Acoustic wave filter, filter circuit and high frequency module

Abstract

To provide a small-sized acoustic wave filter which secures low loss property.SOLUTION: An acoustic wave filter 1 includes a series arm resonator 14 arranged on a series arm path connecting input / output terminals 110 and 120, and a parallel arm resonator 20 connected between the series arm path and a ground, wherein the series arm resonator 14 is a first acoustic wave resonator, the parallel arm resonator 20 includes a parallel arm resonator 24 and an inductor 34 connected in series between the series arm path and the ground, the series arm resonator 14 and the parallel arm resonator 24 are formed on the same piezoelectric substrate 70, a resonance frequency frp 20 of the parallel arm resonator 20 is equal to or less than a low frequency end of a pass band of the acoustic wave filter 1, an antiresonance frequency fap 20 of the parallel arm resonator 20 is equal to or more than a high frequency end of the pass bad, and a frequency difference Δfa between the antiresonance frequency fap 20 and the high frequency end of the pass band is smaller than a frequency difference Δfr between the resonance frequency frp 20 and the low frequency end of the pass band.SELECTED DRAWING: Figure 3A

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave filter, a filter circuit, and a high-frequency module. [Background technology]

[0002] Patent Document 1 discloses a filter module including a bandpass filter and a matching resonator. The passband of the filter is included in the range between the resonant frequency and anti-resonant frequency of the matching resonator, so that the impedance of the passband of the filter module can be made inductive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-088675 Summary of the Invention [Problem to be solved by the invention]

[0004] In the filter module disclosed in Patent Document 1, the matching resonator can make the impedance in the passband inductive, thereby reducing matching loss when connected to an external circuit with capacitive impedance. However, there are cases where the insertion loss of the matching resonator itself cannot be reduced, making it impossible to ensure low loss for the filter module. Furthermore, the addition of the matching resonator increases the size of the filter module.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a compact acoustic wave filter, filter circuit, and high-frequency module that ensure low loss. [Means for solving the problem]

[0006] In order to achieve the above object, an acoustic wave filter according to one aspect of the present invention is a band-pass acoustic wave filter including: a first series arm resonator arranged in a series arm path connecting a first input / output terminal and a second input / output terminal; and a first parallel arm resonator connected between the series arm path and ground, wherein the first series arm resonator includes a first acoustic wave resonator, and the first parallel arm resonator includes a second acoustic wave resonator and a first inductor connected in series between the series arm path and ground, wherein the first acoustic wave resonator and the second acoustic wave resonator are formed on a same piezoelectric substrate, wherein a first resonance frequency of the first parallel arm resonator is equal to or lower than a low-frequency end of a pass band of the acoustic wave filter, and a first anti-resonance frequency of the first parallel arm resonator is equal to or higher than a high-frequency end of the pass band, and a frequency difference between the first anti-resonance frequency and the high-frequency end of the pass band is smaller than a frequency difference between the first resonance frequency and the low-frequency end of the pass band.

[0007] Furthermore, a filter circuit according to one aspect of the present invention includes the above-described acoustic wave filter, a first band-pass filter, and a first switch circuit having a common terminal, a first selection terminal, and a second selection terminal, and switching between a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal, wherein the acoustic wave filter has a first parallel arm resonator and an acoustic wave filter unit, and the first filter has the first parallel arm resonator and the first filter unit, wherein the first parallel arm resonator is connected to the common terminal, the acoustic wave filter unit is connected to the first selection terminal, and the first filter unit is connected to the second selection terminal, a first resonant frequency is equal to or lower than a low-frequency end of a pass band of the acoustic wave filter and a lower-frequency end of the low-frequency end of the pass band of the first filter, and a first anti-resonant frequency is equal to or higher than a high-frequency end of a pass band of the acoustic wave filter and a higher-frequency end of the high-frequency end of the pass band of the first filter.

[0008] A high-frequency module according to one aspect of the present invention includes the above acoustic wave filter and a low-noise amplifier having an input terminal connected to the first input / output terminal. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a compact acoustic wave filter, a filter circuit, and a high-frequency module that ensure low loss. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit configuration diagram of an acoustic wave filter and a high-frequency module according to an embodiment of the present invention; [Figure 2A] 1A and 1B are a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. [Figure 2B] FIG. 4 is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. [Figure 2C] FIG. 10 is a cross-sectional view schematically illustrating a third example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. [Figure 3A] 4 is a graph showing pass characteristics of a band near the pass band of an acoustic wave filter according to an embodiment and impedance characteristics of a first parallel arm resonator. [Figure 3B] 10 is a graph showing the wide-band impedance characteristics of a first parallel arm resonator of an acoustic wave filter according to an embodiment. [Figure 4] 1 is an admittance chart illustrating impedance characteristics of an acoustic wave filter according to an embodiment. [Figure 5] FIG. 10 is a circuit configuration diagram of an acoustic wave filter according to a first modification of an embodiment. [Figure 6A] FIG. 10 is a circuit configuration diagram of a filter circuit and a high-frequency module according to a second modification of the embodiment. [Figure 6B] 10 is a diagram schematically illustrating the pass characteristics of each filter constituting the filter circuit according to the second modification of the embodiment and the impedance characteristics of a first parallel arm resonator. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangements, and connection forms 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 that are not recited in independent claims will be described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0012] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0013] In the circuit configurations disclosed herein, "connected" includes not only direct connection by connection terminals and / or wiring conductors, but also electrical connection via matching elements or switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0014] In the present invention, a "terminal" refers to a point where a conductor within an element terminates. Note that a terminal is not limited to a single point, but may be any point (node) on the conductor between elements or the entire conductor, provided that the impedance of the conductor between elements is sufficiently low.

[0015] Furthermore, in the circuit element arrangement of the present disclosure, "circuit element A is arranged in series on path B" means that the signal input terminal and signal output terminal of circuit element A are connected to two wirings that form at least a part of path B, respectively. At least one of the two wirings may be an electrode or a terminal.

[0016] In the following figures, the x-axis and y-axis are axes that are perpendicular to each other on a plane parallel to the main surface of the module substrate. Specifically, if the module substrate has a rectangular shape in a plan view, the x-axis is parallel to a first side of the module substrate, and the y-axis is parallel to a second side of the module substrate that is perpendicular to the first side. The z-axis is an axis perpendicular to the main surface of the module substrate, with its positive direction indicating the upward direction and its negative direction indicating the downward direction.

[0017] Furthermore, 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 also include substantially equivalent ranges, for example, including an error of a few percent.

[0018] Furthermore, in the component placement of this invention, "planar view of the module substrate" means viewing an object by orthogonally projecting it onto the xy plane from the positive side of the z axis. "A overlaps with B in planar view" means that at least a portion of the area of A orthogonally projected onto the xy plane overlaps with at least a portion of the area of B orthogonally projected onto the xy plane. Furthermore, "A is placed between B and C" means that at least one of multiple line segments connecting any point in B and any point in C passes through A.

[0019] In the component placement of the present invention, "components are placed on a substrate" includes components being placed on the main surface of a substrate and components being placed within a substrate. "Components are placed on the main surface of a substrate" includes components being placed in contact with the main surface of a substrate, as well as components being placed above the main surface without contacting the main surface (for example, components being stacked on top of other components placed in contact with the main surface). "Components are placed on the main surface of a substrate" may also include components being placed in recesses formed in the main surface. "Components are placed within a substrate" includes components being encapsulated within a module substrate, as well as components being entirely placed between the two main surfaces of a substrate but partially not covered by the substrate, and components being only partially placed within the substrate.

