Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-10-15
2004-10-19
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R, C310S31300R, C333S195000
Reexamination Certificate
active
06806619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a interdigital transducer for use in a transversal surface acoustic wave filter, a surface acoustic wave filter, and a radio communication apparatus.
2. Related Art of the Invention
As cellular phone terminals have become popular, their functions have been improved, while their sizes and power consumption have been reduced.
Under these circumstances, SAW (Surface Acoustic Wave) filters, characterized by consuming reduced power and having reduced sizes, have become essential for transmission and reception circuits of the cellular phone terminals.
FIG. 23
is a schematic view of a transversal SAW filter
407
. The SAW filter
407
is mainly used for intermediate frequencies for a communication method such as CDMA.
The SAW filter
407
is composed of a piezoelectric substrate
401
, an input IDT
402
, an output IDT
403
, an input terminal
404
a
, an input terminal
404
b
, an output terminal
405
a
, and an output terminal
405
a
. The IDT stands for an Interdigital Transducer.
Electric signals of intermediate frequencies input to the input terminals
404
a
,
404
b
as a pair of balanced terminals are converted into a surface acoustic wave by the input IDT
402
. Then, the surface acoustic wave
406
propagates through the piezoelectric substrate
401
and is then converted into an electric signal again by the output IDT
403
. The electric signal is output by the output terminals
405
a
,
405
b
as a pair of balanced terminals. In this manner, the SAW filter
407
operates as a transversal SAW filter.
FIG. 25
shows an IDT
1024
used as the input IDT
402
.
The IDT
1024
is structured so that a plurality of electrode fingers are connected an upper bus bar electrode
224
a
and from a lower bus bar electrode
224
b
arranged opposite the upper bus bar electrode
224
a
. The upper bus bar electrode
224
a
and the lower bus bar electrode
224
b
are arranged parallel with a direction in which a surface acoustic wave propagates.
The IDT
1024
is composed of a section in which a surface acoustic wave is propagated in both directions and a section in which a surface acoustic wave is intensely propagated in one direction; the arrangement of the electrode fingers in the first section is different from that in the second section.
A bidirectional electrode
101
propagates a surface acoustic wave in two directions parallel with the upper bus bar electrode
224
a
and the lower bus bar electrode
224
b
. Further, a single phase unidirectional transducer (SPUDT)
102
a
located to the left of the bidirectional electrode
101
in the drawing intensely propagates a surface acoustic wave in a direction P in FIG.
25
. Further, a single phase unidirectional transducer
102
b
located to the right of the bidirectional electrode
101
in the drawing intensely propagates a surface acoustic wave in the direction P in FIG.
25
.
The bidirectional electrode
101
is structured so that a bidirectional electrode unit (a
0
)
1
as a basic unit that propagates a surface acoustic wave in two directions parallel with the upper bus bar electrode
224
a
and a number of lower bus bar electrodes
224
b
are disposed at every distance equal to one wavelength of a surface acoustic wave at the predetermined frequency, and in
FIG. 25
, three successive bidirectional electrode units (a
0
) are disposed. The predetermined frequency of the surface acoustic wave is the center frequency of the surface acoustic wave excited on the piezoelectric substrate.
The bidirectional electrode units (a
0
)
1
are each composed of four electrode fingers. The leftmost electrode finger in the drawing is connected the upper bus bar electrode
224
a
. The three other electrode fingers are connected the lower bus bar electrode
224
b.
These four electrodes each have a width equal to one eighth of the wavelength at the above mentioned predetermined frequency.
The single phase unidirectional transducers
102
a
and
102
b
are called “EWC-SPUDT electrodes” and utilize reflection of a surface acoustic wave therein to propagate this wave in one direction. These electrodes have hitherto been known as a method with a small loss. The single phase unidirectional transducer
102
a
is composed of a number of single phase unidirectional transducer units (a)
2
as basic units which propagates a surface acoustic wave in the direction P and which are disposed at every distance equal to one wavelength at the predetermined frequency. Likewise, the single phase unidirectional transducer
102
b
is composed of a number of single phase unidirectional transducer units (a)
2
as basic units which propagates a surface acoustic wave in the direction P and which are disposed every distance equal to one wavelength at the above mentioned predetermined frequency.
In
FIG. 25
, the single phase unidirectional transducer
102
a
is composed of two successive single phase unidirectional transducer units (a)
2
. The single phase unidirectional transducer
102
b
is also composed of two successive single phase unidirectional transducer units (a)
2
.
The single phase unidirectional transducer unit (a)
2
is composed of three electrode fingers. The leftmost electrode finger in the drawing is connected the upper bus bar electrode
224
a
. The electrode finger located immediately to the right of the leftmost finger is connected the lower bus bar electrode
224
a
. The rightmost electrode finger in the drawing is connected the lower bus bar electrode
224
b
. Further, rightmost electrode finger is wider than the two other electrode fingers. For example, the rightmost electrode finger has a width equal to one-fourth of the wavelength at the predetermined frequency. The two other electrode fingers have a width equal to one-eighth of the wavelength at the predetermined frequency.
In this manner, the IDT
1024
is constructed so that the single phase unidirectional transducers
102
a
and
102
b
are arranged at the respective ends of the bidirectional electrode
101
. For all basic units composed of the single phase unidirectional transducer units (a)
2
and bidirectional electrode units (a
0
)
1
, the space between the excitation centers of adjacent basic units is a multiple of the above described wavelength. Accordingly, in the IDT
1024
as a whole, a surface acoustic wave is intensely propagated in the direction P in FIG.
25
.
Accordingly, the IDT
1024
can be used as the input IDT
402
of the SAW filter
407
in
FIG. 23
by connecting the input terminal
404
a
to the upper bus bar electrode
224
a
and connecting the input terminal
404
b
to the lower bus bar electrode
224
b.
Further,
FIG. 26
shows an IDT
1025
used as the input IDT
402
.
The IDT
1025
is structured so that single phase unidirectional transducers
112
a
and
112
b
are arranged at the respective sides of a bidirectional electrode
111
. As with the IDT
1024
in
FIG. 25
, the bidirectional electrode
111
propagates a surface acoustic wave in two directions parallel with the upper bus bar electrode
224
a
and the lower bus bar electrode
224
b
. Further, both single phase unidirectional transducers
112
a
and
112
b
intensely propagate a surface acoustic wave in the direction P in
FIG. 26
as with the IDT
1024
in FIG.
25
.
The bidirectional electrode
111
is composed of three successive bidirectional electrode units (c
0
). The single phase unidirectional transducers
112
a
and
112
b
are each composed of two successive single phase unidirectional transducer units (c)
12
.
Bidirectional electrode units (c
0
)
11
are each composed of four electrode fingers. The third electrode finger from the left in the drawing are connected the upper bus bar electrode
224
a
, and the other three electrode fingers are all connected the lower bus bar electrode
224
b
. Further, the single phase unidirectional transducer unit (c)
12
is composed of three electrode fingers. The leftmost electrode finger is connected the lower bus bar electrode
224
b
. The second electrode finger from the left is c
Matsunami Ken
Nakamura Hiroyuki
Nishimura Kazunori
Aguirrechea J.
Mullins Burton S.
RatnerPrestia
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