Patent Publication Number: US-9899985-B2

Title: Common mode filter

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an external perspective view of a common mode filter according to an exemplary embodiment in the present disclosure; 
         FIG. 2  is an internal perspective view of  FIG. 1 ; 
         FIG. 3  is a plan view of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along line I-I′ of  FIG. 3 ; 
         FIG. 5  is an equivalent circuit diagram of the present disclosure; 
         FIG. 6  is an LC resonance circuit diagram of the present disclosure; 
         FIG. 7  is a graph illustrating attenuation characteristics of a first filter included in the present disclosure; 
         FIG. 8  is a graph illustrating attenuation characteristics of a second filter included in the present disclosure; 
         FIG. 9  is a graph illustrating attenuation characteristics caused by a series connection of the first filter and the second filter included in the present disclosure; 
         FIG. 10  is a perspective view of a common mode filter according to another exemplary embodiment in the present disclosure; 
         FIG. 11  is a cross-sectional view taken along line II-II′ of  FIG. 10 ; 
         FIGS. 12 through 17  are perspective views illustrating coils of the respective layers included in the present disclosure on each layer; 
         FIG. 18  is a perspective view illustrating only primary coils of first and third layers included in the present disclosure; and 
         FIG. 19  is a perspective view illustrating only secondary coils of second and fourth layers included in the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
     The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. 
     In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
       FIG. 1  is an external perspective view of a common mode filter according to an exemplary embodiment,  FIG. 2  is a perspective view of  FIG. 1 ,  FIG. 3  is a plan view of  FIG. 2 , and  FIG. 4  is a cross-sectional view taken along line I-I′ of  FIG. 3 . 
     Referring to  FIGS. 1 through 4 , a common mode filter  100 , according to an exemplary embodiment, may include a first filter  110  and a second filter  120  connected in series. 
     The first filter  110  and the second filter  120 , which are filters each removing common mode noise of a specific frequency band, may each be configured of primary coils  111  and  121  and secondary coils  112  and  122  which are magnetically coupled to each other. That is, the first filter  110  may be configured of the primary coil  111  and the secondary coil  112  which are magnetically coupled to each other, and the second filter  120  may be configured of the primary coil  121  and the secondary coil  122  which are also magnetically coupled to each other. 
     The primary and secondary coils  111 ,  121 ,  112 , and  122  of the respective filters are metal wires formed in a spiral shape on a plane, and for symmetry, the primary and secondary coils  111  and  112  of the first filter  110  may be formed to have the same number of turns, and the primary and secondary coils  121  and  122  of the second filter  120  may also be formed to have the same number of turns. 
     The primary coils  111  and  121  and the secondary coils  112  and  122  of 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 coil  111  of the first filter  110  and the primary coil  121  of the second filter  120  may be connected in series by a physical connection means, and the secondary coil  112  of the first filter  110  and the secondary coil  122  of the second filter  120  may also be connected in series by a physical connection means. Thus, as in an equivalent circuit according to the exemplary embodiment illustrated in  FIG. 5  and an LC resonance circuit according to the exemplary embodiment illustrated in  FIG. 6 , the first filter  110  and the second filter  120  may have a structure in which they are electrically connected in series. 
     A connection structure of the primary and secondary coils  111 ,  121 ,  112 , and  122  of the respective filters will be described in more detail. The primary coil  111  of the first filter  110  and the primary coil  121  of the second filter  120  may be formed side by side on a common layer, for example, a first layer, and the secondary coil  112  of the first coil  110  and the secondary coil  122  of the second filter  120  may also be formed side by side on a common layer, for example, a second layer. Here, the secondary coil  112  of the first filter  110  may be disposed to face the primary coil  111  of the first filter  110 , and the secondary coil  122  of the second filter  120  may be disposed to face the primary coil  121  of the second filter  120 . 