[0020] In the following embodiments, the passband of a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of insertion loss within the passband.

[0021] An elastic wave resonator is defined as any of the following: (1) a resonant circuit (a parallel connection circuit of an elastic wave resonator and a circuit (or circuit element)) consisting of an elastic wave resonator and a circuit (or circuit element) connected in parallel to the elastic wave resonator; (2) a resonant circuit (a series connection circuit of an elastic wave resonator and a circuit (or circuit element)) consisting of an elastic wave resonator and a circuit (or circuit element) connected to only one of the two input / output terminals of the elastic wave resonator, where the connection node connecting the elastic wave resonator and the circuit (or circuit element) is not connected to other circuits (and other circuit elements) or ground; (3) a resonant circuit (a parallel connection circuit of split resonators) consisting of multiple elastic wave resonators connected in parallel; and (4) a resonant circuit (series connection circuit of split resonators) consisting of multiple elastic wave resonators connected in series, where the connection node connecting the multiple elastic wave resonators is not connected to circuits (and circuit elements) other than the multiple elastic wave resonators or ground.

[0022] In addition, in the embodiments of the present disclosure, the resonance bandwidth refers to the frequency difference between the antiresonance frequency and the resonance frequency of an acoustic wave resonator.

[0023] The resonant frequency and anti-resonant frequency shown in the above embodiments and modifications are derived, for example, by contacting an RF probe with two input and output electrodes of an acoustic wave resonator or acoustic wave oscillator when the acoustic wave resonator or acoustic wave oscillator is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0024] Furthermore, in the present disclosure, the term "band" refers to at least one of an uplink operating band and a downlink operating band of a frequency band predefined by a standardization organization (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers)), etc., for a communication system built using a radio access technology (RAT). In the present embodiment, examples of the communication system that can be used include, but are not limited to, a Long Term Evolution (LTE) system, a 5th Generation (5G)-New Radio (NR) system, and a Wireless Local Area Network (WLAN) system. Note that the uplink operating band of a frequency band refers to a frequency range designated for uplink within the frequency band. Furthermore, the downlink operating band of a frequency band refers to a frequency range designated for downlink within the frequency band.

[0025] (Embodiment) [1. Circuit Configuration of Acoustic Wave Filter 1 and High-Frequency Module 100] 1 is a circuit diagram of an acoustic wave filter 1 and a high-frequency module 100 according to an embodiment. As shown in the figure, the high-frequency module 100 includes an acoustic wave filter 1, a low-noise amplifier 2, and an inductor 31.

[0026] The low-noise amplifier 2 is connected to the acoustic wave filter 1 via an inductor 31. Specifically, an input terminal 130 of the low-noise amplifier 2 is connected to an input / output terminal 120 of the acoustic wave filter 1 via the inductor 31. The low-noise amplifier 2 includes an amplifying transistor, such as a field effect transistor (FET) or a bipolar transistor. The gate (or base) of the amplifying transistor, which is an input terminal of the amplifying transistor, is connected to the input / output terminal 120 via the inductor 31, the drain (or collector) is connected to the output terminal 140, and the source (or emitter) is connected to ground via the inductor. A DC bias voltage (DC bias current) is supplied to the gate (or base) of the amplifying transistor. With the above configuration, the low-noise amplifier 2 amplifies the high-frequency signal that has passed through the acoustic wave filter 1 and outputs the amplified signal to the output terminal 140 by supplying the DC bias voltage (DC bias current) to the gate (or base). The input impedance of the low-noise amplifier 2 is capacitive and high.

[0027] The inductor 31 is a circuit element having one end connected to the input / output terminal 120 of the acoustic wave filter 1 and the other end connected to the input terminal 130 of the low-noise amplifier 2, for achieving impedance matching between the acoustic wave filter 1 and the low-noise amplifier 2. Note that the inductor 31 is not an essential component of the high-frequency module 100 according to this preferred embodiment.

[0028] The acoustic wave filter 1 is a band-pass filter and includes series arm resonators 11, 12, 13, and 14, parallel arm resonators 21, 22, 23, and 24, an inductor 34, and input / output terminals 110 and 120.

[0029] Each of the series arm resonators 11 to 14 is an acoustic wave resonator including an acoustic wave resonator, and is arranged on a series arm path connecting the input / output terminal 110 (second input / output terminal) and the input / output terminal 120 (first input / output terminal). The series arm resonator 11 constitutes one series arm resonator (acoustic wave resonator) by itself, the series arm resonator 12 constitutes one series arm resonator (acoustic wave resonator) by itself, and the series arm resonator 13 constitutes one series arm resonator (acoustic wave resonator) by itself. Each of the series arm resonators 11 to 14 is an example of a first acoustic wave resonator and also an example of a first series arm resonator.

[0030] The series arm resonators 11 to 14 are connected in this order from the input / output terminal 110: series arm resonators 11, 12, 13, and 14.

[0031] Each of the parallel arm resonators 21 to 23 is an acoustic wave resonator including an acoustic wave resonator, and is connected between the series arm path and ground. The parallel arm resonator 21 is connected between the connection point of the series arm resonators 11 and 12 and ground. The parallel arm resonator 22 is connected between the connection point of the series arm resonators 12 and 13 and ground. The parallel arm resonator 23 is connected between the connection point of the series arm resonators 13 and 14 and ground. The parallel arm resonator 21 constitutes one parallel arm resonator (acoustic wave resonator) by itself, the parallel arm resonator 22 constitutes one parallel arm resonator (acoustic wave resonator) by itself, and the parallel arm resonator 23 constitutes one parallel arm resonator (acoustic wave resonator) by itself.

[0032] The parallel arm resonator 24 and the inductor 34, which are connected in series with each other, are an acoustic wave resonator including an acoustic wave resonator and constitute the parallel arm resonator 20. The parallel arm resonator 20 is connected between the connection point of the series arm resonator 14 and the input / output terminal 120 and ground. More specifically, the parallel arm resonator 24 is connected to a series arm path connecting the input / output terminals 110 and 120, and the inductor 34 is connected to ground. The parallel arm resonator 24 is an example of a second acoustic wave resonator, the inductor 34 is an example of a first inductor, and the parallel arm resonator 20 is an example of a first parallel arm resonator.

[0033] The parallel arm resonator 20 has a resonance frequency frp20 (first resonance frequency) and an anti-resonance frequency fap20 (first anti-resonance frequency). The parallel arm resonator 24 has a resonance frequency frp24 and an anti-resonance frequency fap24. By connecting the inductor 34 in series to the parallel arm resonator 24, the resonance frequency frp20 of the parallel arm resonator 20 shifts to the lower frequency side with respect to the resonance frequency frp24 of the parallel arm resonator 24. In other words, by connecting the inductor 34 in series to the parallel arm resonator 24, the resonance bandwidth (fap20-frp20) of the parallel arm resonator 20 becomes wider than the resonance bandwidth (fap24-frp24) of the parallel arm resonator 24.

