Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2002-03-08
2004-05-04
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S192000, C310S321000, C310S348000, C310S366000
Reexamination Certificate
active
06731187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dual mode filters, and more specifically, to a surface-mounted dual mode filter.
2. Description of the Related Art
Well-known dual mode filters including a filter element that is disposed in a package defined by a casing substrate and a conductive cap have been widely used.
FIG. 18
illustrates the structure of a well-known dual mode filter.
In the dual mode filter, an input electrode
51
, an output electrode
52
, and a ground electrode
53
are provided on a casing substrate
50
. These electrodes
51
to
53
are arranged so as to wrap around the casing substrate
50
from the top surface to the bottom surface. On the top surface of the casing substrate
50
, a rectangular-frame shaped insulating layer
54
is provided. As described in Japanese Unexamined Utility Model Application Publication No. 5-25832, a filter element
60
is a piezoelectric resonator defined by connecting a plurality of piezoelectric vibrators via relay capacitors. The filter element
60
includes a composite substrate defined by bonding piezoelectric substrates
61
and
62
having piezoelectric characteristics to a dielectric substrate
63
having dielectric characteristics but no piezoelectric characteristics. Vibrators
64
and
65
are provided on the piezoelectric substrates
61
and
62
, respectively. The vibrators
64
and
65
simultaneously generate two oscillation modes, particularly, a symmetric mode (S mode) and an asymmetric mode (A mode), between a pair of segmented electrodes provided on a first principal surface and a counter electrode provided on a second principal surface.
On the top surface of the filter element
60
, terminal electrodes
66
and
67
are provided at both ends thereof. A capacitance extraction electrode
68
is provided at a central portion of the top and bottom surfaces of the filter element
60
. Since the capacitance extraction electrodes
68
are provided on the dielectric substrate
63
, undesired vibrations in a relay capacitance section are prevented from occurring. The terminal electrodes
66
and
67
on the filter element
60
are connected to the input and output electrodes
51
and
52
on the casing substrate
50
via conductive paste
69
a
and
69
b,
respectively. The capacitance extraction electrodes
68
are connected to the ground electrode
53
on the casing substrate
50
via a conductive paste
69
c.
After mounting the filter element
60
on the casing substrate
50
, silicone rubber
70
is applied to the top surface of the filter element
60
. A conductive cap
71
is attached to the insulating layer
54
so as to cover the filter element
60
, and the interior is sealed. Accordingly, a surface-mounted dual mode filter is obtained.
In the dual mode filter structured described above, the two vibrators
64
and
65
are integrally provided on one element. Interference between the two vibrators
64
and
65
causes undesired vibrations.
FIG. 19
shows amplitude characteristics of the dual mode filter described above. As shown in
FIG. 19
, an in-band ripple R is generated by the interference between the vibrators
64
and
65
. Further, out-of-band attenuation is relatively small.
In this known structure, two vibrators are provided on one element. Thus, a single composite substrate must be formed by integrally bonding the piezoelectric substrates
61
and
62
and the dielectric substrate
63
. As a result, the manufacturing costs are increased, and the reliability of the electrodes at the boundary between the substrates is reduced.
SUMMARY OF THE INVENTION
In order to overcome the above-described problems, preferred embodiments of the present invention provide a dual mode filter in which undesired vibrations due to interference between vibrators are prevented from occurring, which has greatly reduced manufacturing costs, and which has greatly increased connection reliability.
According to a first preferred embodiment of the present invention, a dual mode filter includes a casing substrate on which an input electrode, an output electrode, two ground electrodes, and a relay electrode are provided, first and second filter elements mounted on the casing substrate, and a cap connected to and fixed on the casing substrate so as to cover the filter elements. Each of the first and second filter elements includes a first terminal electrode at a first end of a first principal surface of a piezoelectric substrate, a second terminal electrode in a central portion of the piezoelectric substrate, a pair of segmented electrodes provided in a portion of the piezoelectric substrate between the first and second terminal electrodes and which are connected to the first and second terminal electrodes, respectively, a counter electrode provided on a second principal surface of the piezoelectric substrate and which is opposed to the segmented electrodes to define a dual mode vibrator, and a third terminal electrode provided at a second end of the piezoelectric substrate and which is connected to the counter electrode. The first terminal electrode of the first filter element is connected to the input electrode on the casing substrate via a conductive bonding material, and the third terminal electrode is connected to one ground electrode on the casing substrate via a conductive bonding material. The first terminal electrode of the second filter element is connected to the output electrode on the casing substrate via a conductive bonding material, and the third terminal electrode is connected to the other ground electrode on the casing substrate via a conductive bonding material. The second terminal electrode of the first filter element is connected to the relay electrode on the casing substrate via a conductive bonding material, and the second terminal electrode of the second filter element is connected to the relay electrode on the casing substrate via a conductive bonding material.
According to preferred embodiments of the present invention, instead of providing two vibrators on one element, one dual-mode vibrator is provided on each of the two elements. These two elements are spaced a desired distance from each other on the casing substrate and are connected to each other through the relay electrode on the casing substrate. Thus, undesired vibrations due to interference between the two vibrators are prevented.
It is unnecessary to form a composite substrate by integrally bonding a piezoelectric substrate and a dielectric substrate. Thus, the manufacturing costs are greatly reduced. The dual mode filter according to preferred embodiments of the present invention does not have reduced reliability of electrodes at the boundary between the two substrates.
Since the relay electrode is provided on the casing substrate, the relay electrode is not opposed to the filter elements with the ground electrodes and the piezoelectric substrate therebetween. Thus, undesired vibrations are efficiently suppressed.
Preferably, the first and second filter elements are mounted such that each first terminal electrode, each second terminal electrode, and each pair of segmented electrodes face the casing substrate side. In other words, preferably, the first and second filter elements are mounted such that each counter electrode and each third terminal electrode face upward.
When connecting the first terminal electrodes of the filter elements to the input electrode and the output electrode by the conductive bonding materials and when connecting the second terminal electrodes to the relay electrode via the conductive bonding materials, with these electrodes facing upward (opposite to the casing substrate side), the conductive bonding material, such as a conductive paste or soldering, must continuously be applied to portions from the terminal electrodes on the top surface of each filter element to the electrodes on the casing substrate. In particular, it is difficult to connect the second terminal electrodes to the relay electrode. In other words, because each second terminal electrode is provided in a c
Gamo Masao
Ikeda Yoshihiro
Kurihara Takahiro
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Summons Barbara
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