Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-12-23
2001-01-23
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C333S195000
Reexamination Certificate
active
06177752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a multi-stage connected surface acoustic wave device and a method of connecting surface acoustic wave filters.
2. Description of the Related Art:
According to methods of connecting balanced-connection transversely coupled mode resonator-type SAW filters of the prior art, a plurality of surface acoustic wave (SAW) filters were cascade-connected in a balanced-connection mode, each stage being connected in an electrically balanced state.
In the above-described prior art, however, unwanted electromagnetic coupling occurs between the input and output ports of a device. This electromagnetic coupling raises problems because it causes deterioration in out-of-band attenuation, and therefore improvements have been sought.
Examples of the construction of surface acoustic wave filters of the prior art are shown in FIG.
1
and FIG.
2
. In these examples, first-stage output
31
and second-stage input
40
, as well as first-stage output
33
and second-stage input
42
, are connected in an electrically balanced state and are not connected to a ground, and as a result, adequate out-of-band attenuation could not be obtained. A more detailed explanation follows.
FIG. 3
is a schematic plan view illustrating the structure of a transversely coupled mode resonator-type SAW filter according to the electrically balanced connection method of the prior art.
FIG. 4
is a schematic view illustrating the characteristics of the transversely coupled mode resonator-type cascade-connected SAW filter shown in FIG.
3
.
Referring now to FIG.
3
and
FIG. 4
, in a transversely coupled mode resonator-type cascade-connected SAW filter of the prior art having a balanced input/output port structure, the perimeters of area B and area C are enclosed by a signal line, but the electric potential of these areas is not the ground potential. As a result, unwanted electromagnetic radiation emitted from first-stage area A destabilizes the potential of the signal line of area B, and unwanted electromagnetic coupling from area A to area B tends to occur.
Signals due to this unwanted electromagnetic coupling are transmitted from area B to area C, and the transfer of the above-described unwanted electromagnetic radiation then occurs from area C to area D. As a consequence, a route of unwanted electrical coupling is created that passes directly from input to output. Generally, signals due to this unwanted electromagnetic coupling are not dependent on the parameters that determine the structure of Interdigital Transducers (IDT) of the SAW device. As a result, these signals become feedthrough signals between the input and output electrical ports, and these signals cause deterioration in the out-of-band attenuation and generate in-band ripple.
FIG. 5
is a graph showing the pass characteristics of SAW filter in which the prior art is applied. In
FIG. 5
, taking a resonance peak in the vicinity of 377.25 MHz as a reference, a relative out-of-band attenuation of no more than approximately 45 dB was obtainable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a surface acoustic wave device that increases the relative out-of-band attenuation, as well as a method of connecting surface acoustic wave filters.
The surface acoustic wave device of the present invention has two or more stages of surface acoustic wave filters in cascade connection with at least one of the connection lines of input and output signals that connect the stages of surface acoustic wave filters being connected to ground potential to produce an electrically unbalanced connection.
In addition, the above-described surface acoustic wave filters may be filters having interdigital transducers formed on a piezoelectric substrate.
Further, the surface acoustic wave filters should be transversely coupled mode resonator-type filters that transfer energy in a mode that distributes perpendicularly to the direction the propagation of surface waves.
The surface acoustic wave filter connection method of the present invention is for a case in which surface acoustic wave filters are in a cascade connection of two or more stages, at least one of the connection lines that join input and output signals in the stages of the surface acoustic wave filters being connected to ground potential to produce an electrically unbalanced connection.
Finally, the above-described surface acoustic wave filters may be filters having interdigital transducers, and may be connected on a piezoelectric substrate.
The above and other objects, features, and advantages of the present invention will be better understood from the following description based on the accompanying drawings which illustrate examples of preferred embodiments of the present invention.
REFERENCES:
patent: 5581141 (1996-12-01), Yamada et al.
patent: 5932950 (1999-08-01), Yamada et al.
patent: 5999068 (1999-12-01), Tsutsumi et al.
patent: 0 600 705 A1 (1994-06-01), None
patent: 6-85604 (1994-03-01), None
patent: 6-48233 (1994-06-01), None
patent: 8-237064 (1996-09-01), None
patent: 10-107583 (1998-04-01), None
patent: 10-190404 (1998-07-01), None
Dougherty Thomas M.
McGinn & Gibb PLLC
NEC Corporation
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