Laminated LC filter

Details Laminated LC filter Laminated LC filter

2000-05-08

2002-07-23

Bettendorf, Justin P. (Department: 2817)

Wave transmission lines and networks

Coupling networks

Frequency domain filters utilizing only lumped parameters

C333S184000

Reexamination Certificate

active

06424235

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LC filter, and more particularly, to a high frequency laminated LC filter.
2. Description of the Related Art
In general, a circuit structure of a band pass filter having three or more stages that transmits a signal having a specific frequency is shown in FIG.
8
. The band pass filter is a three-stage band pass filter having LC resonators Q
1
to Q
3
of the first to third stages. These LC resonators Q
1
to Q
3
are such that the adjacent resonators are electrically coupled by the coupling capacitors Cs
1
, Cs
2
.
FIGS. 9
to
11
show conventional laminated band pass filter configurations used in the circuit structure described above. LC filter
1
illustrates a conventional filter used for LC resonators Q
1
to Q
3
of the first to the third stages. The laminate body
21
is constructed by stacking up the square shaped ceramic sheets
2
. LC resonators Q
1
to Q
3
of the circuit shown in
FIG. 8
include LC filters as shown in FIG.
9
.
The inductors L
1
to L
3
of the LC resonators Q
1
to Q
3
, respectively, include inductor patterns
3
,
4
,
5
as shown in FIG.
9
. The inductor patterns
3
,
4
,
5
have the same pattern widths. The capacitors C
1
to C
3
of the LC resonators Q
1
to Q
3
, respectively, are defined by the capacitor patterns
9
,
10
,
11
, and leading edges
6
,
7
,
8
of the inductor patterns
3
,
4
,
5
that are disposed opposite to these capacitor patterns
9
,
10
,
11
. The above-described LC resonators Q
1
to Q
3
are electrically connected by the coupling capacitors Cs
1
, Cs
2
that are defined by the capacitor patterns
9
to
11
and the coupling capacitor patterns
12
,
13
that are disposed opposite these capacitor patterns
9
to
11
. These LC resonators Q
1
and Q
3
are capacitive-coupled to the capacitor pattern
14
to provide an input, and to the capacitor pattern
15
to provide an output, respectively. The shielding patterns
16
a
,
16
b
are arranged to sandwich these patterns
3
to
5
,
9
to
15
.
In the laminated body
21
, an input terminal electrode
26
, an output terminal electrode
27
and shielding terminal electrodes
28
,
29
as shown in
FIG. 10
are provided. The capacitor pattern
14
defining the input is connected to the input terminal electrode
26
, and the capacitor pattern
15
defining the output is connected to the output terminal electrode
27
. The lead portions of the inductor patterns
3
,
4
,
5
and one end portion of the shielding pattern
16
a
,
16
b
are connected to the shielding terminal electrode
28
. The lead portions of the capacitor patterns
9
to
11
and the other end portion of the shielding pattern
16
a
,
16
b
are connected to the shielding terminal electrode
29
.
In general, the inductor pattern
4
that defines the LC resonator Q
2
at the second stage which located at the center is such that the magnetic field concentration at the pattern edge is larger, than the magnetic field concentration of the inductor patterns
3
,
5
that define the LC resonators Q
1
, Q
3
at the first and third stages which are located at the ends. Accordingly, a current density flowing through the inductor pattern
4
becomes larger than a current density flowing through the inductor patterns
3
,
5
, and thus, the current density produced is not uniform. As a result, an LC filter having this construction produces a poor Q characteristic.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a laminated LC filter having an excellent Q characteristic.
A laminated LC filter of a preferred embodiment of the present invention includes a laminated body including a plurality of insulation layers, a plurality of inductor patterns, and a plurality of capacitor patterns which are stacked on each other, and at least three LC resonators having a plurality of inductors that are defined by inductor patterns, and a plurality of capacitors arranged such that the capacitor patterns are disposed opposite to the inductor patterns inside of the laminated body, wherein a filter including at least three stages is constructed 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 end portions thereof.
Each of the inductors of the respective LC resonators has a multiplex structure in which two or more of the inductor patterns having substantially identical shapes are laminated via insulation layers.
The reduced pattern widths of the inductor patterns of the LC resonators at the end portions greatly reduce the magnetic field at the edges of the inductor patterns.
Moreover, the multiplex structure of the inductor greatly reduces the magnetic field generated in the vicinity of the inductor. As a result, the magnetic field at the edges of the inductor patterns is greatly decreased.


REFERENCES:
patent: 5892415 (1999-04-01), Okamura
patent: 6191667 (2001-02-01), Takenaka et al.
patent: 2000-021633 (2000-01-01), None

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