Elastic wave filter

Abstract

Provided is an elastic wave filter with reduced loss and reduced size. An elastic wave filter (10) has a passband including a first frequency band, and is provided with: input / output terminals (111, 112); one or more series arm resonators disposed in a series arm path connecting the input / output terminals (111, 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 disposed in series in the series arm path, the resonance frequency (frs15) and the anti-resonance frequency (fas15) of a parallel arm resonator (15) connected closest to the inductor (31) among the plurality of parallel arm resonators being outside the frequency range of the first frequency band.

Description

Technical Field

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

[0002] A ladder-type elastic wave filter including a series-arm resonator and a shunt-arm resonator each including an elastic wave resonator is disclosed in Patent Document 1. By adjusting the IDT (InterDigital Transducer) electrode structure, the resonance frequency and anti-resonance frequency of the elastic wave resonator are optimized, thereby improving the steepness in the passband.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2021 / 015187. Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the case of a ladder-type elastic wave filter, generally, the anti-resonance frequency of the shunt-arm resonator is located near the center of the passband of the elastic wave filter. However, in this case, the impedance at the anti-resonance frequency of the elastic wave resonator is very high, and thus the impedance in the passband of the shunt-arm resonator becomes very high. In addition, if the elastic wave filter is to be miniaturized, the capacitance of the elastic wave resonator decreases and the impedance of the elastic wave resonator becomes high. As a result, the impedance in the passband of the elastic wave filter becomes higher than the reference impedance, and there is a problem that low loss cannot be ensured.

[0008] 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.

[0009] Means for Solving the Problems

[0010] In order to achieve the above object, an elastic wave filter according to one aspect of the present invention has a passband including a first frequency band, and the elastic wave filter includes: 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; and an inductor connected to the first input / output terminal and serially disposed in the series-arm path, wherein the resonance frequency and anti-resonance frequency of a first shunt-arm resonator that is connected closest to the inductor among the plurality of shunt-arm resonators are outside the frequency range of the first frequency band.

[0011] In addition, a surface acoustic wave filter according to an aspect of the present invention has a passband including a first frequency band, and the surface acoustic wave filter includes: 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; and an inductor serially disposed between the first input / output terminal and the one or more series arm resonators. Each of the plurality of shunt arm resonators has an IDT electrode. When the frequency range of the first frequency band is BWS, the center frequency of the first frequency band is f0S, the electrode finger pitch of the IDT electrode of the first shunt arm resonator that is closest to the inductor among the plurality of shunt arm resonators is P1, and the average value of the electrode finger pitches of the IDT electrodes of the plurality of shunt arm resonators other than the first shunt arm resonator is P PA satisfies the relationship of P1≥P PA ×{1 + (BWS / f0S) / 2}.

[0012] In addition, a surface acoustic wave filter according to an aspect of the present invention has a passband including a first frequency band, and the surface acoustic wave filter includes: 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; and an inductor serially disposed 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 shunt arm resonators has an IDT electrode. When the frequency range of the first frequency band is BWS, the center frequency of the first frequency band is f0S, the electrode finger pitch of the IDT electrode of the first shunt arm resonator that is closest to the inductor among the plurality of shunt arm resonators is P1, and the average value of the electrode finger pitches of the IDT electrodes of the one or more series arm resonators is P SA satisfies the relationship of P1≤P SA ×{1 - (BWS / f0S) / 2}.

[0013] Advantageous Effects of the Invention

[0014] According to the present invention, it is possible to provide a surface acoustic wave filter with reduced loss and miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit structure diagram of a surface acoustic wave filter according to an embodiment.

[0016] Figure 2A is a top view and a cross-sectional view schematically showing a first example of a surface acoustic wave resonator constituting a surface acoustic wave filter according to an embodiment.

[0017] Figure 2B It is a cross-sectional view schematically showing a second example of the elastic wave resonator constituting the elastic wave filter according to the embodiment.

[0018] Figure 2C It is a cross-sectional view schematically showing a third example of the elastic wave resonator constituting the elastic wave filter according to the embodiment.

[0019] Figure 3 It is a graph showing the pass characteristic of the elastic wave filter according to the embodiment and the impedance characteristic of the first parallel arm resonator.

[0020] Figure 4 It is a graph showing the pass characteristic of the elastic wave filter according to the comparative example and the impedance characteristic of the first parallel arm resonator.

[0021] Figure 5 It is a Smith chart showing the impedance in the passband of the elastic wave filter according to the embodiment.

[0022] Figure 6 It is a diagram showing the relationship between the first frequency band of the elastic wave filter according to the embodiment and the anti-resonant frequency of the parallel arm resonator.

[0023] Figure 7 It is a graph showing the pass characteristic of the elastic wave filter when the first parallel arm resonator of the elastic wave filter according to the embodiment is an elastic wave resonator and when it is a capacitive element.

[0024] Figure 8 It is a diagram showing the relationship between the first frequency band of the elastic wave filter according to the modified example of the embodiment and the resonant frequencies of the first parallel arm resonator and the series arm resonator.

[0025] Figure 9 It is a circuit structure diagram of the multiplexer according to the embodiment.

[0026] -Description of Reference Numerals-

[0027] 1 Multiplexer

[0028] 10, 10A Elastic wave filter

[0029] 11, 12, 13 Series arm resonator

[0030] 14, 15 Parallel arm resonator

[0031] 16 Longitudinal coupling type resonator

[0032] 20 Filter

[0033] 31 Inductor

[0034] 50 Piezoelectric substrate

[0035] 51 High acoustic velocity supporting substrate

[0036] 52 Low acoustic velocity film

[0037] 53 Piezoelectric film

[0038] 54 IDT electrode

[0039] 55, 58 Protective layer

[0040] 57 Piezoelectric single crystal substrate

[0041] 60, 161, 162, 163, 164, 165, 166, 167, 168, 169 Elastic wave resonator

[0042] 60a, 60b Comb-shaped electrode

[0043] 61a, 61b Electrode fingers

[0044] 62a, 62b Bus bar electrode

[0045] 65 Supporting substrate

[0046] 66 Lower electrode

[0047] 67 Piezoelectric layer

[0048] 68 Upper electrode

[0049] 100 Common terminal

[0050] 110, 111, 112, 120 Input / output terminals. Detailed implementation manners

[0051] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, all the embodiments described below show general or specific examples. The numerical values, shapes, materials, components, arrangements of components, connection manners, etc. shown in the following embodiments are examples, and the gist thereof is not intended to limit the present invention. Among the components in the following embodiments, the components not recited in the independent claims are described as optional components. In addition, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0052] In addition, each drawing is a schematic diagram that is appropriately emphasized, omitted, or adjusted in ratio for showing the present invention, and is not necessarily strictly drawn, and may be different from the actual shape, positional relationship, and ratio. In each drawing, the same reference numerals are assigned to substantially the same structures, and repeated descriptions may be omitted or simplified.

[0053] In the circuit structure of the present disclosure, the so-called "connection" not only includes a case of direct connection through connection terminals and / or wiring conductors, but also includes a case of electrical connection via matching elements or switching circuits. The so-called "connected between A and B" means being connected to both A and B between A and B.

