Patent Publication Number: US-9431163-B2

Title: Transformer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of priority to Japanese Patent Application No. 2013-026362 filed on Feb. 14, 2013, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present technical field relates to transformers, more particularly to a transformer including two coils. 
     BACKGROUND 
     As an disclosure related to a conventional transformer, a common-mode noise filter described in, for example, Japanese Patent Laid-Open Publication No. 2006-24772 is known.  FIG. 10  is a configuration diagram of the common-mode noise filter  500  described in Japanese Patent Laid-Open Publication No. 2006-24772. 
     The common-mode noise filter  500  includes a first coil  510 , a second coil  520 , lead-out portions  511 ,  512 ,  521 , and  522 , and external electrodes  513 ,  514 ,  523 , and  524 . The first coil  510  and the second coil  520  have the same spiral shape. The second coil  520 , when viewed in a plan view, is positioned so as to deviate slightly from the first coil  510 . 
     The external electrode  513  is provided on the left side surface. The external electrode  523  is provided below the external electrode  513  on the left side surface. The external electrode  514  is provided on the right side surface. The external electrode  524  is provided below the external electrode  514  on the right side surface. The lead-out portion  511  connects the first coil  510  and the external electrode  513 . The lead-out portion  512  connects the first coil  510  and the external electrode  514 . The lead-out portion  521  connects the second coil  520  and the external electrode  523 . The lead-out portion  522  connects the second coil  520  and the external electrode  524 . 
     In the common-mode noise filter  500 , the first coil  510  and the second coil  520  have the same shape, and therefore have the same length. As a result, the first coil  510  and the second coil  520  can be approximated in terms of their inductance values. 
     However, the common-mode noise filter  500  has an issue in that it is liable to cause a difference between the first coil  510  and the second coil  520  in an inductance value. More specifically, the lead-out portion  511  is led out toward the upper left. Accordingly, a current it flowing through the lead-out portion  511  is directed in the opposite direction to a current i 2  flowing near the lead-out portion  511  within the first coil  510 . As a result, the magnetic field that is generated near the lead-out portion  511  within the first coil  510  is directed in the opposite direction to the magnetic field that is generated by the lead-out portion  511 . Therefore, the inductance value of the first coil  510  decreases. 
     On the other hand, the lead-out portion  521  is led out toward the lower left. Accordingly, a current i 3  flowing through the lead-out portion  521  is directed in the same direction as a current i 4  flowing near the lead-out portion  521  within the second coil  520 . As a result, the magnetic field that is generated near the lead-out portion  521  within the second coil  520  is directed in the same direction as the magnetic field that is generated by the lead-out portion  521 . Therefore, the inductance value of the second coil  520  increases. Thus, the common-mode noise filter  500  is liable to cause a difference between the first coil  510  and the second coil  520  in an inductance value. 
     SUMMARY 
     Therefore, an object of the present disclosure provides a transformer capable of making inductance values of two coils thereof approximated. 
     A transformer according to an embodiment of the present disclosure includes: a body; a first coil conductor that is provided in the body, and, when viewed in a plan view in a first predetermined direction, spirals inwardly in a second predetermined direction; a second coil conductor that is provided in the body, and, when viewed in a plan view in the first predetermined direction, spirals along the first coil conductor on the outside relative to the first coil conductor; a first external electrode that, when viewed in a plan view in the first predetermined direction, is provided on a surface of the body in a third predetermined direction relative to a first line passing through a gravity center of the first coil conductor and an outer end of the first coil conductor, the third predetermined direction being perpendicular to the first line; a first lead-out conductor that is connected to the outer end of the first coil conductor and is electrically connected to the first external electrode; a second external electrode that, when viewed in a plan view in the first predetermined direction, is provided on a surface of the body in a fourth predetermined direction relative to the first line, the fourth predetermined direction being opposite to the third predetermined direction; and a second lead-out conductor that is connected to the outer end of the second coil conductor and is electrically connected to the second external electrode, wherein the first coil conductor and the second coil conductor spiral along each other throughout their lengths, and by spiraling in the second predetermined direction, the first coil conductor is, at the outer end, oriented toward a fourth predetermined direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of a transformer. 
