WO2018025961A1 - Surface acoustic wave filter, high-frequency module, and multiplexer - Google Patents

Abstract

Provided is a longitudinally-coupled surface acoustic wave filter provided with a first resonator (13), a second resonator (14), and a third resonator (15), wherein: the second resonator (14) and/or the third resonator (15) includes three or more regions having different electrode finger pitches; the electrode finger pitch in a first region which is closest to the first resonator (13), among the three or more regions, is the smallest; and the electrode finger pitch in a second region which is adjacent to the first region, among the three or more regions, is the largest.

Description

Surface acoustic wave filters, high frequency modules and multiplexers

The present invention relates to a surface acoustic wave filter, a high-frequency module using the surface acoustic wave filter, and the like.

Conventionally, an acoustic wave filter has been used as a filter used in a receiving circuit module of a mobile communication device. With the recent widening of the communication frequency band, there is an increasing demand for low loss in order to improve the receiving sensitivity of the receiving circuit module. In order to satisfy this requirement, for example, a technique using a longitudinally coupled surface acoustic wave filter has been developed (see, for example, Patent Document 1). This longitudinally coupled surface acoustic wave filter has a zero-order mode and a second-order mode as resonance modes.

In the technique described in Patent Document 1, a longitudinally coupled surface acoustic wave filter includes an IDT (InterDigital Transducer) electrode having a plurality of electrode fingers. There are multiple types of electrode finger pitches for IDT electrodes. The plurality of types of electrode finger pitches are arranged so as to change stepwise in the auxiliary excitation region.

International Application No. 2003/003574

There is a method of changing the main pitch of the IDT electrode when the bandwidth is widened in the surface acoustic wave filter according to the conventional technology. However, in this method, the resonance frequency interval of the plurality of resonance modes in the surface acoustic wave filter is widened, so that the coupling between the resonance modes is weakened. When the output terminal side is viewed from the output end of the surface acoustic wave filter, Smith On the chart, the concentration of output impedance windings in the passband deteriorates, that is, the output impedance windings spread. This indicates that the output impedance varies within the pass band.

In view of the above problems, the present invention provides a surface acoustic wave filter, a high-frequency module, and a multiplexer capable of realizing a broad band while suppressing the spread of winding of output impedance in the pass band on the Smith chart. Objective.

In order to achieve the above object, one aspect of a surface acoustic wave filter according to the present invention is a longitudinally coupled surface acoustic wave filter, wherein the surface acoustic wave filter is continuous in the propagation direction of the surface acoustic wave. Each of the three resonators has a pair of comb electrodes each having a bus bar electrode and a plurality of parallel electrode fingers connected to the bus bar electrode, The comb-shaped electrode is arranged such that the plurality of electrode fingers are alternately positioned in the surface acoustic wave propagation direction, and the first resonator arranged at the center of the three resonators is A second resonator connected to one of an input terminal and an output terminal of the surface acoustic wave filter and disposed adjacent to the first resonator; and the first resonator adjacent to the first resonator. For the first resonator A third resonator disposed on the opposite side of the resonator is connected to the other of the input terminal and the output terminal, and at least one of the second resonator and the third resonator Has three or more regions having different pitches of the electrode fingers, and the pitch of the electrode fingers is constant in each of the three or more regions, and the first of the three or more regions is the first The pitch of the electrode fingers in the first region closest to the resonator is the smallest, and among the three or more regions, the pitch of the electrode fingers in the second region adjacent to the first region is the largest. .

As a result, for the resonator disposed at one end of the three resonators constituting the surface acoustic wave filter, the pitch of the electrode fingers in the first region is minimized, and the pitch of the electrode fingers in the second region is Therefore, it is possible to realize a wide band while suppressing the spread of the winding of the output impedance in the pass band on the Smith chart.

Further, both of the second resonator and the third resonator have the three or more regions having different pitches of the electrode fingers, and the second resonator and the third resonator In each of the three or more regions, the pitch of the electrode fingers in the first region is the smallest, and among the three or more regions, the pitch of the electrode fingers in the second region is the largest. May be.

As a result, for both of the resonators arranged at both ends of the three resonators constituting the surface acoustic wave filter, the pitch of the electrode fingers in the first region is minimized, and the electrode fingers in the second region are Therefore, it is possible to further suppress the spread of the winding of the output impedance in the pass band on the Smith chart and further widen the pass band.

Further, each of the three or more regions of the second resonator and the three or more of the third resonator corresponding to each of the three or more regions of the second resonator. The pitch of the electrode fingers may be the same as each of the regions.

Thereby, with respect to the resonators arranged at both ends of the three resonators constituting the surface acoustic wave filter, the pitch of the electrode fingers is symmetric with respect to the electrode finger arranged at the center of the three resonators. Therefore, it is possible to further suppress the spread of the winding of the output impedance in the pass band on the Smith chart and further widen the pass band.

Further, each of the three or more regions of the second resonator and the three or more of the third resonator corresponding to each of the three or more regions of the second resonator. The number of pairs of electrode fingers may be the same as each region of the region.

Thereby, the logarithm of the electrode finger is symmetrical with respect to the electrode finger arranged at the center of the three resonators with respect to the resonator arranged at both ends of the three resonators constituting the surface acoustic wave filter. Therefore, it is possible to further suppress the spread of the winding of the output impedance in the pass band on the Smith chart and further widen the pass band.

In addition, at least one of the second resonator and the third resonator having three or more regions having different pitches of the electrode fingers has a logarithm of the electrode fingers in the first region as the first number. It may be smaller than the total number of pairs of the electrode fingers in the region other than the region.

Accordingly, the pitch of the electrode fingers in the first region is smaller than the pitch of the electrode fingers in the other region, and the number of electrode fingers in the first region is smaller than the number of electrode fingers in the other region. Thus, a surface acoustic wave having a so-called narrow pitch region can be formed. Therefore, a surface acoustic wave filter with better transmission characteristics can be realized.

The first resonator is connected to the input terminal of the surface acoustic wave filter, and the second resonator and the third resonator are connected to the output terminal of the surface acoustic wave filter. It may be.

As a result, even when the first resonator is connected to the input terminal, and the second resonator and the third resonator are connected to the output terminal, the output impedance in the pass band on the Smith chart. The spread of the winding can be suppressed and the pass bandwidth can be widened.

In order to achieve the above object, an aspect of the high-frequency module according to the present invention includes a surface acoustic wave filter having the characteristics described above, and a high-frequency wave connected to the surface acoustic wave filter and passed through the surface acoustic wave filter. And a low noise amplifier for amplifying the signal.

Thus, the matching between the surface acoustic wave filter and the low noise amplifier can be improved, the output impedance in the pass band of the high frequency module can be stabilized, and the pass band width can be widened.

In order to achieve the above object, an aspect of the multiplexer according to the present invention includes a plurality of surface acoustic wave filters having the above-described characteristics, and each of the plurality of surface acoustic wave filters is connected to a common terminal. Yes.

This makes it possible to stabilize the output impedance in the passband of the plurality of surface acoustic wave filters and widen the passband width. Therefore, the multiplexer can stabilize the output impedance of each pass band and widen the pass band width.

According to the present invention, it is possible to provide a surface acoustic wave filter, a high-frequency module, and a multiplexer capable of realizing a broad band while suppressing the spread of winding of output impedance in the pass band on the Smith chart.

