U.S. patent application number 10/727957 was filed with the patent office on 2004-07-15 for noise filter.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kodama, Takashi, Otsuki, Takehiko, Takenaka, Kazuhiko, Uchida, Katsuyuki, Yamamoto, Hidetoshi.
Application Number | 20040135652 10/727957 |
Document ID | / |
Family ID | 31190396 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040135652 |
Kind Code |
A1 |
Uchida, Katsuyuki ; et
al. |
July 15, 2004 |
Noise filter
Abstract
A noise filter includes a laminate body including magnetic
layers, line conductors and ground conductors, with one line
conductor and one ground conductor alternately arranged in
interfaces between the magnetic layers. With an electrical signal
applied to the line conductors with the ground conductors grounded,
a high-frequency noise is attenuated using a magnetic loss of the
magnetic layer.
Inventors: |
Uchida, Katsuyuki;
(Hikone-shi, JP) ; Yamamoto, Hidetoshi;
(Yokohama-shi, JP) ; Kodama, Takashi; (Otsu-shi,
JP) ; Takenaka, Kazuhiko; (Yokaichi-shi, JP) ;
Otsuki, Takehiko; (Omihachiman-shi, JP) |
Correspondence
Address: |
Keating & Bennett LLP
Suite 312
10400 Eaton Place
Fairfax
VA
22030
US
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
Nagaokakyo-shi
JP
|
Family ID: |
31190396 |
Appl. No.: |
10/727957 |
Filed: |
December 4, 2003 |
Current U.S.
Class: |
333/185 |
Current CPC
Class: |
H03H 2001/0085 20130101;
H01F 2017/0026 20130101; H01F 2017/065 20130101; H03H 2001/0092
20130101; H01F 17/0013 20130101 |
Class at
Publication: |
333/185 |
International
Class: |
H03H 007/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2003 |
JP |
2003-004888 |
Mar 28, 2003 |
JP |
2003-091611 |
Claims
What is claimed is:
1. A noise filter comprising: a laminate body including magnetic
layers, line conductors, and ground conductors wherein one of the
line conductors and the ground conductors is disposed in each of a
plurality of interfaces between the magnetic layers such that one
line conductor alternates with one ground conductor in lamination,
with one ground conductor arranged on a top magnetic layer and
another ground conductor arranged on a bottom magnetic layer, and
the line conductors disposed between the magnetic layers being
serially connected; wherein the magnetic layer is made of a
magnetic oxide and causes little or no attenuation of an electrical
signal within a frequency range below a frequency at which a
magnetic loss occurs and attenuates an electrical signal within a
frequency range where the magnetic loss occurs.
2. A noise filter according to claim 1, wherein the frequency at
which the magnetic loss of the magnetic oxide increases to above 1
is approximately equal to or greater than about 80 MHz.
3. A noise filter according to claim 1, wherein the line conductor
has a meandering shape.
4. A noise filter according to claim 1, wherein the line conductor
has a spiral shape.
5. A noise filter according to claim 1, wherein the line conductor
is disposed between the laminated magnetic layers, and is coiled
around a center axis aligned in the direction of lamination of the
magnetic layers.
6. A noise filter according to claim 1, wherein a dielectric layer
is sandwiched between the magnetic layers.
7. A noise filter according to claim 1, further comprising
dielectric layers having the ground conductor sandwiched
therebetween and magnetic layers having the line conductor
sandwiched therebetween.
8. A noise filter according to claim 1, wherein the magnetic body
includes a hole, which is filled with one of glass, a resin, and a
mixture of glass and a resin.
9. A noise filter according to claim 1, wherein the magnetic oxide
is a Ni--Cu--Zn ferrite.
10. A noise filter comprising: a laminate body including magnetic
layers, line conductors, and ground conductors wherein one of the
line conductors and the ground conductors is disposed in each of a
plurality of interfaces between the magnetic layers in a manner
such that one line conductor alternates with one ground conductor
in lamination, with one ground conductor arranged on a top magnetic
layer and another ground conductor arranged on a bottom magnetic
layer, first ends of the line conductors disposed between the
magnetic layers being connected to different signal input
electrodes, and second ends of the line conductors being connected
to different signal output electrodes; wherein the magnetic layer
is made of a magnetic oxide, and the frequency at which the
magnetic loss of the magnetic oxide increases to above 1 is
approximately equal to or greater than about 80 MHz; and the
magnetic layer causes little or no attenuation of an electrical
signal within a frequency range below a frequency at which a
magnetic loss occurs and attenuates an electrical signal within a
frequency range where the magnetic loss occurs.
11 A noise filter according to claim 10, wherein the line conductor
has a meandering shape.
12. A noise filter according to claim 10, wherein the line
conductor has a spiral shape.
13. A noise filter according to claim 10, wherein the line
conductor is disposed between the laminated magnetic layers, and is
coiled around a center axis aligned in the direction of lamination
of the magnetic layers.
14. A noise filter according to claim 10, wherein the line
conductors disposed between the magnetic layers are different from
each other in characteristic impedance.
15. A noise filter according to claim 10, wherein a dielectric
layer is sandwiched between the magnetic layers.
16. A noise filter according to claims 10, wherein the magnetic
body includes a hole, which is filled with one of glass, a resin,
and a mixture of glass and a resin.
17. A noise filter according to claim 10, wherein the magnetic
oxide is a Ni--Cu--Zn ferrite.
18. A noise filter comprising: a magnetic body and at least two
line conductors running alongside each other with a space
maintained therebetween on a major surface of the magnetic body;
wherein the magnetic body is made of a magnetic oxide, and the
frequency at which the magnetic loss of the magnetic oxide
increases to above 1 is approximately equal to or greater than
about 80 MHz; and the magnetic body causes little or no attenuation
of an electrical signal within a frequency range below a frequency
at which a magnetic loss occurs and attenuates an electrical signal
within a frequency range where the magnetic loss occurs.
19. A noise filter according to claim 18, wherein the magnetic body
includes a hole, which is filled with one of glass, a resin, and a
mixture of glass and a resin.
20. A noise filter according to claim 18, wherein the magnetic
oxide is a Ni--Cu--Zn ferrite.
21. A noise filter comprising: a magnetic body and at least a pair
of line conductors facing each other on major surfaces of the
magnetic body such that the line conductors sandwich the magnetic
body; wherein the magnetic body is made of a magnetic oxide, and
the frequency at which the magnetic loss of the magnetic oxide
increase to above 1 is approximately equal to or greater than about
80 MHz; and the magnetic body causes little or no attenuation of an
electrical signal within a frequency range below a frequency at
which a magnetic loss occurs and attenuates an electrical signal
within a frequency range where the magnetic loss occurs.
22. A noise filter according to claim 21, wherein the magnetic body
includes a hole, which is filled with one of glass, a resin, and a
mixture of glass and a resin.
23. A noise filter according to claim 21, wherein the magnetic
oxide is a Ni--Cu--Zn ferrite.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to noise filters for
controlling electromagnetic interference and, in particular, to a
noise filter that attenuates noise by absorbing high-frequency
elements.
[0003] 2. Description of the Related Art
[0004] FIG. 26 illustrates a known noise filter 100. The noise
filter 100 includes a metal line 101, electrodes 102 connected to
both ends of the metal line 101, and a case 103. The electrodes 102
are covered with the case 103. The case 103 is made of a ferrite
resin that is a mixture of sintered ferrite powder, which is a
magnetic powder, and a resin. The sintered ferrite is not limited
to the frequency limit line of a magnetic loss .mu." of a complex
permeability represented by .mu.'-j.mu.".
