Acoustic wave filter

Abstract

To provide a low-loss, miniaturized acoustic wave filter.SOLUTION: An acoustic wave filter 10 has a passband including a first band, and includes input / output terminals 111 and 112, one or more series arm resonators arranged in a series arm path connecting input / output terminals 111 and 112, a plurality of parallel arm resonators connected between the series arm path and ground, and an inductor 31 connected to the input / output terminal 112 and arranged in series in the series arm path, and the resonant frequency frs15 and anti-resonant frequency fas15 of a parallel arm resonator 15 connected closest to an inductor 31 among the plurality of parallel arm resonators is located outside the frequency range of the first band.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an elastic wave filter.

Background Art

[0002] Patent Document 1 discloses a ladder-type elastic wave filter including a series-arm resonator and a parallel-arm resonator each composed of an elastic wave resonator. By adjusting the IDT (InterDigital Transducer) electrode structure, the resonance frequency and the anti-resonance frequency of the elastic wave resonator are optimized to improve the steepness in the passband.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of a ladder-type elastic wave filter, it is common to position the anti-resonance frequency of the parallel-arm resonator near the center of the passband of the elastic wave filter. However, in this case, since the impedance at the anti-resonance frequency of the elastic wave resonator is very high, the impedance in the passband of the parallel-arm resonator becomes very high. Further, when attempting to miniaturize the elastic wave filter, the capacitance of the elastic wave resonator decreases and the impedance of the elastic wave resonator increases. As a result, there is a problem that the impedance in the passband of the elastic wave filter becomes higher than the reference impedance, and low loss cannot be ensured.

[0005] Therefore, the present invention has been made to solve the above problems, and an object thereof is to provide an elastic wave filter with low loss and miniaturization.

Means for Solving the Problems

[0006] In order to achieve the above object, an elastic wave filter according to one aspect of the present invention is an elastic wave filter having a passband including a first band, comprising a first input / output terminal and a second input / output terminal; one or more series arm resonators arranged in a series arm path connecting the first input / output terminal and the second input / output terminal; a plurality of parallel arm resonators connected between the series arm path and the ground; and an inductor connected to the first input / output terminal and arranged in series in the series arm path, wherein the resonance frequency and the anti-resonance frequency of the first parallel arm resonator, which is the closest to the inductor among the plurality of parallel arm resonators, are located outside the frequency range of the first band.

[0007] Also, an elastic wave filter according to one aspect of the present invention is an elastic wave filter having a passband including a first band, comprising a first input / output terminal and a second input / output terminal; one or more series arm resonators arranged in a series arm path connecting the first input / output terminal and the second input / output terminal; a plurality of parallel arm resonators connected between the series arm path and the ground; and an inductor arranged in series between the first input / output terminal and the one or more series arm resonators, wherein each of the plurality of parallel arm resonators has an IDT electrode. Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, the electrode finger pitch of the IDT electrode of the first parallel arm resonator, which is the closest to the inductor among the plurality of parallel arm resonators, be P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators excluding the first parallel arm resonator be P PA When, PA the relational expression P1 ≧ P × {1 + (BWS / f0S) / 2} is satisfied.

[0008] Also, an elastic wave filter according to one aspect of the present invention is an elastic wave filter having a passband including a first band, the elastic wave filter including a first input / output terminal and a second input / output terminal, one or more series arm resonators arranged in a series arm path connecting the first input / output terminal and the second input / output terminal, a plurality of parallel arm resonators connected between the series arm path and the ground, and an inductor arranged in series between the first input / output terminal and the one or more series arm resonators. Each of the one or more series arm resonators and the plurality of parallel arm resonators has an IDT electrode. Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, the electrode finger pitch of the IDT electrode of the first parallel arm resonator that is closest to the inductor among the plurality of parallel arm resonators be P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators be P SA When this is done, P1 ≤ P SA Satisfies the relational expression of ×{1 - (BWS / f0S) / 2}.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an elastic wave filter with reduced loss and miniaturization.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangements of components, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components not described in the independent claims are described as optional components. Also, the sizes or size ratios of the components shown in the drawings are not necessarily precise.

[0012] Each figure is a schematic diagram that has been appropriately emphasized, omitted, or adjusted in ratio to show the present invention, and is not necessarily precisely illustrated, and may differ from the actual shape, positional relationship, and ratio. In each figure, the same reference numerals are given to substantially the same configurations, and duplicate descriptions may be omitted or simplified.

[0013] In the circuit configuration of the present disclosure, "connected" includes not only the case of being directly connected by connection terminals and / or wiring conductors, but also the case of being electrically connected via matching elements or switch circuits. "Connected between A and B" means being connected to both A and B between A and B.

[0014] Also, in the circuit element arrangement of the present disclosure, "circuit element A is arranged in series with path B" means that both the signal input end and the signal output end of circuit element A are connected between two wirings that constitute at least a part of path B. Note that at least one of the two wirings may be an electrode or a terminal.

[0015] Also, terms indicating the relationship between elements such as "parallel" and "perpendicular", terms indicating the shape of elements such as "rectangle", and numerical ranges do not represent only a strict meaning, but also mean including substantially equivalent ranges, for example, an error of about several percent.

[0016] Also, in the following embodiments, the passband of the filter is defined as the frequency band between two frequencies that are 3 dB higher than the minimum value of the insertion loss within the passband.

[0017] Also, in the embodiments of the present disclosure, the resonance bandwidth means the frequency difference between the anti-resonance frequency and the resonance frequency of the elastic wave resonator.

[0018] In the present disclosure, the first band means at least one of an uplink operation band and a downlink operation band of a frequency band predefined by a standardization organization or the like (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.) for a communication system constructed using a radio access technology (RAT). In the present embodiment, as the communication system, for example, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, a WLAN (Wireless Local Area Network) system, etc. can be used, but it is not limited thereto. Note that the uplink operation band of the frequency band means the frequency range designated for uplink among the frequency band. Also, the downlink operation band of the frequency band means the frequency range designated for downlink among the frequency band.

[0019] Also, the first band may include a plurality of the above frequency bands. For example, the first band may include the downlink operation band of band B13 for LTE or band n13 for 5G-NR and the downlink operation band of band B14 for LTE or band n14 for 5G-NR.

[0020] (Embodiment) [1 Circuit Configuration of SAW Filter 10] FIG. 1 is a circuit configuration diagram of a SAW filter 10 according to an embodiment. As shown in the figure, the SAW filter 10 includes input / output terminals 111 and 112, series arm resonators 11, 12, and 13, parallel arm resonators 14 and 15, a longitudinal coupling resonator 16, and an inductor 31.

[0021] The series arm resonators 11 to 13 are one or more series arm resonators arranged in a series arm path connecting the input / output terminal 112 (first input / output terminal) and the input / output terminal 111 (second input / output terminal). Each of the series arm resonators 11 to 13 is an elastic wave resonator, and they are connected in the order of the series arm resonators 11, 12, and 13 in sequence from the input / output terminal 111.

[0022] The parallel arm resonators 14 and 15 are a plurality of parallel arm resonators connected between the series arm path and the ground. Each of the parallel arm resonators 14 and 15 is an elastic wave resonator. The parallel arm resonator 14 is connected between the connection point of the series arm resonators 11 and 12 and the ground. The parallel arm resonator 15 is connected between the connection point of the longitudinal coupling type resonator 16 and the series arm resonator 13 and the ground. The parallel arm resonator 15 is an example of the first parallel arm resonator and is the closest to the inductor 31 among the parallel arm resonators 14 and 15.

