JP2008072301A - In-phase signal reduction circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce in-phase signals superposed on a twist pair cable in a DSL system by a relatively simple configuration, with respect to an in-phase signal reduction circuit for reducing in-phase signals of noise components. <P>SOLUTION: A DSL transmitter-receiver 1 to which a data terminal is connected and a twist pair cable 4 as a transmission line are connected through a transmission/reception transformer 2, and first and second coils 3a and 3b of a differential transformer 3 which presents high impedance to differential signals and presents low impedance to in-phase signals are connected between the twist pair cable 4 and the earth. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a common-mode signal reduction circuit that reduces a common-mode signal of a noise component in a DSL system using a twisted pair cable as a transmission line.

  DSL (Digital Subscriber) and ADSL (Asymmetric Digital Subscriber Line) methods and VDSL (Very high-bit-rate Digital Subscriber Line) methods, which enable relatively large-capacity data transmission, are used. As the transmission line, a configuration using a twisted pair cable applied as a telephone subscriber line is applied. Since various noise components are superimposed on the twisted pair cable, it causes an increase in the data transmission error rate. A DSL transmission signal is transmitted as a differential signal, but the noise component is superimposed as an in-phase signal, so it has a low impedance for the differential signal and a high impedance for the in-phase signal. A common mode choke is connected to a twisted pair cable to reduce the noise component.

  FIG. 4 is an explanatory view of the main part of a conventional DSL system using a common mode choke coil. A transmission / reception transformer 12 and a common mode choke 13 are connected to a DSL transceiver 11 connected to a data terminal such as a personal computer (not shown). In general, the twisted pair cable 14 is connected via the. When the transmission frequency is about 1 MHz or less, in-phase signal components can be removed by the transmission / reception transformer 12, but in order to enable large-capacity transmission, the transmission frequency is a wide frequency band up to about several tens of MHz. Since the common-mode signal component cannot be sufficiently attenuated by the transmission / reception transformer 12 alone, the characteristics of the low impedance with respect to the differential signal of the transmission signal and the high impedance characteristic with respect to the common-mode signal are illustrated. A common mode choke 13 is connected to suppress in-phase signal components that are noise components.

In addition, as a configuration for reducing common-mode signal components using a common mode choke and a capacitor, a configuration applied to a branch line or the like in a power line communication system has been proposed (for example, see Patent Document 1). In addition, a configuration in which a common mode choke is connected to a front stage of a telephone is proposed in a splitter device including a low-pass filter and a high-pass filter for separating transmission data and audio signals in the DSL system (for example, Patent Documents). 2). Also, a splitter in which a common mode choke for reducing in-phase signals is connected to the data transmission path side in the ADSL system, that is, the front stage of the data terminal, and a low pass filter is connected to the voice signal path side, that is, the front stage of the telephone. An apparatus has been proposed (see, for example, Patent Document 3).
JP 2006-33113 A JP 2003-152894 A JP 2003-179454 A

  In a configuration that uses a common mode choke to reduce the common-mode signal, the common-mode choke exhibits high impedance characteristics due to the common-mode choke characteristics. Although it is possible to prevent the input of noise components composed of phase signal components, the voltage due to the in-phase signal components appearing on the transmission line is increased due to high impedance. Therefore, there is a problem that a part of the in-phase signal component reduction effect on the DSL transceiver is canceled out. Further, the in-phase signal component is partially converted into a differential signal component depending on the balance of the transmission line, and is superimposed as a noise component on the transmission / reception signal of the differential signal, so that there is a problem that the transmission error rate increases.

  The present invention solves the above-described conventional problems, and an object thereof is to reduce in-phase signal components with a relatively simple configuration.

  The common-mode signal reduction circuit of the present invention connects a DSL transceiver and a twisted pair cable as a transmission line via a transmission / reception transformer, and has high impedance and in-phase with respect to a differential signal between the twisted pair cable and the ground. It has a configuration in which a differential transformer having low impedance is connected to a signal.

  Further, a difference between the DSL transceiver and a twisted pair cable as a transmission line is connected via a transmission / reception transformer so that the differential signal has a high impedance for a differential signal and a low impedance for an in-phase signal. The first and second coils of the dynamic transformer are each connected via a capacitor.

  Also, a DSL transceiver and a twisted pair cable as a transmission line are connected via a transmission / reception transformer and a common mode choke coil, and a high impedance and in-phase signal with respect to a differential signal is provided between the twisted pair cable and the ground. The first and second coils of the differential transformer having low impedance are connected via the first and second capacitors, respectively, and the first and second coils of the differential transformer and the first and second coils are connected to each other. A telephone is connected to a connection point with the second capacitor.

  By connecting the twisted pair cable to the ground via the first and second coils of the differential transformer, the first and second coils are connected in series between the lines of the twisted pair cable, and the differential signal is converted into a differential signal. On the other hand, since it has high impedance and the data to be transmitted is a differential signal, there is no influence such as attenuation, and the noise component superimposed on the twisted pair cable is an in-phase signal. Since the impedance is low, common-mode signals can be reduced. Therefore, transmission errors due to noise components in the DSL system can be reduced.