[0005] The noise removal range of the noise filter 100 effectively
extends into the range of several GHz above 1 GHz. Attenuation in
the high-frequency range is expected (Japanese Unexamined Patent
Application Publication No. 2000-91125, FIG. 1).
[0006] FIG. 27 illustrates another known noise filter 110. An
internal conductor 112 is coaxially arranged in and penetrates
through a metal cylinder 111 as a cylindrical external conductor.
The spacing defined by the metal cylinder 111 and the internal
conductor 112 is filled with a composite magnetic material 114
including an Si--Fe based magnetic powder as the major
component.
[0007] The Si--Fe based magnetic powder as the main component of
the composite magnetic material 114 is scaly and has a complex
specific permeability of .mu.r'-j.mu.r" and a complex specific
dielectric constant .epsilon.r'-j.epsilon.r".
[0008] The noise filter 110, which is a distributed parameter
circuit, does not experience the degradation in insertion
attenuation characteristics in GHz bands that a noise filter as a
lumped parameter circuit typically suffers from due to resonance.
The composite magnetic material 114 including the Si--Fe based
magnetic powder maintains .mu.r' in a high frequency range. Along
with this, a peak of the .mu.r" is shifted toward a high frequency
region. As a result, the insertion loss characteristic is
maintained at a satisfactory level from a MHz band to a GHz band.
Reference is made to Japanese Unexamined Patent Application
Publication No. 11-273924 (FIG. 1).
[0009] FIG. 28 illustrates another known noise filter 120. The
noise filter 120 is a low-pass filter that reliably absorbs a
high-frequency element in high frequency regions. The noise filter
120 includes a ground electrode 121, a signal line electrode 122,
and an insulating base 123. The ground electrode 121 and the signal
line electrode 122 are arranged on the insulating base 123. The
insulating base 123 is a composite material, including a mixture of
a ferromagnetic metal powder and an insulating resin.
[0010] The insulating base 123 absorbs unwanted high-frequency
elements in a high-frequency range included in a signal conducted
by the signal line electrode 122. Reference is made to Japanese
Unexamined Patent Application Publication No. 8-78218.
[0011] The known noise filter 100 has the following drawbacks. With
the case 103 made of a magnetic material surrounding the metal line
101, the noise filter 100 functions as an impedance element with
the metal line 101 having an inductance response to the
permeability of the case 103. The noise filter 100, connected in
series with a transmission line such as a printed circuit board,
causes an impedance mismatch, thereby reflecting and thus
controlling noise. The complex permeability .mu.'-j.mu." of the
magnetic material forming the case 103 contributes to the impedance
of the noise filter 100. Noise controlling is achieved in a
frequency range where a magnetic loss .mu." does not occur. In
other words, since insertion loss occurs in a low-frequency range,
low-frequency passband characteristics are adversely affected.
[0012] The noise filters 110 and 120 suffer from the following
drawbacks. The noise filters 110 and 120 include a magnetic powder
in the composite magnetic material 114 and the insulating base 123.
Therefore, the magnetic loss .mu." does not sharply increase, the
insertion loss characteristics do not sharply increase, and a large
attenuation is not achieved in a frequency range above a certain
frequency.
SUMMARY OF THE INVENTION
[0013] To overcome the problems described above, preferred
embodiments of the present invention provide a noise filter having
excellent low-frequency passband characteristics, and provide a
noise filter that has sharply rising insertion loss characteristics
and provides a large attenuation above a certain frequency.
[0014] In a preferred embodiment of the present invention, a noise
filter includes a laminate body including magnetic layers, line
conductors, and ground conductors wherein one of the line
conductors and the ground conductors is disposed in each of the
interfaces between the magnetic layers such that one line conductor
alternates with one ground conductor in lamination, and one ground
conductor is arranged on the top magnetic layer, and another ground
conductor is arranged on the bottom magnetic layer. The magnetic
layer is made of a magnetic oxide, and produces no or very little
attenuation of an electrical signal within a frequency range below
a frequency at which a magnetic loss occurs and attenuates an
electrical signal within a frequency range where the magnetic loss
occurs.
[0015] The noise filter provides a magnetic loss .mu." that sharply
rises with frequency, and greatly attenuates the electrical signal
at a frequency at which the magnetic loss rises. The noise filter
does not attenuate the electrical signal within a frequency range
below the frequency at which the magnetic loss occurs, but
attenuates the electrical signal within a frequency range where the
magnetic loss occurs. An excellent low-frequency passband is thus
achieved.
[0016] The noise filters according to preferred embodiments of the
present invention are now described below.
[0017] In a first preferred embodiment of the present invention, a
noise filter includes a laminate body including magnetic layers,
line conductors, and ground conductors wherein one of the line
conductors and the ground conductors is disposed in each of the
interfaces between the magnetic layers such that one line conductor
alternates with one ground conductor in lamination, and one ground
conductor is arranged on the top magnetic layer and another ground
conductor is arranged on the bottom magnetic layer. The line
conductors disposed between the magnetic layers are serially
connected. The magnetic layer is preferably made of a magnetic
oxide, and the frequency at which the magnetic loss of the magnetic
oxide exceeds 1 is preferably equal to or greater than about 80
MHz. The magnetic layer causes no or very little attenuation of an
electrical signal within a frequency range below a frequency at
which a magnetic loss occurs and attenuates an electrical signal
within a frequency range where the magnetic loss occurs.
[0018] In the noise filter according to the first preferred
embodiment of the present invention, the ground conductor is
disposed on each of the top magnetic layer and the bottom magnetic
layer, and the line conductor and the ground conductor are
alternately disposed in interfaces between the magnetic layers. In
this arrangement, the ground conductor overlaps the entire length
of the line conductor sandwiched between the magnetic layers. This
arrangement confines an electrical signal traveling along the line
conductor on each layer between the ground conductors, thereby
preventing the signal from being attenuated in the passband of the
filter. With the ground conductors arranged on the top and bottom
magnetic layers, the noise filter prevents noise from entering into
the line conductor from the outside, thereby reliably conducting
the electrical signal. If the thickness of all of the magnetic
layers are approximately equal to each other and the width of all
of the line conductors are approximately equal to each other,
characteristic impedances of all of the line conductors are
substantially equal to each other. Since the characteristic
impedances of the line conductors connected in series have an
approximately constant characteristic impedance, noise is not
reflected in the middle of the conductor lines. This arrangement
controls resonance of noise and facilitates impedance matching with
an external circuit. When the line conductors interposed between
the magnetic layers are serially connected, the overall length of a
line path is increased, which increases attenuation of noise
conducted by the conductor line.
[0019] In the first preferred embodiment, the line conductor
preferably has a meandering shape. Alternatively, the line
conductor may have a spiral shape. The line conductors, disposed
between the laminated magnetic layers, define a coil around a
center axis aligned in the direction of lamination of the magnetic
layers. The line conductor having a meandering shape or a spiral
shape provides a length that is greater than the length of the
straight-line conductor, which thereby increases attenuation of
noise. Although a coiled conductor increases the overall thickness
of the noise filter, the area of the bottom surface of the noise
filter is approximately equal to the area of an aperture of the
coil. The noise filter is thus provided in a small mounting area.
In comparison with the straight-line conductor, the coiled
conductor provides an increased length. The attenuation of noise is
increased accordingly.
[0020] In a second preferred embodiment of the present invention, a
noise filter includes a laminate body including magnetic layers.