[0054] In addition, in the circuit element configuration of the present disclosure, the so-called "circuit element A is serially arranged in path B" means that both the signal input terminal and the signal output terminal of circuit element A are connected between two wirings that constitute at least a part of path B. In addition, at least one of the two wirings may also be an electrode or a terminal.

[0055] In addition, 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 only represent strict meanings, but mean substantially equivalent ranges, for example, also including an error of about several percent.

[0056] In addition, in the following embodiments, the passband of the filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum value of the insertion loss within the passband.

[0057] In addition, in the embodiments of the present disclosure, the so-called resonance bandwidth means the frequency difference between the anti-resonance frequency and the resonance frequency of the elastic wave resonator.

[0058] In addition, in the present disclosure, the first frequency band means at least one of the uplink operating frequency band and the downlink operating frequency band of the frequency band predefined by a standardization organization or the like (such as 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.) for a communication system constructed using a radio access technology (RAT: Radio Access Technology). 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 to these. In addition, the so-called uplink operating frequency band of the frequency band means the frequency range designated for uplink use in the frequency band. In addition, the so-called downlink operating frequency band of the frequency band means the frequency range designated for downlink use in the frequency band.

[0059] In addition, the first frequency band may also include multiple of the above-mentioned frequency bands. For example, the first frequency band may also include the downlink operating frequency band of Band B13 for LTE or Band n13 for 5G-NR, and the downlink operating frequency band of Band B14 for LTE or Band n14 for 5G-NR.

[0060] (Embodiment)

[0061] [1. Circuit Structure of SAW Filter 10]

[0062] Figure 1 FIG. is a circuit structure diagram of the SAW filter 10 according to the embodiment. As shown in this figure, the SAW filter 10 includes input / output terminals 111 and 112, series arm resonators 11, 12, and 13, shunt arm resonators 14 and 15, a longitudinally coupled resonator 16, and an inductor 31.

[0063] 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 (the first input / output terminal) and the input / output terminal 111 (the second input / output terminal). The series arm resonators 11 to 13 are SAW resonators respectively, and are connected in sequence from the input / output terminal 111 in the order of the series arm resonators 11, 12, and 13.

[0064] The shunt arm resonators 14 and 15 are a plurality of shunt arm resonators connected between the above-mentioned series arm path and the ground. The shunt arm resonators 14 and 15 are SAW resonators respectively. The shunt arm resonator 14 is connected between the connection point of the series arm resonators 11 and 12 and the ground. The shunt arm resonator 15 is connected between the connection point of the longitudinally coupled resonator 16 and the series arm resonator 13 and the ground. The shunt arm resonator 15 is an example of the first shunt arm resonator and is connected closest to the inductor 31 among the shunt arm resonators 14 and 15.

[0065] The inductor 31 is connected to the input / output terminal 112 (the first input / output terminal) and is serially arranged in the above-mentioned 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.

[0066] The longitudinally coupled resonator 16 is composed of SAW 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.

[0067] The elastic wave resonators 161 to 169 each have an IDT electrode, which is disposed on a piezoelectric substrate. The IDT electrodes of the elastic wave resonators 161 to 169 are composed of two comb-shaped electrodes facing each other. One comb-shaped electrode of each of the elastic 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 elastic wave resonators 161, 163, 165, 167, and 169 is connected to ground. One comb-shaped electrode of each of the elastic wave resonators 162, 164, 166, and 168 is connected to the input / output terminal 112 via the series arm resonator 13 and the inductor 31, and the other comb-shaped electrode of each of the elastic wave resonators 162, 164, 166, and 168 is connected to ground. The elastic wave resonators 161 to 169 are arranged in the order of elastic wave resonators 161, 162, 163, 164, 165, 166, 167, 168, and 169 along the elastic wave propagation direction.

[0068] With the above connection structure, the elastic wave filter 10 constitutes a ladder-type band-pass filter including longitudinal-coupled resonators and has a passband including a first frequency band.

[0069] In addition, the first frequency band may also include a plurality of frequency bands standardized by 3GPP (registered trademark). The first frequency band is, for example, a frequency range (746 to 768 MHz) including 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.

[0070] In addition, the elastic wave filter 10 according to the present embodiment only needs to include at least one or more series arm resonators (any one of the series arm resonators 11 to 13), two or more parallel arm resonators including the parallel arm resonator 15 (parallel arm resonators 14 to 15), and the inductor 31. In addition, in addition to the series arm resonators and parallel arm resonators constituting the ladder-type filter, the elastic wave filter 10 according to the present embodiment may also include longitudinal-coupled resonators.

[0071] [2. Structure of Elastic Wave Resonator]

[0072] Next, the structure of the elastic wave resonator constituting the elastic wave filter 10 will be illustrated.

[0073] Figure 2AFIG. 0 is a plan view and a cross-sectional view schematically showing a first example of a surface acoustic wave resonator constituting the surface acoustic wave filter 10 according to the embodiment. In this figure, the basic structure of each of the plurality of surface acoustic wave resonators constituting the surface acoustic wave filter 10 is illustrated. Further, Figure 2A The surface acoustic wave resonator 60 shown is used to illustrate a typical structure of the surface acoustic wave resonator constituting the surface acoustic wave filter 10, and the number and length of electrode fingers constituting the electrode are not limited thereto.

[0074] The surface acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0075] As shown in Figure 2A FIG. (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. In addition, 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 surface acoustic wave propagation direction (X-axis direction).

[0076] In addition, as shown in Figure 2A FIG. (b), the IDT electrode 54 composed of the plurality of electrode fingers 61a and 61b and the bus bar electrodes 62a and 62b has a stacked structure of a close contact layer 540 and a main electrode layer 542.

[0077] The close contact layer 540 is a layer for improving the close contact between the piezoelectric substrate 50 and the main electrode layer 542, and as a material, for example, Ti is used. Regarding the main electrode layer 542, as a material, for example, Al containing 1% of Cu is used. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer for protecting the main electrode layer 542 from the influence of the external environment, adjusting the frequency-temperature characteristics, and improving the moisture resistance, etc., and is, for example, a dielectric film mainly composed of silicon dioxide.

[0078] In addition, the materials constituting the close contact layer 540, the main electrode layer 542, and the protective layer 55 are not limited to the above materials. Further, the IDT electrode 54 may not be the above stacked structure. The IDT electrode 54 may be composed of metals or alloys such as Ti, Al, Cu, Pt, Au, Ag, Pd, etc., and in addition, may be composed of a plurality of stacked bodies composed of the above metals or alloys. In addition, the protective layer 55 may not be formed.

[0079] Next, the stacked structure of the piezoelectric substrate 50 will be described.

[0080] As shown in Figure 2AAs shown in (c) of FIG. 0, 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.

[0081] The piezoelectric film 53 includes, for example, a θ° Y-cut X-propagating LiTaO3 piezoelectric single crystal or a piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut at a plane with a normal axis rotated by θ° from the Y axis centered on the X axis, and a single crystal or ceramic in which a surface acoustic wave propagates in the X-axis direction). In addition, the material of the piezoelectric single crystal used as the piezoelectric film 53 and the cut angle θ are appropriately selected according to the required specifications of each filter.

