JP4182069B2 - Communication device - Google Patents

Description

  The present invention relates to a communication apparatus that superimposes and transmits a normal mode communication signal on a communication line including first and second conductive lines.

  In recent years, there is a demand for communication network systems not only in offices but also in general homes. As communication methods that can be selected when constructing a communication network system in the home, there are a communication method using wireless, a communication method using wire, and a power line communication method using power line. Among these, the power line communication method has advantages such as no wiring work cost is required because an existing power line is used as a communication line, and the appearance in the home is not impaired. In the present application, a power line used as a communication line in power line communication is referred to as a power line communication line.

  FIG. 4 shows a simplified concept of the power line communication system. The power line communication system includes a power line communication line 1 including an L line (live line) 1L and an N line (neutral line) 1N, and a communication device 110 connected to the power line communication line 1 via a pair of terminals 2A and 2B. And. In FIG. 4, symbol Z1 represents the impedance between the L line 1L and ground or ground, and symbol Z2 represents the impedance between the N line 1N and ground or ground. The communication device 110 includes a signal source 100 and inputs / outputs a normal mode communication signal to / from the power line communication line. The signal source 100 is included in, for example, a power line communication modem.

  In the system shown in FIG. 4, the signal source 100 is a balanced signal (normal mode signal) consisting of two signals 101 and 102 having symmetrical voltage waveforms with respect to the ground level G0 on the L line 1L and the N line 1N as communication signals. ). The potential difference between the L line 1L and the N line 1N when this communication signal passes through the power line communication line 1 is V.

  When the power line communication line 1 is in a balanced ideal state, that is, when the impedances Z1 and Z2 are equal, when the communication signal passes through the power line communication line 1, the potential of the L line 1L becomes + V / 2, The potential of the N line 1N is −V / 2. Therefore, the potential difference V1 between the earth or ground and the L line 1L and the potential difference V2 between the N line 1N and the earth or ground are both V / 2. As a result, the radiated electric field generated from the L line 1L and the radiated electric field generated from the N line 1N are out of phase with each other.

  On the other hand, when the power line communication line 1 is unbalanced, that is, when the impedances Z1 and Z2 are not equal, the potential differences V1 and V2 are not equal when the communication signal passes through the power line communication line 1. In this case, since the absolute value differs between the radiation electric field generated from the L line 1L and the radiation electric field generated from the N line 1N, they are not canceled out. In this case, radiation noise having a magnitude corresponding to the difference between the absolute values of the two radiation electric fields is generated from the power line communication line 1. Therefore, as the balance of the power line communication line 1 is lower, a larger radiation noise is generated from the power line communication line 1. This noise is common mode noise caused by unbalanced lines.

As a countermeasure against this radiation noise, a method of inserting a common mode filter for attenuating the common mode noise into the communication line as described in Patent Document 1, for example, is considered.
JP 2004-80436 A

  However, the common mode filter only removes common mode noise and does not fundamentally improve the balance of the communication line. In addition, it is difficult to attenuate only the common mode noise without attenuating the normal mode signal even if it is a common mode filter. Especially in the power line communication that communicates with the normal mode signal, its communication signal component It will also affect. Therefore, a method for fundamentally improving radiation noise is required.

  FIG. 5 shows a configuration example of a communication device in the power line communication system. This communication apparatus includes a modem 210 having a transmission circuit 211 for generating a transmission signal, a balun transformer T100 connected to the modem 210 via a pair of terminals 1A and 1B, and power line communication via a pair of terminals 2A and 2B. First and second conductive lines 3 and 4 connected to the lines 1L and 1N of the line 1 and capacitors C1 and C2 provided on the first and second conductive lines 3 and 4 are provided. . The balun transformer T100 includes a primary side winding 121 to which an unbalanced signal is input, and a secondary side winding 122 coupled to the primary side winding 121. One end and the other end of the primary winding 121 are connected to the transmission circuit 211 in the modem 210 via a pair of terminals 1A and 1B. The other end of the primary winding 121 is grounded. One end of the secondary winding 122 is connected to the first conductive line 3 corresponding to the L line 1L, and the other end of the secondary winding 122 is connected to the second conductive line 4 corresponding to the N line 1N. ing. The capacitors C1 and C2 have a function as a high-pass filter that prevents the frequency component of power from passing through the modem 210 side.

