U.S. patent application number 09/390653 was filed with the patent office on 2002-02-07 for surface acoustic wave filter and multistage surface acoustic wave filter.
Invention is credited to ISHIZAKI, TOSHIO, NAKAMURA, HIROYUKI, NISHIMURA, KAZUNORI, YAMADA, TORU.
Application Number | 20020014934 09/390653 |
Document ID | / |
Family ID | 27276502 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014934 |
Kind Code |
A1 |
NAKAMURA, HIROYUKI ; et
al. |
February 7, 2002 |
SURFACE ACOUSTIC WAVE FILTER AND MULTISTAGE SURFACE ACOUSTIC WAVE
FILTER
Abstract
A surface acoustic wave resonator is constituted by an IDT
electrode and reflector electrodes disposed on both sides thereof,
on a piezoelectric substrate. Two of said surface acoustic wave
resonators are disposed nearby so that the propagation directions
of the respective surface acoustic waves are in parallel to each
other to make acoustic couple to constitute a surface acoustic wave
filter having plural exciting modes with different propagation
frequencies. The bus bar electrodes of each of two IDT electrodes
are electrically separated from each other, and the leading out
electrodes led out from at least two spots on those bus bar
electrodes are electrically connected to each other, by which one
side of the balanced input and output terminal. As a result, the
electrode resistance of the IDT electrode is alleviated to make the
insertion loss less.
Inventors: |
NAKAMURA, HIROYUKI; (OSAKA,
JP) ; YAMADA, TORU; (OSAKA, JP) ; NISHIMURA,
KAZUNORI; (YAWATA-SHI, JP) ; ISHIZAKI, TOSHIO;
(KOBE-SHI, JP) |
Correspondence
Address: |
SMITH GAMBRELL & RUSSELL LLP
THE BEVERIDGE DEGRANDI WEILACHER & YOUNG
INTELLECTUAL PROPERTY GROUP
1850 M STREET SUITE 800
WASHINGTON
DC
20036
|
Family ID: |
27276502 |
Appl. No.: |
09/390653 |
Filed: |
September 7, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09390653 |
Sep 7, 1999 |
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08862383 |
May 23, 1997 |
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5990762 |
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Current U.S.
Class: |
333/195 |
Current CPC
Class: |
H03H 9/6479 20130101;
H03H 9/6443 20130101; H03H 9/14588 20130101; H03H 9/6463 20130101;
H03H 9/0028 20130101; H03H 9/02763 20130101; H03H 9/02913 20130101;
H03H 9/14597 20130101; H03H 9/02992 20130101 |
Class at
Publication: |
333/195 |
International
Class: |
H03H 009/64 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 1996 |
JP |
HEI 8-128,760 |
Aug 30, 1996 |
JP |
HEI 8-230,016 |
Jan 14, 1997 |
JP |
HEI 9-004,894 |
Claims
What is claimed is:
1. A surface acoustic wave filter on a piezoelectric substrate
comprising first and second surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode as
an inter-digital transducer electrode, said resonators being
disposed nearby in positions in which directions of propagation of
respective surface acoustic waves are parallel with each other and
acoustically coupled, an inside bus bar electrode included in the
first IDT electrode of the first surface acoustic wave resonator
and an inside bus bar electrode included in the second IDT
electrode of the second surface acoustic wave resonator being
mutually electrically separated, said first IDT electrode being
connected to a balanced type input terminal, and said second IDT
electrode being connected to a balanced type output terminal, one
terminal of said balanced type input terminal being electrically
connected to leading out electrodes led out directly or indirectly
from at least two places of the inside bus bar electrode of said
first IDT electrode, and one terminal of said balanced type output
terminal being electrically connected to leading out electrodes led
out directly or indirectly from at least two places of the inside
bus bar electrode of said second IDT electrode, thereby performing
balanced operation.
2. A surface acoustic wave filter according to claim 1, wherein the
leading out electrode is formed in a space between the IDT
electrode and said reflector electrode.
3. A surface acoustic wave filter according to claim 1 , wherein
the two leading out electrodes formed in a space between the IDT
electrode and said reflector electrode are connected to make one
terminal of said balanced type input terminal or one terminal of
said balanced type output terminal, and to make the outside bus bar
electrode included in said IDT electrode the other terminal of said
balanced type input terminal or said balanced type output
terminal.
4. A surface acoustic wave filter according to claim 1, wherein the
area between the two leading out electrodes formed in a space
between the IDT electrode and said reflector electrode is connected
by a wiring pattern having a wider line width than the width of
said leading out electrodes formed on said piezoelectric substrate,
the further expanded position in said wiring pattern is a
connection land as one terminal of said balanced type input
terminal or as one terminal of said balanced type output terminal,
and the position of extension in outward direction of the outside
bus bar electrode included in said IDT electrode is the connection
land as the other terminal of said balanced type input terminal or
as the other terminal of said balanced type output terminal.
5. A multi-stage surface acoustic wave filter comprising a
plurality of stages of the surface acoustic wave filters of claim 2
formed on a same piezoelectric substrate, one of the leading out
electrodes on the output side of the front stage surface acoustic
wave filter being connected to the opposed leading out electrodes
on the input side of the next stage, the other of the leading out
electrodes on the output side of the front stage surface acoustic
wave filter being connected to the opposed leading out electrodes
on the input side of the next stage, and remaining one output side
electrode of said front stage surface acoustic wave filter being
connected to remaining one input side electrode of said next stage
surface acoustic wave filter.
6. A multi-stage surface acoustic wave filter comprising a
plurality of stages of the surface acoustic wave filters of claim 2
formed on a same piezoelectric substrate, one of the leading out
electrodes on the output side of the front stage surface acoustic
wave filter and the opposed leading out electrodes on the input
side of the next stage, and the other of the leading out electrodes
on the output side of the front stage surface acoustic wave filter
and the opposed leading out electrodes on the input side of the
next stage, being connected respectively by a first inter-stage
connecting electrode having a wider width than a width of said
leading out electrode, remaining one output side electrode of said
front stage surface acoustic wave filter and remaining one input
side electrode of said next stage surface acoustic wave filer being
connected respectively by a second inter-stage connecting electrode
having a wider width than the width of said leading out electrode,
space between the two leading out electrodes on the input side of
the first stage surface acoustic wave filter being connected by a
wiring pattern having a line path width wider than the width of
said leading out electrode formed on said piezoelectric substrate,
a further expanded part in said wiring pattern being a connecting
land as one terminal of said balanced type input terminals, and an
outwardly expanded part of said outside bus bar electrode included
in said IDT electrode of said first stage surface acoustic wave
filter being a connecting land as the other terminal of said
balanced type input terminals, and space between the two leading
out electrodes on the output side of the last stage surface
acoustic wave filter being connected by a wiring pattern having a
line path width wider than the width of said leading out electrode
formed on said piezoelectric substrate, a further expanded part in
said wiring pattern being a connecting land as one terminal of said
balanced type output terminals, and an outwardly expanded part of
said outside bus bar electrode included in said IDT electrode of
said last stage surface acoustic wave filter being a connecting
land as the other terminal of said balanced type output
terminals.
7. A multi-stage surface acoustic wave filter according to claim 6,
wherein the space between the first and second inter-stage
connection electrodes is connected through the reactance
element.
8. A multi-stage surface acoustic wave filter according to claim 6,
wherein, of the first and second inter-stage connection electrodes,
one is grounded and the other is grounded through the reactance
element.
9. A multi-stage surface acoustic wave filter according to claim 6,
wherein said first inter-stage connection electrode is grounded
through the reactance element, and the second inter-stage
connection electrode is grounded.
10. A surface acoustic wave filter on a piezoelectric substrate
comprising a first surface acoustic wave resonator having reflector
electrodes on both sides of a first IDT electrode for exciting a
surface acoustic wave and a second surface acoustic wave resonator
having reflector electrodes on both sides of a second IDT electrode
being disposed nearby to each other in the positions in which a
propagation direction of the respective surface acoustic waves
becomes parallel and acoustically coupled, an inside first bus bar
electrode included in said first IDT electrode and an inside second
bus bar electrode included in said second IDT electrode being
mutually separated and disposed in opposed manner, one input
terminal of balanced type input terminals, said one input terminal
being constructed by using an electrical connection between leading
out electrodes led out from at least two places on said inside
first bus bar electrode, and one output terminal of balanced type
output terminals , said one input terminal being constructed by
using an electrical connection between leading out electrodes led
out from at least two places on said inside second bus bar
electrode, thereby performing balanced operation.
11. A surface acoustic wave filter comprising first and third
surface acoustic wave resonators each having a reflector electrode
on both sides of an IDT electrode as an inter-digital transducer
electrode, said resonators being disposed in positions in which the
directions of propagation of the respective surface acoustic waves
are parallel with each other, a plurality of strip line electrodes
having substantially the same length as the crossing width of the
electrode fingers of the IDT electrodes being disposed in parallel
between said first and third surface acoustic wave resonators in
the same electrode period as those of the first and third surface
acoustic wave resonators, both end parts of said plural strip line
electrodes being connected one another by bus bar electrodes to
form a second surface acoustic wave resonator comprising periodic
structured electrode rows, said first, second, and third surface
acoustic wave resonators being disposed nearby to one another to
make acoustic couple, and a first and second leading out electrodes
to constitute a part of the balanced type input terminal being
formed in a gap between the reflector electrodes on both sides in
the outside direction from both ends of the inside bus bar
electrode of the IDT electrode of the first surface acoustic wave
resonator, and a third and fourth leading out electrodes to
constitute a part of the balanced type output terminal being formed
in a gap between the reflector electrodes on both sides in the
outside direction from both ends of the inside bus bar electrode of
the IDT electrode of the third surface acoustic wave resonator,
thereby making balanced operation.
12. A surface acoustic wave filter according to claim 11, wherein
said first and second leading out electrodes of said surface
acoustic wave resonators are connected to make one input terminal
of the balanced type input terminal, a bus bar electrode on the
outside of the IDT electrode of said first surface acoustic wave
resonator is made the other input terminal of the balanced type
input terminal, said third and fourth leading out electrodes of
said third surface acoustic wave resonator are connected to make
one output terminal of the balanced type output terminal, and a bus
bar electrode on the outside of the IDT electrode of said third
surface acoustic wave resonator is made the other output terminal
of the balanced type output terminal.
13. A surface acoustic wave filter according to claim 11, wherein
space between said first and second leading out electrodes of said
surface acoustic wave resonators is connected by a wiring pattern
having a line path width wider than the width of the leading out
electrode formed on the piezoelectric substrate, a part of said
wiring pattern is further expanded to form a connection land of one
part of the balanced type input terminals, and a bus bar electrode
on the outside of the IDT electrode of the first surface acoustic
wave resonators is expanded in the external direction to form a
connection land of the other part of the balanced type input
terminals, spece between the third and the fourth leading out
electrodes of said third surface acoustic wave resonators is
connected by a wiring pattern having a line path width wider than
the width of said leading out electrode, a part of said wiring
pattern is further expanded to form a connection land of one part
of the balanced type output terminals of the balanced type output
terminal, and a bus bar electrode on the outside of the IDT
electrode of the third surface acoustic wave resonators is expanded
in the external direction to form a connection land of the other
part of the balanced type input terminals.
14. A multi-stage surface acoustic wave filter comprising a
plurality of stages of the surface acoustic wave filters of claim
12 formed on a same piezoelectric substrate, said third and fourth
leading out electrodes of the front stage surface acoustic wave
filter being connected to the opposed first and second leading out
electrodes of the surface acoustic wave filters of the next stage,
respectively, with the remaining output side electrode of said
front stage surface acoustic wave filter being connected to the
remaining input side electrode of said next stage surface acoustic
wave filter.