Each of the top magnetic layer and the bottom magnetic layer
thereof includes a ground conductor. A line conductor and a ground
conductor are alternately disposed in interfaces between the
magnetic layers. Ends of the line conductors disposed between the
magnetic layers are connected to different signal input electrodes,
and the other ends of the line conductors are connected to
different signal output electrodes. The magnetic layer is
preferably made of a magnetic oxide, and the frequency at which the
magnetic loss rises above 1 is equal to or greater than about 80
MHz. The magnetic layer causes no or very little attenuation of an
electrical signal within a frequency range below a frequency at
which a magnetic loss occurs and attenuates an electrical signal
within a frequency range where the magnetic loss occurs.
[0021] The noise filter according to the second preferred
embodiment of the present invention enables each of the line
conductors to function as a low-pass filter, which, together define
a noise filter array. A plurality of line conductors individually
function as independent low-pass filters, and do not include an
impedance mismatch in the middle of the line conductors. In this
arrangement, noise is not reflected in the middle of the conductor
line. This arrangement controls resonance of noise and facilitates
impedance matching with an external circuit.
[0022] In a third preferred embodiment of the present invention,
the line conductors disposed between the magnetic layers have
different characteristic impedances.
[0023] The noise filter is thus impedance matched with a wiring
having a plurality of characteristic impedance types. By connecting
some or all of line conductors in parallel, the number of
characteristic impedance types is increased. This arrangement
increases the number of types of wirings with which the noise
filter is matched.
[0024] In a fourth preferred embodiment of the present invention,
the noise filter further includes dielectric layers having the
ground conductor sandwiched therebetween and magnetic layers having
the line conductor sandwiched therebetween.
[0025] The characteristic impedance of the noise filter is
adjusted, without changing the structure thereof. A resulting
desired characteristic impedance matching with a line of a circuit
board minimizes the effect of signal reflection. Since an
insulating withstand voltage between the line conductor and the
ground conductor is increased, the thickness of the layer between
the line conductor and the ground conductor is reduced, which
reduces the size of the noise filter.
[0026] In accordance with a fifth preferred embodiment of the
present invention, a noise filter includes a magnetic body and at
least two line conductors running alongside each other with a
spacing maintained therebetween on a major surface of the magnetic
body. The magnetic layer is preferably made of a magnetic oxide,
and the frequency at which the magnetic loss of the magnetic oxide
increases above 1 is equal to or greater than 80 MHz. The magnetic
layer causes no or little attenuation on an electrical signal
within a frequency range below a frequency at which a magnetic loss
develops and attenuates an electrical signal within a frequency
range where the magnetic loss develops.
[0027] The noise filter does not attenuate the electrical signal
within a frequency range below the frequency at which the magnetic
loss develops, but attenuates the electrical signal within a
frequency range where the magnetic loss develops. An excellent
low-frequency passband is achieved.
[0028] In accordance with a sixth preferred embodiment of the
present invention, a noise filter includes a magnetic body and at
least a pair of line conductors facing each other on major surfaces
of the magnetic body such that the line conductors sandwich the
magnetic body. The magnetic layer is preferably made of a magnetic
oxide, and the frequency at which the magnetic loss of the magnetic
oxide rises above 1 is equal to or above 80 MHz. The magnetic layer
causes no or little attenuation on an electrical signal within a
frequency range below a frequency at which a magnetic loss develops
and attenuates an electrical signal within a frequency range where
the magnetic loss develops.
[0029] The noise filter does not attenuate the electrical signal
within a frequency range below the frequency at which the magnetic
loss occurs, but attenuates the electrical signal within a
frequency range where the magnetic loss occurs. An excellent
low-frequency passband is achieved.
[0030] The magnetic body preferably includes a hole, which is
filled with one of glass, a resin, and a mixture of glass and a
resin. In this arrangement, without changing the characteristic
impedance, the frequency of the rising edge of the magnetic loss is
adjusted by adjusting apparent permeability and dielectric constant
of the magnetic layer.
[0031] In each of the above-referenced preferred embodiments, ends
of the line conductors are connected to different signal input
electrodes and the other ends of the line conductors are connected
to different signal output electrodes.
[0032] The above and other elements, characteristics, features,
steps and advantages of the present invention will become clear
from the following description of preferred embodiments taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is an exploded perspective view of a noise filter in
accordance with a first preferred embodiment of the present
invention;
[0034] FIG. 2 is a perspective view of the noise filter of the
first preferred embodiment of the present invention;
[0035] FIG. 3 is a graph plotting results of measurement of
frequency dependency of .mu.' and .mu." of samples Nos. 1-3;
[0036] FIG. 4 is a graph plotting results of measurement of
frequency dependency of .mu.' and .mu." of samples Nos. 4-10;
[0037] FIG. 5 is a graph plotting insertion loss versus frequency
characteristics of sample No. 1-3;
[0038] FIG. 6 is a graph plotting insertion loss versus frequency
characteristics of sample No. 4-10;
[0039] FIG. 7 is a graph plotting impedance versus frequency
characteristics;
[0040] FIG. 8 is a graph plotting insertion loss versus frequency
characteristics;
[0041] FIG. 9 is an exploded perspective view illustrating a
modification of the first preferred embodiment of the present
invention;
[0042] FIG. 10 is a perspective view of the modification of the
first preferred embodiment of the present invention;
[0043] FIG. 11 is an exploded perspective view of another
modification of the first preferred embodiment of the present
invention;
[0044] FIG. 12 is an exploded perspective view of yet another
modification of the first preferred embodiment of the present
invention;
[0045] FIG. 13 is an exploded perspective view of a further
modification of the first preferred embodiment of the present
invention;
[0046] FIG. 14 is an exploded perspective view of a noise filter in
accordance with a second preferred embodiment of the present
invention;
[0047] FIG. 15 is a perspective view of the noise filter of the
second preferred embodiment of the present invention;
[0048] FIG. 16 is an exploded perspective view of a noise filter in
accordance with a third preferred embodiment of the present
invention;
[0049] FIG. 17 is a perspective view of the noise filter in
accordance with the third preferred embodiment of the present
invention;
[0050] FIG. 18 is an exploded perspective view of a modification of
the third preferred embodiment of the present invention;
[0051] FIG. 19 is a plan view illustrating another modification of
the third preferred embodiment of the present invention;
[0052] FIG. 20 is an exploded perspective view illustrating yet
another modification of the third preferred embodiment of the
present invention;
[0053] FIG. 21 is an exploded perspective view illustrating a noise
filter in accordance with a fourth preferred embodiment of the
present invention;
[0054] FIG. 22 is a perspective view illustrating the noise filter
in accordance with the fourth preferred embodiment of the present
invention;
[0055] FIG. 23 is a sectional view of the noise filter of FIG. 22
taken along line X-X';
[0056] FIG. 24 is a perspective view of a noise filter in
accordance with a fifth preferred embodiment of the present
invention;
[0057] FIG. 25 is a perspective view of a noise filter in
accordance with a sixth preferred embodiment of the present
invention;
[0058] FIG. 26 is a perspective view of a known noise filter with a
portion thereof broken away;
[0059] FIG. 27 is a sectional view of another known noise filter;
and
[0060] FIG. 28 is a perspective view of yet another known noise
filter.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0061] The noise filter according to preferred embodiments of the
present invention will now be described in detail.
[0062] FIGS. 1 and 2 illustrate a noise filter 1 according to a
first preferred embodiment of the present invention. The noise
filter 1 includes magnetic layers 2a-2h, line conductors 3-5,
ground conductors 6, signal electrodes 7, and ground electrodes
8.
[0063] A prism-like laminate body 2 defining the external outline
of the noise filter 1 preferably includes eight magnetic layers
2a-2h. The laminate body 2 is manufactured by laminating and
pressing substantially rectangular green sheets of a magnetic oxide
material, and then by sintering the laminate.