         FIG. 2  is an exploded perspective view of a laminate of the transformer. 
         FIG. 3  is a plan view of one coil conductor and one set of lead-out conductors of the transformer. 
         FIG. 4  is a plan view of the other coil conductor and the other set of lead-out conductors of the transformer. 
         FIG. 5  is an overlapping view of the both coil conductors and the both set of lead-out conductors. 
         FIG. 6  is a graph showing the relationship between the frequency and the phase differences for S 21  and S 43  in a first model. 
         FIG. 7  is a graph showing the relationship between the frequency and the phase differences for S 21  and S 43  in a second model. 
         FIG. 8  is a graph showing the relationship of the frequency with Sdc 21  in the first and second models. 
         FIG. 9  is a graph showing the relationship between the frequency and the CMRR in the first and second models. 
         FIG. 10  is a configuration diagram of a common-mode noise filter described in Japanese Patent Laid-Open Publication No. 2006-24772. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a transformer according to an embodiment of the present disclosure will be described with reference to the drawings. 
     Configuration of Transformer 
     First, the configuration of the transformer will be described with reference to the drawings.  FIG. 1  is an external perspective view of the transformer  10 .  FIG. 2  is an exploded perspective view of a laminate  12  of the transformer  10 .  FIG. 3  is a plan view of one coil conductor  20   a  and one set of lead-out conductors  22   a  and  24   a  of the transformer  10 .  FIG. 4  is a plan view of the other coil conductor  20   b  and the other set of lead-out conductors  22   b  and  24   b  of the transformer  10 .  FIG. 5  is an overlapping view of both coil conductors  20   a  and  20   b  and both sets of the lead-out conductors  22   a ,  22   b  and the lead-out conductors  24   a , and  24   b . In the following, the direction of lamination of the laminate  12  will be defined as a z-axis direction. Moreover, when viewed in a plan view in the z-axis direction, the directions in which two sides of the laminate  12  extend will be defined as x- and y-axis directions. The x-, y-, and z-axis directions are perpendicular to one another. 
     The transformer  10  includes the laminate  12 , external electrodes  14   a  to  14   d , the coil conductors  20   a  and  20   b , the lead-out conductors  22   a ,  22   b ,  24   a , and  24   b , and via-hole conductors v 1  and v 2 , as shown in  FIGS. 1 and 2 . 
     The laminate  12  is in the shape of a substantially rectangular solid, and includes magnetic portions  16   a  and  16   b  and a non-magnetic portion  18 , as shown in  FIGS. 1 and 2 . The magnetic portions  16   a  and  16   b  are made of a magnetic material, such as ferrite, and are in the shape of substantially rectangular solids. Moreover, the non-magnetic portion  18  is formed by laminating non-magnetic layers (i.e., insulator layers)  18   a  to  18   e  in this order, from the positive side in the z-axis direction. The non-magnetic layers  18   a  to  18   e  are substantially rectangular, and are made of a non-magnetic material including borosilicate glass and ceramic filler. In the following, the surfaces of the non-magnetic layers  18   a  to  18   e  on the positive side in the z-axis direction will be referred to as the front faces, and the surfaces of the non-magnetic layers  18   a  to  18   e  on the negative side in the z-axis direction will be referred to as the back faces. 
     The coil conductors  20   a  and  20   b  are provided in the laminate  12 , and electromagnetically coupled to each other. More specifically, the coil conductor  20   a  is a linear conductor provided on the front face of the non-magnetic layer  18   c , and when viewed in a plan view in the z-axis direction, it has a spiral shape winding clockwise inwardly, as shown in  FIGS. 2 and 3 . The coil conductor  20   b  is a linear conductor provided on the front face of the non-magnetic layer  18   d , which is located on the negative side in the z-axis direction relative to the non-magnetic layer  18   c  with the coil conductor  20   a  provided thereon, as shown in  FIGS. 2 and 4 , and when viewed in a plan view in the z-axis direction, the coil conductor  20   b  has a spiral shape winding clockwise inwardly. Moreover, the coil conductor  20   b , when viewed in a plan view in the z-axis direction, spirals along the coil conductor  20   a  on the outside relative to the coil conductor  20   a , as shown in  FIGS. 2 and 5 . In the present embodiment, the coil conductor  20   a  and the coil conductor  20   b  overlap in part with each other in the width direction thereof. Moreover, the coil conductor  20   a  and the coil conductor  20   b  spirally wind along each other throughout their lengths. Accordingly, the outer end t 1  of the coil conductor  20   a  and the outer end t 2  of the coil conductor  20   b  are adjacent to each other, and the inner end t 3  of the coil conductor  20   a  and the inner end t 4  of the coil conductor  20   b  are adjacent to each other. Moreover, the coil conductor  20   b  is longer than the coil conductor  20   a.    