15. A multi-stage surface acoustic wave filter comprising: a
plurality of stages of the surface acoustic wave filters of claim
12 formed on a same piezoelectric substrate, the third and fourth
leading out electrodes of the front stage surface acoustic wave
filter and the opposed leading out electrodes of the next stage,
being connected by a first inter-stage connecting electrode having
a wider width than the width of said leading out electrode on said
piezoelectric substrate, another output side electrode and input
side electrode of said front stage and next stage being connected
by a second inter-stage connecting electrode having a wider width
than the width of said leading out electrode, space between the
first and second leading out electrodes of the first stage surface
acoustic wave filter being connected by a wiring pattern having a
line path width wider than the width of said leading out electrode
formed on said piezoelectric substrate, a part of said wiring
pattern being further expanded to form a connecting land for one of
said balanced type input terminals, and an outside bus bar
electrode of IDT electrode of said first stage surface acoustic
wave filter being outwardly expanded to form the other connecting
land of balanced type input terminals, and space between the third
and fourth leading out electrodes of the last stage surface
acoustic wave filter being connected by a wiring pattern having a
line path width wider than the width of said leading out electrode
formed on said piezoelectric substrate, and a part of said wiring
pattern being further expanded to form a connecting land for one of
the balanced type output terminals, and a part of said outside bus
bar electrode on the outside of IDT electrode of said last stage
surface acoustic wave filter being outwardly expanded to form a
connecting land for the other of the balanced type output
terminals.
16. A multi-stage surface acoustic wave filter according to claim
15, wherein the area between the first and the second inter-stage
connecting electrodes is connected through a reactance element.
17. A multi-stage surface acoustic wave filter according to claim
15, wherein, of the first and the second inter-stage connecting
electrodes, one is grounded and the other is grounded through a
reactance element.
18. A multi-stage surface acoustic wave filter according to claim
15, wherein said first inter-stage connecting electrode is grounded
through the reactance element, and the second inter-stage
connecting electrode is grounded.
19. A surface acoustic wave filter according to claim 11, wherein
said two surface acoustic wave resonators are of the constructions
possessing reflector electrodes on both sides of the IDT electrode,
of substantially the same configurations as the first and third
surface acoustic wave resonators, and said IDT electrodes are
grounded.
20. A surface acoustic wave filter according to claim 14, wherein
said two surface acoustic wave resonators are of the constructions
possessing reflector electrodes on both sides of the IDT electrode,
of substantially the same configurations as the first and third
surface acoustic wave resonators, and said IDT electrodes are
grounded.
21. A surface acoustic wave filter on a piezoelectric substrate
comprising a first surface acoustic wave resonator having reflector
electrodes on both sides of a first electrode for exciting a
surface acoustic wave and a third surface acoustic wave resonator
having reflector electrodes on both sides of the third electrode
being disposed each other in the positions in which a propagation
direction of the respective surface acoustic waves becomes
parallel, the first bus bar electrode included in said first
electrode and the third bus bar electrode included in said third
electrode being mutually separated and disposed in opposed manner,
a second surface acoustic wave resonator having a plurality of
strip line electrodes, an electrode for connecting the one end
parts of both ends of those plural strip line electrodes, and
electrodes for connecting the other end parts, being formed between
the opposed first bus bar electrode and third bus bar electrodes,
said first surface acoustic wave resonator and said third surface
acoustic wave resonator being disposed nearby to each other to the
second surface acoustic wave resonator and acoustically coupled,
one input terminal of balanced type input terminals, said one input
terminal being constructed by using an electrical connection
between leading out electrodes led out from at least two places on
said first bus bar electrode, and one output terminal of balanced
type output terminals , said one input terminal being constructed
by using an electrical connection between leading out electrodes
led out from at least two places on said third bus bar electrode,
thereby performing balanced operation.
22. A surface acoustic wave filter on a piezoelectric substrate
comprising first and third surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode as
an inter-digital transducer electrode, said resonators being
disposed on a piezoelectric substrate in positions in which
directions of propagation of the respective surface acoustic waves
are parallel with each other, a plurality of strip line electrodes
being disposed in parallel between said first and third surface
acoustic wave resonators in the same electrode period as those of
the first and third surface acoustic wave resonators, said plural
strip line electrodes being connected one another by bus bar
electrodes to form a second surface acoustic wave resonator having
periodic structured electrode rows, said first and third surface
acoustic wave resonators being disposed nearby to said second
surface acoustic wave resonator to make acoustic couple, and the
adjacent bus bar electrodes between said surface acoustic wave
resonators being electrically separated, and all periodic
structured electrodes of said second surface acoustic wave
resonators being grounded, assuming that an electrode finger
crossing width of IDT electrodes constituting the first and third
surface acoustic wave resonators to be W1, and a strip line length
of said periodic structured electrode rows constituting the second
surface acoustic wave resonator to be W2, the relative size of W1
to W2 being set to 1.ltoreq.W2/W1.
23. A surface acoustic wave filter on a piezoelectric substrate
comprising first, second and third surface acoustic wave resonators
each having a reflector electrode on both sides of an IDT-electrode
as an inter-digital transducer electrode, said resonators being
disposed on a piezoelectric substrate in positions nearby to one
another in which directions of propagation of the respective
surface acoustic waves are parallel with each other to make
acoustic couple, the adjacent bus bar electrodes between said
surface acoustic wave resonators being electrically separated, and
all said IDT electrodes of said second surface acoustic wave
resonators provided between said first and third resonators being
grounded, assuming that an electrode finger crossing width of IDT
electrodes constituting the first and third surface acoustic wave
resonators to be W1, and an electrode finger crossing width of the
IDT electrodes of the second surface acoustic wave resonator to be
W2, the relative size of W1 to W2 being set to 1.ltoreq.W2/W1.
24. A surface acoustic wave filter according to claim 22 , wherein
the relative size of W1 to W2 is set to
1.ltoreq.W2/W1.ltoreq.1.3.
25. A multi-stage surface acoustic wave filter wherein a plurality
of surface acoustic wave filters according to claim 22 are
vertically connected by the first and second inter-stage electrode
patterns formed on the piezoelectric substrate.
26. A multi-stage surface acoustic wave filter according to claim
25, wherein, of the first and second inter-stage connected
electrode patterns, one is directly grounded, and the other is
grounded through a reactance element.
27. A multi-stage surface acoustic wave filter according to claim
25, wherein the first surface acoustic wave resonator electrode of
the front stage surface acoustic wave filter is connected to the
balanced type input terminal, and the third surface acoustic wave
resonator electrode of the back stage surface acoustic wave filter
is connected to the balanced type output terminal.
28. A surface acoustic wave filter on a piezoelectric substrate
comprising at least two surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode as
an inter-digital transducer electrode, at least two of said
resonators being disposed on a piezoelectric substrate in positions
nearby to one another in which directions of propagation of the
respective surface acoustic waves are parallel with one another to
make acoustic couple, characterized in that, of plural electrode
fingers included in at least one IDT electrode, at least a couple
of adjacent electrode fingers are in reverse phase relations to
each other, and said plural electrode fingers are connected so as
not to cancel the respective electric charges.
29. A surface acoustic wave filter according to claim 28, wherein
said IDT electrode has an inside bus bar electrode and an outside
bus bar electrode, said pair of adjacent electrode fingers being in
reverse phase relation means that (1) a pitch between said adjacent
electrode fingers is (m+1/2) .times..lambda. (wherein .lambda. is
wavelength of excited surface acoustic wave and m=0,1,2, . . . )
and both said adjacent electrode fingers are connected to the
inside bus bar electrode, (2) a pitch between said adjacent
electrode fingers is (m+1/2).times..lambda. and both said adjacent
electrode fingers connected to the outside bus bar electrode, or
(3) a pitch between said adjacent electrode fingers is
(m+1).times..lambda., one side electrode finger of both said
adjacent electrode fingers is connected to said inside bus bar, and
the other side electrode finger is connected to said outside bus
bar electrode.
30. A surface acoustic wave filter according to claim 28, wherein
said at least one IDT electrode is constituted by the first,
second, and third divisional IDT electrodes, a pair of electrode
fingers on the position in which said first divisional IDT
electrode and said second divisional IDT electrode are adjacent are
in reverse phase relations, and a pair of electrode fingers on the
position in which said second divisional IDT electrode and said
third divisional IDT electrode are adjacent are in same phase
relations, and further, the outside bus bar electrode of the first
divisional IDT electrode and the inside bus bar electrode of the
second divisional IDT electrode are connected, and the outside bus
bar electrode of the second divisional IDT electrode and the
outside bus bar electrode of the third divisional IDT electrode are
connected.
31. A surface acoustic wave filter according to claim 30, wherein
said first, second, and third divisional IDT electrodes are divided
into groups on the basis of the divisional point of the bus bar
electrode held by said at least one IDT electrode, said pair of
adjacent electrode fingers being in the same phase relation means
that (1) a pitch between said adjacent electrode fingers is (m+1/2)
.times..lambda. (wherein; is wavelength of excited surface acoustic
wave, and m=0,1,2, . . . ), one side electrode finger of both said
adjacent electrode fingers is connected to said inside bus bar, and
the other side electrode finger is connected to said outside bus
bar electrode, (2) a pitch between said adjacent electrode fingers
is (m+1).times..lambda. and both said adjacent electrode fingers
are connected to the inside bus bar electrode, or (3) a pitch
between said adjacent electrode fingers is (m+1).times..lambda. and
both said adjacent electrode fingers are connected to the outside
bus bar electrode.
32. A surface acoustic wave filter according to claim 28, wherein
said at least one IDT electrode is constituted by the first,
second, and third divisional IDT electrodes, a pair of electrode
fingers on a position in which said first divisional IDT electrode
and said second divisional IDT electrode are adjacent are in
reverse phase relations, and a pair of electrode fingers on a
position in which said second divisional IDT electrode and said
third divisional IDT electrode are adjacent are in same phase
relations, and further, the inside bus bar electrode of the first
divisional IDT electrode and the outside bus bar electrode of the
second divisional IDT electrode are connected, and the inside bus
bar electrode of the second divisional IDT electrode and the inside
bus bar electrode of the third divisional IDT electrode are
connected.
33. A surface acoustic wave filter on a piezoelectric substrate
comprising at least two surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode as
an inter-digital transducer electrode, at least two of said
resonators being disposed on a piezoelectric substrate in positions
nearby to one another in which directions of propagation of the
respective surface acoustic waves are parallel with one another to
make acoustic couple, characterized in that, of the plural
electrode fingers included in at least one IDT electrode, any pair
of adjacent electrode fingers are in the same phase relations, and
said plural electrode fingers are connected so as not to cancel the
respective electric charges, said at least one IDT electrode is
constituted by the first, second, and third divisional IDT
electrodes, the inside bus bar electrode of the first divisional
IDT electrode and the inside bus bar electrode of the second
divisional IDT electrode are connected, and the outside bus bar
electrode of the second divisional IDT electrode and the outside
bus bar electrode of the third divisional IDT electrode are
connected.
34. A surface acoustic wave filter according to claim 33, wherein
said pair of adjacent electrode fingers being in the same phase
relation means that (1) a pitch between said adjacent electrode
fingers is (m+1/2) .times..lambda. (wherein .lambda. is wavelength
of excited surface acoustic wave, and m=0,1,2, . . . ), one side
electrode finger of both said adjacent electrode fingers is
connected to said inside bus bar, and the other side electrode
finger is connected to said outside bus bar electrode, (2) a pitch
between said adjacent electrode fingers is (m+1).times..lambda. and
both said adjacent electrode fingers are connected to the inside
bus bar electrode, or (3) a pitch between said adjacent electrode
fingers is (m+1).times..lambda. and both said adjacent electrode
fingers are connected to the outside bus bar electrode.
35. A surface acoustic wave filter according to claim 30, wherein
the electric terminal of IDT electrode constituted by said
divisional IDT electrode is of a balanced type.
36. A surface acoustic wave filter according to claim 30, wherein
said inside electrode and said outside electrode of said second
divisional IDT electrode are connected to the balanced type
positive and negative electric terminals, respectively, and an
electrode which is not connected to any of positive and negative
electric terminals in the first and third divisional IDT electrodes
is grounded.
37. A surface acoustic wave filter according to claim 28, wherein,
by changing the divisional ratio of said divisional IDT electrode,
the total capacity of said IDT electrode is made variable to
control the input and output impedance's.
38. A multi-stage surface acoustic wave filter on a piezoelectric
substrate comprising two surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode, a
plurality of stages of said resonators being disposed on a
piezoelectric substrate in positions nearby to one another in which
directions of propagation of the respective surface acoustic waves
are parallel with one another to make acoustic couple,
characterized in that, of the plural electrode fingers included in
at least one IDT electrode of the top stage and the bottom stage of
said multi-stage surface acoustic wave filter, at least a couple of
adjacent electrode fingers are in reverse phase relations, and said
plural electrode fingers are connected in such manner that the
electric charges do not act to cancel one another.