[0082] 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. Further, the high acoustic velocity support substrate 51 is a substrate in which the acoustic velocity of the bulk wave in the high acoustic velocity support substrate 51 is higher than that of the surface wave, the boundary wave, and other elastic waves propagating in the piezoelectric film 53, and functions to enclose the surface acoustic wave in the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated without leaking to a position 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, semiconductors such as silicon, or materials mainly composed of the above materials can be used. In addition, 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.

[0083] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity film 52 is lower than that of the bulk wave propagating in the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. By this structure and the property that the energy of the elastic wave is essentially concentrated in the medium with a low acoustic velocity, the leakage of the surface acoustic 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.

[0084] In addition, according to the above-described laminated structure of the piezoelectric substrate 50, compared with the conventional structure in which a piezoelectric substrate is used as a single layer, the Q values at the resonance frequency and the anti-resonance frequency can be significantly increased. That is, an elastic wave resonator with a high Q value can be formed, and thus a filter with a small insertion loss can be formed using this elastic wave resonator.

[0085] In addition, the high acoustic velocity supporting substrate 51 may also have a structure in which a high acoustic velocity film layer in which the acoustic velocity of the body wave propagated is higher than that of the surface wave, the boundary wave, and other elastic waves propagated in the piezoelectric film 53 is laminated on the supporting substrate. In this case, as the material of the high acoustic velocity film, the same material as that of the high acoustic velocity supporting substrate 51 can be used. In addition, as the material of the supporting 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.

[0086] In addition, in this specification, the so-called "main component of the material" refers to a component whose proportion in the material exceeds 50% by weight. The above main component may exist in any state of single crystal, polycrystal, and amorphous, or in a state in which they are mixed.

[0087] Figure 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 Figure 2A In the shown elastic wave resonator 60, an example in which the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53 is shown. However, as Figure 2B shown, the substrate on which the IDT electrode 54 is formed may also be a piezoelectric single crystal substrate 57 composed of a single layer of a piezoelectric body layer.

[0088] The piezoelectric single crystal substrate 57 is composed of a piezoelectric single crystal of LiNbO3, for example. The elastic 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 the IDT electrode 54.

[0089] The above-described piezoelectric film 53 and piezoelectric single crystal substrate 57 may be appropriately changed in terms of the laminated structure, material, cutting angle, and thickness according to the requirements and characteristics of the elastic wave filter device. Even an elastic wave resonator using a LiTaO3 piezoelectric substrate or the like having a cutting angle other than the above-described cutting angle can exhibit the same effect as the elastic wave resonator 60 using the above-described piezoelectric film 53.

[0090] In addition, the substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy encapsulation layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film uses, for example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic. The support substrate is a substrate that supports the piezoelectric film, the energy encapsulation layer, and the IDT electrode 54.

[0091] The energy encapsulation layer includes one or more layers, and the velocity of the bulk acoustic wave propagating in at least one of them is greater than the velocity of the elastic wave propagating near the piezoelectric film. For example, the energy encapsulation layer may also have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity layer is lower than the acoustic velocity of the elastic wave propagating in the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the high acoustic velocity layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric film. In addition, the support substrate may be set as the high acoustic velocity layer.

[0092] In addition, the energy encapsulation layer may also be an acoustic impedance layer having a structure in which a low acoustic impedance layer with a relatively low acoustic impedance and a high acoustic impedance layer with a relatively high acoustic impedance are alternately laminated.

[0093] Here, the electrode parameters of the IDT electrode 54 constituting the elastic wave resonator 60 will be described.

[0094] The wavelength of the elastic wave resonator is defined by the repetition period, i.e., the wavelength λ, of the plurality of electrode fingers 61a or 61b constituting the IDT electrode 54 shown in (b) of Figure 2A . In addition, the electrode finger pitch is 1 / 2 of the wavelength λ. When the line width of the electrode fingers 61a and 61b constituting the comb-shaped electrodes 60a and 60b is set to W, and the space width between the adjacent electrode fingers 61a and 61b is set to S, it is defined by (W + S). In addition, the duty ratio of the IDT electrode 54 is the line width occupancy ratio of the electrode fingers 61a and 61b, and is the ratio of this line width to the sum value of the line width and the space width of the electrode fingers 61a and 61b respectively, and is defined by W / (W + S). In addition, the crossover width of the IDT electrode 54 is the length of the overlapping electrode fingers when observing the electrode fingers 61a and 61b from the elastic wave propagation direction (X-axis direction).

[0095] In addition, in the IDT electrode 54, when the interval between adjacent electrode fingers is not fixed, the electrode finger pitch of the IDT electrode 54 is defined by the average electrode finger pitch of the IDT electrode 54. If the total number of the electrode fingers 61a and 61b included in the IDT electrode 54 is set to Ni, and the distance between the centers of the electrode finger at one end and the electrode finger at the other end of the IDT electrode 54 in the elastic wave propagation direction is set to Di, the average electrode finger pitch of the IDT electrode 54 is defined as Di / (Ni - 1).

[0096] In addition, Figure 2C is a cross-sectional view schematically showing a third example of the surface acoustic wave resonator constituting the surface acoustic wave filter 10 according to the embodiment. In Figure 2C a bulk acoustic wave resonator is shown as the surface acoustic wave resonator of the surface acoustic wave filter 10. As shown in this figure, the bulk acoustic wave resonator has, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and has a structure in which the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are laminated in this order.

[0097] 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. In addition, the support substrate 65 is provided with voids in the region in contact with the lower electrode 66. Thereby, the piezoelectric layer 67 can vibrate freely.

[0098] 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. The lower electrode 66 and the upper electrode 68 use, for example, Al containing 1% of Cu as a material.

[0099] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 uses, 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) as a main component.

[0100] The bulk acoustic wave resonator having the above laminated structure applies electric energy between the lower electrode 66 and the upper electrode 68 to induce a bulk acoustic wave in the piezoelectric layer 67, thereby generating resonance. The bulk acoustic wave generated by this bulk acoustic wave resonator propagates in a direction perpendicular to the film surface of the piezoelectric layer 67 between the lower electrode 66 and the upper electrode 68. That is, the bulk acoustic wave resonator is a resonator that utilizes a bulk acoustic wave.

[0101] [3. Resonant characteristics and through characteristics of the surface acoustic wave filter 10]

[0102] First, the basic operating principle of a ladder bandpass filter composed of one series arm resonator and one parallel arm resonator will be described.

[0103] 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, near the resonance frequency frp where the impedance of the parallel-arm resonator approaches 0, it becomes a low-frequency side stop band. Further, if the frequency increases accordingly, near the anti-resonance frequency fap, the impedance of the parallel-arm resonator becomes high, and near the resonance frequency frs, the impedance of the series-arm resonator approaches 0. Thereby, near the anti-resonance frequency fap to the resonance frequency frs, in the signal path as the series-arm path, it becomes a signal pass band. Thereby, a pass band reflecting the electrode parameters and the electromechanical coupling coefficient of the surface acoustic wave resonator can be formed. Further, if the frequency becomes high and is near the anti-resonance frequency fas, the impedance of the series-arm resonator becomes high, thus becoming a high-frequency side stop band.

