JP7213747B2 - Acoustic wave filters, demultiplexers and communication devices - Google Patents

Description

The present invention relates to an acoustic wave filter, a branching filter, and a communication device that utilize an acoustic wave such as a surface acoustic wave (SAW).

As a resonator-type filter using elastic waves, a ladder-type filter in which a plurality of resonators are connected in a ladder shape is known (for example, Patent Document 1). A ladder-type filter has a series arm connecting an input side and an output side, and a plurality of parallel arms connecting different positions of the series arm and a reference potential section in parallel. The series arm has a plurality of series arm resonators connected in series between the input side and the output side. Each of the plurality of parallel arms has a parallel arm resonator connecting the input side or the output side of any one of the plurality of series arm resonators and a reference potential section. The series arm resonator and parallel arm resonator have, for example, a piezoelectric substrate, an IDT (InterDigital Transducer) electrode provided on the main surface of the piezoelectric substrate, and a pair of reflectors arranged on both sides thereof. ing.

Patent Document 1 proposes adding an additional resonator having a resonance frequency equivalent to that of the parallel arm resonator and connected in parallel to the series arm resonator in the ladder filter. Patent document 1 shows that the attenuation characteristic is improved by providing such an additional resonator. Further, Patent Document 1 discloses a mode in which a series resonator and an additional resonator share a reflector positioned between them.

JP 2007-74459 A

In the technique disclosed in Patent Document 1, although the attenuation characteristic is improved, an additional resonator is added to the basic configuration of the ladder-type filter, which increases the size of the filter accordingly. Therefore, it is desirable to provide an acoustic wave resonator having high attenuation characteristics that can be miniaturized, and an acoustic wave filter, branching filter, and communication device using the acoustic wave resonator.

An elastic wave filter according to an aspect of the present disclosure includes a piezoelectric substrate and a resonator including a plurality of electrode fingers forming serial arms of the filter on the piezoelectric substrate. The resonator includes a first resonator, a second resonator, a third resonator, and a reflector. The second resonator and the third resonator are longitudinally coupled with the first resonator on both sides of the elastic wave propagation direction of the first resonator, and have a frequency design different from that of the first resonator. A pair of reflectors are positioned on both sides of the arrangement of the first, second and third resonators.

A duplexer according to an embodiment of the present disclosure includes an antenna terminal, a transmission filter that filters a transmission signal and outputs the signal to the antenna terminal, and a reception filter that filters a signal received from the antenna terminal. At least one of the transmission filter and the reception filter includes the elastic wave filter described above.

A communication device according to an embodiment of the present disclosure includes an antenna, the branching filter in which the antenna terminal is connected to the antenna, and an IC connected to the transmission filter and the reception filter. are doing.

According to the above configuration, it is possible to downsize the elastic wave filter, the branching filter, and the communication device.

It is a top view showing the composition of the resonator used for the elastic wave filter of a 1st embodiment. 2(a) and 2(b) are diagrams showing frequency characteristics of the resonator shown in FIG. 4 is a plan view showing the configuration of a filter F1; FIG. 4(a) and 4(b) are diagrams showing filter characteristics of the filter shown in FIG. FIG. 4 is a plan view showing the configuration of a filter F2; 6(a) and 6(b) are diagrams showing filter characteristics of the filter F2 shown in FIG. FIGS. 7A and 7B are graphs showing filter characteristics of filters according to comparative examples. 8A and 8B are graphs showing filter characteristics of filters according to modifications. 9(a) and 9(b) are diagrams showing filter characteristics. 1 is a block diagram illustrating an embodiment of a duplexer; FIG. 1 is a block diagram illustrating one embodiment of a communication device; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

In the second and subsequent embodiments, configurations that are the same as or similar to the configurations of the already-described embodiments may be given the same reference numerals as those of the configurations of the already-described embodiments, and descriptions thereof will be omitted. Sometimes.

Identical or similar configurations may be referred to by adding different letters to the same name, such as "first comb-teeth electrode 11A" and "second comb-teeth electrode 11B". In some cases, they are simply referred to as "comb-teeth electrodes 11" and are not distinguished from each other.