39. A multi-stage surface acoustic wave filter according to claim
38, wherein at least one side IDT electrode is constituted by the
first, second and third divisional IDT electrodes, a couple of
electrode fingers in a position in which said first divisional IDT
electrode and said second IDT electrode are adjacent to each other
are in reverse phase relations, and a couple of electrode fingers
in a position in which said second divisional IDT electrode and
said third divisional IDT electrode are adjacent to each other are
in the same phase relations, and further, the outside bus bar
electrode of the first divisional IDT electrode and the inside bus
bar electrode of the second divisional IDT electrode are connected,
and the outside bus bar electrode of the second divisional IDT
electrode and the outside bus bar electrode of the third divisional
IDT electrode are connected.
40. A multi-stage surface acoustic wave filter according to claim
38, wherein at least one side IDT electrode is constituted by the
first, second and third divisional IDT electrodes, a couple of
electrode fingers in a position in which said first divisional IDT
electrode and said second IDT electrode are adjacent to each other
are in reverse phase relations, and a couple of electrode fingers
in a position in which said second divisional IDT electrode and
said third divisional IDT electrode are adjacent to each other are
in the same phase relations, and further, the inside bus bar
electrode of the first divisional IDT electrode and the outside bus
bar electrode of the second divisional IDT electrode are connected,
and the inside bus bar electrode of the second divisional IDT
electrode and the inside bus bar electrode of the third divisional
IDT electrode are connected.
41. A multi-stage surface acoustic wave filter on a piezoelectric
substrate comprising two surface acoustic wave resonators each
having a reflector electrode on both sides of an IDT electrode, a
plurality of stages of said resonators being vertically connected
by an inter-stage connection electrode pattern, being disposed on a
piezoelectric substrate in positions nearby to one another in which
a directions of propagation of the respective surface acoustic
waves are parallel with one another to make acoustic couple,
characterized in that, of the plural electrode fingers included in
at least one IDT electrode of the top stage and the bottom stage of
said multi-stage surface acoustic wave filter, any couple of
adjacent electrode fingers are in the same phase relations, and
said plural electrode fingers are connected so that the respective
electric charges do not act to cancel one another, at least one
side IDT electrode is constituted by the first, second and third
divisional IDT electrodes, the inside bus bar electrode of the
first divisional IDT electrode and the inside bus bar electrode of
the second divisional IDT electrode are connected, and the outside
bus bar electrode of the second divisional IDT electrode and the
outside bus bar electrode of the third divisional IDT electrode are
connected.
42. A multi-stage surface acoustic wave filter according to claim
39, wherein the electric terminal of the IDT electrode constituted
by said divisional IDT electrode is of a balanced type.
43. A multi-stage surface acoustic wave filter according to claim
39, wherein said inside electrode and said outside electrode of
said second divisional IDT electrode are connected to the balanced
type positive and negative electric terminals, respectively, and an
electrode which is not connected to any of positive and negative
electric terminals in the first and third divisional IDT electrodes
is grounded.
44. A multi-stage surface acoustic wave filter according to claim
42, wherein said inter-stage connecting electrode patterns are
provided in a plurality of stages, and one part of them are
grounded, and others are grounded through a reactance element.
45. A surface acoustic wave filter comprising three surface
acoustic wave resonators each having a reflector electrode on both
sides of an IDT electrode, being disposed on a piezoelectric
substrate in positions nearby to one another in which directions of
propagation of the respective s are parallel with one another to
make acoustic couple, characterized in that, of the three surface
acoustic wave resonators, the at the center are all electrically
grounded, and the IDT electrodes constituting said surface acoustic
wave resonators disposed outside are electrically made independent,
and further, of a plurality of electric fingers which are included
in IDT electrode of the at least one surface acoustic wave
resonators disposed outside, at least a couple of adjacent
electrode fingers are in the reverse phase relations, and said
plural electrode fingers are connected so that the respective
electric charges do not act to cancel one another.
46. A multi-stage surface acoustic wave filter comprising a
plurality of stages of surface acoustic wave filters according to
claim 45 connected in vertical stages by a plurality of inter-stage
connecting electrode patterns formed on a piezoelectric
substrate.
47. A surface acoustic wave filter according to claim 15, wherein
said two surface acoustic wave resonators are of the constructions
possessing reflector electrodes on both sides of the IDT electrode,
of substantially the same configurations as the first and third
surface acoustic wave resonators, and said IDT electrodes are
grounded.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a surface acoustic wave
filter to be used for a high frequency wave circuit or the like in,
for example, a radiocommunication apparatus.
[0003] 2. Related Art of the Invention
[0004] As the electromechanical function parts using surface
acoustic wave (SAW) have been noted with attention in the current
of making the hardware high density because the acoustic velocity
of wave is several kilometers/second, and the wave energy has
properties to be concentrated on the surface of the propagation
medium. Due to the development of interdigital transducer (IDT)
electrode and progress of the thin film preparing technique which
has made its modified development possible, the same has been
practically utilized for delay line for radar, band-pass filter for
television receiver, etc. At present, the SAW is extensively used
as RF and IF stage filters for receiving and transmitting circuits
in radiocommunication apparatus.
[0005] In recent years, in consequence of the adoption of digital
system for the moving objects, developments of digital portable
telephone and digital cordless telephone are intensively steered.
As the communication systems to be used for these apparatuses have
information on the amplitude and phase of signals, flatness of
amplitude characteristic and group delay deflection characteristic
are required for the filters to be used for IF stage. Also, as the
excellent characteristic is required for the selectivity to
distinguish the signal of adjacent channel and the desired signal,
acute attenuation characteristic having narrow transition bandwidth
is also an essential condition. Also, recently, balanced input and
output of the IC device in the stage before and after the IF filter
have progressed, and the balanced input and output are required for
the IF filter.
[0006] Conventionally, as SAW filter suitable for the IF stage
there are known transversal SAW filter and two kinds of
longitudinal mode coupled and transverse mode coupled type SAW
filters. The transversal SAW filter has excellent group delay
deflection characteristic, but it has large insertion loss, poor
attenuation characteristic, and large element size. On the other
hand, the mode coupled type SAW filter presents acute attenuation
characteristic, shows small insertion loss, and is small in element
size, but its group delay deflection characteristic is inferior to
that of transversal type SAW filter. The longitudinal mode type SAW
is characterized by having relatively large spurious zone on the
high band side in the vicinity of the passing band, and the
transverse mode type SAW filter is characterized by having very
narrow band characteristic. In view of the above characteristics,
as the IF filter for the mobile communication apparatus the
transverse mode coupled type SAW filter which is miniature in size
and excellent in attenuation characteristic has been widely
used.
[0007] Hereinafter, explanation is made on the conventional
transverse mode coupled type SAW filter.
[0008] FIG. 24 is a constitution view showing a transverse mode
coupled resonator type SAW filter according to conventional
technique. In FIG. 24, the part 241 is a single crystal
piezoelectric substrate. By forming an electrode pattern on the
piezoelectric substrate 241, the SAW can be excited. The part 242a
is an IDT electrode formed on the piezoelectric substrate 241, and
by setting the reflector electrodes 242b and 242c on both sides
thereof, an energy sealing in type SAW resonator is formed. On the
piezoelectric substrate 241, there is formed a similar SAW
resonator by the IDT electrode 243a and the reflector electrodes
243b and 243c. And, these two resonators are disposed nearby, and
because of the formation of acoustic couple between them, SAW
filter is constituted.
[0009] In the SAW filter constituted as above, two kinds of
SAW-mode frequencies to be excited on the piezoelectric substrate
are determined by the electrode finger crossing width of IDT
electrodes and the distance between the two SAW resonators disposed
nearby, and the passing band width of the filter is determined.
[0010] In the SAW filter constituted as above, the bandwidth that
can be realized is very narrow, and the specific bandwidth of the
filter to be realized (normalized bandwidth at the central
frequency of the filter) is at most about 0.1%. In order to meet
the recent digital system, it is required to make the filter
passing characteristics wider bandwidth and broaden the flat
bandwidth of the group delay deflection characteristic.
[0011] Also, recently a balanced input and output of IC device in
the pre-and post-stages of IF filter have progressed. Accordingly,
a balanced input and output type is strongly demanded for the IF
filters. However, as shown in FIG. 24, in the conventional SAW
filters, the one side of the electrode fingers of input and output
stages of the IDT electrodes 242a, 243a is grounded, and there is a
problem that the filter cannot be formed in a balanced input and
output type.
[0012] Furthermore, there has been desired the impedance matching
between the IF filter and the IC devices in the pre-and post-stages
thereof, and as the input and output impedance's of the
conventional filters depend on the number of pairs of the electrode
fingers included in the IDT electrodes which are closely related
with the filter characteristic, there has been a problem of it
being difficult to obtain the desired impedance value
simultaneously with obtaining the desired filter
characteristic.
SUMMARY OF THE INVENTION
[0013] The present invention is to settle the above problems in the
prior art, and its objects are (1) to realize a balanced type input
and output constitution and to improve balancing extent of the
balanced type terminal in the input and output terminal and realize
low insertion loss, (2) to make the pass band wide width, and to
make the phase and amplitude characteristics flat, and (3) to
provide a SAW filter having the desired input and output
impedance's.
[0014] In order to attain the above objects, the SAW filter of the
present invention comprises first and second surface acoustic wave
resonators each having a reflector electrode on both sides of an
IDT electrode as an inter-digital transducer electrode, said
resonators being disposed nearby in positions in which directions
of propagation of the respective surface acoustic waves are
parallel with each other and acoustically coupled,
[0015] an inside bus bar electrode included in the first IDT
electrode of the first surface acoustic wave resonator and an
inside bus bar electrode included in the second IDT electrode of
the second surface acoustic wave resonator being mutually
electrically separated,
[0016] said first IDT electrode being connected to a balanced type
input terminal, and said second IDT electrode being connected to a
balanced type output terminal,
[0017] one terminal of said balanced type input terminal being
electrically connected to leading out electrodes led out directly
or indirectly from at least two places of the inside bus bar
electrode of said first IDT electrode, and one terminal of said
balanced type output terminal being electrically connected to
leading out electrodes led out directly or indirectly from at least
two places of the inside bus bar electrode of said second IDT
electrode, thereby performing balanced operation.
[0018] By this constitution, there can be obtained, for example, a
basic electrode pattern of SAW filter having a balanced type input
and output terminal having low insertion loss and favorable
balancing level.
[0019] Also, in order to settle the problems mentioned above, the
SAW filter of the present invention comprises first and third
surface acoustic wave resonators each having a reflector electrode
on both sides of an IDT electrode as an inter-digital transducer
electrode, said resonators being disposed on a piezoelectric
substrate in positions in which directions of propagation of the
respective surface acoustic waves are parallel with each other,
[0020] a plurality of strip line electrodes being disposed in
parallel between said first and third surface acoustic wave
resonators in the same electrode period as those of the first and
third surface acoustic wave resonators, said plural strip line
electrodes being connected one another by bus bar electrodes to
form a second surface acoustic wave resonator having periodic
structured electrode rows, said first and third surface acoustic
wave resonators being disposed nearby to said second surface
acoustic wave resonator to make acoustic couple, and the adjacent
bus bar electrodes between said surface acoustic wave resonators
being electrically separated, and all periodic structured
electrodes of said second surface acoustic wave resonators being
grounded,
[0021] assuming that an electrode finger crossing width of IDT
electrodes constituting the first and third surface acoustic wave
resonators to be W1, and a strip line length of said periodic
structured electrode rows constituting the second surface acoustic
wave resonator to be W2, the relative size of W1 to W2 being set to
1.ltoreq.W2/W1.
[0022] By this constitution, the distance between the three
resonance frequencies becomes equal, and when the input and output
coordination is obtained, the ripples in the pass band decrease to
give excellent pass characteristics. As a result, there can be
obtained the SAW filter having broad bandwidth and flat pass
characteristics and acute attenuation characteristics.
[0023] Furthermore, in order to solve the above problems, the SAW
filter of the present invention comprises at least two surface
acoustic wave resonators each having a reflector electrode on both
sides of an IDT electrode as an inter-digital transducer electrode,
at least two of said resonators being disposed on a piezoelectric
substrate in positions nearby to one another in which directions of
propagation of the respective surface acoustic waves are parallel
with one another to make acoustic couple,
[0024] characterized in that, of plural electrode fingers included
in at least one IDT electrode, at least a couple of adjacent
electrode fingers are in reverse phase relations to each other, and
said plural electrode fingers are connected so as not to cancel the
respective electric charges.