FIG. 1 is a conceptual diagram illustrating a configuration of the high-frequency module according to the first embodiment. FIG. 2A is a schematic diagram illustrating a configuration of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 2B is a schematic diagram illustrating a specific example of the configuration of the surface acoustic wave filter illustrated in FIG. 2A. 3A and 3B are schematic views showing a configuration of a general surface acoustic wave filter, in which FIG. 3A is a plan view, and FIG. FIG. 4 is a schematic diagram illustrating the configuration of the surface acoustic wave filter according to the first embodiment. FIG. 4A is a schematic diagram illustrating a configuration in which regions are divided into regions having different pitches, and FIG. It is the figure which showed the magnitude | size of the pitch in an area | region relatively. FIG. 5 is a schematic diagram illustrating a configuration of one resonator of the surface acoustic wave filter according to the first embodiment. FIG. 6A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 6B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to the first embodiment. FIG. 6C is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 6D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 7 is a diagram illustrating a configuration of the surface acoustic wave filter of the surface acoustic wave filter according to the first comparative example. FIG. 8A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to Comparative Example 1. FIG. 8B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to Comparative Example 1. FIG. 8C is a diagram illustrating pass characteristics of the surface acoustic wave filter according to Comparative Example 1. FIG. 8D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to Comparative Example 1. FIG. 9A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to Comparative Example 2. FIG. 9B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to Comparative Example 2. FIG. 9C is a diagram illustrating pass characteristics of the surface acoustic wave filter according to Comparative Example 2. FIG. 9D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to Comparative Example 2. FIG. 10 is a diagram illustrating a configuration of the surface acoustic wave filter of the surface acoustic wave filter according to the second embodiment, and FIG. 10A is a schematic diagram illustrating a configuration in which regions are divided into regions having different pitches. b) is a diagram relatively showing the size of the pitch in each region. FIG. 11A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the second embodiment. FIG. 11B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to the second embodiment. FIG. 11C is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the second embodiment. FIG. 11D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to the second embodiment. FIG. 12 is a diagram illustrating a configuration of a surface acoustic wave filter of the surface acoustic wave filter according to the third embodiment. FIG. 13A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the third embodiment. FIG. 13B is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to the third embodiment. FIG. 13C is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the third embodiment. FIG. 13D is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to the third embodiment. FIG. 14 is a diagram illustrating a configuration of a surface acoustic wave filter of a surface acoustic wave filter according to a fourth embodiment, and (a) is a schematic diagram illustrating a configuration in which regions are divided into regions having different pitches. b) is a diagram relatively showing the size of the pitch in each region. FIG. 15A is a diagram illustrating pass characteristics of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 15B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter according to the first exemplary embodiment. FIG. 15C is a diagram illustrating a pass characteristic of the surface acoustic wave filter according to the first embodiment. FIG. 15D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter according to the first exemplary embodiment.

Hereinafter, embodiments of the present invention will be described. Note that each of the embodiments described below shows a preferred specific example of the present invention. Therefore, numerical values, shapes, materials, components, arrangement positions and connection forms of components shown in the following embodiments are merely examples, and are not intended to limit the present invention. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims showing the highest concept of the present invention are described as optional constituent elements.

Each figure is a schematic diagram and is not necessarily shown strictly. In each figure, substantially the same components are denoted by the same reference numerals, and redundant descriptions are omitted or simplified. In the illustrated electrode structure, in order to facilitate understanding of the present invention, the number of electrode fingers in the resonator and the reflector is smaller than the actual number of electrode fingers.

(Embodiment 1)
Hereinafter, embodiments will be described with reference to FIGS. 1 to 9D.

[1. Structure of surface acoustic wave filter and high-frequency module]
First, the configuration of the high-frequency module 1 according to the present embodiment will be described. FIG. 1 is a conceptual diagram showing a configuration of a high-frequency module 1 according to the present embodiment.

As shown in FIG. 1, the high-frequency module 1 according to this embodiment includes a surface acoustic wave filter 10 and a low noise amplifier (LNA) 20. The surface acoustic wave filter 10 is once connected to an antenna (not shown) and the other end is connected to the low noise amplifier 20. The low noise amplifier 20 is an amplifier that amplifies a weak radio wave after reception without increasing noise as much as possible.

In the surface acoustic wave filter 10, the input impedance refers to the impedance of the surface acoustic wave filter 10 when the surface acoustic wave filter 10 is viewed from the input terminal IN side of the high frequency module 1. That is, it means the SAW (Surface Acoustic Wave) input side impedance indicated by an arrow in FIG. The output impedance refers to the impedance of the surface acoustic wave filter 10 when the surface acoustic wave filter 10 is viewed from a terminal (not shown) to which the low noise amplifier 20 that is the output destination of the high frequency signal is connected. That is, it means the SAW output side impedance indicated by an arrow in FIG.

The surface acoustic wave filter 10 is a longitudinally coupled surface acoustic wave filter. As shown in FIG. 2A, the surface acoustic wave filter 10 includes a resonator 13, a resonator 14, and a resonator 15, and a reflector 16 and a reflector 17 between the input terminal 11 and the output terminal 12. Yes. The resonator 13, the resonator 14, and the resonator 15 are arranged in this order from the reflector 16 side to the reflector 17 side.

As shown in FIG. 2B, the resonator 13 has a configuration in which two IDT electrodes 13a and 13b are combined. The IDT electrode 13 a of the resonator 13 is connected to the input terminal 11. The IDT electrode 13b is connected to the ground. Similarly, the resonator 15 has a configuration in which two IDT electrodes 15a and 15b are combined. The IDT electrode 15 a of the resonator 15 is connected to the input terminal 11. The IDT electrode 15b is connected to the ground. The resonator 14 disposed between the resonator 13 and the resonator 15 has a configuration in which two IDT electrodes 14a and 14b are combined. The IDT electrode 14a of the resonator 14 is connected to the ground. The IDT electrode 14 b is connected to the output terminal 12.

In addition, the reflector 16 is provided with a plurality of bus bar electrodes 16a and 16b, and between the bus bar electrode 16a and the bus bar electrode 16b, and electrode fingers 16c having both ends connected to the bus bar electrode 16a and the bus bar electrode 16b, respectively. And. Similarly, a plurality of reflectors 17 are provided between two bus bar electrodes 17a and 17b and between the bus bar electrode 17a and the bus bar electrode 17b, and electrode fingers having both ends connected to the bus bar electrode 17a and the bus bar electrode 17b, respectively. 17c.

Here, the configuration of the resonator will be described in more detail using a general resonator 100. 3A and 3B are schematic views showing a configuration of a general surface acoustic wave filter, in which FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along an alternate long and short dash line shown in FIG.

3A and 3B, the resonator 100 includes a piezoelectric substrate 123 and an IDT electrode 101a and an IDT electrode 101b which are comb-shaped electrodes (comb-shaped electrodes).

The piezoelectric substrate 123 is made of, for example, a single crystal of LiNbO ₃ cut at a predetermined cut angle. In the piezoelectric substrate 123, a surface acoustic wave propagates in a predetermined direction.

