JP2010272809A - Common mode choke coil and signal transmission circuit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a common mode choke coil that suppresses an increase of passage loss of a normal mode signal, while blocking the passage of common mode noise by generating an impedance to the common mode noise. <P>SOLUTION: The choke coil includes a toroidal core 2 forming a closed magnetic circuit, a pair of conductor lines 5a, 5b whose outer surfaces are insulated, a shielded conductor 7A coating in block the pair of conductor lines 5a, 5b, and a signal transmission cable 3A wound around the toroidal core 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a common mode choke coil that allows passage of a normal mode signal while preventing passage of common mode noise, and a signal transmission circuit using the common mode choke coil.

A conventional common mode choke coil includes an annular magnetic core and a pair of conductive wires wound around the magnetic core by bifilar winding (see, for example, Patent Document 1).
In a conventional common mode choke coil, when a common mode signal is input from one end of each of a pair of conductors, each magnetic flux generated inside the magnetic core by a magnetic field generated when the common mode signal is transmitted through the conductors is Strengthen each other. For this reason, the conventional common mode choke coil functions as an inductor that generates a large impedance with respect to the common mode signal, and the common mode signal is prevented from moving toward the other end of the conducting wire.

  On the other hand, when the normal mode signal is input from one end of each of the pair of conductors, the magnetic fluxes generated inside the magnetic core cancel each other out due to the magnetic field generated when the normal mode signal is transmitted through the conductors. For this reason, the conventional common mode choke coil does not generate impedance with respect to the normal mode signal. In other words, in a conventional common mode choke coil, when a normal mode signal is input from one end of a pair of conducting wires and signal transmission is performed, the passage of common mode noise that attempts to propagate the conducting wire in the common mode is prevented. It was only possible to pass through.

JP-A-7-29755

  As described above, the conventional common mode choke coil does not generate impedance for the normal mode signal in principle. This is because when a normal mode signal is transmitted through a pair of conductors, the pair of conductors are wound under an equivalent condition with respect to the magnetic core so that the same magnetic flux is generated inside the magnetic core. It is assumed that. However, in reality, it is not easy to wind a pair of conducting wires around the magnetic core under equivalent conditions.

  For example, when a pair of conducting wires are wound so as to be in close contact with the outer peripheral surface of the magnetic core, a gap is actually formed between a part of the conducting wire and the magnetic core. At this time, if the gap between one conductor and the magnetic core and the gap between the other conductor and the magnetic core are non-uniform, the magnitude of each magnetic flux generated when the normal mode signal transmits each of the conductors is reduced. It will be different. As a result, the common mode choke coil functions as an inductor that generates impedance even with respect to the normal mode signal, and a passing loss of the normal mode signal occurs.

  The present invention has been made to solve the above problems, and a common mode choke coil capable of suppressing an increase in the passage loss of a normal mode signal while preventing the passage of common mode noise and a signal transmission using the common mode choke coil The purpose is to obtain a circuit.

  A common mode choke coil according to the present invention has a closed magnetic circuit core that forms a closed magnetic circuit, a pair of conductors that are insulated on the outer surface, and a shield conductor that covers the pair of conductors together, and is wound around the closed magnetic circuit core. A rotated signal transmission cable.

  In the common mode choke coil according to the present invention, since the pair of conductors are covered with the shield conductor, the magnetic flux is not generated in the closed magnetic circuit core even if the normal mode signal propagates through the pair of conductors having the return path as a return path. When the common mode noise propagates through the conducting wire, the common mode noise also propagates to the outer surface of the shield conductor and magnetic flux is generated in the closed magnetic circuit core. Therefore, the common mode choke coil does not generate impedance for the normal mode signal even if the pair of conductors are not wound under the equivalent condition with respect to the closed magnetic circuit core. Since only the impedance is generated, it is possible to suppress an increase in the passage loss of the normal mode signal while preventing the passage of the common mode noise.

It is a figure explaining the structure of the common mode choke coil which concerns on Embodiment 1 of this invention, and the principal part of the signal transmission circuit using a common mode choke coil. It is a figure explaining the principal part of the circuit for signal transmission concerning Embodiment 2 of this invention. It is a figure explaining the principal part of the circuit for signal transmission concerning Embodiment 3 of this invention. It is a figure explaining the principal part of the circuit for signal transmission concerning Embodiment 4 of this invention. It is a figure explaining the principal part of the structure of the common mode choke coil which concerns on Embodiment 5 of this invention, and the signal transmission circuit incorporating the common mode choke coil.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a configuration of a common mode choke coil according to Embodiment 1 of the present invention and a main part of a signal transmission circuit using the common mode choke coil.