[0025] By this constitution, there can be obtained an SAW filter
having the desired input and output impedance.
[0026] As described above, according to this invention, it is
possible to provide a compact SAW filter which shows the smaller
insertion loss than the conventional one, improved balancing level
in the balanced type input and output terminal, or, which can be
provided with flat filter pass characteristic and good extra-band
attenuation characteristic, or which has the desired input and
output impedance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a constitution view showing a SAW filter according
to the first embodiment of the present invention.
[0028] FIG. 2 is a constitution view showing another example of SAW
filter according to the first embodiment of the present
invention.
[0029] FIG. 3 is a constitution view showing a multi-stage SAW
filter according to the first embodiment of the present
invention.
[0030] FIG. 4 is a constitution view showing another example of a
multi-stage SAW filter according to the first embodiment of the
present invention.
[0031] FIG. 5 is a constitution view showing a SAW filter according
to the second embodiment of the present invention.
[0032] FIG. 6 is a constitution view showing another example of a
SAW filter according to the second embodiment of the present
invention.
[0033] FIG. 7 is a constitution view showing another example of a
SAW filter according to the second embodiment of the present
invention.
[0034] FIG. 8 is a constitution view showing a multi-stage SAW
filter according to the second embodiment of the present
invention.
[0035] FIG. 9 is a constitution view showing another example of a
multi-stage SAW filter according to the second embodiment of the
present invention.
[0036] FIG. 10 is a constitution view showing a SAW filter
according to the third embodiment of the present invention.
[0037] FIG. 11 is a distribution chart of an excitation mode for
illustrating the operation of the SAW filter according to the third
embodiment of the present invention.
[0038] FIG. 12 is a characteristic chart of the resonance frequency
of each mode to the value of W specified by the SAW wavelength; in
the case of W1=W2=W in the third embodiment of the present
invention.
[0039] FIG. 13 is a representative actual measurement chart showing
a comparative example of the passing characteristics of the SAW
filter in the third embodiment of the present invention.
[0040] FIG. 14 is an actual measurement view of a resonance mode
frequency difference to W2/W1 in the third embodiment of the
present invention.
[0041] FIG. 15 is an actual measurement view showing the pass
characteristic of SAW filter in the third embodiment of the present
invention.
[0042] FIG. 16 is a constitution view showing another example of
the SAW filter in the third embodiment of the present
invention.
[0043] FIG. 17 is a constitution view showing a SAW filter in the
fourth embodiment of the present invention.
[0044] FIG. 18 is a constitution view showing a SAW filter in the
fifth embodiment of the present invention.
[0045] FIG. 19 is a capacity equivalent circuit diagram of the SAW
filter in the fifth embodiment of the present invention.
[0046] FIG. 20 is a constitution view showing another example of
SAW filter in the fifth embodiment of the present invention.
[0047] FIG. 21 is a constitution view showing another example of
SAW filter in the sixth embodiment of the present invention.
[0048] FIG. 22 is a constitution view showing another example of
SAW filter in the seventh embodiment of the present invention.
[0049] FIG. 23 is a constitution view showing another example of
SAW filter in the eighth embodiment of the present invention.
[0050] FIG. 24 is an electrode pattern diagram of conventional SAW
filter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] Hereinafter, preferred embodiments of the present invention
will be illustrated with reference to the drawings.
[0052] Embodiment 1
[0053] FIG. 1 is a constitution view showing a SAW filter according
to the first embodiment of the present invention. By forming an
electrode pattern having a strip line shaped periodical structure
on a single crystal piezoelectric substrate 11 shown in FIG. 1, SAW
can be excited. On the piezoelectric substrate 11 there is formed a
first SAW resonator of energy strage type constituted by an IDT
electrode 12a and reflector electrodes 12b, 12c. Also, on the
piezoelectric substrate 11, there is constituted a second SAW
resonator of constituted by an IDT electrode 13a and reflector
electrodes 13b, 13c. And, these two SAW resonators are disposed
close to each other, and by formation of acoustic couple between
them, a SAW filter is constituted.
[0054] A remarkable difference in the electrode pattern
constitutions between the SAW filter of the first embodiment of the
present invention shown in FIG. 1 and that of prior art as shown in
FIG. 24 is that the bus bar electrodes 244 common to the two
resonators disposed nearby of conventional style in FIG. 24 are
electrically separated in the IDT electrode part into the inside
first bus bar 14 and the second bus bar 15 in the first embodiment
of the present invention. The first bus bar 14 belongs to the first
SAW resonator, and the second bus bar 15 to the second SAW
resonator. By this bus bar separation constitution, the first and
second SAW resonators can have fully electrically independent input
or output stages. Namely, the balanced input stage of the first SAW
resonator is constituted by an electrode finger formed by being
bound by the first bus bar electrode 14 and an IDT electrode 12a
comprising an electrode finger to be coupled with said electrode
finger. In the same manner, the balanced output stage of the second
SAW resonator is constituted by an IDT electrode 13a comprising an
electrode finger formed by being bound by the second bus bar
electrode 15 and an electrode finger to be coupled with said
electrode finger. Here, the first IDT electrode of the present
invention corresponds to the IDT electrode 12a. The second IDT
electrode of the present invention corresponds to the IDT electrode
13a.
[0055] The connection of the signal line to the balanced circuit
constituted as above may be made to apply an input signal to the
spot between the first bus bar electrode 14 and the third bus bar
electrode 14a positioned outside the IDT electrode to be coupled
therewith, and to take out the output signal from the spot between
the second bus bar electrode 15 and the fourth bus bar electrode
15a positioned outside the IDT electrode to be coupled therewith.
By this step, the object of balancing the input and output
terminals has been attained. When this is observed from the aspect
of the insertion loss, the amount is about 3.2 dB in the case of
the above connection.
[0056] With respect to one terminal of the balanced type input
terminal described above, a connection line is led from one spot of
the first bus bar electrode 14, and as to the one terminal in the
balanced type output terminals, explanation has been given on the
case where a connection line is led from one spot of the second bus
bar electrode 15. Against this, the case of the constitution
leading out the connection lines from the two spots of the first
and second bus bar electrodes 14, 15 is described next.
[0057] With respect to this insertion loss, by leading out two
connection lines (leading out electrode fingers 16a, 16b) from two
spots of the first bus bar electrode 14 to make a terminal of the
input side, and leading out two connection lines (leading out
electrode fingers 17a, 17b) from two spots of the second bus bar
electrode 15 to make a terminal of the input side, improvement of
the balancing level in the balanced type input and output terminal
is realized, the difference of loss formed in each terminal is
decreased to reduce the above insertion loss to a large extent to
about 2.8 dB. This is an effect having an important value in a
miniature type portable communication apparatus which weighs as
being important the minor loss and a balance level in the balanced
type input and output terminal. In other words, in FIG. 1, from
both ends of the first bus bar electrode 14, the leading out
electrode fingers 16a, 16b directed outward are formed on the space
between the IDT electrode 12a and the reflector electrodes 12b,
12c, and by connecting the end parts of these electrode fingers as
illustrated, the effect as mentioned above is obtained. The leading
out electrode fingers 17a, 17b at both ends of the second bus bar
electrode 15 also have the same effect. The leading out electrode
fingers 16a, 16b can be regarded as being constituted by the
electrode fingers having the same length as other electrode fingers
which are connected to the two end parts of the first bus bar
electrode 14 and the leading out electrodes of short length
connected to the front end parts of those two electrode fingers.
Same comments can be made on the leading out electrode fingers 17a,
17b.
[0058] FIG. 2 shows an example of variations of the first
embodiment of the present invention shown in FIG. 1. To the parts
which perform the same functions as those given in FIG. 1 the same
marks are affixed and explanations thereon are omitted.
[0059] The wiring pattern 21 to connect between the leading
electrode fingers 16a and 16b is formed on the piezoelectric
substrate 11 and has a line width wider than the resonator
electrode. A part of it is further expanded as shown in FIG. 2 to
form a one connection land 21a for connecting between the balanced
type input and output terminals and the outside wiring member
25a.
[0060] The wiring pattern 22 for connecting between the leading out
electrode fingers 17a and 17b is formed on the piezoelectric
substrate 11, and has a line width wider than the resonator
electrode width. A part of it is further expanded, as shown in the
same figure, to form one connection land 22a for the connection
line between the balanced type output terminal and the outside
wiring member 26a.
[0061] The bus bar electrode 14a is extended outward to form
another connection land 23 for connecting between the balanced type
output terminal and the outside wiring member 25b. The bus bar
electrode 15a is also extended outward to form another connection
land 24 for connecting between the balanced type output terminal
and the outside wiring member 26b.
[0062] The above constitution is effective for assuring the
characteristics of low insertion loss and good balanced level of
the SAW filter having low insertion loss and balanced type input
and output terminals, and for stabilizing the filter
characteristics.
[0063] Taking an example of a SAW filter of single stage
constitution, explanation has been given above by referring to FIG.
1 and FIG. 2. Such SAW filter can be used in multi-stage
constitution.
[0064] FIG. 3 is an example thereof, and when a multi-stage
connection SAW filter is constituted by connecting a plurality of
SAW filters on the same piezoelectric substrate 31, great
improvement can be obtained in the characteristics in rejection
band and transition band, though there may be some increase in the
insertion loss. The two-stage vertically connected filters shown-in
FIG. 3 comprise a first SAW resonator constituted by an IDT
electrode 12a and reflector electrodes 12b, 12c as explained in
FIG. 1, and a second SAW resonator constituted by an IDT electrode
13a and reflector electrodes 13b, 13c, which are disposed near to
each other to form a SAW filter 32 and a SAW filter 33 of the same
constitution thereof formed on the piezoelectric substrate 31, and
the two members are connected by a connecting wire.
[0065] In FIG. 3, the leading out electrodes 17a and 17b on the
output side of the first stage SAW filter 32 are connected to the
leading out electrodes 16a and 16b on the input side of the next
stage SAW filter 33 with the connecting wires 39a and 39b,
respectively. The bus bar electrode 15a of IDT electrode which is
another output of the first stage output is connected by the
connecting wire 40 to the IDT electrode 14a which is another output
of the next stage.
[0066] In this manner, even between the filter stages, there can be
realized reduction of increase in insertion loss at the time of the
multi-stage operation and improvement to the balance level of
balanced type input and output terminals, by connecting one part of
the IDT electrodes at two places of 39a and 39b.
[0067] The wire connections of the multi-stage filter on the input
side and output side as shown in FIG. 3 are similar to those of
FIG. 1, and have the same action and effect.
[0068] FIG. 4 shows an example where the inter-stage and input and
output wirings are carried out by the wiring patterns formed on the
substrate 41.
[0069] On the piezoelectric substrate 41, there are formed the
first SAW filter 42 and the. second SAW filter 43 which have the
same constitutions as the SAW filters shown in FIG. 1, FIG. 2, and
FIG. 3.
[0070] The leading out electrodes 17a and 17b on the output side of
the first SAW filter 42 are connected to the leading out electrodes
16a and 16b on the input side of the second filter 43 by forming
the first inter-stage connection electrodes 44a, 44b of wider width
than the resonator electrodes on a piezoelectric substrate 41.
Also, another output 15a of the first filter 42 and another input
14a of the second filter 43 are connected by forming the second
inter-stage connecting electrode 45 having wider width than the
electrode of the resonator on the piezoelectric substrate 41.
[0071] The leading out electrodes 16a and 16b on the input side of
the first filter 42 are connected by the wiring pattern 46 having
the wider width than the resonator electrode formed on the
piezoelectric substrate 41. Further, a part of said wiring pattern
48 is further expanded to form one connecting land 46a with the
outer wiring member 47 of the balanced type input terminal, and the
bus bar electrode 14a of outside IDT electrode is expanded outward
to form a connecting land 48a with the external wiring member 47b
of the balanced type input terminal.
[0072] On the other hand, the area between the leading out
electrodes 17a and 17b on the output side of the second filter is
connected by the wiring pattern 46b of wider line width than the
resonator electrode width formed on the piezoelectric substrate 41.
Further, a part of the said wiring pattern is further extended to
form a connection land 46c with the outside wiring member 47c of
the balanced type output terminal, and the bus bar electrode 15a is
extended outward to form a connection land 48a with the external
wiring member 47d of the balanced type output terminal.
[0073] By such a pattern constitution, there can be provided a
balanced type multi-stage SAW filter having low insertion loss and
good balancing level.
