Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2000-09-11
2002-08-13
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S175000
Reexamination Certificate
active
06433653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic LC resonator and a monolithic LC filter, and more particularly, to a monolithic LC resonator and a monolithic LC filter for use in a high frequency wave band.
2. Description of the Related Art
FIGS. 13 and 14
show an example of a conventional monolithic LC resonator. As shown in
FIG. 13
, an LC resonator
100
includes a ceramic sheet
104
having a capacitor pattern
112
provided on the upper surface thereof, a ceramic sheet
105
having an inductor pattern
111
provided on the upper surface thereof, a ceramic sheet
106
having an input capacitor pattern
115
and an output capacitor pattern
116
provided on the upper surface thereof, ceramic sheets
102
and
108
having shield electrodes
113
and
114
provided on the upper surfaces thereof, respectively.
The ceramic sheets
101
to
108
are stacked, and fired to produce a laminate
110
shown in FIG.
14
. On the laminate
110
, an input terminal
121
, an output terminal
122
, and ground terminals
123
and
124
are provided. The input capacitor pattern
115
is connected to the input terminal
121
. The output capacitor pattern
116
is connected to the output terminal
122
. To the ground terminal
123
, the lead-out portion of the inductor pattern
111
, and one end of the shield electrodes
113
and
114
are connected. The lead-out portion of the capacitor pattern
112
to the ground terminal
124
, and the other end of the shield electrodes
113
and
114
are connected.
In the above-described LC resonator
100
, an inductor including the inductor pattern
111
, and a capacitor including a capacitor pattern
112
opposed to the open end of the inductor pattern
111
define an LC parallel resonance circuit. The LC parallel resonance circuit is electrically connected to the input terminal
121
via a coupling capacitor including an inductor pattern
111
and the input capacitor pattern
115
opposed to each other. Similarly, the LC parallel resonance circuit is electrically connected to the output terminal
122
via a coupling capacitor including the inductor pattern
111
and the output capacitor pattern
116
opposed to each other.
The characteristics of the LC resonator depend on the Q value of the inductor in the resonance circuit. The Q value of the inductor is expressed as Q=2&pgr;f
0
L/R, in which L is the inductance of the inductor, R is the resistance of the inductor, and f
0
is the resonance frequency. As seen in this formula, the Q value of the inductor can be increased by decreasing the resistance R of the inductor. The inductance R is inversely proportional to the cross section of the inductor pattern
111
. Hence, the Q value is increased by increasing the cross section S of the inductor pattern
111
.
However, where the thickness of the inductor pattern
111
is increased to increase the cross section S of the inductor pattern
111
, the internal strain of the laminate
110
is substantially increased when the ceramic sheets
101
to
108
are integrally fired, resulting in delamination and other problems.
Further, a magnetic field generated in the periphery of the inductor pattern
111
is concentrated on the edge of the inductor pattern
111
, causing a large eddy current loss. Moreover, in the conventional LC resonator
100
, the magnetic field generated in the periphery of the inductor pattern
111
is interrupted by the capacitor pattern
112
. Thus, the inductance L of the inductor is very low.
As described above, with the conventional LC resonator
100
, it is difficult to attain a high Q value because the resistance R of the inductor pattern
111
constituting the LC resonance circuit is large, and moreover, the inductance L is low.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide a monolithic LC resonator and a monolithic LC filter each including an inductor having a high Q value.
According to a preferred embodiment of the present invention, a monolithic LC resonator includes a laminated body including an insulation layer, an inductor pattern, and a capacitor pattern laminated together, an LC resonance circuit in the laminated body that includes an inductor defined by the inductor pattern, and a capacitor defined such that the capacitor pattern is opposed to the inductor pattern with the insulation layer being sandwiched between the capacitor pattern and the inductor pattern. In the monolithic LC resonator, the inductor of the LC resonance circuit has a tubular structure defined by at least two inductor patterns electrically connected through via-holes provided in the insulation layer, and the capacitor pattern is located inside of the tubular structure of the inductor.
Further, according to another preferred embodiment of the present invention, a monolithic LC filter includes a laminated body including a plurality of insulation layers, a plurality of inductor patterns, and a plurality of capacitor patterns laminated together, a plurality of LC resonators in the laminated body which include the plurality of inductors defined by the inductor patterns, and the plurality of capacitors defined such that the capacitor patterns are opposed to the inductor patterns with the insulation layers being sandwiched between the capacitor patterns and the inductor patterns. In the monolithic LC filter, the inductor of each LC resonator has a tubular structure defined by at least two inductor patterns electrically connected through via-holes provided in the insulation layer, and at least one of the capacitor pattern and a coupling capacitor pattern for capacitance-coupling the LC resonators is located inside of the tubular structure of the inductor.
The surface area of the inductor having the plurality of the tubular structure can be increased without increasing the thickness of the inductor pattern. In general, high frequency current flows so as to be concentrated onto the surface of a conductor, due to the skin effect. Accordingly, the entire inductor, of which the surface area is increased; is effectively used as a path for high frequency current. Accordingly, the resistance of the inductor is greatly decreased as compared with that of a conventional inductor, and the Q value of the inductor is greatly increased.
Further, with high frequency current flowing through the inductor, a magnetic field is generated in the outer periphery of the tubular structure, not the inside of the tubular structure. Thus, the capacitor pattern and the coupling capacitor pattern for capacitance-coupling the resonators, arranged inside of the inductor having the tubular structure, do not substantially interrupt the magnetic field of the inductor.
Further, since the inductor has the tubular structure, the concentration of a magnetic field, generated in the periphery of the inductor, onto the edges of the inductor pattern is substantially reduced.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.
REFERENCES:
patent: 5404118 (1995-04-01), Okamura et al.
patent: 6114925 (2000-09-01), Lo
patent: 0 926 933 (1999-06-01), None
Kato Noboru
Matsumura Sadayuki
Nomura Hiroko
Bettendorf Justin P.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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