Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2001-04-17
2003-01-07
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S175000
Reexamination Certificate
active
06504452
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low-pass filter and a mobile communication device using the same, and more particularly, to a low-pass filter used in a GHz band and a mobile communication device including the same.
2. Description of the Related Art
As known in the art, a low-pass filter operates to pass signals having a frequency lower than a desired frequency to remove a desired level, or higher, of harmonic signals, and includes an inductor and a capacitor.
FIG. 4
is a circuit diagram of a typical low-pass filter. The low-pass filter includes an LC parallel resonance circuit having an inductor L and an ungrounded capacitor C
1
connected between an input terminal Pi and an output terminal Po. The low-pass filter further includes grounded capacitors C
2
and C
3
connected between the ends of the LC parallel resonance circuit and ground, respectively.
FIG. 5
is an exploded perspective view showing a conventional low-pass filter
50
. The low-pass filter
50
includes a laminate defined by six dielectric layers
51
a
to
51
f
, as disclosed in Japanese Unexamined Patent Application Publication No. 7-336176. The dielectric layer
51
a
is a protective layer, the dielectric layer
51
b
has an inductor electrode
52
provided thereon, and the dielectric layers
51
c
and
51
d
have capacitor electrodes
53
a
and
53
b
provided thereon, respectively. The dielectric layer
51
e
has capacitor electrodes
53
c
and
53
d
provided thereon, and the dielectric layer
51
f
has a ground electrode
54
provided thereon.
One end of the inductor electrode
52
extends to one shorter side of the dielectric layer
51
b
and connects to the input terminal Pi, and the other end of the inductor electrode
52
extends to the other shorter side of the dielectric layer
51
b
and connects to the output terminal Po. One end of the capacitor electrode
53
a
extends to one shorter side of the dielectric layer
51
c
, and one end of the capacitor electrode
53
c
extends to one shorter side of the dielectric layer
51
e
to connect to the input terminal Pi. One end of the capacitor electrode
53
b
extends to one shorter side of the dielectric layer
51
d
, and one end of the capacitor electrode
53
d
extends to the other shorter side of the dielectric layer
51
e
to connect to the output terminal Po. Portions of the ground electrode
54
extend to longer opposing sides of the dielectric layer
51
f
to connect to the ground terminals Pg.
The inductor electrode
52
defines the inductor L, and the inductance of the inductor L depends upon the length of the inductor electrode
52
. The capacitor electrodes
53
a
and
53
b
define the ungrounded capacitor C
1
, and the capacitance of the ungrounded capacitor C
1
depends upon the spacing between the capacitor electrodes
53
a
and
53
b
, the overlapping area thereof, and the permittivity of the dielectric layer
51
c
. The capacitor electrodes
53
c
and
53
d
, and the ground electrode
54
define the grounded capacitors C
2
and C
3
, and the capacitances of the grounded capacitors C
2
and C
3
depend upon the spacing between the capacitor electrode
53
c
and the ground electrode
54
, the spacing between the capacitor electrodes
53
d
and the ground electrode
54
, the overlapping area of each of the capacitor electrodes
53
c
and
53
d
with the ground electrode
54
, and the permittivity of the dielectric layer
51
e.
However, the conventional low-pass filter encounters a problem. Specifically, in such a low-pass filter, a capacitor electrode that defines an ungrounded capacitor overlaps, via a dielectric layer, a capacitor electrode and a ground electrode that together define a grounded capacitor. This arrangement produces a capacitance between the capacitor electrode defining the ungrounded capacitor and the capacitor electrode defining the grounded capacitor, and also produces a capacitance between the capacitor defining the ungrounded capacitor and the ground electrode defining the grounded capacitor. Hence, the capacitances of the ungrounded capacitor and the grounded capacitor are not independently controlled, making it difficult to accurately control the pass band of the low-pass filter.
SUMMARY OF THE INVENTION
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide a low-pass filter which facilitates control of the pass band with improved insertion-loss and attenuation characteristics, and a mobile communication device using the same.
A low-pass filter includes a laminate containing an inductor electrode, a plurality of capacitor electrodes, and at least two ground electrodes. The laminate is defined by laminating a plurality of dielectric layers. The low-pass filter includes a grounded capacitor defined by a capacitor electrode and at least two ground electrodes, the capacitor electrode being located between the at least two ground electrodes, and an ungrounded capacitor including a capacitor electrode which is not located between the ground electrodes.
The inductor electrode is provided between the capacitor electrode, which defines the ungrounded capacitor, and the principal plane of the laminate.
According to another preferred embodiment of the present invention, a low-pass filter includes an LC parallel resonance circuit having an inductor and a capacitor connected in parallel, and at least one grounded capacitor provided between at least one end of the LC parallel resonance circuit and ground. The inductor of the LC parallel resonance circuit is defined by an inductor electrode incorporated in a laminate, the laminate being defined by laminating a plurality of dielectric layers. The capacitor of the LC parallel resonance circuit is defined by a first capacitor electrode and a second capacitor electrode. The first and second capacitor electrodes being incorporated in the laminate. The grounded capacitor is defined by a first ground electrode, a second ground electrode, and a capacitor electrode provided between the first and second ground electrodes within the laminate.
Preferably, the at least one grounded capacitor includes first and second grounded capacitors provided at the ends of the LC parallel resonance circuit. The first grounded capacitor is preferably defined by the first ground electrode, the second ground electrode, and a third capacitor electrode provided between the first and second ground electrodes. The second ground capacitor is preferably defined by the first ground electrode, the second ground electrode, and a fourth capacitor electrode provided between the first and second ground electrodes.
The second capacitor electrode may partially overlap the first ground electrode via a dielectric layer, and the first grounded capacitor may also be defined by the second capacitor electrode and the first ground electrode.
The first capacitor electrode may have a portion that overlaps with the first ground electrode without interposition of the second capacitor electrode, and the second grounded capacitor may also be defined by the overlapping portion of the first capacitor electrode and the first ground electrode.
Preferably, the inductor electrode is provided on a dielectric layer opposite to the dielectric layers on which the grounded capacitor is provided, with respect to the dielectric layers on which the first and second capacitor electrodes are provided.
The inductor electrode, the first capacitor electrode, the second capacitor electrode, the first ground electrode, and the second ground electrode may be provided on different dielectric layers.
Accordingly, a low-pass filter according to preferred embodiments of the present invention allows a grounded capacitor to be defined by two ground electrodes and a capacitor electrode held between the two ground electrodes. Therefore, the capacitances of an ungrounded capacitor (i.e., a capacitor of an LC parallel resonance circuit) and the grounded capacitor are independently controlled.
In another preferred embodiment of the present invention,
Furutani Koji
Takada Yoshiki
Ham Seungsook
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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