     Furthermore, the ends t 1  and t 3  and the gravity center C 1  of the coil conductor  20   a  are aligned in the x-axis direction. The gravity center C 1  refers to the gravity center of the coil conductor  20   a  as viewed in a plan view in the z-axis direction. In the present embodiment, the gravity center C 1  substantially coincides with the center of the coil conductor  20   a . The end t 1  is positioned on the negative side in the x-axis direction relative to the gravity center C 1 . Accordingly, by spiraling clockwise, the coil conductor  20   a  has a directional component toward the positive side in the y-axis direction at the outer end t 1 . That is, the coil conductor  20   a  starts spiraling by extending from the outer end t 1  toward the positive side in the y-axis direction. The end t 3  is positioned on the positive side in the x-axis direction relative to the gravity center C 1 . 
     [Furthermore, the ends t 2  and t 4  and the gravity center C 2  of the coil conductor  20   b  are aligned in the x-axis direction. The gravity center C 2  refers to the gravity center of the coil conductor  20   b  as viewed in a plan view in the z-axis direction. In the present embodiment, the gravity center C 2  substantially coincides with the center of the coil conductor  20   b . The end t 2  is positioned on the negative side in the x-axis direction relative to the gravity center C 2 . Accordingly, by spiraling clockwise, the coil conductor  20   b  has a directional component toward the positive side in the y-axis direction at the outer end t 2 . That is, the coil conductor  20   b  starts spiraling by extending from the outer end t 2  toward the positive side in the y-axis direction. The end t 4  is positioned on the positive side in the x-axis direction relative to the gravity center C 2 . 
     Note that in the present embodiment, the gravity center C 1  and the gravity center C 2  substantially coincide with each other when viewed in a plan view in the z-axis direction. Accordingly, the ends t 1  to t 4  and the gravity centers C 1  and C 2  are aligned in the x-axis direction. In the following, a line that passes through the ends t 1  to t 4  and the gravity centers C 1  and C 2  will be referred to as “line  1 ”. Line  1  extends in the x-axis direction. 
     The external electrodes  14   a  and  14   b  are provided in the form of rectangles extending in the z-axis direction on the side surface of the laminate  12  that is located on the negative side in the x-axis direction, as shown in  FIG. 1 . The external electrode  14   a , when viewed in a plan view in the z-axis direction, is positioned on the negative side in the y-axis direction relative to line  1 , as shown in  FIG. 5 . The external electrode  14   b , when viewed in a plan view in the z-axis direction, is positioned on the positive side in the y-axis direction relative to line  1 , as shown in  FIG. 5 . The external electrode  14   a  and the external electrode  14   b  have a line-symmetrical relationship with respect to line  1 . 
     The external electrodes  14   c  and  14   d  are provided in the form of rectangles extending in the z-axis direction on the side surface of the laminate  12  that is located on the positive side in the x-axis direction, as shown in  FIG. 1 . The external electrode  14   c , when viewed in a plan view in the z-axis direction, is positioned on the negative side in the y-axis direction relative to line  1 , as shown in  FIG. 5 . The external electrode  14   d , when viewed in a plan view in the z-axis direction, is positioned on the positive side in the y-axis direction relative to line  1 , as shown in  FIG. 5 . The external electrode  14   c  and the external electrode  14   d  have a line-symmetrical relationship with respect to line  1 . 