[0034] The series arm resonators 11 to 14 and the parallel arm resonators 21 to 24 are formed on the same piezoelectric substrate 70. This enables the acoustic wave filter 1 to be miniaturized. Note that all of the acoustic wave resonators included in the acoustic wave filter 1 do not have to be formed on the same piezoelectric substrate 70, and at least one of the series arm resonators 11 to 14 and the parallel arm resonator 24 may be formed on the same piezoelectric substrate 70. This enables the acoustic wave filter 1 to be miniaturized compared to when the acoustic wave resonators are formed on different piezoelectric substrates.

[0035] Each of the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 (elastic wave resonators) has only one elastic wave resonator. However, each of the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 may be, for example, any of (1) a resonator configured with an elastic wave resonator and a circuit including at least one of a capacitor and an inductor connected in parallel to the elastic wave resonator, (2) a resonator configured with an elastic wave resonator and a circuit including at least one of a capacitor and an inductor connected in series to the elastic wave resonator, (3) a resonator configured with multiple elastic wave resonators connected in parallel, and (4) a resonator configured with multiple elastic wave resonators connected in series.

[0036] Furthermore, acoustic wave filter 1 according to this preferred embodiment may not include other acoustic wave resonators as long as it includes at least one of series arm resonators 11 to 14 and parallel arm resonator 20. Furthermore, acoustic wave filter 1 according to this preferred embodiment may include at least one of a longitudinally coupled resonator, a capacitor, and an inductor in addition to the series arm resonators and parallel arm resonators that form a ladder filter.

[0037] [2. Structure of elastic wave resonators] Next, the structures of the acoustic wave resonators (series arm resonators and parallel arm resonators) that configure the acoustic wave filter 1 will be illustrated.

[0038] 2A is a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator that constitutes the acoustic wave filter 1 according to an embodiment. The drawings illustrate the basic structures of a plurality of acoustic wave resonators that constitute the acoustic wave filter 1. Note that the acoustic wave resonator 60 shown in FIG. 2A is intended to illustrate a typical structure of a surface acoustic wave resonator that constitutes the acoustic wave filter 1, and the number and length of electrode fingers that constitute the electrodes are not limited to this.

[0039] The acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0040] 2A(a), a pair of comb-shaped electrodes 60a and 60b facing each other is formed on a piezoelectric substrate 50. The comb-shaped electrode 60a is composed of a plurality of parallel electrode fingers 61a and a busbar electrode 62a connecting the plurality of electrode fingers 61a. The comb-shaped electrode 60b is composed of a plurality of parallel electrode fingers 61b and a busbar electrode 62b connecting the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction perpendicular to the acoustic wave propagation direction (X-axis direction).

[0041] The IDT electrode 54, which is composed of the electrode fingers 61a and 61b and the bus bar electrodes 62a and 62b, has a laminated structure of an adhesive layer 540 and a main electrode layer 542, as shown in FIG. 2A(b).

[0042] The adhesion layer 540 is a layer for improving adhesion between the piezoelectric substrate 50 and the main electrode layer 542, and is made of, for example, Ti. The main electrode layer 542 is made of, for example, Al containing 1% Cu. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film whose main component is silicon dioxide.

[0043] The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to those described above. Furthermore, the IDT electrode 54 does not have to have the laminated structure described above. The IDT electrode 54 may be made of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above metals or alloys. Furthermore, the protective layer 55 does not necessarily have to be formed.

[0044] Next, the layered structure of the piezoelectric substrate 50 will be described.

[0045] 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 stacked in this order. The piezoelectric substrate 50 is an example of the piezoelectric substrate 70 of the acoustic wave filter 1.

[0046] The piezoelectric film 53 is made of, for example, a θ° Y-cut X-propagation LiTaO3 piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramics cut along a plane whose normal is an axis rotated θ° from the Y axis around the X axis, and through which surface acoustic waves propagate in the X-axis direction). The material and cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected depending on the required specifications of each filter.

[0047] 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 also a substrate in which the acoustic velocity of bulk waves in the high acoustic velocity support substrate 51 is faster than that of acoustic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53, and functions to confine the surface acoustic waves to the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated, preventing leakage below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include 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, diamond-like carbon (DLC), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes an aluminum compound containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0048] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity film 52 is slower than that of the bulk waves propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. This structure and the property of the acoustic waves that energy is concentrated in a medium with an essentially low acoustic velocity suppress leakage of surface acoustic wave energy out of the piezoelectric film 53. The low acoustic velocity film 52 can be made of, for example, a dielectric such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound in which fluorine, carbon, or boron is added to silicon oxide, or a material containing any of the above materials as a main component.

[0049] The above-described laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and anti-resonant frequency compared to a conventional structure using a single-layer piezoelectric substrate. In other words, an acoustic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the acoustic wave resonator.

[0050] The high acoustic velocity support substrate 51 may have a laminated structure of a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk waves is faster than that of the surface waves and boundary waves, etc., that propagate through the piezoelectric film 53. In this case, the high acoustic velocity film may be made of the same material as the high acoustic velocity support substrate 51. The support substrate may be made of, 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; dielectric materials such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials containing any of the above materials as a main component.

[0051] In this specification, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be in a single crystal, polycrystalline, or amorphous state, or a mixture of these.

[0052] 2B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator constituting the acoustic wave filter 1 according to the embodiment. In the acoustic wave resonator 60 illustrated in FIG. 2A, the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 made of a single piezoelectric layer, as illustrated in FIG. 2B.

[0053] The piezoelectric single crystal substrate 57 is made of, for example, a piezoelectric single crystal of LiNbO3. The elastic wave resonator according to this example is made up of the LiNbO3 piezoelectric single crystal substrate 57, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54. The piezoelectric single crystal substrate 57 is an example of the piezoelectric substrate 70 of the elastic wave filter 1.

[0054] The laminate structure, material, cut angle, and thickness of the piezoelectric film 53 and piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required pass characteristics of the acoustic wave filter, etc. An acoustic wave resonator using a LiTaO piezoelectric substrate having a cut angle other than the above-mentioned cut angle can also achieve the same effects as the acoustic wave resonator 60 using the piezoelectric film 53.

[0055] Alternatively, the substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are stacked in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film may be made of, for example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic. The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0056] The energy trapping layer is composed of one or more layers, and the velocity of the bulk acoustic waves propagating through at least one of the layers is greater than the velocity of the acoustic waves propagating near the piezoelectric film. For example, the energy trapping layer may 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 waves in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The support substrate may also be the high acoustic velocity layer.

[0057] The energy trapping layer may also be an acoustic impedance layer having a configuration in which low acoustic impedance layers with a relatively low acoustic impedance and high acoustic impedance layers with a relatively high acoustic impedance are alternately stacked.

[0058] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 will be described.

[0059] The wavelength of the acoustic wave resonator is defined by wavelength λ, which is the repetition period of the electrode fingers 61a or 61b constituting the IDT electrode 54 shown in FIG. 2A (b). The electrode finger pitch is half of the wavelength λ and is defined as (W+S), where W is the line width of the electrode fingers 61a and 61b constituting the interdigital transducers 60a and 60b, respectively, and S is the space width between adjacent electrode fingers 61a and 61b. The duty of the IDT electrode 54 is the line width occupancy rate of the electrode fingers 61a and 61b, which is the ratio of the line width to the sum of the line width and space width of each of the electrode fingers 61a and 61b, and is defined as W / (W+S). The overlap width of the IDT electrode 54 is the length of the overlapping electrode fingers 61a and 61b when viewed from the acoustic wave propagation direction (X-axis direction).