[0064] The line conductors 3-5 are sandwiched between magnetic
layers 2b and 2c, between magnetic layers 2d and 2e, and between
magnetic layers 2f and 2g, respectively. The band-like line
conductors 3-5, made of an electrically conductive material such as
silver paste or palladium, meander on the surface of the magnetic
layers 2a-2h in the length direction thereof.
[0065] The line conductor 3 between the magnetic layers 2b and 2c
includes, on one end thereof, an electrode portion 3A extending to
longitudinal edges of the magnetic layers 2b and 2c. Arranged on
the other end of the line conductor 3 is a via hole 3B that
penetrates through the magnetic layers 2c and 2d. The line
conductor 4 between the magnetic layers 2d and 2e includes, on one
end thereof, a junction portion 4A that is connected to the line
conductor 3 through the via hole 3B, and has, on the other end
thereof, a via hole 4B that penetrates through the magnetic layers
2e and 2f. The line conductor 5 between the magnetic layers 2f and
2g includes, on one end thereof, a junction portion 5A that is
connected to the line conductor 4 through the via hole 4B. The line
conductor 5 includes, on the other end thereof, an electrode
portion 5B that extends to longitudinal edges of the magnetic
layers 2a-2h. The via holes 3B and 4B are filled with an
electrically conductive material such as a silver paste or
palladium to serially connect the line conductors 3-5. The
electrode portions 3A and 5B are respectively connected to the
signal electrodes 7. The line conductors 3-5 meander along the
width direction of the magnetic layers 2a-2h, although such line
conductors 3-5 are not shown.
[0066] The ground conductors 6 are interposed between the magnetic
layers 2a-2h so that the ground conductors 6 sandwich the line
conductors 3-5. More specifically, the ground conductors 6 are
arranged on the top layer 2b and the bottom layer 2g, and the
ground conductor 6 and the line conductors 3-5 are alternately
arranged in the interfaces between the magnetic layers 2b through
2g.
[0067] The ground conductors 6, which are generally rectangular and
planar and are made of an electrically conductive material such as
a silver paste or palladium, extend over substantially the entire
surface of the magnetic layers 2b-2g. Each of the ground conductors
6 has tongue-like electrode portions 6A that extend in the width
direction to both sides from the central portion in the length
direction of the magnetic layers 2b and 2c. The electrode portions
6A are connected to the ground electrodes 8.
[0068] The signal electrodes 7 are respectively arranged on the two
longitudinal end surfaces of the laminate body 2. The signal
electrodes 7 are arranged to cap the two longitudinal ends of the
laminate body 2 such that the signal electrodes 7 cover not only
the longitudinal end surfaces, but also part of the top surface,
the bottom surface and sidewalls of the laminate body 2. The signal
electrodes 7 are manufactured by applying an electrically
conductive material on the two ends of the laminate body 2, and
baking the electrically conductive material. The signal electrodes
7 are respectively connected to the electrode portions 3A and 5B of
the line conductors 3 and 5.
[0069] The ground electrodes 8 are arranged to cover part of the
sidewalls of the laminate body 2 in the central portion of the
laminate body 2. The ground electrodes 8, having a substantially
U-shape in cross section, extend in a band along the sidewall in
the direction of thickness of the laminate body 2 and partially
cover the top and bottom surfaces of the laminate body 2. The
ground electrodes 8 are manufactured by applying an electrically
conductive material on the sidewalls of the laminate body 2 and
baking the electrically conductive material. The ground electrodes
8 are respectively connected to the electrode portions 6A.
[0070] The operation of the noise filter 1 will now be
described.
[0071] The noise filter 1 is mounted on a circuit board having
signal conducting lines thereon. The signal electrodes 7 are
connected to the lines on the circuit board, and the ground
electrodes 8 are connected to a ground terminal of the circuit
board. A signal is transferred through the line conductors 3-5
while the ground conductors 6 are maintained at a ground
potential.
[0072] The magnetic oxide material forming the magnetic layers
2a-2h develops a magnetic loss .mu." as the frequency of a signal
passing through the line conductors 3-5 increases. The noise filter
1 controls noise due to an absorption characteristic thereof
resulting from the magnetic loss, thereby defining a low-pass
filter.
[0073] The noise filter 1 provides a substantially constant
permeability within a frequency range where no magnetic loss
occurs. The dielectric constant of the noise filter 1 remains
almost constant regardless of frequency changes. Inductance and
capacitance are substantially uniformly distributed along the line
of the noise filter 1. Such a line defines a distributed parameter
circuit and has a characteristic impedance represented by
Zo={square root}(.DELTA.L/.DELTA.C). If the characteristic
impedance of the noise filter 1 matches the characteristic
impedance of a circuit board on which the noise filter 1 is
mounted, no reflection is caused, and the effect of reflection on
the waveform of a signal is effectively controlled.
[0074] The noise control of the noise filter 1 is pronounced at a
frequency where the magnetic loss increases. The magnetic loss
depends on an attenuation coefficient .alpha. of a propagation
constant .gamma.=.alpha.+j.beta. of a transmission line. The use of
the magnetic oxide achieves an insertion loss characteristic that
sharply increases with frequency. To achieve even sharper insertion
loss, the frequency at which the magnetic loss increases above 1 is
preferably set to be at least about 80 MHz.
[0075] A manufacturing method of the magnetic layers 2a-2h is
described below. An Fe.sub.2O.sub.3 powder, a ZnO powder, an NiO
powder, a CuO powder, and a Co.sub.3O.sub.4 powder are preferably
prepared as starting materials.
[0076] Sample Nos. 1-10 having compositions as listed in Table are
prepared by weighing the Fe.sub.2O.sub.3 powder, the ZnO powder,
the NiO powder, the CuO powder, and the Co.sub.3O.sub.4 powder. The
weighed powders are mixed. The mixture is introduced together with
an amount of deionized water that is about 0.5 to about 1.5 times
heavier than the mixture and a dispersant of about 0.5 to about 2.5
weight percent into a ball mill holding PSZ balls of about 50
volume percent, each ball having 1 mm diameter. The mixture is
ball-milled for about 20 hours. The PSZ balls may wear, and about
0.02 to about 0.2 weight percent of ZrO.sub.2 and about 0.0006 to
about 0.006 weight percent of Y.sub.2O.sub.3 may be included in the
mixture. This amount presents no particular problems in noise
filter characteristics. A slurry of the mixture is spray-dried at a
temperature within a range of about 150-250.degree. C., and then
loaded into a box. The dried slurry is pre-sintered at a
temperature of about 700.degree. C. for about two hours. During the
pre-sintering operation, a temperature rising rate during
pre-sintering is about 200.degree. C./h, and a temperature falling
rate is about 200.degree. C./h from about 700.degree. C. to about
500.degree. C. Below about 500.degree. C., the mixture is left to
naturally cool down. A resulting pre-sintered powder as a starting
material is introduced together with an amount of deionized water
that is about 0.5 to about 1.5 times heavier than the pre-sintered
powder and a dispersant of about 1.0-3.0 weight percent into a ball
mill holding PSZ balls of about 50 volume percent, each ball having
a diameter of about 1 mm. The powder is ball-milled for about 48
hours. The PSZ balls may wear, and about 0.05-0.5 weight percent of
ZrO.sub.2 and about 0.0015-0.015 weight percent of Y.sub.2O.sub.3
may be included in the power. This amount of inclusion presents no
particular problem in noise filter characteristics. An acrylic
resin binder is mixed with the slurry subsequent to the milling.