  In FIG. 1, a common mode choke coil 1A is made of a magnetic material such as ferrite and iron-based amorphous metal, and a toroidal core 2 as a closed magnetic circuit core that forms a closed magnetic circuit, and a signal transmission wound around the toroidal core 2. Cable 3A.

The signal transmission cable 3A is composed of a covering body 4 made of an insulating material, insulating covering conductors 6a and 6b each having a pair of conductors 5a and 5b covered with the covering body 4, and a pair of insulating covering conductors 6a and 6b. And a shield conductor 7A for covering.
For the shield conductor 7A, a braided structure produced by braiding thin conductive wires into a mesh shape, aluminum tape, or the like can be used.
The signal transmission cable 3A is wound around the toroidal core 2 by two turns, and one end of the signal transmission cable 3A extends from the opening on one end side of the toroidal core 2 to the outside of the toroidal core 2 for signal transmission. The other end of the cable 3 </ b> A extends from the opening on the other end side of the toroidal core 2 to the outside of the toroidal core 2.

  The common mode choke coil 1A is used by being incorporated in a signal transmission path in a signal transmission circuit 10A for transmitting a normal mode signal (current), for example. The signal transmission circuit 10A has a circuit ground 11 (GND11). At this time, the shield conductor 7 </ b> A is arranged in a state of floating from the GND 11.

  Hereinafter, the operation of the signal transmission circuit 10A when a common mode signal and a normal mode signal are input to the conducting wires 5a and 5b of the common mode choke coil 1A will be described.

  When a common mode signal (current) is input to one end of a pair of conductors 5a and 5b and propagated, the common mode signal tries to propagate each of the conductors 5a and 5b in the same direction using the inner surface of the shield conductor 7A as a return path. However, since the shield conductor 7A is floating from the GND 11 at this time, the common mode signal input from the conducting wires 5a and 5b propagates to the outer surface of the shield conductor 7A using the GND 11 as a return path.

  A magnetic flux is generated inside the toroidal core 2 by a magnetic field generated by a signal propagating on the outer surface of the shield conductor 7A. That is, the common mode choke coil 1A functions as an inductor that generates a large impedance with respect to the common mode signal. Therefore, a common mode signal that is to propagate through the conducting wires 5a and 5b using the inner surface of the shield conductor 7A as a return path is prevented from passing from one end of the conducting wires 5a and 5b to the other end.

On the other hand, when the normal mode signal propagates through the pair of conductors 5a and 5b, the conductors 5a and 5b are used as return paths and propagate in different directions between the conductor 5a and the conductor 5b. At this time, the normal mode signal propagates only through the path having the conductors 5a and 5b as return paths, and does not propagate through the conductors 5a and 5b by using the shield conductor 7A as a return path.
Here, if the shield conductor 7A is omitted and the pair of insulation-coated conductors 6a and 6b are not wound around the toroidal core 2 under an equivalent condition, the conventional common mode choke coil is used. Similarly to the above, a magnetic flux is generated in the toroidal core 2 by the magnetic field generated when the normal mode signal propagates through the conducting wires 5a and 5b.

  However, in the common mode choke coil 1A, the normal mode signal propagates only through the conductors 5a and 5b, and the insulation-coated conductors 6a and 6b are covered by the shield conductor 7A, so that the normal mode signal is transmitted through the conductors 5a and 5b. The magnetic field generated by the propagation does not reach the toroidal core 2. That is, even if the pair of insulating coated conductors 6a and 6b are not wound around the toroidal core 2 under equivalent conditions, the normal mode signal is generated by the magnetic field generated by propagating the conductors 5a and 5b. Magnetic flux is not generated in the toroidal core 2. Accordingly, since the common mode choke coil 1A does not generate impedance with respect to the normal mode signal, an increase in loss when the normal mode signal propagates through the conductors 5a and 5b is suppressed.