[0060] In the IDT electrode 54, when the interval between adjacent electrode fingers is not constant, the electrode finger pitch of the IDT electrode 54 is defined as the average electrode finger pitch of the IDT electrode 54. The average electrode finger pitch of the IDT electrode 54 is defined as Di / (Ni-1), where Ni is the total number of electrode fingers 61a, 61b included in the IDT electrode 54, and Di is the center-to-center distance between the electrode finger located at one end of the IDT electrode 54 and the electrode finger located at the other end in the acoustic wave propagation direction.

[0061] 2C is a cross-sectional view schematically illustrating a third example of an acoustic wave resonator included in the acoustic wave filter 1 according to the embodiment. Fig. 2C illustrates a bulk acoustic wave resonator as the acoustic wave resonator of the acoustic wave filter 1. As shown in the figure, the bulk acoustic wave resonator includes, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and is configured such that the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are layered in this order.

[0062] The support substrate 65 is a substrate, such as a silicon substrate, for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68. The support substrate 65 has a cavity in the region that contacts the lower electrode 66. This allows the piezoelectric layer 67 to vibrate freely. The support substrate 65 is an example of the piezoelectric substrate 70 of the acoustic wave filter 1.

[0063] 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 are made of a material such as Al containing 1% Cu.

[0064] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 is mainly composed of at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz crystal, and LiBO (lithium borate).

[0065] A bulk acoustic wave resonator having the above-described layered structure generates resonance by inducing bulk acoustic waves in the piezoelectric layer 67 when electrical energy is applied between the lower electrode 66 and the upper electrode 68. The bulk acoustic waves generated by this bulk acoustic wave resonator propagate between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. In other words, a bulk acoustic wave resonator is a resonator that utilizes bulk acoustic waves.

[0066] [3 Resonance and pass characteristics of acoustic wave filter 1] First, the basic operating principle of a ladder-type bandpass filter composed of one series arm resonator and one parallel arm resonator will be explained.

[0067] The parallel arm resonator has a resonance frequency frp and an antiresonance frequency fap (>frp), while the series arm resonator has a resonance frequency frs and an antiresonance frequency fas (>frs>frp). In series arm and parallel arm resonators having the above resonance characteristics, the antiresonance frequency fap of the parallel arm resonator and the resonance frequency frs of the series arm resonator are generally set close to each other. This results in a low-frequency stopband near the resonance frequency frp, where the impedance of the parallel arm resonator approaches zero. Furthermore, as the frequency increases, the impedance of the parallel arm resonator increases near the antiresonance frequency fap, and the impedance of the series arm resonator approaches zero near the resonance frequency frs. This results in a signal passband in the series arm signal path near the antiresonance frequency fap to the resonance frequency frs. This makes it possible to form a passband that reflects the electrode parameters and electromechanical coupling coefficient of the elastic wave resonator. Furthermore, as the frequency increases and approaches the antiresonance frequency fas, the impedance of the series arm resonator increases, resulting in a high-frequency stopband.

[0068] In addition, in each of the series arm resonators and the parallel arm resonators, the impedance of the resonators is capacitive (C-type) in the frequency band lower than the resonant frequency, and is inductive (L-type) in the frequency band higher than the resonant frequency and lower than the anti-resonant frequency. In addition, the impedance of the resonators is capacitive in the frequency band higher than the anti-resonant frequency.

[0069] When the resonant bandwidth is wider than the desired passband bandwidth, the antiresonant frequency of the parallel arm resonator may be higher than the high-frequency end of the passband, and the resonant frequency of the series arm resonator may be lower than the low-frequency end of the passband. A resonator whose resonant bandwidth, which is the frequency range from the resonant frequency to the antiresonant frequency, at least partially overlaps with the passband of the acoustic wave filter 1 is defined as a resonator that contributes to forming the passband of the acoustic wave filter 1.

[0070] Next, the impedance characteristics and pass characteristics of the acoustic wave filter 1 will be described.

[0071] 3A is a graph showing the passband characteristics of a band near the passband of the acoustic wave filter 1 according to the embodiment and the impedance characteristics of the parallel arm resonator 20. FIG. 3B is a graph showing the wide-band impedance characteristics of the parallel arm resonator 20 according to the embodiment.

[0072] 3A, the resonant frequency frp24 of the parallel arm resonator 24 is located within the pass band. Meanwhile, the resonant frequency frp20 of the parallel arm resonator 20 is equal to or lower than the low-frequency end of the pass band of the acoustic wave filter 1, and the antiresonant frequency fap20 of the parallel arm resonator 20 is equal to or higher than the high-frequency end of the pass band. Furthermore, the frequency difference Δfa between the antiresonant frequency fap20 and the high-frequency end of the pass band is smaller than the frequency difference Δfr between the resonant frequency frp20 and the low-frequency end of the pass band.

[0073] 3A, the resonant frequency of at least one of the series arm resonators 11 to 14 is located within the pass band, and the anti-resonant frequency of at least one of the parallel arm resonators 21 to 23 is located within the pass band, thereby reducing the insertion loss of the ladder-type acoustic wave filter 1.

[0074] In a ladder-type acoustic wave filter, low loss and steep pass characteristics can be achieved by positioning the resonant frequency of the series arm resonators and the anti-resonant frequency of the parallel arm resonators within the passband. Therefore, the impedance of the acoustic wave filter tends to be at least moderate in the passband. Therefore, when connecting a capacitive circuit with a capacitive input impedance, such as a low-noise amplifier 2, to an acoustic wave filter, it is possible to match both the capacitive circuit and the acoustic wave filter at the reference impedance by placing an inductive matching circuit between them.

[0075] In contrast, with the configuration of the acoustic wave filter 1 according to this embodiment, the parallel arm resonator 24, which is formed on the same piezoelectric substrate 70 as the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 that form the passband, is likely to have at least one of its resonant frequency FRP24 and antiresonant frequency FAP24 within the passband. However, by connecting the inductor 34 in series with the parallel arm resonator 24, the resonant bandwidth of the parallel arm resonator 20 is expanded, and the passband is adjusted to be located between the resonant frequency FRP20 and the antiresonant frequency FAP20 of the parallel arm resonator 20. This makes the impedance of the parallel arm resonator 20 in the passband inductive, enabling impedance matching between the capacitive circuit and the acoustic wave filter 1 without providing an inductive matching circuit between them. Furthermore, by positioning the antiresonant frequency FAP20, which has a high impedance, closer to the passband than the resonant frequency FRP20, which has a low impedance, signals in the passband can be transmitted from the input / output terminal 110 to the input / output terminal 120 with low loss. 3B, the parallel arm resonator 20 has high impedance in the DC (direct current) region. This prevents the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the acoustic wave filter 1, eliminating the need to place a DC-blocking capacitor in series in the path connecting the acoustic wave filter 1 and the input terminal of the amplifying transistor of the low-noise amplifier 2. This allows for the provision of a low-loss, compact acoustic wave filter 1 with reduced matching loss and insertion loss.

[0076] 4 is an admittance chart showing the impedance characteristics of the acoustic wave filter 1 according to the embodiment. As shown in FIG. 4(a), the passband impedance (thick solid line in FIG. 4(a)) when viewed from node B (the connection node between the series arm resonator 14 and the parallel arm resonator 20) toward the input / output terminal 110 is located near the reference impedance. In other words, the impedance of the acoustic wave filter without the parallel arm resonator 20 is located near the reference impedance. When the parallel arm resonator 20 is not added and a low-noise amplifier 2 having a capacitive input impedance is connected to the input / output terminal 120, the impedance of the high-frequency module including the acoustic wave filter and the low-noise amplifier 2 deviates from the reference impedance.

