JP3000998B1 - Common mode choke coil for differential transmission line - Google Patents

Abstract

A common mode choke coil for a differential transmission line in which characteristic impedance matches a transmission line to eliminate signal reflection. SOLUTION: Two coil conductors 12a and 12b are wound around a toroidal core 13;
3 is housed in an outer case 14 made of resin. The outer case 14 includes a case part 15 and a lid part 16 thereof. Outer surface of outer peripheral wall 15b of case portion 15, bottom wall 1
A ground conductor 17 made of a chrome plating film or the like is formed on the outer surface of 5c and the outer surface of the lid portion 16. On the ground conductor 17, an insulating film 18 is formed. Terminal plates 19 are respectively adhered on the insulating films 18, and the ends of the coil conductors 12 a and 12 b are soldered to the terminal plates 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a common mode choke coil for a differential transmission line.

[0002]

2. Description of the Related Art In recent years, digital electronic devices for handling digital signals, such as personal computers, have been rapidly spreading. By the way, in these digital electronic devices, electromagnetic interference noise (EMI noise) which is radiated to a space and causes another electronic device to be damaged in accordance with the transmission of a digital signal, or invades an electronic device from a space and causes a problem. Is a problem. For this reason, in digital electronic devices, various measures have been taken against radiation and intrusion of electromagnetic interference noise.

For example, as shown in FIGS. 11 and 12,
The integrated circuit 2 mounted on the printed board 1 and the integrated circuit 4 mounted on the printed board 3 are connected to two signal lines 5 forming an LC distributed constant circuit as shown in FIG.
a and 5b are connected by a cable 5. And
A digital signal output from the integrated circuit 2 is
Differential transmission. In such a system, as shown in FIG. 14, a common mode choke coil 6 is connected to the output side of the integrated circuit 2 to prevent radiation of electromagnetic interference noise. Also, a common mode choke coil 6 is connected to the input side of the integrated circuit 4 to prevent intrusion of electromagnetic interference noise. In FIG. 11, one end of the cable 5 is electrically connected to the integrated circuit 2 via the connector 7 attached to the printed circuit board 1 and the pattern 8a of the printed circuit board 1. The other end of the cable 5 is electrically connected to the integrated circuit 4 via a connector 9 attached to the printed board 3 and a pattern 8b of the printed board 3.

The common mode choke coil 6 has two coil conductors 6a and 6b wound around a magnetic core. The coil conductors 6a and 6b have a function of preventing noise having the same phase input to one end of each of the coil conductors 6a and 6b from passing to the other end.

[0005]

By the way, two signal lines 5a and 5a forming a distributed constant circuit as shown in FIG.
When transmitting a signal using the cable 5 provided with
Pattern 8a of printed circuit board 1, connector 7, signal lines 5a and 5b of cable 5, connector 9, and printed circuit board 3
Transmission lines 10 formed by the respective patterns 8b
It is necessary that the characteristic impedance between each of a and 10b (see FIG. 12) and the ground has a constant value. This is because these two transmission lines 10a, 1
This is because if a portion having a different characteristic impedance exists in the middle of 0b, signal reflection occurs at that position, and the signal waveform is disturbed.

However, the conventional common mode choke coil 6 has a configuration in which two coil conductors 6a and 6b are wound around a magnetic core.
No particular consideration was given to the characteristic impedance between b and the ground. Therefore, when the conventional common mode choke coil 6 is inserted in the middle of the transmission lines 10a and 10b, the transmission lines 10a and 10b are inserted at the insertion positions.
The characteristic impedance of b is different. That is, there is a problem that the signal transmitted through the transmission lines 10a and 10b is reflected by the common mode choke coil 6, and the waveform of the transmission signal is disturbed.

It is an object of the present invention to provide a common mode choke coil for a differential transmission line that can match the characteristic impedance with respect to the ground to the transmission line.

[0008]

In order to achieve the above object, in a common mode choke coil for a differential transmission line according to the present invention, a plurality of coil conductors face a ground conductor with a spacer interposed. It is characterized by. More specifically, the plurality of coil conductors are wound around a magnetic core, and an outer peripheral surface of the magnetic core around which the coil conductor is wound is substantially surrounded by the ground conductor via the spacer.

[0009]

With the above arrangement, each of the coil conductors faces the ground conductor with the spacer interposed therebetween, and a distributed capacitance is formed between the ground conductor and each of the coil conductors. An LC distributed constant circuit is formed between each of the coil conductors and the ground conductor by the distributed capacitance and the inductor of the coil conductor. By appropriately setting the distributed constant circuit, the characteristic impedance of the coil conductor can be matched with the characteristic impedance of the transmission line.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a common mode choke coil for a differential transmission line according to the present invention will be described below with reference to the accompanying drawings.