[0074] The lands 44c, 45a for external wiring provided on the
inter-stage connection electrodes 44b, 45 of FIG. 3 are useful in
the connection of the external circuit element for filter
characteristic adjustment.
[0075] By the way, there may be cases where the desired good
transmission characteristics cannot be obtained because of the
mismatching of the input and output impedance's in the stages.
[0076] In such a case, the reactance element such as an inductor
may be connected as a matching element to the inter-stage
connecting electrode to make adjustment. The lands 44c, 45a for
external wiring are useful for the purpose. Alternatively, by
adopting such a constitution that a reactance element such as a
spiral inductance is formed on the same piezoelectric substrate 41
or on a separate substrate and connected to the inter-stage
connecting electrode, no extra space is necessitated, and reduction
of filter circuit size can be easily realized. The reactance
element for adjustment may be connected to either one of the
inter-stage connecting lands 44c, 45a and the other land may be
grounded. According to the experiment, improvements of the
symmetric property of the filter transmission characteristic is
observed in the case that the reactance element is connected to the
first connection land 44c.
[0077] Embodiment 2
[0078] FIG. 5 is a constitution view showing a SAW filter according
to the second embodiment of the present invention.
[0079] By forming an electrode pattern having a strip line shaped
periodical structure on a piezoelectric substrate 51 shown in FIG.
5, SAW can be excited. On the piezoelectric substrate 51 there is
formed a first SAW resonator of energy strage type constituted by
an IDT electrode 52a and reflector electrodes 52b, 52c. Also, on
the piezoelectric substrate 51, there is constituted a third SAW
resonator constituted by an IDT electrode 54a and reflector
electrodes 54b, 54c.
[0080] The point to be specially noted here is that the IDT
electrode part of the second SAW resonator formed between the first
SAW resonator and the third SAW resonator accompanied with the
reflector electrodes 53b, 53c, has a similar structure to that of
the reflector electrode, and is constituted by a periodic structure
strip line electrode row 53a having approximately the same length
as the crossing width of the electrode fingers of the IDT
electrodes 51a, 54a in the first and third SAW resonators.
[0081] In other words, even if the structure of the electrode part
of the second SAW resonator is not of the same structure as those
of the above-described IDT electrodes 52a, 54a but is changed to
the periodic structured strip line electrode row 53a, if the
electrode period is the same, the SAW can be transmitted in
entirely the same manner. Accordingly, the acoustic behaviors of
the central part second SAW resonator make no difference from the
case of the IDT electrode structure.
[0082] The above three SAW resonators have the acoustic couple
closely disposed to one another. The bus bar electrodes of the
parts adjacent to one another are electrically independent. From
both ends of the bus bar electrode 55 adjacent to the second SAW of
the IDT electrode in the first SAW resonator, there are formed
outward the first and second electrode fingers 57a and 57b which
constitute a part of the balanced type input terminal, in the space
between the IDT electrode 52a and the reflector electrodes 52b,
52c. Also, from both ends of the bus bar electrode 56 adjacent to
the second SAW of the IDT electrode in the third SAW resonator,
there are formed outward the third and fourth electrode fingers 58a
and 58b which constitute a part of the balanced type output
terminal, in the space between the IDT electrode 54a and the
reflector electrodes 54b, 54c. The electrode constitutions
described above are the basic constitutions of the triple mode SAW
filter having the balanced type input and output terminals of low
insertion loss according to the present invention.
[0083] FIG. 6 shows an example of connection of a balanced type
input and output terminal of the present invention for the triple
mode SAW filter as explained in FIG. 5.
[0084] As shown in said figure, the first electrode finger 57a and
the second electrode finger 57b of the first SAW resonator are
connected by the connecting wires 61a, 61b to make one input
terminal of the balanced type input terminal, and the connecting
wire 62 is led out from the bus bar electrode 55a of the outside
IDT electrode to make the other input terminal of the balanced type
input terminal. And, the third electrode finger 58a and the fourth
electrode finger 58b of the third SAW resonator are connected by
the connecting wires 63a, 63b to make one output terminal of the
balanced type input terminal, and the connecting wire 64 is led out
from the bus bar electrode 56a of the outside IDT electrode to make
the other output terminal of the balanced type input terminal.
[0085] FIG. 7 shows another embodiment of the constitution of the
balanced type input and output terminal of the triple mode SAW
filter.
[0086] As shown in said figure, the area between the first
electrode finger 57a of the first SAW resonator and the second
electrode finger 57b is connected by the wiring pattern 71 of wider
line width than the resonator electrode width formed on the
piezoelectric substrate 51. Further, the pattern 71 is further
extended to form a connection land 71a with the external wiring
member 75a, and the bus bar electrode 55a of IDT electrode is
extended outward to form a connection land 73 with the external
wiring member 75, and the area between the third and fourth
electrode fingers 58a and 58b of the third SAW resonator is formed
on a piezoelectric substrate 51 to make a resonator electrode, and
connection is made by the wiring pattern 72 which has the wider
line width than the resonator electrode. The pattern 72 is further
extended to form a connection land 72a with the external wiring
member 76a, and the bus bar electrode 56a of IDT electrode is
extended outward to form a connection land 74 with the external
wiring member 76. According to such a constitution, similarly to
what SAW described in the first embodiment, it becomes possible to
provide a triple mode SAW filter in which the insertion loss is
further reduced and connection with the external circuit is easy,
as explained in the first embodiment.
[0087] FIG. 8 shows an example of the case where a plurality of the
triple mode SAW filters as explained with reference to FIG. 5 are
stepwise connected vertically.
[0088] As shown in the figure, on the piezoelectric substrate 81
there are formed a first triple mode SAW filter 82 and a second
triple mode SAW filter 83. The third and fourth electrode fingers
58a, 58b on the output side of the first filter 82 and the bus bar
electrode 56a on the output side are stepwise connected to the
first and second electrode fingers 57a, 57b on the input side and
the bus bar electrode 55a on the input side, of the second filter
83, by the connecting wires 83a, 83b, and 84. The parallel type
wire connections of the input circuit and output circuit are
entirely same as the wiring constitution of the single stage filter
shown in FIG. 6.
[0089] FIG. 9 shows another example of the input and output
constitutions and the inter-stage constitutions of the vertical
connection triple mode SAW filter as shown in FIG. 8.
[0090] As shown in said figure, on the piezoelectric substrate 91,
there are formed a first triple mode SAW filter 92 and a second
triple mode SAW filter 93. The two filters are Inter-stage
connected by the inter-stage connecting electrodes 94a, 94b, and 95
having wider widths than the width of the resonator electrode which
is formed by placing the third and fourth electrode fingers 58a,
58b on the output side, and the bus bar electrode 56a, of the first
filter 92, and the first and second electrode fingers 57a, 57b on
the input side, and the bus bar electrode 55a on the input side of
the second filter 93, on the piezoelectric substrate 91. The lands
94c, 95a formed on a part of each connecting electrode are
convenient to use for the connection of the external elements for
adjusting filter characteristics. The wiring patterns of the input
circuit and output circuit are entirely same as those of the single
stage filter constitution shown in FIG. 7.
[0091] As described above, according to the embodiments 1 and 2,
because the bus bar electrode of the IDT electrode is electrically
independent, balanced input and output mode can be realized, and
accordingly, the filter characteristics do not have the effects of
floating capacity by the grounding condition of electrode, so that
the characteristics in the rejection band and transition band are
improved, and moreover, due to the leading out electrode structure
which is characterized by the present invention, remarkable
improvement of insertion loss and improvement in balance level in
the balanced type input and output terminal can be realized.
[0092] In the embodiment 3, there is employed an example wherein,
as a balanced type triple mode filter, there is used one in which
the IDT electrode of the central part resonator as shown in FIG. 5
has a periodic structured electrode constitution same as the
reflector electrode. Even when this part is an IDT electrode
structure same as being heretofore used, the effect of improvement
in the filter characteristic by the balanced wiring connection by
the present invention is obtainable in exactly the same manner.
[0093] Embodiment 3
[0094] FIG. 10 is a constitution view showing the third embodiment
of the SAW filter according to the present invention.
[0095] In FIG. 10, the part 101 is a single crystal piezoelectric
substrate. By forming an electrode pattern on the piezoelectric
substrate 101, SAW can be excited. On the piezoelectric substrate
101 there is formed an energy strage type first SAW resonator
constituted by an IDT electrode 102a and reflector electrodes 102b,
102c. Also, on the piezoelectric substrate 101, there is formed a
third SAW resonator constituted by an IDT electrode 104a and
reflector electrodes 104b, 104c. The electrode part 103a of the
second SAW resonator formed between the first SAW resonator and the
third SAW resonator accompanied with the reflector electrodes 103b,
103c has the same structure as that of the reflector electrode.
[0096] As reviewed above, even if the structure of the electrode
part 103a of the second SAW resonator is not of the same structure
as those of the above-described IDT electrodes but is changed to
the periodic structured strip line electrode row, if the electrode
period is the same, the SAW can be transmitted in entirely the same
manner. Accordingly, the acoustic behaviors of the second SAW
resonator disposed at the central part make no difference from the
case of the IDT electrode structure.
[0097] Furthermore, assuming that the electrode finger crossing
width of IDT electrodes 102a, 104a in the first and third SAW
resonators is W1, and the length of the strip line constituting the
IDT electrode part 103a of the second SAW resonator is W2, setting
is so made that the relative size between W1 and W2 becomes:
W1.ltoreq.W2.
[0098] The above three SAW resonators have the acoustic couple
closely disposed to one another. The electrode finger of the IDT
electrode 102a in the first SAW resonator is connected to the
balanced type input terminal IN, and the electrode finger of the
IDT electrode 104a in the third SAW resonator is connected to the
balanced type output terminal OUT. The periodic structure strip
line electrode row 103a in the second SAW resonator is
grounded.
[0099] Hereinafter, the operation of the SAW filter constituted as
above is explained.
[0100] FIG. 11 is an excitation mode distribution chart of the SAW
filter in the present embodiment. To the parts corresponding to
those of FIG. 10 the same marks are assigned. In FIG. 11, (a) is a
constitution view of the electrode of the SAW filter shown in FIG.
10. Due to the closely related disposition of the first to third
SAW resonators, acoustic couple is formed therebetween, and there
are excited the primary, secondary, and tertiary modes having the
potentials as shown in FIG. 11(b). Here, due to all electrical
grounding of the electrode part 103a of the third SAW resonator
disposed at the center, the polarity of the secondary mode
potential distribution is reversible at the center, so that there
can be obtained strong excitation strength on the same level as
that of the primary and tertiary modes. As this permits to
constitute a multi-stage mode filter made by effective utilization
of the three excitation modes, there can be realized a SAW filter
having broad bandwidth with acute attenuation characteristics.
[0101] FIG. 12 shows a change of the resonant frequency of each
mode to the value of W standardized by the SAW wavelength .lambda.
in the case of W1 =W2=W, obtained by the wave guide path mode
analysis. The curves 121, 122, and 123 show the changes of the
resonance frequencies in primary, secondary, and tertiary modes,
respectively. As shown in FIG. 12, to a certain given value W, the
frequency difference .DELTA.1 between the primary mode and the
secondary mode and the frequency difference .DELTA.2 between the
secondary mode and the tertiary mode become the difference values.
Namely, when viewed with 50 .OMEGA. system, as shown in FIG. 13,
the pass characteristic of the SAW filter does not show equal
distance between the peaks of the three resonance modes as in the
curve 131. Accordingly, even when the input and output are matched,
ripples remain in the band as in the curve 132, and the filter
characteristic is degraded.
[0102] Here, an effect of the case where the ratio of the length of
the strip line W2 constituting the electrode part 103a of the
second SAW resonator to the electrode finger cross difference width
W1 of IDT electrodes 102a, 104a in the first and third SAW
resonator (W2/W1) is shown in FIG. 14. In FIG. 14, there is shown a
standardized value of the actually measured amount of the frequency
difference (.DELTA.1, .DELTA.2 in FIG. 13) in resonance mode to
W2/W1 in the SAW filter of the present invention having the
constitution of FIG. 10. FIG. 14 shows the values where the length
W2 of the strip line constituting the electrode part 103a of the
second SAW resonator is varied in the case where the IDT electrode
finger crossing difference width W1 of the first and third SAW
resonators is 6.5 wavelength, and the combined gap length G is 1
wavelength. As shown in FIG. 14, when the value of W2/W1 is about
1.13, the relation becomes:.DELTA.1=.DELTA.2, i.e., the distance
between the three resonance frequencies becomes equal. As to the
allowance range, the relative sizes of W1 and W2 may be set so that
they come into the range of 1.ltoreq.W2/W1.ltoreq.1.3. Practically,
considering the scattering in manufacture, the values of W1 and W2
may be set in the range of 1.ltoreq.W2/W1.ltoreq.1.16.
