Patent Publication Number: US-2020279684-A1

Title: Coil component and filter circuit including same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2018-059405 filed on Mar. 27, 2018 and is a Continuation Application of PCT Application No. PCT/JP2018/037200 filed on Oct. 4, 2018. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coil component and a filter circuit including the coil component. 
     2. Description of the Related Art 
     Filter circuits are often used to reduce noise in electronic devices. For example, such a filter circuit may include an electromagnetic interference (EMI) removal filter and the filter circuit allows a necessary component of a current flowing along a conductor to pass therethrough and removes an unwanted component from the current. A capacitor, which is a capacitance element, may be used in the circuit configuration of such a filter circuit. It is known that the noise suppressing effect of a filter circuit that uses a capacitor is degraded by the equivalent series inductance (ESL), which is a parasitic inductance, of the capacitor. 
     A technique for canceling out the equivalent series inductance of the capacitor is known which consists of widening the frequency band where the attenuation effect of the filter circuit occurs by using a negative inductance generated by two magnetically coupled coils (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-160728). 
     However, there is a problem in that although the equivalent series inductance of the capacitor can be canceled out by the negative inductance generated by the two magnetically coupled coils, widening the frequency band where the attenuation effect of the filter circuit occurs is restricted by stray capacitances generated by the two magnetically coupled coils. Specifically, with generation of a stray capacitance of 1 pF, a noise signal of 1 GHz or higher passes through the filter circuit via the stray capacitance with a loss of several dB, and the attenuation effect of the filter circuit is substantially limited to frequencies lower than the MHz band. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide coil components that are each able to reduce a frequency band of a noise signal that passes through a plurality of magnetically coupled coils, and filter circuits that each include a coil component. 
     A coil component according to a preferred embodiment of the present invention includes a plurality of coils magnetically couple with each other. The coil component includes a first coil, a second coil that magnetically couples with the first coil and causes a negative inductance to be generated, and an electrode that is provided at a position adjacent to or in a vicinity of a portion of the first coil and a portion of the second coil and is grounded. 
     A filter circuit according to a preferred embodiment of the present invention includes a coil component and a capacitor according to a preferred embodiment of the present invention including one end that is connected to the first coil and the second coil. 
     According to preferred embodiments of the present invention, the grounded electrode is provided at a position adjacent to or in the vicinity of a portion of the first coil and a portion of the second coil, and as a result, a noise signal in a frequency band that would pass through the coil component via stray capacitances of the coils is able to be made to flow toward the electrode and the frequency band of a noise signal that passes through the coil component is able to be reduced. In addition, in the filter circuits each including such a coil component, a noise signal of a frequency band that would pass through the coil component via the stray capacitances of the coils is able to be made to flow toward the electrode, and therefore, the frequency band where the attenuation effect of the filter circuit occurs is able to be widened. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are a perspective view and a side view of a coil component according to a preferred embodiment 1 of the present invention. 
         FIGS. 2A to 2E  are exploded plan views illustrating the configuration of the coil component according to preferred embodiment 1 of the present invention. 
         FIG. 3  is a circuit diagram of a filter circuit that includes the coil component according to preferred embodiment 1 of present invention. 
         FIG. 4  is a graph illustrating a transmission characteristic with respect to frequency for a filter circuit including the coil component according to preferred embodiment 1 of the present invention. 
         FIGS. 5A and 5B  are diagrams for comparing sizes of an electrode and a coil wiring line of the coil component according to preferred embodiment 1 of the present invention. 
         FIG. 6  is a graph illustrating a transmission characteristic with respect to frequency for the filter circuit when the width of the electrode of the coil component according to preferred embodiment 1 of the present invention is varied. 
         FIG. 7  is a graph illustrating a transmission characteristic with respect to frequency for the filter circuit when the size of the electrode of the coil component according to preferred embodiment 1 of the present invention is varied. 
         FIGS. 8A and 8B  are a perspective view and a side view of a coil component according to a preferred embodiment 2 of the present invention. 
         FIGS. 9A to 9G  are exploded plan views illustrating the configuration of the coil component according to preferred embodiment 2 of the present invention. 
         FIG. 10  is a side view of a filter circuit according to preferred embodiment 3 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, coil components and filter circuits each including a coil component according to preferred embodiments of the present invention will be described with reference to the drawings. 
     Preferred Embodiment 1 
     First, a coil component according to a preferred embodiment 1 of the present invention and a filter circuit including the coil component will be described.  FIGS. 1A and 1B  are a perspective view and a side view of a coil component according to preferred embodiment 1 of the present invention.  FIGS. 2A to 2E  are exploded plan views illustrating the configuration of the coil component according to preferred embodiment 1 of the present invention.  FIG. 3  is a circuit diagram of a filter circuit that includes the coil component according to preferred embodiment 1 of present invention. 