     The lead-out conductor  22   a  is connected to the outer end t 1  of the coil conductor  20   a , and is electrically connected to the external electrode  14   a , as shown in  FIGS. 2, 3, and 5 . More specifically, the lead-out conductor  22   a  includes lead-out portions  30   a  and  31   a , and a connection  32   a . The lead-out portion  30   a  extends on the front face of the non-magnetic layer  18   c  from the outer end t 1  of the coil conductor  20   a  toward the negative side in the x-axis direction. However, the lead-out portion  30   a  is not led out to the side surface of the laminate  12  that is located on the negative side in the x-axis direction. The lead-out portion  31   a  extends from the end of the lead-out portion  30   a  that is located on the negative side in the x-axis direction toward the negative side in the y-axis direction. Accordingly, the lead-out portions  30   a  and  31   a  form an L-like shape. The connection  32   a , which is located on the front face of the non-magnetic layer  18   c , is connected to the end of the lead-out portion  31   a  that is located on the negative side in the y-axis direction, and the connection  32   a  is led out to the side of the non-magnetic layer  18   c  that is located on the negative side in the x-axis direction. Accordingly, the connection  32   a  is exposed in the form of a line extending in the y-axis direction, at the side surface of the laminate  12  that is located on the negative side in the x-axis direction. As a result, the connection  32   a  is connected to the external electrode  14   a.    
     The lead-out conductor  22   b  is connected to the outer end t 2  of the coil conductor  20   b , and is electrically connected to the external electrode  14   b , as shown in  FIGS. 2, 4, and 5 . More specifically, the lead-out conductor  22   b  includes lead-out portions  30   b  and  31   b  and a connection  32   b . The lead-out portion  30   b  extends on the front face of the non-magnetic layer  18   d  from the outer end t 2  of the coil conductor  20   b  toward the negative side in the x-axis direction. However, the lead-out portion  30   b  is not led out to the side surface of the laminate  12  that is located on the negative side in the x-axis direction. The lead-out portion  31   b  extends from the end of the lead-out portion  30   b  that is located on the negative side in the x-axis direction toward the positive side in the y-axis direction. Accordingly, the lead-out portions  30   b  and  31   b  form an L-like shape. The connection  32   b , which is located on the front face of the non-magnetic layer  18   d , is connected to the end of the lead-out portion  31   b  that is located on the positive side in the y-axis direction, and the connection  32   b  is led out to the side of the non-magnetic layer  18   d  that is located on the negative side in the x-axis direction. Accordingly, the connection  32   b  is exposed in the form of a line extending in the y-axis direction, at the side surface of the laminate  12  that is located on the negative side in the x-axis direction. As a result, the connection  32   b  is connected to the external electrode  14   b.    
     Here, the lead-out conductor  22   a  and the lead-out conductor  22   b  are in a symmetrical relationship with respect to line  1 . Accordingly, the lead-out portion  30   a  and the lead-out portion  30   b  have approximately the same length. Moreover, the lead-out portion  31   a  and the lead-out portion  31   b  have approximately the same length. 
     The lead-out conductor  24   a  is connected to the inner end t 3  of the coil conductor  20   a , and is electrically connected to the external electrode  14   c , as shown in  FIGS. 2, 3, and 5 . More specifically, the lead-out conductor  24   a  includes lead-out portions  34   a  and  35   a  and a connection  36   a . The lead-out portion  34   a  extends on the front face of the non-magnetic layer  18   b  from the inner end t 3  of the coil conductor  20   a  toward the positive side in the x-axis direction. However, the lead-out portion  34   a  is not led out to the side surface of the laminate  12  that is located on the positive side in the x-axis direction. The lead-out portion  35   a  extends from the end of the lead-out portion  34   a  that is located on the positive side in the x-axis direction toward the negative side in the y-axis direction. Accordingly, the lead-out portions  34   a  and  35   a  form an L-like shape. The connection  36   a , which is located on the front face of the non-magnetic layer  18   b , is connected to the end of the lead-out portion  35   a  that is located on the negative side in the y-axis direction, and the connection  36   a  is led out to the side of the non-magnetic layer  18   b  that is located on the positive side in the x-axis direction. Accordingly, the connection  36   a  is exposed in the form of a line extending in the y-axis direction, at the side surface of the laminate  12  that is located on the positive side in the x-axis direction. As a result, the connection  36   a  is connected to the external electrode  14   c.    