<First Embodiment>
(Configuration of basic SAW resonator)
FIG. 1 is a plan view showing the configuration of a resonator 1 used in an acoustic wave filter (SAW filter) 51 (FIG. 3) according to the first embodiment of the invention.

Resonator 1 (SAW filter 51) may be oriented upward or downward, but in the following description, for convenience, an orthogonal coordinate system consisting of axes D1, D2, and D3 will be used. It is defined that the positive side of the D3 axis (the front side of the paper surface of FIG. 1) is defined as the upper side, and terms such as the upper surface are sometimes used. Note that the D1 axis is defined to be parallel to the propagation direction of SAW propagating along the upper surface of the piezoelectric substrate 3 described later (the surface on the front side of the paper, usually the main surface), and the D2 axis is defined by the piezoelectric substrate. 3 and perpendicular to the D1 axis, and the D3 axis is defined perpendicular to the upper surface of the piezoelectric substrate 3 .

The resonator 1 constitutes a so-called 1-port SAW resonator. A signal that causes the resonance is output from the other of the first terminal 31A and the second terminal 31B.

The resonator 1 as such a one-port SAW resonator has, for example, resonator electrode portions 5 provided on the piezoelectric substrate 3 . The resonator electrode section 5 has an IDT electrode 7 and a pair of reflectors 9 located on both sides of the IDT electrode 7 .

The piezoelectric substrate 3 is made of, for example, a piezoelectric single crystal. The single crystal is, for example, a lithium niobate (LiNbO ₃ ) single crystal or a lithium tantalate (LiTaO ₃ ) single crystal. The cut angle may be appropriately set according to the type of SAW to be used. For example, the piezoelectric substrate 3 is of rotational Y-cut X-propagation. That is, the X-axis of the piezoelectric crystal is parallel to the upper surface (D1 axis) of the piezoelectric substrate 3, and the Y-axis is inclined at a predetermined angle with respect to the normal to the upper surface of the piezoelectric substrate 3. FIG. The piezoelectric substrate 3 may be formed relatively thin, and a support substrate made of an inorganic material or an organic material may be directly or indirectly attached to the back surface (the surface on the D3 axis negative side).

The IDT electrode 7 and the reflector 9 are composed of layered conductors provided on the piezoelectric substrate 3 . The IDT electrode 7 and the reflector 9 are made of the same material and thickness, for example. The layered conductors forming these are, for example, metals. The metal is, for example, Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al--Cu alloy. The layered conductor may be configured by laminating a plurality of metal layers. The thickness of the layered conductor is appropriately set according to the electrical characteristics required for the SAW resonator 1 and the like. As an example, the layered conductor has a thickness of 50 nm to 400 nm.

The IDT electrode 7 has a first comb-teeth electrode 11A (hatched for convenience of visibility) and a second comb-teeth electrode 11B. Each comb-teeth electrode 11 has a bus bar 13 , a plurality of electrode fingers 15 extending in parallel from the bus bar 13 , and a plurality of dummy electrodes 17 projecting from the bus bar 13 between the electrode fingers 15 . . A pair of comb-teeth electrodes 11 are arranged such that a plurality of electrode fingers 15 mesh with each other (intersect). That is, the two bus bars 13 of the pair of comb-teeth electrodes 11 are arranged to face each other, and the electrode fingers 15 of the first comb-teeth electrode 11A and the electrode fingers 15 of the second comb-teeth electrode 11B are arranged in the width direction. They are basically arranged alternately. The tips of the plurality of dummy electrodes of one comb-teeth electrode 11 face the tips of the electrode fingers 15 of the other comb-teeth electrode 11 .

The bus bar 13 is formed, for example, in an elongated shape having a substantially constant width and linearly extending in the SAW propagation direction (D1 axis direction). The pair of busbars 13 are opposed to each other in a direction (D2-axis direction) perpendicular to the SAW propagation direction. The width of the bus bar 13 may vary, or may be inclined with respect to the SAW propagation direction.