[0077] In contrast, as shown in FIG. 4(b), the impedance of the passband (thick solid line in FIG. 4(b)) when viewed from node A (input / output terminal 120) to the input / output terminal 110 side moves counterclockwise on the equal conductance circle due to the addition of the inductive impedance of the parallel arm resonator 20 to the impedance at node B, and therefore becomes inductive and has a low impedance.

[0078] This allows the impedance of the high-frequency module 100, which has a configuration in which the acoustic wave filter 1 having inductive impedance and the low-noise amplifier 2 having capacitive impedance are connected, to approach the reference impedance, thereby reducing the matching loss of the acoustic wave filter 1 and the high-frequency module 100.

[0079] In acoustic wave filter 1 according to this preferred embodiment, the first parallel arm resonator (parallel arm resonator 20) is connected closest to input / output terminal 120 among the multiple parallel arm resonators.

[0080] In this way, the resonator whose passband exhibits inductive impedance is positioned closest to the input terminal 130 of the low-noise amplifier 2 exhibiting capacitive impedance, thereby enabling impedance matching between the acoustic wave filter 1 and the low-noise amplifier 2 with high efficiency and precision.

[0081] The first parallel arm resonator does not have to be connected closest to the input / output terminal 120 among the multiple parallel arm resonators, and may be connected to a node on the series arm path from the input / output terminal 110 to the series arm resonator 14.

[0082] 4. Configuration of Acoustic Wave Filter 1A According to Modification 1 5 is a circuit diagram of an elastic wave filter 1A according to a first modification of the embodiment. As shown in the figure, the elastic wave filter 1A according to the first modification is a band-pass filter and includes series arm resonators 11, 12, 13, and 14, parallel arm resonators 21, 22, 23, and 24, an inductor 34, and input / output terminals 110 and 120. The elastic wave filter 1A according to this modification differs from the elastic wave filter 1 according to the embodiment in the configuration of its parallel arm resonator 20A. The following description of the elastic wave filter 1A according to this modification will focus on the different configuration and omit a description of the same configuration as that of the elastic wave filter 1 according to the embodiment.

[0083] The parallel arm resonator 24 and the inductor 34, which are connected in series with each other, are an acoustic wave resonator including an acoustic wave resonator and constitute the parallel arm resonator 20A. The parallel arm resonator 20A is connected between the connection point of the series arm resonator 14 and the input / output terminal 120 and ground. More specifically, the inductor 34 is connected to the series arm path connecting the input / output terminals 110 and 120, and the parallel arm resonator 24 is connected to ground. The parallel arm resonator 24 is an example of a second acoustic wave resonator, the inductor 34 is an example of a first inductor, and the parallel arm resonator 20A is an example of a first parallel arm resonator.

[0084] The parallel arm resonator 20A has a resonance frequency frp20A (first resonance frequency) and an anti-resonance frequency fap20A (first anti-resonance frequency). The parallel arm resonator 24 has a resonance frequency frp24 and an anti-resonance frequency fap24. By connecting the inductor 34 in series to the parallel arm resonator 24, the resonance frequency frp20A of the parallel arm resonator 20A shifts to a lower frequency side with respect to the resonance frequency frp24 of the parallel arm resonator 24. In other words, by connecting the inductor 34 in series to the parallel arm resonator 24, the resonance bandwidth (fap20A-frp20A) of the parallel arm resonator 20A becomes wider than the resonance bandwidth (fap24-frp24) of the parallel arm resonator 24.

[0085] The resonant frequency frp24 of the parallel arm resonator 24 is located within the pass band. Meanwhile, the resonant frequency frp20A of the parallel arm resonator 20A is equal to or lower than the low-frequency end of the pass band of the acoustic wave filter 1A, and the antiresonant frequency fap20A of the parallel arm resonator 20A is equal to or higher than the high-frequency end of the pass band. Furthermore, the frequency difference Δfa between the antiresonant frequency fap20A and the high-frequency end of the pass band is smaller than the frequency difference Δfr between the resonant frequency frp20A and the low-frequency end of the pass band.

[0086] In this configuration, the inductor 34 is connected in series to the parallel arm resonator 24 to expand the resonant bandwidth of the parallel arm resonator 20A, and the pass band is adjusted to be located between the resonant frequency frp20A and the antiresonant frequency fap20A of the parallel arm resonator 20A. This makes the impedance of the parallel arm resonator 20A in the pass band inductive, enabling impedance matching between the capacitive circuit connected to the acoustic wave filter 1A and the acoustic wave filter 1A without providing an inductive matching circuit between the capacitive circuit and the acoustic wave filter 1A. Furthermore, by positioning the antiresonant frequency fap20A, which has a high impedance, closer to the pass band than the resonant frequency frp20A, which has a low impedance, signals in the pass band can be transmitted with low loss from the input / output terminal 110 to the input / output terminal 120. Furthermore, the parallel arm resonator 20A has high impedance in the DC (direct current) domain. This prevents the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the acoustic wave filter 1A, eliminating the need to place a DC blocking capacitor between the acoustic wave filter 1A and the low-noise amplifier 2. This makes it possible to provide a low-loss, compact acoustic wave filter 1A in which both matching loss and insertion loss are reduced.

[0087] [5. Configurations of Filter Circuit 3 and High-Frequency Module 100B According to Modification 2] 6A is a circuit configuration diagram of a filter circuit 3 and a high-frequency module 100B according to a second modification of the embodiment. As shown in the figure, the high-frequency module 100B includes a filter circuit 3, a low-noise amplifier 2, and an inductor 31. The high-frequency module 100B according to this modification differs from the high-frequency module 100 according to the embodiment only in that the acoustic wave filter 1 is replaced with a filter circuit 3. The high-frequency module 100B according to this modification will be described below, focusing on the filter circuit 3 that is different from the high-frequency module 100 according to the embodiment.

[0088] The filter circuit 3 includes a parallel arm resonator 20, filter sections 40A, 40B, and 40C, a switch circuit 80, and input / output terminals 111, 112, 113, and 120.

[0089] The parallel arm resonator 20 is an acoustic wave resonator including a parallel arm resonator 24 and an inductor 35 connected in series to each other. The parallel arm resonator 20 is connected between the connection point of the switch circuit 80 and the input / output terminal 120 and ground. The parallel arm resonator 24 is an example of a second acoustic wave resonator, the inductor 35 is an example of a first inductor, and the parallel arm resonator 20 is an example of a first parallel arm resonator.

[0090] The parallel arm resonator 20 has a resonance frequency frp20 (first resonance frequency) and an anti-resonance frequency fap20 (first anti-resonance frequency). The parallel arm resonator 24 has a resonance frequency frp24 and an anti-resonance frequency fap24. By connecting the inductor 35 in series to the parallel arm resonator 24, the resonance frequency frp20 of the parallel arm resonator 20 shifts to the lower frequency side with respect to the resonance frequency frp24 of the parallel arm resonator 24. In other words, by connecting the inductor 35 in series to the parallel arm resonator 24, the resonance bandwidth (fap20-frp20) of the parallel arm resonator 20 becomes wider than the resonance bandwidth (fap24-frp24) of the parallel arm resonator 24.

