JP2013247190A - Noise filter and signal transmission cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve balancing of a twisted cable relative to earth and suppress the transmission of common mode noise flowing on the twisted cable.SOLUTION: A noise filter includes: a twist holding member 2 having at least two or more through holes 4a, 4b through which a core wire of a twisted cable 5 is inserted, and formed of a plate-like insulator; and an annular magnetic member 3 that is formed of an annular magnetic material and can be fitted onto the outer peripheral surface of the twist holding member 2.

Description

  The present invention relates to a noise filter that suppresses propagation of common mode noise superimposed on a twisted cable and improves the degree of ground balance of the twisted cable, and a signal transmission cable using the noise filter.

  As a technique for realizing high-speed data communication in recent years, a differential transmission method is often adopted. The differential transmission method is a method that can be realized even when two or more transmission paths are used. However, in order to simplify the explanation, the difference in the case of using a pair line (pair line) that is two transmission paths is described below. An outline of dynamic transmission will be described.

  In the differential transmission method, a differential signal composed of a + side signal and a − side signal having opposite phases and the same amplitude is transmitted between a differential driver on the transmission side and a differential receiver on the reception side. The transmission is performed through a balanced cable composed of a pair of conductive wires or two wiring patterns formed on a printed circuit board. This differential transmission method can reduce the rise time because the voltage amplitude per conductor is low, and is suitable for high-speed data transmission.

  Further, the differential transmission system has a feature of suppressing noise radiated from the cable. The two conductors constituting a pair of cables are respectively applied with signals having the same amplitude and opposite phase, and the flowing currents are directed in opposite directions, so that the magnetic fields generated from the respective conductors cancel each other, Little radiation noise is generated. Furthermore, since noises received from the outside are equally superimposed on the two conducting wires, the difference can be taken out on the receiving end side to cancel the noise and remove the influence of the noise. Because of these advantages, the differential transmission method is often used for high-speed data communication.

  As a typical cable used for differential transmission, there is a twisted pair cable in which two insulated wires whose conductors are covered with an insulator are twisted to make a pair. Twisted pair cables are widely used because they are inexpensive and easy to bend. Further, the twisted pair cable has a feature that the degree of ground balance is higher than that of other pair cables.

  The ground balance is a differential mode consisting of a differential transmission circuit composed of a pair of cables and a transceiver, and a common mode consisting of a path including the differential transmission circuit, external ground, and parasitic capacitance. It is a parameter that represents the conversion ratio of signals between modes. This degree of ground balance often depends on the electrical characteristics of the cable, and if the difference in electrical characteristics between the individual conductors of the pair cable is large, it becomes a bad value and mutual mode conversion occurs. It is known to be easier. On the other hand, when the two conductors are close to the same electrical characteristics, the ground balance shows a good value, and mutual mode conversion hardly occurs.

The twisted pair cable described above can average the difference in electrical characteristics of each conducting wire by twisting the conducting wires constituting the pair, and maintain the ground balance at a good value. .
At this time, the degree of ground balance also has a meaning as an index for suppressing the occurrence of noise. For example, the signal converted to the common mode with respect to the differential mode used in the differential transmission system becomes a component that does not contribute to the transmission of the differential signal, and thus acts as common mode noise for the differential transmission circuit. . Therefore, in order to suppress the occurrence of common mode noise in the differential transmission circuit, it is necessary to create a transmission system that is difficult to convert from the differential mode to the common mode. In other words, cables with good ground balance should be used. The conclusion is obtained.

  From the above, in order to reduce the effect of common mode noise in differential transmission circuits, a method of suppressing propagation of common mode noise itself is applied, or the ground balance is improved so that common mode noise is less likely to occur. Apply the method you want to focus on. Therefore, for example, Patent Documents 1-3 disclose a configuration aimed at suppressing noise in a twisted cable.

  In the connection cable according to Patent Document 1, two ferrite beads are integrated into one component, and two holes for passing independent signal lines are provided in the integrated ferrite beads, and the signal twisted in each hole is provided. A cable between connectors is formed by inserting wires. The integrated ferrite beads are handled as one noise filter, and a large number of twisted pair cables are passed, thereby suppressing mutual interference between twisted pair cables and crosstalk.

