Common mode filter

A common mode filter includes a first filter and a second filter formed by a magnetic coupling between primary coils and secondary coils, respectively, and connected in series. In the common mode filter, a resonance frequency f1 of the first filter and a resonance frequency f2 of the second filter are different from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2015-0037455 filed on Mar. 18, 2015, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to a common mode filter, and more particularly, to a common mode filter able to remove wideband noise.

In accordance with technological developments, electronic devices such as mobile phones, home appliances, personal computers (PCs), personal digital assistants (PDAs), liquid crystal displays (LCDs), and the like, have changed from being analog implemented to being digitally implemented, and electronic device speeds have increased due to an increase in an amount of data processed by the electronic devices.

Therefore, a universal serial bus (USB) 2.0, a USB 3.0, and a high-definition multimedia interface (HDMI) have widely been circulated as high speed signal transmitting interfaces, and have been used in many digital devices such as personal computers and digital high-definition televisions.

These high speed interfaces adopt a differential transmission system transmitting signals having a phase difference of 180 degrees using a pair of signal lines, unlike a single-end transmission system that has been generally used for a long period of time.

In a case in which phases of high frequency signals do not coincide with each other in the above-mentioned differential transmission, common mode noise occurs, and this noise is radiated, thereby influencing peripheral communications elements. As a coil component for filtering common mode noise, a common mode filter has been widely used. That is, common mode noise is noise generated in the differential signal line, and the common mode filter removes noises that may not be removed by an existing filter.

Therefore, the common mode filter may advantageously remove noise across a wideband. However, an existing common mode filter using two coils may merely remove noise of a natural frequency band designed according to a target value, and has a disadvantage in that it does not remove the noise across the wideband.

SUMMARY

An aspect of the present disclosure may provide a common mode filter capable of attenuating noise across a wideband by connecting two filters having different resonance frequencies in series.

According to an aspect of the present disclosure, a common mode filter may include a first filter and a second filter formed by a magnetic coupling between primary coils and secondary coils, respectively, and connected in series. A resonance frequency of the first filter and a resonance frequency of the second filter may be different from each other.

The first filter and the second filter may be disposed side by side, and inductance of the first filter and inductance of the second filter may have values different from each other by setting the number of coil turns of the primary and secondary coils of the first filter and the number of coil turns of the primary and secondary coils of the second filter to be different from each other.

Capacitance of the first filter and capacitance of the second filter may have values different from each other by setting a distance between the primary coil of the first filter and the secondary coil of the first filter to be different from a distance between the primary coil of the second filter and the secondary coil of the second filter.

According to another aspect of the present disclosure, a common mode filter may include a primary coil of a first filter and a primary coil of a second filter disposed side by side and connected in series, and a secondary coil of the first filter and a secondary coil of the second filter disposed side by side, connected in series, and disposed to face the primary coils of the first and second filters, respectively. The primary and secondary coils of the first and second filters may be configured of a plurality of layers, and coils having the same order may be interconnected through vias.

The primary coil of the first filter and the primary coil of the second filter disposed on the same plane may be connected in series by a first connection pattern extended from outer end portions of the respective primary coils, and the secondary coil of the first filter and the secondary coil of the second filter disposed on the same plane may be connected in series by a second connection pattern extended from outer end portions of the respective secondary coils.

DETAILED DESCRIPTION

FIG. 1is an external perspective view of a common mode filter according to an exemplary embodiment,FIG. 2is a perspective view ofFIG. 1,FIG. 3is a plan view ofFIG. 2, andFIG. 4is a cross-sectional view taken along line I-I′ ofFIG. 3.

Referring toFIGS. 1 through 4, a common mode filter100, according to an exemplary embodiment, may include a first filter110and a second filter120connected in series.

The first filter110and the second filter120, which are filters each removing common mode noise of a specific frequency band, may each be configured of primary coils111and121and secondary coils112and122which are magnetically coupled to each other. That is, the first filter110may be configured of the primary coil111and the secondary coil112which are magnetically coupled to each other, and the second filter120may be configured of the primary coil121and the secondary coil122which are also magnetically coupled to each other.

The primary and secondary coils111,121,112, and122of the respective filters are metal wires formed in a spiral shape on a plane, and for symmetry, the primary and secondary coils111and112of the first filter110may be formed to have the same number of turns, and the primary and secondary coils121and122of the second filter120may also be formed to have the same number of turns.

