U.S. patent application number 15/636676 was filed with the patent office on 2018-01-18 for multiplexer, high-frequency front-end circuit, and communication device.
The applicant listed for this patent is Murata Manufacturing Co., Ltd.. Invention is credited to Tetsuro OKUDA.
Application Number | 20180019832 15/636676 |
Document ID | / |
Family ID | 60782553 |
Filed Date | 2018-01-18 |
United States Patent
Application |
20180019832 |
Kind Code |
A1 |
OKUDA; Tetsuro |
January 18, 2018 |
MULTIPLEXER, HIGH-FREQUENCY FRONT-END CIRCUIT, AND COMMUNICATION
DEVICE
Abstract
A multiplexer includes filters connected to each other at a
common terminal, a low-frequency filter with a first pass band, and
a high-frequency filter with a second pass band that is higher than
the first pass band. The low-frequency filter includes an
initial-stage filter section including at least one first elastic
wave resonator located on the common terminal side among at least
two elastic wave resonators, and a subsequent-stage filter section
that includes a second elastic wave resonator other than the at
least one first elastic wave resonator. A reflection coefficient in
the second pass band when the initial-stage filter section is
viewed from the common terminal side as a single component is
larger than a reflection coefficient in the second pass band when
the subsequent-stage filter section is viewed from the common
terminal side as a single component.
Inventors: |
OKUDA; Tetsuro;
(Nagaokakyo-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Murata Manufacturing Co., Ltd. |
Nagaokakyo-shi |
|
JP |
|
|
Family ID: |
60782553 |
Appl. No.: |
15/636676 |
Filed: |
June 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 13/22 20130101;
H04B 1/005 20130101; H04J 3/247 20130101; H03H 9/6436 20130101;
H03H 9/25 20130101; H03H 9/605 20130101; H03H 9/706 20130101; H04B
1/48 20130101; H04B 1/406 20130101; H03H 9/72 20130101; H03H
9/02574 20130101; H03H 9/6483 20130101; H03H 9/725 20130101; H04J
3/1682 20130101; H03H 9/145 20130101 |
International
Class: |
H04J 3/24 20060101
H04J003/24; H04B 1/48 20060101 H04B001/48; H04B 1/00 20060101
H04B001/00; H03H 9/72 20060101 H03H009/72; H03H 9/25 20060101
H03H009/25; H03H 9/145 20060101 H03H009/145; H04J 3/16 20060101
H04J003/16; G06F 13/22 20060101 G06F013/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2016 |
JP |
2016-140918 |
Claims
1. A multiplexer comprising: a common terminal; a first
input/output terminal; a second input/output terminal; a plurality
of filters that are connected to each other at the common terminal;
a first filter that includes at least two elastic wave resonators
that are located between the common terminal and the first
input/output terminal, the first filter including a first pass
band; and a second filter that is connected between the common
terminal and the second input/output terminal, the second filter
including a second pass band that is at a different frequency from
the first pass band; wherein the first filter includes: an
initial-stage filter section that includes at least one first
elastic wave resonator located on the common terminal side among
the at least two elastic wave resonators, and a subsequent-stage
filter section that includes a second elastic wave resonator that
is different from the at least one first elastic wave resonator;
and a reflection coefficient of the initial-stage filter section in
the second pass band when the initial-stage filter section is
viewed from the common terminal side as a single component is
larger than a reflection coefficient of the subsequent-stage filter
section in the second pass band when the subsequent-stage filter
section is viewed from the common terminal side as a single
component.
2. The multiplexer according to claim 1, wherein the at least one
first elastic wave resonator of the initial-stage filter section is
one elastic wave resonator that is closest to the common terminal
among the at least two elastic wave resonators.
3. The multiplexer according to claim 1, wherein the first filter
includes a ladder filter structure; and the initial-stage filter
section includes at least either of a series arm resonator and a
parallel arm resonator as the at least one first elastic wave
resonator.
4. The multiplexer according to claim 1, wherein the first filter
has a longitudinally coupled filter structure.
5. The multiplexer according to claim 1, wherein the first pass
band is located closer to a high-frequency side than the second
pass band; the at least one first elastic wave resonator of the
initial-stage filter section is a surface acoustic wave resonator
that includes a substrate including a piezoelectric layer, and an
IDT electrode that is provided on the substrate; and in the
initial-stage filter section, any one of (1) Rayleigh waves that
propagate along the piezoelectric layer, which includes
LiNbO.sub.3, (2) leaky waves that propagate along the piezoelectric
layer, which includes LiTaO.sub.3, and (3) Love waves that
propagate along the piezoelectric layer, which includes
LiNbO.sub.3, are utilized as surface acoustic waves.
6. The multiplexer according to claim 5, wherein, in the
subsequent-stage filter section, the second elastic wave resonator
includes a solidly mounted resonator or a film bulk acoustic
resonator.
7. The multiplexer according to claim 1, wherein the first pass
band is located closer to a high-frequency side than the second
pass band; the at least one first elastic wave resonator of the
initial-stage filter section is a surface acoustic wave resonator
that includes a substrate including a piezoelectric layer, and an
IDT electrode that is provided on the substrate; in the
initial-stage filter section, the at least one first elastic wave
resonator has an acoustic velocity film multilayer structure that
includes the piezoelectric layer that includes the IDT electrode
provided on one main surface thereof, a high-acoustic-velocity
support substrate in which an acoustic velocity of propagating bulk
waves is higher than an acoustic velocity of elastic waves
propagating along the piezoelectric layer, and a
low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer; and in the subsequent-stage filter
section, the second elastic wave resonator includes a solidly
mounted resonator or a film bulk acoustic resonator.
8. The multiplexer according to claim 1, wherein the first pass
band is located closer to a low-frequency side than the second pass
band; and in the initial-stage filter section, (1) Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as surface acoustic waves, (2) the at least one first
elastic wave resonator includes a solidly mounted resonator, or (3)
the at least one first elastic wave resonator includes a film bulk
acoustic resonator.
9. The multiplexer according to claim 8, wherein, in the
subsequent-stage filter section, (1) the second elastic wave
resonator includes an acoustic velocity film multilayer structure
that includes a piezoelectric layer that includes an IDT electrode
provided on one main surface thereof, a high-acoustic-velocity
support substrate in which an acoustic velocity of propagating bulk
waves is higher than an acoustic velocity of elastic waves
propagating along the piezoelectric layer, and a
low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (2) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 are utilized as surface
acoustic waves, or (3) Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves.
10. The multiplexer according to claim 1, wherein the first pass
band is located closer to a low-frequency side than the second pass
band; the at least one first elastic wave resonator and the second
elastic wave resonator that respectively define the initial-stage
filter section and the subsequent-stage filter section are surface
acoustic wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; in the initial-stage filter section, the at least one
first elastic wave resonator includes an acoustic velocity film
multilayer structure that includes the piezoelectric layer that
includes the IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer; and in the subsequent-stage filter
section, (1) leaky waves that propagate along the piezoelectric
layer, which includes LiTaO.sub.3, or (2) Love waves that propagate
along the piezoelectric layer, which includes LiNbO.sub.3, are
utilized as surface acoustic waves.
11. The multiplexer according to claim 1, wherein the first pass
band is located closer to a low-frequency side than the second pass
band; the at least one first elastic wave resonator and the second
elastic wave resonator that respectively define the initial-stage
filter section and the subsequent-stage filter section are surface
acoustic wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; in the initial-stage filter section, leaky waves that
propagate along the piezoelectric layer, which includes
LiTaO.sub.3, are utilized as surface acoustic waves; and in the
subsequent-stage filter section, Love waves that propagate along a
piezoelectric layer, which includes LiNbO.sub.3, are utilized as
surface acoustic waves.
12. The multiplexer according to claim 1, wherein the first pass
band is located closer to a high-frequency side than the second
pass band; in the initial-stage filter section, (1) Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as surface acoustic waves, (2) leaky waves that
propagate along a piezoelectric layer including LiTaO.sub.3 are
utilized as surface acoustic waves, (3) Love waves that propagate
along a piezoelectric layer including LiNbO.sub.3 are utilized as
surface acoustic waves, (4) the at least one first elastic wave
resonator includes a solidly mounted resonator, or (5) the at least
one first elastic wave resonator includes a film bulk acoustic
resonator; and in the subsequent-stage filter section, the second
elastic wave resonator includes an acoustic velocity film
multilayer structure that includes a piezoelectric layer that an
IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer.
13. The multiplexer according to claim 1, wherein the first pass
band is located closer to a high-frequency side than the second
pass band; in the initial-stage filter section, (1) Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as surface acoustic waves, (2) Love waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves, (3) the at least one first
elastic wave resonator includes an acoustic velocity film
multilayer structure that includes a piezoelectric layer that
includes an IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (4) the at least one first elastic
wave resonator includes a solidly mounted resonator, or (5) the at
least one first elastic wave resonator includes a film bulk
acoustic resonator; and in the subsequent-stage filter section,
leaky waves that propagate along a piezoelectric layer including
LiTaO.sub.3 are utilized as surface acoustic waves.
14. The multiplexer according to claim 1, wherein the first pass
band is located closer to a low-frequency side than the second pass
band; in the initial-stage filter section, (1) the at least one
first elastic wave resonator includes an acoustic velocity film
multilayer structure that includes a piezoelectric layer that
includes an IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (2) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 are utilized as surface
acoustic waves, (3) Love waves that propagate along a piezoelectric
layer including LiNbO.sub.3 are utilized as surface acoustic waves,
(4) the at least one first elastic wave resonator includes a
solidly mounted resonator, or (5) at least one first the elastic
wave resonator includes a film bulk acoustic resonator; and in the
subsequent-stage filter section, Rayleigh waves that propagate
along a piezoelectric layer including LiNbO.sub.3 are utilized as
surface acoustic waves.
15. The multiplexer according to claim 1, wherein the first pass
band is located closer to a low-frequency side than the second pass
band; in the initial-stage filter section, (1) Rayleigh waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves, (2) the at least one first
elastic wave resonator has an acoustic velocity film multilayer
structure that includes a piezoelectric layer that includes an IDT
electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (3) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 are utilized as surface
acoustic waves, (4) the at least one first elastic wave resonator
includes a solidly mounted resonator, or (5) the at least one first
elastic wave resonator includes a film bulk acoustic resonator; and
in the subsequent-stage filter section, Love waves that propagate
along a piezoelectric layer including LiNbO.sub.3 are utilized as
surface acoustic waves.
16. The multiplexer according to claim 1, wherein the at least two
elastic wave resonators of the first filter are surface acoustic
wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; in the first filter, leaky waves that propagate along
the piezoelectric layer, which includes LiTaO.sub.3, are utilized
as surface acoustic waves; and the IDT electrode of the
initial-stage filter section and the IDT electrode of the
subsequent-stage filter section have different film thicknesses or
duties from each other.
17. The multiplexer according to claim 1, wherein the at least two
elastic wave resonators of the first filter are surface acoustic
wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; and in the first filter, the elastic wave resonators
each include an acoustic velocity film multilayer structure that
includes the piezoelectric layer that includes the IDT electrode
provided on one main surface thereof, a high-acoustic-velocity
support substrate in which an acoustic velocity of propagating bulk
waves is higher than an acoustic velocity of elastic waves
propagating along the piezoelectric layer, and a
low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer; and any of film thicknesses of the
IDT electrodes, duties of the IDT electrodes, and film thicknesses
of the low-acoustic-velocity films are different from each other in
the initial-stage filter section and the subsequent-stage filter
section.
18. The multiplexer according to claim 1, wherein the at least two
elastic wave resonators of the first filter are surface acoustic
wave resonators that each include a substrate including a
piezoelectric layer, an IDT electrode that is provided on the
substrate, and a protective film that is formed on the IDT
electrode; in the first filter, (1) Rayleigh waves that propagate
along the piezoelectric layer, which includes LiNbO.sub.3, or (2)
Love waves that propagate along the piezoelectric layer, which
includes LiNbO.sub.3, are utilized as surface acoustic waves; and
any of film thicknesses of the IDT electrodes, duties of the IDT
electrodes, and film thicknesses of the protective films are
different from each other in the initial-stage filter section and
the subsequent-stage filter section.
19. The multiplexer according to claim 1, wherein the at least two
elastic wave resonators of the first filter are surface acoustic
wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; in the first filter, the elastic wave resonators each
include an acoustic velocity film multilayer structure that
includes the piezoelectric layer that includes the IDT electrode
provided on one main surface thereof, a high-acoustic-velocity
support substrate in which an acoustic velocity of propagating bulk
waves is higher than an acoustic velocity of elastic waves
propagating along the piezoelectric layer, and a
low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer; the high-acoustic-velocity support
substrate includes silicon crystal; and any of film thicknesses of
the piezoelectric layers, film thicknesses of the
low-acoustic-velocity films, and silicon crystal orientations of
the high-acoustic-velocity support substrates are different from
each other in the initial-stage filter section and the
subsequent-stage filter section.
20. The multiplexer according to claim 1, wherein the at least two
elastic wave resonators of the first filter are surface acoustic
wave resonators that each include a substrate including a
piezoelectric layer, and an IDT electrode that is provided on the
substrate; in the first filter, (1) leaky waves that propagate
along the piezoelectric layer, which includes LiTaO.sub.3, or (2)
Love waves that propagate along the piezoelectric layer, which
includes LiNbO.sub.3, are utilized as surface acoustic waves; and
film thicknesses of the IDT electrodes are different from each
other in the initial-stage filter section and the subsequent-stage
filter section.