[First Embodiment, FIGS. 1-3] FIG. 1 is a perspective view of a common mode choke coil for a differential transmission line according to the present invention, and FIG. 2 is an exploded perspective view thereof.
The differential transmission line common mode choke coil 11 is composed of two coil conductors 1 insulated and coated with polyurethane resin or the like.
2a and 12b are bifilar wound around a ring-shaped toroidal core 13 made of ferrite, and this toroidal core 13 is housed in a resin outer case 14.

As shown in FIG. 2, the outer case 14 includes a case portion 15 and a lid portion 16 thereof. The case portion 15 includes a cylindrical inner peripheral wall 15a and an outer peripheral wall 15b joined by a bottom wall 15c, and has a ring-shaped housing portion 15d for housing the toroidal core 13 therein. The lid 16 has a disk shape having a hole 16a in the center, and closes the housing 15d of the case 15. Four claws 16b are pulled out from the peripheral edge of the lid 16 at regular intervals along the outer surface of the outer peripheral wall 15b of the case 15.

A ground conductor 17 made of a chrome plating film or the like is formed on the outer surface of the outer peripheral wall 15b of the case 15, the outer surface of the bottom wall 15c, and the outer surface of the lid 16. An insulating film 1 made of an insulating resin or the like is formed on the outer peripheral wall 15 b and the ground conductor 17 of the bottom wall 15 c of the case 15.
8 are formed at four locations at equal intervals. Terminal plates 19 made of a metal material such as phosphor bronze are adhered on the insulating film 18, respectively. The ends of the coil conductors 12a and 12b are soldered to these four terminal boards 19, respectively. The lid part 16 is fixed to the case part 15 by engaging its claws 16b with the bottom wall 15c of the case part 15.

Next, the operation and effect of the choke coil 11 when the common mode choke coil 11 for a differential transmission line having the above configuration is inserted in the middle of the transmission lines 10a and 10b shown in FIG. 12 will be described. . The ground conductor 17 of the choke coil 11 is grounded, the four terminal plates 19 are connected to the transmission lines 10a and 10b, and the coil conductors 12a and 12b are inserted into the transmission lines 10a and 10b, respectively. As shown in the equivalent circuit of FIG. 3, the ground conductor 17 has a fixed distance with the outer case 14 interposed therebetween.
As a result, a capacitance (distribution capacitance) having the outer case 14 as a dielectric is formed between the coil conductors 12a and 12b. Due to this capacitance and the inductors of the coil conductors 12a and 12b, the coil conductors 12a and 12b
Is formed between each of them and the ground. The capacitance is determined by the dielectric constant of the resin constituting the outer case 14, the ground conductor 17 and the coil conductor 1.
It is determined by the facing area and the distance to 2a and 12b. Therefore, by appropriately selecting these values, the characteristic impedance between each of the coil conductors 12a and 12b and the ground can be matched with the characteristic impedance between each of the transmission lines 10a and 10b and the ground. It becomes possible. Thereby, the common mode choke coil 11 for a differential transmission line without signal reflection can be obtained.

[Second Embodiment, FIGS. 4 and 5] FIG. 4 is a perspective view of another embodiment of a common mode choke coil for a differential transmission line according to the present invention, and FIG. 5 is an exploded perspective view thereof. . Common mode choke coil 21 for differential transmission line
The two coil conductors 22a and 22b, which are insulated and coated with polyurethane resin or the like, are bifilar wound around a rod-shaped core 23 made of ferrite or the like.

At both ends of the core 23, flange members 24a and 24b made of insulating resin or the like are fixed. That is,
As shown in FIG. 5, a fitting hole 25 is formed in each of the flange members 24a and 24b, and the end of the core 23 is fitted in the fitting hole 25 and adhered with an adhesive. . Two terminal plates 26 made of phosphor bronze or the like are mounted on the outer surfaces of the flange members 24a and 24b, respectively. These terminal plates 26
Are soldered to ends of the coil conductors 22a and 22b, respectively.

The core 23 has a thin plate-shaped ground conductor 27 made of phosphor bronze or the like having an insulating film 28 made of an insulating resin formed on one main surface, and the insulating film 28 is made of a coil conductor 22.
a, 22b side. From the ground conductor 27, a plurality of ground terminal pieces 27a are drawn out. These ground terminal pieces 27a are
Along the surface of a, 24b, it reaches the surface on the side where the terminal plate 26 is mounted.

