Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-10-16
2004-07-20
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S176000, C333S185000
Reexamination Certificate
active
06765458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LC high-pass filter circuit device, a laminated LC high-pass filter device, and a multiplexer which are suitable for use in, for example, a mobile communication device such as a cellular phone, and also relates to a radio communication apparatus.
2. Description of the Related Art
FIG. 16
shows the structure of a known laminated LC high-pass filter device of the type that is related to the present invention pertains. The known LC high-pass filter device, denoted generally by
151
, has insulating sheets
152
to
158
which respectively support, as illustrated, input and output conductors
161
and
162
, a resonance capacitive conductor
163
, coiled conductors
164
to
169
, and a grounding conductor
170
.
The sheets
152
to
158
are stacked and baked to form an integral laminated structure
175
as shown in FIG.
17
. An input terminal
176
, an output terminal
177
, and a grounding terminal G are formed on the laminated structure
175
. The input conductor
161
is connected to the input terminal
176
, and the output conductor
162
is connected to the output terminal
172
. A grounding conductor
170
is connected to the grounding terminal G.
The coiled conductors
164
to
166
are connected in series through via holes
171
b
and
171
c
formed in the insulating sheets
155
and
156
. Likewise, the coiled conductors
167
to
169
are connected in series through via holes
172
b
and
172
c
formed in the insulating sheets
155
and
156
. The series connection of the coiled structures
164
to
165
defines an inductor L
1
, while the series connection of the coiled conductors
167
to
169
defines an inductor L
2
. The inductor L
1
is electrically connected at one end thereof to the input conductor
161
through a via hole
171
a
formed in the insulating sheet
154
. Similarly, the inductor L
2
is electrically connected at one end thereof to the output conductor
162
through a via hole
172
a
formed in the insulating sheet
154
. The other ends of the inductors L
1
and L
2
are electrically connected to the grounding conductor
170
through via holes
171
d
and
172
d
formed in the insulating sheet
157
. The direction of winding of the inductor L
1
and the direction of winding of the inductor L
2
are opposite to each other. The capacitive conductor
163
opposes the input conductor
161
and the output conductor
162
across the insulating sheet
153
so as to define a resonance capacitor C.
FIG. 18
shows a circuit that is electrically equivalent to the laminated LC high-pass filter device
151
having the construction described above. Since the inductors L
1
and L
2
are wound in opposite directions, the inductors L
1
and L
2
are back-coupled to each other. Therefore, the -M produced by the inductive back-coupling of the inductors L
1
and L
2
, the resonance capacitor C and the inductors L
1
and L
2
in combination define a trap circuit.
In the known LC high-pass filter
151
having the above-described construction, the major planes of the input conductor
161
, output conductor
162
and the grounding conductor
170
substantially perpendicularly cross the lines of magnetic force generated by the inductors L
1
and L
2
, due to the fact that the inductors L
1
and L
2
are respectively defined by the coiled conductors
164
to
166
and coiled conductors
167
to
169
. Consequently, the lines of magnetic force generated by the inductors L
1
and L
2
produce large eddy current loss in, for example, the grounding conductor
170
. This leads to production of the LC high-pass filter device
151
having a small Q value. In addition, it has been difficult to reduce the size, in particular the planar area, of the LC high-pass filter device
151
, because the coiled conductors
164
to
166
and the coiled conductors
167
to
169
occupy considerably large areas.
In addition, with the equivalent circuit shown in
FIG. 18
, it is difficult to implement a high-pass filter device in which the attenuation pole of the trap circuit is positioned near the central frequency of the high-pass filter circuit.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide an LC high-pass filter circuit device which has a high Q value and excellent frequency characteristics, and a laminated LC high-pass filter device, a multiplexer and a radio communication apparatus which include such a novel LC high-pass filter circuit device.
According to a preferred embodiment of the present invention, a LC high-pass filter circuit device includes a pair of terminals including an input terminal and an output terminal, at least two high-pass filter circuits including first capacitors connected in series between the input and output terminals and first inductors connected to the input and output terminals in parallel with each other and grounded, each of the high-pass filter circuits having one first capacitor and one first inductor, and a trap circuit including a series connection of a second capacitor and a second inductor, the series connection being grounded at one end and connected between two adjacent high-pass filter circuits so as to shunt from the input and output terminals.
Preferably, the first capacitor of each high-pass filter circuit is connected between the associated first inductor and the trap circuit.
With these unique structural features and arrangement, it is possible to locate the attenuation pole of the trap circuit at a position near the pass band of the high-pass filter circuit and, therefore, to obtain an LC high-pass filter circuit device having a sharp frequency characteristic.
The LC high-pass filter circuit device may further include third capacitors connected between the terminals and the node between the second capacitor and the second inductor of the trap circuit, the third capacitors defining band-adjusting capacitors.
This arrangement permits a signal path of a low impedance to be formed separately. Lower impedance allows greater signal traffic, making it possible to widen the pass-band of the LC high-pass filter circuit device.
According to another preferred embodiment of the present invention, a laminated LC high-pass filter device includes a laminated structure including a stack of a plurality of insulating layers, a plurality of capacitive conductors, and a plurality of coiled conductors, an input terminal, an output terminal, and a grounding terminal provided on surfaces of the laminated structure, a plurality of high-pass filter circuits disposed in the laminated structure, each of the high-pass filter circuits having a first capacitor defined by one of the capacitive conductors and a first inductor defined by one of the coiled conductors, and a trap disposed in the laminated structure and having a series connection of a second capacitor and a second inductor, the second capacitor being defined by one of the capacitive conductors and the second inductor being defined by one of the coiled conductors, wherein the first capacitors of the high-pass filter circuits are connected in series between the input terminal and the output terminal, and the first inductors of the high-pass filter circuits are connected to the input terminal and the output terminal in parallel to each other and are connected also to the grounding terminal, and wherein the trap is connected between two adjacent high-pass filter circuits so as to shunt from the input terminal and the output terminal, the series connection of the second capacitor and the second inductor being connected to the grounding terminal.
The arrangement may be such that at least a portion of the coiled conductor constituting the first inductor and at least a portion of the coiled conductor constituting the second inductor are defined by inductor via holes formed in the insulating layer or, alternatively, by a helical coiled conductor or a spiral coiled conductor. Inductor via holes have axes extending in the direction of the stack of layer
Keating & Bennett LLP
Murata Manufacturing Co. LTD
Summons Barbara
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