Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-09-29
2001-08-21
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R
Reexamination Certificate
active
06278219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to surface acoustic wave devices, and more particularly, to a surface acoustic wave device which reflects a surface acoustic wave.
2. Description of the Related Art
In recent years, portable telephones, cordless telephones, and radio communication devices have been rapidly becoming smaller and lighter, and hence widely spread. Those wireless devices include high-frequency circuits.
Such high-frequency circuits include filters. To obtain a small and light high-frequency circuit, a surface acoustic wave device (hereinafter also called SAW device) is used as a filter. The substrate of the SAW device transmits and receives a surface acoustic wave via reflectors, so that desired filter characteristics can be obtained.
The reflectors of the conventional SAW device consist of the grating of electrode fingers disposed on a piezoelectric substrate. The frequency response of the reflector is determined by the reflectivity of each electrode finger. The reflectivity of each electrode finger is determined by its width.
U.S. Pat. No. 5,270,606 discloses a reflector in which the reflectivity of each electrode finger is continuously changed so as to obtain a frequency response having a desired bandwidth. To continuously change the reflectivity, the widths of the electrode fingers are gradually varied.
However, the reflector has hundreds of electrode fingers, and a long period of time is required to design and manufacture the electrode fingers having widths varied from one another.
To eliminate the above problem, several methods for the weighting of finger width have been suggested. One of such methods is a withdrawal method disclosed in U.S. Pat. No. 4,281,301.
FIG. 1
illustrates a conventional reflector.
A reflector
1
has electrode fingers
2
having uniform widths w
0
disposed at uniform intervals d
0
, as shown in FIG.
1
. Weighting is carried out by withdrawing the electrode fingers
2
in accordance with predetermined rules. Element
2
′ denotes spaces where electrode fingers
2
have been withdrawn.
With this conventional reflector, however, as mentioned above, there has been a problem that a long period of time is required to design and manufacture the electrode fingers whose widths are gradually varied so as to continuously change the reflectivity of the reflector.
Another problem with the withdrawal method is that the reflector is weighted by only two levels of reflectivity. This causes the frequency response to differ from the desired characteristics, because accurate weighting cannot be performed.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide surface acoustic wave devices in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide surface acoustic wave reflectors whose electrode fingers are easy to design and check without degrading the frequency characteristics.
The above objects are achieved by a surface acoustic wave device having a piezoelectric substrate and a plurality of reflection portions formed on the piezoelectric substrate. The reflection portions are divided into groups, and the widths of the reflection portions are varied by the group.
Since the widths of the electrode fingers are varied by the group, it is not necessary to individually set the width of each electrode finger. Even if the number of electrode fingers is large, designing and checking the electrode fingers can be simplified, and the time required for manufacturing the electrode fingers can be shortened.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4204178 (1980-05-01), Mitchell
patent: 4281301 (1981-07-01), Stevens et al.
patent: 4484160 (1984-11-01), Riha
patent: 4635009 (1987-01-01), Ebata
patent: 4701657 (1987-10-01), Grassl
patent: 5084687 (1992-01-01), Vale et al.
patent: 5270606 (1993-12-01), Cho et al.
patent: 5434466 (1995-07-01), Hickernell et al.
patent: 5463361 (1995-10-01), Allen
patent: 5661444 (1997-08-01), Dill et al.
patent: 5682126 (1997-10-01), Plesski et al.
patent: 5838091 (1998-11-01), Watanabe
patent: 196 38 395 A1 (1998-04-01), None
patent: 0 559 343 A1 (1983-09-01), None
patent: 0 579 871 A1 (1994-01-01), None
patent: 0 671 813 A1 (1995-09-01), None
patent: 2-186708 (1990-07-01), None
patent: 7-336187 (1995-12-01), None
Hashimoto Ken-ya
Kaneda Yasufumi
Omori Tatsuya
Tajima Motoyuki
Tsutsumi Jun
Arent Fox KinterPlotkin & Kahn, PLLC
Dougherty Thomas M.
Fujitsu Limited
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