[0023] The inductor 31 is connected to the input / output terminal 112 (first input / output terminal) and is arranged in series in the series arm path. Specifically, one end of the inductor 31 is connected to the input / output terminal 112, and the other end of the inductor 31 is connected to the series arm resonator 13.

[0024] The longitudinal coupling type resonator 16 is composed of elastic wave resonators 161, 162, 163, 164, 165, 166, 167, 168, and 169. One end is connected to the input / output terminal 111 via the series arm resonators 11 and 12, and the other end is connected to the input / output terminal 112 via the series arm resonator 13 and the inductor 31.

[0025] Each of the surface acoustic wave resonators 161 to 169 has an IDT electrode disposed on a piezoelectric substrate. The IDT electrodes of the surface acoustic wave resonators 161 to 169 are composed of two comb-shaped electrodes facing each other. One comb-shaped electrode of each of the surface acoustic wave resonators 161, 163, 165, 167, and 169 is connected to the input / output terminal 111 via the series arm resonators 11 and 12, and the other comb-shaped electrode of each of the surface acoustic wave resonators 161, 163, 165, 167, and 169 is connected to the ground. One comb-shaped electrode of each of the surface acoustic wave resonators 162, 164, 166, and 168 is connected to the input / output terminal 112 via the series arm resonators 13 and the inductor 31, and the other comb-shaped electrode of each of the surface acoustic wave resonators 162, 164, 166, and 168 is connected to the ground. The surface acoustic wave resonators 161 to 169 are arranged along the surface acoustic wave propagation direction in the order of the surface acoustic wave resonators 161, 162, 163, 164, 165, 166, 167, 168, and 169.

[0026] With the above connection configuration, the surface acoustic wave filter 10 constitutes a ladder-type bandpass filter including longitudinal coupling resonators and has a passband including a first band.

[0027] Note that the first band may include a plurality of bands standardized by 3GPP (registered trademark). The first band is, for example, the downlink operating band (746 to 756 MHz) of band B13 for LTE or band n13 for 5G-NR and the downlink operating band (758 to 768 MHz) of band B14 for LTE or band n14 for 5G-NR, and is a frequency range (746 to 768 MHz).

[0028] Note that the surface acoustic wave filter 10 according to the present embodiment only needs to include at least one series arm resonator (any one of the series arm resonators 11 to 13), two or more parallel arm resonators (parallel arm resonators 14 to 15) including the parallel arm resonator 15, and the inductor 31. Further, the surface acoustic wave filter 10 according to the present embodiment may include longitudinal coupling resonators in addition to the series arm resonators and parallel arm resonators that constitute a ladder-type filter.

[0029] [Structure of the elastic wave resonator] Next, the structure of the elastic wave resonator that constitutes the elastic wave filter 10 will be exemplified.

[0030] FIG. 2A is a plan view and a cross-sectional view schematically showing a first example of the elastic wave resonator that constitutes the elastic wave filter 10 according to the embodiment. In the figure, the basic structure of each of the plurality of elastic wave resonators that constitute the elastic wave filter 10 is exemplified. Note that the elastic wave resonator 60 shown in FIG. 2A is for explaining a typical structure of the surface acoustic wave resonator that constitutes the elastic wave filter 10, and the number and length of the electrode fingers that constitute the electrodes are not limited thereto.

[0031] The elastic wave resonator 60 is composed of a piezoelectric substrate 50, and comb-shaped electrodes 60a and 60b.

[0032] As shown in FIG. 2A(a), on the piezoelectric substrate 50, a pair of comb-shaped electrodes 60a and 60b facing each other are formed. The comb-shaped electrode 60a is composed of a plurality of electrode fingers 61a parallel to each other and a bus bar electrode 62a connecting the plurality of electrode fingers 61a. Further, the comb-shaped electrode 60b is composed of a plurality of electrode fingers 61b parallel to each other and a bus bar electrode 62b connecting the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction orthogonal to the elastic wave propagation direction (X-axis direction).

[0033] Also, the IDT electrode 54 composed of the plurality of electrode fingers 61a and 61b, and the bus bar electrodes 62a and 62b has a laminated structure of an adhesion layer 540 and a main electrode layer 542, as shown in FIG. 2A(b).

[0034] The adhesion layer 540 is a layer for improving the adhesion between the piezoelectric substrate 50 and the main electrode layer 542. As the material, for example, Ti is used. As the material of the main electrode layer 542, for example, Al containing 1% Cu is used. The protective layer 55 is formed so as to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer for the purpose of protecting the main electrode layer 542 from the external environment, adjusting the frequency-temperature characteristics, and enhancing the moisture resistance, and is, for example, a dielectric film mainly composed of silicon dioxide.

[0035] Note that the materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to the materials described above. Further, the IDT electrode 54 does not have to have the above-described laminated structure. The IDT electrode 54 may be composed of, for example, a metal or an alloy such as Ti, Al, Cu, Pt, Au, Ag, Pd, or may be composed of a plurality of laminates composed of the above-described metals or alloys. Also, the protective layer 55 does not have to be formed.

[0036] Next, the laminated structure of the piezoelectric substrate 50 will be described.

[0037] As shown in FIG. 2A(c), the piezoelectric substrate 50 includes a high acoustic velocity support substrate 51, a low acoustic velocity film 52, and a piezoelectric film 53, and has a structure in which the high acoustic velocity support substrate 51, the low acoustic velocity film 52, and the piezoelectric film 53 are laminated in this order.

[0038] The piezoelectric film 53 is made of, for example, a θ°Y-cut X-propagation LiTaO3 piezoelectric single crystal or a piezoelectric ceramic (a lithium tantalate single crystal cut along a plane having an axis rotated by θ° from the Y axis around the X axis as the normal, or a ceramic in which an elastic surface wave propagates in the X-axis direction). Note that the material and cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected according to the required specifications of each filter.

[0039] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. The high acoustic velocity support substrate 51 is further a substrate in which the sound velocity of the bulk wave in the high acoustic velocity support substrate 51 is higher than that of elastic waves such as surface waves and boundary waves propagating through the piezoelectric film 53, and confines the elastic surface wave to the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated, functioning so as not to leak below the high acoustic velocity support substrate 51. As the material of the high acoustic velocity support substrate 51, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon, dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, or semiconductors such as silicon, or materials mainly composed of the above materials can be used. Note that the above spinel contains an aluminum compound containing one or more elements selected from Mg, Fe, Zn, Mn, etc. and oxygen. Examples of the above spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0040] The low acoustic velocity film 52 is a film in which the sound velocity of the bulk wave in the low acoustic velocity film 52 is lower than that of the bulk wave propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. Due to this structure and the property that the energy of the elastic wave essentially concentrates in a medium with a low acoustic velocity, the leakage of the elastic surface wave energy outside the piezoelectric film 53 is suppressed. As the material of the low acoustic velocity film 52, for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide, or materials mainly composed of the above materials can be used.