  A midpoint 24C of the secondary winding 122 of the balun transformer T100 is grounded. In this case, if the impedance between the first conductive line 3 and the ground and the impedance between the second conductive line 4 and the ground are equal and the balance between the conductive lines is maintained, as shown in FIG. When a potential difference V is given between both ends of the primary winding 21, the potential difference between the ground and the first conductive line 3 and the potential difference between the second conductive line 4 and the ground are ideal. Both are V / 2. Thus, the balun transformer T100 generates an unbalanced signal composed of two signals having a voltage waveform asymmetric with respect to the ground level G1 on the modem 210 side, and ideally has a voltage waveform symmetric with respect to the ground level G1 on the modem 210 side. It is converted into a balanced signal composed of two signals 101 and 102.

  Here, the ground level G1 on the modem 210 side is generally defined by the frame ground on the modem 210 side, and the ground level G0 on the power line communication line 1 side is generally defined by the ground. For this reason, the ground level G1 on the modem 210 side and the ground level G0 on the power line communication line 1 side are different. Conventionally, since the difference between these ground levels is not taken into consideration, even if the ground point of the balun transformer T100 is set to the middle point 24C of the secondary winding 122, the balance between the conductive lines is not maintained. The two signals 101 and 102 output to each conductive line are not necessarily balanced signals. Therefore, ideally, a part of the signals 101 and 102 that should be in the normal mode is converted into a common mode signal, which causes radiation noise. By the way, even if the balance between the conductive lines cannot be improved, if the normal mode signal having a high balance can be superimposed on the power line communication line 1, it is considered that the problem of radiation noise can be solved.

  Note that the above problem applies not only to power line communication lines, but also to all communication lines that transmit balanced signals.

  The present invention has been made in view of such a problem, and an object thereof is to superimpose an ideal normal mode signal having a high balance on a communication line, thereby preventing generation of radiation noise in the communication line. It is an object of the present invention to provide a communication device that can perform the above-described operation.

A communication apparatus according to the present invention is a communication apparatus that transmits a balanced signal to a communication line including first and second conductive lines, and outputs a first transmission signal in an unbalanced state based on a baseband signal . Transmission circuit, a second transmission circuit that outputs a second transmission signal in an unbalanced state based on the baseband signal, and the first and second transmission signals converted into one balanced signal. A balanced circuit unit that outputs to the two conductive lines and converts the balanced signal transmitted to the first and second conductive lines into an unbalanced received signal and outputs the received signal . A current detection unit that is provided in a subsequent stage and detects a common mode current generated in the communication line, and a signal of the first transmission signal so that the common mode current is reduced based on the common mode current detected by the current detection unit Level and second transmission And control means for adjusting the issue of the signal level, provided between the receiving circuit for receiving a reception signal outputted from the balancing circuit unit, a balancing circuit portion and the first and second transmission circuits and reception circuits The transmission / reception change-over switch is provided.
In the communication device according to the present invention, the balancing circuit unit includes a first primary winding to which the first transmission signal is input, and a second primary winding to which the second transmission signal is input. The first primary winding is magnetically coupled to the first primary winding and one end is connected to the first conductive wire, and the second primary winding is magnetically coupled to the first primary winding. And a second secondary winding having one end connected to the other end of the first secondary winding and the other end connected to the second conductive wire. The number of turns of the secondary winding and the number of turns of the second secondary winding are the same, and the connection point between the first secondary winding and the second secondary winding is grounded It is configured. The transmission / reception selector switch connects the first primary winding and the second primary winding in series when a signal is received by the reception circuit, and the first primary winding connected in series. The first primary winding and the second primary winding are connected to the receiving circuit so that a reception signal received by the first primary winding and the second primary winding is transmitted to the receiving circuit. It is made like that.

  In the communication apparatus according to the present invention, the common mode current generated in the communication line is detected, and the signal level of the first transmission signal and the signal level of the second transmission signal are adjusted so that the common mode current decreases based on the detected common mode current. Is done. The adjusted first and second transmission signals are converted into one balanced signal and output to the communication line. As a result, the common mode current is consequently suppressed, and an ideal normal mode signal with a high balance is superimposed on the communication line.

The communication apparatus according to the present invention further includes a modulation circuit that modulates a baseband signal that is a basis of the first and second transmission signals and outputs the modulated signal to the first and second transmission circuits. May be.
In this case, the control means adjusts the signal levels of the first and second transmission signals by controlling the signal level of the modulation signal output from the modulation circuit.