The primary coils111and121and the secondary coils112and122of the respective filters may be disposed to face each other while having a predetermined distance formed therebetween. As a result, according to the exemplary embodiment, inductance L proportional to the number of coil turns and capacitance C generated by stray capacitance may be resonated in parallel to each other and may be operated as the common mode filter attenuating common mode noise.

The primary coil111of the first filter110and the primary coil121of the second filter120may be connected in series by a physical connection means, and the secondary coil112of the first filter110and the secondary coil122of the second filter120may also be connected in series by a physical connection means. Thus, as in an equivalent circuit according to the exemplary embodiment illustrated inFIG. 5and an LC resonance circuit according to the exemplary embodiment illustrated inFIG. 6, the first filter110and the second filter120may have a structure in which they are electrically connected in series.

A connection structure of the primary and secondary coils111,121,112, and122of the respective filters will be described in more detail. The primary coil111of the first filter110and the primary coil121of the second filter120may be formed side by side on a common layer, for example, a first layer, and the secondary coil112of the first coil110and the secondary coil122of the second filter120may also be formed side by side on a common layer, for example, a second layer. Here, the secondary coil112of the first filter110may be disposed to face the primary coil111of the first filter110, and the secondary coil122of the second filter120may be disposed to face the primary coil121of the second filter120.

In addition, the primary coil111of the first filter110and the primary coil121of the second filter120may be electrically connected to each other by a first connection conductor131formed on another layer, for example, a third layer. That is, the first connection conductor131may be connected to the primary coil111of the first filter110through via131aand connected to the primary coil121of the second filter120through via131b.

Here, inner end portions111aand121aof the primary coil111of the first filter110and the primary coil121of the second filter120, respectively, may be connected to the vias131aand131b, and outer end portions111band121bof the primary coils111and121, respectively, may be connected to external terminals serving as input and output terminals. For example, the outer end portion111bof the primary coil111may be connected to a first input terminal161a, and the outer end portion121bof the primary coil121may be connected to a first output terminal161b.

Through the connection structure described above, a signal input through the first input terminal161amay be output to the first output terminal161bthrough an electrical path from the primary coil111of the first filter110to the primary coil121of the second filter120through the via131a, the first connection conductor131, and the via131b.

A series connection between the secondary coil112of the first filter110and the secondary coil122of the second filter120may also be implemented by the above-mentioned scheme. For example, the second connection conductor132formed on the third layer may be connected to an inner end portion112aof the secondary coil112through via132aand connected to an inner end portion122aof the secondary coil122through via132b. Likewise, an outer end portion112bof the secondary coil112may be connected to a second input terminal162a, and an outer end portion122bof the secondary coil122may be connected to an second output terminal162b.

Through the connection structure described above, a signal input through the second input terminal162amay be output to the second output terminal162bthrough an electrical path from the secondary coil112of the first filter110to the secondary coil122of the second filter120through the via132a, the second connection conductor132, and the via132b.

In the common mode filter100according to the exemplary embodiment, since the coils of the same order of the respective filters are disposed side by side, magnetic flux (m1inFIG. 4) generated around the first filter110and magnetic flux (m2inFIG. 4) generated around the second filter120when current is applied may avoid overlapping each other. As a result, a resonance frequency f1of the first filter110and a resonance frequency f2of the second filter120may be separated from each other.

FIG. 7is a graph illustrating attenuation characteristics of the first filter110,FIG. 8is a graph illustrating attenuation characteristics of the second filter120, andFIG. 9is a graph illustrating attenuation characteristics caused by a series connection of the first filter110and the second filter120.

The separation of the resonance frequency f1of the first filter110and the resonance frequency f2of the second filter120can result in their respective attenuation characteristics shown inFIG. 7andFIG. 8are added to each other as illustrated inFIG. 9. Therefore, according to the exemplary embodiment, as illustrated inFIG. 9, both of a notch band of the first filter110and a notch band of the second filter120may form part of the attenuation characteristics of the series connection. Thus, in a case in which the resonance frequencies of the first filter110and the second filter120, that is, frequencies at which an attenuation ratio becomes greatest, are set to be different from each other, noise may be attenuated across a wide band.