As shown in FIG. 3 (a), a pair of IDT electrodes 101a and IDT electrodes 101b facing each other are formed on the piezoelectric substrate 123. The IDT electrode 101a includes a plurality of electrode fingers 110a that are parallel to each other and a bus bar electrode 111a that connects the plurality of electrode fingers 110a. The IDT electrode 101b includes a plurality of electrode fingers 110b that are parallel to each other and a bus bar electrode 111b that connects the plurality of electrode fingers 110b. The IDT electrode 101a and the IDT electrode 101b are arranged such that a plurality of electrode fingers 110a and 110b are alternately positioned in the surface acoustic wave propagation direction. That is, the IDT electrode 101a and the IDT electrode 101b are configured such that each of the plurality of electrode fingers 110b of the IDT electrode 101b is disposed between each of the plurality of electrode fingers 110a of the IDT electrode 101a.

Further, the IDT electrode 101a and the IDT electrode 101b have a structure in which an adhesion layer 124a and a main electrode layer 124b are laminated as shown in FIG.

The adhesion layer 124a is a layer for improving the adhesion between the piezoelectric substrate 123 and the main electrode layer 124b, and as a material, for example, NiCr is used.

For example, Pt is used as the material for the main electrode layer 124b. The main electrode layer 124b may have a single layer structure composed of one layer, or may have a stacked structure in which a plurality of layers are stacked.

The protective layer 125 is formed so as to cover the IDT electrode 101a and the IDT electrode 101b. The protective layer 125 is a layer for the purpose of protecting the main electrode layer 124b from the external environment, adjusting frequency temperature characteristics, and improving moisture resistance. The protective layer 125 is a film containing, for example, silicon dioxide as a main component. The protective layer 125 may have a single layer structure or a laminated structure.

Note that the materials forming the adhesion layer 124a, the main electrode layer 124b, and the protective layer 125 are not limited to the materials described above. Furthermore, the IDT electrode 101a and the IDT electrode 101b do not have to have the above laminated structure. The IDT electrode 101a and the IDT electrode 101b may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, and a plurality of layers made of the above metal or alloy may be used. You may be comprised by the laminated structure laminated | stacked. Further, the protective layer 125 may not be formed.

Here, design parameters of the IDT electrode 101a and the IDT electrode 101b will be described. Λ shown in FIG. 3B is referred to as the pitch between the electrode finger 110a and the electrode finger 110b constituting the IDT electrode 101a and the IDT electrode 101b. In the surface acoustic wave filter, the wavelength is defined by the pitch λ of the plurality of electrode fingers 110a and electrode fingers 110b constituting the IDT electrode 101a and the IDT electrode 101b. Specifically, the pitch λ refers to the length from the center of the width of one electrode finger to the center of the width of the other electrode finger in adjacent electrode fingers connected to the same bus bar electrode. For example, in FIG. 3B, from the center of the width of one electrode finger 110a connected to the bus bar electrode 111a, it is connected to the same bus bar electrode 111a as the bus bar electrode 111a to which the one electrode finger 110a is connected. , The length to the center of the width of another electrode finger 110a adjacent to one electrode finger 110a.

Note that W shown in FIG. 3B refers to the width of the electrode finger 110a of the IDT electrode 101a and the electrode finger 110b of the IDT electrode 101b in the resonator 100. Further, S shown in (b) of FIG. 3 refers to an interval between the electrode finger 110a and the electrode finger 110b. Further, L shown in FIG. 3A is the cross width of the IDT electrode 101a and the IDT electrode 101b, and is the length of the electrode finger where the electrode finger 110a of the IDT electrode 101a and the electrode finger 110b of the IDT electrode 101b overlap. I mean. The logarithm means the number of electrode fingers 110a or 110b.

In addition, the structure of the resonator 100 is not limited to the structure described in (a) and (b) of FIG. Further, the resonator 13, the resonator 14, and the resonator 15 according to the present embodiment are not limited to the configuration described above. The resonator 13, the resonator 14, and the resonator 15 may have configurations in which the pitches and logarithms of the electrode fingers are different as described below.

Of the three resonators 13, 14 and 15 shown in FIGS. 2A and 2B, the resonators 13 disposed at both ends with the resonator 14 interposed therebetween have the following characteristics. 4A and 4B are schematic diagrams illustrating the configuration of the resonator 13, wherein FIG. 4A is a schematic diagram illustrating a configuration in which regions are divided into regions having different pitches, and FIG. It is the figure shown relatively. FIG. 5 is a schematic diagram showing the configuration of the resonator 13 more specifically.

4A and 4B, the resonator 13, the resonator 14 and the resonator 15 each have a plurality of regions having different pitches.

The resonator 13 has a region I1, a region I2, and a region I3 in order from the reflector 16 side. As shown in FIG. 5, the resonator 13 includes an IDT electrode 13a and an IDT electrode 13b. The IDT electrode 13a and the IDT electrode 13b correspond to comb-shaped electrodes in the present invention. The IDT electrode 13a and the IDT electrode 13b form a pair of comb electrodes.

The IDT electrode 13a includes a bus bar electrode 131a that is commonly arranged in the region I1, the region I2, and the region I3, and a plurality of electrode fingers 132a that are connected at one end to the bus bar electrode 131a. Similarly, the IDT electrode 13b has a bus bar electrode 131b arranged in common to the region I1, the region I2, and the region I3, and a plurality of electrode fingers 132b having one end connected to the bus bar electrode 131b. The pitches of the electrode fingers 132a and 131b are different in the region I1, the region I2, and the region I3, respectively.

In the resonator 13, the region I <b> 1 is disposed outside the surface acoustic wave filter 10, that is, at a position closest to the reflector 16. The region I3 is disposed at the center side of the surface acoustic wave filter 10, that is, at a position closest to the resonator 14. The region I2 is disposed between the region I1 and the region I3. As shown in FIG. 4B, the pitch in each region is the smallest in the most central region I3 and the largest in the region I2 adjacent to the region I3. That is, as shown in FIG. 5, when the pitch in the region I1 is λ1, the pitch in the region I2 is λ2, and the pitch in the region I3 is λ3, the pitch in each region satisfies the relationship of λ3 <λ1 <λ2. For example, λ1 = 5.15 μm, λ2 = 5.21 μm, and λ3 = 4.63 μm. The region I3 corresponds to the first region in the present invention, and the region I2 corresponds to the second region in the present invention.

Further, the logarithm of the electrode finger 110a and the electrode finger 110b in the region I1 is, for example, 17. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I2 is, for example, 6. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I3 is, for example, 3. That is, the number of pairs of the electrode fingers 110a and 110b in the region I3 closest to the resonator 14 is smaller than the total number of pairs of the electrode fingers 110a and 110b in the regions I1 and I2 other than the region I3. The logarithm of the electrode finger 110a and the electrode finger 110b in each region is not limited to the logarithm described above, and may be changed.

The resonator 14 has a region I4, a region I5, and a region I6 in order from the side closer to the resonator 13. That is, the region I4 is disposed closest to the resonator 13, and the region I6 is disposed closest to the resonator 15. The region I5 is arranged between the region I4 and the region I6.

As shown in FIG. 4B, the pitch in each region is the largest in the central region I5, and the pitch in the regions I3 and I5 is smaller than λ5. That is, assuming that the pitch in the region I4 is λ4, the pitch in the region I5 is λ5, and the pitch in the region I6 is λ6, the pitch in each region satisfies the relationship of λ4 <λ5 and λ6 <λ5. For example, λ4 = 4.69 μm, λ5 = 5.18 μm, and λ6 = 4.78 μm.

Note that the pitch λ4 in the region I4 and the pitch λ6 in the region I6 may be the same value or different values. Further, the pitch λ4 and the pitch λ6 may be the same value as the pitch λ3 of the region I3 in the resonator 13 as shown in FIG. 4B, or may be different values. Further, the pitch λ5 in the region I5 may be the same value as the pitch λ1 in the region I1 or the pitch λ2 in the region I2, or may be a different value.

