JPH07183749A - Noise filter - Google Patents

Abstract

PURPOSE:To reduce the inductance of an earth-side line and to reduce the degradation of the filter characteristic even in the high frequency band by forming out-going and coming-in lines so that currents flowing to printed coils of the earth-side line of a noise filter have opposite directions. CONSTITUTION:A first conductive pattern to constitute a first printed coil 3 is formed on one face of an insulating support body 2 made of dielectric. A second conductive pattern of second print coils 4a and 4b as two parallel going and return lines which are connected in the vicinity of the center of the substrate of the support body 2 is formed in the position, which faces the coil 3, on the other face. Then, the high frequency current flowing to the coil 4a flows to the coil 4b in the direction opposite to the current direction in the coil 4a. Since out-going and coming-in lines are so formed that currents flowing to coils 4 of the earth-side line have opposite directions, the inductance of the earth-side line is cancelled and is reduced, and the degradation of the noise filter characteristic for high frequency is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed constant type noise filter having a printed coil used for absorbing high frequency noise.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional distributed constant type noise filter having a print coil used for surface mounting and the like. In a conventional noise filter 11, a first conductive pattern forming a print coil 13 is formed on one surface of a dielectric 12, and a print coil facing the first conductive pattern of the print coil 13 via the dielectric 12. The second conductive pattern forming 14 is the dielectric 12
Is formed on another surface of. A distributed capacitance 17 is formed between the first conductive pattern of the print coil 13 and the second conductive pattern of the print coil 14. The distributed capacitance 17 is formed over the entire length of the print coils 13 and 14. A conventional distributed noise filter 1 shown in FIG.
The equivalent circuit of No. 1 is shown in FIG. External connection terminals 1a, 1
The print coil between 1a and 1b among b, 1c and 1d constitutes the inductance 18 of the signal line. The inductance 18 is generated by the print coil 13. An inductance 19 of the GND (ground side) line is formed between the connection terminals 1c and 1d. The inductance 19 is generated in the print coil 14. The inductance 18 on the signal line side forms a noise filter characteristic in cooperation with the distributed capacitance 17.

FIG. 7 shows another normal mode noise filter 21 according to the prior art. The conductive pattern of the GND line, which faces the first conductive pattern of the print coil 23 of the signal line, is formed of the conductive layer 24 instead of the print coil shown in FIG. FIG. 8 shows an equivalent circuit of the noise filter 21 shown in FIG. 7, and the inductance of the GND line is configured to have a small value. However, the formation of the distributed capacitance 27 over the entire surface of the conductive layer 24 deteriorates the filter characteristics in the high frequency range.

[0004]

In the conventional noise filters 11 and 21 shown in FIG. 4 and FIG. 7, particularly the one shown in FIG. 4, the inductance 19 between the terminal 1c and the terminal 1d formed in the GND line is As the frequency of the signal increases, the inductance value increases, causing a shift in the optimum filter combination with the distributed capacitance 17. That is, G
The increased amount of the inductance 19 formed in the ND line impairs the noise signal removal function of the distributed capacitance 17 and deteriorates the characteristics of the noise filter 11.
Further, in the noise filter 21 shown in FIG. 7, as the signal frequency becomes higher, the inductance value of the GND line of the conductive layer 24 formed on one surface of the dielectric 22 increases, and at the same time the function of the distributed capacitance 27 is deteriorated. , Connection terminal 1
GN is generated by the high-frequency current flowing through the signal lines a and 1b.
An eddy current is generated in the conductive layer 24 of the D line, and the eddy current adversely affects the signal line to deteriorate Q and deteriorate the noise filter characteristic.

[0005]

In order to solve the above-mentioned problems, the present invention provides a first conductive pattern for forming a spiral-shaped first printed coil on one surface of an insulating support, and The other side of the insulating support is provided with a second conductive pattern arranged in parallel to form a second printed coil that constitutes a distributed capacitance by facing a part or all of the first conductive pattern, and the parallel A high-frequency current flows in mutually opposite directions between the configured second print coils to provide a noise filter configured to cancel the inductance of the second print coil. It should be noted that the insulating support may be any material that is not a conductor, such as a dielectric,
What is called an insulator may be used, and since it has a predetermined distributed capacitance, it is made of a material having an appropriate dielectric constant.

[0006]

Since the conductive pattern forming the print coil on the GND line side of the noise filter is a reciprocating line and the magnetic fields generated by the currents flowing through the conductive pattern are offset each other, the inductance of the conductive pattern is high even at high frequencies. Is small, and the noise filter characteristic is improved.

