JP2012195332A - Common mode noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the common mode noise in a wide frequency band.SOLUTION: The common mode noise filter constitutes a first filter part 15 in which a first coil conductor 11 and a third coil conductor 13 adjacent to each other in the lamination direction are magnetically coupled to each other, and also constitutes a second filter part 16 in which a second coil conductor 12 and a fourth coil conductor 14 adjacent to each other in the lamination direction are magnetically coupled to each other. Furthermore, the frequency characteristic of the first filter part 15 and the frequency characteristic of the second filter part 16 are made different from each other, and the coupling coefficient of the first filter part 15 and the second filter part 16 is -0.5 to +0.5.

Description

  The present invention relates to a common mode noise filter used in various electronic devices such as digital devices, AV devices, and information communication terminals.

  As shown in FIG. 12, this type of conventional common mode noise filter includes nonmagnetic layers 1a to 1c and a plurality of magnetic layers 2 formed above and below the nonmagnetic layers 1a to 1c. A laminated body 3 formed by laminating magnetic layers 1a to 1c and a magnetic layer 2, and spiral first coils 4 and second coils 5 formed on the nonmagnetic layers 1a to 1c; The winding direction of the first coil 4 and the winding direction of the second coil 5 are the same as each other when viewed from above.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

JP 2001-60514 A

  In recent years, various digital interfaces such as a USB to a mobile phone are mounted, and noise countermeasures are desired. For example, reduction of common mode noise is desired for a wide frequency band of 800 MHz band to 2 GHz band in a mobile phone and a wide range of 480 MHz band and 960 MHz band in USB 2.0.

  However, in the above-described conventional common mode noise filter, the common mode impedance is reduced in the high frequency region due to the self-resonance due to the stray capacitance of the inductor that is the constituent element, and the common mode attenuation cannot be secured in a wide frequency band. Had problems.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a common mode noise filter capable of removing common mode noise in a wide frequency band.

  In order to achieve the above object, the present invention has the following configuration.

  Invention of Claim 1 of this invention is equipped with the laminated body and the 1st-4th coil conductor formed in the inside of this laminated body, The one end part of said 1st coil conductor, and said 2nd And connecting one end of the third coil conductor and one end of the fourth coil conductor together with the first coil conductor adjacent to the stacking direction and the first coil conductor A first filter unit magnetically coupled with the third coil conductor is configured, and a second filter unit magnetically coupled with the second coil conductor and the fourth coil conductor adjacent in the stacking direction is configured. Further, the frequency characteristics of the first filter section and the frequency characteristics of the second filter section are made different from each other, and the coupling coefficient between the first filter section and the second filter section is −0.5. ~ + 0.5, and according to this configuration, Since the magnetic coupling between the first and second filter parts is connected in series with a weak state, attenuation poles can be created in two frequency bands that differ in common mode attenuation characteristics. It has an operational effect that mode noise can be removed.

  As described above, the common mode noise filter of the present invention constitutes the first filter portion magnetically coupled by the first coil conductor and the third coil conductor adjacent in the stacking direction, and is adjacent to the stacking direction. A second filter part magnetically coupled with the second coil conductor and the fourth coil conductor, and further, the frequency characteristics of the first filter part and the second filter part are made different from each other, Since the coupling coefficient between the first filter unit and the second filter unit is set to -0.5 to +0.5, the magnetic coupling between the first and second common mode filter units can be connected in series with a weak state. As a result, attenuation poles can be made in two frequency bands that differ in common mode attenuation characteristics, so that an excellent effect is achieved in that common mode noise in a wide frequency band can be removed.