The slurry is then dried, granulated, and then introduced into a
hydraulic press having a molding pressure of about 1700 kg/cm.sup.2
to form a toroidal ring having a diameter of about 20 mm, an inner
diameter of about 10 mm and a height of about 2 mm. The toroidal
ring is then sintered in an atmosphere in a temperature profile
having a peak temperature of about 900.degree. C. Thus, test
samples are produced. The test samples have been measured using an
impedance analyzer (Agilent Technology 4291A) in terms of frequency
dependency of .mu.' and .mu..DELTA.. FIGS. 3 and 4 plot measurement
results.
1 TABLE 1 Composition Frequency at Sample Fe.sub.2O.sub.3 ZnO NiO
CuO Co.sub.3O.sub.4 rise of .mu." No. mol % wt % MHz 1 48.0 29.0
14.5 8.5 0 1.2 2 48.0 27.5 16.0 8.5 0 7.4 3 48.0 26.0 17.5 8.5 0
8.0 4 48.0 25.0 18.5 8.5 0 18.0 5 48.0 10.0 33.5 8.5 0 31.7 6 48.0
5.0 38.5 8.5 0 53.5 7 48.0 1.0 42.5 8.5 0 83.3 8 48.0 25.0 18.5 8.5
2.0 117.2 9 48.0 25.0 18.5 8.5 3.0 247.9 10 48.0 25.0 18.5 8.5 5.0
469.1
[0077] A manufacturing method of the noise filter 1 shown in FIGS.
1 and 2 will now be described.
[0078] The pre-sintered powder produced as described above is
introduced together with an amount of deionized water that is about
0.3 to about 1.0 times heavier than the pre-sintered powder and a
dispersant of about 0.5 to about 3.5 weight percent into a ball
mill holding PSZ balls of about 50 volume percent, each ball having
a diameter of about 1 mm. The powder is ball-milled for about 48
hours. An acrylic binder, a plasticiser, and an antifoaming agent
are added to the powder and then further mixed for about 12 hours.
A resulting slurry is deposited on a PET film to form a band-like
sheet having a thickness of about 10 .mu.m to about 150 .mu.m (for
example, about 100 .mu.m) using a doctor blade. The sheet on the
PET film is then dried by electric heaters in a drying chamber. The
drying temperature is reduced to within a range of about 40.degree.
C. to about 100.degree. C., and a fan is used to blow the air.
Preferably the air is heated. Subsequent to the drying operation,
the band-like sheet is punched into a square sheet having
dimensions of about 100 mm by about 100 mm. A predetermined number
of sheets are then subjected to a screen printing operation to form
a meandering conductor pattern and a ground electrode pattern with
a silver paste. The three meandering conductor patterns are
laminated such that each meandering conductor pattern is sandwiched
between the ground electrodes. The meandering conductor patterns
are connected in series through the via holes. A desired number of
external layer sheets are then laminated. A resulting sheet block
is wrapped in rubber sheets, and is press bonded under a pressure
of about 1000 kg/cm.sup.2 in a hydrostatic press. The number of
external sheets is adjusted such that the thickness of the block is
about 1.5 mm. The laminated and bonded block is then cut to a size
of about 4.0 mm (length).times.about 2.0 mm (width).times.about 1.5
mm (thickness). These blocks are then sintered at a temperature
profile having a peak temperature of about 900.degree. C. The
sintering operation is typically performed in an atmosphere,
however, an excellent sintered block may be obtained in an
atmosphere with an oxygen partial pressure of about 19 volume
percent.
[0079] Subsequent to the sintering operation, the element size is
about 3.2 mm (length).times.about 1.6 mm (width).times.about 1.2 mm
(thickness), and the length of the meandering conductor is about 20
mm. After the sintering operation, an external electrode is
arranged on a chip end to be connected to the meandering conductor,
and a ground external electrode is arranged on the chip sidewall to
be connected to the ground electrode.
[0080] In the first preferred embodiment, the conductor pattern is
printed on each of the sheets. However, to achieve a desired layer
thickness, a plurality of sheets having no printed conductor
patterns may be laminated. The magnetic layer may be formed using a
printing method in which a screen printing operation is repeated
until a magnetic layer having a desired thickness is obtained.
[0081] A completed test sample was connected to a network analyzer
(Agilent Technology 8753D) to measure insertion loss
characteristics. The results of the measurements are shown in FIGS.
5 and 6. FIGS. 5 and 6 show that as the frequency at which the
magnetic loss .mu." increases, the insertion loss characteristics
become steep. Test samples have been produced with the layer
thickness between the meandering conductor pattern and the ground
electrode changed such that the characteristic impedances of test
samples No. 1, No. 2, No. 3, and Nos. 4-10 at the frequency where
the magnetic loss begins to increase (within a frequency range
where .mu.' is a substantially constant value) are about 190
.OMEGA., 130 .OMEGA., 90 .OMEGA., and 50 .OMEGA., respectively.
[0082] Test samples Nos. 4-10 provide excellent insertion loss
characteristics if the magnetic loss increases at a frequency of at
least about 80 MHz.
[0083] The insertion loss characteristics of the test samples are
compared with those of a comparative sample as an impedance
element. The comparative sample (comparative example 1) is
manufactured using the same materials as test sample No. 7 and is
identical in structure to test sample No. 7 except that sheets
having no ground electrodes are laminated. In other words, the
comparative sample includes meandering conductor patterns only in
the chip.
[0084] FIG. 7 illustrates the impedance versus frequency
characteristics of this element. FIG. 8 plots the insertion losses
of test sample No. 7 and the comparative example 1 in
comparison.
[0085] Although being made of the same magnetic materials, the
comparative example 1 suffers from insertion loss in a frequency
range where .mu." does not occur. Above about 500 MHz, impedance
drops due to stray capacitance between terminal electrodes and the
insertion loss also drops. In test sample No. 7, insertion loss
occurs from the frequency where .mu." increases and the effect of
insertion loss is maintained at high frequencies in the GHz
range.
[0086] The first preferred embodiment preferably uses an Ni--Cu--Zn
based sintered ferrite. Alternatively, one of an Mg--Cu--Zn based
ferrite, an Ni--Mg--Cu--Zn based ferrite, and a Cu--Zn based
ferrite may be used.
[0087] FIGS. 9 and 10 illustrate a modification of the first
preferred embodiment of the present invention. In the modification,
each ground conductor 6 has a bifurcated electrode portion 6A
extending to each of longitudinal edges of the magnetic layer 2b
and 2c as shown in FIG. 9. As shown in FIG. 10, a signal electrode
7 is arranged on each of the two longitudinal ends of a laminate
body 2 in the central portion along the width direction thereof.
Ground electrodes 8 are arranged on both sides of each signal
electrode 7. The signal electrodes 7 are respectively spaced apart
from the ground electrodes 8 by a desired distance. The
modification of the first preferred embodiment is specifically
intended for connection with a coplanar guide.
[0088] FIG. 11 illustrates another modification of the first
preferred embodiment. As shown, the modification includes straight
line conductors 3-5.
[0089] FIG. 12 illustrates yet another modification of the first
preferred embodiment of the present invention. As shown, the
modification includes spiral line conductors 3-5.
[0090] FIG. 13 illustrates a further modification of the first
preferred embodiment of the present invention. As shown, the
modification includes substantially U-shaped line conductors 3-5
having bending portions. With the magnetic layers laminated, the
line conductors 3-5, sandwiched between the magnetic layers, form a
coil around a center axis extending in the direction of lamination
of the magnetic layers.
[0091] As shown in FIGS. 9-13, elements that are identical to those
shown in FIG. 1 are designated with the same reference numerals,
and the discussion thereof is omitted here.
[0092] FIGS. 14 and 15 illustrate a noise filter 11 in accordance
with a second preferred embodiment of the present invention. The
noise filter 11 of the second preferred embodiment of the present
invention includes a first line conductor and a second line
conductor on the same surface of each layer. The first and second
line conductors, and the ground conductor are alternately laminated
in the interfaces between the magnetic layers. The plurality of
first line conductors are serially connected, and the plurality of
second line conductors, separately arranged from the first line
conductors, are serially connected.