The logarithm of the electrode finger 110a and the electrode finger 110b in the region I4 is, for example, 2. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I5 is, for example, 10. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I6 is, for example, 4. The logarithm of the electrode finger 110a and the electrode finger 110b in each region is not limited to the logarithm described above, and may be changed.

The resonator 15 has a region I7, a region I8, and a region I9 in order from the side closer to the resonator 14. The regions I7, I8, and I9 of the resonator 15 correspond to the regions I3, I2, and I1 of the resonator 13, respectively. The region I7 is disposed at the center side of the surface acoustic wave filter 10, that is, at a position closest to the resonator 14. The region I9 is disposed outside the surface acoustic wave filter 10, that is, at a position closest to the reflector 17. The region I8 is disposed between the region I7 and the region I9. As shown in FIG. 4B, the pitch in each region is the smallest in the most central region I7 and the largest in the region I8 adjacent to the region I7. That is, assuming that the pitch in the region I7 is λ7, the pitch in the region I8 is λ8, and the pitch in the region I9 is λ9, the pitch in each region satisfies the relationship of λ7 <λ9 <λ8. For example, λ7 = 4.88 μm, λ8 = 5.18 μm, and λ9 = 5.13 μm. The region I7 corresponds to the first region in the present invention, and the region I8 corresponds to the second region in the present invention.

As shown in FIG. 4B, the pitch λ7 in the region I7 may be the same as or different from the pitch λ3 in the region I3, the pitch λ4 in the region I4, and the pitch λ6 in the region I6. It may be. Further, the pitch λ8 in the region I8 may be the same as or different from the pitch λ2 in the region I2. Further, the pitch λ9 in the region I9 may be the same value as the pitch λ1 in the region I1, or may be a different value.

The logarithm of the electrode finger 110a and the electrode finger 110b in the region I7 is, for example, 5. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I8 is, for example, 5. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I9 is, for example, 15. The logarithm of the electrode finger 110a and the electrode finger 110b in each region is not limited to the logarithm described above, and may be changed.

[2. Transmission characteristics of surface acoustic wave filter]
Here, the transmission characteristic of the surface acoustic wave filter 10 having the resonators 13, 14 and 15 having the above-described configuration will be described. 6A and 6C are diagrams showing the pass characteristics of the surface acoustic wave filter 10 according to the present embodiment. FIG. 6B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. FIG. 6D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. 6A to 6D, as described above, the surface acoustic wave filter 10 in which the pitch relationship in the resonator 13 is λ3 <λ1 <λ2 and the pitch relationship in the resonator 15 is λ7 <λ9 <λ8 is used. The solid line A represents the characteristic when using a surface acoustic wave filter (original surface acoustic wave filter) in which the characteristic is the broken line B and the pitch relationship between the resonator 13 and the resonator 15 is not changed as described above. Yes. 6B and 6D, the impedance characteristics in the pass band of the surface acoustic wave filter 10 are indicated by bold lines.

As shown in FIG. 6A, the surface acoustic wave filter 10 includes a resonance frequency of a zeroth-order resonance mode and a resonance frequency of a second-order resonance mode for obtaining a pass band. FIG. 6A shows the pass characteristic of the surface acoustic wave filter 10 when mismatch loss is removed in order to make the change in bandwidth easy to understand.

6A, the relationship between the pitches of the region I1, the region I2, and the region I3 of the resonator 13 is λ3 <λ1 <λ2, and the relationship between the pitches of the region I7, the region I8, and the region I9 of the resonator 15 is λ7 <λ9. The transmission characteristic (dashed line B) of the surface acoustic wave filter 10 with <λ8 is 0 as compared with the pass characteristic (solid line A) of the surface acoustic wave filter when the pitch of the resonators 13 and 15 is not changed. The resonance frequency of the next resonance mode moves to the low frequency side. Further, the resonance frequency of the secondary resonance mode does not change. Therefore, since the interval between the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode does not widen, the coupling between these resonance modes is not weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 6B, the Smith chart center of the input impedance (broken line B) in the passband of the surface acoustic wave filter 10 is used. Is smaller than the deviation of the input impedance (solid line A) of the originally designed surface acoustic wave filter.

Further, as described above, since only the resonance frequency of the zeroth-order resonance mode moves to the lower frequency side and the resonance frequency of the second-order resonance mode does not change, as shown in FIG. 6C, the passband of the surface acoustic wave filter 10 The width (broken line B) is larger than the passband width (solid line A) of the original surface acoustic wave filter. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 6D, the winding of the output impedance (broken line B) in the passband on the Smith chart is the original design. It does not spread beyond the winding of the output impedance (solid line A) of the surface acoustic wave filter. Therefore, in the surface acoustic wave filter 10, it can be said that the variation in output impedance is smaller than that in the case of the originally designed surface acoustic wave filter.

As described above, the surface acoustic wave filter 10 according to the present embodiment can realize a wide band while suppressing the spread of the winding of the output impedance in the pass band on the Smith chart.

[3. Comparative Example 1]
Here, the surface acoustic wave filter 30 according to Comparative Example 1 will be described with reference to FIGS. 7 and 8A to 8D. FIG. 7 is a diagram showing a configuration of the surface acoustic wave filter 30 according to this comparative example.

In the surface acoustic wave filter 30 according to this comparative example, the resonator 23 disposed at a position closest to the reflector 16 and the resonator 25 disposed at a position closest to the reflector 17 include an electrode finger 132a and an electrode finger, respectively. 132b has two regions with different pitches.

As shown in FIG. 7, the resonator 23 has a region I11 arranged on the reflector 16 side and a region I13 arranged on the resonator 14 side. The pitch λ11 of the electrode finger 132a and the electrode finger 132b in the region I11 is larger than the pitch λ13 of the electrode finger 132a and the electrode finger 132b in the region I13. That is, the pitch in each region satisfies the relationship of λ13 <λ11.

Similarly, the resonator 25 has a region I17 disposed on the resonator 14 side and a region I18 disposed on the reflector 17 side. The pitch λ18 of the electrode finger 132a and the electrode finger 132b in the region I18 is larger than the pitch λ17 of the electrode finger 132a and the electrode finger 132b in the region I17. That is, the pitch in each region satisfies the relationship of λ17 <λ18.

Note that the configuration of the resonator 14 disposed between the resonator 23 and the resonator 25 is the same as that of the resonator 14 in the surface acoustic wave filter 10 shown in the first embodiment, and thus the description thereof is omitted.

Hereinafter, transmission characteristics of the surface acoustic wave filter 30 having the above-described configuration will be described. 8A and 8C are diagrams illustrating the pass characteristics of the surface acoustic wave filter 30 according to the present embodiment. FIG. 8B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 30 according to the present exemplary embodiment. FIG. 8D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 30 according to the present embodiment. 8A to 8D, as described above, the characteristics when the surface acoustic wave filter 30 in which the relationship of the pitch in the resonator 23 is λ13 <λ11 and the relationship of the pitch in the resonator 25 is λ17 <λ18 are used are the broken line C The solid line A shows the characteristics when a surface acoustic wave filter (original surface acoustic wave filter) whose pitch relationship between the resonator 23 and the resonator 25 is not changed as described above is used. 8B and 8D, the impedance characteristics within the pass band of the surface acoustic wave filter 30 are indicated by bold lines.