21. The multiplexer according to claim 1, further comprising: a
third input/output terminal; and a third filter that includes at
least two elastic wave resonators that are located between the
common terminal and the third input/output terminal, the third
filter including a third pass band that is at a different frequency
from the second pass band; wherein the third filter includes: the
initial-stage filter section; and a second subsequent-stage filter
section that includes a third elastic wave resonator, which is
different from the at least one first elastic wave resonator of the
initial-stage filter section, that is located on the third
input/output terminal side among the at least two elastic wave
resonators; the first filter and the third filter further include:
a switch that is located between the initial-stage filter section,
and the subsequent-stage filter section and the second
subsequent-stage filter section, and that switches a connection
between the initial-stage filter section and the subsequent-stage
filter section, and a connection between the initial-stage filter
section and the second subsequent-stage filter section; and a
reflection coefficient of the initial-stage filter section in the
second pass band when the initial-stage filter section is viewed
from the common terminal side as a single component is larger than
a reflection coefficient of the second subsequent-stage filter
section in the second pass band when the second subsequent-stage
filter section is viewed from the common terminal side as a single
component.
22. A high-frequency front-end circuit comprising: the multiplexer
according to claim 1; and an amplification circuit that is
connected to the multiplexer.
23. A communication device comprising: an RF signal processing
circuit that processes a high-frequency signal transmitted or
received by an antenna element; and the high-frequency front-end
circuit according to claim 22 that transmits the high-frequency
signal between the antenna element and the RF signal processing
circuit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority to Japanese
Patent Application No. 2016-140918 filed on Jul. 15, 2016. The
entire contents of this application are hereby incorporated herein
by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a multiplexer that includes
an elastic wave filter, to a high-frequency front-end circuit, and
to a communication device.
2. Description of the Related Art
[0003] In recent years, there has been a demand for cellular phones
to be able to handle a plurality of frequency bands and a plurality
of wireless systems, so called multiband and multimode, as a single
terminal. In order to realize this, a multiplexer that separates
high-frequency signals having a plurality of wireless carrier
frequencies is arranged immediately next to a single antenna. Such
a multiplexer has a configuration in which a plurality of band pass
filters are connected in parallel with an antenna common
terminal.
[0004] Japanese Unexamined Patent Application Publication No.
2004-88143 discloses a surface acoustic wave splitter having a
configuration in which an antenna element and a plurality of
surface acoustic wave filters are connected to each other without a
switch, and the size of the surface acoustic wave splitter is able
to be reduced.
[0005] However, when a plurality of filters are connected to each
other at a single antenna terminal as in the surface acoustic wave
splitter disclosed in the above-cited patent document, the filter
characteristics of one filter are greatly affected by the filter
characteristics of the other filter(s). For example, in the case
where return loss of the other filter(s) seen from the antenna
terminal side increases in the pass band of the one filter, the
insertion loss of the one filter in the pass band of the one filter
is increased by the reflection characteristics of the other
filter(s).
SUMMARY OF THE INVENTION
[0006] Preferred embodiments of the present invention provide
small-sized multiplexers, high-frequency front-end circuits, and
communication devices in which propagation loss of a high-frequency
signal is significantly reduced or prevented.
[0007] A multiplexer according to a preferred embodiment of the
present invention includes a common terminal, a first input/output
terminal, a second input/output terminal, and a plurality of
filters that are connected to each other at the common terminal.
The multiplexer includes a first filter that includes at least two
elastic wave resonators between the common terminal and the first
input/output terminal, the first filter including a first pass
band; and a second filter that is connected between the common
terminal and the second input/output terminal, the second filter
including a second pass band that is at a different frequency from
the first pass band. The first filter includes an initial-stage
filter section that includes at least one first elastic wave
resonator located on the common terminal side among the at least
two elastic wave resonators, and a subsequent-stage filter section
that includes a second elastic wave resonator other than the at
least one first elastic wave resonator among the at least two
elastic wave resonators. A reflection coefficient of the
initial-stage filter section in the second pass band when the
initial-stage filter section is viewed from the common terminal
side as a single component is larger than a reflection coefficient
of the subsequent-stage filter section in the second pass band when
the subsequent-stage filter section is viewed from the common
terminal side as a single component.
[0008] In the case of a configuration in which the first filter and
the second filter are connected to each other at the common
terminal, the insertion loss of the second filter in the second
pass band is affected by the reflection characteristic of the first
filter seen from the common terminal side in addition to the
insertion loss of the second filter itself. More specifically, the
insertion loss of the second filter in the second pass band
decreases as the reflection coefficient of the first filter in the
second pass band seen from the common terminal side increases
(referred to as connection loss).
[0009] According to the above configuration, the reflection
coefficient of the initial-stage filter section of the first filter
in the second pass band is larger than the reflection coefficient
of the subsequent-stage filter section of the first filter in the
second pass band, and therefore, the return loss in the second pass
band when the first filter is viewed from the common terminal side
is able to be further significantly reduced or prevented. Thus, the
connection loss of the second filter is able to be significantly
reduced or prevented, and therefore the insertion loss of the
entire multiplexer is able to be significantly reduced or
prevented.
[0010] Furthermore, the at least one first elastic wave resonator
that defines the initial-stage filter section may include one
elastic wave resonator that is closest to the common terminal among
the at least two elastic wave resonators, for example.
[0011] In a filter including of a plurality of elastic wave
resonators, the return loss of the one elastic wave resonator that
is closest to the common terminal is dominant in the return loss
seen from the common terminal side, and the connection loss of the
second filter is able to be significantly reduced or prevented.
[0012] Furthermore, the first filter may include a ladder filter
structure, and the initial-stage filter section may include at
least either of a series arm resonator and a parallel arm resonator
as the at least one first elastic wave resonator, for example.
[0013] Thus, connection loss of the second filter is able to be
significantly reduced or prevented while providing a low loss
characteristic for the first filter.
[0014] In addition, the first filter may include a longitudinally
coupled type filter structure, for example.
[0015] Thus, the first filter is able to be adapted to a filter
characteristic which strengthens attenuation, for example.
[0016] In addition, the first pass band may be located closer to a
high-frequency side than the second pass band, the at least one
first elastic wave resonator that defines the initial-stage filter
section may be a surface acoustic wave resonator that includes a
substrate including a piezoelectric layer, and an IDT electrode
that is provided on the substrate, and in the initial-stage filter
section, any one of (1) Rayleigh waves that propagate along the
piezoelectric layer, which includes LiNbO.sub.3, (2) leaky waves
that propagate along the piezoelectric layer, which includes
LiTaO.sub.3, and (3) Love waves that propagate along the
piezoelectric layer, which includes LiNbO.sub.3, may be utilized as
surface acoustic waves, for example.
[0017] The return loss in a region including frequencies lower than
the resonance point and the anti-resonance point of the elastic
wave resonator is smaller in the case where any of Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3,
leaky waves that propagate along a piezoelectric layer including
LiTaO.sub.3, and Love waves that propagate along a piezoelectric
layer including LiNbO.sub.3 are utilized as surface acoustic waves
than in the case where another type of elastic wave is
utilized.
[0018] Therefore, in the case where the first filter is a
high-frequency filter and the second filter is a low-frequency
filter, the reflection coefficient of the initial-stage filter
section of the first filter in the second pass band is able to be
made larger than the reflection coefficient of the subsequent-stage
filter section of the first filter in the second pass band. Thus,
the connection loss of the second filter is able to be
significantly reduced or prevented.
[0019] In addition, in the subsequent-stage filter section, the
second elastic wave resonator may include a solidly mounted
resonator or a film bulk acoustic resonator, for example.
[0020] With the above configuration, a low loss characteristic and
a steep pass band characteristic are able to be provided for the
first filter by including the configuration of the subsequent-stage
filter section while the return loss of the first filter is able to
be significantly reduced or prevented by including the
configuration of the initial-stage filter section.
[0021] Furthermore, the first pass band may be located closer to a
high-frequency side than the second pass band, the at least one
first elastic wave resonator that defines the initial-stage filter
section may be a surface acoustic wave resonator that includes a
substrate including a piezoelectric layer, and an IDT electrode
that is provided on the substrate, in the initial-stage filter
section, the at least one first elastic wave resonator may include
an acoustic velocity film multilayer structure that includes the
piezoelectric layer that includes the IDT electrode provided on one
main surface thereof, a high-acoustic-velocity support substrate in
which an acoustic velocity of propagating bulk waves is higher than
an acoustic velocity of elastic waves propagating along the
piezoelectric layer, and a low-acoustic-velocity film that is
located between the high-acoustic-velocity support substrate and
the piezoelectric layer and in which an acoustic velocity of
propagating bulk waves is lower than an acoustic velocity of
elastic waves propagating along the piezoelectric layer, and in the
subsequent-stage filter section, the second elastic wave resonator
may include a solidly mounted resonator or a film bulk acoustic
resonator, for example.
[0022] The reflection coefficient in a region including frequencies
lower than the resonance point and the anti-resonance point of the
elastic wave resonator is larger in the case where the elastic wave
resonator has an acoustic velocity film multilayer structure than
in the case where the elastic wave resonator includes a solidly
mounted resonator or a film bulk acoustic resonator.
[0023] Therefore, in the case where the first filter is a
high-frequency filter and the second filter is a low-frequency
filter, the reflection coefficient of the initial-stage filter
section of the first filter in the second pass band is able to be
made larger than the reflection coefficient of the subsequent-stage
filter section of the first filter in the second pass band. Thus,
the connection loss of the second filter is able to be
significantly reduced or prevented. In addition, a low loss
characteristic and a steep pass band characteristic is able to be
provided for the first filter by including the configuration of the
subsequent-stage filter section while the return loss of the first
filter is able to be significantly reduced or prevented by
including the configuration of the initial-stage filter
section.
[0024] Furthermore, the first pass band may be located closer to a
low-frequency side than the second pass band, and in the
initial-stage filter section, (1) Rayleigh waves that propagate
along a piezoelectric layer including LiNbO.sub.3 may be utilized
as surface acoustic waves, (2) the at least one first elastic wave
resonator may include a solidly mounted resonator, or (3) the at
least one first elastic wave resonator may include a film bulk
acoustic resonator, for example.
[0025] Unwanted waves are generated by leakage of bulk waves in a
region including frequencies higher than the resonance point and
the anti-resonance point of the elastic wave resonator, and the
strength of the unwanted waves is able to be significantly reduced
in the case where Rayleigh waves that propagate along a
piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves, the elastic wave resonator includes a solidly
mounted resonator, or the elastic wave resonator includes a film
bulk acoustic resonator.
[0026] Therefore, in the case where the first filter is a
low-frequency filter and the second filter is a high-frequency
filter, the reflection coefficient of the initial-stage filter
section of the first filter in the second pass band is able to be
made larger than the reflection coefficient of the subsequent-stage
filter section of the first filter in the second pass band. Thus,
the connection loss of the second filter is able to be
significantly reduced or prevented.
[0027] Furthermore, in the subsequent-stage filter section, (1) the
second elastic wave resonator may include an acoustic velocity film
multilayer structure that includes a piezoelectric layer that
includes an IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (2) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 may be utilized as
surface acoustic waves, or (3) Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, for example.
[0028] With the above configuration, a low loss characteristic and
excellent temperature characteristics are able to be provided for
the first filter in the case where the acoustic velocity film
multilayer structure is provided for the subsequent-stage filter
section or a wide band width is able to be provided for the first
filter in the case where Love waves generated by LiNbO.sub.3 are
utilized as surface acoustic waves in the subsequent-stage filter
section while the reflection coefficient of the first filter is
able to be increased by including the configuration of the
initial-stage filter section.
[0029] In addition, the first pass band may be located closer to a
low-frequency side than the second pass band, the at least one
first elastic wave resonator and the second elastic wave resonator
that respectively define the initial-stage filter section and the
subsequent-stage filter section may be surface acoustic wave
resonators that each include a substrate including a piezoelectric
layer, and an IDT electrode that is provided on the substrate, in
the initial-stage filter section, the at least one first elastic
wave resonator may include an acoustic velocity film multilayer
structure that includes the piezoelectric layer that includes the
IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, and in the subsequent-stage filter
section, (1) leaky waves that propagate along the piezoelectric
layer, which includes LiTaO.sub.3, or (2) Love waves that propagate
along the piezoelectric layer, which includes LiNbO.sub.3, may be
utilized as surface acoustic waves, for example.
[0030] Unwanted waves are generated by leakage of bulk waves in a
region including frequencies higher than the resonance point and
the anti-resonance point of the elastic wave resonator, and the
strength of the unwanted waves is able to be made smaller in the
case where the acoustic velocity film multilayer structure is
provided compared with the case where leaky waves from LiTaO.sub.3
are utilized as surface acoustic waves or Love waves from
LiNbO.sub.3 are utilized as surface acoustic waves.
[0031] Therefore, in the case where the first filter is a
low-frequency filter and the second filter is a high-frequency
filter, the reflection coefficient of the initial-stage filter
section of the first filter in the second pass band is able to be
made larger than the reflection coefficient of the subsequent-stage
filter section of the first filter in the second pass band. Thus,
the connection loss of the second filter is able to be
significantly reduced or prevented. Furthermore, a wide band width
is able to be provided for the first filter in the case where Love
waves generated by LiNbO.sub.3 are utilized as surface acoustic
waves in the subsequent-stage filter section.