  Furthermore, a pair of first signal lines connecting the first primary winding and the first transmission circuit, and a pair of first signal lines connecting the second primary winding and the second transmission circuit. 2 signal lines may be further provided. When the transmission / reception selector switch receives a signal by the receiving circuit, the signal line corresponding to the first conductive line of the pair of first signal lines and the second conductive line of the pair of second signal lines The connection state of each signal line may be switched so that the reception signal from the balancing circuit unit is transmitted to the reception circuit via the corresponding signal line.

  According to the communication device of the present invention, the signal level of the first transmission signal and the signal level of the second transmission signal are detected so that the common mode current generated in the communication line is detected and the common mode current is reduced based on the detected common mode current. Since the adjusted first and second transmission signals are converted into one balanced signal and output to the communication line, an ideal normal mode signal having a high balance is provided on the communication line. Superimposition can be performed, thereby preventing generation of radiation noise in the communication line.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows the overall configuration of a communication apparatus according to an embodiment of the present invention. This communication apparatus is applied to, for example, a power line communication system, and includes an L line (live line) 1L and an N line (neutral line) 1N constituting the power line communication line 1 via a pair of terminals 2A and 2B. Connected to. In the power line communication system including this communication device, as in the power line communication system shown in FIG. 4, two signals 101, 102 having symmetrical voltage waveforms with respect to the ground level G0 are respectively transmitted to the L line 1L and the N line 1N as communication signals. A balanced signal (normal mode signal) consisting of In addition, a balanced signal output from another communication device (not shown) is received.

  The communication apparatus includes a modem 10 having first and second transmission circuits 11A and 11B and a reception circuit 12, a balancing circuit unit 20 connected to the modem 10 via a pair of terminals 1A and 1B, and balancing. A current detection unit 30 provided at a subsequent stage of the circuit unit 20, and first and second conductive lines 3, 4 connected to the lines 1L, 1N of the power line communication line 1 via a pair of terminals 2A, 2B; And capacitors C1 and C2 provided on the first and second conductive lines 3 and 4, respectively. The communication apparatus also connects a pair of first signal lines 13 (13A, 13B), a pair of terminals 1A, 1B, and a pair of second signal lines to connect the modem 10 and the balancing circuit unit 20. 14 (14A, 14B) and a pair of terminals 1C, 1D. In this communication apparatus, the connection state of the signal lines 13 and 14 between the modem 10 and the balancing circuit unit 20 differs between signal transmission and reception, but in FIG. 1, it corresponds to the connection state during transmission. The structure to be shown is shown.

  The communication apparatus also converts an analog common mode current signal detected by the current detection unit 30 into a digital signal and outputs it as a current level signal 41, and the first and first based on the current level signal 41. A transmission level controller 50 for adjusting and controlling the levels of the transmission signals 201 and 202 output from the two transmission circuits 11A and 11B. The transmission level controller 50 corresponds to a specific example of “control means” in the present invention.

  The capacitors C1 and C2 have a function as a high-pass filter that prevents the frequency component of power from passing through the modem 10 side. The current detection unit 30 includes a magnetic core 31 and windings 32, 33, and 34 that are wound around the magnetic core 31 and are magnetically coupled to each other. One end of the winding 32 is connected to one end of the first secondary winding 22A of the first transformer T1A on the first conductive line 3, and the other end is connected to one end of the capacitor C1. One end of the winding 33 is connected to the other end of the second secondary winding 22B of the second transformer T1B on the second conductive line 4, and the other end is connected to one end of the capacitor C2. Both ends of the winding 34 are connected to the AD converter 40. A resistor R1 is connected in parallel between the winding 34 and the AD converter 40.

  The first transmission circuit 11 </ b> A outputs the unbalanced first transmission signal 201 to the balancing circuit unit 20. The second transmission circuit 11B outputs the unbalanced second transmission signal 202 to the balancing circuit unit 20. The receiving circuit 12 receives a balanced signal transmitted from another communication device (not shown) to the communication line 1 as a reception signal 203 in an unbalanced state via the balancing circuit unit 20.

  The balancing circuit unit 20 has a function of converting the first and second transmission signals 201 and 202, which are unbalanced signals, into one balanced signal 101 and 102 and outputting them to the first and second conductive lines 3 and 4. have. The balancing circuit unit 20 also has a function of converting a received signal received as a balanced signal into an unbalanced signal and outputting it to the receiving circuit 12. The balancing circuit unit 20 includes first and second transformers T1A and T1B. The first transformer T1A includes a first primary winding 21A to which the first transmission signal 201 from the first transmission circuit 11A is input, and the first primary winding 21A. The first secondary winding 22A is magnetically coupled via the magnetic core 23A. The second transformer T1B includes a second primary winding 21B to which the second transmission signal 202 from the second transmission circuit 11B is input, and a second primary winding 21B. It has a second secondary winding 22B magnetically coupled via a magnetic core 23B. For example, the number of turns of the first primary winding 21A and the number of the second primary winding 21B are the same.