[0041] According to the above-described laminated structure of the piezoelectric substrate 50, it is possible to significantly increase the Q value at the resonance frequency and the anti-resonance frequency as compared with the conventional structure in which a single-layer piezoelectric substrate is used. That is, since an elastic wave resonator with a high Q value can be configured, it is possible to configure a filter with low insertion loss using the elastic wave resonator.

[0042] Note that the high-velocity acoustic support substrate 51 may have a structure in which a support substrate and a high-velocity acoustic film in which the sound velocity of the bulk wave to be propagated is higher than that of elastic waves such as surface waves and boundary waves propagating through the piezoelectric film 53 are laminated. In this case, the same material as that of the high-velocity acoustic support substrate 51 can be used as the material of the high-velocity acoustic film. Further, as the material of the support substrate, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors such as silicon and gallium nitride, or resins, or materials mainly composed of the above materials can be used.

[0043] In this specification, the "main component of the material" refers to a component that occupies a proportion exceeding 50% by weight in the material. The above main component may exist in any state of single crystal, polycrystal, and amorphous, or in a state in which these are mixed.

[0044] FIG. 2B is a cross-sectional view schematically showing a second example of the elastic wave resonator constituting the elastic wave filter 10 according to the embodiment. In the elastic wave resonator 60 shown in FIG. 2A, an example in which the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53 is shown. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 composed of a single layer of a piezoelectric layer, as shown in FIG. 2B.

[0045] The piezoelectric single crystal substrate 57 is composed of, for example, a piezoelectric single crystal of LiNbO3. The surface acoustic wave resonator according to this example is composed of a piezoelectric single crystal substrate 57 of LiNbO3, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and on the IDT electrode 54.

[0046] The above-described piezoelectric film 53 and piezoelectric single crystal substrate 57 may be appropriately changed in laminated structure, material, cut angle, and thickness according to the required pass characteristics of the surface acoustic wave filter device. Even a surface acoustic wave resonator using a LiTaO3 piezoelectric substrate having a cut angle other than the above-described cut angle can achieve the same effect as the surface acoustic wave resonator 60 using the above-described piezoelectric film 53.

[0047] Further, the substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy confinement layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. As the piezoelectric film, for example, a LiTaO3 piezoelectric single crystal or piezoelectric ceramics is used. The support substrate is a substrate that supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

[0048] The energy confinement layer is composed of one or a plurality of layers, and the velocity of the bulk acoustic wave propagating through at least one of the layers is greater than the velocity of the acoustic wave propagating in the vicinity of the piezoelectric film. For example, the energy confinement layer may have a laminated structure of a low sound velocity layer and a high sound velocity layer. The low sound velocity layer is a film in which the sound velocity of the bulk wave in the low sound velocity layer is lower than the sound velocity of the acoustic wave propagating through the piezoelectric film. The high sound velocity layer is a film in which the sound velocity of the bulk wave in the high sound velocity layer is higher than the sound velocity of the acoustic wave propagating through the piezoelectric film. Note that the support substrate may be used as the high sound velocity layer.

[0049] Further, the energy confinement layer may be an acoustic impedance layer having a configuration in which a low acoustic impedance layer having a relatively low acoustic impedance and a high acoustic impedance layer having a relatively high acoustic impedance are alternately laminated.

[0050] Here, the electrode parameters of the IDT electrode 54 that constitutes the elastic wave resonator 60 will be described.

[0051] The wavelength of the elastic wave resonator is defined as the wavelength λ, which is the repetition period of the plurality of electrode fingers 61a or 61b that constitute the IDT electrode 54 shown in FIG. 2A(b). Also, the electrode finger pitch is 1 / 2 of the wavelength λ. When the line width of the electrode fingers 61a and 61b that respectively constitute the comb-shaped electrodes 60a and 60b is W and the space width between the adjacent electrode fingers 61a and 61b is S, it is defined as (W + S). Also, the duty of the IDT electrode 54 is the line width occupancy rate of the electrode fingers 61a and 61b, and is the ratio of the line width to the added value of the line width and the space width of the electrode fingers 61a and 61b respectively, and is defined as W / (W + S). Also, the crossover width of the IDT electrode 54 is the length of the overlapping electrode fingers when the electrode fingers 61a and 61b are viewed from the elastic wave propagation direction (X-axis direction).

[0052] In the case where the interval between adjacent electrode fingers in the IDT electrode 54 is not constant, the electrode finger pitch of the IDT electrode 54 is defined by the average electrode finger pitch of the IDT electrode 54. When the total number of electrode fingers 61a and 61b included in the IDT electrode 54 is Ni and the center-to-center distance between the electrode finger located at one end and the electrode finger located at the other end of the IDT electrode 54 in the elastic wave propagation direction is Di, it is defined as Di / (Ni - 1).

[0053] Also, FIG. 2C is a cross-sectional view schematically showing a third example of the elastic wave resonator that constitutes the elastic wave filter 10 according to the embodiment. In FIG. 2C, a bulk elastic wave resonator is shown as the elastic wave resonator of the elastic wave filter 10. As shown in the figure, the bulk elastic wave resonator has, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are laminated in this order.

[0054] The support substrate 65 is a substrate for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68, and is, for example, a silicon substrate. Note that the support substrate 65 is provided with a cavity in a region in contact with the lower electrode 66. Thereby, the piezoelectric layer 67 can vibrate freely.

[0055] The lower electrode 66 is formed on one surface of the support substrate 65. The upper electrode 68 is formed on one surface of the support substrate 65. As the material, for example, Al containing 1% Cu is used for the lower electrode 66 and the upper electrode 68.

[0056] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 mainly contains, for example, at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz, and LiBO (lithium borate).

[0057] The bulk acoustic wave resonator having the above-described stacked structure induces a bulk acoustic wave in the piezoelectric layer 67 by applying electrical energy between the lower electrode 66 and the upper electrode 68 to generate resonance. The bulk acoustic wave generated by this bulk acoustic wave resonator propagates between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. That is, the bulk acoustic wave resonator is a resonator that uses a bulk acoustic wave.

[0058] [3 Resonance Characteristics and Pass Characteristics of Elastic Wave Filter 10] First, the basic operating principle of a ladder-type band-pass filter composed of one series-arm resonator and one parallel-arm resonator will be described.

[0059] The parallel arm resonator has a resonance frequency frp and an anti-resonance frequency fap (> frp), and the series arm resonator has a resonance frequency frs and an anti-resonance frequency fas (> frs > frp). In the series arm resonator and the parallel arm resonator having the above resonance characteristics, generally, the anti-resonance frequency fap of the parallel arm resonator is made close to the resonance frequency frs of the series arm resonator. Thereby, in the vicinity of the resonance frequency frp where the impedance of the parallel arm resonator approaches 0, it becomes a low-frequency side stop band. Also, when the frequency increases from this, the impedance of the parallel arm resonator becomes high in the vicinity of the anti-resonance frequency fap, and the impedance of the series arm resonator approaches 0 in the vicinity of the resonance frequency frs. Thereby, in the vicinity of the anti-resonance frequency fap to the resonance frequency frs, it becomes a signal passing band in the signal path which is the series arm path. Thereby, it becomes possible to form a pass band reflecting the electrode parameters and the electromechanical coupling coefficient of the elastic wave resonator. Further, when the frequency becomes high and it reaches the vicinity of the anti-resonance frequency fas, the impedance of the series arm resonator becomes high, and it becomes a high-frequency side stop band.