  In addition, the noise filter according to Patent Document 2 has a small through hole at the center of a disk made of metal, and an annular ferrite core that matches the thickness of the external output cable that passes through the through hole is formed in the groove inside the through hole. It is provided and configured. This realizes a common mode noise filter that does not require a ferrite core to be attached to the external output cable and at the same time can close the gap between the cable outlets.

  In addition, the signal cable according to Patent Document 3 is configured by twisting signal lines other than the power supply line and the ground line among the core wires included in the twisted pair cable at a pitch of 2 cm / 1 times or less. This suppresses malfunctions such as malfunctions and malfunctions caused by common-mode burst noise induced in the cable.

JP-A-10-208818 Japanese Patent Application Laid-Open No. 11-214941 JP 2000-357421 A

  However, in the technique disclosed in Patent Document 1 described above, since the two wires constituting the pair are configured to pass beads through the pair of cables, the propagation of the common mode is suppressed. However, the function of improving the ground balance of the twisted pair cable is not included. For this reason, a cable with a low degree of ground balance other than the IEEE 1394 cable shown in Patent Document 1 has a problem that a noise suppression effect cannot be sufficiently obtained.

  Moreover, in the technique disclosed in Patent Document 2 described above, a through hole is provided in the housing, and a filter is mounted in the through hole. Therefore, the housing has a shape for connecting a cable such as a connector instead of the through hole. Has a problem that it cannot be applied. In addition, there is a problem that the twisted pair cable is not effective in improving the ground balance.

  Furthermore, in the above-mentioned Patent Document 3, since the twisting pitch of the twisted pair cable signal lines is changed, the ground balance is expected to be improved, but the structure such as a jig for fixing the twisting pitch is specified. However, there is a problem that it is difficult to apply other than the USB cable shown in Patent Document 3. In addition, to suppress propagation of common mode noise, the twisted pair cable signal line, power line, and ground line must be separately wound in order to insert the annular ferrite core, which takes time and effort. There were issues such as.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to improve the degree of ground balance of a twisted cable and to suppress the propagation of common mode noise flowing on the twisted cable.

  The noise filter according to the present invention includes a twist holding member formed of a flat plate-like insulator having at least two or more through holes through which a core wire is inserted, and an annular magnetic body that can be fitted to the outer peripheral surface of the twist holding member And an annular magnetic member formed of

  According to the present invention, the twisting of the core wires constituting the twist cable can be densely arranged, the ground balance can be improved, and the occurrence of common mode noise can be reduced. In addition, since the core members are bundled and the annular magnetic member is attached, the common mode impedance of the twisted cable can be increased, and propagation of common mode noise can be suppressed.

1 is a perspective view illustrating a configuration of a noise filter according to Embodiment 1. FIG. 3 is a perspective view showing a configuration of a twist holding member according to Embodiment 1. FIG. 2 is a perspective view showing a configuration of an annular magnetic member according to Embodiment 1. FIG. It is a figure which shows the state which mounted | wore the twist cable with the noise filter which concerns on Embodiment 1. FIG. It is a figure which shows the state which mounted | wore two twist filters with the noise filter which concerns on Embodiment 1. FIG. 6 is a perspective view illustrating a configuration of a noise filter according to Embodiment 2. FIG.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a configuration of a noise filter according to Embodiment 1 of the present invention.
The noise filter 1 is configured by fitting a twist holding member 2 and an annular magnetic member 3. Details of the twist holding member 2 and the annular magnetic member 3 are shown in FIGS.

FIG. 2 is a perspective view showing the configuration of the twist holding member according to Embodiment 1 of the present invention.
The twist holding member 2 is formed of a disk-shaped insulator having an outer diameter 2a and a width 2b. In addition, a plurality of through holes 4 are formed in the twist holding member 2. The inner diameter of the through hole 4 is set to a value larger than the outer diameter of each core wire of the twist cable to which the noise filter 1 is attached. Further, the number of through holes 4 is determined by the number of core wires of the twisted cable to be attached. In FIG. 2, two through holes 4a and 4b are provided on the assumption that a twisted pair cable having two core wires is attached. .
Although FIG. 2 shows a twist holding member that assumes a case where a twisted pair cable having two core wires is attached, the number of core wires of the twist cable and the number of through holes 4 can be changed as appropriate. 1 can be attached to twisted cables having various types and core wires.

