Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1999-06-01
2001-05-08
Donovan, Lincoln (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S083000
Reexamination Certificate
active
06229425
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a common mode inductor, and more particularly, to a common mode inductor which is constructed to be used as a noise filter, for example.
2. Description of the Related Art
A conventional common mode inductor of this type is, for instance, a multilayer common mode inductor having an electrical equivalent circuit arrangement shown in FIG.
4
. This common mode inductor includes a coil La which is connected between an input electrode
1
a
and an output electrode
1
b,
a coil Lb which is connected between an input electrode
2
a
and an output electrode
2
b,
and a coil Lc which is connected between an input electrode
3
a
and an output electrode
3
b.
The coils La, Lb and Lc are electromagnetically coupled together and are arranged to prevent passage of common mode noise in the same phase.
In this type of common mode inductor, the lower the dc resistance values of the three coils La-Lc, the better the signal propagation characteristics of the inductor. Therefore, in the conventional common mode inductor, a material having low resistivity is used to form the coil conductors which define the coils La-Lc, and the dc resistance values of all the coils La-Lc are lowered by increasing the thickness of the coil conductors.
However, the importance of the dc resistance values of the three coils La-Lc is sometimes different, depending on the circuit in which the common mode inductor is used. For instance, consider a case where the common mode inductor is used as a filter for eliminating noise in an audio circuit of an audio device, such as a stereo. An audio circuit is a three-wire circuit which includes left and right signal lines and a common ground line. Normally, the coils La-Lc of the common mode inductor are arranged in a parallel configuration, and the coils La and Lc on each end are respectively connected to the left and right signal lines of the audio circuit. The coil Lb located in the center of the three coils La-Lc is connected to the common ground line of the audio circuit. The purpose of this type of connection is to ensure that the electromagnetic coupling between the left signal line and the ground line is substantially equal to the electromagnetic coupling between the right signal line and the ground line.
When the in-phase inductor is connected to the audio circuit in this manner, a phenomenon known as crosstalk may occur, in which signals leak between the left and right signal lines. Crosstalk is mainly caused when the center coil Lb, which is connected to the ground line, has a high dc resistance value, which acts as what is referred to as a common-mode impedance of the left and right sides of the audio circuit. On the other hand, the dc resistance values of the coil La and the coil Lc have almost no effect on generating crosstalk. In other words, when a common mode inductor is used as a filter for eliminating noise in an audio circuit, it is only necessary to lower the dc resistance value of the centrally located coil Lb which is connected to the ground line of the audio circuit.
Therefore, when an expensive material having low resistivity is used to reduce the dc resistance values of all the coils La-Lc, the manufacturing cost increases and the more expensive, low resistivity material is also wasted. In addition, increasing the thickness of the coil conductors is likely to cause separation of layers (delamination) when the laminated body is fired.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a common mode inductor which has a very small size and high reliability, is constructed to be inexpensively manufactured, and, when connected to an electronic circuit, the dc resistance of the coil of the common mode inductor has little or no effect on the electronic circuit.
According to one preferred embodiment of the present invention, a common mode inductor includes:
(a) a laminated body including a plurality of insulating layers and a plurality of coil conductors stacked on each other in a stacking direction;
(b) at least three coils defined by electrically connecting the coil conductors, the coils being magnetically coupled together;
(c) at least three pairs of external input and output electrodes, provided on a surface of the laminated body and electrically connected to the coils; wherein
(d) the at least three coils are arranged in the stacking direction of the laminated body, and one of the coils includes a first coil portion and a second coil portion which are located spaced apart from each other, and the remaining coils are disposed between the first coil portion and the second coil portion in the stacking direction of the laminated body, a dc resistance value of the coil having the first coil portion and the second coil portion is smaller than dc resistance values of the remaining coils.
With the above-described unique arrangement and construction, it is no longer necessary to reduce the dc resistance values of all of the coils, and the dc resistance value of only one specific coil can be reduced. Then, when the common mode inductor is incorporated into an electronic circuit such as an audio circuit, the specific coil having relatively lower dc resistance value can be connected to the line which requires the lowest dc resistance value, thereby reducing the effect of the dc resistance of the coils on the electronic circuit caused by the connection of the common mode inductor to the electronic circuit, and making it possible to achieve an electronic circuit having desired performance characteristics.
Furthermore, according to preferred embodiments of the common mode inductor of the present invention, the pair of external input and output electrodes which are electrically connected to the coil having the first coil portion and the second coil portion are provided in the approximate center of the laminated body, and multiple pairs of external input and output electrodes which are electrically connected to the remaining coils, are provided in the laminated body on either side of the above-mentioned pair of external input and output electrodes.
As a result, the in-phase inductor has a structure which can be easily incorporated into an audio circuit. That is, the ground line which is located in the approximate center of the three-line audio circuit, is electrically connected to the external input and output electrodes of the coil having the relatively lower dc resistance value, which is located in the approximate center of the in-phase inductor. On the other hand, the signal lines on the left and right sides of the audio circuit are electrically connected to the coils having relatively higher dc resistance values, which are provided on the left and right ends of the common mode inductor, without intersecting the ground line.
The above and further objects, characteristics and advantages of the present invention will more fully appear from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5278526 (1994-01-01), Ikeda
patent: 5578981 (1996-11-01), Tokuda
patent: 5583470 (1996-12-01), Okubo
patent: 6023214 (2000-02-01), Ohta et al.
patent: 8-138938 (1996-05-01), None
Donovan Lincoln
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Nguyen Tuyen T.
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