  In the signal transmission circuit 10A, when the normal mode signal is transmitted by inputting the normal mode signal from one end of the pair of conductors 5a and 5b between the conductors 5a and 5b, the normal mode signal is attenuated. However, when noise is about to propagate as a common mode signal on the conductors 5a and 5b, the noise is prevented from passing from one end of the conductors 5a and 5b to the other end. . Hereinafter, noise propagating through the conductive wires 5a and 5b in common mode is referred to as common mode noise.

The common mode choke coil 1A according to the first embodiment is configured by covering a pair of insulating coated conductors 6a and 6b wound around a toroidal core 2 with a shield conductor 7A. The magnetic field generated by the normal mode signal propagating through the conductors 5a and 5b is shielded by the shield conductor 7A and does not reach the toroidal core 2, and the normal mode signal propagates through the conductors 5a and 5b. However, no magnetic flux is generated in the toroidal core 2. Further, when the common mode signal propagates through the conductors 5a and 5b, the signal flows on the outer surface of the shield conductor 7A, and a magnetic flux is generated in the toroidal core 2 by the magnetic field generated by the signal, and the impedance is not generated for the common mode signal. Occurs.
That is, by incorporating the common mode choke coil 1A into the signal transmission path, it is possible to suppress an increase in the passage loss of the normal mode signal while preventing the passage of the common mode noise. In other words, when the common mode choke coil 1A transmits the normal mode signal using the signal transmission circuit 10A incorporated in the signal transmission path, the passage loss of the normal mode signal is increased while the passage of the common mode noise is prevented. Can be suppressed.

  In the first embodiment, the common mode choke coil 1A has been described as being incorporated in the signal transmission circuit 10A with the shield conductor 7A in a floating state. However, both ends or one end of the shield conductor 7A and the GND 11 are connected to the inductor 11 as an inductor. It may be connected via That is, the shield conductor 7A may be lifted from the GND 11 in terms of high frequency.

Embodiment 2. FIG.
FIG. 2 is a diagram for explaining a main part of a signal transmission circuit according to Embodiment 2 of the present invention.
In FIG. 2, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 2, the signal transmission circuit 10B includes a ground conductor 12a in which the common mode choke coil 1A is incorporated in the signal transmission path and connects the GND 11 and one end of the shield conductor 7A. Other configurations of the signal transmission circuit 10B are the same as those of the signal transmission circuit 10A.

  Hereinafter, the operation of the signal transmission circuit 10B when the common mode signal and the normal mode signal are input to the conductive wires 5a and 5b of the common mode choke coil 1A will be described.

  When a common mode signal is input and propagated to one end of a pair of conductors 5a and 5b, the common mode signal tries to propagate each of the conductors 5a and 5b using the inner surface of the shield conductor 7A as a return path. However, since one end of the shield conductor 7A is grounded to the GND 11 by the grounding conductor 12a and the other end is floating from the GND 11 of the signal transmission circuit 10B, it is also input from the conductors 5a and 5b to the outer surface of the shield conductor 7A. The common mode signal propagates through the GND 11 connected through the grounding conductor 12a as a return path.

The common mode choke coil 1A functions as an inductor that generates a large impedance to the common mode signal by the signal propagating on the outer surface of the shield conductor 7A, as in the first embodiment. Therefore, a common mode signal that is to propagate through the conducting wires 5a and 5b using the inner surface of the shield conductor 7A as a return path is prevented from passing from one end of the conducting wires 5a and 5b to the other end.
The normal mode signal is propagated in the same manner as in the first embodiment.

  As described above, according to the signal transmission circuit 10B, as in the case of the signal transmission circuit 10A, when transmitting a normal mode signal, when noise is transmitted as a common mode signal on the conductors 5a and 5b, Thus, it is possible to suppress an increase in the passage loss of the normal mode signal while preventing the passage of the common mode noise.

  The other end of the shield conductor 7A has been described as floating from the GND 11, but the other end of the shield conductor 7A and the GND 11 may be connected via an inductor. That is, it is only necessary that the other end of the shield conductor 7A and the GND 11 float with respect to the high-frequency signal.

  Further, one end of the shield conductor 7A and the GND 11 may be connected by a capacitor instead of the grounding conductor 12a. That is, one end of the shield conductor 7A and the GND 11 may be connected to the high frequency signal with a low impedance.