     A filter circuit  10  is preferably, for example, an EMI removal filter and is a third order T-type LC filter circuit. A coil component  1  is used in the filter circuit  10 . In preferred embodiment 1, it is described that, for example, a third-order T-type LC filter circuit is used as the configuration of the filter circuit  10 , but the present invention can be similarly applied to a fifth-order T-type LC circuit or an even higher order T-type LC circuit, for example. First, as illustrated in  FIG. 3 , the filter circuit  10  includes a capacitor C 1 , electrodes  4   a  to  4   d , a coil L 1  (first coil), and a coil L 2  (second coil). 
     As illustrated in  FIG. 3 , one terminal of the capacitor C 1  is connected to the electrode  4   c  and the other terminal of the capacitor C 1  is connected to a GND wiring line. The capacitor C 1  is not limited to being a multilayer ceramic capacitor including BaTiO 3  (barium titanate) as a main component and may instead be a multilayer ceramic capacitor including another material as a main component or may be another type of capacitor, such as, for example, an aluminum electrolytic capacitor rather than a multilayer ceramic capacitor. Although not illustrated, the capacitor C 1  has a parasitic inductance (equivalent series inductance (ESL)). 
     In addition to the capacitor C 1 , the coil L 1  and the coil L 2  are also connected to the electrode  4   c . The coil L 1  and the coil L 2  are magnetically coupled with each other and generate a negative inductance component. The parasitic inductance of the capacitor C 1  can be canceled out by using this negative inductance component and the inductance component of the capacitor C 1  can be effectively reduced. The filter circuit  10 , which includes the capacitor C 1 , the coil L 1 , and the coil L 2 , is able to improve a high-frequency-band noise suppression effect by canceling out the parasitic inductance of the capacitor C 1  by using the negative inductance component generated by the mutual inductance between the coil L 1  and the coil L 2 . 
     However, widening of the frequency band where the attenuation effect of the filter circuit  10  occurs is restricted by stray capacitances C 2  and C 3  generated by the magnetically coupled coil L 1  and coil L 2 . In other words, since the impedance of a capacitor decreases as the frequency of a signal increases, a high-frequency noise signal may pass through the filter circuit  10  via the stray capacitances C 2  and C 3  and this will restrict the attenuation effect of the filter circuit  10 . For example, in the case where the capacitance of the stray capacitances C 2  and C 3  is about 1 pF, a noise signal of about 1 GHz or higher passes through the filter circuit  10  via the stray capacitances C 2  and C 3  with a loss of several dB and the attenuation effect of the filter circuit  10  is substantially limited to frequencies less than the MHz band. 
     Although it is conceivable to increase the distance between the coil L 1  and the coil L 2  in order reduce the capacitances of the stray capacitances C 2  and C 3  so that the attenuation effect of the filter circuit  10  is not limited, the magnetic coupling would be weakened and the required negative inductance would not be obtained when the distance between the coil L 1  and the coil L 2  is large. In order to obtain the required negative inductance while increasing the distance between the coil L 1  and the coil L 2 , it would be necessary to increase the size of the coils L 1  and L 2  and the filter circuit  10  would be undesirably increased in size. 
     Accordingly, in the coil component  1  according to preferred embodiment 1, an electrode  2  is provided at a position that is adjacent to or in the vicinity of a portion of the coil L 1  and a portion of the coil L 2 . As is clear from  FIGS. 1A and 1B , the electrode  2  is electrically connected to the electrode  4   d  that is connected to GND, but is not electrically connected to the coil L 1  and the coil L 2 . Therefore, the electrode  2  is equivalent to the circuit configuration illustrated in  FIG. 3 , which includes an inductor  2 L as a parasitic inductance and a capacitor  2 C as a parasitic capacitance. The inductor  2 L and the capacitor  2 C are connected in series with each other between the coil L 1  and the coil L 2  and the electrode  4   d.    
     In the coil component  1 , a high-frequency noise signal that has passed through the stray capacitances C 2  and C 3  can be made to flow to GND from the electrode  4   d  via the capacitor  2 C by providing the electrode  2  at a position adjacent to or in the vicinity of the coil L 1  and the coil L 2 . However, since the inductor  2 L exists due to the electrode  2  being provided, the impedance with respect to GND cannot be reduced over a wide band. Basically, a noise signal in the vicinity of the resonant frequency of an series LC circuit including the inductor  2 L, which is a parasitic inductance, and the capacitor  2 C, which is a parasitic capacitance, generated due to the electrode  2  being provided can be made to flow to GND. Therefore, the frequency band where the attenuation effect of the filter circuit  10  that includes the coil component  1  occurs can be widened by making the resonant frequency of the series LC circuit generated due to the electrode  2  match the frequency at which attenuation cannot be obtained due to the stray capacitances C 2  and C 3  generated by the magnetically coupled coils L 1  and L 2 . 