  One end of the first secondary winding 22A is connected to the first conductive line 3 corresponding to the L line 1L. One end of the second secondary winding 22B is connected to the other end of the first secondary winding 22A, and the other end is connected to the second conductive line 4 corresponding to the N line 1N. The number of turns of the first secondary winding 22A and the number of the second secondary winding 22B are the same. A connection point 24C between the first secondary winding 22A and the second secondary winding 22B is grounded. The first secondary winding 22A and the second secondary winding 22B are configured, for example, by dividing a single winding at a midpoint and grounding the midpoint as a connection point 24C. The grounding point of the connection point 24C is, for example, the frame ground of the ground level G1.

  One end of the first primary winding 21A is connected to one signal line 13A of the pair of first signal lines 13, and the other end is connected to the other signal line 13B. One end of the second primary winding 21B is connected to one signal line 14A of the pair of second signal lines 14, and the other end is connected to the other signal line 14B. The signal line 13 </ b> A corresponds to the first conductive line 3, and the signal line 14 </ b> B corresponds to the second conductive line 4.

  FIG. 2 shows a configuration example of a circuit in the modem 10. In addition to the first and second transmission circuits 11A and 11B and the reception circuit 12, the modem 10 includes a baseband circuit (modem / demodulation circuit) 70 and changeover switches SW1, SW2, and SW3. The baseband circuit 70 corresponds to a specific example of “a modulation circuit” in the invention. The changeover switches SW1, SW2, and SW3 correspond to a specific example of “transmission / reception changeover switch” in the present invention.

  The first transmission circuit 11A converts a digital modulation signal output from the baseband circuit 70 into an analog signal, and extracts a signal in a predetermined communication band for transmission from the output signal from the DA converter 81A. A transmission filter 82A and a transmission amplifier 83A that amplifies the signal in the communication band filtered by the transmission filter 82A are included. Similarly, the second transmission circuit 11B includes a DA converter 81B, a transmission filter 82B, and a transmission amplifier 83B. The reception circuit 12 includes a reception amplifier 91 that amplifies the reception signal 203, a reception filter 92 that removes unnecessary frequency components from the output of the reception amplifier 91 and extracts a signal in a predetermined communication band, and a communication band that is filtered by the reception filter 92. And an AD converter 93 that converts the signal into a digital signal and outputs the digital signal to the baseband circuit.

  The change-over switches SW1, SW2, SW3 have a function of switching the connection state between the first and second transmission circuits 11A, 11B and the reception circuit 12 and the primary windings 21A, 21B of the balancing circuit unit 20. Yes. Each change-over switch SW1, SW2, SW3 is constituted by a semiconductor switch, for example, and performs a switching operation based on a switch control signal 71 from the baseband circuit 70.

  FIG. 2 shows a configuration corresponding to the connection state at the time of transmission as the state of the selector switches SW1, SW2, and SW3. As shown in the figure, during transmission, the changeover switch SW2 is turned off, and the changeover switches SW1 and SW3 are turned on. At the time of reception, the switch SW2 is turned on and the switches SW1 and SW3 are turned off, contrary to the state shown in the figure. The changeover switch SW1 selectively connects the signal line 13B to the first transmission circuit 11A and selectively connects the signal line 13B to the ground. The changeover switch SW2 selectively interconnects the signal line 13B and the signal line 14A. The changeover switch SW3 selectively connects the signal line 14A to the second transmission circuit 11B.

  The first primary winding 21A is connected to the first transmission circuit 11A via the pair of first signal lines 13 (13A, 13B) and the pair of terminals 1A, 1B during signal transmission. It has become. The second primary winding 21B is connected to the second transmission circuit 11B via the pair of second signal lines 14 (14A, 14B) and the pair of terminals 1C, 1D during signal transmission. It has become. The other signal line 13B of the pair of first signal lines 13 and the other signal line 14B of the pair of second signal lines 14 are grounded during signal transmission. The grounding destination is, for example, a frame ground of the ground level G1.

