JP2006295511A - Power line carrier communication modem and signal transformer circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power line carrier communication modem capable of suppressing a common mode component not only in a transmitting signal but also in a receiving signal. <P>SOLUTION: The power line carrier communication modem using a power line as a transmission line is provided with a signal transformer 1 where a pair of signal lines 9 are connected to one side and a power line 3 is connected to the other side, a low impedance circuit 5 for reducing the impedance between the pair of signal lines 9 and GND of a common mode signal and a switch circuit 2 to be driven on the basis of a prescribed control signal, where the pair of signal lines 9 are connected to the GND through both of the low impedance circuit 5 and the switch circuit 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power line carrier communication modem applied to a power line carrier communication system using an existing power line as a transmission line, and in particular, a power line carrier capable of effectively reducing a leakage electromagnetic field radiated from the power line. The present invention relates to a communication modem and a signal transformer circuit.

  In power line communication (Power Line Communication: hereinafter abbreviated as “PLC”) in which communication is performed using an existing power line as a transmission line, a leakage electromagnetic field emitted from the power line during communication is a problem. The PLC signal is injected into a power line in a mode called a differential (differential) mode. However, a mode signal (common mode signal) called a common (common mode) may occur due to circuit imbalance of the communication line.

  The common mode signal is transmitted through the two power lines in the same phase, and forms a current loop with the ground as a feedback path. The leakage electromagnetic field emitted from the power line is considered to be proportional to the magnitude of this common mode current. Therefore, in order to reduce the leakage electromagnetic field, it is necessary to suppress the common mode current flowing through the power line.

  Under such circumstances, there is a publication that discloses a technique for reducing the amount of unnecessary electromagnetic radiation in a high-frequency region in a balanced transmission circuit provided in an input / output unit on the equipment side of an information communication device that performs balanced transmission (for example, Patent Documents). 1, see FIG.

  In this patent document 1, in a balanced transmission circuit that outputs a balanced signal via a forced transformer, an impedance element is inserted between the lines on the secondary side of the forced transformer, and the electrical middle point of the impedance element is replaced with a capacitive element. And connecting to the frame ground (FG) or at least one of the signal ground (SG) and connecting the electrical midpoint to the center tap of the forced transformer, The common mode midpoint potential is the same potential, so that the balance of the transmission line is improved.

JP-A-9-36817

  However, in the conventional technique shown in Patent Document 1, the common mode component in the transmission signal can increase the effect of reducing the amount of unnecessary electromagnetic radiation by flowing into the FG. For the common mode component in the received signal that has propagated, there has been a problem that the common mode current is increased as a result of a decrease in the impedance against FG.

  In addition, since the transmission line in the PLC system is an existing power line, the circuit balance configuration is generally poor and it is difficult to say that the transmission line is an ideal balanced line. At this time, in the prior art disclosed in Patent Document 1, since the coupling circuit with the ground exists on the secondary side (communication path side) of the transformer, if the transformer midpoint is not ideal, the common mode signal between the ground and the ground However, there is a problem that the common mode current increases due to the coupling.

  The present invention has been made in view of the above, and provides a power line carrier communication modem and a signal transformer circuit capable of suppressing an increase in common mode current not only in a transmission signal but also in a common mode component in a reception signal. With the goal. It is another object of the present invention to provide a power line carrier communication modem and a signal transformer circuit capable of suppressing an increase in common mode current even if the connected transmission line is not an ideal balanced line.

  In order to solve the above-described problems and achieve the object, a power line carrier communication modem according to the present invention uses a power line as a transmission line. In the power line carrier communication modem, a signal line pair is connected to one side and the power line is A signal transformer connected to the other side; a low-impedance circuit that reduces the impedance between GND in the common mode signal; and a switch circuit that operates based on a predetermined control signal, the low-impedance circuit and the switch circuit The signal line pair and GND are connected via both of the above.

  According to the power line carrier communication modem of the present invention, a low impedance circuit that lowers the impedance between the common mode signal and the GND is provided on the side opposite to the power line connected to the signal transformer, and further provided with a switch circuit. Since the low-impedance circuit functions only in such a case, an increase in the common mode component in the received signal propagating through the communication path can be suppressed. Moreover, since the low impedance circuit is arranged on the side opposite to the power line, an increase in coupling between the communication path and GND can be prevented, and the connected communication path is an ideal balanced line. Even if it is not, the effect that the increase of the common mode current can be suppressed is obtained.

  Embodiments of a power line carrier communication modem and a signal transformer circuit according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a circuit configuration of a power line carrier communication modem according to a first embodiment of the present invention. In the figure, a modem device 8 having an input / output terminal is connected to a power line 3 which is an existing power line, for example. For example, the modem device 8 corresponding to the power line carrier communication modem of the present invention performs predetermined communication using the power line 3 as a transmission line.

