Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-03-15
2002-11-12
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C310S31300R, C333S133000
Reexamination Certificate
active
06480077
ABSTRACT:
The present application claims priority under 35 U.S.C. § 119 to Japanese Application No. 076584/2000 filed on Mar. 17, 2000, which is hereby incorporated by reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave filter device utilizing surface acoustic waves.
2. Description of the Related Art
With the recent rapid spread of automobile telephones and portable telephones, the necessity for small-sized and high-performance high-frequency Surface Acoustic Wave (SAW) filters has increased.
FIG. 18
shows a conventional SAW filter device
1
. The SAW filter device
1
has a SAW filter
2
and a multi-layer ceramic package. The SAW filter
2
has a series arm
3
, a first parallel arm
4
and a second parallel arm
5
. The first series arm
3
is disposed between a filter input terminal TFi and a filter output terminal TFo, and the first parallel arm
4
and the second parallel arm
5
are disposed between the series arm
3
and a reference potential.
The series arm
3
has a first series resonator S
1
, a second series resonator S
2
, and a third series resonator S
3
. These resonators are disposed in series between the filter input terminal TFi and the filter output terminal TFo. One terminal of the first series resonator S
1
is connected to the filter input terminal TFi, and another terminal of the first series resonator S
2
is connected to a node n
1
. One terminal of the second series resonator S
2
is connected to the node n
1
, and another terminal of the second series resonator S
2
is connected to a node n
2
. One terminal of the third series resonator S
3
is connected to the node n
2
, and another terminal of the third series resonator S
3
is connected to the filter output terminal TFo.
The first parallel arm
4
has a first parallel resonator P
1
, and the second parallel arm
5
has a second parallel resonator P
2
. One terminal of the first parallel resonator P
1
is connected to the node n
1
, and another terminal of the first parallel resonator P
1
is connected to a parallel arm reference potential terminal TPg. One terminal of the second parallel resonator P
2
is connected to the node n
2
, and another terminal of the second parallel resonator P
2
is connected to the parallel arm reference potential terminal TPg.
The filter input terminal TFi is connected to a package input electrode TPCi via a bonding wire Wi. The filter output terminal TFo is connected to a package output electrode TPCo via a bonding wire Wo. The parallel arm reference potential terminal TPg is connected to a package reference potential electrode TPCg
1
via a bonding wire Wg
1
. The SAW filter device
1
is applied to a band pass filter, therefore it is preferable to decrease signals within an attenuating wave band properly.
However, an input/output impedance of the SAW filter varies because of manufacturing error. An impedance of the package also varies because of manufacturing error. The bonding wires and interconnects on a package have parasitic inductances and parasitic capacitors, which also vary an input/output impedance of the SAW filter device
1
. Therefore, a sufficient impedance matching between the package and the SAW filter
2
is not provided in order to achieve a proper characteristic as a SAW filter device.
SUMMARY OF THE INVENTION
The present invention is therefore directed to a surface acoustic wave device which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
These and other objects are provided by a surface acoustic wave device including a piezoelectric substrate, a first plurality of resonators which are connected in series and formed on said piezoelectric substrate, a second plurality of resonators which are connected in parallel, and formed on said piezoelectric substrate, an input signal line receiving input signals, a floating electrode being in a floating state, and a wire connecting a point of said input signal line to said floating electrode.
REFERENCES:
patent: 5999069 (1999-12-01), Ushiroku
patent: 2-224388 (1990-09-01), None
patent: 06334468 (1994-02-01), None
patent: 10-256869 (1998-09-01), None
Oki Electric Industry Co. Ltd.
Pascal Robert
Summons Barbara
Volentine & Francos, PLLC
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