[0093] More specifically, the noise filter 11 of the second
preferred embodiment includes, as the major elements thereof,
magnetic layers 12a-12j, first line conductors 13-16, second line
conductors 17-20, ground conductors 21, first signal electrodes 22,
and second signal electrodes 23.
[0094] A prism-like laminate body 12 defines the external outline
of the noise filter 11 and is manufactured by laminating ten
magnetic layers 12a-12j. Each of the magnetic layers 12a-12j is
preferably substantially rectangular and made of a magnetic oxide
material.
[0095] The first line conductors 13-16 are arranged on four layers,
specifically, between the magnetic layers 12b and 12c, between the
magnetic layers 12d and 12e, between the magnetic layers 12f and
12g, and between the magnetic layers 12h and 12i. Each of the line
conductors 13-16, made of an electrically conductive material, has
a spiral shape. The first conductors 13-16 face each other in the
direction of thickness of the laminate body 12.
[0096] The line conductor 13 has, on one end thereof, an electrode
portion 13A that extends to a longitudinal end of the laminate body
12, and, on the other end thereof, a via hole 13B that is located
at the approximate center of the spiral shape, and penetrates the
magnetic layers 12c and 12d.
[0097] The line conductor 14 has, on one end thereof, a junction
portion 14A that is located at the approximate center of the spiral
shape, and is connected to the line conductor 13 through the via
hole 13B. The line conductor 14 has, on the other end thereof, a
via hole 14B that is located at the external end of the spiral
shape and penetrates through the magnetic layers 12e and 12f.
Likewise, the line conductor 15 has, on one end thereof, a junction
portion 15A that is located at the external end of the spiral shape
and, on the other end thereof, a via hole 15B that is located at
the approximate center of the spiral shape.
[0098] The line conductor 16 has, on one end thereof, a junction
portion 16A that is located at the approximate center of the spiral
shape and is connected to the line conductor 15 through the via
hole 15B. The line conductor 16 has, on the other end, an electrode
portion 16B that is located at the external end of the spiral
shape, particularly, at the longitudinal end of the laminate body
12.
[0099] The via holes 13B, 14B, and 15B are filled with an
electrically conductive material such as a silver paste or
palladium, and the line conductors 13-16 are serially
connected.
[0100] The second line conductors 17-20 are arranged on four
magnetic layers, more specifically, between the magnetic layers 12b
and 12c, between the magnetic layers 12d and 12e, between the
magnetic layers 12f and 12g, and between the magnetic layers 12h
and 12i. The locations of the second line conductors 17-20 are
shifted from the first line conductors 13-16 in a length direction
of the laminate body 12, and are respectively insulated from the
first line conductors 13-16. Each of the second line conductors
17-20, made of an electrically conductive material, has a spiral
shape. The second line conductors 17-20 face each other in the
direction of thickness of the laminate body 12.
[0101] The second line conductors 17-20 are substantially identical
in shape to the first line conductors 13-16. The second line
conductor 17 has, on one end thereof, an electrode portion 17A and,
on the other end thereof, a via hole 17B. Likewise, the second line
conductors 18 and 19 have, respective ends thereof, junction
portions 18A and 19A and, on the other ends thereof, via holes 18B
and 19B. The second line conductor 20 has, on one end thereof, a
junction portion 20A and, on the other end thereof, an electrode
portion 20B.
[0102] The via holes 17B, 18B and 19B are filled with an
electrically conductive material such as a silver paste or
palladium, and are serially connected.
[0103] The ground conductors 21 are arranged between the magnetic
layers 12a-12j such that the first line conductors 13-16 and the
second line conductors 17-20 are sandwiched therebetween. One
ground conductor 21 is arranged on the top magnetic layer 12b,
another ground conductor 21 is arranged on the bottom magnetic
layer 12j, and further each of the remaining ground conductors 21
alternates with a corresponding one of the first line conductors
13-16 and a corresponding one of the second line conductors 17-20
in arrangement in the interfaces between the magnetic layers
12b-12i.
[0104] The ground conductors 21, made of an electrically conductive
material, are substantially rectangular, and substantially cover
one entire surface of the respective magnetic layers 12b-12i. Like
the ground conductors 6 in accordance with the first preferred
embodiment, each of the ground conductors 21 includes electrode
portions 21A that projects toward the longitudinal end of the
laminate body 12. The electrode portions 21A are connected to
ground electrodes 24.
[0105] The first signal electrodes 22 are arranged on both
sidewalls of the laminate body 12 (the magnetic layers 12a-12j)
closer to the longitudinal end of the laminate body 12. The first
signal electrodes 22, made of an electrically conductive material,
are connected to signal lines. One first signal electrode 22 is
connected to the electrode portion 13A of the line conductor 13
while the other first signal electrode 22 is connected to the
electrode portion 16B of the line conductor 16.
[0106] The second signal electrodes 23 are arranged on both
sidewalls of the laminate body 12 (the magnetic layers 12a-12j).
The locations of the second signal electrode 23, made of an
electrically conductive material, are shifted from those of the
first signal electrodes 22 in the longitudinal direction of the
laminate body 12, and isolated from the first signal electrodes 22.
One second signal electrode 23 is connected to the electrode
portion 17A of the second line conductor 17 while the other second
signal electrode 23 is connected to the electrode portion 20B of
the second line conductor 20.
[0107] One first signal electrode 22 and one signal electrode 23
define signal input electrodes, and the other first signal
electrode 22 and the other second signal electrode 23 define signal
output electrodes. Alternatively, one first signal electrode 22 and
one second signal electrode 23 may define the signal output
electrodes, and the other first signal electrode 22 and the other
second signal electrode 23 may define the signal input
electrodes.
[0108] The ground electrodes 24 are arranged on both longitudinal
ends of the laminate body 12. The ground electrodes 24, made of an
electrically conductive material, are connected to the electrode
portions 21A of the ground conductors 21.
[0109] The second preferred embodiment provides substantially the
same advantages as the first preferred embodiment. Since the first
line conductors 13-16 are electrically isolated from the second
line conductors 17-20, a single laminate body 12 includes a
low-pass filter defined by the first line conductors 13-16 and
another low-pass filter defined by the second line conductors
17-20. The noise filter 11 is thus a noise filter array including
the two low-pass filters. Compared to using two separate low-pass
filters, the noise filter 11 provides a compact design because the
ground conductors 21, and the ground electrodes 24 are shared by
the two low-pass filters.
[0110] FIGS. 16-17 illustrate a noise filter 31 in accordance with
a third preferred embodiment of the present invention.
[0111] In the noise filter 31 of the third preferred embodiment of
the present invention, a line conductor alternates with a ground
conductor in interfaces between laminated magnetic layers with each
of the top and bottom magnetic layer having the ground conductor
thereon. Ends of the plurality of line conductors are connected to
different signal input electrodes, and the other ends of the
plurality of line conductors are connected to different signal
output electrodes.
[0112] More specifically, the noise filter 31 of the third
preferred embodiment of the present invention includes magnetic
layers 32a-32j, a first line conductor 33 through a fourth line
conductor 36, ground conductors 37, first signal electrodes 38
through fourth signal electrodes 41, and ground electrodes 42.
[0113] A prism-like laminate body 32 defines the external outline
of the noise filter 31. The laminate body 32 includes ten magnetic
layers 32a-32j. The magnetic layers 32a-32j preferably have a
substantially rectangular and planar shape, and are preferably made
of a magnetic oxide material.
