JPH0744049B2 - Shielded cable for communication - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shielded cable for communication for suppressing unnecessary electromagnetic waves radiated from a communication cable connected to electronic equipment and communication equipment.

[0002]

2. Description of the Related Art With the spread of electronic devices in recent years, obstacles to various broadcasting such as televisions and radios and wireless communication systems due to unnecessary electromagnetic waves emitted from the devices are rapidly increasing. Therefore, major countries have set regulations and demanded to suppress the level of this unwanted electromagnetic wave to below a certain level. Electronics,
The communication cable connected to the wired communication device is one of the main personnel for radiating unnecessary electromagnetic waves because it easily acts as a linear antenna. Such radiation is due to high frequency currents flowing in the outer sheath of coaxial and shielded cables.

Conventionally, as a means for suppressing unnecessary electromagnetic wave radiation from a cable, that is, high-frequency current flowing in the outer cover, a shield layer 2 is provided around a signal line 5 as shown in the perspective view of FIG. There is a special communication cable 1 for signal transmission that has a magnetic shield structure in which a tape-shaped foil 11 made of a ferromagnetic material is spirally wound (for example,
See JP-A-58-30012 "Communication cable electromagnetic induction protection structure"). As shown in the perspective views of FIGS. 9 and 10, there is a structure in which the cable 1 or its signal line 5 is penetrated through the ferrite core 12 and the ferrite bead 13 to increase the impedance of the cable surface (for example,
See Japanese Utility Model Laid-Open No. 62-47079 "Cable connector for preventing radio interference" and Japanese Utility Model Laid-Open No. 1-172281 "Shielded cable connector"). Moreover, a method of suppressing the high-frequency current from flowing to the outer skin of the cable by using a connector having a good shield performance (see, for example, "Points of electromagnetic shield and earth system design" published by Japan Industrial Technology Center) has been used.

[0004]

In the above-mentioned conventional shielded cable for communication, a cable wound with a magnetic tape is expensive, and it is inconvenient to handle due to its large weight and external shape and poor flexibility, and its surface There is a problem that the impedance is not sufficiently high and the radiation suppressing effect is small especially in a high frequency band. Further, as shown in the perspective view of FIG. 11, in order to enhance the effect of the ferrite core, a structure in which the cable 1 is wound around the ferrite core 12 several times is also adopted, but due to the complicated structure and increase in parasitic capacitance, high frequency There is a problem that the effect decreases in the belt. Further, the shielded connector has a problem that the structure tends to be complicated and large due to the need to improve the shielding performance, and a sufficient space for connecting the connector is required at the connection portion on the housing side.

Therefore, the object of the present invention is that it can be applied to a cable connecting portion where a shield connector cannot be used because of its shape and space, and it is inexpensive and has a structure in which a high-frequency current hardly flows through the outer layer of the shield layer. To provide the cable.

[0006]

SUMMARY OF THE INVENTION A communication shielded cable of the present invention for solving the above problems has an electronic device, a signal line for inputting and outputting a signal by connecting to a communication device, and a shield layer. In the shielded cable for communication configured as described above, a cylindrical conductor is concentrically provided outside the shield layer at the end of the cable, and one end of the cylindrical conductor and the shield layer are short-circuited, and, The space formed by the shield layer and the cylindrical conductor has a structure filled with a magnetic material. Further, the communication shielded cable of the present invention has a conductor for short-circuiting the shield layer and the housing or the reference potential surface of the device connected to the shield layer.

