Elastic wave filter, filter circuit, and high-frequency module

Abstract

Provided are a compact elastic wave filter, a filter circuit, and a high-frequency module that ensure low loss. An elastic wave filter (1) is provided with: a series arm resonator (14) disposed in a series arm path connecting input / output terminals (110, 120); and a parallel arm resonator (20) connected between the series arm path and the ground, the series arm resonator being a first elastic wave resonator, the parallel arm resonator including a parallel arm resonator (24) and an inductor (34) connected in series between the series arm path and the ground, the series arm resonator and the parallel arm resonator being formed on the same piezoelectric substrate (70), and the inductor (34) being a second elastic wave resonator. The resonant frequency (frp20) of the parallel arm resonator is equal to or less than the low-frequency end of the passband of the elastic wave filter, the anti-resonant frequency (fap 20) of the parallel arm resonator is equal to or greater than the high-frequency end of the passband, and the frequency difference ([delta] fa) between the anti-resonant frequency and the high-frequency end of the passband is smaller than the frequency difference ([delta] fr) between the resonant frequency and the low-frequency end of the passband.

Description

Technical Field

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

[0002] A filter module including a band-pass filter and a matching resonator is disclosed in Patent Document 1. The passband of the filter is included in the range between the resonance frequency and the anti-resonance frequency of the matching resonator, whereby the impedance of the passband of the filter module can be made inductive.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-088675

[0006] In the filter module disclosed in Patent Document 1, the impedance of the passband can be made inductive by the matching resonator, so that the matching loss in the case of connecting to an external circuit having a capacitive impedance can be reduced. However, sometimes the insertion loss of the matching resonator itself cannot be reduced, and the low-loss property of the filter module cannot be ensured. In addition, since the matching resonator is added, the filter module is enlarged. Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Therefore, the present invention has been made to solve the above problems, and an object thereof is to provide a small-sized elastic wave filter, a filter circuit, and a high-frequency module that ensure low-loss property.

[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 is a band-pass elastic wave filter, including: a first series arm resonator disposed on 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. The first series arm resonator includes a first elastic wave resonator, and the first parallel arm resonator includes a second elastic wave resonator and a first inductor connected in series between the series arm path and ground. The first elastic wave resonator and the second elastic wave resonator are formed on the same piezoelectric substrate. A first resonance frequency, which is the resonance frequency of the first parallel arm resonator, is equal to or lower than the low-frequency end of the passband of the elastic wave filter, and a first anti-resonance frequency, which is the anti-resonance frequency of the first parallel arm resonator, is equal to or higher than the high-frequency end of the passband. The frequency difference between the first anti-resonance frequency and the high-frequency end of the passband is smaller than the frequency difference between the first resonance frequency and the low-frequency end of the passband.

[0011] In addition, a filter circuit according to one aspect of the present invention includes: the above-described surface acoustic wave filter; a band-pass type first filter; and a first switch circuit having a common terminal, a first selection terminal, and a second selection terminal, which switches the connection between the common terminal and the first selection terminal and the connection between the common terminal and the second selection terminal. The surface acoustic wave filter has a first parallel arm resonator and a surface acoustic wave filter section, the first filter has a first parallel arm resonator and a first filter section, the first parallel arm resonator is connected to the common terminal, the surface acoustic wave filter section is connected to the first selection terminal, the first filter section is connected to the second selection terminal, the first resonance frequency is equal to or lower than the lower frequency end of the low-frequency side among the low-frequency end of the passband of the surface acoustic wave filter and the low-frequency end of the passband of the first filter, and the first anti-resonance frequency is equal to or higher than the higher frequency end of the high-frequency side among the high-frequency end of the passband of the surface acoustic wave filter and the high-frequency end of the passband of the first filter.

[0012] In addition, a high-frequency module according to one aspect of the present invention includes: the above-described surface acoustic wave filter; and a low-noise amplifier, the input terminal of which is connected to the first input / output terminal.

[0013] Advantageous Effects of the Invention

[0014] According to the present invention, it is possible to provide a small-sized surface acoustic wave filter, a filter circuit, and a high-frequency module that ensure low loss characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit structure diagram of the surface acoustic wave filter and the high-frequency module according to the embodiment.