  When the signal is received by the reception circuit 12, the signal line 13A corresponding to the first conductive line 3 and the pair of second signals out of the pair of first signal lines 13 by the switching operation of the selector switches SW1, SW2, and SW3. The connection state of each signal line is switched so that the reception signal 203 from the balancing circuit unit 20 is transmitted to the reception circuit 12 through the signal line 14B corresponding to the second conductive line 4 among the lines 14. It has become. In this case, when the switch SW2 is turned on, the other signal line 13B of the pair of first signal lines 13 and the one signal line 14A of the pair of second signal lines 14 are connected, As a result, the other end of the first primary side winding 21A and one end of the second primary side winding 21B are connected, and the first primary side winding 21A and the second primary side winding 21B are connected. Are connected in series. In this case, the grounding state of the signal line 13B is released by turning off the changeover switch SW1. Further, when the switch SW3 is turned off, the connection state between the signal line 14A and the second transmission circuit 11B is released. Thus, at the time of reception, the first primary side winding 21A and the second primary side winding 21B are connected in series, and compared with the case where reception is performed using only one primary side winding. Thus, a received signal having a large amplitude can be captured.

  The baseband circuit 70 includes a modulation circuit and a demodulation circuit. At the time of signal transmission, the baseband circuit 70 modulates a digital baseband signal that is the basis of the first and second transmission signals 201 and 202 by a predetermined method (for example, OFDM method), and converts the modulated signal to The signals are output to the first and second transmission circuits 11A and 11B. In this case, the baseband circuit 70 adjusts the level of the modulation signal output to the first and second transmission circuits 11A and 11B based on the signal level control signal 51 from the transmission level controller 50. . The baseband circuit 70 also demodulates the digital reception signal output from the reception circuit 12 by a predetermined method to generate a digital baseband signal when receiving the signal.

  The transmission level controller 50 outputs a signal level control signal 51 based on the current level signal 41 of the common mode current detected by the current detector 30, and outputs the modulation from the baseband circuit 70 so that the common mode current decreases. The signal level of the signal is controlled. Thereby, adjustment control of the signal levels of the first and second transmission signals 201 and 202 is performed. Since the degree of balance of the power line communication line 1 (the degree of balance of the first and second conductive lines 3 and 4) can be considered to vary with time, control by the transmission level controller 50 is performed at a predetermined interval (for example, power frequency). It is desirable to carry out at a period synchronized with the half wave of the above.

Next, the operation of this communication apparatus, particularly the operation for controlling the signal level during transmission will be described with reference to FIG.
FIG. 3 shows a control operation at the time of transmission in this communication apparatus. In this communication apparatus, an unbalanced signal is output as the transmission signal 201 from the first transmission circuit 11A to the first primary winding 21A of the first transformer T1A via the pair of first signal lines 13. Is done. An unbalanced signal is output as the transmission signal 202 from the second transmission circuit 11B to the second primary winding 21B of the second transformer T1B via the pair of second signal lines 14. The first and second transformers T1A and T1B convert the first and second transmission signals 201 and 202, which are unbalanced signals, into one balanced signal 101 and 102, and the first and second conductive lines 3, 4 is output.

  Here, the number of turns of the first primary side winding 21A and the number of turns of the second primary side winding 21B are the same, and the number of turns of the first secondary side winding 22A and the second secondary side winding are the same. Consider a case where the number of turns of the winding 22B is the same. In this case, if the first and second conductive lines 3 and 4 are in an ideal equilibrium state, the signal level of the first transmission signal 201 and the signal level of the second transmission signal 202 are set to the same level. The ideal normal mode signal is superimposed on the first and second conductive lines 3 and 4. However, in practice, this is not necessarily an ideal balanced state, and in the initial state, there is a possibility that a common mode current is included in the output signal from the balancing circuit unit 20. The current detection unit 30 detects the common mode current. The AD converter 40 converts the analog common mode current detection signal detected by the current detection unit 30 into a digital signal, and outputs it as a current level signal 41 to the transmission level controller 50 (step S11). The transmission level controller 50 looks at the current level signal 41 and determines whether or not the common mode current is detected (whether or not the signal level is zero) (step S12). If the common mode current is not detected (step S12; N), the current level signal 41 is detected again after a predetermined period.

  When the common mode current is detected (step S12; Y), the transmission level controller 50 outputs the signal level control signal 51 to control the baseband circuit 70 (FIG. 2), thereby performing the first transmission. The signal level of the signal 201 and the signal level of the second transmission signal 202 are adjusted and controlled (step S13). This level adjustment control is performed so that the common mode current decreases. Then, the common mode current is detected again, and this control is repeated until the common mode current is no longer detected (until the signal level of the common mode current becomes zero). As a result, even if the ground level G1 on the modem 10 side and the ground level G0 on the power line communication line 1 side are different, the common mode current generated by the difference is suppressed and ideally balanced between the conductive lines. Normal mode signals can be superimposed.