[0104] In addition, in each of the series-arm resonator and the parallel-arm resonator, in a frequency band on the lower-frequency side than the resonance frequency, the impedance of the resonator shows capacitive (C-type), and in a 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-type). Further, in a frequency band on the higher-frequency side than the anti-resonance frequency, the impedance of the resonator shows capacitive.

[0105] Next, the pass characteristics of the surface acoustic wave filter 10 will be described.

[0106] Figure 3 It is a graph showing (a) the pass characteristics of the surface acoustic wave filter 10 according to the embodiment and (b) the impedance characteristics of the parallel-arm resonator 15. Further, Figure 4 It is a graph showing (a) the pass characteristics of the surface acoustic wave filter according to the comparative example and (b) the impedance characteristics of the parallel-arm resonator 15.

[0107] In addition, Table 1 shows the electrode parameters of the series-arm resonator and the parallel-arm resonator constituting the surface acoustic wave filter according to the embodiment and the comparative example.

[0108]

Table 1

[0109]

[0110] In addition, regarding the surface acoustic wave filter according to the comparative example, compared with 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, the circuit structure and the electrode parameters are the same.

[0111] In the surface acoustic wave filter according to the comparative example, as shown in Figure 4 (b) thereof, the anti-resonant frequency fas15 of the parallel arm resonator 15 is within the frequency range of the first frequency band. In addition, although not shown, the resonant frequencies of the series arm resonators 11 to 13 and the anti-resonant frequency of the parallel arm resonator 14 are within the frequency range of the first frequency band.

[0112] Accordingly, as shown in Figure 4 (a) thereof, the surface acoustic wave filter according to the comparative example constitutes a band-pass filter having a passband including the first frequency band. However, the insertion loss in the first frequency band is greater than 1 dB. In the surface acoustic wave filter according to the comparative example, the impedance in the passband of the parallel arm resonators 14 and 15 is very high, and thus the impedance in the passband of the surface acoustic wave filter is higher than the reference impedance, and the insertion loss is greater than the matching loss.

[0113] On the other hand, in the surface acoustic wave filter 10 according to the embodiment, as shown in Figure 3 (b) thereof, the anti-resonant frequency fas15 of the parallel arm resonator 15 is located on the lower frequency side than the first frequency band. In addition, although not shown, the resonant frequencies of the series arm resonators 11 to 13 and the anti-resonant frequency of the parallel arm resonator 14 are within the frequency range of the first frequency band.

[0114] In addition, the anti-resonant frequencies of a plurality of parallel arm resonators other than the parallel arm resonator 15 (in the embodiment, only the parallel arm resonator 14) and the resonant frequencies of one or more series arm resonators (in the embodiment, the series arm resonators 11 to 13) may not all be within the frequency range of the first frequency band. The plurality of parallel arm resonators other than 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 surface acoustic wave filter 10. Specifically, as long as at least a part of the frequency range from the resonant frequency to the anti-resonant frequency, that is, the resonant band, overlaps with the first frequency band.

[0115] Accordingly, as shown in Figure 3 (a) thereof, the surface acoustic wave filter 10 according to the embodiment constitutes a band-pass filter having a passband including the first frequency band. In addition, the insertion loss in the first frequency band becomes 1 dB or less. In the surface acoustic wave filter 10 according to the embodiment, the impedance in the passband of the parallel arm resonator 15 is capacitive (C-type in Figure 3 (b)), and thus the impedance in the passband of the surface acoustic wave filter 10 can be reduced. Therefore, compared with the surface acoustic wave filter according to the comparative example, the impedance in the passband can be made closer to the reference impedance, and the insertion loss caused by the matching loss can be reduced.

[0116] Here, use Figure 5The fact that the elastic wave filter 10 according to the embodiment can have a low impedance in the passband will be described in detail below.

[0117] Figure 5 It is a Smith chart showing the impedance of the passband of the elastic wave filter 10 according to the embodiment. In the Smith chart of this figure, the states A, B, and C of the impedance of the passband are shown.

[0118] First, state A shows the impedance of the passband of the series arm resonator 13 side observed 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-resonant frequency fas15 of the parallel arm resonator 15 is within the first frequency band, the impedance of the passband is in a region where the impedance ratio is higher than the reference impedance and in an inductive region.

[0119] Next, state B is the impedance of the passband of the series arm resonator 13 side observed from the connection node N in the elastic wave filter 10 according to the embodiment. Since the anti-resonant frequency fas15 of the parallel arm resonator 15 is located on the low-frequency side with respect to the first frequency band, the capacitive region of the parallel arm resonator 15 overlaps with the passband of the elastic wave filter 10. As a result, the impedance of the passband of the elastic wave filter 10 becomes an impedance connected in parallel with a capacitive element (capacitive component of the parallel arm resonator 15), and is shifted clockwise on the constant conductance circle with respect to state A and is in the capacitive region.

[0120] Next, state C is the impedance of the passband of the elastic wave filter 10 observed from the input / output terminal 112 in the elastic wave filter 10 according to the embodiment. The impedance of the passband of the elastic wave filter 10 becomes an impedance in which the inductor 31 is connected in series, and is shifted clockwise on the constant resistance circle with respect to state B and approaches the reference impedance.

[0121] In a general ladder-type elastic wave filter, the impedance at the anti-resonant frequency of the elastic wave resonator is very high, so the impedance in the passband of the parallel arm resonator becomes very high. In addition, if it is desired to miniaturize the elastic wave filter, the capacitance of the elastic wave resonator decreases and the impedance of the elastic wave resonator becomes higher.

[0122] In contrast, in the surface acoustic wave filter 10 according to the present embodiment, the anti-resonant frequency fas15 of the shunt arm resonator 15 that is connected closest to the inductor 31 among the plurality of shunt arm resonators can be located on the lower frequency side than the first frequency band, so that the impedance of the shunt arm resonator 15 in the first frequency band can be capacitive. That is, the impedance of the shunt arm resonator 15 in the first frequency band can be made capacitive by making the anti-resonant frequency fas15 and the resonant frequency frs15 of the shunt arm resonator 15 that is connected closest to the inductor 31 among the plurality of shunt arm resonators fall outside the frequency range of the first frequency band. Accordingly, the impedance of the surface acoustic wave filter 10 in the first frequency band can be shifted to a low impedance by the parallel capacitance component of the shunt arm resonator 15 and the series inductance component of the inductor 31, and can be made close to the reference impedance. As a result, the matching loss can be reduced, and a surface acoustic wave filter 10 with low loss and miniaturization can be provided.

[0123] Next, in the surface acoustic wave filter 10 according to the embodiment, the fact that the anti-resonant frequency fas15 of the shunt arm resonator 15 is located on the lower frequency side than the first frequency band is expressed using the electrode finger pitch (half of the wavelength λ).