Embodiment 3 FIG.
FIG. 3 is a diagram for explaining a main part of a signal transmission circuit according to Embodiment 3 of the present invention.
In FIG. 3, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 3, a signal transmission circuit 10C has a common mode choke coil 1A incorporated in the signal transmission path, and has a grounding conductor 12a that connects GND 11 and any part of the intermediate portion excluding both ends of the shield conductor 7A. .

  Hereinafter, the operation of the signal transmission circuit 10C when a common mode signal and a normal mode signal are input to the conducting wires 5a and 5b of the common mode choke coil 1A will be described.

  When the common mode signal is input to one end of the pair of conductive wires 5a and 5b, the inner surface of the shield conductor 7A tries to propagate as a return path. However, since both ends of the shield conductor 7A are floating from the GND 11, and a part of the intermediate portion of the shield conductor 7A is grounded to the GND 11 by the grounding conductor 12a, the conductors 5a and 5b are also connected to the outer surface of the shield conductor 7A. The input common mode signal propagates as a return path through the GND 11 connected to the shield conductor 7A via the grounding conductor 12a.

A magnetic flux is generated inside the toroidal core 2 by a magnetic field generated by a signal propagating on the outer surface of the shield conductor 7A. That is, the common mode choke coil 1A functions as an inductor that generates a large impedance with respect to the common mode signal. Therefore, a common mode signal that is to propagate through the conducting wires 5a and 5b using the inner surface of the shield conductor 7A as a return path is prevented from passing from one end of the conducting wires 5a and 5b to the other end.
The normal mode signal is propagated in the same manner as in the first embodiment.

  As described above, according to the signal transmission circuit 10C of the third embodiment, as in the case of the signal transmission circuit 10A, when transmitting a normal mode signal, noise is carried on the conductors 5a and 5b as a common mode signal. When propagating, it is possible to suppress an increase in the passage loss of the normal mode signal while preventing the passage of the common mode noise.

  In the third embodiment, the both ends of the shield conductor 7A have been described as floating from the GND 11. However, at least one end of the shield conductor 7A and the GND 11 are connected via an inductor. May be. That is, at least one end of the shield conductor 7A and the GND 11 may be connected so as to float with respect to the high-frequency signal.

  Further, the intermediate portion of the shield conductor 7A and the GND 11 may be connected by a capacitor instead of the grounding conductor 12a. That is, the intermediate portion of the shield conductor 7A and the GND 11 may be connected with a low impedance with respect to the high-frequency signal.

Embodiment 4 FIG.
FIG. 4 is a diagram for explaining a main part of a signal transmission circuit according to Embodiment 4 of the present invention.
In FIG. 4, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

In FIG. 4, the signal transmission circuit 10 </ b> D has different types of grounds in which the common mode choke coil 1 </ b> A is incorporated in the signal transmission path and separated from each other. Examples of the different types of ground include an analog ground, a digital ground, and a frame ground.
Hereinafter, the analog ground is referred to as a first GND 11a, and the digital ground is referred to as a second GND 11b.
The signal transmission circuit 10D includes a grounding conductor 12a that connects one end of the shield conductor 7A and the first GND 11a, and a grounding conductor 12b that connects the other end of the shield conductor 7A and the second GND 11b.

  Hereinafter, the operation of the signal transmission circuit 10D when the common mode signal and the normal mode signal are input to the conducting wires 5a and 5b of the common mode choke coil 1A will be described.

  When the common mode signal is input from one end of the pair of conductors 5a and 5b, the conductors 5a and 5b tend to propagate through the inner surface of the shield conductor 7A as a return path. At this time, both ends of the shield conductor 7A are grounded by the connecting conductors 12a and 12b to the separated first GND 11a and second GND 11b. Accordingly, the common mode signal input to the conductors 5a and 5b is also transmitted to the outer surface of the shield conductor 7A via the first GND 11a connected to the shield conductor 7A via the ground conductor 12a or the shield conductor 12b. The second GND 11b connected to 7A is propagated as a return path. When the first GND 11a and the second GND 11b are separated, the return path of the common mode signal is limited as compared with the case where the first GND 11a and the second GND 11b are not separated, so that the impedance increases with respect to the common mode signal.