FIG. 3 is a perspective view showing the configuration of the annular magnetic member according to Embodiment 1 of the present invention.
The annular magnetic member 3 has a hollow ring shape having an inner diameter 3a, a width 3b, and a thickness 3c. The inner diameter 3 a of the annular magnetic member 3 is equal to the outer diameter 2 a of the twist holding member 2, and the twist holding member 2 can be fitted into the annular magnetic member 3. In FIG. 3, the width 3b of the annular magnetic member 3 and the width 2b of the twist holding member 2 are configured to be equal. However, the configuration is not limited to this, and the width 3b and the width 2b may be different. .

By fitting the annular magnetic member 3 to the twist holding member 2 and attaching it to the twist cable, the annular magnetic member 3 functions as a ferrite core attached to the core wire of the twist cable.
A ferrite core is a component made up of only a magnetic material in a cylindrical state, and has the effect of increasing only the impedance to the common mode in twisted pair cables and differential transmission cables, so it is well known as a member for suppressing the propagation of common mode noise. It has been. However, the ferrite core is a component that is additionally attached to the ready-made twisted pair cable, and there is a problem that the ferrite core itself has large dimensions and high cost. However, like the noise filter 1 of the first embodiment, the twist holding member 2 and the annular magnetic member 3 are fitted to each other, so that the annular magnetic member 3 is equivalent to a ferrite core and has a common mode noise suppression effect. Demonstrate.

Next, a method for attaching the noise filter 1 to the twist cable will be described.
FIG. 4 is a diagram showing a state in which the noise filter according to the first embodiment of the present invention is attached to the twist cable.

First, the cable connector 6a is attached to one end of the twisted cable 5, and the attachment of the noise filter 1 is started without attaching the cable connector to the other end.
The two core wires on the side where the cable connector is not attached are twisted as a pair, and the twisted core wires are inserted into the through hole 4a and the through hole 4b of the twist holding member 2, respectively. At this time, one core wire is inserted through one through hole. Further, the two core wires coming out of the through holes 4a and 4b are bundled and pulled to narrow the twisting pitch of the twisted cable 5. A redundant portion of the twisted cable 5 having a sufficiently narrow twist pitch is cut, and the cable connector 6b is attached. As a result, the twisted cable 5 having a dense twisting pitch in the vicinity of the cable connector 6b is formed.

In addition, when each core wire is not fully hold | maintained with the one noise filter 1 with which it mounted | worn, it is assumed that the twist pitch of the twisted cable 5 is not narrowed but untwisted. An example of mounting the noise filter 1 in such a case is shown in FIG.
First, the first noise filter 1 is attached by the method described above, and the two core wires of the twisted cable 5 are held and fixed. Further, the two core wires coming out from the through holes 4a and 4b of the first noise filter 1 are further twisted as a pair, and the twisted core wires are respectively connected to the through holes 4a 'and 4b of the twist holding member 2'. Insert ´. The two core wires coming out of the through holes 4a ′ and 4b ′ are bundled and pulled, the twisting pitch of the twisted cable 5 is narrowed, the redundant portion is cut, and the cable connector 6b is attached. Thereby, a twist can be kept densely in the section A between the first noise filter 1 and the second noise filter 1 ′.

  As described above, according to the first embodiment, since the twisted core wire is inserted and the twist holding member 2 that holds each core wire is provided, a twist cable having a denser pitch is formed. The difference in the electrical characteristics of the conductors constituting each core wire of the twisted cable can be averaged more finely, and the degree of ground balance can be improved. Furthermore, the level at which the signal transmitted by the twist cable is converted into common mode noise can be suppressed.