[0032] In addition, the first pass band may be located closer to a
low-frequency side than the second pass band, the at least one
first elastic wave resonator and the second elastic wave resonator
that respectively define the initial-stage filter section and the
subsequent-stage filter section may be surface acoustic wave
resonators that each include a substrate including a piezoelectric
layer, and an IDT electrode that is provided on the substrate, in
the initial-stage filter section, leaky waves that propagate along
the piezoelectric layer, which includes LiTaO.sub.3, may be
utilized as surface acoustic waves, and in the subsequent-stage
filter section, Love waves that propagate along the piezoelectric
layer, which includes LiNbO.sub.3, may be utilized as surface
acoustic waves, for example.
[0033] Unwanted waves are generated by leakage of bulk waves in a
region including frequencies higher than the resonance point and
the anti-resonance point of the elastic wave resonator, and the
strength of the unwanted waves is able to be made smaller in the
case where leaky waves from LiTaO.sub.3 are utilized as surface
acoustic waves compared with the case where Love waves from
LiNbO.sub.3 are utilized as surface acoustic waves.
[0034] Therefore, in the case where the first filter is a
low-frequency filter and the second filter is a high-frequency
filter, the reflection coefficient of the initial-stage filter
section of the first filter in the second pass band is able to be
made larger than the reflection coefficient of the subsequent-stage
filter section of the first filter in the second pass band. Thus,
the connection loss of the second filter is able to be
significantly reduced or prevented. Furthermore, a wide band width
is able to be provided for the first filter in the case where Love
waves generated by LiNbO.sub.3 are utilized as surface acoustic
waves in the subsequent-stage filter section.
[0035] Furthermore, the first pass band may be located closer to a
high-frequency side than the second pass band, in the initial-stage
filter section, (1) Rayleigh waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (2) leaky waves that propagate along a
piezoelectric layer including LiTaO.sub.3 may be utilized as
surface acoustic waves, (3) Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (4) the at least one first elastic wave
resonator may include a solidly mounted resonator, or (5) the at
least one first elastic wave resonator may include a film bulk
acoustic resonator, and in the subsequent-stage filter section, the
second elastic wave resonator may include an acoustic velocity film
multilayer structure that includes a piezoelectric layer that
includes an IDT electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, for example.
[0036] A Rayleigh wave spurious signal is generated at a frequency
about 0.76 times the resonant frequency of the elastic wave
resonator when an elastic wave resonator has the acoustic velocity
film multilayer structure, for example. Therefore, the reflection
coefficient of the first filter in the second pass band is able to
be made large by including the acoustic velocity film multilayer
structure in the subsequent-stage filter section of the first
filter and not including the acoustic velocity film multilayer
structure in the initial-stage filter section of the first
filter.
[0037] Therefore, in the case where the first filter is a
high-frequency filter and the second filter is a low-frequency
filter, the connection loss of the second filter is able to be
significantly reduced or prevented.
[0038] In addition, the first pass band may be located closer to a
high-frequency side than the second pass band, in the initial-stage
filter section, (1) Rayleigh waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (2) Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (3) the at least one first elastic wave
resonator may include an acoustic velocity film multilayer
structure that includes a piezoelectric layer that includes an IDT
electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (4) the at least one first elastic
wave resonator may include a solidly mounted resonator, or (5) the
at least one first elastic wave resonator may include a film bulk
acoustic resonator, and in the subsequent-stage filter section,
leaky waves that propagate along a piezoelectric layer including
LiTaO.sub.3 may be utilized as surface acoustic waves, for
example.
[0039] A Rayleigh wave spurious signal is generated at a frequency
about 0.76 times the resonant frequency of the elastic wave
resonator in the case where leaky waves from LiTaO.sub.3 are
utilized as elastic waves, for example. Therefore, the reflection
coefficient of the first filter in the second pass band is able to
be made large by utilizing leaky waves from LiTaO.sub.3 as elastic
waves in the subsequent-stage filter section of the first filter
and not utilizing leaky waves from LiTaO.sub.3 as elastic waves in
the initial-stage filter section of the first filter.
[0040] Therefore, in the case where the first filter is a
high-frequency filter and the second filter is a low-frequency
filter, the connection loss of the second filter is able to be
significantly reduced or prevented.
[0041] Furthermore, the first pass band may be located closer to a
low-frequency side than the second pass band, in the initial-stage
filter section, (1) the at least one first elastic wave resonator
may include an acoustic velocity film multilayer structure that
includes a piezoelectric layer that includes an IDT electrode
provided on one main surface thereof, a high-acoustic-velocity
support substrate in which an acoustic velocity of propagating bulk
waves is higher than an acoustic velocity of elastic waves
propagating along the piezoelectric layer, and a
low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (2) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 may be utilized as
surface acoustic waves, (3) Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (4) the at least one first elastic wave
resonator may include a solidly mounted resonator, or (5) the at
least one first elastic wave resonator may include a film bulk
acoustic resonator, and in the subsequent-stage filter section,
Rayleigh waves that propagate along a piezoelectric layer including
LiNbO.sub.3 may be utilized as surface acoustic waves, for
example.
[0042] A high-order mode is generated at a frequency that is about
1.2 times the resonant frequency of the elastic wave resonator in
the case where Rayleigh waves from LiNbO.sub.3 are utilized as
elastic waves, for example. Therefore, the reflection coefficient
of the first filter in the second pass band is able to be made
large by utilizing Rayleigh waves from LiNbO.sub.3 as elastic waves
in the subsequent-stage filter section of the first filter and not
utilizing Rayleigh waves from LiNbO.sub.3 as elastic waves in the
initial-stage filter section of the first filter.
[0043] Therefore, connection loss of the second filter is able to
be significantly reduced or prevented in the case where the first
filter is a low-frequency filter and the second filter is a
high-frequency filter.
[0044] Furthermore, the first pass band may be located closer to a
low-frequency side than the second pass band, in the initial-stage
filter section, (1) Rayleigh waves that propagate along a
piezoelectric layer including LiNbO.sub.3 may be utilized as
surface acoustic waves, (2) the at least one first elastic wave
resonator may include an acoustic velocity film multilayer
structure that includes a piezoelectric layer that includes an IDT
electrode provided on one main surface thereof, a
high-acoustic-velocity support substrate in which an acoustic
velocity of propagating bulk waves is higher than an acoustic
velocity of elastic waves propagating along the piezoelectric
layer, and a low-acoustic-velocity film that is located between the
high-acoustic-velocity support substrate and the piezoelectric
layer and in which an acoustic velocity of propagating bulk waves
is lower than an acoustic velocity of elastic waves propagating
along the piezoelectric layer, (3) leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 may be utilized as
surface acoustic waves, (4) the at least one first elastic wave
resonator may include a solidly mounted resonator, or (5) the at
least one first elastic wave resonator may include a film bulk
acoustic resonator, and in the subsequent-stage filter section,
Love waves that propagate along a piezoelectric layer including
LiNbO.sub.3 may be utilized as surface acoustic waves, for
example.
[0045] A high-order mode is generated at a frequency that is about
1.2 times the resonant frequency of the elastic wave resonator in
the case where Love waves from LiNbO.sub.3 are utilized as elastic
waves, for example. Therefore, the reflection coefficient of the
first filter in the second pass band is able to be made large by
utilizing Love waves from LiNbO.sub.3 as elastic waves in the
subsequent-stage filter section of the first filter and not
utilizing Love waves from LiNbO.sub.3 as elastic waves in the
initial-stage filter section of the first filter.
[0046] Therefore, connection loss of the second filter is able to
be significantly reduced or prevented in the case where the first
filter is a low-frequency filter and the second filter is a
high-frequency filter.
[0047] In addition, the at least two elastic wave resonators that
define the first filter may be surface acoustic wave resonators
that each include a substrate including a piezoelectric layer, and
an IDT electrode that is provided on the substrate, in the first
filter, leaky waves that propagate along the piezoelectric layer,
which includes LiTaO.sub.3, may be utilized as surface acoustic
waves, and the IDT electrode of the initial-stage filter section
and the IDT electrode of the subsequent-stage filter section may
have different film thicknesses or duties from each other, for
example.
[0048] A Rayleigh wave spurious signal is generated at a frequency
that is lower than the resonant frequency of the elastic wave
resonator in the case where leaky waves from LiTaO.sub.3 are
utilized as elastic waves. The frequency at which the Rayleigh wave
spurious signal is generated in the initial-stage filter section is
able to be shifted to outside the second pass band by making the
film thicknesses or duties of the IDT electrodes different from
each other in the initial-stage filter section and the
subsequent-stage filter section. The reflection coefficient of the
first filter in the second pass band is able to be made large, and
connection loss of the second filter is able to be significantly
reduced or prevented.
[0049] In addition, the at least two elastic wave resonators that
define the first filter may be surface acoustic wave resonators
that each include a substrate including a piezoelectric layer, and
an IDT electrode that is provided on the substrate, and in the
first filter, the elastic wave resonators may each include an
acoustic velocity film multilayer structure that includes the
piezoelectric layer that includes the IDT electrode provided on one
main surface thereof, a high-acoustic-velocity support substrate in
which an acoustic velocity of propagating bulk waves is higher than
an acoustic velocity of elastic waves propagating along the
piezoelectric layer, and a low-acoustic-velocity film that is
located between the high-acoustic-velocity support substrate and
the piezoelectric layer and in which an acoustic velocity of
propagating bulk waves is lower than an acoustic velocity of
elastic waves propagating along the piezoelectric layer, and any of
film thicknesses of the IDT electrodes, duties of the IDT
electrodes and film thicknesses of the low-acoustic-velocity films
may be different from each other in the initial-stage filter
section and the subsequent-stage filter section, for example.
[0050] A Rayleigh wave spurious signal is generated at a frequency
that is lower than the resonant frequency of the elastic wave
resonator in the case where the acoustic velocity film multilayer
structure is provided. The frequency at which the Rayleigh wave
spurious signal is generated in the initial-stage filter section is
able to be shifted to outside the second pass band by making the
film thicknesses or duties of the IDT electrodes different from
each other in the initial-stage filter section and the
subsequent-stage filter section. Thus, the reflection coefficient
of the first filter in the second pass band is able to be made
large, and connection loss of the second filter is able to be
significantly reduced or prevented.
[0051] Furthermore, the at least two elastic wave resonators that
define the first filter may be surface acoustic wave resonators
that each include a substrate including a piezoelectric layer, an
IDT electrode that is provided on the substrate, and a protective
film that is provided on the IDT electrode, in the first filter,
(1) Rayleigh waves that propagate along the piezoelectric layer,
which includes LiNbO.sub.3, or (2) Love waves that propagate along
the piezoelectric layer, which includes LiNbO.sub.3, may be
utilized as surface acoustic waves, and any of film thicknesses of
the IDT electrodes, duties of the IDT electrodes and film
thicknesses of the protective films may be different from each
other in the initial-stage filter section and the subsequent-stage
filter section, for example.
[0052] A high-order mode is generated at a frequency that is higher
than the resonant frequency of the elastic wave resonator in the
case where Rayleigh waves from LiNbO.sub.3 or Love waves from
LiNbO.sub.3 are utilized as surface acoustic waves. The frequency
at which the high-order mode is generated in the initial-stage
filter section is able to shifted to outside the second pass band
by making the film thicknesses of the IDT electrodes, the duties of
the IDT electrodes or the film thicknesses of the protective films
different from each other in the initial-stage filter section and
the subsequent-stage filter section. Thus, the reflection
coefficient of the first filter in the second pass band is able to
be made large, and connection loss of the second filter is able to
be significantly reduced or prevented.
[0053] In addition, the at least two elastic wave resonators that
define the first filter may be surface acoustic wave resonators
that each include a substrate including a piezoelectric layer, and
an IDT electrode that is provided on the substrate, in the first
filter, the elastic wave resonators may each include an acoustic
velocity film multilayer structure that includes the piezoelectric
layer that includes the IDT electrode provided on one main surface
thereof, a high-acoustic-velocity support substrate in which an
acoustic velocity of propagating bulk waves is higher than an
acoustic velocity of elastic waves propagating along the
piezoelectric layer, and a low-acoustic-velocity film that is
located between the high-acoustic-velocity support substrate and
the piezoelectric layer and in which an acoustic velocity of
propagating bulk waves is lower than an acoustic velocity of
elastic waves propagating along the piezoelectric layer, the
high-acoustic-velocity support substrate may be made of silicon
crystal, and any of film thicknesses of the piezoelectric layers,
film thicknesses of the low-acoustic-velocity films and silicon
crystal orientations of the high-acoustic-velocity support
substrates may be different from each other in the initial-stage
filter section and the subsequent-stage filter section, for
example.
[0054] A high-order mode is generated at a frequency that is higher
than the resonant frequency of the elastic wave resonator in the
case where the acoustic velocity film multilayer structure is
provided. The frequency at which the high-order mode is generated
in the initial-stage filter section is able to shifted to outside
the second pass band by making the film thicknesses of the
piezoelectric layers, the film thicknesses of the
low-acoustic-velocity films or the silicon crystal orientations of
the high-acoustic-velocity support substrates different from each
other in the initial-stage filter section and the subsequent-stage
filter section. Thus, the reflection coefficient of the first
filter in the second pass band is able to be made large, and
connection loss of the second filter is able to be significantly
reduced or prevented.