     As illustrated in  FIGS. 1A and 1B , the coil component  1  is provided by stacking a plurality of substrates on which coil wiring lines are provided. One end of a wiring line L 1   a  of the coil L 1  stacked as an upper layer is electrically connected to the electrode  4   a  and the other end of the wiring line L 1   a  is electrically connected to a wiring line Lib of the coil L 1  in the layer below the upper layer through a via  5 . One end of the wiring line Lib of the coil L 1  is electrically connected to an electrode  4   c  and the other end of the wiring line Lib is electrically connected to the wiring line L 1   a  of the coil L 1  in the upper layer through the via  5 . The coil L 1  is defined by the wiring line L 1   a  and the wiring line Lib. In the coil component  1  illustrated in of  FIG. 1A , the short side direction is an X direction, the long side direction is a Y direction, and the height direction is a Z direction. In addition, the stacking direction of the substrates is a Z direction and the direction of the arrow indicates the direction of an upper layer. 
     Similarly, one end of a wiring line L 2   a  of the coil L 2  stacked below the coil L 1  is electrically connected to the electrode  4   c  and the other end of the wiring line L 2   a  is electrically connected to a wiring line L 2   b  of the coil L 2  in the layer therebelow through a via  6 . One end of the wiring line L 2   b  of the coil L 2  is electrically connected to the electrode  4   b  and the other end of the wiring line L 2   b  is electrically connected to the wiring line L 2   a  of the coil L 2  in the layer thereabove through the via  6 . The coil L 2  is defined by the wiring line L 2   a  and the wiring line L 2   b.    
     In the coil component  1 , furthermore, the electrode  2  is stacked between the wiring line Lib of the coil L 1  and the wiring line L 2   a  of the coil L 2 . One end of the electrode  2  is electrically connected to the electrode  4   d  and the electrode  2  is not electrically connected to the wiring line Lib and the wiring line L 2   a.    
     As illustrated in  FIGS. 2A to 2E , wiring line patterns are provided on ceramic green sheets  3   a  to  3   e  by performing printing with a conductive paste (for example, Ni paste) using a screen printing method, for example. The wiring line L 1   a  and additionally a wiring line pattern  40  that is connected to the electrode  4   a  and a wiring line pattern  5   a  that is connected to the via  5  are provided on the ceramic green sheet  3   a  illustrated in  FIG. 2A . 
     The wiring line Lib and additionally a wiring line pattern  41  that is connected to the electrode  4   c  and a wiring line pattern  5   b  that is connected to the via  5  are provided on the ceramic green sheet  3   b  illustrated in  FIG. 2B . The coil L 1  is provided on the ceramic green sheets  3   a  and  3   b.    
     The electrode  2  and additionally a wiring line pattern  42  that is connected to the electrode  4   d  are provided on the ceramic green sheet  3   c  illustrated in  FIG. 2C . 
     The wiring line L 2   a  and additionally a wiring line pattern  43  that is connected to the electrode  4   c  and a wiring line pattern  6   a  that is connected to the via  6  are provided on the ceramic green sheet  3   d  illustrated in  FIG. 2D . The wiring line L 2   b  and additionally a wiring line pattern  44  that is connected to the electrode  4   b  and a wiring line pattern  6   b  that is connected to the via  6  are provided on the ceramic green sheet  3   e  illustrated in  FIG. 2E . The coil L 2  is provided on the ceramic green sheets  3   d  and  3   e.    
     In the coil component  1 , the plurality of ceramic green sheets  3   a  to  3   e  illustrated in  FIGS. 2A to 2E  are stacked on top of one another, and a plurality of ceramic green sheets on which wiring line patterns have not been provided by printing (dummy layers) are stacked above and below these stacked ceramic green sheets (refer to  FIG. 1B ). The plurality of ceramic green sheets  3  including the dummy layers are subjected to pressure bonding and an unfired multilayer body is formed. The multilayer body is fired and the electrodes  4   a  to  4   d  are formed by, for example, baking copper electrodes on the outside of the fired multilayer body so that the electrodes are electrically connected to the wiring line patterns  40  to  44 . 
       FIG. 4  is a graph illustrating a transmission characteristic with respect to frequency for the filter circuit  10  including the coil component  1  according to preferred embodiment 1 of the present invention. A circuit simulation was performed for the filter circuit  10  illustrated in  FIG. 3  and the results of the circuit simulation depicting a transmission characteristic with respect to frequency are illustrated as a graph in  FIG. 4 . In the graph illustrated in  FIG. 4 , the horizontal axis represents frequency Freq (MHz) and the vertical axis represents a transmission characteristic S 21  (dB). 