A magnetic flux is generated inside the toroidal core 2 by a magnetic field generated by a signal propagating on the outer surface of the shield conductor 7A. That is, the common mode choke coil 1A functions as an inductor that generates a large impedance with respect to the common mode signal. Therefore, a common mode signal that is to propagate through the conducting wires 5a and 5b using the inner surface of the shield conductor 7A as a return path is prevented from passing from one end of the conducting wires 5a and 5b to the other end.
The normal mode signal is propagated in the same manner as in the first embodiment.

  As described above, according to the signal transmission circuit 10D of the fourth embodiment, similarly to the signal transmission circuit 10A, when the normal mode signal is transmitted, noise propagates as the common mode signal along the conductors 5a and 5b. When trying to do so, it is possible to suppress an increase in the passage loss of the normal mode signal while preventing the passage of the common mode noise.

In the fourth embodiment, the different types of GND have been described as being completely separated. However, if the connection is made so that a large impedance is generated between the different types of GND, a wiring pattern, a connecting conductor, Different types of GNDs may be connected by capacitors, coils, resistors, and the like.
In addition, as long as both ends of the shield conductor 7A are connected to the separated GNDs, the type of GND connected to each of the both ends of the shield conductor 7A is not limited.
Further, the grounding conductors 12a and 12b may be omitted.

Embodiment 5 FIG.
FIG. 5 is a diagram for explaining the configuration of a common mode choke coil according to Embodiment 5 of the present invention and the main part of a signal transmission circuit incorporating the common mode choke coil.
In FIG. 5, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

In FIG. 5, the common mode choke coil 1B includes a signal transmission cable 3B instead of the signal transmission cable 3A.
Then, the shield conductor 7B of the signal transmission cable 3B is divided so as to cover the insulation-coated conductors 6a and 6b with a gap therebetween in the longitudinal direction of the insulation-coated conductors 6a and 6b (conductors 5a and 5b). It is comprised by the shield conductor 7a and the division | segmentation shield conductor 7b. That is, the coating of the insulation coated conductors 6a and 6b is interrupted at a part of the middle portion of the insulation coated conductors 6a and 6b, and the shield conductor 7B is separated into the divided shield conductor 7a and the divided shield conductor 7b. Other configurations of the common mode choke coil 1B are the same as those of the common mode choke coil 1A.

The common mode choke coil 1B is used by being incorporated in a signal transmission path of a signal transmission circuit 10E for transmitting a normal mode signal, for example.
The signal transmission circuit 10 </ b> E extends from the ground conductor 12 a that connects the end of the split shield conductor 7 a that extends from one end opening of the toroidal core 2 and the GND 11, and the other end opening of the toroidal core 2. And a grounding conductor 12b for connecting the end of the divided shield conductor 7b and the GND 11 to each other.

  Hereinafter, the operation of the signal transmission circuit 10E when a common mode signal and a normal mode signal are input from one end of the conducting wires 5a and 5b of the common mode choke coil 1A will be described.

  When a common mode signal is input and propagated to one end of a pair of conductors 5a and 5b, the common mode signal attempts to propagate the conductors 5a and 5b using the inner surfaces of the divided shield conductors 7a and 7b as return paths. However, since both ends of the split shield conductors 7a and 7b extending from the toroidal core 2 are grounded to the GND 11 by the grounding conductors 12a and 12b, and the split shield conductors 7a and 7b are separated, the split shield conductor 7a is separated. , 7b also propagates the common mode signal input to the conductors 5a, 5b using the GND 11 as a return path.

  Then, a magnetic flux is generated inside the toroidal core 2 by a magnetic field generated by a signal propagating through the outer surfaces of the divided shield conductors 7a and 7b. That is, the common mode choke coil 1B functions as an inductor that generates a large impedance with respect to the common mode signal. Therefore, a common mode signal that is to propagate through the conducting wires 5a and 5b using the inner surface of the shield conductor 7A as a return path is prevented from passing from one end of the conducting wires 5a and 5b to the other end.

  In addition, in the area | region where the insulation coating conducting wires 6a and 6b are wound around the toroidal core 2, only a part of the shield release portion of the insulation coating conducting wires 6a and 6b by the shield conductor 7B is released. That is, since the magnetic field generated by the normal mode signal propagating through the conductors 5a and 5b is shielded by the divided shield conductors 7a and 7b, the magnetic field hardly reaches the toroidal core 2, and the toroidal core is generated by the normal mode signal. The magnetic flux generated in 2 is small. Therefore, since the common mode choke coil 1B generates almost no impedance with respect to the normal mode signal, an increase in loss when the normal mode signal propagates through the conducting wires 5a and 5b is suppressed.