     The lead-out conductor  24   b  is connected to the inner end t 4  of the coil conductor  20   b , and is electrically connected to the external electrode  14   d , as shown in  FIGS. 2, 4, and 5 . More specifically, the lead-out conductor  24   b  includes lead-out portions  34   b  and  35   b  and a connection  36   b . The lead-out portion  34   b  extends on the front face of the non-magnetic layer  18   e  from the inner end t 4  of the coil conductor  20   b  toward the positive side in the x-axis direction. However, the lead-out portion  34   b  is not led out to the side surface of the laminate  12  that is located on the positive side in the x-axis direction. The lead-out portion  35   b  extends from the end of the lead-out portion  34   b  that is located on the positive side in the x-axis direction toward the positive side in the y-axis direction. Accordingly, the lead-out portions  34   b  and  35   b  form an L-like shape. The connection  36   b , which is located on the front face of the non-magnetic layer  18   e , is connected to the end of the lead-out portion  35   b  that is on the positive side in the y-axis direction, and the connection  36   b  is led out to the side of the non-magnetic layer  18   e  that is located on the positive side in the x-axis direction. Accordingly, the connection  36   b  is exposed in the form of a line extending in the y-axis direction, at the side surface of the laminate  12  that is located on the positive side in the x-axis direction. As a result, the connection  36   b  is connected to the external electrode  14   d.    
     Here, the lead-out conductor  24   a  and the lead-out conductor  24   b  are in a symmetrical relationship with respect to line  1 . Accordingly, the lead-out portion  34   a  and the lead-out portion  34   b  have approximately the same length. Moreover, the lead-out portion  35   a  and the lead-out portion  35   b  have approximately the same length. 
     The via-hole conductor v 1  pierces through the non-magnetic layer  18   b  in the z-axis direction, so as to connect the inner end t 3  of the coil conductor  20   a  and the end of the lead-out portion  34   a  that is located on the negative side in the x-axis direction. The via-hole conductor v 2  pierces through the non-magnetic layer  18   d  in the z-axis direction, so as to connect the inner end t 4  of the coil conductor  20   b  and the end of the lead-out portion  34   b  that is located on the negative side in the x-axis direction. 
     In the transformer  10  thus configured, a magnetic flux generated by the coil conductor  20   a  passes through the coil conductor  20   b , and a magnetic flux generated by the coil conductor  20   b  passes through the coil conductor  20   a . Accordingly, the coil conductor  20   a  and the coil conductor  20   b  are magnetically coupled, so that the coil conductor  20   a  and the coil conductor  20   b  constitute a common-mode choke coil. In addition, the external electrodes  14   a  and  14   b  are used as input terminals, and the external electrodes  14   c  and  14   d  are used as output terminals. Specifically, differential transmission signals are inputted into the external electrodes  14   a  and  14   b , and outputted from the external electrodes  14   c  and  14   d . Moreover, when the differential transmission signals contain common-mode noise, the coil conductors  20   a  and  20   b  generate magnetic fluxes in the same direction because of the common-mode noise. As a result, the magnetic fluxes intensify each other, thereby generating impedance to the common-mode noise. Thus, the common-mode noise is transformed into heat, and therefore is prevented from passing through the coil conductors  20   a  and  20   b.    
     Effects 
     The transformer  10  according to the present embodiment allows the inductance value of the coil conductor  20   a  and the inductance value of the coil conductor  20   b  to become approximate to each other. More specifically, the external electrode  14   a , when viewed in a plan view in the z-axis direction, is provided on the negative side in the y-axis direction relative to line  1 . Accordingly, the lead-out conductor  22   a  extends toward the negative side in the y-axis direction. Therefore, when a current flows clockwise through the coil conductor  20   a , a current i 11  flows through the lead-out portion  31   a  toward the positive side in the y-axis direction. As a result, a magnetic field toward the negative side in the z-axis direction is generated on the positive side in the x-axis direction relative to the lead-out portion  31   a . On the other hand, when such a current flowing clockwise through the coil conductor  20   a  occurs, a magnetic field toward the negative side in the z-axis direction is generated within the coil conductor  20   a . As a result, in the coil conductor  20   a , the magnetic field generated by the lead-out portion  31   a  and the magnetic field generated by the coil conductor  20   a  are oriented in the same direction, so that the inductance value of the coil conductor  20   a  becomes relatively high. 