[0103] FIG. 15 shows the passing characteristic of the SAW filter
in he case of W1=6.5 wavelengths, W2=7.5 wavelengths, i.e.,
W2/W1=1.15. In FIG. 15, the numeral 151 shows the characteristic of
the case observed in 50 .OMEGA. system, and 152 shows the
characteristic of the case of matching taken. It can be seen that,
in comparison with the case of FIG. 13, the ripples in the pass
band apparently decrease to give excellent passing
characteristic.
[0104] As described above, according to the embodiment 3 of the
present invention, three SAW resonators are disposed in-adjacent
relations with one another, and the electrode part of the central
SAW resonator is constituted by a strip line having slightly longer
periodic structure than the cross difference width of he IDT
electrode fingers of the first and third SAW resonators, and all of
them are grounded. By such constitution, there can be obtained a
SAW filter having wide bandwidth and flat pass characteristic and
acute attenuation characteristic.
[0105] Furthermore, due to the electrical isolation of the bus bar
at the central part of the IDT electrode, it becomes possible to
wire the IDT electrode 102a of the first SAW resonator and the SAW
resonator 104a of the third SAW resonator all independently, so
that the balanced input and output of the SAW filter can be made.
Consequently, the filter characteristic becomes free from the
effect of the floating capacity or the like depending on the
grounding condition of the electrode, and the characteristics of
the rejection band and transition band are further improved. In
addition, it becomes possible to connect the balanced type elements
such as IC to the front and rear stages of the filter without using
any external extra circuit such as Balun, thus improving the noise
characteristics of the whole circuit.
[0106] In FIG. 10, the electrode part 103a of the second SAW
resonator is grounded through the electrode pattern existing in the
space between the IDT electrode 104a of the third SAW resonator and
the reflector electrode 104c, but the constitution is not limited
to it; and the grounding may be made through the reflector
electrodes 103b, 103c on both sides of the electrode part 103a.
[0107] In this embodiment 3, explanation is given by taking an
example of a SAW filter of single stage constitution. However, as
shown in FIG. 16, when a multi-stage connection type SAW filter is
constituted by vertically connecting a plurality of SAW filters
162, 163 on the same piezoelectric substrate 161, though the
insertion loss increases to some extent, the characteristics of the
rejection band and transition band are remarkably improved to give
more excellent filter characteristics. In this case, it is
preferable for the first SAW resonator electrode of the front stage
SAW filter to be connected to the balanced type input terminal, and
the third SAW resonator electrode of the rear stage SAW resonator
to be connected to the balanced type output terminal. This is
because the filter can be easily connected to the peripheral
circuit such as a balanced type front end IC, making it unnecessary
to secure ground for wiring, so that the stabilized filter
characteristics are obtainable with less effect of floating
capacity.
[0108] By the way, a simple vertical connection of the SAW filters
may not give good transmission characteristic due to the
mismatching of the input and output impedances in each stage. In
such a case, the reactance elements such as inductance may be
connected as matching elements to the inter-stage connecting
electrode patterns 164, 165. In this case, in order to make full
coordination with the balanced type input and output circuit, a
matching element is required to be connected between the electrode
patterns 164 and 165. However, in practice, the inter-stage
portions have no electrical connection with the input and output
terminals but have acoustic couple only. Accordingly, if one
electrode pattern (e.g., electrode pattern 165) is directly
grounded, and the other electrode pattern (e.g., electrode pattern
164) is grounded through the reactance element, the operation
similar to the case of a reactance element having been connected
between the two can be realized. And, when such a constitution is
adopted, the wiring for grounding can be made on an electrode
pattern, and therefore the use of bonding wires can be reduced.
[0109] Embodiment 4
[0110] FIG. 17 is a constitution view showing the fourth embodiment
of the SAW filter according to the present invention.
[0111] In FIG. 17, the part 171 shows a single crystal
piezoelectric substrate. By forming an electrode pattern on the
piezoelectric substrate 171, a SAW can be excited in the same
manner as in the third embodiment. On the piezoelectric substrate
171, there is formed a first SAW resonator of energy strage type
constituted by an IDT electrode 172a and reflector electrodes 172b,
172b. Also, on the piezoelectric substrate 171, there are formed a
second SAW resonator of energy strage type constituted by an IDT
electrode 173a and reflector electrodes 173b, 173c and a third SAW
resonator of energy strage type constituted by an IDT electrode
174a and reflector electrodes 174b, 174c. And, these three SAW
resonators are disposed in close relations to one another, and the
bus bar electrodes of mutually adjacent IDT electrodes are
electrically independent. Also, the reflector electrodes are
connected by the common bus bar. The electrode finger of the IDT
electrode 172a in the first SAW resonator is connected to the
balanced type input terminal IN, and the electrode finger of the
IDT electrode 174a in the third SAW resonator is connected to the
balanced type output terminal OUT. The electrode fingers of the IDT
electrode 173a in the second SAW resonator are all grounded.
Furthermore, when the electrode finger crossing difference width of
the IDT electrodes 172a and 174a in the first and third SAW
resonator is assumed to be W1, and the electrode finger crossing
difference width of the IDT electrode 173a in the second SAW
resonator is assumed to be W2, setting is so made that the relative
sizes of W1 and W2 become: W1.ltoreq.W2.
[0112] With respect to the SAW filter having the above
constitution, the electrode structure of the second SAW resonator
at the central part is changed from the periodic structure strip
line electrode rows in the above third embodiment to the IDT
electrode 173a, but as the transmission of the SAW is carried out
in exactly the same manner, the basic operation is same as the case
of the third embodiment shown in FIG. 10. Accordingly, flattening
of passing characteristic of SAW filter and inhibition of spurious
in the rejection band are realized in the same manner as in the
third embodiment.
[0113] According to this embodiment 4, three SAW resonators are
disposed in adjacent relations with one another, and all the IDT
electrodes 173a constituting the central second SAW resonator are
grounded, and their crossing widths are made slightly longer than
the crossing width of the IDT electrode fingers of the first and
the third SAW resonators, by which there can be obtained a SAW
filter having wide bandwidth and flat pass characteristic and acute
attenuation characteristic. Furthermore, due to the electrical
isolation of the bus bar at the central part of the IDT electrode,
it becomes possible to wire the IDT electrode 172a of the first SAW
resonator and the SAW resonator 174a of the second SAW resonator
all independently, so that the balanced input and output of the SAW
filter can be realized. Consequently, the filter characteristic
becomes free from the effect of the floating capacity or the like
depending on the grounding condition of the electrode, and the
characteristics of the rejection band and transition band are
improved. In addition, it becomes possible to connect the balanced
type elements such as IC to the front and rear stages of the filter
without using any external extra circuit such as Balun, thus
improving the noise characteristics of the whole circuit.
[0114] Furthermore, in this embodiment 4, when a plurality of SAW
filters are vertically connected to constitute a multi-stage
connection SAW filter, the characteristics of the transition band
and the rejection band are remarkably improved. The method of
vertical connection and method of connecting the reactance element
(matching element) to the inter-stage part are exactly the same as
those of the third embodiment shown in FIG. 16, and the effect on
the filter characteristic is same as that described in the third
embodiment.
[0115] In the above third embodiment, as shown in FIG. 10, the IDT
electrode 102a of the first SAW resonator and the IDT electrode
104a of the second SAW resonator are disposed to be in reverse
phase to each other. However, the invention is not necessarily
limited to this constitution but the electrode dispositions may be
of the same phase. Even in this case, except the slight difference
in the mode of presence of extra-band spurious, the action and
effect make no difference. In this respect, same thing applies to
the fourth embodiment.
[0116] In the above third and fourth embodiments, the input and
output terminals are of balanced type, but they are not necessarily
limited to the said constitution but it is possible to ground the
unilateral sides of the input and output terminals respectively to
adopt an unbalanced type. Moreover, in case of the grounding of
either one side, a SAW filter having balanced-unbalanced terminals
can be constituted.
[0117] Embodiment 5
[0118] FIG. 18 shows a constitution view of an electrode pattern
according to Embodiment 5 of the SAW filter of the present
invention.
[0119] In FIG. 18, the part 181 is a single crystal piezoelectric
substrate. By forming an electrode pattern of periodic structure on
the piezoelectric substrate 181, a SAW can be excited. On the
piezoelectric substrate 181, there is formed a first SAW resonator
of energy strage type constituted by an IDT electrode 182a and
reflector electrodes 182b, 182c. Also, on the piezoelectric
substrate 181, there is formed a second SAW resonator of energy
strage type constituted by an IDT electrode 183a and reflector
electrodes 183b, 183c.
[0120] As shown in FIG. 18, the IDT electrode 183a which
constitutes the second SAW resonator is constituted by the
connection of the three groups of the first, second, and third
divisional IDT electrodes 184a, 184b and 184c. Here, the first
divisional IDT electrode 184a and the second divisional IDT
electrode 184b are disposed in reverse phases, and the second
divisional IDT electrode 184b and the third divisional IDT
electrode 184c are disposed in the same phase. With respect to the
same phase and reverse phase, description will be given later.
[0121] The connection methods for these three groups are as noted
below.
[0122] The lower electrode (outside bus bar electrode) 1841o of the
first divisional IDT electrode 184a and the upper electrode (inside
bus bar electrode) 1842i of the second divisional IDT electrode
184b are mutually connected through the fifth electrode finger
184a5 included in the first divisional IDT electrode 184a and a
short connecting electrode 184ab. Also, the lower electrode
(outside bus bar electrode) 1842o of the second divisional IDT
electrode 184b and the lower electrode (outside bus bar electrode)
1843o of the third divisional IDT electrode 84c are connected.
[0123] By the above, an IDT electrode 183a which constitutes the
second SAW resonator is formed.
[0124] The above grouping method is based on the divisional
condition of the inside bus bar electrode and the divisional
condition of the outside bus bar electrode.
[0125] Namely, due to the division of the upper electrode 1843iand
the upper electrode 1842i, division is made to the third divisional
IDT electrode 184c and the second divisional IDT electrode 184b.
Also, due to the division of the lower electrode 1942o and the
lower electrode 1841o, division is made to the second divisional
IDT electrode 184b and the first divisional IDT electrode 184a.
[0126] And, these two first and second SAW resonators are disposed
in adjacent relations with each other, and by the formation of
acoustic couple between them an SAW filter is constituted.
[0127] Furthermore, the upper electrode and lower electrode of the
IDT electrode 182a are connected respectively to the balanced type
input terminal IN. The lower electrode of the first divisional IDT
electrode 184a and the upper electrode of the second divisional IDT
electrode 184b which constitute the IDT electrode 183a are
connected to one of the balanced type output terminal OUT, and the
lower electrode of the second divisional IDT electrode 184b and the
lower electrode of the third divisional IDT electrode 184c are
connected to the other of the balanced type output terminal OUT,
and the upper electrode of the first divisional IDT electrode 184a
and the upper electrode of the third divisional IDT electrode 184c
are grounded, by which a balanced type input and output terminal is
formed.
[0128] Here, explanation is given on the same phase and reverse
phase as described above.
[0129] First, structural disposition relations of adjacent two
electrode fingers (a pair of adjacent electrode fingers )are
described.
[0130] That the adjacent two electrode fingers are in the same
phase relations means that they are in such connection relations
that one of the said two electrode fingers is connected to the
inside bus bar electrode and extends outward from inside, and the
other is connected to the outside bus bar electrode and extends
inward from outside. Also, the adjacent two electrode fingers are
in reverse phase relations means such connection relations that
both of said two electrode fingers are connected to the inside bus
bar electrodes and extend outward from inside, or that they are
connected to the outside bus bar electrode and extend inward from
outside. Here, it is assumed that the electric charges of the
inside and outside bus bar electrodes are different, and that the
pitch (distance between centers) between said adjacent two
electrode fingers is 1/2.times..lambda. (wherein .lambda. is
wavelength of excited surface acoustic wave). The pitch between the
electrode fingers may be (m+1/2).times..lambda. (m=0,1,2,3. . . ).