     First, graph A in  FIG. 4  is a graph illustrating the transmission characteristic of a filter circuit including only the capacitor C 1 . In the filter circuit including only the capacitor C 1 , the transmission characteristic S 21  is high at frequencies greater than or equal to about 1.0 MHz and a noise signal in a high-frequency band cannot be reduced or prevented. Furthermore, graph B in  FIG. 4  is a graph illustrating the transmission characteristic of a filter circuit including the capacitor C 1  and the coils L 1  and L 2 . In this filter circuit, the transmission characteristic S 21  suddenly increases at frequencies greater than or equal to about 300.0 MHz and a noise signal in a 1 GHz high-frequency band cannot be reduced or prevented. 
     On the other hand, graph C in  FIG. 4  is a graph illustrating the transmission characteristic of the filter circuit  10 . In the filter circuit  10 , the transmission characteristic S 21  is sufficiently low at a frequency Freq of about 1 GHz and the effect of reducing or preventing noise in a high-frequency band can be improved. 
     Next, changes that occur in the transmission characteristic S 21  when the sizes the wiring lines of the coils L 1  and L 2  and the electrode  2  are varied will be described.  FIGS. 5A and 5B  are diagrams for comparing sizes of the electrode and coil wiring lines of the coil component according to preferred embodiment 1 of the present invention. The inductor  2 L including the parasitic inductance and the capacitor  2 C including the parasitic capacitance change depending on the overlapping state of the wiring lines of the coils L 1  and L 2  and the electrode  2 , and therefore, the transmission characteristic S 21  of the filter circuit  10  also changes. 
     In  FIG. 5A , a width  2 W of the electrode  2  is larger than a width LW of the wiring line L 1   a  of the coil L 1 . In the following description, the widths of the wiring line Lib of the coil L 1  and the wiring lines L 2   a  and L 2   b  of the coil L 2  are preferably the same or substantially the same as the width LW of the wiring line Lia of the coil L 1 . However, the widths of the wiring line Lib of the coil L 1  and the wiring line L 2   a  and L 2   b  of the coil L 2  may instead be different from the width LW of the wiring line L 1   a  of the coil L 1 . 
     The electrode  2  and the wiring line L 1   a  of the coil L 1  overlap each other. Therefore, it is preferable that a width difference arising from manufacturing variations be equivalent to the difference between the width  2 W of the electrode  2  and the width LW of the wiring line L 1   a  of the coil L 1 . For example, in order to reduce the effect of manufacturing variations, the width  2 W of the electrode  2  is set to be larger than the width LW of the wiring line L 1   a  of the coil L 1  so that the area of the overlapping portion does not change even when the electrode  2  and the wiring line L 1   a  of the coil L 1  overlap but are shifted relative to each other. However, when the width  2 W of the electrode  2  is larger than the width LW of the wiring line L 1   a  of the coil L 1 , the transmission characteristic S 21  of the filter circuit  10  in a high-frequency band deteriorates. 
       FIG. 6  is a graph illustrating a transmission characteristic with respect to frequency for the filter circuit when the width of the electrode of the coil component according to preferred embodiment 1 of the present invention is varied. A circuit simulation was performed for the filter circuit  10  illustrated in  FIG. 3  by varying the width of the electrode  2  and the results of the circuit simulation showing the transmission characteristic S 21  with respect to frequency are illustrated as a graph in  FIG. 6 . In the graph illustrated in  FIG. 6 , the horizontal axis represents frequency Freq (MHz) and the vertical axis represents the transmission characteristic S 21  (dB). 
     Graph a in  FIG. 6  is a graph illustrating the transmission characteristic S 21  of the filter circuit  10  for a case where the width LW of the wiring line L 1   a  of the coil L 1  is about 100 μm and the width  2 W of the electrode  2  is about 220 μm, for example. In the filter circuit  10  in which the width  2 W is about 220 μm, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is high and a noise signal in a high-frequency band cannot be reduced or prevented. Graph b in  FIG. 6  is a graph illustrating the transmission characteristic S 21  of the filter circuit  10  for a case where the width LW of the wiring line L 1   a  of the coil L 1  is about 100 μm and the width  2 W of the electrode  2  is about 200 μm, for example. In the filter circuit in which the width  2 W is about 200 μm, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is high and a noise signal in a high-frequency band cannot be reduced or prevented. 