     The external electrode  14   b , when viewed in a plan view in the z-axis direction, is provided on the positive side in the y-axis direction relative to line  1 . Accordingly, the lead-out conductor  22   b  extends toward the positive side in the y-axis direction. Therefore, when a current flows clockwise through the coil conductor  20   b , a current i 12  flows through the lead-out portion  31   b  toward the negative side in the y-axis direction. As a result, a magnetic field toward the positive side in the z-axis direction is generated on the positive side in the x-axis direction relative to the lead-out portion  31   b . On the other hand, when such a current flowing clockwise through the coil conductor  20   b  occurs, a magnetic field toward the negative side in the z-axis direction is generated within the coil conductor  20   b . As a result, in the coil conductor  20   b , the magnetic field generated by the lead-out portion  31   b  and the magnetic field generated by the coil conductor  20   b  are oriented in opposite directions, so that the inductance value of the coil conductor  20   b  becomes relatively low. In this manner, the lead-out conductors  22   a  and  22   b  might cause the inductance value of the coil conductor  20   b  to be less than the inductance value of the coil conductor  20   a.    
     Therefore, in the transformer  10 , the coil conductor  20   b , when viewed in a plan view in the z-axis direction, spirals along the coil conductor  20   a  on the outside relative to the coil conductor  20   a . In addition, the coil conductor  20   a  and the coil conductor  20   b  spirally wind along each other throughout their lengths. Therefore, the coil conductor  20   b  is longer than the coil conductor  20   a . That is, the magnetic field generated by the coil conductor  20   b  is stronger than the magnetic field generated by the coil conductor  20   a . As a result, the inductance value of the coil conductor  20   a  and the inductance value of the coil conductor  20   b  become approximate to each other. 
     In the case where the transformer  10  is used as a common-mode choke coil, as the inductance value of the coil conductor  20   a  and the inductance value of the coil conductor  20   b  become approximate to each other, as described above, the difference between the phases of first and second signals that constitute a differential transmission signal approximates 180 degrees. 
     Furthermore, in the case where the transformer  10  is used as a common-mode choke coil, as the inductance value of the coil conductor  20   a  and the inductance value of the coil conductor  20   b  become approximate to each other, the magnetic flux that a first signal causes the coil conductor  20   a  to generate and the magnetic flux that a second signal causes the coil conductor  20   b  to generate are cancelled out efficiently when a differential-mode signal consisting of the first and second signals passes through the transformer  10 . Thus, the differential-mode signal is inhibited from being converted into common-mode noise in the transformer  10 . 
     Furthermore, in the case where the transformer  10  is used as a balun, as the inductance value of the coil conductor  20   a  and the inductance value of the coil conductor  20   b  become approximate to each other, the transformer  10  starts to output a differential signal consisting of first and second signals which are out of phase by 180 degrees. Thus, common-mode noise is inhibited from being included in output signals. 
     To more clearly demonstrate the effects achieved by the transformer  10 , the present inventors carried out the following computer simulations. The inventors created a first model with the structure of the transformer  10 , and a second model in which the coil conductor  20   a  and the coil conductor  20   b  of the transformer  10 , when viewed in a plan view in the z-axis direction, coincide with each other in an entirely overlapping manner. The first model is a model according to an example, and the second model is a model according to a comparative example. Each of the first and second models was used as a common-mode choke coil, and S-parameters were computed by inputting differential transmission signals to the first and second models. The computed S-parameters were S 21 , S 43 , and Sdc 21 . The parameters S 21  and S 43  are transmission characteristics of the first and second models. Specifically, the parameter S 21  is the ratio of the intensity of a first signal inputted to the external electrode  14   a  to the intensity of the first signal outputted from the external electrode  14   c . The parameter S 43  is the ratio of the intensity of a second signal inputted to the external electrode  14   b  to the intensity of the second signal outputted from the external electrode  14   d . The parameter Sdc 21  represents the rate of a differential-mode signal being converted into common-mode noise. 