[0114] The first line conductor 33 is arranged between the magnetic
layers 32b and 32c. The first line conductor 33, in a narrow band
configuration and made of an electrically conductive material,
meanders in several turns in the width direction of the laminate
body 32. The first line conductor 33 has, on both ends thereof,
electrode portions 33A reaching the sidewalls of the laminate body
32. The electrode portions 33A are arranged closer to one
longitudinal end of the laminate body 32.
[0115] The second line conductor 34 is arranged between the
magnetic layers 32d and 32e. The second line conductor 34 has
substantially the same dimensions as the first line conductor 33.
The second line conductor 34, in a narrow band configuration and
made of an electrically conductive material, meanders in several
turns in the width direction of the laminate body 32. The second
line conductor 34 has, on both ends thereof, electrode portions 34A
extending to the sidewalls of the laminate body 32. The locations
of the electrode portions 34A are shifted from those of the first
electrode portion 33A to be closer to the center of the sidewall of
the laminate body 32 in the longitudinal direction thereof.
[0116] The third line conductor 35 is arranged between the magnetic
layers 32f and 32g. The third line conductor 35 preferably has
substantially the same dimensions as the first line conductor 33.
Like the first line conductor 33, the third line conductor 35, made
of an electrically conductive material, meanders in several turns.
The third line conductor 35 has, on both ends thereof, electrode
portions 35A extending to the sidewalls of the laminate body 32.
The location of the electrode portion 35A is shifted from those of
the first electrode portion 33A and the second electrode portion
34A, and for example, is located between the second electrode
portion 34A and the other longitudinal end of the laminate body
32.
[0117] The fourth line conductor 36 is arranged between the
magnetic layers 32h and 32i. The fourth line conductor 36 has
substantially the same dimensions as the first line conductor 33.
Like the first line conductor 33, the fourth line conductor 36,
made of an electrically conductive material, meanders in several
turns. The fourth line conductor 36 has, on both ends thereof,
electrode portions 36A extending to the sidewalls of the laminate
body 32. The location of the electrode portion 36A is shifted from
those of the first electrode portion 33A, the second electrode
portion 34A and the third electrode position 35A, and for example,
is located closer to the other longitudinal end of the laminate
body 32.
[0118] Each of the ground conductors 37 is arranged between the
magnetic layers 32a-32j such that the first through fourth line
conductors 33-36 are respectively sandwiched therebetween. Ground
conductors 37 are respectively arranged on the top and bottom
magnetic layers 32b and 32i, and each of the remaining ground
conductors 37 alternates with each of the line conductors 33-36 in
the interfaces between the magnetic layers 32b-32i.
[0119] The ground conductors 37, which are substantially
rectangular and planar and are made of an electrically conductive
material, substantially cover the magnetic layers 32b-32i. Similar
to the ground conductor 6 in the first preferred embodiment, each
ground conductor 37 includes electrode portions 37A projecting
toward both longitudinal ends of the laminate body 32. The
electrode portions 37A are connected to the ground electrodes
42.
[0120] The first through fourth signal electrodes 38-41 are made of
an electrically conductive material. The first through fourth
signal electrodes 38-41 include respective pairs of electrode
portions, arranged on both sidewalls along the direction of length
of the laminate body 32. The first through fourth signal electrodes
38-41 are located at different positions along the direction of
length of the laminate body 32, for example, on the sidewalls from
one longitudinal end to the other longitudinal end of the laminate
body 32, and are isolated from each other.
[0121] The first signal electrodes 38 are respectively connected to
the electrode portions 33A of the first line conductor 33, the
second signal electrodes 39 are respectively connected to the
electrode portions 34A of the second line conductor 34, the third
signal electrodes 40 are respectively connected to the third line
conductors 35A of the third line conductor 35, and the fourth
signal electrodes 41 are respectively connected to the electrode
portions 36A of the fourth line conductor 36.
[0122] Of the first through fourth pairs of signal electrodes
38-41, one terminal defines a signal input terminal, and the other
terminal defines a signal output terminal.
[0123] The ground electrodes 42 are arranged on both longitudinal
ends of the laminate body 32. The ground electrodes 42 are made of
an electrically conductive material, and are connected to the
electrode portions 37A of the ground conductors 37.
[0124] The third preferred embodiment of the present invention
provides substantially the same advantages as the first preferred
embodiment of the present invention. Since the plurality of line
conductors 33-36 are respectively connected to different signal
electrodes 38-41 in accordance with the third preferred embodiment
of the present invention, the plurality of line conductors 33-36
define different low-pass filters. The line conductors 33-36
together define a noise filter array.
[0125] Since the plurality of line conductors 33-36 define
respective low-pass filters in accordance with the third preferred
embodiment of the present invention, the number of low-pass filters
is increased by merely increasing the number of magnetic layers
32a-32j. Even if a large number of low-pass filters are arranged in
the noise filter 31, the noise filter 31 remains compact.
[0126] Since no via holes are used, the third preferred embodiment
is free from impedance mismatch caused by open via holes. Thus, no
noise reflection is produced in the middle of the line conductors
33-36, noise resonance is controlled, and impedance matching with
an external circuit is facilitated. Since no via holes are drilled
in the magnetic layers 32a-32j, the magnetic layers 32a-32j are
substantially covered with the first line conductors 33-36. This
arrangement enables the line conductors 33-36 to be lengthened,
thereby increasing noise attenuation. Since no via hole drilling
operation is required, the manufacturing process of the noise
filter 31 is simplified, and the manufacturing costs of the noise
filter 31 are reduced.
[0127] In accordance with the third preferred embodiment of the
present invention, the arrangement of each of the ground conductors
37 between the line conductors 33-36 prevents cross-talk from
taking place between adjacent line conductors 33-36. An electrical
signal is thus reliably transferred.
[0128] Since the plurality of line conductors 33-36 on respective
layers are isolated from each other, there is no need to arrange
the input signal electrodes 38-41 so as to face the output signal
electrodes 38-41. The plurality of line conductors 33-36 are
arranged independently and freedom of design is assured.
[0129] FIG. 18 illustrates a modification of the third preferred
embodiment of the present invention. As shown, the line conductors
33-36 are straight lines.
[0130] FIG. 19 illustrates another modification of the third
preferred embodiment of the present invention. As shown, the line
conductors 33-36 have a spiral shape.
[0131] FIG. 20 illustrates yet another modification of the third
preferred embodiment of the present invention. In this
modification, the line widths of the line conductors 33-36 are
different. The plurality of line conductors 33-36 having different
characteristic impedances are impedance matched to external lines
having a plurality of characteristic impedances when the line
conductors 33-36 are connected to the external lines. The plurality
of line conductors 33-36 having different characteristic impedances
define low-pass filters having four types of characteristic
impedances which depend upon the number of layers having the line
conductors 33-36 when the line conductors 33-36 are used
independently.
[0132] When two layers, three layers or all layers (four layers) of
the plurality of line conductors 33-36 are used in a parallel
connection, a plurality of types (10 types, for example) of
characteristic impedances are achieved. As compared to the case in
which the line conductors 33-36 are set to have same characteristic
impedance, the number of types of characteristic impedances is
large, and the number of types of matching lines is thus
increased.
[0133] In the third preferred embodiment, not only the line width
of the line conductors 33-36, but also the width dimensions of the
magnetic layers 32b-32i may be different from each other to
differentiate the characteristic impedance of each low-pass filter.
Both the line width of the line conductors 33-36 and the thickness
of the magnetic layers 32b-32i may be different from each
other.
[0134] FIGS. 21-23 illustrate a noise filter 51 in accordance with
a fourth preferred embodiment of the present invention. The noise
filter 51 of the fourth preferred embodiment includes a dielectric
layer between magnetic layers.