[0091] The filter unit 40A is an example of an elastic wave filter unit, and has one end connected to the selection terminal 80b of the switch circuit 80 and the other end connected to the input / output terminal 111. The filter unit 40A has the same circuit configuration as the elastic wave filter 1 according to the embodiment except for the parallel arm resonator 20, and includes series arm resonators 11, 12, 13, and 14 and parallel arm resonators 21, 22, and 23. In other words, the filter unit 40A and the parallel arm resonator 20 separated by the switch circuit 80 have the same circuit configuration as the elastic wave filter 1 according to the embodiment.

[0092] The filter unit 40B is an example of a first filter unit, and has one end connected to the selection terminal 80c of the switch circuit 80 and the other end connected to the input / output terminal 112. The filter unit 40B has at least one of an acoustic wave resonator, an inductor, and a capacitor. The filter unit 40B and the parallel arm resonator 20 (first parallel arm resonator) are connected by the switch circuit 80 to form a band-pass first filter.

[0093] One end of the filter unit 40C is connected to the selection terminal 80d of the switch circuit 80, and the other end is connected to the input / output terminal 113. The filter unit 40C has at least one of an acoustic wave resonator, an inductor, and a capacitor. The filter unit 40C and the parallel arm resonator 20 (first parallel arm resonator) are connected by the switch circuit 80 to form a bandpass filter.

[0094] All of the acoustic wave resonators (series arm resonators 11 to 14 and parallel arm resonators 21 to 23) included in the filter section 40A and the parallel arm resonator 24 included in the parallel arm resonator 20 are formed on the same piezoelectric substrate 70. This allows the filter circuit 3 to be miniaturized.

[0095] If the filter sections 40B and 40C have acoustic wave resonators, the acoustic wave resonators of the filter sections 40B and 40C may also be formed on the piezoelectric substrate .

[0096] The switch circuit 80 is an example of a first switch circuit and includes switches 181, 182, 183, 184, 185, and 186, a common terminal 80a, a selection terminal 80b (first selection terminal), a selection terminal 80c (second selection terminal), and a selection terminal 80d, and switches between the connection between the common terminal 80a and the selection terminal 80b, the connection between the common terminal 80a and the selection terminal 80c, and the connection between the common terminal 80a and the selection terminal 80d. The switch 181 has one end connected to the common terminal 80a and the other end connected to the selection terminal 80b. The switch 183 has one end connected to the common terminal 80a and the other end connected to the selection terminal 80c. The switch 185 has one end connected to the common terminal 80a and the other end connected to the selection terminal 80d. The switch 182 has one end connected to the connection point between the other end of the switch 181 and the selection terminal 80b, and the other end connected to ground. One end of switch 184 is connected to the connection point between the other end of switch 183 and selection terminal 80c, and the other end is connected to ground. One end of switch 186 is connected to the connection point between the other end of switch 185 and selection terminal 80d, and the other end is connected to ground.

[0097] In the above configuration, when a high-frequency signal is transmitted from the input / output terminal 111 to the input / output terminal 120, the switches 181, 184, and 186 are conductive, and the switches 182, 183, and 185 are non-conductive, thereby connecting the filter section 40A and the parallel arm resonator 20. When a high-frequency signal is transmitted from the input / output terminal 112 to the input / output terminal 120, the switches 183, 182, and 186 are conductive, and the switches 184, 181, and 185 are non-conductive. When a high-frequency signal is transmitted from the input / output terminal 113 to the input / output terminal 120, the switches 185, 182, and 184 are conductive, and the switches 186, 181, and 183 are non-conductive.

[0098] In the filter circuit 3 according to this modification, the filter section 40C may be omitted, in which case the input / output terminal 113, the selection terminal 80d, and the switches 185 and 186 may be omitted.

[0099] 6B is a diagram schematically illustrating the passband characteristics of the filters constituting the filter circuit 3 according to the second modification of the embodiment and the impedance characteristics of the parallel arm resonator 20. As shown in the figure, in order from the high frequency side, there are a passband formed by the filter unit 40A and the parallel arm resonator 20, a passband formed by the filter unit 40B and the parallel arm resonator 20, and a passband formed by the filter unit 40C and the parallel arm resonator 20.

[0100] The order of high and low frequencies of the three passbands is not limited to the above, and the three passbands may overlap at least partially.

[0101] As shown in FIG. 6B, the resonant frequency frp20 of the parallel arm resonator 20 is equal to or lower than the low-frequency end of the lowest-frequency pass band among the three pass bands, and the antiresonant frequency fap20 of the parallel arm resonator 20 is equal to or higher than the high-frequency end of the highest-frequency pass band among the three pass bands.

[0102] According to this, the parallel arm resonator 24, which is formed on the same piezoelectric substrate 70 as the series arm resonators 11-14 and the parallel arm resonators 21-23 of the filter section 40A that form the passband, is likely to have at least one of its resonant frequency frp24 and antiresonant frequency fap24 within the passband. However, by connecting the inductor 35 in series with the parallel arm resonator 24, the resonant bandwidth of the parallel arm resonator 20 is expanded, and the above three passbands are adjusted to be located between the resonant frequency frp20 and the antiresonant frequency fap20 of the parallel arm resonator 20. As a result, the impedance of the parallel arm resonator 20 in the above three passbands becomes inductive, making it possible to match the impedances of the low-noise amplifier 2 (capacitive circuit) connected to the input / output terminal 120 and the filter circuit 3 without providing an inductive matching circuit between them. In addition, the parallel arm resonator 20 has high impedance in the DC (direct current) domain. This prevents the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the filter circuit 3, eliminating the need to arrange a DC blocking capacitor in series in the path connecting the filter circuit 3 and the low-noise amplifier 2. This makes it possible to provide a low-loss, small-sized filter circuit 3 and high-frequency module 100B.

[0103] [6 Effects etc.] As described above, the acoustic wave filter 1 according to this embodiment includes the series arm resonator 14 disposed in the series arm path connecting the input / output terminals 110 and 120, and the parallel arm resonator 20 connected between the series arm path and ground. The series arm resonator 14 is a first acoustic wave resonator. The parallel arm resonator 20 includes the parallel arm resonator 24 and the inductor 34 connected in series between the series arm path and ground. The series arm resonator 14 and the parallel arm resonator 24 are formed on the same piezoelectric substrate 70. The parallel arm resonator 20 has a resonant frequency frp20 that is equal to or lower than the low-frequency end of the pass band of the acoustic wave filter 1. The parallel arm resonator 20 has an antiresonant frequency fap20 that is equal to or higher than the high-frequency end of the pass band. The frequency difference Δfa between the antiresonant frequency fap20 and the high-frequency end of the pass band is smaller than the frequency difference Δfr between the resonant frequency frp20 and the low-frequency end of the pass band.