[0060] Note that in each of the series arm resonator and the parallel arm resonator, in the frequency band on the lower frequency side than the resonance frequency, the impedance of the resonator shows capacitive (C property), and in the frequency band on the higher frequency side than the resonance frequency and on the lower frequency side than the anti-resonance frequency, the impedance of the resonator shows inductive (L property). Also, in the frequency band on the higher frequency side than the anti-resonance frequency, the impedance of the resonator shows capacitive property.

[0061] Next, the passing characteristics of the elastic wave filter 10 will be described.

[0062] FIG. 3 is a graph showing (a) the passing characteristics of the elastic wave filter 10 and (b) the impedance characteristics of the parallel arm resonator 15 according to the embodiment. Also, FIG. 4 is a graph showing (a) the passing characteristics of the elastic wave filter according to the comparative example and (b) the impedance characteristics of the parallel arm resonator 15.

[0063] Table 1 also shows the electrode parameters of the series arm resonators and parallel arm resonators that make up the surface acoustic wave filters according to the embodiments and comparative examples.

[0064] [Table 1]

[0065] Note that the surface acoustic wave filter according to the comparative example has the same circuit configuration and electrode parameters as the surface acoustic wave filter 10 according to the embodiment, except that the wavelength λ of the IDT electrode of the parallel arm resonator 15 is different.

[0066] In the surface acoustic wave filter according to the comparative example, as shown in FIG. 4(b), the anti-resonance frequency fas15 of the parallel arm resonator 15 is located within the frequency range of the first band. Although not shown, the resonance frequencies of the series arm resonators 11 to 13 and the anti-resonance frequency of the parallel arm resonator 14 are located within the frequency range of the first band.

[0067] As a result, the surface acoustic wave filter according to the comparative example constitutes a band-pass filter having a passband including the first band as shown in FIG. 4(a). However, the insertion loss in the first band is greater than 1 dB. In the surface acoustic wave filter according to the comparative example, since the impedances in the passbands of the parallel arm resonators 14 and 15 are very high, the impedance in the passband of the surface acoustic wave filter becomes higher than the reference impedance, and the insertion loss increases due to the matching loss.

[0068] On the other hand, in the surface acoustic wave filter 10 according to the embodiment, as shown in FIG. 3(b), the anti-resonance frequency fas15 of the parallel arm resonator 15 is located on the lower frequency side than the first band. Although not shown, the resonance frequencies of the series arm resonators 11 to 13 and the anti-resonance frequency of the parallel arm resonator 14 are located within the frequency range of the first band.

[0069] Note that not all of the anti-resonance frequencies of a plurality of parallel-arm resonators (only the parallel-arm resonator 14 in the embodiment) excluding the parallel-arm resonator 15 and the resonance frequencies of one or more series-arm resonators (series-arm resonators 11 to 13 in the embodiment) need to be located within the frequency range of the first band. The plurality of parallel-arm resonators excluding the parallel-arm resonator 15 and the one or more series-arm resonators may be resonators that contribute to the formation of the passband of the elastic wave filter 10. Specifically, at least a part of the resonance band, which is the frequency range from the resonance frequency to the anti-resonance frequency, may overlap with the first band.

[0070] As a result, the elastic wave filter 10 according to the embodiment constitutes a band-pass filter having a passband including the first band as shown in FIG. 3(a). Also, the insertion loss in the first band is 1 dB or less. In the elastic wave filter 10 according to the embodiment, since the impedance in the passband of the parallel-arm resonator 15 is capacitive (C property in FIG. 3(b)), the impedance in the passband of the elastic wave filter 10 can be lowered. Therefore, compared with the elastic wave filter according to the comparative example, the impedance in the passband can be made closer to the reference impedance, and the insertion loss due to the matching loss can be reduced.

[0071] Here, the fact that the elastic wave filter 10 according to the embodiment can achieve a low impedance in the passband will be described in detail with reference to FIG. 5.

[0072] FIG. 5 is a Smith chart showing the impedance of the passband of the elastic wave filter 10 according to the embodiment. The Smith chart in the figure shows the impedance states A, B, and C in the passband.

[0073] First, state A shows the impedance of the passband when viewed from the series-arm resonator 13 side from the connection node N between the inductor 31 and the series-arm resonator 13 in the elastic wave filter according to the comparative example. Since the anti-resonance frequency fas15 of the parallel-arm resonator 15 is located within the first band, the impedance of the passband is higher than the reference impedance and is located in the inductive region.

[0074] Next, state B is the impedance in the passband when viewed from the connection node N in the surface acoustic wave filter 10 according to the embodiment toward the series arm resonator 13. Since the anti-resonant frequency fas15 of the parallel arm resonator 15 is located on the lower frequency side than the first band, the capacitive region of the parallel arm resonator 15 overlaps with the passband of the surface acoustic wave filter 10. As a result, the impedance in the passband of the surface acoustic wave filter 10 becomes that of a capacitive element (capacitive component of the parallel arm resonator 15) connected in parallel, and the constant-conductance circle shifts clockwise with respect to state A and is located in the capacitive region.

[0075] Next, state C is the impedance in the passband when the surface acoustic wave filter 10 according to the embodiment is viewed from the input / output terminal 112 toward the surface acoustic wave filter 10. The impedance in the passband of the surface acoustic wave filter 10 becomes that of an inductor 31 connected in series, and the constant-resistance circle shifts clockwise with respect to state B and approaches the reference impedance.

[0076] In a general ladder-type surface acoustic wave filter, since the impedance at the anti-resonant frequency of the surface acoustic wave resonator is very high, the impedance in the passband of the parallel arm resonator becomes very high. Further, when attempting to miniaturize the surface acoustic wave filter, the capacitance of the surface acoustic wave resonator decreases and the impedance of the surface acoustic wave resonator increases.

[0077] On the other hand, according to the surface acoustic wave filter 10 according to the present embodiment, by positioning the anti-resonance frequency fas15 of the parallel-arm resonator 15 that is closest to the inductor 31 among the plurality of parallel-arm resonators on the lower frequency side than the first band, the impedance of the parallel-arm resonator 15 in the first band can be made capacitive. That is, by positioning the anti-resonance frequency fas15 and the resonance frequency frs15 of the parallel-arm resonator 15 that is closest to the inductor 31 among the plurality of parallel-arm resonators outside the frequency range of the first band, the impedance of the parallel-arm resonator 15 in the first band can be made capacitive. According to this, the impedance in the first band of the surface acoustic wave filter 10 can be shifted to a low impedance by the parallel capacitance component of the parallel-arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, it is possible to reduce the matching loss and provide a surface acoustic wave filter 10 with low loss and miniaturization.

[0078] Next, in the surface acoustic wave filter 10 according to the embodiment, the fact that the anti-resonance frequency fas15 of the parallel-arm resonator 15 is located on the lower frequency side than the first band is expressed using the electrode finger pitch (half of the wavelength λ).