Further, the present invention comprises a signal line for inputting and outputting a signal by connecting to an electronic device or a communication device, and a shield layer, the end of which is electrically connected to the shield layer. In a shielded cable for communication having a shielded connector shell, a cylindrical conductor is provided concentrically in the shield layer at a position adjacent to the connector shell, and one end of the cylindrical conductor and the shield layer can be short-circuited. The space formed by the shield layer and the cylindrical conductor has a structure filled with a magnetic material.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. 1 is a perspective view showing a first embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. Figure 1,
In FIG. 2, the signal line 5 is introduced inside the equipment housing 8. A cylindrical conductor 3 is concentrically provided outside the shield layer 2 at the end of the shielded cable 1 for signal communication composed of the signal line 5 and the shield layer 2. The cylindrical conductor 3 is short-circuited to the shield layer 2 by the short-circuit plate 4,
A cylindrical magnetic body 7 is inserted between the shield layer 2 and the shield layer 2. When viewed from the end of the cable, the magnetic body 7 has an electromagnetically exposed structure. The shield layer 2 and the housing 8 or the reference potential surface are connected by the shield conductor 6 provided at the end of the cable. In order to protect the cylindrical conductor 3 from external impact and corrosion, the periphery thereof may be covered with a covering material 9 similar to the covering material used for the cable 1. In the shielded cable for communication of the present embodiment, since the position where the magnetic body 7 is attached is limited to the end of the cable, it is inexpensive and flexible, and its weight is slightly increased as compared with the conventional shielded cable. Is.

Next, the principle of suppressing unnecessary electromagnetic wave radiation by the structure shown in FIGS. 1 and 2 will be described. As shown in the cross-sectional view of FIG. 7, the high-frequency current that causes unnecessary electromagnetic wave radiation induced inside the housing 8 by the operation of the device flows to the shield layer 2 of the cable via the conductor 6 at the connection portion of the cable 1. . The conductor 6 is composed of a strip of metal or a metal braided wire. At this time, since the conductor 6 has an inductance component, a high-frequency current flows outside the shield layer 2 of the cable 1 to cause a potential difference between the housing 8 and the cable outer cover. This causes unnecessary electromagnetic radiation. In order to suppress this radiation, it is sufficient to create a state in which the high-frequency current easily flows into the shield layer 2 and reduce the amount of the high-frequency current flowing outside the shield layer 2. In the structure shown in FIGS. 1 and 2, the surface impedance on the exposed surface of the magnetic body 7 is effectively increased in the space formed by the shield layer 2 and the cylindrical conductor 3 whose one end is short-circuited by the short-circuit plate 4. . Therefore, the high-frequency current flows into the inside of the shield layer 2 having a relatively low impedance, and the emission of unnecessary electromagnetic waves is suppressed. The impedance of the exposed surface largely depends on the magnetic permeability of the magnetic body 7 and the distance from the exposed surface to the short-circuit plate 4. The larger the magnetic permeability and the longer the cylindrical conductor 3, the larger the impedance. For the magnetic body 7, for example, a NiZn-based ferrite sintered body having a high magnetic permeability even in a high frequency band, or a rubber ferrite in which ferrite such as magnetite is mixed in rubber is used. Since these have magnetic loss in the high frequency band, there is an advantage that a part of the high frequency current is absorbed and the radiation suppressing effect can be further increased.

FIG. 3 is a perspective view showing a second embodiment of the present invention, and FIG. 4 is a sectional view taken along the line BB in FIG. In FIG. 3 and FIG. 4, at the end of the signal communication shielded cable 1 composed of the signal line 5 and the shield layer 2,
A cylindrical conductor 3 is concentrically provided outside the shield layer 2, and the end of the shield layer 2 and the cylindrical conductor 3 are short-circuited to the short-circuit plate 4 at the cable end. The outer circumference of the cylindrical conductor 3 is covered with a covering material 9 similar to that used for the communication cable 1. A cylindrical magnetic body 7 is inserted in the space between the shield layers 2 of the cylindrical conductor 3, and the shield layer 2 and the housing 8 are directly connected by a conductor 6 extending from the short-circuit plate 4.