     Graph c in  FIG. 6  is a graph illustrating the transmission characteristic S 21  of the filter circuit  10  for a case where the width LW of the wiring line L 1   a  of the coil L 1  is about 100 μm and the width  2 W of the electrode  2  is about 180 μm, for example. In the filter circuit  10  in which the width  2 W is about 180 μm, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is slightly lower than when the width  2 W is about 220 μm or about 200 μm and a noise signal in a high-frequency band can be slightly reduced or prevented. Graph d in  FIG. 6  is a graph illustrating the transmission characteristic S 21  of the filter circuit  10  for a case where the width LW of the wiring line L 1   a  of the coil L 1  is about 100 μm and the width  2 W of the electrode  2  is about 160 μm, for example. In the filter circuit  10  in which the width  2 W is about 160 μm, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is sufficiently low and a noise signal in a high-frequency band can be reduced or prevented. 
     As illustrated in  FIG. 6 , the transmission characteristic S 21  of the filter circuit  10  rapidly deteriorates around the point where the width  2 W of the electrode  2  exceeds about 180 μm. This is thought to be because the width  2 W of the electrode  2  is larger than the width LW of the wiring line L 1   a  of the coil L 1  and, consequently, the magnetic fields of the coils L 1  and L 2  are obstructed and the inductance and magnetic coupling are caused to deteriorate. As a result, the transmission characteristic S 21  of the filter circuit  10  is caused to rapidly deteriorate. 
     Accordingly, if a noise signal in a high-frequency band is to be more greatly reduced or prevented in the filter circuit  10 , it is preferable for the width  2 W of the electrode  2  to be less than or equal to about 1.8 times the width LW of the wiring line L 1   a  of the coil L 1  in the case where the width of the electrode  2  is larger than the width LW of the wiring line L 1   a  of the coil L 1 . 
     On the other hand, in order to reduce the effect of manufacturing variations, in the case where the width  2 W of the electrode  2  is smaller than the width LW of the wiring line L 1   a  of the coil L 1 , it is necessary to increase a length  2 D of the electrode  2  in accordance with the amount by which the width  2 W of the electrode  2  has been reduced as illustrated in  FIG. 5B  because the value of the capacitor  2 C generated by the electrode  2  is determined by the area of the electrode  2 . In  FIG. 5B , the relationship between the width  2 W of the electrode  2  and the length  2 D of the electrode  2  is illustrated. For example, when the width  2 W of the electrode  2  is about 90 μm and the length  2 D of the electrode  2  is about 1800 μm, the width  2 W of the electrode  2  is about 1/20 the length  2 D of the electrode  2 . When the width  2 W of the electrode  2  illustrated in  FIG. 5A  is about 160 μm and the length  2 D of the electrode  2  is about 1120 μm, for example, the width  2 W of the electrode  2  is about 1/7 the length  2 D of the electrode  2 . When the length  2 D of the electrode  2  is increased, the length of the electrode  2  is increased along the wiring line L 1   a  of the coil L 1  as illustrated in  FIG. 5B . 
     The resonant frequency of the series LC circuit including the inductor  2 L, which is a parasitic inductance, and the capacitor  2 C, which is a parasitic capacitance, generated due to the provision of the electrode  2  is determined by the sizes of the values of the inductor  2 L and the capacitor  2 C. As the capacitance of the capacitor  2 C increases, the bandwidth of the resonant frequency of the series LC circuit becomes larger. Therefore, in order to increase the capacitance of the capacitor  2 C, it is necessary to increase the width  2 W of the electrode  2  or increase the length  2 D by an amount corresponding to the reduction of the width  2 W of the electrode  2 . In the case where the width  2 W of the electrode  2  is larger than the width LW of the wiring line L 1   a  of the coil L 1 , the transmission characteristic S 21  of the filter circuit  10  may rapidly deteriorate when the width  2 W of the electrode  2  exceeds an upper limit as illustrated in  FIG. 6 . 
       FIG. 7  is a graph illustrating the transmission characteristic with respect to frequency for the filter circuit when the size of the electrode of the coil component according to preferred embodiment 1 of the present invention is varied. A circuit simulation was performed for the filter circuit  10  illustrated in  FIG. 3  by varying the size of the electrode  2  and the results of the circuit simulation showing the transmission characteristic with respect to frequency are illustrated as a graph in  FIG. 7 . In the graph illustrated in  FIG. 7 , the horizontal axis represents frequency Freq (MHz) and the vertical axis represents the transmission characteristic S 21  (dB). 
     Graph d in  FIG. 7  is a graph illustrating the transmission characteristic of the filter circuit  10  for a case where the width  2 W of the electrode  2  is about 160 μm and the length  2 D of the electrode  2  is about 1120 μm, for example. In this filter circuit, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is sufficiently low and a noise signal in a high-frequency band can be reduced or prevented. Graph e in  FIG. 7  is a graph illustrating the transmission characteristic of the filter circuit  10  for a case where the width  2 W of the electrode  2  is about 90 μm and the length  2 D of the electrode  2  is about 1800 μm, for example. In this filter circuit, the transmission characteristic S 21  at a frequency Freq of about 1 GHz is high and a noise signal in a high-frequency band cannot be reduced or prevented. 