     In addition, the primary coil  111  of the first filter  110  and the primary coil  121  of the second filter  120  may be electrically connected to each other by a first connection conductor  131  formed on another layer, for example, a third layer. That is, the first connection conductor  131  may be connected to the primary coil  111  of the first filter  110  through via  131   a  and connected to the primary coil  121  of the second filter  120  through via  131   b.    
     Here, inner end portions  111   a  and  121   a  of the primary coil  111  of the first filter  110  and the primary coil  121  of the second filter  120 , respectively, may be connected to the vias  131   a  and  131   b , and outer end portions  111   b  and  121   b  of the primary coils  111  and  121 , respectively, may be connected to external terminals serving as input and output terminals. For example, the outer end portion  111   b  of the primary coil  111  may be connected to a first input terminal  161   a , and the outer end portion  121   b  of the primary coil  121  may be connected to a first output terminal  161   b.    
     Through the connection structure described above, a signal input through the first input terminal  161   a  may be output to the first output terminal  161   b  through an electrical path from the primary coil  111  of the first filter  110  to the primary coil  121  of the second filter  120  through the via  131   a , the first connection conductor  131 , and the via  131   b.    
     A series connection between the secondary coil  112  of the first filter  110  and the secondary coil  122  of the second filter  120  may also be implemented by the above-mentioned scheme. For example, the second connection conductor  132  formed on the third layer may be connected to an inner end portion  112   a  of the secondary coil  112  through via  132   a  and connected to an inner end portion  122   a  of the secondary coil  122  through via  132   b . Likewise, an outer end portion  112   b  of the secondary coil  112  may be connected to a second input terminal  162   a , and an outer end portion  122   b  of the secondary coil  122  may be connected to an second output terminal  162   b.    
     Through the connection structure described above, a signal input through the second input terminal  162   a  may be output to the second output terminal  162   b  through an electrical path from the secondary coil  112  of the first filter  110  to the secondary coil  122  of the second filter  120  through the via  132   a , the second connection conductor  132 , and the via  132   b.    
     In the common mode filter  100  according to the exemplary embodiment, since the coils of the same order of the respective filters are disposed side by side, magnetic flux (m 1  in  FIG. 4 ) generated around the first filter  110  and magnetic flux (m 2  in  FIG. 4 ) generated around the second filter  120  when current is applied may avoid overlapping each other. As a result, a resonance frequency f 1  of the first filter  110  and a resonance frequency f 2  of the second filter  120  may be separated from each other. 
       FIG. 7  is a graph illustrating attenuation characteristics of the first filter  110 ,  FIG. 8  is a graph illustrating attenuation characteristics of the second filter  120 , and  FIG. 9  is a graph illustrating attenuation characteristics caused by a series connection of the first filter  110  and the second filter  120 . 
     The separation of the resonance frequency f 1  of the first filter  110  and the resonance frequency f 2  of the second filter  120  can result in their respective attenuation characteristics shown in  FIG. 7  and  FIG. 8  are added to each other as illustrated in  FIG. 9 . Therefore, according to the exemplary embodiment, as illustrated in  FIG. 9 , both of a notch band of the first filter  110  and a notch band of the second filter  120  may form part of the attenuation characteristics of the series connection. Thus, in a case in which the resonance frequencies of the first filter  110  and the second filter  120 , 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 f 1  of the first filter  110  and the resonance frequency f 2  of the second filter  120  to be different from each other may be achieved by allowing inductance L 1  of the first filter  110  and inductance L 2  of the second filter  120  illustrated in  FIG. 6  to be different from each other, or by allowing capacitance C 1  of the first filter  110  and capacitance C 2  of the second filter  120  to be different from each other. 
     Since the resonance frequency f 1  of the first filter  110  is determined by the following Equation 1 and the resonance frequency f 2  of the second filter  120  is determined by the following Equation 2, the resonance frequencies of the first filter  110  and the second filter  120  may be set to be different from each other where either or both of conditions L 1 ≠L 2  and C 1 ≠C 2  are satisfied. 
     