  That is, in the signal transmission circuit 10E, when the normal mode signal is input from one end of the pair of conductors 5a and 5b between the conductors 5a and 5b and signal transmission is performed, the normal mode signal is not attenuated without being attenuated. When noise passes through the conductors 5a and 5b as a common mode signal, the noise is prevented from passing from one end of the conductors 5a and 5b to the other end.

  As described above, the common mode choke coil 1B according to the fifth embodiment is incorporated in the signal transmission path as in the first embodiment, thereby preventing the passage of the common mode noise and increasing the passage loss of the normal mode signal. Can be suppressed. In other words, even when the common mode choke coil 1B transmits the normal mode signal by the signal transmission circuit 10E incorporated in the signal transmission path, the passage loss of the normal mode signal is increased while blocking the passage of the common mode noise. Can be suppressed.

  In the fifth embodiment, the end of one side of the toroidal core 2 of the split shield conductor 7a, one end and the GND 11 are connected by the grounding conductor 12a, and the toroidal of the split shield conductor 7b is connected. Although the description has been made assuming that the end portion of the core 2 extending from the opening on the other end side is connected by the grounding conductor 12b, the grounding conductors 12a and 12b may be omitted. Even in this case, when the common mode signal is input to the conducting wires 5a and 5b, the signal is also propagated to the outer surfaces of the divided shield conductors 7a and 7b, so that the above effect is obtained.

  Further, the divided shield conductor 7a and the divided shield conductor 7b may be connected by an inductor. That is, the shield conductor 7B only needs to have a portion separated from the high-frequency signal.

Further, between the end of the split shield conductor 7a extended from the one end side opening of the toroidal core 2 and the GND 11, and the end of the split shield conductor 7b extended from the other end side opening of the toroidal core 2 and the GND 11 May be connected by a capacitor instead of the grounding conductors 12a and 12b.
The shield conductor 7B is composed of a pair of segmented shield conductors 7a and 7b, but is composed of three or more segmented shield conductors arranged with a gap therebetween in the longitudinal direction of the conducting wires 5a and 5b. It may be.

Further, in each of the embodiments described above, the winding is performed on the toroidal core 2 by two turns, but the number of turns of the signal transmission cable may be one turn or three turns or more.
In addition, the closed magnetic path core has been described as being the toroidal core 2, but if the closed magnetic path core forms a closed magnetic path, such as a cylindrical shape whose outer shape is different from the toroidal shape, the shape is It is not limited.

  1A, 1B common mode choke coil, 2 toroidal core, 5a, 5b conductor, 7A, 7B shield conductor, 7a, 7b split shield conductor, 10A-10E signal transmission circuit, 11 GND, 11a, 11b Different types of GND.

Claims (6)

A closed magnetic circuit core that forms a closed magnetic circuit;
A signal transmission cable wound around the closed magnetic circuit core, having a pair of conducting wires with insulation treatment on the outer surface, and a shield conductor covering the pair of conducting wires together;
A common mode choke coil comprising:   The common mode choke coil according to claim 1, wherein the shield conductor is constituted by a plurality of divided shield conductors covering the conductive wire with a gap between each other in a longitudinal direction of the conductor. The common mode choke coil according to claim 1 is a signal transmission circuit incorporated in a signal transmission path,
A signal transmission circuit having GND, wherein only one end of the shield conductor is grounded to the GND. The common mode choke coil according to claim 1 is a signal transmission circuit incorporated in a signal transmission path,
A signal transmission circuit comprising GND, wherein both ends of the shield conductor are floating from the GND, and at least one point of an intermediate portion of the shield conductor is grounded to the GND. The common mode choke coil according to claim 1 or 2 is a signal transmission circuit incorporated in a signal transmission path,
A signal transmission circuit comprising GND, wherein the shield conductor is floating from the GND. The common mode choke coil according to claim 1 or 2 is a signal transmission circuit incorporated in a signal transmission path,
A signal transmission circuit comprising different types of GNDs separated from each other, wherein both ends of the shield conductor are grounded to the different types of GNDs separated from each other.

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