If, in such case, the pitch is (m+1).times..lambda., then the
contents of meaning fully reverse with respect to the above same
phase relation and reverse phase relation.
[0131] Concretely, when observed with the first divisional IDT
electrode 184a, as shown in FIG. 18, for example, the first
electrode finger 184al and the second electrode finger 184a2 are in
the same phase relation, and the fourth electrode finger 184a4 and
the fifth electrode finger 184a5 are also in the same phase
relation, and accordingly, all electrode fingers included in the
first divisional IDT electrode 184a are in the same phase
relations. Similarly, all electrode fingers included in the second
and third divisional IDT electrodes 184b, 184c are in the same
phase relations.
[0132] Next, with respect to the pair of electrode fingers 184a5
and 184b1, because the electrode finger 184a5 is connected to the
outside bus bar electrode 1841o and the electrode finger 184b1 to
the outside bus bar electrode 1842o, they are in the reverse phase
relations. These adjacent two electrodes are disposed at the
separating point between the first divisional IDT electrode 184a
and the second IDT electrode 184b.
[0133] Accordingly, needless to say, the reverse phase or same
phase referred to in respect to the above disposition of the three
groups is based on the relations of the adjacent two electrode
fingers as described above. This point is the same in other
embodiments.
[0134] In addition, the width in the short length direction of the
fifth electrode finger 184a5 will be related to below.
[0135] In FIG. 18, the constitution in which the width of the fifth
electrode finger 184a5 is the same as that of other electrode
finger is shown. However, without being limited to it, the width
may of course be wider than that of other electrode finger. By so
providing, the resistance value of the electrode finger is lowered,
and accordingly the resistance value of the IDT electrode
containing it becomes small to give an effect of decrease in
insertion loss. This applies to the case of other embodiments.
[0136] With respect to the SAW filter in the fifth embodiment
constituted as above, the operation is explained below.
[0137] FIG,. 19 is a capacity equivalent circuit diagram according
to the fifth embodiment, wherein C.sub.1 is a capacity of the IDT
electrode 182a which constitutes the first SAW resonator. Ca, Cb
and Cc are the capacities of the first, second, and third
divisional IDT electrodes 184a, 184b, and 184c, and the synthesized
capacity of Ca, Cb and Cc becomes the total capacity C.sub.2 of the
second SAW resonator IDT electrode 183a. Here, assuming the number
of couples of the electrode fingers included in the IDT electrode
183a to be n, and the respective number of couples of the third
divisional IDT electrodes 184a, 184b, and 184c to be na, nab, and
nc, the relation can be expressed by the following equation:
n=na+nb+
[0138] In the SAW filter as described above, the capacities of the
IDT electrodes 182a, 183a are dominated by the number of couples of
the electrode. Assuming the number of couples of the IDT electrode
182a to be n, and the electrode capacity of a couple of IDT
electrode fingers to be C, the values of C.sub.1, Ca, Cb and Cc can
be expressed, respectively, as follows:
C.sub.1=n.times.C
Ca=na.times.C=C.sub.1.times.na/n=C.sub.1.times.na/(na+nb+nc)
Cb=nb.times.C=C.sub.1.times.nb/n=C.sub.1.times.nb/(na+nb+nc)
Cc=nc.times.C=C.sub.1.times.nc/n=C.sub.1.times.nc/(na+nb+nc)
[0139] Accordingly, from the capacity equivalent circuit diagram of
FIG. 19, the total capacity C.sub.2 can be expressed by the
Expression 1, by using Ca, Cb, and Cc.
[0140] Expression 1: 1 C 2 = C c C b + C b C c + C c C a C a + C c
= ( n a n b + n b n c + n c n a ) .times. C 1 ( n a + n c ) .times.
n
[0141] For example, assuming that the number of couples of the
divisional IDT electrodes 184a, 184b, and 184c are equal, i.e.,
na=nb=nc=n/3, the relation becomes C.sub.2=C.sub.1.times.1/2, and
the capacity of C.sub.2 becomes half of that of Cl. By changing the
number of couples na, nb, and nc of the divisional IDT electrodes
184a, 184b, and 184c, the total capacity C.sub.2 of the IDT
electrode 183a varies according to Expression 1 in the range of
C.sub.1.times.1/4<C.sub.2<C.sub.1. Namely, the total capacity
of the IDT electrode 183a can be controlled by the divisional ratio
of the divisional IDT electrodes 184a, 184b, and 184c.
[0142] Also, in this case, the electric charges on the electrodes
of the first, second, and third divisional IDT electrodes 184a,
184b, and 184c are not mutually cancelled, and the SAWs formed by
the first, second, and third divisional IDT electrods 184a, 184b,
and 184c become the same phase. So that the second SAW resonator
has the equivalent resonance characteristics to those of the first
SAW resonator. Accordingly, by disposing the first SAW resonator
and the second SAW resonator near to each other, they operate as
the lateral mode combined resonance type filters in the same manner
as in the conventional system.
[0143] As described above, according to the present Embodiment 5,
the SAW filter having balanced type input and output shows
excellent characteristics in the extra-band selectivity with narrow
bandwidth, and also it can control the output impedance of the SAW
filter by the electrode structure of IDT electrode which is formed
by the divisional IDT electrode which is characterized by the
present invention.
[0144] In the fifth embodiment, description has been made on the
IDT electrode 183a which constitutes the second SAW resonator,
relating to the case where the first, second, and third divisional
IDT electrodes 184a, 184b, and 184c which constitute the IDT
electrode 183a are laid from left side to right side in order in
the drawing, but the laying order may not be limited to the above
but be from right side to left side as 184a, 184b, and 184c. The
electrode pattern of the IDT electrode 183a may be inverted upside
down. In such a case, as shown in FIG. 20, the IDT electrode 203a
which constitutes the second SAW resonator on the piezoelectric
substrate 201 is constituted by the connection of the three groups
of first, second and third divisional IDT electrodes 204a, 204b and
204c. The first divisional IDT electrode 204a and the second
divisional IDT electrode 104b are disposed in reverse mode, and the
second divisional electrode 204b and the third divisional IDT
electrode 204c are disposed in the same phase, the upper electrode
of the first divisional IDT electrode 1204a and the lower electrode
of the second divisional IDT electrode 204b are connected, and the
upper electrode of the second divisional IDT electrode 204b and the
upper electrode of the third divisional IDT electrode 204c are
connected to form an IDT electrode 203a which constitute the second
SAW resonator. Also, in FIG. 20, the divisional IDT electrodes
204a, 204b, and 204c are laid in order of 204a, 204b, and 204c from
the left, but the order may be from the right. In these cases, the
difference in IDT electrodes lies only in the electrode structures,
and in respect to the characteristics of the SAW filter, the same
effect as in the case of FIG. 18 is obtainable.
[0145] In Embodiment 5, the number of couples of the IDT electrode
182a and the total of the number of couples of the first, second
and third divisional IDT electrodes 184a, 184b, and 184c,
respectively, are equal. However, they need not be exactly same
number of couples, and the ratio of the number of couples of the
first, second and third divisional IDT electrodes 184a, 184b, and
184c can be optionally set. Further, the number of division of the
IDT electrode 183a is set to be 3, but the number may be other than
that number. Furthermore, though the electric terminal for the ID
electrode 182a is exemplified to be of balanced type, either one of
the upper electrode or the lower electrode may be grounded to make
unbalanced electric terminal. In such a case, a SAW filter having
balanced-unbalanced terminals can be constituted. There has been
adopted a constitution wherein the reflector electrodes 182b and
183b, and 182c and 183c are electrically separated, but the two
members may be connected and grounded. Furthermore, though it is
designed for the IDT electrode 183a constituted by the divisional
IDT electrode 184a, 184b and 184c to constitute the second SAW
resonator, it may constitute a first SAW resonator, or both of
them, and in such a case there can be realized a SAW filter capable
of controlling the impedance of both input and output sides.
[0146] Embodiment 6
[0147] FIG. 21 shows a constitution view of an electric pattern of
SAW filter according to Embodiment 6 of the present invention.
[0148] In FIG. 21, the part 211 is a single crystal piezoelectric
substrate. By constituting a periodic structure strip line form
electrode pattern on said piezoelectric substrate 211, SAW can be
excited. On the piezoelectric substrate 211 there is formed a first
SAW resonator of energy strage type constituted by an IDT electrode
212a and reflector electrodes 212b, 212c. Also, on the
piezoelectric substrate 211 there is formed a second SAW resonator
of energy strage type constituted by an IDT electrode 213a and
reflector electrodes 213b, 213c.
[0149] The IDT electrode 213a which constitutes the second SAW
resonator is constituted by the connection of the three groups of
first, second and third divisional IDT electrodes 214a, 214b and
214c. The first, second and third divisional IDT electrodes 214a,
214b and 214c are all disposed in the same phase, and the upper
electrode of the first divisional IDT electrode 214a and the upper
electrode of the second divisional IDT electrode 214b are
connected, and by the connection of the lower electrode of the
second divisional IDT electrode 214b and the lower electrode of the
third divisional IDT electrode 214c, an IDT electrode 213a which
constitutes the second SAW resonator is formed. And, as these two
first and second SAW resonators are disposed in nearby relations
and acoustic couple is formed therebetween, a SAW filter is
constituted.
[0150] Furthermore, the upper electrode and lower electrode of the
IDT electrode 212a are respectively connected to the balanced type
input terminals IN. Also, the upper electrode of the first
divisional IDT electrode 214a and the upper electrode of the second
divisional IDT electrode 214b which constitute the IDT electrode
213a are connected to one side of the balanced type output terminal
OUT, and the lower electrode of the second divisional IDT electrode
214b and the lower electrode of the third divisional IDT electrode
214c are connected to the other side of the balanced type output
terminal OUT, and the lower electrode of the first divisional IDT
electrode 214a and the upper electrode of the third divisional IDT
electrode 214c are grounded to form the balanced type input and
output terminals.
[0151] In the SAW filter constituted as above, the first SAW
resonator has the same construction as that of the SAW resonator of
the fifth embodiment, and the second SAW resonator is different
from that of the fifth embodiment only in respect of the electrode
pattern and its connection method of the IDT electrode 213a of the
former from that of the IDT 183a of the latter. Even in this case,
the electric charges on the divisional IDT electrodes 214a, 214b,
and 214c are not mutually canceled but the SAWs formed by the
divisional IDT electrodes 214a, 214b, and 214c are of the same
phase, and the second SAW resonator has the same resonance
characteristics as the first SAW resonator. Therefore, by disposing
the first SAW resonator and the second SAW resonator nearby to each
other, the SAW filter of this Embodiment 6 operates as a
conventional lateral mode combined resonator type filter, in the
same manner as in Embodiment 5. Additionally, the SAW filter having
balanced type input and output possesses excellent characteristics
of extra-band selectivity with narrow band, and can control the
input and output impedance of SAW filter, thus giving the same
effect as the SAW filter of the fifth embodiment.
[0152] In the sixth embodiment, the divisional IDT electrodes 214a,
214b, and 214c are designated as 214a, 214b, and 214c from the left
side, but this sequence may be taken from the right side.
Alternatively, the divisional number of IDT electrode 213a which is
given as 3 may be set to any other number. The electric terminal of
IDT electrode 212a which is exemplified as being of balanced type
may be changed to unbalanced type electric terminal by grounding
either the upper electrode or the lower electrode. In such a case,
a SAW filter having balanced-unbalanced terminals can be
constituted. Although the constitution is such that the reflector
electrodes 212b, and 213b , and 212c and 213c are electrically
separated, the two members may be connected and grounded
Furthermore, though it is defined that the IDT electrode 213a
constituted by the divisional IDT electrode 214a, 214b and 214c is
to constitute the second SAW resonator, this may constitute a first
SAW resonator, or both the first and second SAW resonators. In the
latter case, a SAW filter capable of controlling the impedance's of
both input and output can be realized.
[0153] Embodiment 7
[0154] In Embodiments 5 and 6, explanation has been given on the
case of SAW filter of single stage constitution taken as examples.
Such SAW filters may be used in multi-stage constitution.
[0155] FIG. 22 is an example of multi-stage constitution showing an
electrode pattern constitution view of SAW filter according to
Embodiment 7 of the present invention. In FIG. 22, the part 221
shows a single crystal piezoelectric substrate. When a plurality of
SAW filters are vertically connected on the piezoelectric substrate
221 to constitute a multi-stage connection SAW filter, remarkable
improvements are obtainable in the characteristics of rejection
band and transition band, though some increase in the insertion
loss occurs.