The disassembled perspective view of the common mode noise filter in one embodiment of this invention Perspective view of the common mode noise filter An exploded perspective view of another example of the common mode noise filter Internal connection diagram of the common mode noise filter Comparison of common mode attenuation characteristics of the common mode noise filter and the conventional common mode noise filter The figure which shows the common mode attenuation | damping characteristic in case the coupling coefficient of two filter parts can be regarded as almost 0 The figure which shows the common mode attenuation characteristic when the coupling coefficient of two filter parts is +0.5 The figure which shows the common mode attenuation | damping characteristic in case the coupling coefficient of two filter parts is +0.6 The figure which shows the common mode attenuation characteristic when the coupling coefficient of two filter parts is +0.9 The figure which shows the common mode attenuation | damping characteristic in case the coupling coefficient of two filter parts is -0.5 The figure which shows the common mode attenuation | damping characteristic in case the coupling coefficient of two filter parts is -0.9 Exploded perspective view of a conventional common mode noise filter

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an exploded perspective view of a common mode noise filter according to an embodiment of the present invention, and FIG. 2 is a perspective view of the common mode noise filter.

  As shown in FIGS. 1 and 2, the common mode noise filter according to one embodiment of the present invention includes a multilayer body 10 and first to fourth coil conductors 11 to 14 formed inside the multilayer body 10. And connecting one end 11a of the first coil conductor 11 and one end 12a of the second coil conductor 12, and one end 13a of the third coil conductor 13 and the fourth coil. The one end 14a of the conductor 14 is connected. The first coil conductor 11 and the third coil conductor 13 adjacent to each other in the stacking direction constitute a first filter portion 15 that is magnetically coupled, and the second coil conductor 12 adjacent to the stacking direction is included. And the fourth coil conductor 14 constitute a second filter unit 16 that is magnetically coupled, and the frequency characteristics of the first filter unit 15 and the frequency characteristics of the second filter unit 16 are different. Thus, the coupling coefficient of the first filter unit 15 and the second filter unit 16 is set to −0.5 to +0.5.

  The said structure WHEREIN: The said 1st-4th coil conductors 11-14 are each formed by plating electrically conductive materials, such as silver, in a spiral shape. The first coil conductor 11 and the second coil conductor 12 are formed on the upper surface of the first insulator layer 17a, and the third coil conductor 13 and the fourth coil conductor 14 are the second insulator. Each is formed on the upper surface of the layer 17b. Then, the first coil conductor 11 and the third coil conductor 13, and the second coil conductor 12 and the fourth coil conductor 14 are opposed to and adjacent to each other in the stacking direction.

  The other end portion 11b of the first coil conductor 11 and the other end portion 12b of the second coil conductor 12 are respectively a first lead conductor 18 and a second lead conductor 18 provided on the upper surface of the third insulator layer 17c. The lead conductor 19 is connected to via electrodes 20a and 20b formed in the first insulator layer 17a.

  Furthermore, the other end portion 13b of the third coil conductor 13 and the other end portion 14b of the fourth coil conductor 14 are respectively a third lead conductor 21 and a fourth lead conductor 21 provided on the upper surface of the fourth insulator layer 17d. The lead conductor 22 is connected to via electrodes 20c and 20d formed in the fourth insulator layer 17d.

  A predetermined number of fifth insulator layers 17e are provided on the lower surface of the third insulator layer 17c and on the upper surfaces of the third lead conductor 21 and the fourth lead conductor 22.

  The first to fourth insulator layers 17a to 17d are arranged in the order of the third insulator layer 17c, the first insulator layer 17a, the second insulator layer 17b, and the fourth insulator layer 17d from the bottom. The first insulator layer 17a, the second insulator layer 17b, the fourth insulator layer 17d, and the fifth insulator layer 17e are made of a sheet of magnetic material such as Ni—Cu—Zn ferrite. The third insulator layer 17c is formed in a sheet shape from a nonmagnetic material such as Cu—Zn ferrite. The number of the first to fifth insulator layers 17a to 17e is not limited to the number shown in FIG.

  The first to fourth lead conductors 18, 19, 21, and 22 are connected to first to fourth external electrodes 23 a to 23 d provided on both end surfaces of the multilayer body 10, respectively. The first to fourth external electrodes 23a to 23d are formed by printing silver on the end face of the laminate 10, and a nickel plating layer is formed on these surfaces by plating, and the surface of the nickel plating layer A low melting point metal plating layer such as tin or solder is formed by plating. The first and third external electrodes 23a and 23c are provided on the same surface, and the second and fourth external electrodes 23b and 23d are provided on the other same surface.