As shown in FIG. 8A, the surface acoustic wave filter 10 in which the relationship between the pitches of the regions I11 and I13 of the resonator 23 is λ13 <λ11, and the relationship between the pitches of the regions I17 and I18 of the resonator 25 is λ17 <λ18. The pass characteristic (broken line C) indicates that both the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode are on the lower frequency side than the pass characteristic (solid line A) of the originally designed surface acoustic wave filter. Moving. Accordingly, since the interval between the resonance frequencies of the zeroth-order resonance mode and the second-order resonance mode is widened, the coupling between these resonance modes is weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is weakened, as shown in FIG. 8B, in the surface acoustic wave filter 30, the input impedance (broken line C) in the passband is the elastic surface of the original design. Compared with the input impedance (solid line A) of the wave filter, the center of the Smith chart is deviated.

Further, as described above, both the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode move to the lower frequency side, and the resonance frequency of the second-order resonance mode is the zeroth-order resonance mode. The resonance frequency changes more greatly than the resonance frequency. Therefore, as shown in FIG. 8C, the pass bandwidth (dashed line C) of the surface acoustic wave filter 30 is larger than the pass bandwidth (solid line A) of the original surface acoustic wave filter. However, as described above, in the surface acoustic wave filter 30, the coupling between the zeroth-order resonance mode and the second-order resonance mode is weakened, and the input impedance in the band deviates from the center of the Smith chart. On the Smith chart of the surface acoustic wave filter 30, the winding of the output impedance (broken line C) in the pass band is wider than the winding of the output impedance (solid line A) of the original surface acoustic wave filter. Therefore, in the surface acoustic wave filter 30 according to this modification, it can be said that the variation in output impedance is larger than that in the surface acoustic wave filter of the original design.

In contrast, in the surface acoustic wave filter 10 according to the present embodiment, as shown in FIGS. 6C and 6D, the surface acoustic wave filter 10 according to the present embodiment has an output within the passband on the Smith chart. Broadband can be realized while suppressing the spread of the winding of impedance.

[4. Comparative Example 2]
Next, Comparative Example 2 will be described with reference to FIGS. 9A to 9D.

The surface acoustic wave filter according to this comparative example includes a resonator 13, a resonator 14, and a resonator 15, similar to the surface acoustic wave filter 10 described above. The resonator 13 has three regions I1, I2, and I3 having different pitches of the electrode fingers 132a and the electrode fingers 132b. The resonator 15 has three regions I7, I8, and I9 having different pitches of the electrode fingers 132a and the electrode fingers 132b.

In the resonator 13, the pitch in the region I3 on the most central side is the smallest, and the pitch in the region I1 that is not adjacent to the region I3 is the largest. That is, the pitch in each region satisfies the relationship of λ3 <λ2 <λ1.

Similarly, in the resonator 15, the pitch in the most central region I7 is the smallest, and the pitch in the region I9 not adjacent to the region I7 is the largest. That is, the pitch in each region satisfies the relationship of λ7 <λ8 <λ9.

Note that the configuration of the resonator 14 disposed between the resonator 13 and the resonator 15 is the same as that of the resonator 14 in the surface acoustic wave filter 10 shown in the first embodiment, and thus the description thereof is omitted.

Here, the transmission characteristics of the surface acoustic wave filter configured as described above will be described. 9A and 9C are diagrams showing pass characteristics of the surface acoustic wave filter 10 according to the present embodiment. FIG. 9B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. FIG. 9D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. 9A to 9D, as described above, the characteristics in the case of using the surface acoustic wave filter in which the pitch relationship in the resonator 13 is λ3 <λ2 <λ1 and the pitch relationship in the resonator 15 is λ7 <λ8 <λ9. The solid line A shows the characteristics when using a surface acoustic wave filter (original surface acoustic wave filter) in which the relationship between the broken line D and the pitch of the resonator 13 and the resonator 15 is not changed as described above. . 9B and 9D, the impedance characteristics within the pass band of the surface acoustic wave filter 10 are indicated by bold lines.

As shown in FIG. 9A, the relationship between the pitches of the region I1, the region I2, and the region I13 of the resonator 13 is λ3 <λ2 <λ1, and the relationship between the pitches of the region I7, the region I8, and the region I9 of the resonator 15 is λ7 <λ8. The pass characteristic (dashed line D) of the surface acoustic wave filter with <λ9 moves to the low frequency side in the secondary resonance mode compared to the pass characteristic (solid line A) of the original surface acoustic wave filter. . Further, the resonance frequency of the zeroth-order resonance mode does not change. Accordingly, since the interval between the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode is widened, the coupling between these resonance modes is weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is weakened, as shown in FIG. 9B, in the surface acoustic wave filter according to this modification, the input impedance (broken line D) in the passband is Compared with the input impedance (solid line A) of the surface acoustic wave filter of the design, it will deviate from the center of the Smith chart.

Further, as described above, as shown in FIG. 9C, the pass bandwidth (dashed line D) of the surface acoustic wave filter according to the present modification is compared with the pass bandwidth (solid line A) of the original surface acoustic wave filter. Does not change. Further, as described above, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is weakened, and the input impedance in the passband deviates from the center of the Smith chart, as shown in FIG. 9D, the passband on the Smith chart. The winding of the output impedance (broken line D) is wider than the winding of the output impedance (solid line A) of the original surface acoustic wave filter. Therefore, in the surface acoustic wave filter according to this modification, it can be said that the variation in output impedance is larger than that in the surface acoustic wave filter of the original design.

On the other hand, in the surface acoustic wave filter 10 according to the present embodiment, as shown in FIGS. 6C and 6D, a wide band is realized while suppressing the spread of the output impedance winding in the pass band on the Smith chart. can do.

[5. Effect]
As described above, according to the surface acoustic wave filter 10 according to the present embodiment, it is possible to realize a wide band while suppressing the spread of the winding of the output impedance in the pass band on the Smith chart.

(Embodiment 2)
Next, Embodiment 2 will be described with reference to FIG. 10 and FIGS. 11A to 11D. The surface acoustic wave filter 10a according to the present embodiment differs from the surface acoustic wave filter 10 according to the first embodiment in that the resonator 13 disposed on the reflector 16 side has a different pitch in the surface acoustic wave filter 10a. Although the three regions I1, I2, and I3 are provided, the resonator 25 disposed on the reflector 17 side has two regions I17 and I18 having different pitches.

10A and 10B are diagrams showing the configuration of the surface acoustic wave filter 10a according to the present embodiment, in which FIG. 10A is a schematic diagram showing the configuration divided into regions having different pitches, and FIG. It is the figure which showed the magnitude | size of the pitch in an area | region relatively.

As shown in FIG. 10A, the surface acoustic wave filter 10a is a longitudinally coupled surface acoustic wave filter, like the surface acoustic wave filter 10 shown in the first embodiment. The surface acoustic wave filter 10 a includes resonators 13, 14, and 25 in order from the reflector 16 side to the reflector 17 side between the reflector 16 and the reflector 17.

The configuration of the resonator 13 includes regions I1, I2, and I3 having different pitches, like the surface acoustic wave filter 10 shown in the first embodiment. As shown in FIG. 10B, the pitch in each region satisfies the relationship of λ3 <λ1 <λ2. The region I3 corresponds to the first region in the present invention, and the region I2 corresponds to the second region in the present invention.