[0055] Furthermore, the at least two elastic wave resonators that
define the first filter may be surface acoustic wave resonators
that each include a substrate including a piezoelectric layer, and
an IDT electrode that is provided on the substrate, in the first
filter, (1) leaky waves that propagate along the piezoelectric
layer, which includes LiTaO.sub.3, or (2) Love waves that propagate
along the piezoelectric layer, which includes LiNbO.sub.3, may be
utilized as surface acoustic waves, and film thicknesses of the IDT
electrodes may be different from each other in the initial-stage
filter section and the subsequent-stage filter section, for
example.
[0056] Bulk waves (unwanted waves) are generated at a higher
frequency than the resonant frequency of the elastic wave resonator
in the case where leaky waves from LiTaO.sub.3 or Love waves from
LiNbO.sub.3 are utilized as surface acoustic waves. The frequency
at which the bulk waves are generated in the initial-stage filter
section is able to be shifted to outside the second pass band by
making the film thicknesses of the IDT electrodes different from
each other in the initial-stage filter section and the
subsequent-stage filter section. Thus, the reflection coefficient
of the first filter in the second pass band is able to be made
large, and connection loss of the second filter is able to be
significantly reduced or prevented.
[0057] In addition, the multiplexer may further include a third
input/output terminal; and a third filter that includes at least
two elastic wave resonators that are located between the common
terminal and the third input/output terminal, the third filter
including a third pass band that is at a different frequency from
the second pass band. The third filter includes the initial-stage
filter section, and a second subsequent-stage filter section that
includes a third elastic wave resonator, which is different from
the at least one first elastic wave resonator of the initial-stage
filter section, that is located on the third input/output terminal
side among the at least two elastic wave resonators. The first
filter and the third filter may further include a switch that is
located between the initial-stage filter section, and the
subsequent-stage filter section and the second subsequent-stage
filter section, and that switches a connection between the
initial-stage filter section and the subsequent-stage filter
section, and a connection between the initial-stage filter section
and the second subsequent-stage filter section. A reflection
coefficient of the initial-stage filter section in the second pass
band when the initial-stage filter section is viewed from the
common terminal side as a single component may be larger than a
reflection coefficient of the second subsequent-stage filter
section in the second pass band when the second subsequent-stage
filter section is viewed from the common terminal side as a single
component, for example.
[0058] With the above configuration, even in a case where the
frequency bands of the first filter and the third filter overlap,
for example, the connection loss of the second filter is able to be
significantly reduced or prevented without causing the insertion
losses of the first filter and the third filter to deteriorate by
switching the switch. In addition, since the first filter and the
third filter share the initial-stage filter section, a significant
reduction in the overall size of the multiplexer is able to be
achieved.
[0059] Furthermore, a high-frequency front-end circuit according to
a preferred embodiment of the present invention includes any of the
above-described multiplexers; and an amplification circuit that is
connected to the multiplexer.
[0060] With the above configuration, a high-frequency front-end
circuit is able to be provided that is able to significantly reduce
or prevent the connection loss of the second filter.
[0061] In addition, a communication device according to a preferred
embodiment of the present invention includes an RF signal
processing circuit that processes a high-frequency signal
transmitted or received by an antenna element; and the
above-described high-frequency front-end circuit that transmits the
high-frequency signal between the antenna element and the RF signal
processing circuit.
[0062] With the above configuration, a communication device is able
to be provided that is able to significantly reduce or prevent
connection loss of the second filter.
[0063] The multiplexers, the high-frequency front-end circuits, and
the communication devices according to preferred embodiments of the
present invention are able to significantly reduce or prevent
propagation loss of a high-frequency signal while achieving a
significant reduction in size.
[0064] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] FIG. 1A is a diagram of the circuit configuration of a
multiplexer according to a first preferred embodiment of the
present invention.
[0066] FIG. 1B is a diagram showing a reflection characteristic of
the multiplexer according to the first preferred embodiment of the
present invention.
[0067] FIG. 2A is a diagram of the circuit configuration of a
multiplexer according to a first modification of the first
preferred embodiment of the present invention.
[0068] FIG. 2B is a diagram showing a reflection characteristic of
the multiplexer according to the first modification of the first
preferred embodiment of the present invention.
[0069] FIG. 3 is a diagram of the circuit configuration of a
low-frequency filter according to the first preferred embodiment of
the present invention.
[0070] FIG. 4 is a diagram showing an issue that arises when two
filters are connected to each other at a common terminal.
[0071] FIG. 5 is a graph that shows the relationship between the
pre-connection return loss of one filter and the connection loss of
another filter.
[0072] FIG. 6A is a diagram of a circuit that measures return loss
in a state where a resistance component is added to each resonator
of a ladder filter.
[0073] FIG. 6B is a graph that shows the relationship between the
position of each resonator to which a resistance component is added
and the change in return loss.
[0074] FIG. 7 shows examples of a plan view and a sectional view
that schematically show a resonator of a multiplexer according to
the first preferred embodiment of the present invention.
[0075] FIG. 8A is a diagram showing a reflection characteristic of
a multiplexer according to a second modification of the first
preferred embodiment of the present invention in a low-frequency
region.
[0076] FIG. 8B shows combinations of the configurations of an
initial-stage filter section and a subsequent-stage filter section
according to the second modification of the first preferred
embodiment of the present invention.
[0077] FIG. 9A is a diagram showing bulk wave leakage in a
high-frequency region of a multiplexer according to a third
modification of the first preferred embodiment of the present
invention.
[0078] FIG. 9B shows combinations of the configurations of an
initial-stage filter section and a subsequent-stage filter section
according to the third modification of the first preferred
embodiment of the present invention.
[0079] FIG. 10A is a diagram showing generation of a spurious
signal in a low-frequency region of a multiplexer according to a
fourth modification of the first preferred embodiment of the
present invention.
[0080] FIG. 10B shows combinations of the configurations of an
initial-stage filter section and a subsequent-stage filter section
according to the fourth modification of the first preferred
embodiment of the present invention.
[0081] FIG. 11A is a diagram showing generation of a high-order
mode in a high-frequency region of a multiplexer according to a
fifth modification of the first preferred embodiment of the present
invention.
[0082] FIG. 11B shows combinations of the configurations of an
initial-stage filter section and a subsequent-stage filter section
according to the fifth modification of the first preferred
embodiment of the present invention.
[0083] FIG. 12A is a graph that shows degradation of return loss
caused by a high-order mode in a low-frequency filter according to
the first preferred embodiment of the present invention.
[0084] FIG. 12B shows parameters that are used to make the
structures of an initial-stage filter section and a
subsequent-stage filter section according to a sixth modification
of the first preferred embodiment of the present invention
different from each other.
[0085] FIG. 12C shows parameters that are used to make the
structures of an initial-stage filter section and a
subsequent-stage filter section according to a seventh modification
of the first preferred embodiment of the present invention
different from each other.
[0086] FIG. 13 shows parameters that are used to make the
structures of an initial-stage filter section and a
subsequent-stage filter section according to an eighth modification
of the first preferred embodiment of the present invention
different from each other.
[0087] FIG. 14 is a diagram of the circuit configuration of a
low-frequency filter according to a ninth modification of the first
preferred embodiment of the present invention.
[0088] FIG. 15A is a diagram of the circuit configuration of a
low-frequency filter according to a tenth modification of the first
preferred embodiment of the present invention.
[0089] FIG. 15B is a diagram of the circuit configuration of a
low-frequency filter according to an eleventh modification 11 of
the first preferred embodiment of the present invention.
[0090] FIG. 15C is a diagram of the circuit configuration of a
low-frequency filter according to a twelfth modification of the
first preferred embodiment of the present invention.
[0091] FIG. 15D is a diagram of the circuit configuration of a
low-frequency filter according to a thirteenth modification of the
first preferred embodiment of the present invention.
[0092] FIG. 15E is a diagram of the circuit configuration of a
low-frequency filter according to a fourteenth modification of the
first preferred embodiment of the present invention.
[0093] FIG. 16A is a diagram of the circuit configuration of a
low-frequency filter according to a fifteenth modification of the
first preferred embodiment of the present invention.
[0094] FIG. 16B is a diagram of the circuit configuration of a
low-frequency filter according to a sixteenth modification of the
first preferred embodiment of the present invention.
[0095] FIG. 17 is a diagram of the circuit configuration of a
multiplexer according to a seventeenth modification of the first
preferred embodiment of the present invention.
[0096] FIG. 18 is a diagram of the circuit configurations of a
high-frequency front-end circuit and a communication device
according to a second preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0097] Hereafter, preferred embodiments of the present invention
will be described in detail with reference to the drawings. The
preferred embodiments described hereafter are general or specific
examples of the present invention. The numerical values, shapes,
materials, elements, arrangements of the elements, the ways in
which the elements are connected and the like described with
respect to the following preferred embodiments are merely examples
and are not intended to limit the present invention. Furthermore,
elements that are not described in the independent claims among
elements described in the following preferred embodiments are
described as arbitrary elements. In addition, the sizes or size
ratios of the elements shown in the drawings are not necessarily
strictly accurate. It is to be noted that the preferred embodiments
described in this specification are merely examples, and that the
configurations, elements, features, etc. in the preferred
embodiments are able to be partly replaced or combined between
different preferred embodiments.
First Preferred Embodiment
[0098] FIG. 1A is a diagram of the circuit configuration of a
multiplexer 1A according to a first preferred embodiment of the
present invention. As shown in FIG. 1A, the multiplexer 1A includes
a low-frequency filter 11A, a high-frequency filter 12A, a common
terminal 101, and input/output terminals 102 and 103. The
multiplexer 1A is a composite elastic wave filter device that
includes the low-frequency filter 11A and the high-frequency filter
12A, which are connected to each other at the common terminal
101.
[0099] For example, the common terminal 101 is able to be connected
to an antenna element, and the input/output terminals 102 and 103
are able to be connected to a high-frequency signal processing
circuit via an amplification circuit.
[0100] The low-frequency filter 11A is a first filter that is
located between the common terminal 101 and the input/output
terminal 102 (first input/output terminal) and has a first pass
band. The low-frequency filter 11A includes an initial-stage filter
section 11F and a subsequent-stage filter section 11R.
[0101] The initial-stage filter section 11F includes at least one
elastic wave resonator that is located on the common terminal 101
side among at least two elastic wave resonators. On the other hand,
the subsequent-stage filter section 11R includes an elastic wave
resonator that is located on the input/output terminal 102 side and
is an elastic wave resonator other than the at least one elastic
wave resonator among the at least two elastic wave resonators that
define the initial-stage filter section 11F. The structure of the
elastic wave resonators of the initial-stage filter section 11F and
the subsequent-stage filter section 11R is described in detail in
FIG. 3 onwards.
[0102] The high-frequency filter 12A is a second filter that is
located between the common terminal 101 and the input/output
terminal 103 (second input/output terminal) and has a second pass
band that is located closer to the high-frequency side than the
first pass band.
[0103] FIG. 1B is a diagram showing a reflection characteristic of
the multiplexer 1A according to the first preferred embodiment.
FIG. 1B shows the filter bandpass characteristics of the
low-frequency filter 11A and the high-frequency filter 12A, and the
reflection characteristics of the initial-stage filter section 11F
and the subsequent-stage filter section 11R. Here, in the
multiplexer 1A according to this preferred embodiment, the
reflection coefficient of the initial-stage filter section 11F in a
pass band 12H (second pass band) when the initial-stage filter
section 11F is viewed from the common terminal 101 side as a single
component is larger than the reflection coefficient of the
subsequent-stage filter section 11R in the pass band 12H (second
pass band) when the subsequent-stage filter section 11R is viewed
from the common terminal 101 side as a single component.
[0104] A filter that includes an initial-stage filter section and a
subsequent-stage filter section is not limited to a low-frequency
filter, and the first filter may instead be a high-frequency
filter, for example, as shown in FIG. 2A.
[0105] FIG. 2A is a diagram of the circuit configuration of a
multiplexer 1B according to a first modification of the first
preferred embodiment. As shown in FIG. 2A, the multiplexer 1B
includes a low-frequency filter 11B, a high-frequency filter 12B, a
common terminal 101, and input/output terminals 102 and 103. The
multiplexer 1B is a composite elastic wave filter device that
includes the low-frequency filter 11B and the high-frequency filter
12B that are connected to each other at the common terminal
101.
[0106] The high-frequency filter 12B is a first filter that is
located between the common terminal 101 and the input/output
terminal 103 (first input/output terminal) and has a first pass
band. The high-frequency filter 12B includes an initial-stage
filter section 12F and a subsequent-stage filter section 12R.
[0107] The initial-stage filter section 12F includes at least one
elastic wave resonator that is located on the common terminal 101
side among two or more elastic wave resonators. On the other hand,
the subsequent-stage filter section 12R includes an elastic wave
resonator that is located on the input/output terminal 103 side and
is an elastic wave resonator other than the at least one elastic
wave resonator among the at least two elastic wave resonators that
define the initial-stage filter section 12F.
[0108] The low-frequency filter 11B is a second filter that is
located between the common terminal 101 and the input/output
terminal 102 (third input/output terminal) and has a second pass
band that is located closer to the low-frequency side than the
first pass band.
