Lamination type LC filter

Details Lamination type LC filter Lamination type LC filter

2001-12-27

2003-06-24

Ham, Seungsook (Department: 2817)

Wave transmission lines and networks

Coupling networks

Frequency domain filters utilizing only lumped parameters

C333S185000

Reexamination Certificate

active

06583687

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lamination type LC filter.
2. Description of the Related Art
Conventionally, among filters used in portable telephones and other electronic apparatuses, a lamination type LC filter is known. The lamination type LC filter is a chip electronic component including inductor electrodes and capacitor electrodes that constitute a resonance circuit and are laminated through dielectric sheets. Such a component is suitable for miniaturization.
Such a lamination type LC filter is shown in
FIGS. 14
to
16
.
FIG. 14
is an exploded perspective view of a conventional lamination type LC filter,
FIG. 15
is a perspective appearance of the LC filter, and
FIG. 16
is an equivalent circuit diagram of the LC filter.
As shown in
FIG. 14
, the lamination type LC filter
1
includes a dielectric sheet
3
a
on the surface of which an internal ground electrode
2
is provided, a dielectric sheet
3
b
on the surface of which inductor electrodes
4
a
and
4
b
are provided, a dielectric sheet
3
c
on the surface of which an input capacitor electrode
5
a
and an output capacitor electrode
5
b
are provided, a dielectric sheet
3
d
on the surface of which resonance capacitor electrodes
6
a
and
6
b
are provided, a dielectric sheet
3
e
on the surface of which an internal ground electrode
7
is provided, and a dielectric sheet
3
f
constituting an external layer.
Each internal electrode is made of Ag, Pd, Cu, Ni, Au, or Ag—Pd, and is formed via printing, sputtering, or evaporation. Furthermore, a dielectric powder mixed and kneaded together with a binder, is made into sheets which are used as the dielectric sheets
3
a
to
3
f.
The internal ground electrode
2
is formed on substantially the entire area, excluding the left and right end portions, of the surface of the dielectric sheet
3
a
, such that a first end portion
2
a
of the internal ground electrode
2
is exposed at the front of the dielectric sheet
3
a,
and a second end portion
2
b
is exposed at the rear thereof.
The inductor electrodes
4
a
and
4
b
include a spiral coil of about two turns, the inductor electrode
4
a
is provided at a left portion of the dielectric sheet
3
b,
and the inductor electrode
4
b
is provided at a right portion of the dielectric sheet
3
b.
A first end portion
4
a
1
of the inductor electrode
4
a
is connected to the resonance capacitor
6
a
through a via hole, and a second end portion
4
a
2
of the inductor electrode
4
a
is connected to the internal ground electrode
2
through another via hole. In the same way, the first end portion
4
b
1
of the inductor electrode
4
b
is connected to the resonance capacitor
6
b
through a via hole, and the second end portion
4
b
2
of the inductor electrode
4
b
is connected to the internal ground electrode
2
through another via hole.
In the input capacitor electrode
5
a,
a first end portion
5
a
1
is exposed at a left portion of the dielectric sheet
3
c,
and a second end portion
5
a
2
has a large area and faces the resonance capacitor electrode
6
a
through the dielectric sheet
3
d.
In the same way, in the output capacitor electrode
5
b,
a first end portion
5
b
1
is exposed at the right portion of the dielectric sheet
3
c,
and a second end portion
5
b
2
has a large area and faces the resonance capacitor electrode
6
b
through the dielectric sheet
3
d.
Both of the resonance capacitor electrodes
6
a
and
6
b
are rectangular and have longer sides extending in the direction from the front to the rear of the dielectric sheet
3
d,
the resonance capacitor electrode
6
a
is provided at a left portion of the dielectric sheet
3
d,
and the resonance capacitor electrode
6
b
is provided at a right portion of the dielectric sheet
3
d.
As described above, the resonance capacitor electrode
6
a
is connected to the first end portion
4
a
1
of the inductor electrode
4
a
through a via hole and faces the input capacitor electrode
5
a.
In the same way, the resonance capacitor electrode
6
b
is connected to the first end portion
4
b
1
of the inductor electrode
4
b
through a via hole and faces the input capacitor electrode
5
b.
The internal ground electrode
7
is formed along substantially the entire area, excluding the left and right end portions, of the surface of the dielectric sheet
3
e
, such that a first end portion
7
a
is exposed at the front of the dielectric sheet
3
e,
and a second end portion
7
b
is exposed at the rear of the dielectric sheet
3
e.
Each dielectric sheet having the above-described construction is put one on top of another in order, and then they are integrally fired to form a laminated body.
Next, as shown in
FIG. 15
, external ground electrodes
8
a
and
8
b
are formed on the front and rear surfaces of the obtained laminated body, respectively. Furthermore, an external input electrode
9
a
and an external output electrode
9
b
are formed on the left and right surfaces of the laminated body, respectively. Each external electrode is formed by means of coating, baking, sputtering, and evaporation. Then, a first end portion
2
a
of the internal ground electrode
2
and a first end portion
7
a
of the internal ground electrode
7
are connected to the external ground electrode
8
a,
and the second end portion
2
b
and the second end portion
7
b
of the internal ground electrode
7
are connected to the external ground electrode
8
b.
Furthermore, the first end portion
5
a
1
of the input capacitor electrode
5
a
is connected to the external input electrode
9
a,
and the first end portion
5
b
1
of the output capacitor electrode
5
b
is connected to the external output electrode
9
b.
The lamination type LC filter
1
described above constitutes the equivalent circuit diagram of a bandpass filter as shown in FIG.
16
. That is, an inductance L
1
generated by the inductor electrode
4
a
and a capacitance C
1
generated between the resonance capacitor electrode
6
a
and the internal ground electrode
7
are connected in parallel and constitute a parallel LC resonance circuit Q
1
on the input side. In the same way, an inductance L
2
generated by the inductor electrode
4
b
and a capacitance C
2
generated between the resonance capacitor electrode
6
b
and the internal ground electrode
7
are connected in parallel and constitute a parallel LC resonance circuit Q
2
on the output side. Then, a mutual inductance M is formed between the inductance L
1
and the inductance L
2
, and the parallel LC resonance circuits Q
1
and Q
2
are magnetically coupled.
Furthermore, a capacitance formed by a capacitive coupling between the second end portion
5
a
2
of the input capacitor electrode
5
a
and the resonance capacitor electrode
6
a
is connected in series to the parallel resonance circuit Q
1
to constitute an input adjustment capacitance C
3
. In the same way, a capacitance formed by a capacitive coupling between the second end portion
5
b
2
of the output capacitor electrode
5
b
and the resonance capacitor electrode
6
b
is connected in series to the parallel resonance circuit Q
2
to constitute an output adjustment capacitance C
4
.
Here, in a perspective view, when the above-described lamination type LC filter
1
is seen in the direction of an arrow A in
FIG. 15
(from the top), the input capacitor electrode
5
a
located above the inductor electrode
4
a
is disposed inside the inductor electrode
4
a,
the resonance capacitor electrode
6
a
is disposed so as to completely cover the inductor electrode
4
a,
and the internal ground electrode
7
is disposed so as to completely cover the inductor electrode
4
a.
On the other hand, the internal ground electrode
2
below the inductor electrode
4
a
is disposed so as to completely enclose the inductor electrode
4
a.
In the same way, the second end portion
5
b
2
of the output capacitor electrode
5
b
located above the inductor electrode
4
b
is disposed inside the inductor electrode
4
b
, the resonance capacito

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