[0124] Figure 6 FIG. shows the relationship between the first frequency band of the surface acoustic wave filter 10 according to the embodiment and the anti-resonant frequency of the shunt arm resonator. Here, the frequency range of the first frequency band is set to BWS, the center frequency of the first frequency band is set to f0S, and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of shunt arm resonators other than the shunt arm resonator 15 (in the present embodiment, only the shunt arm resonator 14) is set to P PA , and the electrode finger pitch of the IDT electrode of the shunt arm resonator 15 is set to P1. As Figure 6 shown, the average value fasA of the anti-resonant frequencies of the plurality of shunt arm resonators other than the shunt arm resonator 15 (in the present embodiment, only the shunt arm resonator 14) is made to be approximately the same as the center frequency f0S. Thus, the fact that the anti-resonant frequency fas15 of the shunt arm resonator 15 is located on the lower frequency side than the first frequency band is equivalent to the anti-resonant frequency fas15 being shifted by BWS / 2 or more to the lower frequency side compared to the average value fasA. If this is expressed using the electrode finger pitch of the shunt arm resonator, it becomes Equation 1.

[0125] P1 ≥ P PA × {1 + (BWS / f0S) / 2} (Equation 1)

[0126] In Equation 1, it is shown that the electrode finger pitch P1 of the shunt arm resonator 15 is larger than the average value P of the electrode finger pitches of the IDT electrodes of the plurality of shunt arm resonators other than the shunt arm resonator 15 PA, at least greater than an amount corresponding to the electrode finger pitch of half of the relative bandwidth of the first frequency band (BWS / f0S) / 2.

[0127] For example, a case is shown where the first frequency band is a combined frequency band of the downlink operating frequency band (746 to 756 MHz) of Band B13 for LTE and the downlink operating frequency band (758 to 768 MHz) of Band B14 for LTE. In this case, BWS = 22 MHz (= 768 - 746 MHz), and f0S = 757 MHz. Further, according to 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).

[0128] If the above BWS, f0S, and P PA are substituted into Equation 1, the right side of Equation 1 becomes: P PA ×{1 + (BWS / f0S) / 2} = 2.623 μm. On the other hand, according to Table 1, P1 of the surface acoustic wave filter 10 = 2.653 μm, and it can be understood that the relationship of Equation 1 is satisfied.

[0129] Accordingly, by making the electrode finger pitch P1 of the parallel arm resonator 15 larger than the average value P of the electrode finger pitches of the parallel arm resonators other than the parallel arm resonator 15 PA , by an amount corresponding to the electrode finger pitch of half of the frequency range BWS of the first frequency band (= P PA ×(BWS / f0S) / 2), the anti-resonant frequency fas15 of the parallel arm resonator 15 can be located on the lower frequency side than the first frequency band. Thus, the impedance in the first frequency 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 can be made close to the reference impedance. Thereby, the matching loss can be reduced, and a surface acoustic wave filter 10 with low loss and miniaturization can be provided.

[0130] Further, it is also possible to satisfy Equation 2 when 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) other than the parallel arm resonator 15 is set as P A .

[0131] (P SA - P PA ) / P A > BWS / f0S (Equation 2)

[0132] If the capacitive region of the parallel-arm resonator 15 is located in the first frequency band, there is a tendency for the capacitive component of the passband of the surface acoustic wave filter 10 to increase, thereby narrowing the passband of the surface acoustic wave filter 10. In contrast, Equation 2 shows that the difference between the resonance frequencies of a plurality of parallel-arm resonators other than the parallel-arm resonator 15 and the resonance frequencies of one or more series-arm resonators is greater than the frequency range BWS of the first frequency band. Therefore, even if the passband of the surface acoustic wave filter 10 is narrowed due to the capacitive component of the parallel-arm resonator 15, the passband can achieve low loss while ensuring the first frequency band.

[0133] Next, a case where the first parallel-arm resonator (parallel-arm resonator 15) is a surface acoustic wave resonator and a case where the first parallel-arm resonator (parallel-arm resonator 15) is a capacitive element are compared. Figure 7 It is a graph showing the transmission characteristics in the case where the parallel-arm resonator 15 of the surface acoustic wave filter 10 according to the embodiment is a surface acoustic wave resonator and in the case where the parallel-arm resonator 15 is a capacitive element.

[0134] As shown in this figure, compared with the case where the parallel-arm resonator 15 is a capacitive element, in the case where the parallel-arm resonator 15 is a surface acoustic wave resonator, the attenuation amount in the attenuation band on the lower frequency side than the passband is larger. 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 a surface acoustic wave resonator having a strongly frequency-dependent impedance characteristic, the attenuation characteristic of the surface acoustic wave filter 10 can be improved.

[0135] [4. Resonance characteristics and transmission characteristics of the surface acoustic wave filter 10A according to the modified example]

[0136] In the surface acoustic 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 frequency band, the surface acoustic wave filter 10 is made low-loss and miniaturized. In contrast, in the surface acoustic wave filter 10A according to the modified example, low loss and miniaturization are achieved by overlapping the capacitive region on the lower frequency side than the resonance frequency frs15 of the parallel-arm resonator 15 with the first frequency band.

[0137] The surface acoustic wave filter 10A according to this modified example includes input / output terminals 111 and 112, series-arm resonators 11, 12, and 13, parallel-arm resonators 14 and 15, a longitudinally coupled resonator 16, and an inductor 31. That is, the circuit structure of the surface acoustic wave filter 10A according to the modified example is the same as the circuit structure of the surface acoustic wave filter 10 according to the embodiment. Compared with the surface acoustic wave filter 10 according to the embodiment, the positions of the resonance frequency and the anti-resonance frequency of the parallel-arm resonator 15 are different in the surface acoustic wave filter 10A according to this modified example.

[0138] Figure 8 It is a diagram showing the relationship between the first frequency band of the surface acoustic wave filter 10A related to the modified 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 this diagram, in the surface acoustic wave filter 10A related to the modified example, the resonance frequency frs15 of the parallel arm resonator 15 is located on the higher frequency side than the first frequency band. In addition, the resonance frequencies of the series arm resonators 11 to 13 and the anti-resonance frequency of the parallel arm resonator 14 are within the frequency range of the first frequency band.

[0139] In addition, the anti-resonance frequencies of multiple parallel arm resonators other than the parallel arm resonator 15 (in the embodiment, only the parallel arm resonator 14) and the resonance frequencies of one or more series arm resonators (in the embodiment, the series arm resonators 11 to 13) may not all be within the frequency range of the first frequency band. The multiple parallel arm resonators other than the parallel arm resonator 15 and the one or more series arm resonators only need to be resonators that contribute to the passband of the surface acoustic wave filter 10A. Specifically, as long as at least a part of the frequency range from the resonance frequency to the anti-resonance frequency, that is, the resonance band, overlaps with the first frequency band.

[0140] Thus, the surface acoustic wave filter 10A related to the modified example constitutes a band-pass filter having a passband including the first frequency band. In the surface acoustic wave filter 10A, the impedance in the passband of the parallel arm resonator 15 is capacitive ( Figure 8 C property in ), so that the impedance in the passband of the surface acoustic wave filter 10A can be reduced. Therefore, compared with the surface acoustic wave filter related to the comparative example, the impedance in the passband can be made closer to the reference impedance, and the insertion loss caused by the matching loss can be reduced.