  The common-mode signal reduction circuit of the present invention will be described with reference to FIG. 1. A DSL transceiver 1 and a twisted pair cable 4 as a transmission line are connected via a transmission / reception transformer 2, and between the twisted pair cable 4 and the ground. Further, a differential transformer 3 having a high impedance for a differential signal and a low impedance for an in-phase signal is connected.

  FIG. 1 is an explanatory diagram of Embodiment 1 of the present invention, where 1 is a DSL transceiver, 2 is a transmission / reception transformer, 3 is a differential transformer, and 4 is a twisted pair cable. A data terminal (not shown) is connected to the DSL transceiver 1, and a twisted pair cable 4 is connected to the DSL transceiver 1 via a transmission / reception transformer 2. The differential transformer 3 includes first and second coils 3a and 3b. One end of each of the first and second coils 3a and 3b is connected to the ground, and the other end is connected to the twisted pair cable 4. . Accordingly, the first and second coils 3a and 3b of the differential transformer 3 are connected in series between the wires of the twisted pair cable 4, and the connection point of the first and second coils 3a and 3b is connected to the ground. Thus, the differential transformer 3 has a high impedance characteristic for a differential signal transmitted through the twisted pair cable 4 and a low impedance characteristic for an in-phase signal. Thereby, the in-phase signal of the noise component can be attenuated without affecting the differential signal as the transmission signal. Therefore, unlike the common mode choke coil, the differential transformer 3 does not have a problem of an increase of the common mode signal voltage due to high impedance with respect to the common mode signal, and can reduce the common mode signal of the noise component.

  FIG. 2 is an explanatory diagram of a second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same parts, and C1 and C2 are first and second capacitors. In the second embodiment, the first and second coils 3a and 3b of the differential transformer 3 are connected to the ground via first and second capacitors C1 and C2, respectively. The capacitors C1 and C2 can select capacitance values in consideration of the frequency band of the transmission / reception signal by the DSL transceiver 1 and the inductance of the differential transformer 3 with respect to the in-phase signal.

  FIG. 3 is an explanatory diagram of a third embodiment of the present invention, in which 1 is a DSL transceiver, 2 is a transmission / reception transformer, 3 is a differential transformer, 3a and 3b are first and second coils, 4 is a twisted pair cable, 5 is a common mode choke, 6 is a telephone, and C1 and C2 are first and second capacitors. In the third embodiment, a DSL transceiver 1 is connected to a twisted pair cable 4 via a common mode choke 5 and a transmission / reception transformer 2, and a telephone 6 is connected via a differential transformer 3. The first and second coils 3a and 3b and the telephone 6 are connected to the ground via the first and second capacitors C1 and C2, and the differential transformer 3 functions as a splitter. It is.

  The DSL transceiver 1 prevents the noise component from being input due to the high impedance characteristic of the common mode choke 5 with respect to the in-phase signal, and even if the voltage of the in-phase signal component increases, Since the two capacitors C1 and C2 have low impedance characteristics with respect to the in-phase signal component, the voltage increase of the in-phase signal component can be reliably suppressed. Further, the differential transformer 3 has a characteristic of passing a voice signal band by the telephone 6 and blocking a data transmission band of a higher frequency band than the voice signal band. Therefore, the differential transformer 3 is operated as a splitter. Can do.

It is explanatory drawing of Example 1 of this invention. It is explanatory drawing of Example 2 of this invention. It is explanatory drawing of Example 3 of this invention. It is principal part explanatory drawing of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DSL transmitter / receiver 2 Transmission / reception transformer 3 Differential transformer 4 Twisted pair cable 5 Common mode choke coil C1, C2 Capacitor

Claims (3)

  A DSL transceiver and a twisted pair cable as a transmission line are connected via a transmission / reception transformer, and a differential having a high impedance for a differential signal and a low impedance for an in-phase signal between the twisted pair cable and ground. A common-mode signal reduction circuit characterized by connecting a transformer.   A DSL transceiver and a twisted pair cable as a transmission line are connected via a transmission / reception transformer, and a differential having a high impedance for a differential signal and a low impedance for an in-phase signal between the twisted pair cable and ground. A common-mode signal reduction circuit, wherein the first and second coils of the transformer are connected to each other via a capacitor.   A DSL transceiver and a twisted pair cable as a transmission line are connected via a transmission / reception transformer and a common mode choke coil, and a high impedance and in-phase signal with respect to a differential signal between the twisted pair cable and ground. The first and second coils of the differential transformer having low impedance are connected via the first and second capacitors, respectively, and the first and second coils of the differential transformer and the first and second coils are connected to each other. A common-mode signal reduction circuit, wherein a telephone is connected to a connection point of the capacitor (2).

Images