[0104] According to this configuration, the parallel arm resonator 24, which is formed on the same piezoelectric substrate 70 as the series arm resonator 14 that defines the pass band, is likely to have at least one of its resonant frequency FRP24 and antiresonant frequency FAP24 within the pass band. However, by connecting the inductor 34 in series with the parallel arm resonator 24, the resonant bandwidth of the parallel arm resonator 20 is expanded, and the pass band is adjusted to be located between the resonant frequency FRP20 and antiresonant frequency FAP20 of the parallel arm resonator 20. This makes the impedance of the parallel arm resonator 20 in the pass band inductive, enabling impedance matching between the capacitive circuit and the acoustic wave filter 1 without providing an inductive matching circuit between the low-noise amplifier 2 having capacitive impedance connected to the acoustic wave filter 1 and the acoustic wave filter 1. Furthermore, by positioning the antiresonant frequency FAP20, which has a high impedance, closer to the pass band than the resonant frequency FRP20, which has a low impedance, signals in the pass band can be transmitted with low loss from the input / output terminal 110 to the input / output terminal 120. Furthermore, since the parallel arm resonator 20 has high impedance in the DC (direct current) region, it is possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the acoustic wave filter 1, eliminating the need to arrange a DC blocking capacitor in series in the path connecting the acoustic wave filter 1 and the low-noise amplifier 2. This makes it possible to provide a low-loss, compact acoustic wave filter 1 in which both matching loss and insertion loss are reduced.

[0105] Furthermore, for example, in the acoustic wave filter 1, the resonant frequency frp24 of the parallel arm resonator 24 is located within the passband.

[0106] According to this, it is assumed that the resonant bandwidth of the parallel arm resonator 24 is smaller than the pass band, but the resonant bandwidth of the parallel arm resonator 20 can be widened by connecting the inductor 34 in series to the parallel arm resonator 24. This makes it possible to make the impedance of the parallel arm resonator 20 inductive in the pass band using a small parallel arm resonator 24.

[0107] Furthermore, for example, in the acoustic wave filter 1, all of the acoustic wave resonators included in the acoustic wave filter 1 are formed on the piezoelectric substrate .

[0108] This allows the acoustic wave filter 1 to be miniaturized.

[0109] For example, the acoustic wave filter 1 includes a plurality of series arm resonators and a plurality of parallel arm resonators, and the parallel arm resonator 20 is connected closest to the input / output terminal 120 among the plurality of parallel arm resonators.

[0110] In this configuration, the parallel arm resonator 20, whose passband exhibits inductive impedance, is arranged closest to the input terminal 130 of the low-noise amplifier 2, which exhibits capacitive impedance, among the multiple parallel arm resonators. This enables impedance matching between the acoustic wave filter 1 and the low-noise amplifier 2 with high efficiency and high precision.

[0111] Furthermore, for example, in the acoustic wave filter 1, the parallel arm resonator 24 is connected to the series arm path, and the inductor 34 is connected to ground.

[0112] This allows the wiring connecting the parallel arm resonator 24 and the series arm resonator 14 and the wiring connecting the parallel arm resonator 24 and the inductor 34 to be short when the parallel arm resonator 24 and the series arm resonator 14 are formed on a single piezoelectric substrate 70. This reduces the loss of the acoustic wave filter 1.

[0113] Furthermore, for example, in the acoustic wave filter 1A according to the first modification, the parallel arm resonator 24 is connected to the ground, and the inductor 34 is connected to the series arm path.

[0114] For example, a filter circuit 3 according to a second modification includes an elastic wave filter 1 (or 1A), a band-pass first filter, and a switch circuit 80 having a common terminal 80a, selection terminals 80b and 80c, and switching between the connection between the common terminal 80a and the selection terminal 80b and the connection between the common terminal 80a and the selection terminal 80c. The elastic wave filter 1 includes a parallel arm resonator 20 and a filter unit 40A. The first filter includes a parallel arm resonator 20 and a filter unit 40B. The parallel arm resonator 20 is connected to the common terminal 80a, the filter unit 40A is connected to the selection terminal 80b, and the filter unit 40B is connected to the selection terminal 80c. A resonance frequency frp20 is equal to or lower than the low-frequency end of the pass band of the elastic wave filter 1 and the lower-frequency end of the low-frequency end of the pass band of the first filter. An anti-resonance frequency fap20 is equal to or higher than the high-frequency end of the pass band of the elastic wave filter 1 and the higher-frequency end of the high-frequency end of the pass band of the first filter.

[0115] According to this configuration, the parallel arm resonator 24, which is formed on the same piezoelectric substrate 70 as the series arm resonator 14 of the filter section 40A that defines the passband, is likely to have at least one of its resonant frequency frp24 and anti-resonant frequency fap24 within the passband. However, by connecting the inductor 35 in series with the parallel arm resonator 24, the resonant bandwidth of the parallel arm resonator 20 is expanded, and the passband of the acoustic wave filter 1 and the passband of the first filter are adjusted to be positioned between the resonant frequency frp20 and anti-resonant frequency fap20 of the parallel arm resonator 20. This makes the impedance of the parallel arm resonator 20 in the two passbands inductive, enabling impedance matching between the low-noise amplifier 2 (capacitive circuit) connected to the input / output terminal 120 and the filter circuit 3 without providing an inductive matching circuit between them. Furthermore, the parallel arm resonator 20 has high impedance in the DC (direct current) domain. This makes it possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the filter circuit 3, eliminating the need to arrange a DC blocking capacitor in series in the path connecting the filter circuit 3 and the low-noise amplifier 2. This makes it possible to provide a low-loss, small-sized filter circuit 3.

[0116] Further, for example, the high-frequency module 100 according to the embodiment includes the acoustic wave filter 1 and the low-noise amplifier 2 having the input terminal 130 connected to the input / output terminal 120.

[0117] This prevents the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the acoustic wave filter 1, eliminating the need to arrange a DC-blocking capacitor in series in the path connecting the acoustic wave filter 1 and the low-noise amplifier 2. This makes it possible to provide a low-loss, compact high-frequency module 100 in which both matching loss and insertion loss are reduced.

[0118] Furthermore, for example, in the high-frequency module 100, a capacitor is not arranged in series in the path connecting the input end of the amplifying transistor included in the low-noise amplifier 2 and the input / output terminal 120.

[0119] This allows the high-frequency module 100 to be made smaller.

[0120] Further, for example, a high-frequency module 100B according to the second modification includes a filter circuit 3 and a low-noise amplifier 2 in which the input terminal 130 is connected to the connection point between the common terminal 80a and the parallel arm resonator 20.

[0121] This makes it possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the filter circuit 3, eliminating the need to arrange a DC blocking capacitor in series in the path connecting the filter circuit 3 and the low-noise amplifier 2. This makes it possible to provide a low-loss, small-sized high-frequency module 100B in which both matching loss and insertion loss are reduced.

[0122] Furthermore, for example, in the high-frequency module 100B, no capacitor is arranged in series in the path connecting the input terminal 130 of the low-noise amplifier 2 and the above-mentioned connection point.

[0123] This allows the high-frequency module 100B to be miniaturized.

[0124] (Other embodiments) Although the acoustic wave filter, filter circuit, and high-frequency module according to the present invention have been described above with reference to the embodiments and modifications thereof, the present invention is not limited to the above embodiments and modifications. The present invention also includes modifications that can be made by those skilled in the art without departing from the spirit of the present invention, as well as various devices incorporating the acoustic wave filter, filter circuit, and high-frequency module according to the present invention.

[0125] Furthermore, for example, in the acoustic wave filters, filter circuits, and high-frequency modules according to the above-described embodiments and modifications, matching elements such as inductors and capacitors, and switch circuits may be connected between the respective components.

[0126] The features of the acoustic wave filter, the filter circuit, and the high-frequency module described based on the above-described embodiment and modifications will be described below.