  In FIG. 1, a modem device 8 includes a primary winding and a secondary winding that is magnetically coupled to the primary winding, and the primary winding side (hereinafter referred to as the “primary side”) is a signal within itself. The signal transformer 1 connected to the line 9 and the secondary winding side (hereinafter referred to as “secondary side”) to the power line 3, and the primary winding side (hereinafter referred to as primary side) of the signal transformer 1 A communication control circuit 7 that performs transmission and reception of transmission signals and predetermined communication control, and an amplifier 4 that amplifies the transmission signal transmitted from the power line 3 via the signal transformer 1 and outputs the amplified signal to the communication control circuit 7. 1, an amplifier 4-2 that amplifies a signal (communication signal) output from the communication control circuit 7 and outputs the amplified signal to the signal transformer 1, and a pair of switches connected to each of the signal line pair 9, a switch circuit 2, switch circuit 2 and ground (hereinafter referred to as “G And a low impedance circuit 5, which connects between the inserted signal line pair 9 and the ground (hereinafter referred to as "GND") between abbreviated) and D ". The low impedance circuit 5 is a circuit configured so that the impedance is lowered only with respect to the common mode signal, and a typical example is a normal mode choke element.

  Next, features of the modem device 8 shown in FIG. 1 will be described. In the figure, a common mode signal may be generated on the primary side of the signal transformer 1 due to, for example, imbalance in the circuit configuration. The common mode signal generated in this way is propagated to the power line 3 through the signal transformer 1. In particular, when the coupling capacitance between the primary winding and the secondary winding of the signal transformer 1 is large, a common mode signal having a high signal level is propagated to the power line 3.

  On the other hand, in this embodiment, the low impedance circuit 5 is provided on the primary side of the signal transformer 1 in order to suppress the propagation of the common mode signal to the power line 3. With this configuration, the common mode current generated on the primary side of the signal transformer 1 based on the common mode signal can be guided to the GND side, and propagation to the power line 3 can be suppressed. Since the low impedance circuit 5 is arranged on the primary side of the signal transformer 1, there is a problem in the prior art that the common mode current is increased due to the common mode signal transmitted from the power line 3 side ( Which increases the coupling between ground).

  A switch circuit 2 is provided between the low impedance circuit 5 and the signal line pair 9, and only when the modem device 8 performs a transmission operation, a switch is made based on the switch control signal 6 output from the communication control circuit 7. The circuit 2 is controlled to be turned on.

  With this configuration, the impedance between the pair of common mode signals on the primary side of the signal transformer 1 during transmission is kept low by the low impedance circuit 5, and the common mode signal output to the power line 3 side is suppressed. On the other hand, since the connection between the low-impedance circuit 5 and the signal line pair 9 is limited only at the time of transmission, the impedance between the GND of the common mode signal input from the power line 3 side during reception is kept high and flows to the power line 3 side. An increase in common mode current is suppressed.

  Next, the operation of the modem apparatus shown in FIG. 1 will be described with reference to FIGS. 2 is a diagram showing an operation waveform of the main part of the modem device at the time of transmission / reception and the impedance between the common mode signal and the GND, and FIG. 3 is a diagram of the common mode signal at the time of transmission / reception. It is a figure which shows a state.

  First, in FIG. 2, when a transmission operation is performed in the modem device 8, a switch control signal 6 (ON signal) is output and held from the communication control circuit 7 to the switch circuit 2, and is transmitted via the switch circuit 2. Thus, the signal line pair 9 and the low impedance circuit 5 are connected, and the impedance between the common mode signal pair GND is reduced to approximately 0Ω. Therefore, when an ON signal is output from the communication control circuit 7, as shown in FIG. 3, the common mode signal flows into the GND by the action of the low impedance circuit 5, and the propagation of the common mode signal to the power line 3 side is prevented. The

  On the other hand, when the modem device 8 performs a reception operation (for example, when the modem device 8 enters a reception operation following a transmission operation), the communication control circuit 7 sends a switch control signal 6 to the switch circuit 2. (OFF signal) is output and held, the connection between the signal line pair 9 and the low impedance circuit 5 is released, and the impedance between the common mode signal pair GND becomes high impedance. Therefore, when the off signal is output from the communication control circuit 7, as shown in FIG. 3, the common mode current propagating from the power line 3 is prevented from flowing into the GND, and the increase of the common mode current on the power line 3 side is prevented. It is suppressed.

  In the above description, the switch circuit 2 is turned on (make) when the switch control signal 6 (ON signal) is output and held, and when the switch control signal 6 (OFF signal) is output and held. Although described as a switch mechanism that operates so as to be turned off (break), it is made when the switch control signal 6 (ON signal) is output and breaks when the switch control signal 6 (OFF signal) is output. It may be a switch mechanism that operates in a short time. That is, it is not always necessary to hold the on signal or the off signal when making or breaking the switch.

  As described above, according to the power line carrier communication modem of this embodiment, the low-impedance circuit for lowering the impedance between the common mode signal and GND is provided on the primary side (modem internal side) of the signal transformer, and the switch circuit. Since the low impedance circuit functions only when necessary, it is possible to suppress an increase in the common mode component in the received signal propagating through the power line.