       FIG. 6  is a graph showing the relationship between the frequency and the phase differences for the parameters S 21  and S 43  in the first model.  FIG. 7  is a graph showing the relationship between the frequency and the phase differences for the parameters S 21  and S 43  in the second model.  FIG. 8  is a graph showing the relationship of the frequency with the parameter Sdc 21  in the first and second models. In  FIGS. 6 and 7 , the vertical axis represents the phase difference, and the horizontal axis represents the frequency. In  FIG. 8 , the vertical axis represents the intensity ratio, and the horizontal axis represents the frequency. 
     From  FIG. 7 , it can be appreciated that in the second model, the frequency at which the same phase difference occurs varies between S 21  and S 43 . Specifically, it can be appreciated that in the second model, the phase difference between the inputted first signal and the outputted first signal deviates from the phase difference between the inputted second signal and the outputted second signal. Thus, it can be appreciated that in the second model, the phase difference between the first and second signals to be outputted tends to deviate from 180 degrees. 
     On the other hand, from  FIG. 6 , it can be appreciated that in the first model, the frequency at which the same phase difference occurs is equal between S 21  and S 43 . Specifically, it can be appreciated that in the first model, the phase difference between the inputted first signal and the outputted first signal is less subject to deviating from the phase difference between the inputted second signal and the outputted second signal. Thus, it can be appreciated that in the first model, the phase difference between the first and second signals to be outputted is less subject to deviating from 180 degrees. 
     Furthermore, from  FIG. 8 , it can be appreciated that Sdc 21  is lower in the first model than in the second model. Accordingly, it can be appreciated that conversion of the differential-mode signal into common-mode noise is inhibited in the first model more than in the second model. 
     Furthermore, the present inventors carried out the following computer simulations using the first and second models. Specifically, the first and second models were used as baluns, and common-mode rejection ratios (CMRRs) were computed by inputting first signals to the first and second models.  FIG. 9  is a graph showing the relationship between the frequency and the CMRR in the first and second models. In  FIG. 9 , the vertical axis represents the CMRR, and the horizontal axis represents the frequency. 
     From  FIG. 9 , it can be appreciated that the CMRR is higher in the first model than in the second model. Thus, it can be appreciated that the intensity of the common-mode component in an output signal is lower in the first model than in the second model. 
     Other Embodiments 
     The present disclosure is not limited to the transformer  10 , and variations can be made within the spirit and scope of the disclosure. 
     Note that the transformer  10  may be provided with a core made of a magnetic material and piercing through the gravity center of the coil conductor  20   a  and the gravity center of the coil conductor  20   b  in the z-axis direction. This renders it possible to increase a coefficient of coupling between the coil conductor  20   a  and the coil conductor  20   b.    
     Note that in the transformer  10 , the coil conductor  20   a  and the coil conductor  20   b , when viewed in a plan view in the z-axis direction, overlap in part in the width direction, as shown in  FIG. 5 . However, the coil conductor  20   a  and the coil conductor  20   b  do not necessarily overlap in the width direction. In such a case, when viewed in a plan view in the z-axis direction, the coil conductor  20   b  is positioned between adjacent winds of the coil conductor  20   a , and the coil conductor  20   a  is positioned between adjacent winds of the coil conductor  20   b . In this configuration, the coil conductor  20   a  and the coil conductor  20   b  do not overlap each other, resulting in a reduced difference in thickness in the z-axis direction between the area in which the coil conductor  20   a  is provided and the area in which the coil conductor  20   b  is provided. Thus, the laminate  12  can be inhibited from having irregularities formed therein. 
     Furthermore, in the case where the coil conductors  20   a  and  20   b  are to be provided so as not to overlap in the z-axis direction, the coil conductors  20   a  and  20   b  may be provided on the same insulator layer. 
     Furthermore, the coil conductors  20   a  and  20   b  have circular outlines, but they may have rectangular or elliptical outlines. 
     Note that a plate-like substrate may be used in place of the laminate  12 . In such a case, the coil conductor  20   a  is provided on the principal surface of the substrate that is located on the positive side in the z-axis direction, and the coil conductor  20   b  is provided on the principal surface of the substrate that is located on the negative side in the z-axis direction. 
     Although the present disclosure has been described in connection with the preferred embodiment above, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the disclosure.