Each electrode finger 15 is formed, for example, in an elongated shape having a substantially constant width and linearly extending in a direction orthogonal to the SAW propagation direction (D2 axis direction). The plurality of electrode fingers 15 are arranged, for example, in the SAW propagation direction and have the same length. The IDT electrode 7 may be subjected to so-called apodization, in which the lengths (intersection widths from another point of view) of the plurality of electrode fingers 15 change according to the position in the propagation direction.

The number of electrode fingers 15 may be appropriately set according to the electrical characteristics required for the SAW resonator 1 and the like. Since FIG. 1 and the like are schematic diagrams, the number of electrode fingers 15 is shown to be small. Actually, more electrode fingers 15 than illustrated (for example, 100 or more) may be arranged. The same applies to the strip electrodes 21 of the reflector 9, which will be described later.

The pitch p (electrode finger pitch) of the plurality of electrode fingers 15 is, for example, the center-to-center distance between two adjacent electrode fingers 15 (or strip electrodes 21 to be described later). The pitch p is basically set to half the wavelength λ (p=λ/2) of the SAW that propagates on the piezoelectric substrate 3 and has a frequency equal to the frequency to be resonated.

The plurality of dummy electrodes 17 are formed, for example, in an elongated shape that protrudes linearly in a direction perpendicular to the SAW propagation direction (D2 axis direction) with a substantially constant width. The gaps between the tips thereof and the tips of the plurality of electrode fingers 15 are, for example, the same among the plurality of dummy electrodes 17 . The width, number and pitch of the plurality of dummy electrodes 17 are the same as those of the plurality of electrode fingers 15 .

Note that the IDT electrode 7 may not have the dummy electrode 17 . In the following description, description and illustration of the dummy electrode 17 are omitted.

The reflector 9 is formed, for example, in a lattice shape. That is, the reflector 9 has a pair of busbars 19 facing each other and a plurality of strip electrodes 21 extending between the pair of busbars 19 .

The shape of the busbars 19 and strip electrodes 21 may be similar to the busbars 13 and electrode fingers 15 of the IDT electrodes 7 except that both ends of the strip electrodes 21 are connected to a pair of busbars 19 .

Although not shown, the upper surface of the piezoelectric substrate 3 may be covered with a protective film made of SiO ₂ or the like over the IDT electrodes 7 and the reflectors 9 . The protective film may simply suppress corrosion of the IDT electrode 7 or the like, or may contribute to temperature compensation. Further, when a protective film is provided, an additional film made of an insulator or a metal may be provided on the upper or lower surface of the IDT electrode 7 and the reflector 9 in order to improve the SAW reflection coefficient.

In the SAW device including the SAW resonator 1, for example, although not shown, a space is formed on the piezoelectric substrate 3 to allow vibration of the upper surface of the piezoelectric substrate 3 and facilitate SAW propagation. This space is formed, for example, by forming a box-shaped cover that covers the upper surface of the piezoelectric substrate 3, or by facing the main surface of the circuit board and the upper surface of the piezoelectric substrate 3 with bumps interposed therebetween. be.

Here, the IDT electrode 7 has three resonating portions (first resonating portion 23, second resonating portion 25, and third resonating portion 27). These resonators 23 , 25 , 27 are arranged along the propagation direction of elastic waves, and the first resonator 23 is positioned between the second resonator 25 and the third resonator 27 .

The second resonating section 25 and the third resonating section 27 are each longitudinally coupled to the first resonating section 23 . That is, one bus bar is shared by the first resonance section 23, the second resonance section 25, and the third resonance section 27, and the other bus bar is separated. The bus bar on the side where the second resonance section 25 and the third resonance section 27 are separated is connected to the reference potential. One of the bus bars 19 may also be divided among the first resonating section 23, the second resonating section 25, and the third resonating section 27, and wiring may be connected to each of them so that high-frequency signals can be input and output.

The frequency designs of the first resonance section 23, the second resonance section 25, and the third resonance section 27 are different. The first resonator 23 controls the resonance characteristics of the SAW resonator 1, and adjusts the thickness, pitch, and duty ratio of the electrode fingers 15 so as to achieve a desired resonance frequency of the SAW resonator 1. .