[0079] FIG. 6 is a diagram showing the relationship between the first band of the surface acoustic wave filter 10 according to the embodiment and the anti-resonance frequency of the parallel-arm resonator. Here, the frequency range of the first band is BWS, the center frequency of the first band is f0S, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel-arm resonators (only the parallel-arm resonator 14 in this embodiment) excluding the parallel-arm resonator 15 is P PA Let it be, and the electrode finger pitch of the IDT electrode of the parallel-arm resonator 15 be P1. As shown in FIG. 6, the average value fasA of the anti-resonance frequencies of the plurality of parallel-arm resonators (only the parallel-arm resonator 14 in this embodiment) excluding the parallel-arm resonator 15 is assumed to substantially coincide with the center frequency f0S. From this, the fact that the anti-resonance frequency fas15 of the parallel-arm resonator 15 is located on the lower frequency side than the first band is equivalent to the anti-resonance frequency fas15 being shifted to the lower frequency side by BWS / 2 or more than the average value fasA. When this is expressed using the electrode finger pitch of the parallel-arm resonator, it becomes Equation 1.

[0080] P1 ≥ P PA ×{1 + (BWS / f0S) / 2} (Equation 1)

[0081] In Equation 1, the electrode finger pitch P1 of the parallel arm resonator 15 is the average value P of the electrode finger pitches of the IDT electrodes of a plurality of parallel arm resonators excluding the parallel arm resonator 15 PA It is shown that it is at least larger by an electrode finger pitch corresponding to half of the fractional bandwidth (BWS / f0S) / 2 of the first band than

[0082] For example, a case is shown where the first band is a combined band of the downlink operating band (746 - 756 MHz) of band B13 for LTE and the downlink operating band (758 - 768 MHz) of band B14 for LTE. In this case, BWS = 22 MHz (= 768 - 746 MHz) and f0S = 757 MHz. Also, from Table 1, P of the surface acoustic wave filter 10 PA = 2.5855 μm (= 5.171 μm / 2: electrode finger pitch of the parallel arm resonator 14).

[0083] Substituting the above BWS, f0S, and P into Equation 1 PA results in the right side of Equation 1: P PA ×{1 + (BWS / f0S) / 2} = 2.623 μm. On the other hand, from Table 1, P1 of the surface acoustic wave filter 10 = 2.653 μm, and it can be seen that the relationship of Equation 1 is satisfied.

[0084] According to this, the electrode finger pitch P1 of the parallel arm resonator 15 is larger than the average value P of the electrode finger pitches of the parallel arm resonators excluding the parallel arm resonator 15 by an electrode finger pitch corresponding to half of the frequency range BWS of the first band (= P PA by an electrode finger pitch corresponding to half of the frequency range BWS of the first band (= P PABy increasing only (BWS / f0S) / 2, the anti-resonant frequency fas15 of the parallel-arm resonator 15 can be positioned on the lower frequency side than the first band. As a result, the impedance in the first band of the surface acoustic wave filter 10 can be shifted to a low impedance by the parallel capacitance component of the parallel-arm resonator 15 and the series inductance component of the inductor 31, and can be made to approach the reference impedance. Therefore, the matching loss can be reduced, and a surface acoustic wave filter 10 with low loss and miniaturization can be provided.

[0085] Further, the average value of the electrode finger pitches of the IDT electrodes of a plurality of parallel-arm resonators (in the embodiment, only the parallel-arm resonator 14) and one or more series-arm resonators (in the embodiment, the series-arm resonators 11 to 13) excluding the parallel-arm resonator 15 is P A In the case of, the formula 2 may be satisfied.

[0086] (P SA -P PA ) / P A >BWS / f0S (Formula 2)

[0087] When the capacitive region of the parallel-arm resonator 15 is positioned in the first band, the capacitive component in the passband of the surface acoustic wave filter 10 increases, and the passband of the surface acoustic wave filter 10 tends to become narrow. On the other hand, the formula 2 indicates that the difference between the resonant frequencies of a plurality of parallel-arm resonators excluding the parallel-arm resonator 15 and the resonant frequencies of one or more series-arm resonators is larger than the frequency range BWS of the first band. Thereby, even if the passband of the surface acoustic wave filter 10 becomes narrow due to the capacitive component of the parallel-arm resonator 15, the passband can achieve low loss while securing the first band.

[0088] Next, the case where the first parallel-arm resonator (parallel-arm resonator 15) is a surface acoustic wave resonator and the case where it is a capacitive element are compared. FIG. 7 is a graph showing the pass characteristics when the parallel-arm resonator 15 of the surface acoustic wave filter 10 according to the embodiment is a surface acoustic wave resonator and when it is a capacitive element.

[0089] As shown in the figure, when the parallel arm resonator 15 is an elastic wave resonator, the attenuation amount in the attenuation band on the lower frequency side than the pass band is larger than when the parallel arm resonator 15 is a capacitive element. This is because the resonance frequency frs15 of the parallel arm resonator 15 overlaps with the above attenuation band. That is, since the parallel arm resonator 15 is an elastic wave resonator having impedance characteristics with strong frequency dependence, it is possible to improve the attenuation characteristics of the elastic wave filter 10.

[0090] [Resonance characteristics and passing characteristics of the elastic wave filter 10A according to the 4th modification example] In the elastic wave filter 10 according to the embodiment, by overlapping the capacitive region on the higher frequency side than the anti-resonance frequency fas15 of the parallel arm resonator 15 with the first band, the elastic wave filter 10 is made to have low loss and small size. On the other hand, in the elastic wave filter 10A according to the modification example, by overlapping the capacitive region on the lower frequency side than the resonance frequency frs15 of the parallel arm resonator 15 with the first band, low loss and small size are achieved.

[0091] The elastic wave filter 10A according to this modification example includes input / output terminals 111 and 112, series arm resonators 11, 12, and 13, parallel arm resonators 14 and 15, a longitudinal coupling type resonator 16, and an inductor 31. That is, the circuit configuration of the elastic wave filter 10A according to the modification example is the same as the circuit configuration of the elastic wave filter 10 according to the embodiment. The elastic wave filter 10A according to this modification example has different positions of the resonance frequency and the anti-resonance frequency of the parallel arm resonator 15 compared to the elastic wave filter 10 according to the embodiment.

[0092] FIG. 8 is a diagram showing the relationship between the first band of the elastic wave filter 10A according to the modification example of the embodiment and the resonance frequencies of the parallel arm resonator 15 and the series arm resonators 11 to 13. As shown in the figure, in the elastic wave filter 10A according to the modification example, the resonance frequency frs15 of the parallel arm resonator 15 is located on the higher frequency side than the first band. The resonance frequencies of the series arm resonators 11 to 13 and the anti-resonance frequency of the parallel arm resonator 14 are located within the frequency range of the first band.

[0093] Note that not all of the anti-resonance frequencies of a plurality of parallel-arm resonators (in the embodiment, only the parallel-arm resonator 14) excluding the parallel-arm resonator 15 and the resonance frequencies of one or more series-arm resonators (in the embodiment, the series-arm resonators 11 to 13) need to be located within the frequency range of the first band. The plurality of parallel-arm resonators excluding the parallel-arm resonator 15 and the one or more series-arm resonators may be resonators that contribute to the passband of the elastic wave filter 10A. Specifically, at least a part of the resonance band, which is the frequency range from the resonance frequency to the anti-resonance frequency, may overlap with the first band.

[0094] Thereby, the elastic wave filter 10A according to the modified example constitutes a band-pass filter having a passband including the first band. In the elastic wave filter 10A, since the impedance in the passband of the parallel-arm resonator 15 is capacitive (C-type in FIG. 8), the impedance in the passband of the elastic wave filter 10A can be lowered. Therefore, compared with the elastic wave filter according to the comparative example, the impedance in the passband can be made closer to the reference impedance, and the insertion loss due to the mismatch loss can be reduced.