In the differential transmission line common mode choke coil 21 having such a configuration, the ground conductor 27 is secured at a certain distance with the insulating film 28 interposed between the coil conductors 22a and 22b. And an insulating film 2 between them.
An electrostatic capacitance (distributed capacitance) using 8 as a dielectric is formed.
An LC distributed constant circuit is formed between each of the coil conductors 22a and 22b and the ground by the capacitance and the inductors of the coil conductors 22a and 22b. The capacitance is determined by the dielectric constant of the insulating film 28 and its thickness, and the facing area between the coil conductors 22a and 22b and the ground conductor 27. Therefore, by appropriately selecting these values, the characteristic impedance between each of the coil conductors 22a and 22b and the ground can be changed, for example, as shown in FIG.
2 can be matched with the characteristic impedance between each of the transmission lines 10a and 10b and the ground. Thereby, it is possible to obtain the differential transmission line common mode choke coil 21 having no signal reflection.

[Third Embodiment, FIGS. 6 to 8] FIG. 6 is a perspective view of a common mode choke coil for a differential transmission line according to the present invention, and FIG. FIG. 8 is a vertical sectional view. In the differential transmission line common mode choke coil 31, two coil conductors 32a and 32b insulated and coated with polyurethane resin or the like are bifilar wound around a core 34 made of ferrite or the like.
The core 34 has flange portions 3 at both ends of the columnar body portion 33.
3a and 33b are provided. A signal electrode 35 and a ground electrode 36 are formed on the flange 33a. The ends of the coil conductors 32a and 32b are soldered to the signal electrode 35, respectively.

The body 33 of the core 34 has a resin film 3
A thin plate-shaped ground conductor 37 made of copper or the like having a tin-plated film or the like formed on the surface thereof is wound via the base 8. From the ground conductor 37, a ground terminal strip 37a is drawn out. These ground terminal pieces 37a are connected to the ground electrode 3
6 is soldered.

In the differential transmission line common mode choke coil 31 having such a configuration, the ground conductor 37 is secured at a certain distance with the resin film 38 interposed therebetween.
The capacitance (distributed capacitance) having the resin film 38 as a dielectric is formed between the coil conductors 32a and 32b. This capacitance and the coil conductors 32a, 32b
Of the coil conductors 32a, 3
An LC distributed constant circuit is formed between each of 2b and the ground. The capacitance is determined by the dielectric constant of the resin film 38 and its thickness, and the facing area between the coil conductors 32a and 32b and the ground conductor 37. Therefore, by properly selecting these values, the coil conductor 32
The characteristic impedance between each of the transmission lines 10a and 10b described with reference to FIG.
Can be matched with the characteristic impedance between each of them and the ground. This makes it possible to obtain the differential transmission line common mode choke coil 31 having no signal reflection.

Fourth Embodiment, FIGS. 9 and 10 FIG. 9 is an exploded perspective view of still another embodiment of a common mode choke coil for a differential transmission line according to the present invention, and FIG. Each is shown in FIG. The common mode choke coil 41 for a differential transmission line forms conductor patterns 42a and 42b on the surfaces of sheet materials 43 and 44 made of a magnetic material such as ferrite by printing, sputtering, vapor deposition, or the like. In addition to laminating the members 43 and 44, the spacer sheet members 45 and 45 are respectively laminated on the upper and lower sides thereof, and the ground conductor patterns 49a and 49b are further formed on the upper and lower sides in the same manner as above. Sheet material 4 formed on the surface
6, 47, respectively, and sheet materials 48, 48 for the cover are further laminated on the upper and lower sides. If the sheet members 44 and 46 are used as spacers, the spacer sheet member 45 is not necessarily required.

As shown in FIG. 10, sheet materials 43 to 48
A conductor pattern 42a,
External signal electrodes 55 that are electrically connected to the respective ends of the ground conductor pattern 4
External ground electrode 5 electrically connected to 9a, 49b
6 are formed.

In the differential transmission line common mode choke coil 41 having such a configuration, the ground conductor patterns 49a and 49b are separated from the conductor patterns 42a and 42
b, a capacitance (distribution capacitance) is formed between the sheet materials 45 and 45 as a dielectric. With this capacitance and the inductors of the conductor patterns 42a and 42b, an LC distributed constant circuit is formed between each of the conductor patterns 42a and 42b and the ground. The capacitance is determined by the permittivity and thickness of the sheet materials 45, 45, and the facing area between the conductor patterns 42a, 42b and the ground conductor patterns 49a, 49b.
Therefore, by appropriately selecting these values, the characteristic impedance between each of the conductor patterns 42a and 42b and the ground can be reduced, for example, by using the transmission line 1 described with reference to FIG.
This makes it possible to match the characteristic impedance between each of Oa and 10b and the ground. Thereby, it is possible to obtain the differential transmission line common mode choke coil 41 having no signal reflection.