     In other words, in the case where the width  2 W of the electrode  2  is smaller than the width LW of the wiring line L 1   a  of the coil L 1 , the transmission characteristic S 21  of the filter circuit  10  at a frequency Freq of about 1 GHz is sufficiently low and a noise signal in a high-frequency band can be reduced or prevented to a greater extent if, for example, the width  2 W of the electrode  2  lies in a range from about 1/7 to about ⅛ the length D of the electrode  2 . 
     The relationship between the width LW of the wiring lines of the coils L 1  and L 2  and the width  2 W of the electrode  2  in the coil component  1  has been described above, and next the spacing between the wiring lines of each of the coils L 1  and L 2  and the spacing between the electrode  2  and the wiring lines of the coils L 1  and L 2  will be described. As illustrated in  FIG. 1B , the spacing between the electrode  2  and the wiring lines of the coils L 1  and L 2  is smaller than the spacing between the wiring lines of each of the coils L 1  and L 2 . For example, the spacing between the wiring lines of each of the coils L 1  and L 2  is preferably about 50 μm, and the spacing between the electrode  2  and the wiring lines of the coils L 1  and L 2  is preferably smaller than about 20 μm. In other words, in order to secure a sufficient parasitic capacitance capacitor  2 C to obtain the resonant frequency required for the LC series circuit, the spacing between the electrode  2  and the wiring lines of the coils L 1  and L 2  is set to be smaller than the spacing between the wiring lines of each of the coils L 1  and L 2 . 
     As described above, the coil component  1  according to preferred embodiment 1 of the present invention includes a plurality of coils magnetically couple with each other, and includes the coil L 1 , the coil L 2  that magnetically couples with the coil L 1 , and the electrode  2  that is provided at a position adjacent to or in the vicinity of a portion of each of the coils L 1  and L 2  and is grounded. With this configuration, in the coil component  1  according to preferred embodiment 1 of the present invention, since the electrode  2  is provided at a position adjacent to or in the vicinity of a portion of each of the coils L 1  and L 2 , a noise signal in a frequency band that would pass through the coil component  1  via the stray capacitances of the coils L 1  and L 2  can be made to flow toward the electrode  2  and the frequency band of a noise signal that passes through the coil component  1  can be reduced. 
     Furthermore, the spacing between the electrode  2  and the coils L 1  and L 2  may be smaller than the spacing between the wiring lines of each of the coils L 1  and L 2 . With this configuration, a noise signal of a frequency band that would pass through the coil component  1  via the stray capacitances of the coils L 1  and L 2  can be made to flow toward the electrode  2 . 
     In the case where the width  2 W of the electrode  2  is smaller than the width LW of the wiring lines of the coils L 1  and L 2 , the width  2 W of the electrode  2  may preferably be, for example, greater than or equal to about ⅛ the length  2 D of the electrode  2 . With this configuration, a noise signal of a frequency band that would pass through the coil component  1  via the stray capacitances of the coils L 1  and L 2  can be made to flow toward the electrode  2 . 
     In the case where the width  2 W of the electrode  2  is larger than the width LW of the wiring lines of the coils L 1  and L 2 , the width  2 W of the electrode  2  may preferably be, for example, less than or equal to about 1.8 times the width LW of the wiring lines of the coils L 1  and L 2 . With this configuration, a noise signal of a frequency band that would pass through the coil component  1  via the stray capacitances of the coils L 1  and L 2  can be made to flow toward the electrode  2 . 
     The filter circuit  10  according to a preferred embodiment of the present invention includes the coil component  1  and the capacitor C 1  that has one end that is connected to the coils L 1  and L 2 . With this configuration, in the filter circuit  10  according to the present preferred embodiment of the present invention, a noise signal of a frequency band that would pass through the coil component  1  via the stray capacitances of the coils can be made to flow toward the electrode  2 , and therefore, the frequency band where the attenuation effect of the filter circuit  10  occurs can be widened. 
     Preferred Embodiment 2 
     In the coil component  1  according to preferred embodiment 1 of the present invention, one electrode  2  is provided at a position adjacent to or in the vicinity of a portion of each of the coils L 1  and L 2  as illustrated in  FIGS. 1A and 1B , but a plurality of such electrodes may instead be provided.  FIGS. 8A and 8B  are a perspective view and a side view of a coil component according to a preferred embodiment 2 of the present invention.  FIGS. 9A to 9G  are exploded plan views illustrating the configuration of the coil component according to preferred embodiment 2 of the present invention. The circuit configuration of a filter circuit including the coil component according to preferred embodiment 2 is the same or substantially the same as the circuit configuration illustrated in  FIG. 3 , and therefore, detailed description thereof will not be repeated. 