[0095] Note that the impedance in the passband of the elastic wave filter 10A according to the modified example transitions in the same manner as the impedance states A, B, and C shown in FIG. 5.

[0096] According to the elastic wave filter 10A according to this modification example, by positioning the resonance frequency frs15 of the parallel arm resonator 15 that is most closely connected to the inductor 31 among the plurality of parallel arm resonators on the higher frequency side than the first band, the impedance of the parallel arm resonator 15 in the first band can be made capacitive. That is, by positioning the anti-resonance frequency fas15 and the resonance frequency frs15 of the parallel arm resonator 15 that is most closely connected to the inductor 31 among the plurality of parallel arm resonators outside the frequency range of the first band, the impedance of the parallel arm resonator 15 in the first band can be made capacitive. According to this, the impedance of the elastic wave filter 10A in the first band can be shifted to a low impedance by the parallel capacitance component of the parallel arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, the matching loss can be reduced, and an elastic wave filter 10A with low loss and miniaturization can be provided.

[0097] Next, in the elastic wave filter 10A according to the modification example, the fact that the resonance frequency frs15 of the parallel arm resonator 15 is located on the higher frequency side than the first band is expressed using the electrode finger pitch (half of the wavelength λ).

[0098] Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of series arm resonators (series arm resonators 11 to 13 in this embodiment) be P SA And let the electrode finger pitch of the IDT electrode of the parallel arm resonator 15 be P1. As shown in FIG. 8, the average value frsA of the resonance frequencies of the plurality of series arm resonators (series arm resonators 11 to 13 in this embodiment) is assumed to substantially coincide with the center frequency f0S. From this, the fact that the resonance frequency frs15 of the parallel arm resonator 15 is located on the higher frequency side than the first band is equivalent to the resonance frequency frs15 being shifted to the higher frequency side by BWS / 2 or more than the average value frsA. Expressing this using the electrode finger pitches of the parallel arm resonator 15 and the series arm resonators 11 to 13, it becomes Equation 3.

[0099] P1 ≧ P SA ×{1 - (BWS / f0S) / 2} (Equation 3)

[0100] In Equation 3, the electrode finger pitch P1 of the parallel arm resonator 15 is the average value P of the electrode finger pitches of the IDT electrodes of the plurality of series arm resonators SA It has been shown that it is at least smaller by an electrode finger pitch corresponding to half of the fractional bandwidth (BWS / f0S) / 2 of the first band than

[0101] For example, the case where the first band is a combined band of the downlink operating band (746 to 756 MHz) of band B13 for LTE and the downlink operating band (758 to 768 MHz) of band B14 for LTE is shown. In this case, BWS = 22 MHz and f0S = 757 MHz. Also, from Table 1, P of the surface acoustic wave filter 10 SA = 2.4905 μm (= 4.981 μm / 2: average electrode finger pitch of the series arm resonators 11 to 13).

[0102] Substituting the above BWS, f0S, and P into Equation 3, the right side of Equation 3: P SA ×{1 - (BWS / f0S) / 2} = 2.454 μm. That is, the condition is that P1 ≤ 2.454 μm. SA SA

[0103] According to this, by making the electrode finger pitch P1 of the parallel arm resonator 15 smaller by an electrode finger pitch corresponding to half of the frequency range BWS of the first band (= P SA (BWS / f0S) / 2), it becomes possible to position the resonance frequency frs15 of the parallel arm resonator 15 on the higher frequency side than the first band. As a result, the impedance in the first band of the surface acoustic wave filter 10A can be shifted to a low impedance by the parallel capacitance component of the parallel arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, it is possible to reduce the matching loss and provide a surface acoustic wave filter 10A with low loss and miniaturization. SA (BWS / f0S) / 2), it becomes possible to position the resonance frequency frs15 of the parallel arm resonator 15 on the higher frequency side than the first band. As a result, the impedance in the first band of the surface acoustic wave filter 10A can be shifted to a low impedance by the parallel capacitance component of the parallel arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, it is possible to reduce the matching loss and provide a surface acoustic wave filter 10A with low loss and miniaturization.

[0104] [Circuit Configuration of 5 - Multiplexer] Next, the multiplexer 1 including the surface acoustic wave filter 10 according to the embodiment will be described. FIG. 9 is a circuit configuration diagram of the multiplexer 1 according to the embodiment. As shown in the figure, the multiplexer 1 includes a surface acoustic wave filter 10, a filter 20, a common terminal 100, and input / output terminals 110 and 120.

[0105] The common terminal 100 is connected to, for example, an antenna.

[0106] The surface acoustic wave filter 10 is the surface acoustic wave filter 10 according to the embodiment and has a passband including a first band. One end of the surface acoustic wave filter 10 is connected to the common terminal 100, and the other end is connected to the input / output terminal 110.

[0107] The filter 20 has a passband including a second band. One end of the filter 20 is connected to the common terminal 100, and the other end is connected to the input / output terminal 120. That is, the surface acoustic wave filter 10 and the filter 20 are commonly connected. Note that the structure of the filter 20 is not particularly limited, and for example, it may be a surface acoustic wave filter or an LC filter including an inductor and a capacitor.

[0108] According to the above configuration, since the surface acoustic wave filter 10 with reduced loss and miniaturization is provided, the multiplexer 1 can be reduced in loss and miniaturized.

[0109] Note that the passband of the filter 20 is preferably located on the lower frequency side than the passband of the surface acoustic wave filter 10. According to this, the resonance frequency frs15 of the shunt arm resonator 15 of the surface acoustic wave filter 10 can overlap with the passband of the filter 20, so that the insertion loss of the passband of the filter 20 can be reduced.

[0110] Also, in the multiplexer 1, an elastic wave filter 10A according to a modified example may be arranged instead of the elastic wave filter 10. In this case, it is desirable that the passband of the filter 20 is located on the higher frequency side than the passband of the elastic wave filter 10A. According to this, since the anti-resonance frequency fas15 of the shunt arm resonator 15 of the elastic wave filter 10A can overlap with the passband of the filter 20, the insertion loss in the passband of the filter 20 can be reduced.

[0111] In addition, in the multiplexer 1 according to the present embodiment, filters other than the elastic wave filter 10 and the filter 20 may be connected to the common terminal 100. Also, an impedance matching circuit including at least one of an inductor and a capacitor may be connected to at least one of the path connecting the common terminal 100 and the input / output terminal 110 and the path connecting the common terminal 100 and the input / output terminal 120. Further, the common terminal 100, the input / output terminals 110 and 120 may not be provided in the multiplexer 1.

[0112] [6 Effects, etc.] As described above, the elastic wave filter 10 according to the present embodiment has a passband including a first band, and includes input / output terminals 111 and 112, one or more series arm resonators arranged in a series arm path connecting the input / output terminals 111 and 112, a plurality of shunt arm resonators connected between the series arm path and the ground, and an inductor 31 connected to the input / output terminal 112 and arranged in series with the series arm path. The resonance frequency frs15 and the anti-resonance frequency fas15 of the shunt arm resonator 15 that is closest to the inductor 31 among the plurality of shunt arm resonators are located outside the frequency range of the first band.