Similarly to the surface acoustic wave filter 30 shown in the first comparative example of the first embodiment, the resonator 25 includes a region I17 disposed on the resonator 14 side and a region I18 disposed on the reflector 17 side. Have. The pitch λ18 of the electrode finger 132a and the electrode finger 132b in the region I18 is larger than the pitch λ17 of the electrode finger 132a and the electrode finger 132b in the region I17. That is, the pitch in each region satisfies the relationship of λ17 <λ18, as shown in FIG.

The configuration of the resonator 14 disposed between the resonator 13 and the resonator 25 is the same as that of the resonator 14 in the surface acoustic wave filter 10 shown in the first embodiment, and thus the description thereof is omitted.

Here, the transmission characteristics of the surface acoustic wave filter 10a configured as described above will be described. 11A and 11C are diagrams showing the pass characteristics of the surface acoustic wave filter 10 according to the present embodiment. FIG. 11B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. FIG. 11D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. 11A to 11D, the characteristics when the surface acoustic wave filter 10a is used in which the pitch relationship in the resonator 13 is λ3 <λ1 <λ2 and the pitch relationship in the resonator 25 is λ17 <λ18 as described above. A solid line A indicates the characteristics when a surface acoustic wave filter (original surface acoustic wave filter) in which the relationship between the broken line E, the pitch of the resonator 13 and the resonator 25 is not changed as described above is used. 11B and 11D, the impedance characteristics within the pass band of the surface acoustic wave filter 10a are indicated by bold lines.

As shown in FIG. 11A, the relationship between the pitch of the region I1, the region I2 and the region I3 of the resonator 13 is λ3 <λ1 <λ2, and the relationship between the pitch of the region I17 and the region I18 of the resonator 25 is λ17 <λ18. The pass characteristic (dashed line E) of the surface wave filter 10a is both the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode compared to the pass characteristic (solid line A) of the originally designed surface acoustic wave filter. Moves to the low frequency side. At this time, the resonance frequency of the zeroth-order resonance mode changes more greatly than the resonance frequency of the second-order resonance mode. Therefore, the interval between the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode does not increase. Therefore, the coupling of these resonance modes is not weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 11B, the surface acoustic wave filter 10a has a Smith chart of the input impedance (broken line E) in the passband. The deviation from the center is smaller than the deviation of the input impedance (solid line A) of the originally designed surface acoustic wave filter. The deviation at this time is smaller than the deviation from the center of the Smith chart of the input impedance (broken line B) in the passband of the surface acoustic wave filter 10 shown in FIG. 6B.

Further, as shown in FIG. 11C, the pass bandwidth (dashed line E) of the surface acoustic wave filter 10a is larger than the pass bandwidth (solid line A) of the original surface acoustic wave filter. The pass bandwidth (broken line E) at this time is larger than the pass bandwidth (broken line B) of the surface acoustic wave filter 10 shown in FIG. 6C. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 11D, the winding of the output impedance (broken line E) in the passband on the Smith chart is the original design. It is not as wide as the winding of the output impedance (solid line A) of the surface acoustic wave filter. Further, the winding of the output impedance (broken line E) at this time is smaller than the winding of the output impedance (broken line B) of the surface acoustic wave filter 10 shown in FIG. 6D. Therefore, in the surface acoustic wave filter 10a, it can be said that the variation in output impedance is smaller than in the case of the originally designed surface acoustic wave filter.

As described above, according to the surface acoustic wave filter 10a according to the present embodiment, it is possible to realize a wide band while suppressing the spread of the winding of the output impedance in the pass band on the Smith chart.

In the surface acoustic wave filter 10a described above, the resonator 13 on the reflector 16 side has three regions having different pitches, and the resonator 25 on the reflector 17 side has two regions having different pitches. However, the resonator on the reflector 17 side may have three regions with different pitches, and the resonator on the reflector 16 side may have two regions with different pitches. Further, the pitch value and the logarithm of the electrode finger 132a and the electrode finger 132b may be changed as appropriate.

(Embodiment 3)
Next, Embodiment 3 will be described with reference to FIG. 12 and FIGS. 13A to 13D. The surface acoustic wave filter 10b according to the present embodiment is different from the surface acoustic wave filter 10 according to the first embodiment in that the resonator 13 and the reflector 17 arranged on the reflector 16 side in the surface acoustic wave filter 10b. The configuration of the resonator 35 disposed on the side is symmetrical with respect to the resonator 14 disposed between the resonator 13 and the resonator 35. In the surface acoustic wave filter 10 b, the resonator 13 and the resonator 35 are connected to the output terminal 12, and the resonator 14 is connected to the input terminal 11.

FIG. 12 is a diagram showing a configuration of the surface acoustic wave filter 10b according to the present embodiment.

As shown in FIG. 12, the surface acoustic wave filter 10b is a longitudinally coupled surface acoustic wave filter, like the surface acoustic wave filter 10 shown in the first embodiment. The surface acoustic wave filter 10 b includes a resonator 13, a resonator 14, and a resonator 15 between the reflector 16 and the reflector 17 in order from the reflector 16 side to the reflector 17 side.

The configuration of the resonator 13 has regions I1, I2, and I3 having different pitches in order from the side closer to the reflector 16, as in the surface acoustic wave filter 10 shown in the first embodiment. The pitch in each region satisfies the relationship of λ3 <λ1 <λ2. For example, λ1 = 5.15 μm, λ2 = 5.21 μm, and λ3 = 4.62 μm.

Further, the logarithm of the electrode finger 110a and the electrode finger 110b in the region I1 is 18, for example. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I2 is, for example, 6. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I3 is, for example, 3.

Similarly to the surface acoustic wave filter 10 shown in the first embodiment, the resonator 35 has regions I7, I8, and I9 having different pitches in order from the side closer to the resonator 14. The region I7, region I8, and region I9 of the resonator 35 correspond to the region I3, region I2, and region I1 of the resonator 13, respectively. The pitches in the regions I7, I8, and I9 satisfy the relationship of λ7 <λ9 <λ8. For example, λ7 = 4.62 μm, λ8 = 5.21 μm, and λ9 = 5.15 μm. That is, λ3 = λ7, λ2 = λ8, and λ1 = λ9, and the pitches of the electrode fingers in the regions I7, I8, and I9 of the resonator 35 are the electrode fingers in the regions I1, I2, and I3 of the resonator 13, respectively. The pitch is the same.

Further, the logarithm of the electrode finger 110a and the electrode finger 110b in the region I7 is, for example, 3. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I8 is, for example, 6. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I9 is, for example, 18. That is, the logarithms of the electrode fingers 132a and 132b in the region I7, the region I8, and the region I9 in the resonator 35 are the logarithms of the electrode fingers 132a and 132b in the region I1, the region I2, and the region I3 in the resonator 13, respectively. Are the same. The region I3 and the region I7 correspond to the first region in the present invention, and the region I2 and the region I8 correspond to the second region in the present invention.

The configuration of the resonator 14 arranged between the resonator 13 and the resonator 35 is the same as that of the resonator 14 in the surface acoustic wave filter 10 shown in the first embodiment, and thus the description thereof is omitted.

As described above, in the surface acoustic wave filter 10b, the resonator 13 and the resonator 35 are symmetrical with respect to the resonator 14.