[0141] In addition, the impedance of the passband of the surface acoustic wave filter 10A related to the modified example changes in the same way as the impedance states A, B, and C shown in Figure 5

[0142] According to the elastic wave filter 10A according to this modification example, by setting the resonance frequency frs15 of the parallel arm resonator 15 connected closest to the inductor 31 among the plurality of parallel arm resonators to a position on the higher frequency side than the first frequency band, the impedance of the parallel arm resonator 15 in the first frequency band can be made capacitive. That is, by setting the anti-resonance frequency fas15 and the resonance frequency frs15 of the parallel arm resonator 15 connected closest to the inductor 31 among the plurality of parallel arm resonators outside the frequency range of the first frequency band, the impedance of the parallel arm resonator 15 in the first frequency band can be made capacitive. Accordingly, the impedance of the elastic wave filter 10A in the first frequency 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 can be made close to the reference impedance. Thereby, the matching loss can be reduced, and the elastic wave filter 10A with low loss and miniaturization can be provided.

[0143] Next, in the elastic wave filter 10A according to the modification example, the resonance frequency frs15 of the parallel arm resonator 15 being located on the higher frequency side than the first frequency band is expressed using the electrode finger pitch (half of the wavelength λ).

[0144] Let the frequency range of the first frequency band be BWS, the center frequency of the first frequency band be f0S, the average value of the electrode finger pitches of the IDT electrodes of the plurality of series arm resonators (in this embodiment, the series arm resonators 11 to 13) be P SA , and the electrode finger pitch of the IDT electrode of the parallel arm resonator 15 be P1. As Figure 8 shown, the average value frsA of the resonance frequencies of the plurality of series arm resonators (in this embodiment, the series arm resonators 11 to 13) is made to be substantially the same as the center frequency f0S. Accordingly, the resonance frequency frs15 of the parallel arm resonator 15 being located on the higher frequency side than the first frequency band is equivalent to the resonance frequency frs15 being shifted by BWS / 2 or more to the higher frequency side compared to the average value frsA. If this is expressed using the electrode finger pitches of the parallel arm resonator 15 and the series arm resonators 11 to 13, it becomes Equation 3.

[0145] P1 ≤ P SA ×{1 - (BWS / f0S) / 2} (Equation 3)

[0146] In Equation 3, it is shown that the electrode finger pitch P1 of the parallel arm resonator 15 is smaller than the average value P of the electrode finger pitches of the IDT electrodes of the plurality of series arm resonators SA , by at least the amount corresponding to the electrode finger pitch equivalent to half of the relative bandwidth (BWS / f0S) / 2 of the first frequency band.

[0147] For example, a case is shown where the first frequency band is a combined frequency band of the downlink operating frequency band (746 to 756 MHz) of Band B13 for LTE and the downlink operating frequency band (758 to 768 MHz) of Band B14 for LTE. In this case, BWS = 22 MHz and f0S = 757 MHz. Further, according to Table 1, P SA = 2.4905 μm (= 4.981 μm / 2: average electrode finger pitch of the series arm resonators 11 to 13).

[0148] If the above BWS, f0S, and P SA are substituted into Equation 3, the right side of Equation 3 becomes: P SA × {1 - (BWS / f0S) / 2} = 2.454 μm. That is, the condition is P1 ≤ 2.454 μm.

[0149] Accordingly, by making the electrode finger pitch P1 of the shunt arm resonator 15 smaller than the average electrode finger pitch P SA of the series arm resonators by an amount corresponding to half of the frequency range BWS equivalent to the first frequency band (= P SA × (BWS / f0S) / 2), the resonance frequency frs15 of the shunt arm resonator 15 can be positioned on the higher frequency side than the first frequency band. Thus, the impedance in the first frequency band of the SAW filter 10A can be shifted to a low impedance by the shunt capacitance component of the shunt arm resonator 15 and the series inductance component of the inductor 31, and it can be made close to the reference impedance. Thereby, the matching loss can be reduced, and a low-loss and miniaturized SAW filter 10A can be provided.

[0150] [5. Circuit Structure of Multiplexer]

[0151] Next, the multiplexer 1 including the SAW filter 10 according to the embodiment will be described. Figure 9 is a circuit structure diagram of the multiplexer 1 according to the embodiment. As shown in this figure, the multiplexer 1 includes a SAW filter 10, a filter 20, a common terminal 100, and input / output terminals 110 and 120.

[0152] The common terminal 100 is connected to an antenna, for example.

[0153] The SAW filter 10 is the SAW filter 10 according to the embodiment and has a passband including the first frequency band. One end of the SAW filter 10 is connected to the common terminal 100, and the other end is connected to the input / output terminal 110.

[0154] The filter 20 has a passband including the second frequency 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. In addition, the structure of the filter 20 is not particularly limited. For example, it may be a surface acoustic wave filter or an LC filter including an inductor and a capacitor.

[0155] According to the above structure, since the surface acoustic wave filter 10 with low loss and miniaturization is provided, the multiplexer 1 can achieve low loss and miniaturization.

[0156] In addition, preferably, the passband of the filter 20 is located on the lower frequency side than the passband of the surface acoustic wave filter 10. Accordingly, 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, and thus the insertion loss of the passband of the filter 20 can be reduced.

[0157] In addition, in the multiplexer 1, the surface acoustic wave filter 10A according to the modified example may be arranged instead of the surface acoustic wave filter 10. In this case, preferably, the passband of the filter 20 is located on the higher frequency side than the passband of the surface acoustic wave filter 10A. Accordingly, the anti-resonance frequency fas15 of the shunt arm resonator 15 of the surface acoustic wave filter 10A can overlap with the passband of the filter 20, and thus the insertion loss of the passband of the filter 20 can be reduced.

[0158] In addition, in the multiplexer 1 according to the present embodiment, a filter other than the surface acoustic wave filter 10 and the filter 20 may be connected to the common terminal 100. In addition, 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. In addition, the multiplexer 1 may not include the common terminal 100, the input / output terminals 110 and 120.

[0159] [6. Effects, etc.]

[0160] As described above, the surface acoustic wave filter 10 according to the present embodiment has a passband including the first frequency band, includes the input / output terminals 111 and 112, one or more series arm resonators arranged in the 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 serially arranged in the series arm path. The resonance frequency frs15 and the anti-resonance frequency fas15 of the shunt arm resonator 15 connected closest to the inductor 31 among the plurality of shunt arm resonators are outside the frequency range of the first frequency band.

[0161] Accordingly, by setting the anti-resonant frequency fas15 and the resonant frequency frs15 of the parallel-arm resonator 15 outside the frequency range of the first frequency band, the impedance of the parallel-arm resonator 15 in the first frequency band can be made capacitive. Thereby, the impedance in the first frequency 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 close to the reference impedance. Thereby, a surface acoustic wave filter 10 with low loss and miniaturization can be provided.