[0113] According to this, by positioning the anti-resonant frequency fas15 and the resonant frequency frs15 of the parallel-arm resonator 15 outside the frequency range of the first band, the impedance of the parallel-arm resonator 15 in the first band can be made capacitive. As a result, the impedance of the surface acoustic wave filter 10 in the first band can be shifted to a low impedance by the parallel capacitance component of the parallel-arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, a surface acoustic wave filter 10 with reduced loss and miniaturization can be provided.

[0114] Also, for example, in the surface acoustic wave filter 10, the anti-resonant frequency fas15 of the parallel-arm resonator 15 is located on the lower frequency side than the first band.

[0115] According to this, by positioning the anti-resonant frequency fas15 of the parallel-arm resonator 15 on the lower frequency side than the first band, the impedance of the parallel-arm resonator 15 in the first band can be made capacitive.

[0116] Also, for example, in the surface acoustic wave filter 10A according to the modified example, the resonant frequency frs15 of the parallel-arm resonator 15 is located on the higher frequency side than the first band.

[0117] According to this, by positioning the resonant frequency frs15 of the parallel-arm resonator 15 on the higher frequency side than the first band, the impedance of the parallel-arm resonator 15 in the first band can be made capacitive.

[0118] Also, for example, in the surface acoustic wave filters 10 and 10A, the anti-resonant frequencies of each of the plurality of parallel-arm resonators excluding the parallel-arm resonator 15 are located within the frequency range of the first band.

[0119] According to this, the surface acoustic wave filters 10 and 10A constitute a ladder-type band-pass filter having a pass band including the first band.

[0120] In addition, in the acoustic wave filter 10 according to the present embodiment, each of the parallel arm resonators has an IDT electrode, the frequency range of the first band is denoted by BWS, the center frequency of the first band is denoted by f0S, the electrode finger pitch of the IDT electrode of the parallel arm resonator 15 is denoted by P1, and the average value of the electrode finger pitch of the IDT electrodes of the parallel arm resonators excluding the parallel arm resonator 15 is denoted by P PA In this case, P1 ≧ P PA ×{1+(BWS / f0S) / 2}.

[0121] According to this, the electrode finger pitch P1 of the parallel arm resonator 15 is set to the average electrode finger pitch P PA By making the electrode finger pitch larger by half the frequency range BWS of the first band than the first band, the anti-resonance frequency fas15 of the parallel arm resonator 15 can be positioned on the lower frequency side than the first band. This makes it possible to shift the impedance of the acoustic wave filter 10 in the first band to a lower impedance by the parallel capacitance component of the parallel arm resonator 15 and the series inductance component of the inductor 31, and to make it closer to the reference impedance. This makes it possible to provide an acoustic wave filter 10 with low loss and small size.

[0122] In addition, in an acoustic wave filter 10A according to a modified example of the embodiment, each of the one or more series arm resonators and the multiple parallel arm resonators has an IDT electrode. The frequency range of the first band is denoted by BWS, the center frequency of the first band is denoted by f0S, the electrode finger pitch of the IDT electrode of the parallel arm resonator 15 is denoted by P1, and the average electrode finger pitch of the IDT electrodes of the one or more series arm resonators is denoted by P SA In this case, P1≦P SA ×{1-(BWS / f0S) / 2}.

[0123] According to this, the electrode finger pitch P1 of the parallel arm resonator 15 is set to the average electrode finger pitch P SABy making it smaller by an electrode finger pitch corresponding to half of the frequency range BWS of the first band, the resonance frequency frs15 of the parallel-arm resonator 15 can be positioned on the higher frequency side than the first band. As a result, the impedance in the first band of the surface acoustic wave filter 10A can be shifted to a low impedance by the parallel capacitance component of the parallel-arm resonator 15 and the series inductance component of the inductor 31, and it becomes possible to approach the reference impedance. Therefore, it is possible to provide a surface acoustic wave filter 10A with reduced loss and miniaturization.

[0124] Also, for example, in the surface acoustic wave filters 10 and 10A, the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel-arm resonators excluding the parallel-arm resonator 15 is P PA Let it be, and the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series-arm resonators is P SA Let it be, and the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel-arm resonators excluding the parallel-arm resonator 15 and each of the one or more series-arm resonators is P A In the case of letting it be, (P SA -P PA ) / P A Satisfies the relational expression of > BWS / f0S.

[0125] When the capacitive region of the parallel-arm resonator 15 is positioned in the first band, the capacitive component in the passband of the surface acoustic wave filter 10 increases, and the passband of the surface acoustic wave filter 10 tends to become narrow. According to this, even if the passband of the surface acoustic wave filter 10 becomes narrow due to the capacitance component of the parallel-arm resonator 15, the passband can achieve low loss while securing the first band.

[0126] Also, for example, the surface acoustic wave filters 10 and 10A further include a longitudinally coupled resonator 16 connected between the input / output terminal 111 and the inductor 31.

[0127] According to this, it becomes possible to improve at least one of the pass characteristics and the attenuation characteristics.

[0128] For example, in the surface acoustic wave filters 10 and 10A, the first band includes a plurality of bands standardized by 3GPP (registered trademark).

[0129] According to this, it becomes possible to make the surface acoustic wave filters 10 and 10A into filters having a plurality of bands with close frequencies as passbands.

[0130] For example, in the surface acoustic wave filters 10 and 10A, the first band includes the downlink operation band of band B13 for LTE or band n13 for 5G-NR, and the downlink operation band of band B14 for LTE or band n14 for 5G-NR.

[0131] According to this, it becomes possible to make the surface acoustic wave filters 10 and 10A into a coband filter having the B13 downlink operation band and the B14 downlink operation band with close frequencies as passbands.

[0132] (Other embodiments) As described above, the surface acoustic wave filter according to the present invention has been described with reference to embodiments and modifications. However, the present invention is not limited to the above embodiments and modifications. Modifications obtained by making various modifications conceivable by those skilled in the art without departing from the gist of the present invention, and various devices incorporating the surface acoustic wave filter according to the present invention are also included in the present invention.

[0133] Also, for example, in the surface acoustic wave filter according to the above embodiments and modifications, matching elements such as inductors and capacitors, and a switch circuit may be connected between the respective components.

[0134] Note that the resonance frequency and the anti-resonance frequency shown in the above embodiments and modifications are derived, for example, by measuring the reflection characteristics by bringing RF probes into contact with two input / output electrodes of the surface acoustic wave resonator.

[0135] The characteristics of the elastic wave filter described based on the above embodiments and modified examples are shown below.

[0136] <1> An elastic wave filter having a passband including a first band, a first input / output terminal and a second input / output terminal, one or more series arm resonators arranged in a series arm path connecting the first input / output terminal and the second input / output terminal, a plurality of shunt arm resonators connected between the series arm path and ground, an inductor connected to the first input / output terminal and arranged in series with the series arm path, and comprising: an elastic wave filter in which the resonance frequency and the anti-resonance frequency of a first shunt arm resonator, which is the closest to the inductor among the plurality of shunt arm resonators, are located outside the frequency range of the first band.

[0137] <2> The elastic wave filter according to <1>, wherein the anti-resonance frequency of the first shunt arm resonator is located on the lower frequency side than the first band.