Here, the transmission characteristics of the surface acoustic wave filter 10b configured as described above will be described. 13A and 13C are diagrams showing the pass characteristics of the surface acoustic wave filter 10 according to the present embodiment. FIG. 13B is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. FIG. 13D is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. 13A to 13D, the characteristics when the surface acoustic wave filter 10b in which the configurations of the resonator 13 and the resonator 35 are symmetrical with respect to the resonator 14 are used as described above are shown by the broken line F, the resonator 13 and the resonance. A solid line A indicates the characteristics when a surface acoustic wave filter (originally designed surface acoustic wave filter) whose configuration of the element 35 is not symmetrical with respect to the resonator 14 is used. Further, for the solid line A and the broken line F in FIGS. 13B and 13D, the impedance characteristics in the passband of the surface acoustic wave filter 10b are indicated by bold lines.

As shown in FIG. 13A, the pass characteristic (dashed line F) of the surface acoustic wave filter 10b when the configuration of the resonator 13 and the resonator 35 is symmetrical with respect to the resonator 14 is the original surface acoustic wave filter. The resonance frequency of the zeroth-order resonance mode moves to the low frequency side compared to the pass characteristic (solid line A). The resonance frequency of the secondary resonance mode does not change. Therefore, since the interval between the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode does not widen, the coupling between these resonance modes is not weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 13D, the surface acoustic wave filter 10b has a Smith chart of output impedance (broken line F) in the passband. The deviation from the center is smaller than the deviation of the output impedance (solid line A) of the original surface acoustic wave filter. In the surface acoustic wave filter 10b, the resonator 13 and the resonator 35 are connected to the output terminal 12, and the resonator 14 is connected to the input terminal 11. Therefore, the relationship between the input impedance and the output impedance is shown in the first embodiment. The surface acoustic wave filter 10 shown in FIG.

Further, as shown in FIG. 13C, the pass bandwidth (dashed line F) of the surface acoustic wave filter 10b is larger than the pass bandwidth (solid line A) of the original surface acoustic wave filter. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 13B, the winding of the input impedance (broken line F) in the passband on the Smith chart is the original design. It does not spread as much as the winding of the input impedance (solid line A) of the surface acoustic wave filter. Therefore, in the surface acoustic wave filter 10b, it can be said that the variation in the input and output impedances is smaller than that in the original surface acoustic wave filter.

As described above, according to the surface acoustic wave filter 10b according to the present embodiment, it is possible to realize a wide band while suppressing the spread of the winding of the input impedance and the output impedance in the pass band on the Smith chart.

In the surface acoustic wave filter 10b, the resonator 13 and the resonator 35 are connected to the output terminal 12, and the resonator 14 is connected to the input terminal 11. However, the surface acoustic wave described in the first embodiment is used. Similar to the filter 10, the resonator 13 and the resonator 35 may be connected to the input terminal 11, and the resonator 14 may be connected to the output terminal 12. Further, the pitch value and the logarithm of the electrode fingers 132 a and 132 b may be changed as appropriate as long as the resonator 13 and the resonator 35 are symmetric with respect to the resonator 14.

(Embodiment 4)
Next, Embodiment 4 will be described with reference to FIG. 14 and FIGS. 15A to 15D. The surface acoustic wave filter 10c according to the present embodiment is different from the surface acoustic wave filter 10 according to the first embodiment in that the resonator 43 on the reflector 16 side and the resonator 45 on the reflector 17 side have different pitches. It is divided into four different areas.

14A and 14B are diagrams showing the configuration of the surface acoustic wave filter 10c according to the present embodiment, in which FIG. 14A is a schematic diagram showing a configuration in which regions are divided into regions having different pitches, and FIG. It is the figure which showed the magnitude | size of the pitch in an area | region relatively.

As shown in FIG. 14 (a), the surface acoustic wave filter 10c is a longitudinally coupled surface acoustic wave filter, similar to the surface acoustic wave filter 10 shown in the first embodiment. The surface acoustic wave filter 10 a includes a resonator 43, a resonator 14, and a resonator 45 between the reflector 16 and the reflector 17 in order from the reflector 16 side to the reflector 17 side.

The resonator 43 has a region I21, a region I22, a region I23, and a region I24 having different pitches in order from the side closer to the reflector 16. As shown in FIG. 14B, the pitch in each region is the smallest in the region I24 on the most central side and the largest in the region I23 adjacent to the region I24. That is, as shown in FIG. 14B, when the pitch in the region I21 is λ21, the pitch in the region I22 is λ22, the pitch in the region I23 is λ23, and the pitch in the region I24 is λ24, the pitch in each region is λ24. The relations of <λ21 <λ23 and λ24 <λ22 <λ23 are satisfied. The region I24 corresponds to the first region in the present invention, and the region I23 corresponds to the second region in the present invention. Note that λ21 and λ22 may be the same value or different values. For example, λ21 = 5.15 μm, λ22 = 5.16 μm, λ23 = 5.20 μm, and λ24 = 4.63 μm.

Further, the logarithm of the electrode finger 110a and the electrode finger 110b in the region I21 is, for example, 10. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I22 is, for example, 4. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I23 is, for example, 8. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I24 is, for example, 3.

The resonator 45 has a region I26, a region I27, a region I28, and a region I29 having different pitches in order from the side closer to the resonator. As shown in FIG. 14B, the pitch in each region is the smallest in the most central region I26 and the largest in the region I27 adjacent to the region I26. That is, as shown in FIG. 14B, when the pitch in the region I26 is λ26, the pitch in the region I27 is λ27, the pitch in the region I28 is λ28, and the pitch in the region I29 is λ29, the pitch in each region is λ26. The relations of <λ28 <λ27 and λ26 <λ29 <λ27 are satisfied. The region I26 corresponds to the first region in the present invention, and the region I27 corresponds to the second region in the present invention. Note that λ28 and λ29 may be the same value or different values. For example, λ26 = 4.88 μm, λ27 = 5.18 μm, λ28 = 5.13 μm, and λ29 = 5.12 μm.

Further, the logarithm of the electrode finger 110a and the electrode finger 110b in the region I26 is, for example, 5. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I27 is, for example, 10. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I28 is, for example, 3. The logarithm of the electrode finger 110a and the electrode finger 110b in the region I29 is, for example, 7.

Note that the configuration of the resonator 14 arranged between the resonator 43 and the resonator 45 is the same as that of the resonator 14 in the surface acoustic wave filter 10 shown in the first embodiment, and thus the description thereof is omitted.

Here, the transmission characteristics of the surface acoustic wave filter 10c configured as described above will be described. 15A and 15C are diagrams showing the pass characteristics of the surface acoustic wave filter 10 according to the present embodiment. FIG. 15B is a diagram illustrating reflection characteristics on the input terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. FIG. 15D is a diagram illustrating reflection characteristics on the output terminal side of the surface acoustic wave filter 10 according to the present exemplary embodiment. 15A to 15D, as described above, the pitch relationship in the resonator 43 is λ24 <λ21 <λ23, λ24 <λ22 <λ23, and the pitch relationship in the resonator 45 is λ26 <λ28 <λ27, λ26 <λ29 <λ27. When the surface acoustic wave filter 10c is used, the surface acoustic wave filter whose characteristics are the broken line G and the pitch relationship between the resonator 43 and the resonator 45 is not changed as described above (original surface acoustic wave filter). The solid line A indicates the characteristics when using. 15B and 15D, the impedance characteristics within the pass band of the surface acoustic wave filter 10c are indicated by thick lines.