[0109] FIG. 2B is a diagram showing a reflection characteristic of
the multiplexer 1B according to the first modification of the first
preferred embodiment. FIG. 2B shows the filter bandpass
characteristics of the high-frequency filter 12B and the
low-frequency filter 11B, and the reflection characteristics of the
initial-stage filter section 12F and the subsequent-stage filter
section 12R. Here, in the multiplexer 1B according to this
modification, the reflection coefficient of the initial-stage
filter section 12F in a pass band 11L (second pass band) when the
initial-stage filter section 12F is viewed from the common terminal
101 side as a single component is larger than the reflection
coefficient of the subsequent-stage filter section 12R in the pass
band 11L (second pass band) when the subsequent-stage filter
section 12R is viewed from the common terminal 101 side as a single
component.
[0110] FIG. 3 is an example of a circuit configuration diagram of
the low-frequency filter 11A of the multiplexer 1A according to the
first preferred embodiment. As shown in FIG. 3, the low-frequency
filter 11A includes series arm resonators s11, s12, s13, and s14,
and parallel arm resonators p11, p12, and p13. The series arm
resonators s11, s12, s13, and s14 are connected to each other in
order from the common terminal 101 side in a series arm that
connects the common terminal 101 and the input/output terminal 102
to each other. In addition, the parallel arm resonators p11, p12,
and p13 are connected to parallel arms that connect the series arm
and ground terminals to each other. As a result of the series arm
resonators s11, s12, s13, and s14 and the parallel arm resonators
p11, p12, and p13 being configured as described above, the
low-frequency filter 11A defines a ladder band pass filter. In
addition, the low-frequency filter 11A is not limited to being a
ladder band pass filter, for example. The configuration of the
resonators of the low-frequency filter 11A will be described below
with respect to FIGS. 15A to 16B.
[0111] Surface acoustic wave (SAW) resonators, solidly mounted
resonators (SMRs), or film bulk acoustic resonators (FBARs) that
utilize bulk acoustic waves (BAWs) may be included as the
structures of the series arm resonators s11, s12, s13, and s14 and
the parallel arm resonators p11, p12, and p13, for example.
[0112] Here, the initial-stage filter section 11F includes the
series arm resonator s11 that is closest to the common terminal 101
among the series arm resonators s11, s12, s13, and s14 and the
parallel arm resonators p11, p12, and p13, and the subsequent-stage
filter section 11R includes the resonators other than the series
arm resonator s11 of the initial-stage filter section 11F, in other
words, the series arm resonators s11, s12 s13, and s14 and the
parallel arm resonators p11, p12, and p13.
[0113] In addition, the number of filters that are connected to
each other at the common terminal 101 in the multiplexers 1A and 1B
according to this preferred embodiment is not limited to two, and
may be three or more, for example.
[0114] FIG. 4 is a diagram showing an issue that arises when two
filters (filter A and filter B) are connected to each other at a
common terminal. As shown in FIG. 4, a multiplexer includes a
filter A (pass band A) and a filter B (pass band B) connected to
each other at a common terminal. The insertion loss of the
multiplexer in this case is described below.
[0115] The insertion loss of the filter A in the pass band A is
degraded by the effect of the filter B in addition to the insertion
loss of the filter A itself. The amount of degradation of the
insertion loss of the filter A caused by the filter B is called
"connection loss". Here, the connection loss of the filter A is
affected by the reflection characteristics of the filter B in the
pass band A.
[0116] FIG. 5 is a graph that shows the relationship between the
pre-connection return loss of the filter B and the connection loss
of the filter A. The horizontal axis in FIG. 5 represents the
return loss of the filter B before the filter B is connected to the
filter A at the common terminal when the filter B is viewed from
the common terminal side, and the vertical axis in FIG. 5
represents the connection loss of the filter A (amount of
degradation of insertion loss in pass band A) when the filter A is
connected to the filter B at the common terminal. As shown in FIG.
5, the connection loss of the filter A decreases as the
pre-connection return loss of the filter B becomes smaller. In
other words, the connection loss of the filter A decreases as the
pre-connection reflection coefficient of the filter B
increases.
[0117] Next, the contribution of each elastic wave resonator of the
filter to the reflection characteristic will be described.
[0118] FIG. 6A is a diagram of a circuit that measures return loss
in a state where a resistance component R is added to each elastic
wave resonator of a ladder filter. When the resistance component R
is added to any of series arm resonators s51, s52, s53, s54, and
s55 and parallel arm resonators p51, p52, p53, and p54 of the
ladder filter, the impedance of the resonator to which the
resistance component R has been added becomes higher, and the
return loss increases.
[0119] FIG. 6B is a graph that shows the relationship between the
position of the resonator to which a resistance component R has
been added and the change in return loss. The horizontal axis in
FIG. 6B represents the position of the resonator to which the
resistance component R has been added (positions 1 to 9 in FIG.
6A), and the vertical axis in FIG. 6B represents the change in
return loss when the ladder filter is viewed from Port1. As shown
in FIG. 6B, the change in return loss increases as the resonator
becomes closer to Port1 (connection side), and the change in return
loss decreases as the resonator becomes further from Port1
(connection side), until there is no effect or substantially no
effect on the return loss.
[0120] In other words, it is preferable, for example, to make the
return loss small (make reflection coefficient large) in the pass
band A in the resonator of the filter B that is adjacent to or in a
vicinity of the connection side of the filter B in order to
significantly reduce or prevent the connection loss of the filter
A. On the other hand, it is preferable, for example, to provide
filter characteristics for the filter B, for example, the bandpass
characteristic, the attenuation characteristic, the temperature
characteristics, the bandwidth and the like in accordance with the
preferred specifications and the like while significantly improving
the reflection characteristic of the filter B as described above.
Depending on the configurations of the elastic wave resonators,
there are cases where it may not be possible to obtain both the
desired reflection characteristic and the desired filter
characteristics, for example.
[0121] The inventors of preferred embodiments of the present
invention discovered a structure of the filter B that prioritizes
making the reflection coefficient large in the initial-stage filter
section, which greatly affects the reflection characteristic, and
that provides filter characteristics, for example, the bandpass
characteristic, the attenuation characteristic, the temperature
characteristics, and the bandwidth in the subsequent-stage filter
section, which have little effect on the reflection
characteristic.
[0122] As shown in FIG. 3, in the multiplexer 1A according to this
preferred embodiment, the initial-stage filter section 11F includes
the series arm resonator s11, which is located on the common
terminal 101 side, and the subsequent-stage filter section 11R
includes the series arm resonators s12, s13, and s14 and the
parallel arm resonators p11, p12, and p13, which are located on the
input/output terminal 102 side. Here, the reflection coefficient of
the initial-stage filter section 11F in the second pass band (of
the high-frequency filter 12A) is larger than the reflection
coefficient of the subsequent-stage filter section 11R in the
second pass band (of the high-frequency filter 12A), and therefore,
the return loss of the first filter in the second pass band when
the first filter (the low-frequency filter 11A) is viewed from the
common terminal 101 side, is able to be further significantly
reduced or prevented. Thus, since the connection loss of the
high-frequency filter 12A is able to be significantly reduced or
prevented, the insertion loss of the entire multiplexer 1A is able
to be significantly reduced or prevented.
[0123] In addition, from the results shown in FIG. 6B, the
initial-stage filter section may include, for example, of the
series arm resonator s51 and the parallel arm resonator p51, which
have a large effect on the reflection characteristic, from among
the series arm resonators s51, s52, s53, s54, and s55 and the
parallel arm resonators p51, p52, p53, and p54. In other words, the
initial-stage filter section may include two elastic wave
resonators that are adjacent to or in a vicinity of the common
terminal among a plurality of elastic wave resonators.
[0124] On the other hand, from the viewpoint of contributing to an
increase of the reflection coefficient of only the minimum or
substantially minimum number of elastic wave resonators that affect
the connection loss, and significantly improving the filter
characteristics of the rest of the elastic wave resonators, it is
preferable for the initial-stage filter section 11F to include only
the series arm resonator s11 and for the subsequent-stage filter
section 11R to include the rest of the resonators as in this
preferred embodiment, for example.
[0125] Hereafter, combinations of specific configurations that
increase the reflection coefficient in the initial-stage filter
section and significantly improve the filter characteristics, for
example, the bandpass characteristic, the attenuation
characteristic, the temperature characteristics, the bandwidth and
the like in the subsequent-stage filter section will be
described.
[0126] First, an example of the structure of an elastic wave
resonator will be described.
[0127] FIG. 7 shows examples of a plan view and a sectional view
that schematically show a resonator of the multiplexer according to
the first preferred embodiment. FIG. 7 shows a case in which the
elastic wave resonators (series arm resonators and parallel arm
resonators) according to this preferred embodiment are surface
acoustic wave (SAW) resonators, for example. FIG. 7 shows a
schematic plan view and a schematic sectional view of the structure
of the series arm resonator s11 from among the plurality of
resonators of the low-frequency filter 11A shown in FIG. 3. In
addition, the purpose of the series arm resonator s11 shown in FIG.
7 is to show one example of the structure of the plurality of
resonators, and the number, length, and the like of the electrode
fingers of the electrodes are not limited to those shown in FIG.
7.
[0128] Each resonator of the low-frequency filter 11A includes a
substrate 80 that includes a piezoelectric layer 83 and comb-shaped
interdigital transducer (IDT) electrodes 71a and 71b.
[0129] As shown in the plan view of FIG. 7, the pair of IDT
electrodes 71a and 71b, which face each other, are provided on the
piezoelectric layer 83. The IDT electrode 71a includes a plurality
of electrode fingers 172a, which are parallel or substantially
parallel to each other, and a busbar electrode 171a that connects
the plurality of electrode fingers 172a to each other. In addition,
the IDT electrode 71b includes a plurality of electrode fingers
172b, which are parallel or substantially parallel to each other,
and a busbar electrode 171b that connects the plurality of
electrode fingers 172b to each other. The plurality of electrode
fingers 172a and 172b extend in a direction that is orthogonal or
substantially orthogonal to an X-axis direction.
[0130] Furthermore, as shown in the sectional view of FIG. 7, the
IDT electrodes 71, which include the plurality of electrode fingers
172a and 172b and the busbar electrodes 171a and 171b, have a
multilayer structure including an adhesive layer 72 and a main
electrode layer 73.
[0131] The adhesive layer 72 is a layer that provides adhesion
between the piezoelectric layer 83 and the main electrode layer 73,
and Ti is included as the material of the adhesive layer 72, for
example. The film thickness of the adhesive layer 72 is about 10
nm, for example.
[0132] An Al material including about 1% Cu preferably is included
as the material of the main electrode layer 73, for example. The
film thickness of the main electrode layer 73 preferably is about
130 nm, for example.
[0133] A protective film 84 covers the IDT electrodes 71a and 71b.
The protective film 84 is a layer that protects the main electrode
layer 73 from the external environment, adjusts the
frequency-temperature characteristics, provides moisture
resistance, and the like, and is a film including silicon dioxide
as a main component, for example. The film thickness of the
protective film 84 preferably is about 30 nm, for example.
[0134] The materials of the adhesive layer 72, the main electrode
layer 73 and the protective film 84 are not limited to those
described above, for example. In addition, the IDT electrodes 71 do
not need to have a multilayer structure, for example. The IDT
electrodes 71 may be made of a metal such as Ti, Al, Cu, Pt, Au, Ag
or Pd, or an alloy of such metals, and may include a plurality of
multilayer bodies including any of the metals or an alloy of any of
the metals, for example. In addition, the protective film 84 may be
omitted, for example.
[0135] Next, the multilayer structure of the substrate 80 will be
described.
[0136] As shown in the lower portion of FIG. 7, the substrate 80
includes a high-acoustic-velocity support substrate 81, a
low-acoustic-velocity film 82 and the piezoelectric layer 83, and
has a structure in which the high-acoustic-velocity support
substrate 81, the low-acoustic-velocity film 82, and the
piezoelectric layer 83 are stacked in this order (acoustic velocity
film multilayer structure).
[0137] For example, the piezoelectric layer 83 preferably includes
a 42.degree. Y-cut X-propagation LiTaO.sub.3 piezoelectric single
crystal or piezoelectric ceramic (lithium tantalate single crystal
cut along a plane having, as a normal line, an axis rotated by
42.degree. from a Y axis about an X axis, and in which a surface
acoustic wave propagates in an X-axis direction or ceramic). In
this case, the elastic wave resonator utilizes leaky waves as
elastic waves.
[0138] Alternatively, the piezoelectric layer 83 preferably
includes a 128.degree. Y-cut X-propagation LiNbO.sub.3
piezoelectric single crystal or piezoelectric ceramic, for example.
In this case, the elastic wave resonator utilizes Rayleigh waves as
elastic waves.
[0139] Alternatively, the piezoelectric layer 83 includes a Y-cut
X-propagation LiNbO.sub.3 piezoelectric single crystal or
piezoelectric ceramic, for example. In this case, the elastic wave
resonator utilizes Love waves as elastic waves.
[0140] In addition, the single crystal material, cut angles, and
multilayer structure of the piezoelectric layer 83 are
appropriately selected in accordance with the preferred
specifications of the filter (filter characteristics, for example,
bandpass characteristic, attenuation characteristic, temperature
characteristics and bandwidth), and the like, for example.
[0141] The high-acoustic-velocity support substrate 81 preferably
is a substrate that supports the low-acoustic-velocity film 82, the
piezoelectric layer 83, and the IDT electrodes 71. In addition, the
high-acoustic-velocity support substrate 81 is a substrate in which
the acoustic velocity of a bulk wave propagating inside the
high-acoustic-velocity support substrate 81 is higher than the
acoustic velocity of an elastic wave, for example, surface acoustic
wave or a boundary wave propagating along the piezoelectric layer
83, and, due to the high-acoustic-velocity support substrate 81, a
surface acoustic wave is confined or substantially confined to a
portion of the substrate 80 where the piezoelectric layer 83 and
the low-acoustic-velocity film 82 are stacked and does not leak or
substantially does not leak into the region below the
high-acoustic-velocity support substrate 81. The
high-acoustic-velocity support substrate 81 preferably is a silicon
substrate and has a thickness of about 200 .mu.m, for example.