     As illustrated in  FIGS. 8A and 8B , a coil component  1   a  is provided by stacking a plurality of substrates on which coil wiring lines are provided. One end of a wiring line L 1   a  of a coil L 1  stacked as an upper layer is electrically connected to an electrode  4   a  and the other end of the wiring line L 1   a  is electrically connected to a wiring line Lib of the coil L 1  in the layer below the upper layer through a via  5 . One end of the wiring line Lib of the coil L 1  is electrically connected to an electrode  4   c  and the other end of the wiring line Lib is electrically connected to the wiring line L 1   a  of the coil L 1  in the upper layer through the via  5 . The coil L 1  is defined by the wiring line L 1   a  and the wiring line Lib. In addition, an electrode  20   a  is stacked between the wiring line L 1   a  and the wiring line Lib of the coil L 1 . One end of the electrode  20   a  is electrically connected to an electrode  4   d  and the electrode  20   a  is not electrically connected to the wiring line L 1   a  and the wiring line Lib. Here, in the coil component illustrated in  FIG. 1A , the short side direction is an X direction, the long side direction is a Y direction, and the height direction is a Z direction. In addition, the stacking direction of the substrates is a Z direction and the direction of the arrow indicates the direction of an upper layer. 
     In the coil component  1   a , an electrode  20   b  is stacked between the wiring line Lib of the coil L 1  and the wiring line L 2   a  of the coil L 2 . One end of the electrode  20   b  is electrically connected to the electrode  4   d  and the electrode  20   b  is not electrically connected to the wiring line Lib and the wiring line L 2   a.    
     One end of a wiring line L 2   a  of the coil L 2  stacked below the coil L 1  is electrically connected to the electrode  4   c  and the other end of the wiring line L 2   a  is electrically connected to a wiring line L 2   b  of the coil L 2  in the layer therebelow through a via  6 . One end of the wiring line L 2   b  of the coil L 2  is electrically connected to the electrode  4   b  and the other end of the wiring line L 2   b  is electrically connected to a wiring line L 2   a  of the coil L 2  in the layer thereabove through the via  6 . The coil L 2  is defined by the wiring line L 2   a  and the wiring line L 2   b . In addition, an electrode  20   c  is stacked between the wiring line L 2   a  and the wiring line L 2   b  of the coil L 2 . One end of the electrode  20   c  is electrically connected to the electrode  4   d  and the electrode  20   c  is not electrically connected to the wiring line L 2   a  and the wiring line L 2   b.    
     The three electrodes  20   a  to  20   c  are provided in the coil component  1   a , instead of the electrode  2  illustrated in  FIGS. 1A and 1B . Since a parasitic capacitance can be increased by providing a plurality of electrodes rather than as a single electrode, the sizes of the electrodes themselves can be decreased provided that the same capacitance is obtained. Specifically, for example, for the case of one electrode  2  having a width  2 W of about 160 μm and a length  2 D of about 1120 μm, the length  2 D of each of the three electrodes  20   a  to  20   c  can be decreased to about 500 μm while taking into account the reduction in parasitic inductance. 
     As illustrated in  FIGS. 9A to 9G , wiring line patterns are provided on ceramic green sheets  3   a  to  3   g  by performing printing with a conductive paste (for example, Ni paste) using a screen printing method, for example. The wiring line L 1   a  and additionally a wiring line pattern  40  that is connected to the electrode  4   a  and a wiring line pattern  5   a  that is connected to the via  5  are provided on the ceramic green sheet  3   a  illustrated in  FIG. 9A . 
     The electrode  20   a  and additionally a wiring line pattern  42   a  that is connected to the electrode  4   d  are provided on the ceramic green sheet  3   b  illustrated in  FIG. 9B . 
     The wiring line Lib and additionally a wiring line pattern  41  that is connected to the electrode  4   c  and a wiring line pattern  5   b  that is connected to the via  5  are provided on the ceramic green sheet  3   c  illustrated in  FIG. 9C . The coil L 1  is provided on the ceramic green sheets  3   a  and  3   c.    
     The electrode  20   b  and additionally a wiring line pattern  42   b  that is connected to the electrode  4   d  are provided on the ceramic green sheet  3   d  illustrated in  FIG. 9D . 
     The wiring line L 2   a  and additionally a wiring line pattern  43  that is connected to the electrode  4   c  and a wiring line pattern  6   a  that is connected to the via  6  are provided on the ceramic green sheet  3   e  illustrated in  FIG. 9E . 