As shown in FIG. 15A, the relationship between the pitches of the regions I21, I22, I23, and I24 of the resonator 43 is λ24 <λ21 <λ23 and λ24 <λ22 <λ23, the region I26, the region I27, and the region of the resonator 45. The pass characteristic (dashed line G) of the surface acoustic wave filter 10c in which the relationship between the pitches of I28 and the region I29 is λ26 <λ28 <λ27 and λ26 <λ29 <λ27 is the pass characteristic (solid line A) of the original surface acoustic wave filter. In contrast, both the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode move to the low frequency side. At this time, the resonance frequency of the zeroth-order resonance mode changes more greatly than the resonance frequency of the second-order resonance mode. Therefore, the interval between the resonance frequency of the zeroth-order resonance mode and the resonance frequency of the second-order resonance mode does not increase. Therefore, the coupling of these resonance modes is not weakened. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 15B, in the surface acoustic wave filter 10c, the Smith chart of the input impedance (broken line G) in the passband The deviation from the center is smaller than the deviation of the input impedance (solid line A) of the originally designed surface acoustic wave filter.

Further, as shown in FIG. 15C, the pass bandwidth (dashed line G) of the surface acoustic wave filter 10c is larger than the pass bandwidth (solid line A) of the original surface acoustic wave filter. Further, since the coupling between the zeroth-order resonance mode and the second-order resonance mode is not weakened, as shown in FIG. 15D, the winding of the output impedance (broken line G) in the passband on the Smith chart is the original design. It does not spread as much as the winding of the output impedance (solid line A) of the surface acoustic wave filter. Therefore, in the surface acoustic wave filter 10c, it can be said that the variation in output impedance is smaller than in the case of the originally designed surface acoustic wave filter.

As described above, according to the surface acoustic wave filter 10c according to the present embodiment, it is possible to realize a wide band while suppressing the spread of the winding of the output impedance in the pass band on the Smith chart.

(Other embodiments)
In addition, this invention is not limited to the structure described in embodiment mentioned above, For example, you may add a change suitably like the modification shown below.

For example, the surface acoustic wave filter according to the above-described embodiment may be used for a high-frequency module. At this time, as shown in FIG. 1, the surface acoustic wave filter 10 may be connected to a low noise amplifier 20 that amplifies the high-frequency signal that has passed through the surface acoustic wave filter 10.

Further, the surface acoustic wave filter according to the above-described embodiment may be used for a multiplexer. In this case, the multiplexer has a plurality of surface acoustic wave filters, and each of the plurality of surface acoustic wave filters is connected to a common terminal.

In the above-described embodiment, at least one of the three resonators used in the surface acoustic wave filter arranged at the end has three or more regions having different electrode finger pitches. . For example, in the first embodiment, the resonator 13 has three regions, that is, the region I1, the region I2, and the region I3. However, the present invention is not limited to this, and the resonator 13 may have four regions, or the number of regions may be further increased as long as it includes three or more regions.

Further, the number of resonators having three or more regions having different electrode finger pitches is not limited to one, but two resonators disposed at both ends of three resonators used in a surface acoustic wave filter. May be. In this case, the pitches of the electrode fingers in the corresponding regions of the two resonators may be the same or different. Further, the number of electrode fingers in each corresponding region of the two resonators may be the same or different.

Also, the materials for the substrate, electrodes, protective layer, etc. constituting the resonator are not limited to those described above, and may be appropriately changed. The pitch and logarithm of the electrode fingers of each resonator may be changed as long as the above-described conditions are satisfied.

In addition, the form obtained by making various modifications conceived by those skilled in the art with respect to the above-described embodiments and modifications, or the components and functions in the above-described embodiments and modifications without departing from the spirit of the present invention. Forms realized by arbitrarily combining these are also included in the present invention.

The present invention can be used for high-frequency modules, duplexers, multiplexers, receivers, etc. using surface acoustic wave filters.

DESCRIPTION OF SYMBOLS 1 High frequency module 10, 10a, 10b, 10c, 30 Surface acoustic wave filter 11 Input terminal 12 Output terminal 13, 14, 15, 23, 25, 35, 43, 45, 100 Resonator 13a, 13b, 14a, 14b, 15a , 15b, 101a, 101b IDT electrodes (comb electrodes)
16, 17 Reflector 16a, 16b, 17a, 17b, 111a, 111b, 131a, 131b Busbar electrode 16c, 17c, 110a, 110b, 132a, 132b Electrode finger 123 Piezoelectric substrate 124a Adhesion layer 124b Main electrode layer 125 Protective layer

Claims (8)

1. A longitudinally coupled surface acoustic wave filter,
   The surface acoustic wave filter includes three resonators arranged continuously in the propagation direction of the surface acoustic wave,
   Each of the three resonators has a pair of comb electrodes having a bus bar electrode and a plurality of parallel electrode fingers connected to the bus bar electrode,
   The pair of comb-shaped electrodes are arranged such that the plurality of electrode fingers are alternately positioned in the surface acoustic wave propagation direction,
   The first resonator disposed at the center of the three resonators is connected to one of an input terminal and an output terminal of the surface acoustic wave filter,
   A second resonator disposed adjacent to the first resonator; and a second resonator disposed adjacent to the first resonator and disposed opposite to the second resonator with respect to the first resonator. A third resonator connected to the other of the input terminal and the output terminal;
   At least one of the second resonator and the third resonator has three or more regions having different pitches of the electrode fingers, and in each of the three or more regions, the electrode fingers The pitch is constant,
   Of the three or more regions, the pitch of the electrode fingers in the first region closest to the first resonator is the smallest,
   Of the three or more regions, the pitch of the electrode fingers in the second region adjacent to the first region is the largest,
   Surface acoustic wave filter.
2. Both the second resonator and the third resonator have the three or more regions having different pitches of the electrode fingers,
   In each of the second resonator and the third resonator,
   Of the three or more regions, the pitch of the electrode fingers in the first region is the smallest,
   Of the three or more regions, the pitch of the electrode fingers in the second region is the largest,
   The surface acoustic wave filter according to claim 1.
3. Each of the three or more regions of the second resonator and each of the three or more regions of the third resonator corresponding to each of the three or more regions of the second resonator. The pitch of the electrode fingers is the same as each region of
   The surface acoustic wave filter according to claim 2.
4. Each of the three or more regions of the second resonator and each of the three or more regions of the third resonator corresponding to each of the three or more regions of the second resonator. Each region has the same number of pairs of electrode fingers,
   The surface acoustic wave filter according to claim 2.
5. At least one of the second resonator and the third resonator having three or more regions having different pitches of the electrode fingers is such that the number of pairs of the electrode fingers in the first region is the first region. Less than the total number of pairs of electrode fingers in the region other than
   The surface acoustic wave filter according to any one of claims 1 to 4.
6. The first resonator is connected to the input terminal of the surface acoustic wave filter;
   The second resonator and the third resonator are connected to the output terminal in the surface acoustic wave filter,
   The surface acoustic wave filter according to any one of claims 1 to 5.
7. The surface acoustic wave filter according to any one of claims 1 to 6,
   A low noise amplifier that is connected to the surface acoustic wave filter and amplifies a high-frequency signal that has passed through the surface acoustic wave filter;
   High frequency module.
8. A plurality of the surface acoustic wave filters according to any one of claims 1 to 6, wherein each of the plurality of surface acoustic wave filters is connected to a common terminal.
   Multiplexer.

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