In the structure shown in FIGS. 3 and 4, the high-frequency current flowing through the conductor 6 is divided into a current flowing into the shield layer 2 and a current flowing from the short-circuit plate 4 to the outer wall of the cylindrical conductor 3. Since the magnetic body 7 is provided between the shield layers 2 of the cylindrical conductor 3, the impedance is effectively high on the exposed surface of the magnetic body 7 for the same reason as described above.
Therefore, the current flowing through the outer wall of the cylindrical conductor 3 is reflected or absorbed at this portion. As a result, the amount of current flowing into the outer wall of the shield layer 2 is reduced, and the emission of unnecessary electromagnetic waves is suppressed. In this embodiment, part of the high frequency current is the cylindrical conductor 3.
Since it flows through the outer wall of No. 1, the radiation amount may increase compared to the first embodiment. However, since the conductor 6 may be provided on any portion of the outer wall of the short-circuit plate 4 or the cylindrical conductor 3, it has a feature that structural restrictions on the conductor 6 such as shape and number can be relaxed as compared with the first embodiment. ing.

FIG. 5 is a perspective view showing an end portion of a signal communication shielded cable 1 having a connector shell 10 according to a third embodiment of the present invention, and FIG. 6 is a sectional view taken along line C--C of FIG. FIG. The connector shell 10 is made of metal, metal-plated or plastic coated with conductive material, and has conductivity, and is kept at the same potential as the shield wire 2 of the cable 1. The structure is such that a shield effect can be obtained by directly connecting the connector shell 10 and the receiving side connector provided in the device housing. A cylindrical conductor 3 is provided outside the shield layer 2 of the cable 1,
Further, there is a covering material 9 on the outer side thereof, and one end of the cylindrical conductor 3 is short-circuited to the shield layer 2 by the short-circuit plate 4. A magnetic body 7 is provided between the shield layer 2 and the cylindrical conductor 3.

Due to the above-mentioned reasons, when the shield layer 2 and the connector shell 10 or the connector shell 10 and the equipment housing are not completely in contact with each other, the high frequency current leaked from that portion is effectively high in impedance. Since it is reflected or absorbed on the exposed surface of the body 7,
The current flowing on the outer skin side of the shield layer 2 is reduced, and the emission of unnecessary electromagnetic waves can be suppressed.

[0014]

As described above, the present invention can be applied to the cable connection portion of the housing where the shield connector cannot be used due to the shape and space, and the high frequency current flows through the outer layer of the shield layer while being inexpensive. The effect is that a shielded cable for communication having a difficult structure can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of FIG. 1 taken along the line AA.

FIG. 3 is a perspective view showing a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of FIG. 3 taken along the line BB.

FIG. 5 is a perspective view showing a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of FIG. 5 taken along the line C-C.

FIG. 7 is a cross-sectional view illustrating the principle of the present invention.

FIG. 8 is a perspective view of a conventional communication shielded cable.

FIG. 9 is a perspective view of a conventional cable connector.

FIG. 10 is a perspective view of another cable connector according to the related art.

FIG. 11 is a perspective view showing a state in which a cable is wound around a ferrite core according to a conventional technique.

[Explanation of symbols]

 1 Communication Cable 2 Shield Layer 3 Cylindrical Conductor 4 Short Circuit Plate 5 Signal Line 6 Shielding Conductor 7 Magnetic Material 8 Device Housing 9 Cover Material 10 Connector Shell 11 Tape Foil Made of Ferromagnetic Material 12 Ferrite Core 13 Ferrite Bead

Claims (3)

[Claims] 1. A shielded cable for communication comprising a signal line for inputting and outputting a signal by connecting to an electronic device and a communication device, and a shield layer at the end of the cable. A cylindrical conductor is concentrically formed with the shield layer on the outside, one end of the cylindrical conductor and the shield layer are short-circuited, and the space formed by the shield layer and the cylindrical conductor is a magnetic body. A shielded cable for communication, which is characterized by 2. The shielded cable for communication according to claim 1, further comprising a conductor for short-circuiting the shield layer and a housing or a reference potential surface of the device connected to the shield layer. 3. A shield connector which is configured to have a signal line for inputting and outputting a signal by connecting to an electronic device or a communication device and a shield layer, and whose end portion is electrically connected to the shield layer. In a shielded cable for communication having a shell, a cylindrical conductor is concentrically provided on the shield layer at a position adjacent to the connector shell, one end of the cylindrical conductor and the shield layer are short-circuited, and A shielded cable for communication, wherein a space formed by the shield layer and the cylindrical conductor is filled with a magnetic material.