The setting of the resonance frequency f1of the first filter110and the resonance frequency f2of the second filter120to be different from each other may be achieved by allowing inductance L1of the first filter110and inductance L2of the second filter120illustrated inFIG. 6to be different from each other, or by allowing capacitance C1of the first filter110and capacitance C2of the second filter120to be different from each other.

Since the resonance frequency f1of the first filter110is determined by the following Equation 1 and the resonance frequency f2of the second filter120is determined by the following Equation 2, the resonance frequencies of the first filter110and the second filter120may be set to be different from each other where either or both of conditions L1≠L2and C1≠C2are satisfied.

The inductances of the respective filters may be adjusted by varying the number of coil turns of the primary and secondary coils111,121,112, and122included in the respective filters. For example, as illustrated inFIG. 3, in a case in which the primary and secondary coils111and112of the first filter110have 5 turns and the primary and secondary coils121and122of the second filter120have 3 turns, the inductance L1of the first filter110and the inductance L2of the second filter120may have values different from each other. As a result, the resonance frequency f1of the first filter110may be different from the resonance frequency f2of the second filter120.

In addition, the capacitances of the respective filters may be adjusted by varying distances between the primary coils111and121and the secondary coils112and122included in the respective filters. The stray capacitance is in inverse proportion to a distance between two metals. Therefore, as illustrated inFIG. 4, in a case in which a distance d1between the primary coil111and the secondary coil112of the first filter110, and a distance d2between the primary coil121and the secondary coil122of the second filter120are different from each other, the capacitance C1of the first filter110and the capacitance C2of the second filter120may have values different from each other. As a result, the resonance frequency f1of the first filter110and the resonance frequency f2of the second filter120may be set to be different from each other.

Although only an internal structure has been described for convenience of explanation, the primary and secondary coils111,121,112, and122of the first and second filters110and120, and the first and second connection conductors131and132may have a shape enclosed by an insulating layer140made of a polymer material such as an epoxy resin, a phenol resin, a urethane resin, a silicon resin, a polyimide resin, or the like, in order to secure insulation properties between the wires and protect the wires from external factors such as humidity, heat, or the like.

More specifically, a first insulating layer, a base layer, may be coated on a bottom surface, and the primary coil111of the first filter110and the primary coil121of the second filter120may be formed side by side over the bottom surface coated with the first insulating layer. A second insulating layer may be coated to cover the primary coil111of the first filter110and the primary coil121of the second filter120. The secondary coil112of the first filter110and the secondary coil122of the second filter120may be formed over the second insulating layer to face the primary coil111of the first filter110and the primary coil121of the second filter120, respectively. A third insulating layer may be formed to cover the second coils112and122, the first and second connection conductors131and132may be formed over the third insulating layer at appropriate positions. The insulating layers of the respective layers laminated as described above may be compressed and sintered under a predetermined condition.

In order to secure high permeability, magnetic members150, which are movement paths of magnetic flux, may be formed on upper and lower portions of the insulating layer140. As a result, the magnetic fluxes generated around the first and second filters110and120when current is applied may form a closed magnetic path via the upper and lower magnetic members150, thereby implementing high permeability.

Any magnetic material may be used to form the magnetic members150, including an Ni-based ferrite, an Ni—Zn-based ferrite, an Ni—Zn—Cu ferrite, or the like, as long as it may obtain predetermined inductance. In order to increase permeability and mechanical strength, the magnetic members150may also be formed in a magnetic-resin composition form having excellent impact resistance by sintering magnetic powder of the above-mentioned material under a predetermined condition, or immersing a fluidic resin in the magnetic powder.

The common mode filter100, according to the exemplary embodiment, may be implemented as a laminator having the magnetic members150laminated on the upper and lower portions of the insulating layer140as a basic configuration. The first and second input and output terminals161a,161b,162a, and162bmay be installed to be connected to the outer end portions111b,121b,112b, and122bof the respective coils exposed to end surfaces of the laminator.

Hereinafter, a common mode filter according to another exemplary embodiment will be described.

FIG. 10is a perspective view of a common mode filter according to another exemplary embodiment, andFIG. 11is a cross-sectional view taken along line II-II′ ofFIG. 10.