Furthermore, the high-acoustic-velocity support substrate 81 may
include any of (1) aluminum nitride, aluminum oxide, silicon
carbide, silicon nitride, silicon, sapphire, or a piezoelectric
body such as lithium tantalate, lithium niobate or quartz, (2) any
of various ceramics such as alumina, zirconia, cordierite, mullite,
steatite or forsterite, (3) magnesia or diamond, (4) a material
including any of the above-listed materials as a main component,
and (5) a material including a mixture of any of the above-listed
materials as a main component, for example.
[0142] The low-acoustic-velocity film 82 is a film in which the
acoustic velocity of a bulk wave propagating inside the
low-acoustic-velocity film 82 is lower than the acoustic velocity
of an elastic wave propagating along the piezoelectric layer 83,
and the low-acoustic-velocity film 82 is disposed between the
piezoelectric layer 83 and the high-acoustic-velocity support
substrate 81. Leaking of energy of surface acoustic waves to
outside the IDT electrodes is significantly reduced or prevented by
this structure and energy of elastic waves is concentrated in a
low-acoustic-velocity medium. The low-acoustic-velocity film 82 is
a film including silicon dioxide as a main component, for example.
The thickness of the low-acoustic-velocity film 82 preferably is
about 500 nm, for example.
[0143] According to the above-described acoustic velocity film
multilayer structure of the substrate 80, the Q value at the
resonant frequency and anti-resonant frequency is able to be
significantly improved compared with a structure of the related art
in which a piezoelectric substrate is implemented as a single
layer. That is, a surface acoustic wave resonator with a high Q
value is able to be provided, and therefore, it is possible to
provide a filter with small insertion loss including the surface
acoustic wave resonator.
[0144] The high-acoustic-velocity support substrate 81 may include
a structure in which a support substrate and a
high-acoustic-velocity film in which the acoustic velocity of a
propagating bulk wave is higher than the acoustic velocity of an
elastic wave, for example, a surface acoustic wave or a boundary
wave propagating along the piezoelectric layer 83 are stacked one
on top of the other. In this case, sapphire, a piezoelectric body
such as lithium tantalate, lithium niobate or quartz, any of
various ceramics such as alumina, magnesia, silicon nitride,
aluminum nitride, silicon carbide, zirconia, cordierite, mullite,
steatite or forsterite, a dielectric such as glass, a semiconductor
such as silicon or gallium nitride, or a resin substrate may be
included as the material of the support substrate, for example.
Furthermore, any of a variety of high-acoustic-velocity materials
such as aluminum nitride, aluminum oxide, silicon carbide, silicon
nitride, silicon oxynitride, a DLC film, diamond, a substance
including any of the above-listed materials as a main component, or
a substance including a mixture of any of the above listed
materials as a main component may be included as the material of
the high-acoustic-velocity film, for example.
[0145] In addition, although an example is provided in the above
description in which the IDT electrodes 71 that define the elastic
wave resonators are provided on the substrate 80 that includes the
piezoelectric layer 83, the substrate on which the IDT electrodes
71 are provided may instead be a piezoelectric substrate including
a single layer that is the piezoelectric layer 83, for example. In
this case, the piezoelectric substrate is preferably made of a
piezoelectric single crystal, for example, LiTaO.sub.3 or
LiNbO.sub.3.
[0146] In addition, so long as the substrate on which the IDT
electrodes 71 are provided includes the piezoelectric layer 83, the
substrate may include a structure other than a structure entirely
defined by a piezoelectric layer and may include a structure in
which a piezoelectric layer is stacked on a support substrate, for
example.
[0147] Next, the design parameters of the IDT electrodes 71 will be
described. The wavelength of a surface acoustic wave resonator is
defined as a wavelength .lamda. that is the period at which the
plurality of electrode fingers 172a or 172b that define the IDT
electrode 71 in the center of FIG. 7 repeat. In addition, the
electrode pitch is about 1/2 the wavelength .lamda., and is defined
as (W+S), where W is the line width of the electrode fingers 172a
and 172b that define the IDT electrodes 71a and 71b and S is the
spacing between an electrode finger 172a and an electrode finger
172b that are adjacent to or in a vicinity of each other.
Furthermore, as shown in the upper portion of FIG. 7, an
intersection width L of the IDT electrodes is an overlapping
electrode finger length over which the electrode fingers 172a of
the IDT electrode 71a and the electrode fingers 172b of the IDT
electrode 71b overlap when viewed from the X-axis direction. In
addition, the electrode duty of the resonators is a line width
occupation ratio of the plurality of electrode fingers 172a and
172b, and is a ratio between the line width of the plurality of
electrode fingers 172a and 172b and the sum of the line width and
the spacing of the plurality of electrode fingers 172a and 172b,
defined as W(W+S).
[0148] Hereafter, combinations of specific configurations that
increase the reflection coefficient in the initial-stage filter
section and significantly improve the filter characteristics, for
example, the bandpass characteristic, the attenuation
characteristic, the temperature characteristics, the bandwidth and
the like in the subsequent-stage filter section will be
described.
[0149] FIG. 8A is a diagram showing the reflection characteristic
of a multiplexer 1B according to a second modification of the first
preferred embodiment in a low-frequency region 1. As shown in the
lower portion of FIG. 8A, the resonance point at which the
impedance has a minimum or substantially minimum value and the
anti-resonant point at which the impedance has a maximum or
substantially maximum value are able to be determined in the
impedance characteristic of an elastic wave resonator. Here, in the
region including frequencies lower than the resonance point
(low-frequency region 1 in FIG. 8A), the impedance differs
depending on the structure of the elastic wave resonator, and the
reflection characteristics become better or worse depending on the
size of the impedance. More specifically, the return loss is
smaller in the low-frequency region 1 than in the case of an SMR or
an FBAR in a structure in which any of (1) Rayleigh waves that
propagate along a piezoelectric layer including LiNbO.sub.3, (2)
leaky waves that propagate along a piezoelectric layer including
LiTaO.sub.3 and (3) Love waves that propagate along a piezoelectric
layer including LiNbO.sub.3 are utilized as surface acoustic waves,
and in (4) the acoustic velocity film multilayer structure
described above.
[0150] FIG. 8B shows combinations of the configurations of the
initial-stage filter section 12F and the subsequent-stage filter
section 12R according to the second modification of the first
preferred embodiment.
[0151] From the return loss relationship described above, as shown
in FIG. 8B, the initial-stage filter section 12F of the
high-frequency filter 12B of the multiplexer 1B according to the
first modification may include a structure in which any of (1)
Rayleigh waves that propagate along a piezoelectric layer including
LiNbO.sub.3, (2) leaky waves that propagate along a piezoelectric
layer including LiTaO.sub.3 and (3) Love waves that propagate along
a piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves, for example.
[0152] In the multiplexer 1B, the reflection coefficient of the
initial-stage filter section 12F of the high-frequency filter 12B
in the second pass band (pass band of low-frequency filter 11B) is
able to be made larger than the reflection coefficient of the
subsequent-stage filter section 12R in the second pass band (pass
band of low-frequency filter 11B). Thus, the connection loss of the
low-frequency filter 11B is able to be significantly reduced or
prevented.
[0153] On the other hand, the elastic wave resonators of the
subsequent-stage filter section 12R may be include SMRs or FBARs,
for example.
[0154] Thus, low loss and steep pass band characteristics are able
to be provided in the high-frequency filter 12B by the
configuration of the subsequent-stage filter section 12R while the
reflection coefficient of the high-frequency filter 12B is
increased by the configuration of the initial-stage filter section
12F.
[0155] Furthermore, as shown in FIG. 8B, the elastic wave resonator
of the initial-stage filter section 12F may include the
above-described acoustic velocity film multilayer structure, and
the elastic wave resonators of the subsequent-stage filter section
12R may include SMRs or FBARs, for example.
[0156] In the multiplexer 1B, the reflection coefficient of the
initial-stage filter section 12F of the high-frequency filter 12B
in the second pass band (pass band of low-frequency filter 11B) is
able to be made larger than the reflection coefficient of the
subsequent-stage filter section 12R in the second pass band (pass
band of low-frequency filter 11B). Therefore, the connection loss
of the low-frequency filter 11B is able to be significantly reduced
or prevented. Low loss and steep pass band characteristics are able
to be provided in the high-frequency filter 12B by the
configuration of the subsequent-stage filter section 12R while the
reflection coefficient of the high-frequency filter 12B is
increased by the configuration of the initial-stage filter section
12F.
[0157] FIG. 9A is a diagram showing bulk wave leakage in a
high-frequency region 1 of a multiplexer 1A according to a third
modification of the first preferred embodiment. As shown in the
lower portion of FIG. 9A, in the region including frequencies
higher than the anti-resonance point of the elastic wave resonator
(high-frequency region 1 in FIG. 9A), a change in impedance is
generated due to bulk wave leakage (unwanted waves), and the
reflection characteristic may become better or worse depending on
the change in the impedance. More specifically, return loss due to
bulk wave leakage in the high-frequency region 1 increases in the
order of (1) return loss in a structure in which Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as elastic waves, an SMR, or an FBAR, (2) return loss
in the acoustic velocity film multilayer structure, (3) return loss
in a structure in which leaky waves that propagate along a
piezoelectric layer including LiTaO.sub.3 are utilized as elastic
waves, and (4) return loss in a structure in which Love waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as elastic waves.
[0158] FIG. 9B shows combinations of the configurations of the
initial-stage filter section 11F and the subsequent-stage filter
section 11R according to the third modification of the first
preferred embodiment.
[0159] From the above-described return loss ranking, as shown in
FIG. 9B, in the initial-stage filter section 11F of the
low-frequency filter 11A of the multiplexer 1A, (1) a structure in
which Rayleigh waves that propagate along a piezoelectric layer
including LiNbO.sub.3 are utilized as surface acoustic waves may be
provided, (2) the elastic wave resonator may include an SMR, or (3)
the elastic wave resonator may include an FBAR, for example.
[0160] In the multiplexer 1A, the reflection coefficient of the
initial-stage filter section 11F of the low-frequency filter 11A in
the second pass band (pass band of high-frequency filter 12A) is
able to be made larger than the reflection coefficient of the
subsequent-stage filter section 11R of the low-frequency filter 11A
in the second pass band (pass band of high-frequency filter 12A).
Therefore, the connection loss of the high-frequency filter 12A is
able to be significantly reduced or prevented.
[0161] On the other hand, the subsequent-stage filter section 11R
may include any of (1) the acoustic velocity film multilayer
structure, (2) a structure in which leaky waves that propagate
along a piezoelectric layer including LiTaO.sub.3 are utilized as
surface acoustic waves, and (3) a structure in which Love waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as surface acoustic waves, for example.
[0162] Thus, low loss and excellent temperature characteristics are
able to be provided in the low-frequency filter 11A in the case
where the acoustic velocity film multilayer structure is provided
for the subsequent-stage filter section 11R while the reflection
coefficient of the low-frequency filter 11A is increased by the
configuration of the initial-stage filter section 11F. Furthermore,
in the case where Love waves generated by LiNbO.sub.3 are utilized
as surface acoustic waves in the subsequent-stage filter section
11R, a large bandwidth is able to be provided in the low-frequency
filter 11A.
[0163] Furthermore, the elastic wave resonator of the initial-stage
filter section 11F may include the acoustic velocity film
multilayer structure, and the subsequent-stage filter section 11R
may include (1) a structure in which leaky waves that propagate
along a piezoelectric layer including LiTaO.sub.3 are utilized as
surface acoustic waves or (2) a structure in which Love waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves, for example.
[0164] In the multiplexer 1A, the reflection coefficient of the
initial-stage filter section 11F of the low-frequency filter 11A in
the second pass band (pass band of high-frequency filter 12A) is
able to be made larger than the reflection coefficient of the
subsequent-stage filter section 11R of the low-frequency filter 11A
in the second pass band (pass band of high-frequency filter 12A).
Therefore, the connection loss of the high-frequency filter 12A is
able to be significantly reduced or prevented. Furthermore, in the
case where Love waves generated by LiNbO.sub.3 are utilized as
surface acoustic waves in the subsequent-stage filter section 11R,
a large bandwidth is able to be provided in the low-frequency
filter 11A.
[0165] In addition, the initial-stage filter section 11F may
include a structure in which leaky waves that propagate along a
piezoelectric layer including LiTaO.sub.3 are utilized as surface
acoustic waves, and the subsequent-stage filter section 11R may
include a structure in which Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves, for example.
[0166] Therefore, in the multiplexer 1A, the reflection coefficient
of the initial-stage filter section 11F of the low-frequency filter
11A in the second pass band (pass band of high-frequency filter
12A) is able to be made larger than the reflection coefficient of
the subsequent-stage filter section 11R of the low-frequency filter
11A in the second pass band (pass band of high-frequency filter
12A). Therefore, the connection loss of the high-frequency filter
12A is able to be significantly reduced or prevented. Furthermore,
in the case where Love waves generated by LiNbO.sub.3 are utilized
as surface acoustic waves in the subsequent-stage filter section
11R, a large bandwidth is able to be provided in the low-frequency
filter 11A.