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

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

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

[0019] Figure 3A is a coordinate diagram showing the passing characteristics in the frequency band near the passband of the surface acoustic wave filter according to the embodiment and the impedance characteristics of the first parallel arm resonator.

[0020] Figure 3B is a coordinate diagram showing the impedance characteristics of the wide-area first parallel arm resonator of the surface acoustic wave filter according to the embodiment.

[0021] Figure 4It is an admittance diagram showing the impedance characteristics of the elastic wave filter related to the embodiment.

[0022] Figure 5 It is a circuit structure diagram of the elastic wave filter related to Modification Example 1 of the embodiment.

[0023] Figure 6A It is a circuit structure diagram of the filter circuit and the high-frequency module related to Modification Example 2 of the embodiment.

[0024] Figure 6B It is a diagram schematically showing the pass characteristics of each filter constituting the filter circuit related to Modification Example 2 of the embodiment and the impedance characteristics of the first parallel arm resonator.

[0025] Description of Reference Numerals

[0026] 1, 1A Elastic wave filter;

[0027] 2 Low-noise amplifier;

[0028] 3 Filter circuit;

[0029] 11, 12, 13, 14 Series arm resonators;

[0030] 20, 20A Parallel arm resonators;

[0031] 21, 22, 23, 24 Parallel arm resonators;

[0032] 31, 34, 35 Inductors;

[0033] 40A, 40B, 40C Filter sections;

[0034] 50, 70 Piezoelectric substrates;

[0035] 51 High-velocity acoustic support substrate;

[0036] 52 Low-velocity acoustic film;

[0037] 53 Piezoelectric film;

[0038] 54 IDT electrode;

[0039] 55, 58 Protective layers;

[0040] 57 Piezoelectric single crystal substrate;

[0041] 60 Elastic wave resonator;

[0042] 60a, 60b Comb electrodes;

[0043] 61a, 61b Electrode fingers;

[0044] 62a, 62b bus bar electrodes;

[0045] 65 support base plate;

[0046] 66 lower electrode;

[0047] 67 piezoelectric layer;

[0048] 68 upper electrode;

[0049] 80 switch circuit;

[0050] 80a common terminal;

[0051] 80b, 80c, 80d select terminals;

[0052] 100, 100B high frequency modules;

[0053] 110, 111, 112, 113, 120 input and output terminals;

[0054] 130 input terminal;

[0055] 140 output terminals;

[0056] 181, 182, 183, 184, 185, 186 switches;

[0057] 540 close contact layer;

[0058] 542 Main electrode layer. DETAILED DESCRIPTION

[0059] Hereinafter, the embodiments of the present disclosure will be described in detail using the accompanying drawings. In addition, the embodiments described below are all general or specific examples. The numerical values, shapes, materials, components, configurations of components, and connection methods shown in the following embodiments are examples, and their purpose is not to limit the present invention. Among the components in the following embodiments, the components that are not described in the independent claims are described as arbitrary components. In addition, the sizes or size ratios of the components shown in the drawings may not be rigorous.

[0060] In addition, the figures are schematic diagrams that have been appropriately emphasized, omitted, or adjusted in proportion to illustrate the present invention, and are not necessarily strictly illustrated and may differ from actual shapes, positional relationships, and proportions. In the figures, substantially the same structures are marked with the same reference numerals, and repeated descriptions may be omitted or simplified.

[0061] In the circuit structure of the present disclosure, the so-called "connection" includes not only the case of direct connection through connection terminals and / or wiring conductors, but also the 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.

[0062] In the present invention, the so-called "terminal" means the point where the conductor in an element ends. In addition, when the impedance of the conductor between elements is sufficiently low, the terminal can be interpreted not only as a single point, but also as any point (node) on the conductor between elements or the entire conductor.

[0063] In addition, in the circuit element configuration of the present disclosure, the so-called "circuit element A is serially arranged on path B" means that the signal input terminal and the signal output terminal of circuit element A are respectively connected to 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.

[0064] In the following respective figures, the x-axis and the y-axis are axes orthogonal to each other in a plane parallel to the main surface of the module substrate. Specifically, when the module substrate has a rectangular shape in a top view, the x-axis is parallel to the first side of the module substrate, and the y-axis is parallel to the second side orthogonal to the first side of the module substrate. In addition, the z-axis is an axis perpendicular to the main surface of the module substrate, the positive direction thereof represents the upward direction, and the negative direction thereof represents the downward direction.