Referring toFIGS. 10 and 11, according to the present exemplary embodiment, the primary and secondary coils included in the respective filters may be configured of a plurality of layers. That is, in the first filter110, the primary coil, may be configured of the primary coil111disposed on the first layer and the primary coil113disposed on the third layer, and the secondary coil may be configured of the secondary coil112disposed on the second layer and a secondary coil124disposed on a fourth layer. Likewise, in the second filter120, the primary coil may be configured of the primary coil121disposed on the first layer and the primary coil123disposed on the third layer, and the secondary coil may be configured of the secondary coil122disposed on the second layer and the secondary coil124disposed on the fourth layer.

As such, according to the exemplary embodiment, the coils111to114and121to124configuring the respective filters may be configured of the plurality of layers, wherein the primary coils111,113,121, and123and the secondary coils112,114,122, and124on the respective layers may be alternately disposed, and the coils having the same order may be interconnected to each other through vias.

For a clearer understanding, a description will be provided with reference toFIGS. 12 through 17in which the coils of the respective layers are illustrated for each layer.

As shown inFIG. 12, the primary coil111of the first filter110and the primary coil121of the second filter120may be formed side by side on the first layer. The secondary coil112of the first filter110and the secondary coil122of the second filter120may be formed on the second layer to face the primary coils111and121as shown inFIG. 13. The intervening insulating layers140are omitted fromFIGS. 12-19for convenience of explanation.

As shown inFIG. 14, vias133aand133bfor connection between the layers may be formed at positions corresponding to the inner end portions of the primary coils111and121, respectively. The vias133aand133bmay be connected to the primary coils113and123of the respective filters penetrating through the second layer to be formed on the third layer, as shown inFIG. 15. That is, the primary coil111of the first filter110formed on the first layer may be connected to the primary coil113of the first filter110formed on the third layer through the via133a, and the primary coil121of the second filter120formed on the first layer may be connected to the primary coil123of the second filter120formed on the third layer through the via133b.

As shown inFIG. 16, vias134aand134bconnected to the inner end portions of the secondary coils112and122, respectively, formed on the second layer may be formed to penetrate through the third layer. Thus, as shown inFIG. 17, the secondary coil114of the first filter110formed on the fourth layer may be connected to the secondary coil112of the first filter110formed on the second layer through the via134a, and the secondary coil124of the second filter120formed on the fourth layer may be connected to the secondary coil122of the second filter120formed on the second layer through the via134b.

According to the present exemplary embodiment, the first filter110and the second filter120may be connected in series by a physical connection between the coils having the same order formed on the same plane. For example, the primary coil113of the first filter110and the primary coil123of the second filter120formed on the third layer may be connected to each other, and the secondary coil114of the first filter110and the secondary coil124of the second filter120formed on the fourth layer may be connected to each other.

The physical connection between the coils having the same order may be implemented by extending the outer end portions of the respective coils. For example, the primary coil113of the first filter110and the primary coil123of the second filter120may be connected to each other by a first connection conductor133, as shown inFIG. 15, extended from the outer end portions of the respective coils. Likewise, the second coil114of the first filter110and the second coil124of the second filter120may be connected to each other by a second connection conductor134, as shown inFIG. 17, extended from the outer end portions of the respective coils.

FIG. 18is a view illustrating only the primary coils111,113,121, and123formed on the first and third layers. Referring toFIG. 18, a signal to the primary coil may be externally output through an electrical path from the primary coil111of the first filter110to the primary coil121of the second filter120through the via133a, the primary coil113of the first filter110, the first connection pattern133, the primary coil123of the second filter120, and the via133b.

FIG. 19is a view illustrating only the secondary coils112,114,122, and124formed on the second and fourth layers. Referring toFIG. 19, a signal to the secondary coil may be externally output through an electrical path from the secondary coil112of the first filter110to the secondary coil122of the second filter120through the via134a, the secondary coil114of the first filter110, the second connection pattern134, the secondary coil124of the second filter120, and the via134b.

As such, according to the exemplary embodiment, the primary and secondary coils111,113,121,123,112,114,122, and124of the respective filters are configured of the plurality of layers, and thus a variable range of the resonance frequency may be further increased by the number of coil turns. As a result, wideband noise may be further attenuated.

As set forth above, according to the exemplary embodiments, the common mode filter may have attenuation characteristics in the two different resonance frequency bands, and consequently, may remove common mode noise of a wide frequency band.