     The electrode  20   c  and additionally a wiring line pattern  42   c  that is connected to the electrode  4   d  are provided on the ceramic green sheet  3   f  illustrated in  FIG. 9F . 
     The wiring line L 2   b  and additionally a wiring line pattern  44  that is connected to the electrode  4   b  and a wiring line pattern  6   b  that is connected to the via  6  are provided on the ceramic green sheet  3   g  illustrated in  FIG. 9G . The coil L 2  is provided on the ceramic green sheets  3   e  and  3   g.    
     In the coil component  1   a , the plurality of ceramic green sheets  3   a  to  3   g  illustrated in  FIGS. 9A to 9G  are stacked on top of one another, and a plurality of ceramic green sheets on which wiring line patterns have not been provided by printing (dummy layers) are stacked above and below these stacked ceramic green sheets (refer to  FIG. 8B ). The plurality of ceramic green sheets  3  including the dummy layers are subjected to pressure bonding and an unfired multilayer body is formed. The multilayer body is fired and the electrodes  4   a  to  4   d  are formed by baking copper electrodes, for example, on the outside of the fired multilayer body so that the electrodes are electrically connected to the wiring line patterns  40  to  44 . 
     As described above, in the coil component  1   a  according to preferred embodiment 2 of the present invention, electrodes  20   a  to  20   c  may be defined by a plurality of electrodes and the electrodes  20   a  to  20   c  may be respectively provided at a position between wiring lines of the coil L 1 , a position between a wiring line of the coil L 1  and a wiring line of the coil L 2 , and a position between the wiring lines of the coil L 2 . With this configuration, the sizes of the electrodes  20   a  to  20   c  can be reduced. Three electrodes  20   a  to  20   c  have been exemplified above, but the present invention is not limited to this example and two or a greater number of electrodes may be provided. 
     Preferred Embodiment 3 
     The configurations of only the coil components  1  and  1   a  have been described in preferred embodiments 1 and 2 of the present invention. In a preferred embodiment 3 of the present invention, the configuration of a filter circuit in which such a coil component is integrated with a capacitor will be described.  FIG. 10  is a side view of a filter circuit according to preferred embodiment 3 of the present invention. The circuit configuration of a filter circuit according to preferred embodiment 3 is the same or substantially the same as the circuit configuration illustrated in  FIG. 3 , and therefore detailed description thereof will not be repeated. In addition, the coil component used in the filter circuit is the same or substantially the same as the coil component  1  or  1   a  described in preferred embodiments 1 and 2, and therefore detailed description thereof will not be repeated. 
     In the filter circuit  10  illustrated in  FIG. 10 , the coil component  1  is provided in a layer above the capacitor C 1 , which is a multilayer ceramic capacitor. In the capacitor C 1 , an inner electrode  50 , which is electrically connected to the electrode  4   c , and an inner electrode  51  that is electrically connected to the electrode  4   d  (refer to  FIGS. 1A and 1B ) is repeated stacked (for example, 200 times) in order to provide the required capacitance. In other words, the capacitor C 1  is provided by stacking a plurality of ceramic green sheets  30  (dielectric layers) and a plurality of inner electrodes  50  and  51 . 
     It is preferable for a material having a low relative dielectric constant to be used for the coil component  1  in order to reduce or prevent the stray capacitances C 2  and C 3 , whereas it is preferable that a material having a high relative dielectric constant is used for the capacitor C 1  in order to provide the required capacitance. In particular, in order to integrate the coil component  1  and the capacitor C 1  and provide a small thin filter circuit  10 , ceramic green sheets  3  (for example, titanium oxide-based ceramic green sheets) having a low relative dielectric constant (for example, about 10 or lower) are preferably used for the coil component  1  and ceramic green sheets  30  (for example, barium titanate-based ceramic green sheets) having a high relative dielectric constant (for example, about 100 or lower) are preferably used for the capacitor C 1 . 
     As described above, the capacitor C 1  according to preferred embodiment 3 of the present invention is provided in a layer below the coil component  1  in which the coils L 1  and L 2  are stacked and is provided by stacking a plurality of ceramic green sheets  30  and a plurality of inner electrodes  50  and  51 . With this configuration, in the filter circuit  10  according to preferred embodiment 3 of the present invention, the coil component  1  and the capacitor C 1  can be integrated with each other. 
     Furthermore, it is preferable that the relative dielectric constant of the ceramic green sheets  30  is higher than the relative dielectric constant of the coil component  1 . With this configuration, the filter circuit  10  in which the coil component  1  and the capacitor C 1  are integrated with each other can be reduced in size and thickness. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.