  Further, the via electrodes 20a to 20d are formed by drilling holes at predetermined locations of the first insulator layer 17a and the fourth insulator layer 17d and filling the holes with silver.

  Here, the first coil conductor 11 and the third coil conductor 13 substantially overlap each other when viewed from above, and are thereby configured to be magnetically coupled to each other. A first filter portion 15 is formed by the coil conductor 13. Similarly, the second coil conductor 12 and the fourth coil conductor 14 substantially overlap each other when viewed from above, and are configured to be magnetically coupled to each other. A second filter portion 16 is formed by the coil conductor 14. In FIG. 1, the first filter unit 15 and the second filter unit 16 are arranged so as to be in the horizontal direction, but may be arranged so as to be in the stacking direction.

  Furthermore, the first coil conductor 11 and the third coil conductor 13, and the second coil conductor 12 and the fourth coil conductor 14 are reversed in the winding direction in the top view. At this time, when the common mode current enters from the first and third external electrodes 23a and 23c, the magnetic flux generated in the first filter unit 15 and the magnetic flux generated in the second filter unit 16 strengthen each other. The coupling coefficient k is positive. On the other hand, as shown in FIG. 3, in the top view, the first coil conductor 11 to the fourth coil conductor 14 have the same winding direction of the coil conductor, and the magnetic flux generated in the first filter unit 15 When the magnetic fluxes generated by the second filter unit 16 cancel each other, the coupling coefficient k becomes negative.

  The common mode noise filter of the present invention shown in FIG. 1 has a configuration in which a first filter unit 15 and a second filter unit 16 are connected in series as shown in FIG.

  Further, the number of turns of the first filter unit 15 is made smaller than the number of turns of the second filter unit 16, thereby making the frequency characteristics of the first filter unit 15 and the second filter unit 16 different. In addition to changing the number of turns, the frequency characteristics can also be made different by changing the distance between lines or changing the area surrounded by the outermost periphery when viewed from above. In the common mode noise filter shown in FIG. 1, since the number of turns of the first filter unit 15 is less than the number of turns of the second filter unit 16, the resonance frequency of the first filter unit 15 is the second. The resonance frequency of the filter unit 16 is higher. That is, the attenuation pole corresponding to the first filter unit 15 is on the higher frequency side than the attenuation pole corresponding to the second filter unit 16.

And the coupling coefficient of the 1st filter part 15 and the 2nd filter part 16 when a common mode electric current is applied is -0.5- + 0.5. Here, the coupling coefficient k is the self-inductance of the first filter unit 15 in the common mode L1, the self-inductance of the second filter unit 16 in the common mode L2, and the mutual inductance of both the common modes M. In this case, k ² = M ² / (L1 × L2). Therefore, the coupling coefficient is set to a predetermined value by adjusting the number of turns and the distance between the first filter unit 15 and the second filter unit 16 and the positional relationship between the first filter unit 15 and the second filter unit 16. Can be a value.

  FIG. 5 is a diagram comparing the attenuation characteristics of the common mode noise filter of the present invention and the conventional common mode noise filter.

  As can be seen from FIG. 5, the common mode noise filter of the present invention creates attenuation poles in two different frequency bands, thereby removing common mode noise in a wide frequency band. Here, attenuation poles can be formed in two different frequency bands because the frequency characteristics of the first filter unit 15 and the second filter unit 16 are different, so that attenuation poles are generated at frequencies corresponding to the frequency characteristics of the respective filter units. This is because the magnetic coupling between the first filter unit 15 and the second filter unit 16 is weak. Therefore, if the frequency characteristics of the two filter sections are made the same by making the number of turns of the first to fourth coil conductors 11 to 14 the same, an attenuation pole is created in the same frequency band, and a wide frequency band is obtained. Common mode noise cannot be removed.