  As described above, according to the present embodiment, the common mode current generated in the communication line is detected, and the signal level of the first transmission signal 201 and the second level are reduced so that the common mode current decreases based on the detected common mode current. The signal level of the transmission signal 202 is adjusted, and the adjusted first and second transmission signals 201 and 202 are converted into one balanced signal 101 and 102 and output to the respective conductive lines 3 and 4. Therefore, an ideal normal mode signal with a high balance can be superimposed on the power line communication line 1, thereby preventing radiation noise from being generated in the power line communication line 1.

  In addition, this invention is not limited to the said embodiment, A various change is possible. For example, the present invention is not limited to a system using a power line as a communication line, but can be applied to any communication system using a communication line that transmits a balanced signal.

It is a circuit diagram which shows one structural example of the communication apparatus which concerns on one embodiment of this invention. It is a circuit diagram which shows the structural example in the modem in the communication apparatus which concerns on one embodiment of this invention. It is a flowchart explaining operation | movement of the communication apparatus which concerns on one embodiment of this invention. It is a circuit diagram which shows the outline of a power line communication system. It is a circuit diagram which shows the structural example of the conventional power line communication apparatus using a balun transformer. It is a circuit diagram explaining the effect | action of a balun transformer.

Explanation of symbols

3, 4 ... conductive wire, 10 ... modem, 11A, 11B ... transmission circuit, 12 ... reception circuit, 20 ... balancing circuit section, 30 ... current detection section, 50 ... transmission level controller, 70 ... baseband circuit (modulation / demodulation circuit) ).

Claims (3)

A communication device for transmitting a balanced signal to a communication line including first and second conductive lines,
A first transmission circuit for outputting an unbalanced first transmission signal based on a baseband signal ;
A second transmission circuit for outputting an unbalanced second transmission signal based on the baseband signal ;
The first and second transmission signals are converted into one balanced signal and output to the first and second conductive lines, and the balanced signal transmitted to the first and second conductive lines A balanced circuit unit that converts the signal into an unbalanced received signal and outputs the received signal ,
A current detection unit provided at a subsequent stage of the balancing circuit unit to detect a common mode current generated in the communication line;
Control means for adjusting the signal level of the first transmission signal and the signal level of the second transmission signal so that the common mode current decreases based on the common mode current detected by the current detection unit; ,
A receiving circuit for receiving the received signal output from the balancing circuit unit;
A transmission / reception selector switch provided between the balancing circuit unit and the first and second transmission circuits and the reception circuit;
With
The balancing circuit section is
A first primary winding to which the first transmission signal is input;
A second primary winding to which the second transmission signal is input;
A first secondary winding coupled magnetically to the first primary winding and having one end connected to the first conductive line;
A second magnetically coupled to the second primary winding, one end connected to the other end of the first secondary winding and the other end connected to the second conductive line. Secondary winding of
The number of turns of the first secondary winding and the number of turns of the second secondary winding are the same, and the first secondary winding and the second secondary winding The connection point is grounded,
The transmission / reception selector switch is:
The first primary winding and the second primary winding are connected in series when a signal is received by the receiving circuit, and the first primary winding and the first primary winding connected in series are connected. The first primary winding and the second primary winding are connected to the receiving circuit so that the reception signal received by the two primary windings is transmitted to the receiving circuit. communication apparatus characterized by being adapted to connect to. By modulating the baseband signal which is the basis of the first and second transmission signals, further comprising a modulation circuit for outputting a signal after the modulation to the first and second transmission circuit,
2. The communication apparatus according to claim 1, wherein the control unit adjusts signal levels of the first and second transmission signals by controlling a signal level of a modulation signal output from the modulation circuit. 3. . A pair of first signal lines connecting the first primary winding and the first transmission circuit;
A pair of second signal lines connecting the second primary winding and the second transmission circuit; and
The transmission / reception selector switch is:
During reception of a signal by the receiving circuit, the signal line corresponding to the first conductive line of the pair of first signal lines and the second conductive line of the pair of second signal lines. claim wherein the received signal from the balancing circuit unit via the signal line to be transmitted to the receiving circuit, wherein said it has been made to switch the connection state of each signal line 1 or 2 The communication apparatus as described in.

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