Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2000-05-08
2002-08-20
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S204000
Reexamination Certificate
active
06437665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LC filter, and more particularly, to a laminated LC filter for use with high frequencies.
2. Description of the Related Art
In general, a band pass filter that allows a signal of a specific frequency band to pass through includes a plurality of LC resonators. A configuration of one example of a conventional band pass filter is shown in FIG.
13
. As shown in
FIG. 13
, the band pass filter
1
includes the first and second stage LC resonators Q
1
and Q
2
within a laminate body constructed of layered ceramic sheets
3
.
The inductances of the LC resonators Q
1
and Q
2
are generated by the inductor patterns
4
a
,
4
b
,
5
a
, and
5
b
. The capacitances of the LC resonators Q
1
and Q
2
are generated by the capacitor patterns
6
a
to
6
c
,
7
a
to
7
c
, and the inductor patterns
4
a
,
4
b
,
5
a
, and
5
b
are arranged on the surface of the ceramic sheets
3
such that the inductor patterns
4
a
,
4
b
,
5
a
, and
5
b
do not contact the capacitor patterns
6
a
to
6
c
,
7
a
to
7
c
. The above-described LC resonators Q
1
and Q
2
are electro-magnetically coupled together.
A leading edge of the inductor pattern
4
a
is connected to an input lead pattern
14
that is provided on a left side of the sheet
3
. A leading edge of the inductor pattern
5
a
is connected to an output lead pattern
15
that is provided on a right side of the sheet
3
. The inductor patterns
4
a
,
4
b
,
5
a
, and
5
b
and the capacitor patterns
6
a
to
6
c
and
7
a
to
7
c
are arranged in a layered configuration with alternating layers. The shielding patterns
12
a
and
12
b
are provided on either side of this layered configuration.
FIGS. 14 and 15
illustrate another example of a conventional laminated band pass filter. This band pass filter
21
includes first and second stage LC resonators Q
1
and Q
2
within a laminate body
41
constructed of layered ceramic sheets
23
.
The inductances of the LC resonators Q
1
and Q
2
are generated by the inductor patterns
24
and
25
. The capacitances of the LC resonators Q
1
, Q
2
are generated by the capacitor patterns
26
and
27
, and the leading edges
24
a
and
25
a
of the inductor patterns
24
and
25
are arranged on the surface of the ceramic sheets
23
such that the inductor patterns
24
and
25
do not contact the capacitor patterns
26
and
27
. The above-described LC resonators Q
1
and Q
2
are electrically coupled by a coupling capacitor that is provided by these inductor patterns
24
and
25
and the coupling capacitor pattern
28
that is located opposite to these inductor patterns
24
and
25
. These LC resonators Q
1
and Q
2
are capacitive-coupled to an input lead pattern
29
and an output lead pattern
30
, respectively. The shielding patterns
32
a
and
32
b
are provided on either side of the layered patterns
24
to
30
.
In the laminated body
41
, an input terminal electrode
42
, an output terminal electrode
43
and shielding terminal electrodes
44
and
45
are provided as shown in FIG.
15
. An input lead pattern
29
is connected to the input terminal electrode
42
, and an output lead pattern
30
is connected to the output terminal electrode
43
. The lead portions of the inductor patterns
24
and
25
and the end portions of the shielding pattern
32
a
and
32
b
are connected to the shielding terminal electrode
44
. The lead portions of the capacitor patterns
26
and
27
and the other end portions of the shielding pattern
32
a
and
32
b
are connected to the shielding terminal electrode
45
.
The band pass filter
1
as shown in
FIG. 13
is laminated such that the inductor patterns
4
a
to
5
b
are sandwiched by the capacitor patterns
6
a
to
6
c
,
7
a
to
7
c
, so that electric currents flow into each of the inductor patterns
4
a
,
4
b
,
5
a
, and
5
b
from two capacitor patterns arranged on both sides. Accordingly, the amount of electric current (a current density) flowing through the inductor patterns
4
a
to
5
b
increases. As a result, relatively poor Q characteristics of the LC resonators Q
1
are Q
2
are produced.
Further, in the band pass filter
21
as shown in
FIGS. 14 and 15
, the magnetic field H generated in the vicinity of the inductor patterns
24
and
25
does not effectively utilize the area S enclosed by a dotted line in
FIG. 16
as a magnetic path. As a result, the inductances of the LC resonators Q
1
and Q
2
are small. Additionally, because the magnetic field H is concentrated at the edges of the inductor patterns
24
and
25
, substantial eddy current loss arises, and thus, poor Q characteristics are produced.
Moreover, as shown in
FIG. 17
, the magnetic field H generated in the vicinity of the inductor patterns
24
and
25
is blocked by the coupling capacitor pattern
28
and the input/output lead patterns
29
,
30
. Accordingly, the inductances of the LC resonators Q
1
, Q
2
are also reduced.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a laminated LC filter having a greatly increased inductance and an excellent Q characteristic.
According to one preferred embodiment of the present invention, a laminated LC filter includes a laminated body including a plurality of insulation layers stacked on each other, a plurality of inductor patterns, and a plurality of capacitor patterns. The laminated LC filter further includes a plurality of LC resonators having a plurality of inductors constructed of inductor patterns, and a plurality of capacitors in which capacitor patterns are arranged such that the capacitor patterns do not contact the inductor patterns, at an inside of the laminated body. The inductor of each LC resonator has a multiplex structure defined by laminating two or more of the inductor patterns having approximately the same shapes via the insulation layers, and coupling capacitor patterns for capacitive-coupling between the LC resonators are laminated between the inductor patterns of the inductors.
In one preferred embodiment of the present invention, capacitor patterns for an input/output are laminated between the inductor patterns of the inductors.
Preferably, three or more stages of filters are provided by connecting at least three of the LC resonators. The pattern widths of the inductor patterns defining the LC resonators at locations other than both ends thereof are wider than the pattern widths of the inductor patterns defining the LC resonators at both end locations. Further, the pattern widths of the inductor patterns defining the LC resonators are reduced at the ends thereof.
A preferred embodiment of the present invention further includes patterns for pole adjustment which are laminated between the inductor patterns of the inductors.
With the above-described configuration, no magnetic field is generated between two or more of the inductor patterns having approximately identical shapes which constitute the respective inductors. Further coupling capacitor patterns and/or capacitor patterns for an input/output that are arranged between the inductor patterns do not block the magnetic field of the inductors.
Moreover, by constructing the inductor to have a multiplex structure, the magnetic field generated in the vicinity of the inductor is alleviated from being concentrated at the edge of the inductor patterns. Further, the inductor patterns in the respective LC resonators correspond to the capacitor patterns at least one-to-one. As a result, the amount of electric current flowing into the respective inductor patterns from the capacitor patterns is much less than in the conventional LC filter. Accordingly, the current density flowing through the inductor patterns is reduced, and the Q characteristic of the respective LC resonators is greatly improved.
Further, the laminated LC filter according to a preferred embodiment of the present invention includes three or more stages of filters which are constructed by connecting at least three of the
Bettendorf Justin P.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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