[0135] The noise filter 51 of the fourth preferred embodiment
includes magnetic layers 53a-53f, dielectric layers 54a-54h, line
conductors 55-57, ground conductors 58, signal electrodes 59, and
ground electrodes 60.
[0136] The prism-like laminate body 52 defines the external outline
of the noise filter 51. The laminate body 52 is manufactured by
pressing the six magnetic layers 53a-53f and the eight dielectric
layers 54a-54h in the alternately laminated state thereof, and then
by sintering the laminate of the six magnetic layers 53a-53f and
the eight dielectric layers 54a-54h.
[0137] The magnetic layers 53a-53f and the dielectric layers
54a-54h are laminated such that two magnetic layers alternate with
two dielectric layers. The line conductor 55 is arranged between
the magnetic layers 53a and 53b, the line conductor 56 is arranged
between the magnetic layers 53c and 53d, and the line conductor 57
is arranged between the magnetic layers 53e and 53f. The ground
conductors 58 are respectively arranged between the dielectric
layers 54a and 54b, between the dielectric layers 54c and 54d,
between the dielectric layers 54e and 54f, and between the
dielectric layers 54g and 54h.
[0138] The magnetic layers 53a-53f are substantially rectangular
and planar and are made of an electrically conductive material. The
dielectric layers 54a-54h are substantially rectangular and planar
and are made of a dielectric material.
[0139] The order of lamination and the number of magnetic layers
53a-53f and the dielectric layers 54a-54h are not limited to the
fourth preferred embodiment of the present invention. For example,
any layer having no conductor pattern printed thereon may be
interposed between the magnetic layers 53a-53f and the dielectric
layers 54a-54h.
[0140] The remainder of the structure of the noise filter 51 of the
fourth preferred embodiment is unchanged from the first preferred
embodiment of the present invention and a further discussion of the
fourth preferred embodiment is omitted.
[0141] The fourth preferred embodiment provides substantially the
same advantages as the first preferred embodiment of the present
invention. Since the dielectric layer is interposed between the
magnetic layers in the fourth preferred embodiment, a noise filter
with adjustable characteristic impedance is provided without
significantly changing the structure of the noise filter.
[0142] The characteristic impedance Zo of the noise filters of
preferred embodiments of the present invention is expressed by
Zo={square root}(.DELTA.L/.DELTA.C), and is determined by an
inductance of the line conductor and a capacitance between the line
conductor and the ground conductor. More specifically, if the
dielectric constant of the dielectric layer is less than the
dielectric constant of the magnetic layer with the dielectric layer
interposed between the magnetic layers in the noise filter 51, the
characteristic impedance of the noise filter 51 is high as compared
to a noise filter that includes only magnetic layers without any
dielectric layer. If the dielectric constant of the dielectric
layer is greater than the dielectric constant of the magnetic
layer, the characteristic impedance of the noise filter 51 is low
as compared to a noise filter that includes only magnetic layers
without any dielectric layer. In view of this fact, the
characteristic impedance of the noise filter 51 is matched to the
characteristic impedance of a circuit board on which the noise
filter 51 is to be mounted. The effect of signal reflection is
effectively controlled.
[0143] Since dielectric materials typically have a higher
insulating withstand voltage than magnetic materials, the noise
filter 51 has increased insulating withstand voltage between the
line conductor and the ground conductor. In the noise filter 51,
the dielectric layers sandwich the ground conductor, and the
magnetic layers sandwich the line conductor. This arrangement
reduces the thickness of the layer between the line conductor and
the ground conductor. A compact noise filter 51 is thus
achieved.
[0144] FIG. 24 illustrates a noise filter 71 in accordance with a
fifth preferred embodiment of the present invention. As shown, the
noise filter 71 of the fifth preferred embodiment of the present
invention includes a magnetic body 72 and line conductors 73a and
73b that are arranged at the same level on the surface of the
magnetic body 72 and extend alongside each other with a space
maintained therebetween.
[0145] The fifth preferred embodiment of the present invention thus
constructed provides substantially the same advantages as the first
preferred embodiment of the present invention.
[0146] FIG. 25 illustrates a noise filter 71 in accordance with a
sixth preferred embodiment of the present invention. As shown, the
noise filter 71 of the sixth preferred embodiment includes line
conductors 73a and 73b that face each other with a magnetic body 72
interposed therebetween.
[0147] The sixth preferred embodiment of the present invention
provides substantially the same advantages as the first preferred
embodiment of the present invention.
[0148] In the noise filters of preferred embodiments of the present
invention, cavities may be provided in the magnetic layer and the
cavities may be filled with one of glass, a resin, or a composite
material containing glass and a resin.
[0149] The method of manufacturing the magnetic layer will now be
discussed with reference to the discussion of the first preferred
embodiment of the present invention.
[0150] The magnetic body having cavities is produced by adding
beads in a pre-sintered powder and the rest of the manufacturing
process of the magnetic layers is the same as the first preferred
embodiment. The magnetic body having the cavities therein is thus
obtained. More specifically, a resin or carbon that disperses
during a sintering process is used for the beads. The diameter of
the beads preferably ranges from several .mu.m to several tens of
.mu.m. The size of cavities is proportional to the diameter of the
beads. The amount of the beads added determines the volume of the
cavities in the magnetic body. The diameter and the amount of the
beads are adjusted depending upon the volume of the glass, the
resin, or the composite material of glass and resin that fills the
cavities. The formation method of the cavities may be applied to
the noise filter 1 illustrated in FIGS. 1 and 2, the noise filter 1
illustrated in FIGS. 9-13, the noise filter 11 illustrated in FIGS.
14 and 15, the noise filter 31 illustrated in FIG. 16 and FIG. 17,
the noise filter 31 illustrated in FIG. 18, the noise filter 31
illustrated in FIG. 20, the noise filter 51 illustrated in FIGS. 21
and 22, the noise filter 71 illustrated in FIG. 24, and the noise
filter 71 illustrated in FIG. 25.
[0151] This preferred embodiment of the present invention provides
substantially the same advantage as the first preferred embodiment
of the present invention. In this preferred embodiment, the
cavities are provided in the magnetic body made of the magnetic
oxide material and are filled with the glass, the resin, or the
composite material of glass and resin. The frequency at which the
magnetic loss .mu." increases is adjusted without changing the
characteristic impedance by adjusted apparent permeability and
dielectric constant.
[0152] As the permeability .mu. of the magnetic material is
changed, the frequency at which the magnetic loss .mu." increases
changes. In the noise filters of preferred embodiments of the
present invention, the permeability of the magnetic oxide material
must be changed to change the frequency at which the magnetic loss
rises. The characteristic impedance Zo of the noise filters of
preferred embodiments of the present invention is expressed by
Zo={square root}(.DELTA.L/.DELTA.C), and is determined by an
inductance of the line conductor and a capacitance between the line
conductor and the ground conductor. If the permeability of the
magnetic oxide material is changed, the characteristic impedance Zo
also changes.
[0153] In this preferred embodiment of the present invention, the
cavities are formed in the magnetic layers, and then the cavities
are filled with the glass, the resin, or the composite material of
glass and resin. By adjusting the dielectric constant .epsilon. of
the glass, the resin, or the composite material of glass and resin,
a noise filter having the same characteristic impedance but a
different frequency at which the magnetic loss increases is
produced.
[0154] The present invention is not limited to each of the
above-described preferred embodiments, and various modifications
are possible within the range described in the claims. An
embodiment obtained by appropriately combining technical features
disclosed in each of the different preferred embodiments is
included in the technical scope of the present invention.
* * * * *