Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-07-01
2001-09-18
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R
Reexamination Certificate
active
06291924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Surface-acoustic wave (SAW) device for modifying and passing a signal and, more particularly, to a SAW device which includes switches for providing connections to selected SAW Interdigital Transducer (IDT) fingers of the SAW device producing a plurality of SAW characteristics from a common set of SAW IDT fingers.
2. Description of the Prior Art
Referring to
FIG. 1
, a typical SAW device
10
includes an input transducer
12
and an output transducer
14
. Each input
12
and output
14
transducer has a plurality of SAW IDT fingers
16
formed on a substrate
18
. Interconnections between selected SAW IDT fingers
16
are provided by connecting each SAW IDT finger
16
to either a first
20
, second
22
, third
24
or fourth
26
sum line. A radio-frequency (RF) signal voltage
28
is applied between the first
20
second
22
sum lines which provide the voltages
28
to the SAW IDT fingers
16
of the input transducer
12
creating strains in the piezoelectric substrate
18
. If the strains occur with the proper periodic pattern across the length of the SAW device
10
, an acoustic surface wave will be generated. The spacing between SAW IDT fingers
16
, the interconnection pattern of the SAW IDT fingers
16
, and the frequency content of the applied voltage difference determines the magnitude and phase of the surface acoustic wave. The acoustic wave which is launched by this input transducer
12
travels to the output transducer
14
, where it is converted to an output electrical signal. If the SAW IDT fingers
16
have the proper spacing and are connected to the sum lines
20
-
26
with the proper interconnection pattern, a SAW device
10
having a desired signal modification in the time and frequency domains will be generated.
SAW devices
10
formed on a piezoelectric substrate
18
are typically metal film formed from photolithography and thin film processes with either etching or lift-off techniques. These techniques are typically required since the width of each SAW IDT finger
16
and the spacing between adjacent SAW fingers
16
are on the micron or submicron level. For typical prior art SAW devices
10
, the SAW IDT fingers
16
and the sum lines
20
-
26
are formed on the substrate
18
resulting in the SAW fingers
16
, the sum lines
20
-
26
and the interconnection pattern between SAW IDT fingers
16
being fixed on the substrate
18
. Since the SAW IDT fingers
16
and sum lines
20
-
26
are fixed on the substrate
18
, the typical prior art SAW device
10
provides only a single interconnect pattern between SAW fingers
16
and can generate a surface acoustic wave only with fixed signal modifications in the time and frequency domains. If a different surface acoustic wave is desired, a new SAW device having a new interconnect pattern must be fabricated.
One method used to provide for more than one signal modification is to fabricate a plurality of SAW transducers on a single substrate. Then, the input or output signal can be switched among several transducers each of which provides different properties. The drawback of this method is that it gives only a small amount of flexibility and requires more space on the substrate. Therefore, what is needed is a SAW device which can provide a plurality of signal modification properties from a common set of SAW IDT fingers such that the resulting SAW device properties can be changed without the need to fabricate a new SAW device.
SUMMARY OF THE INVENTION
The aforementioned need in the prior art is satisfied by this invention, which provides an adjustable SAW device.
An adjustable SAW device, in accordance with the invention, comprises a plurality of SAW IDT fingers formed on a substrate where the SAW IDT fingers together define one set of SAW IDT fingers. Means to provide a plurality of interconnection patterns between selected SAW IDT fingers is provided whereby the plurality of interconnection patterns can be provided from the one set of SAW IDT fingers.
For a first embodiment of the invention, a plurality of miniature switches are positioned on the substrate and are coupled together by a plurality of sum lines. The switches are controlled by a plurality of control lines.
For a second embodiment of the invention, the adjustable SAW device is an adjustable filter utilized for a variety of applications.
REFERENCES:
patent: 3446974 (1969-05-01), Seiwatz
patent: 3446975 (1969-05-01), Adler et al.
patent: 3745564 (1973-07-01), Gandolfo et al.
patent: 3903486 (1975-09-01), Bert et al.
patent: 3962652 (1976-06-01), Zarin et al.
patent: 4056803 (1977-11-01), White et al.
patent: 4209725 (1980-06-01), Dieulesaint et al.
patent: 5115160 (1992-05-01), Knoll et al.
patent: 5144262 (1992-09-01), Hunsinger
“MEMS Programmable Universal Processor”, Dr. Rob Stokes, Proposal Abstract, Dated: Nov. 20, 1997.
Housholder Steven E.
Kasparek Ronald D.
Kong Alvin M.
Lau Kei-Fung
Stokes Robert B.
Budd Mark O.
Thousand Connie M.
TRW Inc.
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