[0167] FIG. 10A is a diagram showing generation of a spurious
signal in a low-frequency region 2 of a multiplexer 1B according to
a fourth modification of the first preferred embodiment. As shown
in the lower portion of FIG. 10A, a Rayleigh wave spurious signal
is generated at a frequency about 0.76 times the resonant frequency
in the region including frequencies lower than the resonance point
of the elastic wave resonator (low-frequency region 2 in FIG. 10A),
particularly, in the acoustic velocity film multilayer structure or
a structure in which leaky waves that propagate along a
piezoelectric layer including LiTaO.sub.3 are utilized as elastic
waves. The impedance changes due to the generation of spurious
signal, and the reflection coefficient becomes smaller in response
to the change in the impedance.
[0168] FIG. 10B shows combinations of the configurations of the
initial-stage filter section 12F and the subsequent-stage filter
section 12R according to the fourth modification of the first
preferred embodiment.
[0169] As shown in FIG. 10B, in the high-frequency filter 12B of
the multiplexer 1B, the initial-stage filter section 12F may
include (1) a structure in which Rayleigh waves that propagate
along a piezoelectric layer including LiNbO.sub.3 are utilized as
surface acoustic waves, (2) a structure in which leaky waves that
propagate along a piezoelectric layer including LiTaO.sub.3 are
utilized as surface acoustic waves, (3) a structure in which Love
waves that propagate along a piezoelectric layer including
LiNbO.sub.3 are utilized as surface acoustic waves, (4) the elastic
wave resonator of the initial-stage filter section 12F may include
an SMR, or (5) the elastic wave resonator of the initial-stage
filter section 12F may include an FBAR, and the elastic wave
resonators of subsequent-stage filter section 12R may include the
acoustic velocity film multilayer structure, for example.
[0170] In other words, as a result of the subsequent-stage filter
section 12R of the high-frequency filter 12B including the acoustic
velocity film multilayer structure and the initial-stage filter
section 12F of the high-frequency filter 12B not including the
acoustic velocity film multilayer structure, the reflection
coefficient of the high-frequency filter 12B in the second pass
band (pass band of low-frequency filter 11B) is able to be made
large. Therefore, the connection loss of the low-frequency filter
11B is able to be significantly reduced or prevented in the case of
the multiplexer 1B.
[0171] Furthermore, as shown in FIG. 10B, in the high-frequency
filter 12B of the multiplexer 1B, the initial-stage filter section
12F may include (1) a structure in which Rayleigh waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves, (2) a structure in which Love
waves that propagate along a piezoelectric layer including
LiNbO.sub.3 are utilized as surface acoustic waves, (3) the
acoustic velocity film multilayer structure, (4) the elastic wave
resonator of the initial-stage filter section 12F may include an
SMR, or (5) the elastic wave resonator of the initial-stage filter
section 12F may include an FBAR, and the subsequent-stage filter
section 12R may include a structure in which leaky waves that
propagate along a piezoelectric layer including LiTaO.sub.3 are
utilized as surface acoustic waves, for example.
[0172] In other words, as a result of leaky waves from LiTaO.sub.3
being utilized as elastic waves in the subsequent-stage filter
section 12R of the high-frequency filter 12B and leaky waves from
LiTaO.sub.3 not being utilized as elastic waves in the
initial-stage filter section 12F of the high-frequency filter 12B,
the reflection coefficient of the high-frequency filter 12B in the
second pass band (pass band of low-frequency filter 11B) is able to
be made large. Therefore, the connection loss of the low-frequency
filter 11B is able to be significantly reduced or prevented in the
case of the multiplexer 1B.
[0173] FIG. 11A is a diagram showing generation of a high-order
mode in a high-frequency region 2 of a multiplexer 1A according to
a fifth modification of the first preferred embodiment. As shown in
the lower portion of FIG. 11A, a high-order mode is generated at a
frequency about 1.2 times the resonant frequency in the region
including frequencies higher than the resonance point of the
elastic wave resonator (high-frequency region 2 in FIG. 11A),
particularly, in a structure in which Rayleigh waves that propagate
along a piezoelectric layer including LiNbO.sub.3 are utilized as
surface acoustic waves or a structure in which Love waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves. The impedance changes due to
the generation of this high-order mode, and return loss increases
in response to the change in impedance.
[0174] FIG. 11B shows combinations of the configurations of the
initial-stage filter section 11F and the subsequent-stage filter
section 11R according to the fifth modification of the first
preferred embodiment.
[0175] As shown in FIG. 11B, in the low-frequency filter 11A of the
multiplexer 1A, the initial-stage filter section 11F may include
(1) the acoustic velocity film multilayer structure, (2) a
structure in which leaky waves that propagate along a piezoelectric
layer including LiTaO.sub.3 are utilized as surface acoustic waves,
(3) a structure in which Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves, (4) an SMR or (5) an FBAR, and the subsequent-stage
filter section 11R may include a structure in which Rayleigh waves
that propagate along a piezoelectric layer including LiNbO.sub.3
are utilized as surface acoustic waves, for example.
[0176] In other words, as a result of Rayleigh waves from
LiNbO.sub.3 being utilized as elastic waves in the subsequent-stage
filter section 11R of the low-frequency filter 11A and Rayleigh
waves from LiNbO.sub.3 not being utilized as elastic waves in the
initial-stage filter section 11F of the low-frequency filter 11A,
the reflection coefficient of the low-frequency filter 11A in the
second pass band (pass band of high-frequency filter 12A) is able
to be made large. Therefore, the connection loss of the
high-frequency filter 12A of the multiplexer 1A is able to be
significantly reduced or prevented.
[0177] In addition, as shown in FIG. 11B, in the low-frequency
filter 11A of the multiplexer 1A, the initial-stage filter section
11F may include (1) a structure in which Rayleigh waves that
propagate along a piezoelectric layer including LiNbO.sub.3 are
utilized as surface acoustic waves, (2) the acoustic velocity film
multilayer structure, (3) a structure in which leaky waves that
propagate along a piezoelectric layer including LiTaO.sub.3 are
utilized as surface acoustic waves, (4) an SMR or (5) an FBAR, and
the subsequent-stage filter section 11R may include a structure in
which Love waves that propagate along a piezoelectric layer
including LiNbO.sub.3 are utilized as surface acoustic waves, for
example.
[0178] In other words, as a result of Love waves from LiNbO.sub.3
being utilized as elastic waves in the subsequent-stage filter
section 11R of the low-frequency filter 11A and Love waves from
LiNbO.sub.3 not being utilized as elastic waves in the
initial-stage filter section 11F of the low-frequency filter 11A,
the reflection coefficient of the low-frequency filter 11A in the
second pass band (pass band of high-frequency filter 12A) is able
to be made large. Therefore, the connection loss of the
high-frequency filter 12A of the multiplexer 1A is able to be
significantly reduced or prevented.
[0179] FIG. 12A is a graph that shows degradation of return loss
caused by a high-order mode in the low-frequency filter 11A of the
multiplexer 1A according to the first preferred embodiment. As
shown in FIG. 12A, the return loss of the low-frequency filter 11A
seen from the common terminal 101 (Port 1) is increased by the
high-order mode in the region including frequencies higher than the
resonance point (broken line region in FIG. 12A). Here, the
frequency at which the return loss is increased by the high-order
mode is able to be shifted toward the high-frequency side or the
low-frequency side by changing the structural parameters of the
elastic wave resonator. Alternatively, an increase in the return
loss (decrease in reflection coefficient) caused by the high-order
mode is able to be significantly reduced or prevented by changing
the structural parameters of the elastic wave resonator.
[0180] The inventors of preferred embodiments of the present
invention discovered shifting the frequency at which a high-order
mode, spurious signal or the like is generated in the filter B to
outside the passband of the filter A by changing the structural
parameters of the initial-stage filter section, which greatly
affects the reflection characteristic, of the filter B, and
significantly improves the structural parameters in the
subsequent-stage filter section, which has a small effect on the
reflection characteristic, of the filter B in order to provide
filter characteristics, for example, the bandpass characteristic,
the attenuation characteristic, the temperature characteristics,
and the pass band width.
[0181] FIG. 12B shows the parameters that are used to make the
structures of the initial-stage filter section 12F and the
subsequent-stage filter section 12R of the multiplexer 1B according
to a sixth modification of the first preferred embodiment different
from each other.
[0182] Each elastic wave resonator of the high-frequency filter 12B
preferably is a surface acoustic wave resonator that includes the
substrate 80, including the piezoelectric layer 83, and the IDT
electrodes 71 provided on the substrate 80. In the high-frequency
filter 12B, as shown in FIG. 12B, leaky waves that propagate along
a piezoelectric layer including LiTaO.sub.3 are utilized as surface
acoustic waves, and the IDT electrodes 71 of the initial-stage
filter section 12F and the IDT electrodes 71 of the
subsequent-stage filter section 12R have different electrode film
thicknesses or duties from each other.
[0183] Rayleigh wave spurious signal is generated at a frequency
that is lower than the resonant frequency of the elastic wave
resonator in the case where leaky waves from LiTaO.sub.3 are
utilized as elastic waves. The frequency at which Rayleigh wave
spurious signal is generated in the initial-stage filter section
12F is able to be shifted to outside the second pass band (pass
band of low-frequency filter 11B) by making the electrode film
thicknesses or duties of the IDT electrodes 71 different from each
other in the initial-stage filter section 12F and the
subsequent-stage filter section 12R. Thus, the reflection
coefficient of the high-frequency filter 12B in the second pass
band (pass band of low-frequency filter 11B) is able to be made
large and the connection loss of the low-frequency filter 11B is
able to be significantly reduced or prevented.
[0184] Furthermore, in the high-frequency filter 12B, as shown in
FIG. 12B, the elastic wave resonators may each include the acoustic
velocity film multilayer structure, and any of the electrode film
thicknesses of the IDT electrodes 71, the duties of the IDT
electrodes 71 and the film thicknesses of the low-acoustic-velocity
films 82 may be made different from each other in the initial-stage
filter section 12F and the subsequent-stage filter section 12R, for
example.
[0185] A Rayleigh wave spurious signal is generated at a frequency
that is lower than the resonant frequency of the elastic wave
resonator in the case where the acoustic velocity film multilayer
structure is provided. The frequency at which Rayleigh wave
spurious signal is generated in the initial-stage filter section
12F is able to be shifted to outside the second pass band (pass
band of low-frequency filter 11B) by making the electrode film
thicknesses or duties of the IDT electrodes 71 different from each
other in the initial-stage filter section 12F and the
subsequent-stage filter section 12R. Thus, the reflection
coefficient of the high-frequency filter 12B in the second pass
band (pass band of low-frequency filter 11B) is able to be made
large and the connection loss of the low-frequency filter 11B is
able to be significantly reduced or prevented.
[0186] FIG. 12C shows parameters that are used to make the
structures of the initial-stage filter section 11F and the
subsequent-stage filter section 11R of the multiplexer 1A according
to a seventh modification of the first preferred embodiment
different from each other.
[0187] Each elastic wave resonator of the low-frequency filter 11A
is a surface acoustic wave resonator that includes the substrate 80
including the piezoelectric layer 83, the IDT electrodes 71
provided on the substrate 80, and the protective film 84 provided
on the IDT electrodes 71. In the low-frequency filter 11A, as shown
in FIG. 12C, Rayleigh waves that propagate along a piezoelectric
layer including LiNbO.sub.3 or Love waves that propagate along a
piezoelectric layer including LiNbO.sub.3 are utilized as surface
acoustic waves, and any of the electrode film thicknesses of the
IDT electrodes 71, the duties of the IDT electrodes 71 and the film
thicknesses of the protective films 84 are made different from each
other in the initial-stage filter section 11F and the
subsequent-stage filter section 11R.
[0188] A high-order mode is generated at a frequency that is higher
than the resonant frequency of the elastic wave resonator in the
case where Rayleigh waves from LiNbO.sub.3 or Love waves from
LiNbO.sub.3 are utilized as surface acoustic waves. The frequency
at which a high-order mode is generated in the initial-stage filter
section 11F is able to shifted to outside the second pass band
(pass band of high-frequency filter 12A) by making the electrode
film thicknesses of the IDT electrodes 71, the duties of the IDT
electrodes 71 or the film thicknesses of the protective films 84
different from each other in the initial-stage filter section 11F
and the subsequent-stage filter section 11R. Thus, the reflection
coefficient of the low-frequency filter 11A in the second pass band
(pass band of high-frequency filter 12A) is able to be made large,
and the connection loss of the high-frequency filter 12A is able to
be significantly reduced or prevented.
[0189] Furthermore, in the low-frequency filter 11A, as shown in
FIG. 12C, each elastic wave resonator may include the acoustic
velocity film multilayer structure, the high-acoustic-velocity
support substrate 81 may be made of silicon crystal, and any of the
film thicknesses of the piezoelectric layers 83, the film
thicknesses of the low-acoustic-velocity films 82 and the silicon
crystal orientations of the high-acoustic-velocity support
substrates 81 may be different from each other in the initial-stage
filter section 11F and the subsequent-stage filter section 11R, for
example.