  6 shows that the coupling coefficient k of the first filter unit 15 and the second filter unit 16 is almost zero, FIG. 7 shows that the coupling coefficient k is +0.5, and FIG. 8 shows that the coupling coefficient k is +0.6. 9 shows the common mode attenuation characteristic when the coupling coefficient k is +0.9, and the magnetic coupling between the first filter unit 15 and the second filter unit 16 is the frequency characteristic of the common mode attenuation amount. We will explain the effect on the following.

  Here, the state in which the coupling coefficient k of the first filter unit 15 and the second filter unit 16 shown in FIG. 6 is almost zero is almost no magnetic coupling, and the magnetic structure of each filter unit is the first. In this case, the attenuation pole on the high frequency side is an attenuation pole corresponding to the first filter section 15 in FIG. The attenuation pole on the frequency side is an attenuation pole corresponding to the second filter unit 16 in FIG. For comparison, FIG. 6 also shows common mode attenuation characteristics of only the first filter unit 15 and only the second filter unit 16. 7 to 9 also show the common mode attenuation characteristics of only the first filter unit 15 and only the second filter unit 16 for comparison.

  As is apparent from FIGS. 6 to 9, as the coupling coefficient increases, a magnetic coupling structure that reinforces each other is formed between the first filter unit 15 and the second filter unit 16. From the side, the common mode impedance increases, the common mode attenuation increases, and the resonance frequency also decreases. When the coupling coefficient is +0.9, the attenuation pole on the low frequency side becomes dominant.

  At this time, as shown in FIG. 8, when the coupling coefficient k is +0.6, the common mode attenuation amount on the high frequency side is compared with the common mode attenuation amount when the coupling coefficient k is substantially 0 at the attenuation pole on the high frequency side. Since a series resonance state occurs between the first filter unit 15 and the second filter unit 16 that exceeds the resonance point frequency between the two attenuation poles, the common mode attenuation accompanying the decrease in the common mode impedance As a result, the amount of deterioration of the amount increases, and thus the common mode attenuation becomes smaller than 10 dB, the common mode attenuation in a wide frequency band cannot be secured, and the common mode noise cannot be removed. As a result, the coupling coefficient k needs to be +0.5 or less.

  When the coupling coefficient k becomes +0.9, the attenuation pole on the low frequency side becomes dominant, so that common mode noise in a wide frequency band cannot be removed. This is because in the strengthening magnetic coupling state between the first and second filter portions 15 and 16, the stronger the coupling coefficient approaches 1, the stronger the magnetic coupling state. This is because the two filter sections 15 and 16 approach a state that can be regarded as one filter section, have a large common mode impedance on the low frequency side, and the common mode attenuation pole becomes monopolar. As can be seen from FIG. 9, in such a strong coupling state, the common mode attenuation on the high frequency side cannot be ensured, and therefore, the common mode attenuation in a wide frequency band cannot be ensured. For this reason, the coupling coefficient k between the first filter unit 15 and the second filter unit 16 needs to be +0.5 or less.

  6 to 9 show the case where the coupling coefficient k is positive, the cases where the coupling coefficient k is negative are shown in FIGS. 10 and 11. 10 shows a case where the coupling coefficient k of the first filter unit 15 and the second filter unit 16 is −0.5, and FIG. 11 shows a case where the coupling coefficient k is −0.9. The common mode attenuation characteristics of only the first filter unit 15 and only the second filter unit 16 are also shown.

  As is apparent from FIGS. 10 and 11, when the magnetic coupling between the first filter unit 15 and the second filter unit 16 weakens each other, the inductor component decreases with respect to the common mode. , The common mode impedance is lowered, and the common mode attenuation is also reduced accordingly. In the high frequency region, the common mode impedance increases in proportion to the frequency, so that the common mode attenuation can be secured, and the resonance frequency is also shifted to the high frequency side. As the coupling coefficient k is decreased, the attenuation pole on the high frequency side becomes dominant. This is because the coupling coefficient approaches −1 in the destructive magnetic coupling state between the first and second filter sections 15 and 16. As the magnetic structure approaches the state where the first and second filter parts 15 and 16 can be regarded as one common mode filter part that strongly cancels each other equivalently, the common mode impedance is extremely small on the low frequency side, The common mode attenuation pole becomes monopolar on the high frequency side. In such a magnetic coupling state in which the first filter 15 and the second filter unit 16 strongly cancel each other, the common mode attenuation amount on the low frequency side cannot be ensured, and therefore, the common mode attenuation amount in a wide frequency band is ensured. I can't. For this reason, the coupling coefficient k between the 1st filter part 15 and the 2nd filter part 16 needs to be more than -0.5.