Specifically, the second resonance section 25 and the third resonance section 27 are designed to have a higher resonance frequency than the first resonance section 23 . In order to make the resonance frequencies different in this manner, the thickness, pitch, duty ratio (ratio of the width of the electrode fingers 15 to the electrode finger pitch), etc. of the electrode fingers 15 may be changed in each resonance portion. For example, compared to the pitch of the first resonance section 23, the pitch of the second resonance section 25 and the third resonance section 27 may be smaller.

The ratio of the second resonance portion 25 and the third resonance portion 27 to the first resonance portion 23 is particularly limited if the ratio of the first resonance portion 23 is maximized so as to determine the main resonance frequency of the first resonance portion 23. no. For example, the number of electrode fingers 15 forming the second resonance section 25 and the number of the electrode fingers 15 forming the third resonance section 27 may each be 20% or less of the number of electrode fingers 15 forming the first resonance section 23 . In that case, deterioration of the resonance characteristic of the main resonance frequency can be suppressed. Furthermore, if the content is 10% or less, the above effects can be further enhanced.

Further, the electrode finger designs (the number, pitch, duty, etc.) of the electrode fingers 15 forming the second resonating section 25 and the third resonating section 27 may be the same. In that case, unintended spurious emissions can be reduced.

By dividing the IDT electrode 7 and longitudinally coupling them in this manner, another resonance can be created between the resonance frequency and the anti-resonance frequency of the resonator 1 . As a result, Δf can be reduced, so if this is applied to a filter (for example, the SAW filter 51 described later), the steepness can be improved on the high frequency side of the passband, and the attenuation characteristic can be improved. can.

FIG. 2 shows the frequency characteristics of such a resonator 1. As shown in FIG. In FIG. 2, the horizontal axis indicates the frequency, the vertical axis indicates the absolute value of the impedance in FIG. 2(a), and the phase in FIG. 2(b). In FIG. 2, the solid line indicates the characteristics of the resonator 1 of the present disclosure, and the dashed line indicates the characteristics of a conventional resonator in which the IDT electrode 7 is composed of one resonator.

A specific electrode finger design of the resonator 1 is as follows.
Electrode finger intersection width of IDT electrode 7: 70.5 μm
Film thickness of electrode fingers: 360 nm
First resonance part 23: Number of electrode fingers 15: 150
Pitch of electrode fingers 15 2.35 μm
Second resonance part 25: Number of electrode fingers 15: 10
Pitch of electrode fingers 15 2.21 μm
Third resonance part 27: Number of electrode fingers 15: 10
Pitch of electrode fingers 15 2.21 μm
Thickness of strip electrode 21 of reflector 9: 360 nm
Number of strip electrodes 21: 30
Pitch of strip electrode 21: 2.35 μm
As is clear from FIG. 2, the resonator 1 of the present disclosure can create another resonance between the resonance frequency and the anti-resonance frequency. difference from the anti-resonance frequency) can be reduced. Moreover, as indicated by arrows in FIG. 2(b), a narrow .DELTA.f resonator with less loss can be provided because of the excellent shoulder characteristics on the high frequency side. Furthermore, the SAW element 1 of the present disclosure can increase the anti-resonance frequency. This is presumed to be due to the following mechanism. That is, the resonance frequency changes little because the center of the IDT electrode 7, that is, the first resonance portion 23, has a large proportion of vibration. On the other hand, at the anti-resonant frequency, the entire IDT electrode 7 vibrates from the whole to the end. Here, since the frequencies of the second resonating portion 25 and the third resonating portion 27 located at the ends are high, the anti-resonant frequency shifts to the high frequency side. As a result, when the SAW element 1 is applied to a filter, the characteristics on the high frequency side of the passband can be improved.

Next, an example of using such a resonator as a series resonator constituting the filter F1 will be described.

FIG. 3 shows a ladder type filter 51 which is the filter F1. Ladder-type filter 51 has series resonators S1 and S2 connected in series between input/output terminals P1 and P2 and parallel resonators P1 and P2 connected between these and a reference potential. These series resonators S1, S2 and parallel resonators P1, P2 are connected in a ladder configuration.