[0138] <3> The elastic wave filter according to <1>, wherein the resonance frequency of the first shunt arm resonator is located on the higher frequency side than the first band.

[0139] <4> The elastic wave filter according to <2> or <3>, wherein the anti-resonance frequency of each of the plurality of shunt arm resonators excluding the first shunt arm resonator is located within the frequency range of the first band.

[0140] <5> An elastic wave filter having a passband including a first band, a first input / output terminal and a second input / output terminal, one or more series arm resonators arranged in a series arm path connecting the first input / output terminal and the second input / output terminal, a plurality of shunt arm resonators connected between the series arm path and ground, an inductor serially arranged between the first input / output terminal and the one or more series-arm resonators each of the plurality of parallel-arm resonators has an IDT electrode Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, the electrode finger pitch of the IDT electrode of the first parallel-arm resonator that is most closely connected to the inductor among the plurality of parallel-arm resonators be P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel-arm resonators excluding the first parallel-arm resonator be P PA when P1 ≧ P PA ×{1 + (BWS / f0S) / 2} a surface acoustic wave filter satisfying the relational expression

[0141] <6> a surface acoustic wave filter having a passband including a first band, comprising a first input / output terminal and a second input / output terminal one or more series-arm resonators arranged in a series-arm path connecting the first input / output terminal and the second input / output terminal a plurality of parallel-arm resonators connected between the series-arm path and ground an inductor serially arranged between the first input / output terminal and the one or more series-arm resonators each of the one or more series-arm resonators and the plurality of parallel-arm resonators has an IDT electrode Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, the electrode finger pitch of the IDT electrode of the first parallel-arm resonator that is most closely connected to the inductor among the plurality of parallel-arm resonators be P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series-arm resonators be P SA when P1 ≦ P SA ×{1 - (BWS / f0S) / 2} a surface acoustic wave filter satisfying the relational expression

[0142] <7> Let the frequency range of the first band be BWS, the center frequency of the first band be f0S, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators excluding the first parallel arm resonator be P PA Let the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators be P SA Let the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators excluding the first parallel arm resonator and the one or more series arm resonators be P A When this is the case, (P SA - P PA ) / P A > BWS / f0S The surface acoustic wave filter according to <5> or <6>, which satisfies the relational expression.

[0143] <8> Furthermore, the surface acoustic wave filter according to any one of <1> to <7>, comprising a vertically coupled resonator connected between the second input / output terminal and the inductor.

[0144] <9> The surface acoustic wave filter according to any one of <1> to <8>, wherein the first band includes a plurality of bands standardized by 3GPP (registered trademark).

[0145] <10> The surface acoustic wave filter according to <9>, wherein the first band includes a downlink operation band of band B13 for LTE or band n13 for 5G-NR, and a downlink operation band of band B14 for LTE or band n14 for 5G-NR.

Industrial Applicability

[0146] The present invention can be widely used in communication devices such as mobile phones as a low-loss surface acoustic wave filter applicable to a multi-band frequency standard.

Explanation of Symbols

[0147] 1 multiplexer 10, 10A Elastic Wave Filter 11, 12, 13 Series Arm Resonator 14, 15 Parallel Arm Resonator 16 Vertical Coupling Resonator 20 Filter 31 Inductor 50 Piezoelectric Substrate 51 High-Speed Support Substrate 52 Low-Speed Film 53 Piezoelectric Film 54 IDT Electrode 55, 58 Protective Layer 57 Piezoelectric Single Crystal Substrate 60, 161, 162, 163, 164, 165, 166, 167, 168, 169 Elastic Wave Resonator 60a, 60b Comb Electrode 61a, 61b Electrode Finger 62a, 62b Busbar Electrode 65 Support Substrate 66 Lower Electrode 67 Piezoelectric Layer 68 Upper Electrode 100 Common Terminal 110, 111, 112, 120 Input / Output Terminal

Claims

1. An elastic wave filter having a passband including a first band, comprising: a first input / output terminal and a second input / output terminal; one or more series arm resonators disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a plurality of shunt arm resonators connected between the series arm path and ground; an inductor connected to the first input / output terminal and disposed in series in the series arm path, wherein the resonance frequency and the anti-resonance frequency of a first shunt arm resonator, which is the closest to the inductor among the plurality of shunt arm resonators, are located outside the frequency range of the first band. Elastic wave filter.

2. The anti-resonance frequency of the first shunt arm resonator is located on the lower frequency side than the first band. The elastic wave filter according to claim 1.

3. The resonance frequency of the first shunt arm resonator is located on the higher frequency side than the first band. The elastic wave filter according to claim 1.

4. The anti-resonance frequency of each of the plurality of shunt arm resonators excluding the first shunt arm resonator is located within the frequency range of the first band. The elastic wave filter according to claim 2 or 3.

5. An elastic wave filter having a passband including a first band, comprising: a first input / output terminal and a second input / output terminal; one or more series arm resonators disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a plurality of shunt arm resonators connected between the series arm path and ground; an inductor disposed in series between the first input / output terminal and the one or more series arm resonators, wherein each of the plurality of shunt arm resonators has an IDT (InterDigital Transducer) electrode and Let the frequency range of the first band be BWS, and the center frequency of the first band be f ０ S. Let the electrode finger pitch of the IDT electrode of the first parallel arm resonator, which is the closest to the inductor among the plurality of parallel arm resonators, be P1, and let the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel arm resonators excluding the first parallel arm resonator be P ＰＡ When this is the case, P1 ≥ P ＰＡ × {1 + (BWS / f ０ S) / 2} satisfies a certain relational expression. Elastic wave filter.

6. An elastic wave filter having a passband including a first band, comprising: a first input / output terminal and a second input / output terminal; one or more series arm resonators disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a plurality of shunt arm resonators connected between the series arm path and ground; an inductor disposed in series between the first input / output terminal and the one or more series arm resonators, wherein each of the one or more series arm resonators and the plurality of shunt arm resonators has an IDT electrode and Let the frequency range of the first band be BWS, and the center frequency of the first band be f ０ S. Let the electrode finger pitch of the IDT electrode of the first parallel arm resonator, which is connected closest to the inductor among the plurality of parallel arm resonators, be P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators be P ＳＡ When this is the case, P1 ≤ P ＳＡ × {1 - (BWS / f ０ S) / 2} satisfies a certain relational expression. Elastic wave filter.

7. Let the frequency range of the first band be BWS, and the center frequency of the first band be f ０ S. Let the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators excluding the first parallel arm resonator be P ＰＡ And let the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators be P ＳＡ And let the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators excluding the first parallel arm resonator and the one or more series arm resonators be P Ａ When this is the case, (P ＳＡ - P ＰＡ ) / P Ａ > BWS / f ０ S Satisfies a certain relational expression. The elastic wave filter according to claim 5 or 6.

8. Furthermore, a longitudinally coupled resonator connected between the second input / output terminal and the inductor is provided. The surface acoustic wave filter according to any one of claims 1, 5, and 6. **Claim 9** The first band includes a plurality of bands standardized by 3GPP (registered trademark). The surface acoustic wave filter according to any one of claims 1, 5, and 6. **Claim 10** The first band includes a downlink operation band of band B13 for LTE or band n13 for 5G-NR, and a downlink operation band of band B14 for LTE or band n14 for 5G-NR. The surface acoustic wave filter according to claim 9.

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