  Further, according to the power line carrier communication modem of this embodiment, since the low impedance circuit is arranged on the primary side (the side opposite to the communication path), the coupling between the communication path and the GND is increased. Even if the connected communication path is not an ideal balanced line, an increase in common mode current can be suppressed.

Embodiment 2. FIG.
FIG. 4 is a diagram illustrating a schematic configuration of the signal transformer circuit according to the second embodiment of the present invention. The characteristics of the signal transformer 1, which is the main part of the signal transformer circuit shown in FIG.
(1) The metal coating 1-2 is given on the surface at the side of the primary winding of the core (transformer core) 1-1 inserted in its own primary winding 1-3.
(2) The metal coating 1-2 is configured to be connected to the GND via the switch circuit 11.
As the core material of the signal transformer 1, it is preferable to use an insulating material such as ferrite, but an insulating material other than ferrite may be used as long as the function of the transformer is not significantly impaired. The metal coating 1-2 may be anything as long as it can adhere to the surface of the core 1-1. However, in order to enhance the effect of the signal transformer circuit, a metal having a highly conductive property is preferable.

  In FIG. 4, since the primary winding 1-3 of the signal transformer 1 has strong capacitive coupling with the metal coating 1-2, the common mode signal generated on the primary side of the signal transformer 1 is the metal coating 1- 2 to GND via the switch circuit 11. By this action, a common mode signal output to a transmission line (not shown) (for example, a power line) is suppressed.

  The switch circuit 11 is controlled to be turned on only at the time of transmission by a switch control signal 6 from a control means (not shown). For example, at the time of transmission, the common mode current based on the common mode signal generated on the primary side of the signal transformer 1 is connected to the GND by connecting the metal coating 1-2 to the GND via the switch circuit 11 as described above. It becomes easy to flow and the effect of a metal coating is acquired.

  On the other hand, when receiving a common mode current from the secondary winding 1-4 side (power line side) during reception, the metal coating 1-2 is prevented from flowing into the GND in order to prevent the propagated common mode current from flowing into the GND. It is controlled so that the connection with GND is cut off.

  As described above, according to the signal transformer circuit of this embodiment, the metal coating applied to the primary winding side of the signal transformer core is connected to the GND via the switch circuit, and is switched only during transmission. Since the circuit is controlled to be turned on, the common mode current based on the common mode signal generated on the primary side of the signal transformer 1 easily flows to GND, and the common mode component in the received signal that has propagated through the communication path Can also be suppressed.

  Further, according to the signal transformer circuit of this embodiment, since the low impedance circuit is arranged on the primary side (the side opposite to the communication path), an increase in coupling between the communication path and GND is prevented. Even if the connected communication path is not an ideal balanced line, an increase in common mode current can be suppressed.

  As described above, the power line carrier communication modem according to the present invention is useful as a communication modem applicable to a power line carrier communication system using an existing power line as a transmission line, and is particularly effective for a leakage electromagnetic field radiated from the power line. It is suitable for the case where it is desired to reduce it.

It is a figure which shows the circuit structure of the power line carrier communication modem concerning Embodiment 1 of this invention. It is a figure which shows the principal part operation waveform of the modem apparatus at the time of transmission / reception, and the impedance between GND of a common mode signal. It is a figure which shows the state of the common mode signal in each at the time of transmission / reception. It is a figure which shows schematic structure of the signal transformer circuit concerning Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Signal transformer 1-1 Core 1-2 Metal coating 1-3 Primary winding 1-4 Secondary winding 2,11 Switch circuit 3 Power line 4-1, 4-2 Amplifier 5 Low impedance circuit 6 Switch control signal 7 Communication control circuit 8 Modem device 9 Signal line pair

Claims (4)

In a power line carrier communication modem that uses a power line as a transmission line,
A signal transformer in which a signal line pair is connected to one side and the power line is connected to the other side;
A low-impedance circuit that reduces the impedance between GND in the common mode signal;
A switch circuit that operates based on a predetermined control signal;
With
A power line carrier communication modem, wherein the signal line pair and GND are connected through both the low impedance circuit and the switch circuit.   2. The power line carrier communication modem according to claim 1, wherein the switch circuit is turned on only when a communication signal is transmitted from the signal line pair to the power line side. In a signal transformer circuit applied to a power line carrier communication modem using a power line as a transmission line,
A transformer core, a primary winding wound around the transformer core, and a secondary winding wound around the transformer core and magnetically coupled to the primary winding. A signal transformer connected to the winding and the power line connected to the secondary winding;
A switch circuit that operates based on a predetermined control signal;
With
A signal transformer in which a metal coating is applied to a surface of a transformer core on a primary winding side of the signal transformer, and the transformer core to which the metal coating is applied is connected to GND through the switch circuit. circuit. 4. The signal transformer circuit according to claim 3, wherein the switch circuit is turned on only when a communication signal is transmitted from the signal line pair to the power line side.

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