The number of series resonators S and the number of parallel resonators P can be appropriately increased or decreased according to desired filter characteristics. Also, the number of electrode fingers 15 of the series resonator S and the parallel resonator P, the pitch, the duty, etc. can be freely set as appropriate.

Here, the resonator 1 described above is used as the series resonator S2. Specifically, the first terminal 31A of the resonator 1 is electrically connected to the series resonator S1, and the second terminal 31B is electrically connected to the input/output terminal P2. Note that the resonators (the series resonator S1 and the parallel resonators P1 and P2) other than the series resonator S2 have the IDT electrode 7 as one resonator. Hereinafter, such a resonator in which the IDT electrode 7 is composed of one resonating portion will be referred to as a "conventional resonator".

FIG. 4 shows the filter characteristics of such a ladder-type filter 51. As shown in FIG. In FIG. 4, the horizontal axis indicates frequency and the vertical axis indicates transmission characteristics, and FIG. 4(b) is an enlarged view of the main part of FIG. In FIG. 4, the characteristic of the ladder-type filter 51 is indicated by a line LE1. A line LC1 indicates the frequency characteristic of the filter according to Comparative Example 1 thus constructed.

As is clear from FIG. 4, it can be confirmed that the ladder-type filter 51 has improved shoulder characteristics on the high frequency side of the band compared to the filter of Comparative Example 1. FIG. In addition, it can be confirmed that the pass characteristics within the passband are also maintained.

As described above, by applying the resonator 1 to the series resonator S of the ladder-type filter 51, a steep attenuation characteristic of the filter can be realized.

Further, as shown in FIG. 2, the resonator 1 has two maximum impedance values on the higher frequency side than the resonance frequency. Among them, the maximum impedance value on the low frequency side (adjacent to the resonance point) is higher than the passband and lower than the anti-resonance frequency of the other series resonators S, thereby improving the attenuation characteristics of the filter. be able to.

<Second embodiment>
Next, FIG. 5 shows a filter F2 in which two series resonators S1 and S2 and a longitudinally coupled filter 52 positioned therebetween are connected in series between input/output terminals P1 and P2. Here, the longitudinally coupled filter 52 is a DMS filter, and the series resonators S1 and S2 are the resonator 1 described above.

FIG. 6 shows the filter characteristics of the filter F2 having such a configuration. In FIG. 6, the horizontal axis indicates the frequency and the vertical axis indicates the transmission characteristic. FIG. 6(b) is an enlarged view of the main part of FIG. In FIG. 6, a line LE2 indicates the characteristic of the filter F2, and a dashed line LC2 indicates the frequency characteristic of the filter according to Comparative Example 2 in which the series resonators S1 and S2 are replaced with conventional resonators.

As is clear from FIG. 6, it can be confirmed that the filter F2 has improved shoulder characteristics on the high frequency side of the band compared to the filter of Comparative Example 2. FIG. In addition, it can be confirmed that the pass characteristics within the passband are also maintained.

It is generally known that adding a capacitance in parallel to a conventional resonator as a method of narrowing the Δf of the resonator and increasing the steepness. Therefore, in the configuration of the filter F2, the series resonators S1 and S2 are conventional resonators, and additional capacitances are added in parallel to each of them (referred to as Comparative Example 3). . FIG. 7 is similar to FIG. 6, in which line LC3 indicates the filter characteristic of Comparative Example 3 and line LE2 indicates the filter characteristic of filter F2.

As is clear from FIG. 7, it was found that the filter characteristic of the filter F2 can realize an attenuation characteristic equivalent to that of a filter using an additional capacitance. However, when the additional capacitor is used, a new component (or a new electrode pattern that constitutes the additional capacitor) is simply required, which may lead to an increase in the size of the device. On the other hand, when using the resonator 1 of the present disclosure, it is possible to improve the damping characteristic with a single resonator, so it is possible to realize a filter that is small and has a high damping characteristic.

<Modified Example of Resonator 1>
In the above example, the case where the pitches of the electrode fingers 15 are made different among the resonating portions 23 to 27 of the resonator 1 has been described as an example, but the frequency design may be made different by other means.