[0127] <1> A band-pass acoustic wave filter, a first series arm resonator disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a first parallel arm resonator connected between the series arm path and ground, the first series arm resonator includes a first acoustic wave resonator, the first parallel arm resonator includes a second acoustic wave resonator and a first inductor connected in series between the series arm path and ground; the first acoustic wave resonator and the second acoustic wave resonator are formed on the same piezoelectric substrate; a first resonance frequency of the first parallel arm resonator is equal to or lower than a low frequency end of a pass band of the acoustic wave filter, and a first anti-resonance frequency of the first parallel arm resonator is equal to or higher than a high frequency end of the pass band; an elastic wave filter in which a frequency difference between the first antiresonant frequency and the high frequency end of the pass band is smaller than a frequency difference between the first resonant frequency and the low frequency end of the pass band;

[0128] <2> the resonant frequency of the second acoustic wave resonator is located within the passband. <1> The acoustic wave filter according to claim 1.

[0129] <3> a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, each of the plurality of series arm resonators and the plurality of parallel arm resonators includes an acoustic wave resonator; all of the acoustic wave resonators included in the acoustic wave filter are formed on the piezoelectric substrate; <1> or <2> The acoustic wave filter according to claim 1.

[0130] <4> a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, the first parallel arm resonator is connected closest to the first input / output terminal among the plurality of parallel arm resonators; <1> or <2> The acoustic wave filter according to claim 1.

[0131] <5> the second acoustic wave resonator is connected to the series arm path, and the first inductor is connected to ground. <1> ~ <4> 10. The acoustic wave filter according to claim 9, wherein

[0132] <6> the second acoustic wave resonator is connected to ground, and the first inductor is connected to the series arm path. <1> ~ <4> 10. The acoustic wave filter according to claim 9, wherein

[0133] <7> <1> ~ <6> an acoustic wave filter according to any one of the preceding claims; a first bandpass filter; a first switch circuit having a common terminal, a first selection terminal, and a second selection terminal, and switching a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal; the acoustic wave filter includes the first parallel arm resonator and an acoustic wave filter unit, the first filter includes the first parallel arm resonator and a first filter section, the first parallel arm resonator is connected to the common terminal; the acoustic wave filter unit is connected to the first selection terminal, the first filter unit is connected to the second selection terminal, a filter circuit in which the first resonant frequency is equal to or lower than the low-frequency end of the pass band of the elastic wave filter and the lower-frequency end of the low-frequency end of the pass band of the first filter, and the first anti-resonant frequency is equal to or higher than the high-frequency end of the pass band of the elastic wave filter and the higher-frequency end of the high-frequency end of the pass band of the first filter.

[0134] <8> <1> ~ <6> an acoustic wave filter according to any one of the preceding claims; a low-noise amplifier having an input terminal connected to the first input / output terminal.

[0135] <9> a capacitor is not arranged in series in a path connecting an input end of an amplifying transistor included in the low-noise amplifier and the first input / output terminal; <8> The high-frequency module according to claim 1.

[0136] <10> <7> a filter circuit according to a low-noise amplifier having an input terminal connected to a connection point between the common terminal and the first parallel arm resonator;

[0137] <11> No capacitor is arranged in series in a path connecting the input terminal and the connection point. <10> The high-frequency module according to claim 1. [Industrial Applicability]

[0138] INDUSTRIAL APPLICABILITY The present invention can be widely used in communication devices such as mobile phones as a low-loss acoustic wave filter, filter circuit, and high-frequency module that can be applied to multi-band frequency standards. [Explanation of symbols]

[0139] 1, 1A acoustic wave filter 2. Low noise amplifier 3. Filter Circuit 11, 12, 13, 14 Series arm resonators 20, 20A parallel arm resonator 21, 22, 23, 24 Parallel arm resonators 31, 34, 35 Inductors 40A, 40B, 40C filter section 50, 70 Piezoelectric substrate 51 High-sonic support substrate 52 Low sound velocity membrane 53 Piezoelectric film 54 IDT electrode 55, 58 protective layer 57 Piezoelectric single crystal substrate 60 Elastic wave resonator 60a, 60b comb-shaped electrode 61a, 61b electrode fingers 62a, 62b Busbar electrodes 65 Support substrate 66 Lower electrode 67 Piezoelectric layer 68 Upper electrode 80 Switch Circuit 80a common terminal 80b, 80c, 80d selection terminals 100, 100B high frequency module 110, 111, 112, 113, 120 input / output terminals 130 Input terminal 140 output terminal 181, 182, 183, 184, 185, 186 switches 540 Adhesion layer 542 Main electrode layer

Claims

1. A band-pass acoustic wave filter, a first series arm resonator disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a first parallel arm resonator connected between the series arm path and ground, the first series arm resonator includes a first acoustic wave resonator, the first parallel arm resonator includes a second acoustic wave resonator and a first inductor connected in series between the series arm path and ground, the first acoustic wave resonator and the second acoustic wave resonator are formed on the same piezoelectric substrate; a first resonance frequency of the first parallel arm resonator is equal to or lower than a low frequency end of a pass band of the acoustic wave filter, and a first anti-resonance frequency of the first parallel arm resonator is equal to or higher than a high frequency end of the pass band; a frequency difference between the first anti-resonance frequency and the high frequency end of the pass band is smaller than a frequency difference between the first resonant frequency and the low frequency end of the pass band; Acoustic wave filters.

2. a resonant frequency of the second acoustic wave resonator is located within the passband; The acoustic wave filter according to claim 1 .

3. a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, each of the plurality of series arm resonators and the plurality of parallel arm resonators includes an acoustic wave resonator; all of the acoustic wave resonators included in the acoustic wave filter are formed on the piezoelectric substrate; The acoustic wave filter according to claim 1 .

4. a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, the first parallel arm resonator is connected closest to the first input / output terminal among the plurality of parallel arm resonators; The acoustic wave filter according to claim 1 .

5. the second acoustic wave resonator is connected to the series arm path, and the first inductor is connected to ground. The acoustic wave filter according to claim 1 .

6. the second acoustic wave resonator is connected to ground, and the first inductor is connected to the series arm path. The acoustic wave filter according to claim 1 .

7. an acoustic wave filter according to any one of claims 1 to 6; a first bandpass filter; a first switch circuit having a common terminal, a first selection terminal, and a second selection terminal, and switching a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal; the acoustic wave filter includes the first parallel arm resonator and an acoustic wave filter unit, the first filter includes the first parallel arm resonator and a first filter unit, the first parallel arm resonator is connected to the common terminal; the acoustic wave filter unit is connected to the first selection terminal, the first filter unit is connected to the second selection terminal, the first resonant frequency is equal to or lower than a lower frequency end of a pass band of the elastic wave filter and a lower frequency end of a pass band of the first filter, and the first anti-resonant frequency is equal to or higher than a higher frequency end of a pass band of the elastic wave filter and a higher frequency end of a pass band of the first filter. Filter circuit.

8. an acoustic wave filter according to any one of claims 1 to 6; a low noise amplifier having an input terminal connected to the first input / output terminal; High frequency module.

9. a capacitor is not arranged in series in a path connecting an input end of an amplifying transistor included in the low-noise amplifier and the first input / output terminal; The high frequency module according to claim 8 .

10. a filter circuit according to claim 7; a low-noise amplifier having an input terminal connected to a connection point between the common terminal and the first parallel arm resonator, High frequency module.

11. No capacitor is arranged in series in a path connecting the input terminal and the connection point. The high frequency module according to claim 10.

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