[0190] A high-order mode is generated at a frequency that is higher
than the resonant frequency of the elastic wave resonator in the
case where the acoustic velocity film multilayer structure is
provided. The frequency at which a high-order mode is generated in
the initial-stage filter section 11F is able to shifted to outside
the second pass band (pass band of high-frequency filter 12A) by
making the film thicknesses of the piezoelectric layers 83, the
film thicknesses of the low-acoustic-velocity films 82 or the
silicon crystal orientations of the high-acoustic-velocity support
substrates 81 different from each other in the initial-stage filter
section 11F and the subsequent-stage filter section 11R. Thus, the
reflection coefficient of the low-frequency filter 11A in the
second pass band (pass band of high-frequency filter 12A) is able
to be made large, and the connection loss of the high-frequency
filter 12A is able to be significantly reduced or prevented.
[0191] FIG. 13 shows parameters that are used to make the
structures of the initial-stage filter section 11F and the
subsequent-stage filter section 11R of the multiplexer 1A according
to an eighth modification of the first preferred embodiment
different from each other.
[0192] Each elastic wave resonator of the low-frequency filter 11A
is a surface acoustic wave resonator that includes the substrate 80
including the piezoelectric layer 83, and the IDT electrodes 71
provided on the substrate 80. In the low-frequency filter 11A,
leaky waves that propagate along a piezoelectric layer including
LiTaO.sub.3 or Love waves that propagate along a piezoelectric
layer including LiNbO.sub.3 are utilized as surface acoustic waves,
and the electrode film thicknesses of the IDT electrodes 71 are
made different from each other in the initial-stage filter section
11F and the subsequent-stage filter section 11R.
[0193] Bulk waves (unwanted waves) are generated at a frequency
that is higher than the resonant frequency of the elastic wave
resonator in the case where leaky waves from LiTaO.sub.3 or Love
waves from LiNbO.sub.3 are utilized as surface acoustic waves. The
frequency at which bulk waves are generated in the initial-stage
filter section 11F is able to be shifted to outside the second pass
band (pass band of high-frequency filter 12A) by making the
electrode film thicknesses of the IDT electrodes 71 different from
each other in the initial-stage filter section 11F and the
subsequent-stage filter section 11R. Thus, the reflection
coefficient of the low-frequency filter 11A in the second pass band
(pass band of high-frequency filter 12A) is able to be made large,
and the connection loss of the high-frequency filter 12A is able to
be significantly reduced or prevented.
[0194] FIG. 14 is a diagram of the circuit configuration of a
low-frequency filter 11A according to a ninth modification of the
first preferred embodiment. The circuit configuration of the
low-frequency filter shown in FIG. 14 is the same as or similar to
the circuit configuration of the low-frequency filter according to
the first preferred embodiment, except that, in addition to the
initial-stage filter section 11F and the subsequent-stage filter
section 11R, a final-stage filter section 11N is also defined.
[0195] Here, the initial-stage filter section 11F includes the
series arm resonator s11 that is closest to the common terminal 101
among the series arm resonators s11, s12, s13, and s14 and the
parallel arm resonators p11, p12, and p13, the subsequent-stage
filter section 11R includes the series arm resonators s12 and s13
and the parallel arm resonators p11 and p12, and the final-stage
filter section 11N includes the series arm resonator s14 and the
parallel arm resonator p13. In this case, a reflection coefficient
of the initial-stage filter section 11F in a pass band 12H (second
pass band) when the initial-stage filter section 11F is viewed from
the common terminal 101 side as a single component is larger than a
reflection coefficient of the subsequent-stage filter section 11R
in the pass band 12H (second pass band) when the subsequent-stage
filter section 11R is viewed from the common terminal 101 side as a
single component. In contrast, the return loss of the final-stage
filter section 11N has no effect or substantially no effect on the
return loss of the low-frequency filter 11A when the low-frequency
filter 11A is viewed from the common terminal 101 side as a single
component, and therefore may be arbitrarily set, for example.
[0196] In addition, the low-frequency filter 11A of the multiplexer
1A and the high-frequency filter 12B of the multiplexer 1B may each
include a ladder filter structure, for example. As a result,
connection losses of the high-frequency filter 12A and the
low-frequency filter 11B are able to be significantly reduced or
prevented while providing low loss characteristics for the
low-frequency filter 11A and the high-frequency filter 12B. In this
case, it is sufficient for the initial-stage filter section to
include at least either of a series arm resonator and a parallel
arm resonator.
[0197] FIG. 15A is a diagram of the circuit configuration of a
low-frequency filter 11A according to a tenth modification of the
first preferred embodiment. In addition, FIG. 15B is a diagram of
the circuit configuration of a low-frequency filter 11A according
to an eleventh modification of the first preferred embodiment. As
shown in FIG. 15A, it is sufficient for the low-frequency filter
11A to include at least one series arm resonator and at least one
parallel arm resonator. In the configuration shown in FIG. 15A, the
initial-stage filter section 11F includes a series arm resonator,
and the subsequent-stage filter section 11R includes a parallel arm
resonator. Furthermore, in the configuration shown in FIG. 15B, the
initial-stage filter section 11F includes one series arm resonator,
and the subsequent-stage filter section 11R includes two series arm
resonators and two parallel arm resonators.
[0198] FIGS. 15C, 15D, and 15E are diagrams of the circuit
configurations of low-frequency filters 11A according to a twelfth
modification, a thirteenth modification, and a fourteenth
modification of the first preferred embodiment. As shown in FIGS.
15C, 15D, and 15E, the low-frequency filter 11A may include a
longitudinally coupled filter structure. Therefore, the
low-frequency filter 11A and the high-frequency filter 12B are able
to be adapted to a filter characteristic which strengthens
attenuation, for example.
[0199] FIG. 16A is a diagram of the circuit configuration of a
low-frequency filter 11A according to a fifteenth modification of
the first preferred embodiment, and FIG. 16B is a diagram of the
circuit configuration of a low-frequency filter 11A according to a
sixteenth modification of the first preferred embodiment. As shown
in FIGS. 16A and 16B, the elastic wave resonator that is closest to
the common terminal 101 may be a series arm resonator or may be a
parallel arm resonator, for example.
[0200] FIG. 17 is a diagram of the circuit configuration of a
multiplexer according to a seventeenth modification of the first
preferred embodiment. The multiplexer shown in FIG. 17 differs from
the multiplexer 1A according to the first preferred embodiment in
that two low-frequency filters 11L1 and 11L2 are provided instead
of the low-frequency filter 11A. Hereafter, the multiplexer
according to the seventeenth modification will be described while
focusing on the features of the multiplexer of this modification
that differ from the multiplexer 1A according to the first
preferred embodiment.
[0201] The multiplexer according to this modification includes a
common terminal 101, input/output terminal 102A (first input/output
terminal), input/output terminal 102B (third input/output
terminal), input/output terminal 103 (second input/output
terminal), the low-frequency filter 11L1 located between the common
terminal 101 and the input/output terminal 102A, the low-frequency
filter 11L2 (third filter) located between the common terminal 101
and the input/output terminal 102B and including a third pass band
that is at a different frequency from the pass band of the
low-frequency filter 11L1, and a high/low frequency filter 12
located between the common terminal 101 and the input/output
terminal 103.
[0202] The low-frequency filter 11L2 includes an initial-stage
filter section 11F, and a second subsequent-stage filter section
11R2 that is located on the input/output terminal 102B side of at
least two elastic wave resonators, and includes elastic wave
resonators other than those of the initial-stage filter section
11F.
[0203] The low-frequency filter 11L1 and the low-frequency filter
11L2 further include a switch 13 that is located between the
initial-stage filter section 11F and the subsequent-stage filter
section 11R1 and the second subsequent-stage filter section 11R2,
the switch 13 switching a connection between the initial-stage
filter section 11F and the subsequent-stage filter section 11R1 and
a connection between the initial-stage filter section 11F and the
second subsequent-stage filter section 11R2. Here, the reflection
coefficient of the initial-stage filter section 11F in the pass
band of the high/low frequency filter 12 when the initial-stage
filter section 11F is viewed as a single component from the common
terminal 101 side is larger than the reflection coefficient of the
second subsequent-stage filter section 11R2 in the pass band of the
high/low frequency filter 12 when the second subsequent-stage
filter section 11R2 is viewed as a single component from the common
terminal 101 side.
[0204] Thus, for example, even in the case where the frequency
bands of the low-frequency filter 11L1 and the low-frequency filter
11L2 overlap each other, connection loss of the high/low frequency
filter 12 is able to be significantly reduced or prevented without
degrading the insertion losses of the low-frequency filters 11L1
and 11L2 by switching the switch 13. In addition, the low-frequency
filters 11L1 and 11L2 share the initial-stage filter section 11F,
and therefore the overall size of the multiplexer is able to be
significantly reduced.
Second Preferred Embodiment
[0205] The multiplexers according to the first preferred embodiment
and the modifications thereof described above are able to be
applied to a high-frequency front-end circuit, and to a
communication device that includes the high-frequency front-end
circuit. Accordingly, in a second preferred embodiment of the
present invention, such a high-frequency front-end circuit and such
a communication device will be described.
[0206] FIG. 18 is a diagram of the circuit configurations of a
high-frequency front-end circuit 30 and a communication device 40
according to the second preferred embodiment. In FIG. 18, an
antenna element 5 that is connected to the communication device 40
is also shown. The communication device 40 preferably includes the
high-frequency front-end circuit 30, an RF signal processing
circuit (RFIC) 6 and a baseband signal processing circuit (BBIC)
7.
[0207] The high-frequency front-end circuit 30 includes a
multiplexer 1A, a switch 25 and a low-noise amplifier circuit
26.
[0208] The multiplexer 1A of the second preferred embodiment
preferably is the multiplexer 1A according to the first preferred
embodiment, for example.
[0209] The switch 25 is a switch circuit that includes two
selection terminals that are individually connected to the
input/output terminals 102 and 103 of the multiplexer 1A, and a
common terminal that is connected to the low-noise amplifier
circuit 26. The switch 25 connects the common terminal and a signal
path corresponding to a prescribed band in accordance with a
control signal from a control component (not shown), and includes a
single pole double throw switch (SPDT), for example. The number of
selection terminals connected to the common terminal is not limited
to one and may be a plurality, for example. In other words, the
high-frequency front-end circuit 30 may support carrier
aggregation.
[0210] The low-noise amplifier circuit 26 is a reception
amplification circuit that amplifies a high-frequency signal (in
this case, high-frequency reception signal) supplied thereto via
the antenna element 5, the multiplexer 1A and the switch 25, and
that outputs the amplified high-frequency signal to the RF signal
processing circuit 6.
[0211] The RF signal processing circuit 6 subjects the
high-frequency reception signal, which is input thereto from the
antenna element 5 via a reception signal path, to signal processing
with down-conversion or the like, and outputs a reception signal
generated through the signal processing to the baseband signal
processing circuit 7. The RF signal processing circuit 6 is an
RFIC, for example.
[0212] A signal that has undergone processing by the baseband
signal processing circuit 7 is able to be used as an image signal
in image display or as an audio signal in a telephone conversation,
for example.
[0213] The high-frequency front-end circuit 30 may include other
circuit elements between the above-described elements.
[0214] According to the high-frequency front-end circuit 30 and
communication device 40 described above, transmission loss of a
high-frequency signal is able to be significantly reduced or
prevented, and significant reductions in size and cost are able to
be provided as a result of the high-frequency front-end circuit 30
and the communication device 40 including a multiplexer according
to the first preferred embodiment or a modification thereof.
[0215] The high-frequency front-end circuit 30 may include a
triplexer or a quadplexer that is able to handle both transmission
and reception instead of the multiplexer 1A according to the first
preferred embodiment, for example.
[0216] Furthermore, the communication device 40 does not
necessarily need to include the baseband signal processing circuit
(BBIC) 7 depending on the high-frequency signal processing method
used, for example.
Other Modifications
[0217] Multiplexers, high-frequency front-end circuits, and
communication devices according to preferred embodiments of the
present invention have been described above with respect to the
preferred embodiments and modifications of the preferred
embodiments of the present invention, but other preferred
embodiments provided, for example, by combining arbitrary elements,
features, structural characteristics, etc. of the above-described
preferred embodiments and modifications, modifications obtained by
a person skilled in the art modifying the above-described preferred
embodiments and modifications in various ways without departing
from the gist of the present invention, and various devices
including the high-frequency front-end circuit and the
communication device according to a preferred embodiment of the
present invention incorporated therein are also included in the
scope of the present invention.
[0218] For example, in the above description, a two-branch
demultiplexing/multiplexing circuit in which two reception signal
paths are connected to each other at a common terminal is described
as an example of a multiplexer, but the present invention is able
to also be applied to a circuit including both a transmission path
and a reception path and to demultiplexing/multiplexing circuit in
which three or more signal paths are connected to each other at a
common terminal, for example.
[0219] In addition, in each filter of the multiplexer, an inductor
or capacitor may be connected between terminals such as the
input/output terminals, ground terminals, and the like, and circuit
elements other than inductors and capacitors such as resistance
elements may be added, for example.
[0220] Preferred embodiments of the present invention and
modifications thereof are able to be included in wide variety of
communication devices, for example, cellular phones, as
multiplexers, high-frequency front-end circuits, and communication
devices with low loss, small size, and low cost that are able to be
applied to frequency standards that handle multiple bands and
multiple modes.
[0221] While preferred embodiments of the present invention and
modifications thereof have been described above, it is to be
understood that variations and modifications will be apparent to
those skilled in the art without departing from the scope and
spirit of the present invention. The scope of the present
invention, therefore, is to be determined solely by the following
claims.
* * * * *