[0007]

1 is an exploded perspective view of a noise filter 1 according to the present invention. 2A is a front view of the noise filter, and FIG. 2B is a back view thereof. Figure 3
Is an electrical equivalent circuit of the noise filter 1. A first conductive pattern forming the first printed coil 3 is formed on one surface of the insulating support 2 made of a dielectric material. Further, on another surface, a second print coil 4 is formed in a reciprocating manner at a position facing the first print coil 3.
A second conductive pattern composed of a and 4b is formed.
The second printed coils 4a and 4b of the second conductive pattern formed in the reciprocating manner are electrically connected near the center of the substrate of the insulating support 2 and at one end of the second printed coil 4. The second second print coils 4a and 4b are reciprocating lines. As a result, the high frequency current flowing through the second print coil 4a flows through the second print coil 4b exactly in the opposite direction to the current direction of the second print coil 4a.

That is, in the equivalent circuit of FIG. 3, the electromagnetic field caused by the high frequency current that has entered from the connection terminal 1c or 1d is canceled. Therefore, the inductance 9 due to the second print coils 4a and 4b can be reduced. An inductance 8 is formed by the first printed coil 3 between the connection terminals 1a and 1b, and as shown in the equivalent circuit of FIG. 3, the inductance between the first printed coil 3 and the second printed coil 4 on the other surface is increased. The distributed capacitance 7 and the inductance 8 of the first print coil 3 constitute a noise filter. As the dielectric material forming the insulating support 2 according to the present invention, a dielectric substrate such as a ceramic material is generally used. Since it may be assembled as a surface mount (SMD) component, a material having good machinability is suitable. The conductive patterns forming the print coils 3 and 4 are made of a material such as copper, silver, silver alloy such as silver palladium, aluminum or the like.
Print coils are formed on both sides of.

On the other hand, it is desirable that the second print coil 4a and the second print coil 4b are as close to each other as possible, while the second print coil 4 of the reciprocating line is provided.
Since the stray capacitance generated between a and 4b is small, the noise filter characteristic is not adversely affected. Connection terminals 1a, 1b, 1
c and 1d are drawn out as electrodes on the outer surface of the noise filter so that they can be configured as surface mount components, and become input / output connection terminals 1a, 1b, 1c and 1d. Connection pattern 6
Are formed on the insulator layer 5 and are provided on the first printed coil 3
It is connected to one end of the center part of the through hole.
The connection terminal 1b is formed on the outer surface of the noise filter 1.

[0010]

As described in detail above, the noise filter of the present invention has a structure in which the front and back surfaces of the dielectric substrate face each other.
In the printed coil forming the distributed capacitance, the GND
Since the currents flowing through the print coils of the (ground side) line are reciprocating lines so as to be opposite to each other, the inductance of the GND line can be small and deterioration of the noise filter characteristics at high frequencies can be suppressed.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a noise filter according to the present invention.

FIG. 2A is a front view of the noise filter shown in FIG. FIG. 2B is a rear view of the noise filter shown in FIG.

FIG. 3 is an electrical equivalent circuit diagram of the noise filter of the present invention.

FIG. 4 is an exploded perspective view of a conventional noise filter.

5 is a front view of the noise filter shown in FIG.

6 is an electrical equivalent circuit diagram of the noise filter shown in FIG.

FIG. 7 is an exploded perspective view of a conventional noise filter.

FIG. 8 is an electrical equivalent circuit diagram of a conventional noise filter.

[Explanation of symbols]

 1 Noise Filter 1a, 1b, 1c, 1d Connection Terminal 2 Insulation Support 3 First Print Coil 13, 23 Print Coil 4 Second Print Coil 4a, 4b, 14 Print Coil (GND Side) 5 Insulator Layer 6 Connection pattern 7,17,27 Distributed capacitance 8,18,28 Inductance 9,9a, 9b, 19 Inductance (GND side) 11,21 Conventional noise filter 12,22 Dielectric 24 Conductive layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01P 1/20 Z (72) Inventor Matsumoto Hatsuo 6-7-1 Koriyama, Taichiro-ku, Sendai City, Miyagi Prefecture Issue Tokin Co., Ltd.

Claims (1)

[Claims] 1. A noise filter comprising a printed coil spirally formed on an insulating support, wherein a first conductive coil forming a first printed coil spirally formed on one surface of the insulating support. A pattern and a second conductive pattern arranged in parallel on the other surface of the insulating support to form a second printed coil that faces a part or all of the first conductive pattern and forms a distributed capacitance. A noise filter, comprising: the second print coils arranged in parallel, wherein high-frequency currents flow in opposite directions to cancel the inductance of the second print coils.