[Other Embodiments] The present invention is not limited to the above embodiment, and can be variously modified within the scope of the gist. For example, in the first embodiment, the ground conductor 17 is also provided on the outer surface of the inner peripheral wall 15a of the case portion 15, and the coil conductor 1 is provided.
The entire circumference of 2a and 12b may be surrounded by the ground conductor 17. In the second embodiment, a cylindrical core is used in place of the rod-shaped core 23, a resin film is formed on the inner peripheral surface of the cylindrical core, and a ground conductor is arranged on the surface of the resin film. It may be something. Further, as a material of the spacer, a dielectric material or an insulating material is used, and a resin, a ceramic, or the like may be used.

[0026]

As is clear from the above description, according to the present invention, since each of the plurality of coil conductors faces the ground conductor with the spacer interposed therebetween, each of the ground conductor and the coil conductor is provided. Between them, capacitances each having a spacer as a dielectric are formed. Therefore, an LC distributed constant circuit is formed between each of the coil conductors and the ground by the capacitance and the inductor of the coil conductor. By appropriately setting the distributed constant circuit, the characteristic impedance between each of the coil conductors and the ground can be matched with the characteristic impedance of the transmission line, thereby providing a differential transmission having good transmission characteristics without reflection. A common mode choke coil for a transmission line can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of a first embodiment of a common mode choke coil for a differential transmission line according to the present invention.

FIG. 2 is an exploded perspective view of the differential transmission line common mode choke coil shown in FIG. 1;

3 is an electric equivalent circuit diagram of the common mode choke coil for a differential transmission line shown in FIG.

FIG. 4 is a perspective view showing the appearance of a second embodiment of a common mode choke coil for a differential transmission line according to the present invention.

FIG. 5 is an exploded perspective view of the common mode choke coil for a differential transmission line shown in FIG. 4;

FIG. 6 is a perspective view showing an appearance of a third embodiment of a common mode choke coil for a differential transmission line according to the present invention.

FIG. 7 is an exploded perspective view of the common mode choke coil for a differential transmission line shown in FIG. 6;

FIG. 8 is a longitudinal sectional view of the differential transmission line common mode choke coil shown in FIG. 6;

FIG. 9 is an exploded perspective view of a fourth embodiment of a common mode choke coil for a differential transmission line according to the present invention.

FIG. 10 is a perspective view showing the appearance of the differential transmission line common mode choke coil shown in FIG. 9;

FIG. 11 is an explanatory diagram of a digital signal transmission system.

FIG. 12 is an explanatory diagram of a differential transmission line.

FIG. 13 is an explanatory diagram of a distributed constant circuit of a differential transmission line.

FIG. 14 is a circuit diagram of a conventional differential transmission line common mode choke coil inserted into the differential transmission line.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Common mode choke coil for differential transmission lines 12a, 12b ... Coil conductor 13 ... Toroidal core 14 ... Outer case 17 ... Ground conductor 21 ... Common mode choke coil for differential transmission line 22a, 22b ... Coil conductor 23 ... Core 27 ... ground conductor 28 ... insulating film 31 ... common mode choke coil for differential transmission line 32a, 32b ... coil conductor 34 ... core 37 ... ground conductor 38 ... resin film 41 ... common mode choke coil for differential transmission line 42a, 42b ... Signal conductor patterns 43 to 48: Sheet materials 49a, 49b: Ground conductor patterns

Claims (4)

(57) [Claims] A plurality of coil conductors opposing a ground conductor via a spacer capable of forming a capacitance;
A common mode choke coil for differential transmission lines, characterized in that the distance from the ground conductor is constant . (2) The distance between the plurality of coil conductors is constant
2. The differential transmission line connector according to claim 1, wherein
Monmode choke coil. (3) The plurality of coil conductors are bifilar wound
3. The device according to claim 1, wherein the device is mounted.
Common mode choke coil for differential transmission line. 4. A plurality of coil conductors are wound around a magnetic core, and an outer peripheral surface of the magnetic core around which the coil conductor is wound is substantially surrounded by the ground conductor via the spacer. Claim 1 or Claim characterized by the above-mentioned.
Item 4. A common mode choke coil for a differential transmission line according to Item 3 .