FIG. 8 shows the frequency characteristics of the resonator 1A in which the duties of the electrode fingers 15 are varied between the resonators 23-27. Specifically, the duties of the second resonance portion 25 and the duty of the third resonance portion 27 are made smaller than the duty of the first resonance portion 23 . FIG. 8 is a diagram corresponding to FIG. In FIG. 8, the dashed line indicates the characteristics of the conventional resonator (without division), the solid line indicates the characteristics of the resonator 1A, and the dashed-dotted line indicates the characteristics of the resonator 1, respectively.

As is clear from FIG. 8, it was confirmed that Δf can be reduced similarly to resonator 1 by changing the duty.

It should be noted that both the pitch and the duty may be varied between the resonators to vary the frequency design.

<Modified Example of Resonator 1>
In the resonator 1, the pitches of the second resonating portion 25 and the third resonating portion 27 with respect to the first resonating portion 23 were varied from 89% to 99%. Specifically, the pitch of the first resonating portion 23 was set to 2.35 μm, and the pitches of the second and third resonating portions 25 and 27 were set to 2.1 μm to 2.35 μm. The results are shown in FIG.

FIG. 9(a) shows the results of the filter F1 shown in FIG. 3 when the pitches of the second resonating section 25 and the third resonating section 27 with respect to the first resonating section 23 of the resonator 1 are changed from 89% to 99%. It shows how the filter characteristics change. FIG. 9(b) is a partially enlarged view of FIG. 9(a). In FIG. 9, the horizontal axis indicates frequency, and the vertical axis indicates transmission characteristics. In the figure, arrows indicate positions where attenuation is observed in the shoulder characteristic on the high frequency side, and pitch numbers (unit: μm) that realize the attenuation are indicated.

As is clear from FIG. 9, if the pitch of the second and third resonating portions 25 and 27 is too close to the pitch of the first resonating portion 23 (for example, 2.3 μm), sufficient attenuation cannot be obtained. On the other hand, if the pitch of the second and third resonating sections 25 and 27 is too far (for example, 2.1 μm) from the pitch of the first resonating section 23, the attenuation pole will be too close to that of a normal filter, resulting in less effect. Therefore, the pitch of the second and third resonating parts 25 and 27 is 2.15 to 2.25 μm, that is, the pitch of the second resonating part 25 and the third resonating part 27 with respect to the first resonating part 23 is 90% or more. % or less, a filter with higher steepness can be realized.

<Diplexer>
(Structure of branching filter)
FIG. 10 is a schematic diagram showing a demultiplexer 101 as an application example of the filters according to the above-described embodiments. In the description of this figure, the configuration and reference numerals of the filter F1 (ladder-type filter 51) of the first embodiment are cited, but SAW filters of other embodiments may be used instead of the filter F1.

The branching filter 101 includes, for example, a transmission filter 109 that filters a transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and a reception signal that is filtered from the antenna terminal 103 and outputs it to a pair of reception terminals 107. and a reception filter 111 .

The transmission filter 109 is composed of a multistage ladder filter including the filter F1.

The reception filter 111 is composed of, for example, a SAW resonator 61 and a SAW filter 63 connected in series. The IDT electrodes 7 and the reflectors 9 constituting these are provided on the same piezoelectric substrate 3, for example. The piezoelectric substrate 3 forming the reception filter 111 may be the same as or different from the piezoelectric substrate 3 forming the transmission filter 109 .

The reception filter 111 and the SAW resonator 61 have, for example, conventional resonator configurations. The SAW filter 63 is, for example, a longitudinally coupled multimode (including double mode) resonator filter, and includes a plurality of IDT electrodes 7 arranged in the SAW propagation direction and a pair of electrodes arranged on both sides thereof. and a reflector 9 .

In the above example, the filter F1 is used as the transmission filter 109, but the filter F2 may be used as the reception filter 111. FIG.

<Communication device>
FIG. 11 is a block diagram showing a main part of a communication device 151 as an example of using the demultiplexer 101 described above.