  Further, according to the first embodiment, since the noise filter 1 in which the annular magnetic member 3 is fitted to the twist holding member 2 is configured to be inserted into the core wire of the twist cable, the annular magnetic member 3 is attached to the core wire. It is possible to obtain a common mode noise suppression effect equivalent to the ferrite core. Thereby, suppression of common mode noise propagation can be realized simultaneously with improvement of the degree of ground balance.

  Further, according to the first embodiment, after the first noise filter 1 is mounted and the twist cable is fixed, the second noise filter 1 ′ is further mounted and twisted at a dense pitch by the twist cable. Since it has comprised so that it may have, ground balance degree can be improved more.

  In the first embodiment described above, an example in which a noise filter is attached to a twisted cable having two core wires has been described. However, the number of core wires can be changed as appropriate. By providing a through hole corresponding to the type and number of core wires, it can be attached to various twisted cables.

Embodiment 2. FIG.
In the first embodiment described above, the example in which the noise filter 1 is configured by the disk-shaped twist holding member 2 and the annular annular magnetic member 3 has been described. However, the twist holding member and the annular magnetic member have other shapes. And can be configured.
FIG. 6 is a perspective view showing the configuration of the noise filter according to Embodiment 2 of the present invention.
The noise filter 11 shown in FIG. 6 includes a hexagonal plate-like insulator twist holding member 12 and a hexagonal annular magnetic member 13. The twist holding member 12 and the annular magnetic member 13 are configured with shapes and sizes that can be fitted to each other.

  The noise filter 11 has the same function as that of the first embodiment as long as the noise filter 11 includes a twist holding member 12 formed of a flat plate-like insulator having a through hole and an annular magnetic member 13 formed of an annular magnetic body. Can be realized. The shape of the twist holding member 12 and the annular magnetic member 13 hardly affects the function of the noise filter. That is, when the noise filter 11 having the shape shown in FIG. 6 is used, or when a noise filter having another shape is used, the same effect as that of the first embodiment can be obtained.

  As described above, the shapes of the annular magnetic members 3 and 13 can be variously configured as long as they are magnetic members formed in at least a continuous annular shape (applicable to various shapes such as a circle, a square, and a hexagon). In addition, a method may be used in which the magnetic member is divided into two semicircular shapes or two or more arc shapes and combined in a ring shape when the noise filter is configured. When two or more magnetic members are combined in an annular shape, the respective magnetic members are brought into close contact with each other to form a continuous annular shape. On the other hand, the twist holding members 2 and 12 may be any members and shapes having the strength to hold the twist of the twist cable 5 and shapes that can be fitted to the annular magnetic members 3 and 13.

  As described above, according to the second embodiment, even when the shapes of the twist holding member and the annular magnetic member are variously changed, the ground balance improvement effect similar to that of the first embodiment, and the common mode noise propagation can be achieved. The suppression effect can be obtained, and the shape of the noise filter can be given flexibility.

  In addition, in Embodiment 1 and Embodiment 2 mentioned above, although the structure which provides a circular through-hole was shown, if it is the shape which can insert each core wire of a twist cable, it can change suitably.

  Further, in the first and second embodiments described above, the width 2b of the twist holding members 2 and 12 is a value within a range that can ensure a strength that is not damaged by the tension of the conductor constituting the core wire or the insulation coating. If it is within, it can be changed as appropriate.

  Furthermore, in Embodiment 1 and Embodiment 2 described above, the annular magnetic members 3 and 13 have a function of suppressing propagation of common mode noise by increasing only the impedance with respect to the common mode with respect to the cable to which the noise filter is attached. Have Therefore, the suitable width 3b or thickness 3c of the annular magnetic members 3 and 13 is associated with the impedance of the magnetic member. In general, since inductance acts dominantly on the impedance of the magnetic material, the amount of suppression of common mode noise depends on the inductance of the magnetic material. The size can be calculated. Specifically, the inductance value increases as the thickness 3c of the annular magnetic members 3 and 13 increases, and the inductance value increases as the width 3b of the annular magnetic members 3 and 13 increases.