[0156] The two-stage vertically connected filter in FIG. 22
comprises a first SAW filter comprising a first SAW resonator
constituted by an IDT electrode 222a and reflector electrodes 222b,
222c and a second SAW resonator constituted by an IDT electrode
223a and reflector electrodes 223b, 223c, which are disposed near
to each other, and a second SAW filter comprising a third SAW
resonator constituted by an IDT electrode 224a and reflector
electrodes 224b, 224c and a fourth SAW resonator constituted by an
IDT electrode 225a and reflector electrodes 225b, 225c, which are
disposed near to each other, being formed on the piezoelectric
substrate 221. The IDT electrode 225a constituting the fourth SAW
resonator in the second SAW filter is composed by connecting the
three groups of the first, second, and third divisional IDT
electrodes 226a, 226b and 226c. The first divisional IDT electrode
226a and the second divisional IDT electrode 226b are disposed in
reverse phase, and the second divisional IDT electrode 226b and the
third divisional IDT electrode 226c are disposed in same phase.
Then, the lower electrode of the first divisional IDT electrode
226a and the upper electrode of the second divisional IDT electrode
226b are mutually connected, and the lower electrode of the second
divisional IDT electrode 226b and the lower electrode of the third
divisional IDT electrode 226c are connected, by which an IDT
electrode 225a which constitutes the fourth SAW resonator is
formed. One of the leading out electrodes on the output side of the
first stage SAW filter is connected to the opposite leading out
electrode on the input side of the opposite next stage SAW filter
by an inter-stage connecting electrode pattern 227a, and another
first stage IDT electrode on the output side is connected to
another next stage IDT electrode on the input side by an
inter-stage connecting electrode pattern 227b, by which a two-stage
SAW filter is formed.
[0157] Furthermore, the upper electrode and the lower electrode of
the IDT electrode 222a which constitutes the first SAW resonator in
the first SAW filter are connected respectively to the balanced
type input terminal IN. Also, in the IDT electrode 225a which
constitutes the fourth SAW resonator in the second SAW filter, the
lower electrode of the first divisional IDT electrode 226a and the
upper electrode of the second divisional IDT electrode 226b are
connected to one side of the balanced type output terminal OUT, the
lower electrode of the second divisional IDT electrode 226b and the
lower electrode of the third divisional IDT electrode 225c are
connected to the other side of the balanced type output terminal
OUT, and the upper electrode of the first divisional IDT electrode
226a and the upper electrode of the third divisional IDT electrode
226c are grounded to form a balanced type input and output
terminal.
[0158] However, there may be cases where the purported good
transmission characteristics cannot be obtained by a simple
vertical connection of the SAW filters, due to the non-matching of
the input and output impedance's of stages. In such a case, a
reactance element such as inductor may be connected as a matching
element to the inter-stage connection electrode to make adjustment.
Alternatively, there may be adopted such a constitution as to form
a reactance element represented by a spiral inductor on the same
piezoelectric substrate 221 or on a separate substrate and connect
it to the inter-stage connection electrode, by which size reduction
of the filter circuit can be easily realized without requiring
extra space. With respect to the reactance element for adjustment,
connection may be made to either one of the first inter-stage
connection electrode pattern 227a or 227b, and other inter-stage
electrode connecting pattern may be grounded. According to the
experiment, as shown in FIG. 22, connection of the reactance
element 228 to the inter-stage connection electrode pattern 227a
proved to give improvement to the symmetry of filter transmission
characteristics.
[0159] By the above constitution, the SAW filter having balanced
type input and output in this Embodiment 7 shows narrow band
characteristics, and by connecting two SAW filters by inter-stage
connection electrode patterns 227a, 227b, the extra-band
selectivity comes to show more acute characteristic than in the
case of a single stage, and also it becomes possible to control the
output impedance of the SAW filter.
[0160] In the seventh embodiment, in the IDT electrode 225a
constituting the fourth SAW resonator in the second SAW filter, the
first, second and third divisional IDT electrodes 226a, 226b, and
226c which constitute the IDT electrode 225a are designated as
226a, 226b, and 226c from the left side facing the drawing, but
this sequence may be taken from the right side. The electrode
pattern of the IDT electrode 225a may be reversed upside down.
[0161] In this Embodiment 7, the divisional number of IDT electrode
225a is given as 3, but it may be set to any other number. The
electric terminal IDT electrode 222a which is exemplified as being
of balanced type may be changed to unbalanced type electric
terminal by grounding either the upper electrode or the lower
electrode. In such a case, a SAW filter having balanced-unbalanced
terminals can be constituted. The IDT electrode 225a may be an IDT
electrode 213a shown in Embodiment 6. In these cases, the IDT
electrode 234a is different only in electrode constitution, and as
to the SAW filter characteristic, the same effect as in FIG. 22 can
be obtained. Though there is adopted such constitution that the
reflector electrodes 222b and 223b, and 222c and 223c are
electrically separated, the two members may be connected and
grounded. Furthermore, though it is defined that the IDT electrode
225a constituted by the divisional IDT electrode 226a, 226b and
226c is to constitute the fourth SAW resonator, this may constitute
a first SAW resonator, or both the first and fourth SAW resonators.
In the latter case, a SAW filter capable of controlling the
impedance's of both input and output can be realized. Also, the
number of stages of SAW is shown as two stages, but the number may
be larger, in which case the filter characteristics are acute, with
more excellent extra-band selectivity.
[0162] Embodiment 8
[0163] FIG. 23 shows a constitution view of an electrode pattern of
SAW filter according to Embodiment 8 of the present invention. In
FIG. 23, the part 231 is a single crystal piezoelectric substrate.
By forming an electrode pattern on said piezoelectric substrate
231, SAW can be excited. On the piezoelectric substrate 231 there
is formed a first SAW resonator of energy strage type constituted
by an IDT electrode 232a and reflector electrodes 232b, 232c. Also,
on the piezoelectric substrate 231 there is formed a third SAW
resonator constituted by an IDT electrode 234a and reflector
electrodes 234b, 234c. The electrode part 233a of the second SAW
resonator formed between the first SAW resonator and the third SAW
resonator, accompanied with reflector electrodes 233b, 233c, has
the same construction as the reflector electrode. In this way, even
when the structure of the electrode part 223a of the second SAW
resonator is not the IDT electrode structure but a periodic
structure strip line electrode row, if the electrode period is the
same, SAW can be propagated in exactly the same manner, so that the
acoustic behaviors of the second SAW resonator disposed at the
central part make no difference from those of the case of IDT
electrode structure.
[0164] Furthermore, the IDT electrode 234a which constitute the
third SAW is constituted by the connection of the three groups of
first, second and third divisional IDT electrodes 235a, 235b and
235c. The first divisional IDT electrode 235a and the second
divisional IDT electrode 235b are disposed in reverse phases; the
second divisional IDT electrode 235b and the third divisional IDT
electrode 235c are disposed in the same phase; the lower electrode
of the first divisional IDT electrode 235a and the upper electrode
of the second divisional IDT electrode 235b are connected; and the
lower electrode of the second divisional IDT electrode 235b and the
lower electrode of the third divisional IDT electrode 235c are
connected to form an IDT electrode 234a which constitutes the third
SAW resonator.
[0165] The above three SAW resonators are disposed in nearby
relations one another, and the bus bar electrodes of the mutually
adjacent parts are electrically independent. The upper electrode
and the lower electrode of IDT electrode 232a which constitutes the
first SAW resonator in the first SAW filter are connected
respectively to the balanced type input terminal IN. Also, in the
IDT electrode 234a which constitutes the third SAW resonator, the
lower electrode of the first divisional IDT electrode 235a which
constitutes the IDT electrode 234a and the upper electrode of the
second divisional IDT electrode 235b are connected to one side of
the balanced type output terminal OUT, and the lower electrode of
the second divisional IDT electrode 235b and the lower electrode of
the third divisional IDT electrode 235c are connected to the other
side of the balanced type output terminal OUT, and the upper
electrode of the first divisional IDT electrode 235a and the upper
electrode of the third divisional IDT electrode 235c are grounded
to form a balanced type input and output terminal, and the periodic
structured strip line electrode line 233a in the second SAW
resonator is grounded.
[0166] As described above, the SAW filter according to this
Embodiment 8 is characterized by realizing a filter characteristic
by disposing the three SAW resonators nearby in parallel with the
direction of propagation of the SAW to make acoustic couple.
[0167] At this time, the SAW filter is a substitution of the IDT
electrode 233a which constitutes the second SAW resonator in the
SAW filter of the present invention for the IDT electrode in the
SAW multi-mode filter of Japanese Patent Kokai Publication No.
8-51334 published by the present inventors, and it shows the same
operation as that described in said Publication No. 8-51334.
Namely, by making the SAW resonator in three stages, the filter can
have wide band width, and characteristics excellent in extra-band
selectivity, and also can control the output impedance of the SAW
filter.
[0168] In the eighth embodiment, in the IDT electrode 234a
constituting the third SAW resonator, the first, second and third
divisional IDT electrodes 235a, 235b, and 235c which constitute the
IDT electrode 234a are designated as 235a, 235b, and 235c from the
left side facing the drawing, but this sequence may be taken from
the right side. The electrode pattern of the IDT electrode 234a may
be reversed upside down. The IDT electrode 234a may be the IDT
electrode 213a of the constitution shown in Embodiment 6. In these
cases, the IDT electrode 234a is different only in electrode
constitution, and as to the SAW filter characteristic, the same
effect as in FIG. 23 can be obtained.
[0169] Also, the divisional number of IDT electrode 234a is given
as 3, but it may be set to any other number. The electric terminal
of IDT electrode 232a which is exemplified as being of balanced
type may be changed to unbalanced type electric terminal by
grounding either the upper electrode or the lower electrode. In
such a case, a SAW filter having balanced-unbalanced terminals can
be constituted. Though there is adopted such constitution that the
reflector electrodes 232b and 233b, and 232c and 233c are
electrically separated, the two members may be connected and
grounded. Furthermore, though it is defined that the IDT electrode
234a constituted by the divisional IDT electrode 235a, 235b and
235c is to constitute the third SAW resonator, this may constitute
a first SAW resonator, or both the first and third SAW resonators.
In the latter case, a SAW filter capable of controlling the
impedance's of both input and output can be realized.
[0170] In this Embodiment 8, the IDT electrode 233a is described as
being grounded through the electrode pattern provided in the space
between the IDT electrode 232a and the reflector electrode 233c on
the right side thereof. However, it may be grounded through the
electrode pattern provided in the space between the IDT electrode
233a and the reflector electrode 233a on the left side thereof, or
alternatively it may be grounded through the electrode pattern
provided in the space between the IDT electrode 234a and either one
of the reflector electrode 234b or 234c. Though there is adopted
such constitution that the reflector electrodes 232b and 233b, and
232c and 233c are electrically separated on each SAW resonator,
they may be respectively connected and grounded.
[0171] Furthermore, the IDT electrode 233a may be grounded through
any of the reflector electrodes 232b, 232c, 233b, 233c, 234b, and
234c. The IDT electrode 233a may be of the electrode structure of
the same constitution as that of the IDT electrode 232a. In this
case also, propagation of SAW is performed in the same manner, and
the similar characteristic as that of the SAW filter of this
Embodiment 8 is obtainable. Furthermore, though it is described
that the divisional IDT electrode 234a is to constitute a third SAW
resonator, it may be constituted by a first SAW resonator, or both
of them. In the latter case, a SAW filter capable of controlling
the impedance's of both input and output can be realized. Although
the first to the third SAW resonators are shown to be of the same
constitution, they need not necessarily be the same. The SAW
filters of Embodiment 8 may be of two stage vertical connection, in
which case the extra-band selectivity characteristic becomes
further acute.
[0172] As to the piezoelectric substrate in the present invention,
use of an ST cut crystal having excellent temperature
characteristics is preferable, but there may be used as substrates
LiTaO.sub.3, LiNbO.sub.3, Li.sub.2B.sub.4O.sub.7,
La.sub.3Ga.sub.3SiO,.sub.14 and the like. As an electrode material,
use of relatively low density aluminum whose film thickness control
is easy is preferable, but use of gold electrode is also
possible.
[0173] Furthermore, the present invention is applicable to
resonators using not only the SAW described above but also
SSBW(Surface Skimming Balk Wave) which is one of the SAW or Pseudo
surface waves, and the like.
* * * * *