In the communication device 151, a transmission information signal TIS including information to be transmitted is modulated and frequency-raised (conversion of the carrier frequency to a high-frequency signal) by an RF-IC (Radio Frequency Integrated Circuit) 153 to form a transmission signal TS. be done. The transmission signal TS is filtered by the band-pass filter 155 to remove unnecessary components outside the transmission passband, amplified by the amplifier 157, and input to the demultiplexer 101 (transmission terminal 105). Demultiplexer 101 removes unnecessary components outside the transmission passband from input transmission signal TS, and outputs transmission signal TS after removal from antenna terminal 103 to antenna 159 . Antenna 159 converts an input electrical signal (transmission signal TS) into a radio signal (radio waves) and transmits the radio signal.

In the communication device 151 , a radio signal (radio wave) received by the antenna 159 is converted by the antenna 159 into an electric signal (received signal RS) and input to the branching filter 101 . The demultiplexer 101 removes unnecessary components outside the pass band for reception from the input reception signal RS and outputs the signal to the amplifier 161 . The output reception signal RS is amplified by an amplifier 161 and a bandpass filter 163 removes unnecessary components outside the passband for reception. Then, the reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 153 to be a reception information signal RIS.

The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, such as analog audio signals or digitized audio signals. The passband for radio signals may conform to various standards such as UMTS (Universal Mobile Telecommunications System). The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. In FIG. 11, the direct conversion system is exemplified as the circuit system, but other appropriate systems may be used, such as a double superheterodyne system. Also, FIG. 11 schematically shows only the main part, and low-pass filters, isolators, etc. may be added at appropriate positions, and the positions of amplifiers, etc. may be changed.

The present invention is not limited to the above embodiments, and may be implemented in various modes.

In the embodiment, the plurality of resonators and the plurality of resonator sections are assumed to have the same parameters (for example, electrode finger material, electrode finger thickness or duty ratio) other than the electrode finger pitch. However, the plurality of resonators and the plurality of resonators may differ from each other in parameters affecting the resonance frequency other than the electrode finger pitch.

Resonators 1, 3 Piezoelectric substrate 15 Electrode finger 23 First resonance part 25 Second resonance part 27 Third resonance part 9 Reflector F1 SAW filter (acoustic wave filter).

Claims (7)

a piezoelectric substrate;
A resonator including a plurality of electrode fingers constituting a series arm of a filter on the piezoelectric substrate, comprising: a first resonator; a second resonator and a third resonator having a frequency design different from that of the first resonator, which are longitudinally coupled to the resonator; a resonator comprising a pair of reflectors located at
with
each of the first resonance section, the second resonance section, and the third resonance section has a pair of comb-teeth electrodes;
one comb tooth electrode of the pair of comb tooth electrodes of the first resonance section is connected to a first terminal and the other comb tooth electrode is connected to a second terminal;
Of the pair of comb-teeth electrodes of each of the second resonance portion and the third resonance portion, one comb-teeth electrode is connected to the first terminal and the other comb-teeth electrode is connected to a reference potential portion.
Acoustic wave filter. 2. The acoustic wave filter according to claim 1, wherein said second resonator and said third resonator have the same number and pitch of said electrode fingers. 3 . The elastic wave filter according to claim 1 , wherein said second resonance section and said third resonance section have different pitches of said electrode fingers from said first resonance section. 4. The filter according to any one of claims 1 to 3, wherein said filter is a ladder type filter in which a series resonator and a parallel resonator are connected in a ladder configuration, and said resonator is used as said series resonator. Acoustic wave filter. 4. The elastic wave filter according to claim 1, wherein said filter is formed by connecting a series resonator and a longitudinally coupled filter in series, and said resonator is used as said series resonator. antenna terminal,
a transmission filter that filters a transmission signal and outputs it to the antenna terminal;
a reception filter for filtering a signal received from the antenna terminal;
and
A branching filter, wherein at least one of the transmission filter and the reception filter includes the elastic wave filter according to any one of claims 1 to 5. an antenna;
A branching filter according to claim 6, wherein the antenna terminal is connected to the antenna;
an IC connected to the transmission filter and the reception filter;
A communication device having a

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