  That is, whether the noise filter is effective is determined depending on whether the impedance is high or low. At this time, the criterion of whether the impedance is high or low is determined by the numerical value of the common mode impedance of the circuit or device in which the noise filter is inserted. When the common mode impedance is high, the annular magnetic members 3 and 13 having a larger inductance value are required. When the common mode impedance is low, the annular magnetic members 3 and 13 having a small inductance value are suppressed. can do.

Ｗ［ｍ］：円筒長、π：円周率、μ０：（真空の透磁率＝４×π×１０^-7）、μｒ：磁性体の比透磁率、Ｒｏｕｔ［ｍ］：外半径、Ｒｉｎ［ｍ］：内半径、ｌｎ（ ）：自然対数をとる演算子
式（２）により算出した値に基づいて環状磁性部材３，１３の幅３ｂおよび厚み３ｃを決定し、ノイズフィルタを構成する。 The specific calculation of the suitable width 3b and thickness 3c of the annular magnetic members 3 and 13 is configured as follows, for example.
・ When suppressing noise propagation from a device with a certain common mode impedance First, at the frequency of the propagating noise, a noise filter having an impedance larger than the common mode impedance of the device is constructed, and an inductance for obtaining the impedance is set. It calculates from the following formula | equation (1).
Z = 2πf · L (1)
Z [Ω]: Impedance of magnetic material, π: Circumference ratio, f [Hz]: Frequency of common mode noise, L [H]: Inductance of magnetic material Ring magnetism to obtain inductance calculated by equation (1) The dimension values and physical property values of the members 3 and 13 are calculated based on the following equation (2).

W [m]: cylinder length, π: circularity, μ0: (vacuum permeability = 4 × π × 10 ⁻⁷ ), μr: relative permeability of magnetic material, Rout [m]: outer radius, Rin [ m]: inner radius, ln (): operator taking natural logarithm Based on the value calculated by the equation (2), the width 3b and the thickness 3c of the annular magnetic members 3 and 13 are determined, and a noise filter is configured.

• When suppressing noise propagation of cables wired in an environment with certain mounting constraints First, substitute the noise filter dimensions or the physical properties of the noise filter magnetic material determined by the cable and wiring environment into the above formula (2). Then, the obtained inductance value is calculated. Further, the impedance obtained from the calculated inductance value and the frequency of the propagating noise is calculated by the above-described equation (1). Analyze whether the required noise attenuation can be obtained from the calculated impedance, and if sufficient attenuation is not obtained, adjust the parameters that can be changed among the dimensions of the noise filter and the physical properties of the magnetic material, or A large number of noise filters are used in combination. As described above, the width 3b and the thickness 3c of the annular magnetic members 3 and 13 are determined to constitute a noise filter.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  1, 1 ', 11 Noise filter, 2, 12 Twist holding member, 3, 3', 13 Annular magnetic member, 4, 4 ', 4a, 4b, 4a', 4b 'Through hole, 5 Twist cable, 6a, 6b Cable connector.

Claims (4)

A noise filter that suppresses noise propagating through a twisted cable having at least two core wires,
A twist holding member formed of a flat plate-like insulator having at least two or more through holes through which the core wire is inserted;
A noise filter comprising: an annular magnetic member formed of an annular magnetic body that can be fitted to the outer peripheral surface of the twist holding member. The twist holding member is formed of a disk-shaped insulator,
The noise filter according to claim 1, wherein the annular magnetic member is formed of an annular magnetic body that can be fitted to an outer peripheral surface of the twist holding member. The twist holding member is formed of a hexagonal flat insulator.
The noise filter according to claim 1, wherein the annular magnetic member is formed of a hexagonal annular magnetic body that can be fitted to an outer peripheral surface of the twist holding member. A twisted cable having at least two core wires;
A twist holding member formed of a flat plate-like insulator provided with the same number of through holes through which the at least two core wires twisted together are provided, and the twist holding member formed of an annular magnetic body At least one noise filter composed of an annular magnetic member fitted to the outer peripheral surface of
A signal transmission cable comprising: a pair of cable connectors that bundle and hold both ends of at least two core wires inserted through the through holes of the noise filter.

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