       
         
           
             
               
                 
                   
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     The inductances of the respective filters may be adjusted by varying the number of coil turns of the primary and secondary coils  111 ,  121 ,  112 , and  122  included in the respective filters. For example, as illustrated in  FIG. 3 , in a case in which the primary and secondary coils  111  and  112  of the first filter  110  have 5 turns and the primary and secondary coils  121  and  122  of the second filter  120  have 3 turns, the inductance L 1  of the first filter  110  and the inductance L 2  of the second filter  120  may have values different from each other. As a result, the resonance frequency f 1  of the first filter  110  may be different from the resonance frequency f 2  of the second filter  120 . 
     In addition, the capacitances of the respective filters may be adjusted by varying distances between the primary coils  111  and  121  and the secondary coils  112  and  122  included in the respective filters. The stray capacitance is in inverse proportion to a distance between two metals. Therefore, as illustrated in  FIG. 4 , in a case in which a distance d 1  between the primary coil  111  and the secondary coil  112  of the first filter  110 , and a distance d 2  between the primary coil  121  and the secondary coil  122  of the second filter  120  are different from each other, the capacitance C 1  of the first filter  110  and the capacitance C 2  of the second filter  120  may have values different from each other. As a result, the resonance frequency f 1  of the first filter  110  and the resonance frequency f 2  of the second filter  120  may be set to be different from each other. 
     Although only an internal structure has been described for convenience of explanation, the primary and secondary coils  111 ,  121 ,  112 , and  122  of the first and second filters  110  and  120 , and the first and second connection conductors  131  and  132  may have a shape enclosed by an insulating layer  140  made 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 coil  111  of the first filter  110  and the primary coil  121  of the second filter  120  may 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 coil  111  of the first filter  110  and the primary coil  121  of the second filter  120 . The secondary coil  112  of the first filter  110  and the secondary coil  122  of the second filter  120  may be formed over the second insulating layer to face the primary coil  111  of the first filter  110  and the primary coil  121  of the second filter  120 , respectively. A third insulating layer may be formed to cover the second coils  112  and  122 , the first and second connection conductors  131  and  132  may 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 members  150 , which are movement paths of magnetic flux, may be formed on upper and lower portions of the insulating layer  140 . As a result, the magnetic fluxes generated around the first and second filters  110  and  120  when current is applied may form a closed magnetic path via the upper and lower magnetic members  150 , thereby implementing high permeability. 
     Any magnetic material may be used to form the magnetic members  150 , 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 members  150  may 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 filter  100 , according to the exemplary embodiment, may be implemented as a laminator having the magnetic members  150  laminated on the upper and lower portions of the insulating layer  140  as a basic configuration. The first and second input and output terminals  161   a ,  161   b ,  162   a , and  162   b  may be installed to be connected to the outer end portions  111   b ,  121   b ,  112   b , and  122   b  of the respective coils exposed to end surfaces of the laminator. 
     Hereinafter, a common mode filter according to another exemplary embodiment will be described. 
       FIG. 10  is a perspective view of a common mode filter according to another exemplary embodiment, and  FIG. 11  is a cross-sectional view taken along line II-II′ of  FIG. 10 . 
     Referring to  FIGS. 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 filter  110 , the primary coil, may be configured of the primary coil  111  disposed on the first layer and the primary coil  113  disposed on the third layer, and the secondary coil may be configured of the secondary coil  112  disposed on the second layer and a secondary coil  124  disposed on a fourth layer. Likewise, in the second filter  120 , the primary coil may be configured of the primary coil  121  disposed on the first layer and the primary coil  123  disposed on the third layer, and the secondary coil may be configured of the secondary coil  122  disposed on the second layer and the secondary coil  124  disposed on the fourth layer. 
     As such, according to the exemplary embodiment, the coils  111  to  114  and  121  to  124  configuring the respective filters may be configured of the plurality of layers, wherein the primary coils  111 , 113 , 121 , and  123  and the secondary coils  112 , 114 , 122 , and  124  on 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 to  FIGS. 12 through 17  in which the coils of the respective layers are illustrated for each layer. 
     As shown in  FIG. 12 , the primary coil  111  of the first filter  110  and the primary coil  121  of the second filter  120  may be formed side by side on the first layer. The secondary coil  112  of the first filter  110  and the secondary coil  122  of the second filter  120  may be formed on the second layer to face the primary coils  111  and  121  as shown in  FIG. 13 . The intervening insulating layers  140  are omitted from  FIGS. 12-19  for convenience of explanation. 
     As shown in  FIG. 14 , vias  133   a  and  133   b  for connection between the layers may be formed at positions corresponding to the inner end portions of the primary coils  111  and  121 , respectively. The vias  133   a  and  133   b  may be connected to the primary coils  113  and  123  of the respective filters penetrating through the second layer to be formed on the third layer, as shown in  FIG. 15 . That is, the primary coil  111  of the first filter  110  formed on the first layer may be connected to the primary coil  113  of the first filter  110  formed on the third layer through the via  133   a , and the primary coil  121  of the second filter  120  formed on the first layer may be connected to the primary coil  123  of the second filter  120  formed on the third layer through the via  133   b.    
     As shown in  FIG. 16 , vias  134   a  and  134   b  connected to the inner end portions of the secondary coils  112  and  122 , respectively, formed on the second layer may be formed to penetrate through the third layer. Thus, as shown in  FIG. 17 , the secondary coil  114  of the first filter  110  formed on the fourth layer may be connected to the secondary coil  112  of the first filter  110  formed on the second layer through the via  134   a , and the secondary coil  124  of the second filter  120  formed on the fourth layer may be connected to the secondary coil  122  of the second filter  120  formed on the second layer through the via  134   b.    
     According to the present exemplary embodiment, the first filter  110  and the second filter  120  may be connected in series by a physical connection between the coils having the same order formed on the same plane. For example, the primary coil  113  of the first filter  110  and the primary coil  123  of the second filter  120  formed on the third layer may be connected to each other, and the secondary coil  114  of the first filter  110  and the secondary coil  124  of the second filter  120  formed 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 coil  113  of the first filter  110  and the primary coil  123  of the second filter  120  may be connected to each other by a first connection conductor  133 , as shown in  FIG. 15 , extended from the outer end portions of the respective coils. Likewise, the second coil  114  of the first filter  110  and the second coil  124  of the second filter  120  may be connected to each other by a second connection conductor  134 , as shown in  FIG. 17 , extended from the outer end portions of the respective coils. 
       FIG. 18  is a view illustrating only the primary coils  111 ,  113 ,  121 , and  123  formed on the first and third layers. Referring to  FIG. 18 , a signal to the primary coil may be externally output through an electrical path from the primary coil  111  of the first filter  110  to the primary coil  121  of the second filter  120  through the via  133   a , the primary coil  113  of the first filter  110 , the first connection pattern  133 , the primary coil  123  of the second filter  120 , and the via  133   b.    
       FIG. 19  is a view illustrating only the secondary coils  112 ,  114 ,  122 , and  124  formed on the second and fourth layers. Referring to  FIG. 19 , a signal to the secondary coil may be externally output through an electrical path from the secondary coil  112  of the first filter  110  to the secondary coil  122  of the second filter  120  through the via  134   a , the secondary coil  114  of the first filter  110 , the second connection pattern  134 , the secondary coil  124  of the second filter  120 , and the via  134   b.    
     As such, according to the exemplary embodiment, the primary and secondary coils  111 ,  113 ,  121 ,  123 ,  112 ,  114 ,  122 , and  124  of 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. 
     While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.