7 serves as the two-wire/four-wire converting circuit and cancels the impedance between both windings to an in-phase noise generated between both lines of the subscriber circuit and the ground, so a feeding detecting circuit 1 is short-circuited to the in-phase noise to evade malfunction.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a circuit that accommodates a two-wire communication line, such as a subscriber circuit of a digital exchange, and is equipped with a two-wire/four-wire conversion circuit. The present invention relates to an improvement in a common mode noise cancellation method for eliminating common mode noise generated between both lines and the ground of the two-wire communication line.

Prior Art and Problems Figure 1 is a diagram showing an example of a conventional common mode noise cancellation method in a subscriber circuit of a digital exchange. In FIG. 1, a power supply/detection circuit 1 supplies talking current to a subscriber line, which is a two-wire communication line, and detects a DC loop circuit formed in the subscriber line. Further, the two-wire/four-wire conversion circuit 2 converts the subscriber line into a four-wire system and connects it to a code decoding circuit (not shown). If such common mode noise occurs between the line and the ground of the subscriber line, it will cause the power supply/detection circuit 1 to malfunction. In order to eliminate the common mode noise, a common mode noise canceling circuit 6 consisting of a flow wire 3 and capacitors 4 and 5 is provided in FIG. Each of the windings 1-1 and 3-2 of the blocking wire ring 3 has the same number of turns, and the winding start terminal of one winding 3-1 is grounded via the capacitor 4.
The winding end terminal of the other winding 3-2 is grounded via a capacitor 5. In such a common mode noise canceling circuit 6,
Since the impedance of both windings 3-1 and 3-2 of the blocking wire ring 3 with respect to the common mode noise generated between both lines of the subscriber line and the ground cancels out, the power supply/detection circuit 1 is short-circuited against the common mode noise. This will prevent malfunctions.

As is clear from the above explanation, in the conventional common mode noise cancellation method, the common mode noise cancellation circuit 6 composed of the blockage wire ring 3 and the capacitors 4 and 5 is connected to the two-wire four-wire conversion circuit 2.
was established independently. Therefore, the subscriber circuit has the disadvantage of being large and relatively expensive.

(C) Object of the Invention The object of the present invention is to eliminate the drawbacks of the conventional common-mode noise canceling method as described above, and to realize a common-mode noise canceling means that is as small and economical as possible.

(d) Structure of the invention This object is to provide a circuit that accommodates a two-wire communication line and is equipped with a two-wire and four-wire conversion circuit, in which a hybrid transformer is used in the two-wire and four-wire conversion circuit, and the hybrid transformer This is achieved by dividing the two-wire side winding into two at the midpoint, and connecting the midpoint side terminal of each of the two-wire side windings to either ground air or a DC power supply via a capacitor.

(e) Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a common mode noise cancellation method according to an embodiment of the present invention. Note that the same reference numerals refer to the same objects throughout the plan. In FIG. 2, the two-wire and four-wire conversion circuit 2 (first
Fig.) is composed of a hybrid transformer 7, and a parallel wire network 8 is connected to the midpoint of the four-wire side winding 7-2. The two-wire side winding 7-1 of the hybrid transformer 7 is divided into two windings 7-1a and 7-1b at the midpoint. Each winding 7
-1a and 7-1b each have the same number of windings, the winding 7-1a has the terminal at the center point at the beginning, and the winding 7-1b
The end of the winding becomes the midpoint side terminal. The midpoint side terminal of the winding 7-1a is connected to the DC power supply via the capacitor 4.
The midpoint side terminal of -1b is grounded via the capacitor 5. The hybrid transformer 7 plays the role of a two-wire/four-wire conversion circuit, and also has both stirring wires 7-1a of the hybrid transformer 7 to deal with common mode noise generated between both lines of the subscriber line and the ground.
Since the impedances of 7-1b and 7-1b are canceled out, the power supply/detection circuit 1 becomes short-circuited against common-mode noise.
Malfunctions can be avoided.

As is clear from the above description, according to this embodiment, the two-wire side winding 7-1 of the hybrid transformer 7 is connected to the capacitor 4.
and 5, it plays the same role as the common mode noise canceling circuit 6 in FIG.

Note that FIG. 2 is only one embodiment of the present invention, and for example, the capacitor 4 is not limited to being connected to a DC power source, and the capacitor 5 is not limited to being connected to the ground, but may be connected to the ground air or a DC power source. The effect of the present invention remains the same no matter which connection is made. Further, the configuration of the power supply/detection circuit 1 is not G1° as defined by the present invention (it goes without saying that the present invention is not limited to subscriber circuit companies of digital exchanges).

(fl) Effects of the Invention According to the present invention, in the circuit, the hybrid transformer serves both as a two-wire and four-wire conversion circuit and as a common-mode noise canceling means, so that the circuit can be made smaller and more economical. promoted.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional common mode noise cancellation method, and FIG. 2 is a diagram showing a common mode noise cancellation method according to an embodiment of the present invention. In the figure, 1 is a power supply/detection circuit, 2 is a two-wire/four-wire conversion circuit, 3 is an obstructing coil, 3-1 and 3-2 are windings of the obstructing coil, 4 and 5 are capacitors, and 6 is in phase. noise cancellation circuit,
7 is a hybrid transformer, 7-1 is a two-wire side winding, ? -1
8 and 7-1b were bisected. 7-2 indicates a four-wire side winding, and 8 indicates a parallel connection network.

Claims (1)

[Claims] In a circuit that accommodates a two-wire communication line and is equipped with a two-wire and four-wire conversion circuit, the two-wire and four-wire conversion circuit is configured with a hybrid transformer, and the two-wire side winding of the A common-mode noise cancellation method characterized in that the voltage is divided into two at a midpoint, and the midpoint side terminal of each of the two-wire side windings is connected to either the earth or a DC power source via a capacitor.