[0162] In addition, for example, in the surface acoustic wave filter 10, the anti-resonant frequency fas15 of the parallel-arm resonator 15 is located at a position on the lower frequency side than the first frequency band.

[0163] Accordingly, by setting the anti-resonant frequency fas15 of the parallel-arm resonator 15 at a position on the lower frequency side than the first frequency band, the impedance of the parallel-arm resonator 15 in the first frequency band can be made capacitive.

[0164] In addition, 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 at a position on the higher frequency side than the first frequency band.

[0165] Accordingly, by setting the resonant frequency frs15 of the parallel-arm resonator 15 at a position on the higher frequency side than the first frequency band, the impedance of the parallel-arm resonator 15 in the first frequency band can be made capacitive.

[0166] In addition, for example, in the surface acoustic wave filters 10 and 10A, the anti-resonant frequencies of the plurality of parallel-arm resonators other than the parallel-arm resonator 15 are within the frequency range of the first frequency band.

[0167] Accordingly, the surface acoustic wave filters 10 and 10A constitute a ladder-type band-pass filter having a passband including the first frequency band.

[0168] In addition, in the surface acoustic wave filter 10 according to the present embodiment, the plurality of parallel-arm resonators each have an IDT electrode. When the frequency range of the first frequency band is set to BWS, the center frequency of the first frequency band is set to f0S, the electrode finger pitch of the IDT electrode of the parallel-arm resonator 15 is set to P1, and the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel-arm resonators other than the parallel-arm resonator 15 is set to P PA the case where, P1≥P PA satisfies the relational expression of ×{1+(BWS / f0S) / 2}.

[0169] Accordingly, by making the electrode finger pitch P1 of the parallel-arm resonator 15 larger than the average value P of the electrode finger pitches of the parallel-arm resonators other than the parallel-arm resonator 15PA , a quantity corresponding to an electrode finger pitch greater than half of the frequency range BWS of the first frequency band is used to make the anti-resonant frequency fas15 of the parallel arm resonator 15 located on the lower frequency side than the first frequency band. Thereby, the impedance in the first frequency 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 can be made closer to the reference impedance. Thereby, a surface acoustic wave filter 10 with low loss and miniaturization can be provided.

[0170] In addition, in the surface acoustic wave filter 10A according to the modified example of the embodiment, one or more series arm resonators and a plurality of parallel arm resonators each have an IDT electrode. When the frequency range of the first frequency band is set as BWS, the center frequency of the first frequency band is set as f0S, the electrode finger pitch of the IDT electrode of the parallel arm resonator 15 is set as P1, and the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators is set as P SA in the case of, P1 ≤ P SA ×{1 - (BWS / f0S) / 2} relationship.

[0171] Accordingly, by making the electrode finger pitch P1 of the parallel arm resonator 15 smaller than the average value P of the electrode finger pitches of the series arm resonators SA , a quantity corresponding to an electrode finger pitch smaller than half of the frequency range BWS of the first frequency band, the resonant frequency frs15 of the parallel arm resonator 15 can be located on the higher frequency side than the first frequency band. Thereby, the impedance in the first frequency 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 can be made closer to the reference impedance. Thereby, a surface acoustic wave filter 10A with low loss and miniaturization can be provided.

[0172] In addition, for example, in the surface acoustic wave filters 10 and 10A, when the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators other than the parallel arm resonator 15 is set as P PA , the average value of the electrode finger pitches of the IDT electrodes of each of the one or more series arm resonators is set as P SA , and the average value of the electrode finger pitches of the IDT electrodes of each of the plurality of parallel arm resonators other than the parallel arm resonator 15 and the one or more series arm resonators is set as P A in the case of, (P SA - P PA ) / P A >BWS / f0S relationship.

[0173] If the capacitive region of the parallel-arm resonator 15 is located in the first frequency band, there is a tendency for the capacitive component of the passband of the surface acoustic wave filter 10 to increase, thereby narrowing the passband of the surface acoustic wave filter 10. Accordingly, even if the passband of the surface acoustic wave filter 10 is narrowed due to the capacitive component of the parallel-arm resonator 15, the passband can achieve low loss while ensuring the first frequency band.

[0174] In addition, 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.

[0175] Accordingly, at least any one of the pass characteristics and the attenuation characteristics can be improved.

[0176] In addition, for example, in the surface acoustic wave filters 10 and 10A, the first frequency band includes a plurality of frequency bands standardized by 3GPP (registered trademark).

[0177] Accordingly, the surface acoustic wave filters 10 and 10A can be configured as filters having passbands at a plurality of frequency bands that are close to each other.

[0178] In addition, for example, in the surface acoustic wave filters 10 and 10A, the first frequency band includes a downlink operation frequency band of band B13 for LTE or band n13 for 5G-NR, and a downlink operation frequency band of band B14 for LTE or band n14 for 5G-NR.

[0179] Accordingly, the surface acoustic wave filters 10 and 10A can be configured as band-pass filters having passbands at the B13 downlink operation frequency band and the B14 downlink operation frequency band that are close to each other in frequency.

[0180] (Other embodiments)

[0181] As described above, embodiments and modified examples have been described for the surface acoustic wave filter according to the present invention. However, the present invention is not limited to the above embodiments and modified examples. Modified examples obtained by making various modifications conceived by those skilled in the art to the above embodiments and modified examples within the scope not 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.

[0182] In addition, for example, in the surface acoustic wave filter according to the above embodiments and modified examples, matching elements such as inductors and capacitors and a switch circuit may be connected between the respective components.

[0183] In addition, for example, the reflection characteristics can be measured by bringing an RF probe into contact with two input / output electrodes of the surface acoustic wave resonator, and thereby the resonance frequency and the anti-resonance frequency shown in the above embodiments and modified examples can be derived.

[0184] The features of the surface acoustic wave filter described based on the above-described embodiments and modifications are shown below.

[0185] <1>

[0186] A surface acoustic wave filter having a passband including a first frequency band, the surface acoustic wave filter comprising:

[0187] A first input / output terminal and a second input / output terminal;

[0188] One or more series-arm resonators disposed in a series-arm path connecting the first input / output terminal and the second input / output terminal;

[0189] A plurality of shunt-arm resonators connected between the series-arm path and ground; and

[0190] An inductor connected to the first input / output terminal and serially disposed in the series-arm path,

[0191] The resonance frequency and the anti-resonance frequency of a first shunt-arm resonator that is connected closest to the inductor among the plurality of shunt-arm resonators are outside the frequency range of the first frequency band.

[0192] <2>

[0193] In the surface acoustic wave filter according to <1>, the anti-resonance frequency of the first shunt-arm resonator is located on the lower frequency side than the first frequency band.

[0194] <3>

[0195] In the surface acoustic wave filter according to <1>, the resonance frequency of the first shunt-arm resonator is located on the higher frequency side than the first frequency band.

[0196] <4>

[0197] In the surface acoustic wave filter according to <2> or <3>, the anti-resonance frequency of each of the plurality of shunt-arm resonators other than the first shunt-arm resonator is within the frequency range of the first frequency band.