  From the above, two filter sections 15 and 16 having different frequency characteristics are connected in series, and the coupling coefficient k is -0.5 ≦ k ≦ + 0.5. In the frequency characteristic of the quantity, it has two attenuation poles, can secure a common mode attenuation amount in a wide frequency band, and can remove common mode noise.

  As described above, in the common mode noise filter according to the embodiment of the present invention, the first filter unit 15 that is magnetically coupled by the first coil conductor 11 and the third coil conductor 13 that are adjacent to each other in the stacking direction is configured. The second filter conductor 16 and the fourth coil conductor 14 which are adjacent to each other in the stacking direction are magnetically coupled to each other, and the frequency characteristics of the first filter section 15 are Since the frequency characteristics of the second filter unit 16 are made different and the coupling coefficient of the first filter unit 15 and the second filter unit 16 is set to −0.5 to +0.5, the two filter units are weak with each other. Since it can be connected by coupling, this makes it possible to create attenuation poles in two frequency bands that differ in common mode attenuation characteristics, so it is possible to eliminate common mode noise in a wide frequency band. One in which the effect is obtained that that.

  That is, by making the frequency characteristic of the first filter unit 15 and the frequency characteristic of the second filter unit 16 different, attenuation poles are created in two different frequency bands in the common mode attenuation characteristic. By weakly coupling the filter unit 15 and the second filter unit 16, the two filter units are equivalent to one common mode filter, resulting in a single attenuation pole. The frequency of the two attenuation poles is adjusted by adjusting the coupling coefficient to the plus side that strengthens and the minus side that weakens by changing the winding direction of the coil conductors of the first filter portion 15 and the second filter portion 16. As a result, common mode noise in a wide frequency band can be removed.

  In addition, when it is necessary to attenuate in two frequency bands by an electronic device, the frequency of the attenuation pole corresponding to each of the two filter units can be adjusted so as to be the same frequency without using two components. Therefore, the electronic device can be downsized.

  In the above-described embodiment of the present invention, two filter units are connected in series. However, three or more filter units may be connected in series. Also in this case, the frequency characteristics of the respective filter units are made different, and the mutual coupling coefficient is also set to -0.5 to +0.5.

  Furthermore, a magnetic core made of a ferrite material or the like may be provided for each of the first to fourth coil conductors 11 to 14 to adjust the coupling coefficient of the filter unit.

  The common mode noise filter according to the present invention has an effect of removing common mode noise in a wide frequency band, and is particularly used as a noise countermeasure for various electronic devices such as digital devices, AV devices, and information communication terminals. This is useful in common mode noise filters.

DESCRIPTION OF SYMBOLS 10 Laminated body 11 1st coil conductor 11a One end part of 1st coil conductor 12 2nd coil conductor 12a One end part of 2nd coil conductor 13 3rd coil conductor 13a One end part of 3rd coil conductor 14 Four coil conductors 14a One end of the fourth coil conductor 15 First filter portion 16 Second filter portion

Claims (1)

A laminated body and first to fourth coil conductors formed inside the laminated body, connecting one end of the first coil conductor and one end of the second coil conductor; and The first coil conductor is connected to the one end of the third coil conductor and the one end of the fourth coil conductor, and is magnetically coupled between the first coil conductor and the third coil conductor adjacent to each other in the stacking direction. A second filter unit magnetically coupled by the second coil conductor and the fourth coil conductor adjacent to each other in the stacking direction, and further, the first filter unit A common mode noise filter in which the frequency characteristics of the second filter section and the frequency characteristics of the second filter section are made different, and the coupling coefficient between the first filter section and the second filter section is -0.5 to +0.5.

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