[0198] <5>

[0199] A surface acoustic wave filter having a passband including a first frequency band, the surface acoustic wave filter comprising:

[0200] A first input / output terminal and a second input / output terminal;

[0201] One or more series-arm resonators disposed in a series-arm path connecting the first input / output terminal and the second input / output terminal;

[0202] A plurality of parallel-arm resonators, connected between the series-arm path and ground; and

[0203] An inductor, serially disposed between the first input / output terminal and the one or more series-arm resonators,

[0204] The plurality of parallel-arm resonators each have an IDT electrode,

[0205] When the frequency range of the first frequency band is set as BWS, the center frequency of the first frequency band is set as f0S, the electrode finger pitch of the IDT electrode of the first parallel-arm resonator that is connected closest to the inductor among the plurality of parallel-arm resonators is set as P1, and the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel-arm resonators other than the first parallel-arm resonator is set as P PA in the case of,

[0206] the relation P1≥P PA ×{1+(BWS / f0S) / 2} is satisfied.

[0207] <6>

[0208] An elastic wave filter having a passband including a first frequency band, the elastic wave filter comprising:

[0209] A first input / output terminal and a second input / output terminal;

[0210] One or more series-arm resonators, disposed in a series-arm path connecting the first input / output terminal and the second input / output terminal;

[0211] A plurality of parallel-arm resonators, connected between the series-arm path and ground; and

[0212] An inductor, serially disposed between the first input / output terminal and the one or more series-arm resonators,

[0213] The one or more series-arm resonators and the plurality of parallel-arm resonators each have an IDT electrode,

[0214] When the frequency range of the first frequency band is set as BWS, the center frequency of the first frequency band is set as f0S, the electrode finger pitch of the IDT electrode of the first parallel-arm resonator that is connected closest to the inductor among the plurality of parallel-arm resonators is set as P1, and the average value of the electrode finger pitches of the IDT electrodes of the one or more series-arm resonators is set as P SA in the case of,

[0215] the relation P1≤P SAThe relational expression of ×{1 - (BWS / f0S) / 2}.

[0216] <7>

[0217] For the surface acoustic wave filter according to <5> or <6>, when setting the frequency range of the first frequency band as BWS, the center frequency of the first frequency band as f0S, and the average value of the electrode finger pitch of the IDT electrodes of each of the plurality of parallel arm resonators other than the first parallel arm resonator as P PA , and setting the average value of the electrode finger pitch of the IDT electrodes of each of the one or more series arm resonators as P SA , and setting the average value of the electrode finger pitch of the IDT electrodes of each of the plurality of parallel arm resonators other than the first parallel arm resonator and the one or more series arm resonators as P A , in this case

[0218] satisfy the relational expression of (P SA - P PA ) / P A > BWS / f0S.

[0219] <8>

[0220] For the surface acoustic wave filter according to any one of <1> to <7>, the surface acoustic wave filter further includes a longitudinally coupled resonator connected between the second input / output terminal and the inductor.

[0221] <9>

[0222] For the surface acoustic wave filter according to any one of <1> to <8>, the first frequency band includes a plurality of frequency bands standardized by 3GPP (registered trademark).

[0223] <10>

[0224] For the surface acoustic wave filter according to <9>, the first frequency band includes a downlink operation frequency band of band B13 for LTE or band n13 for 5G-NR, and a downlink operation frequency band of band B14 for LTE or band n14 for 5G-NR.

[0225] Industrial applicability

[0226] As a low-loss surface acoustic wave filter that can be applied to a multi-band frequency standard, the present invention can be widely used in communication devices such as mobile phones.

Claims

1. An elastic wave filter having a passband including a first frequency band, the elastic wave filter comprising: A first input / output terminal and a second input / output terminal; One or more series arm resonators are 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 paths and ground; and an inductor connected to the first input / output terminal and arranged in series with the series arm path, A resonant frequency and an anti-resonant frequency of a first parallel arm resonator connected closest to the inductor among the plurality of parallel arm resonators are outside a frequency range of the first frequency band.

2. The elastic wave filter according to claim 1, wherein: The antiresonance frequency of the first parallel arm resonator is located at a lower frequency side than the first frequency band.

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

4. The elastic wave filter according to claim 2 or 3, wherein: The anti-resonance frequencies of the plurality of parallel arm resonators except the first parallel arm resonator are respectively within a frequency range of the first frequency band.

5. An elastic wave filter having a passband including a first frequency band, the elastic wave filter comprising: A first input / output terminal and a second input / output terminal; One or more series arm resonators are 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 paths and ground; and an inductor, arranged in series between the first input / output terminal and the one or more series arm resonators, The plurality of parallel arm resonators respectively have interdigital transducer IDT electrodes, When the frequency range of the first frequency band is set to BWS, the center frequency of the first frequency band is set to f0S, the electrode finger pitch of the IDT electrode of the first parallel arm resonator connected closest to the inductor among the plurality of parallel arm resonators is set to P1, and the average value of the electrode finger pitch of the IDT electrode of each of the plurality of parallel arm resonators except the first parallel arm resonator is set to P PA In the case of Satisfy P1≥P PA ×{1+(BWS / f0S) / 2}.

6. An elastic wave filter having a passband including a first frequency band, the elastic wave filter comprising: A first input / output terminal and a second input / output terminal; One or more series arm resonators are 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 paths and ground; and an inductor, arranged in series between the first input / output terminal and the one or more series arm resonators, The one or more series arm resonators and the plurality of parallel arm resonators each have an IDT electrode. The frequency range of the first frequency band is set to BWS, the center frequency of the first frequency band is set to f0S, the electrode finger pitch of the IDT electrode of the first parallel arm resonator connected closest to the inductor among the plurality of parallel arm resonators is set to P1, and the average value of the electrode finger pitch of the IDT electrode of each of the one or more series arm resonators is set to P SA In the case of Satisfy P1≤P SA ×{1-(BWS / f0S) / 2}.

7. The elastic wave filter according to claim 5 or 6, wherein: When the frequency range of the first frequency band is set to BWS, the center frequency of the first frequency band is set to f0S, and the average value of the electrode finger pitch of the IDT electrodes of the plurality of parallel arm resonators except the first parallel arm resonator is set to P PA , the average value of the electrode finger pitch of the IDT electrode of each of the one or more series arm resonators is set to P SA , and the average value of the electrode finger pitches of the IDT electrodes of the plurality of parallel arm resonators other than the first parallel arm resonator and the one or more series arm resonators is set to P A In the case of Satisfaction (P SA -P PA ) / P A >BWS / f0S relationship.

8. The elastic wave filter according to any one of claims 1 to 7, wherein: The elastic wave filter further includes a longitudinally coupled resonator connected between the second input / output terminal and the inductor.

9. The elastic wave filter according to any one of claims 1 to 8, wherein: The first frequency band includes a plurality of frequency bands standardized by 3GPP which is a registered trademark.

10. The elastic wave filter according to claim 9, wherein: The first frequency band includes a downlink operation frequency band of frequency band B13 for LTE or frequency band n13 for 5G-NR, and a downlink operation frequency band of frequency band B14 for LTE or frequency band n14 for 5G-NR.

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