[0065] In addition, terms indicating the relationality between elements such as "parallel" and "perpendicular", terms indicating the shape of elements such as "rectangular", and numerical ranges do not only represent strict meanings, but rather mean substantially equivalent ranges, for example, they also include errors of about several percent.

[0066] In addition, in the component configuration of the present invention, the so-called "top view of the module substrate" means observing an object by orthographically projecting it onto the xy plane from the positive side of the z-axis. The so-called "A overlaps B in a top view" means that at least a part of the region of A orthographically projected onto the xy plane overlaps at least a part of the region of B orthographically projected onto the xy plane. In addition, the so-called "A is arranged between B and C" means that at least one of the plurality of line segments connecting any point in B and any point in C passes through A.

[0067] In the component configuration of the present invention, the so-called "component is disposed on the substrate" includes that the component is disposed on the main surface of the substrate and that the component is disposed within the substrate. The so-called "component is disposed on the main surface of the substrate" includes, in addition to the component being disposed in contact with the main surface of the substrate, that the component is disposed above the main surface without contacting the main surface (for example, the component is stacked on another component disposed in contact with the main surface). Further, "the component is disposed on the main surface of the substrate" may also include that the component is disposed in a recess formed in the main surface. The so-called "component is disposed within the substrate" includes, in addition to the component being encapsulated within the module substrate, that all of the component is disposed between the two main surfaces of the substrate but a part of the component is not covered by the substrate, and that only a part of the component is disposed within the substrate.

[0068] 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.

[0069] In addition, an elastic wave resonator is defined as any one of the following resonant circuits: (1) a resonant circuit composed of an elastic wave resonator and a circuit (or circuit element) connected in parallel with the elastic wave resonator (a parallel connection circuit of the elastic wave resonator and the circuit (or circuit element)), (2) a resonant circuit composed 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, and having a structure in which the connection node connecting the elastic wave resonator and the circuit (or circuit element) is not connected to other circuits (and other circuit elements) and is not grounded (a series connection circuit of the elastic wave resonator and the circuit (or circuit element)), (3) a resonant circuit composed of a plurality of elastic wave resonators connected in parallel with each other (a parallel connection circuit of divided resonators), and (4) a resonant circuit composed of a plurality of elastic wave resonators connected in series with each other, and having a structure in which the connection node connecting between the plurality of elastic wave resonators is not connected to a circuit (and circuit elements) other than the plurality of elastic wave resonators and is not grounded (a series connection circuit of divided resonators).

[0070] 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.

[0071] In addition, the resonance frequency and the anti-resonance frequency shown in the above embodiments and modification examples are derived, for example, by bringing an RF probe into contact with the two input / output electrodes of the elastic wave resonator or the elastic wave resonator in a state where the elastic wave resonator or the elastic wave resonator is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) with a network analyzer or the like.

[0072] In addition, in the present disclosure, the so-called "frequency band" means at least one of the uplink operating frequency band and the downlink operating frequency band of the frequency band pre-defined for a communication system constructed for utilizing radio access technology (RAT) by a standardization organization or the like (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.). 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 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 among the frequency band. Further, the so-called downlink operating frequency band of the frequency band means the frequency range designated for downlink use among the frequency band.

[0073] (Embodiment)

[0074] [1 Circuit Structure of SAW Filter 1 and High-Frequency Module 100]

[0075] Figure 1 It is a circuit structure diagram of the SAW filter 1 and the high-frequency module 100 according to the embodiment. As shown in this figure, the high-frequency module 100 includes a SAW filter 1, a low-noise amplifier 2, and an inductor 31.

[0076] The low-noise amplifier 2 is connected to the surface acoustic wave filter 1 via an inductor 31. Specifically, the input terminal 130 of the low-noise amplifier 2 is connected to the input / output terminal 120 of the surface acoustic wave filter 1 via the inductor 31. The low-noise amplifier 2 includes, for example, an amplifying transistor that is a field effect transistor (FET: Field Effect Transistor) or a bipolar transistor (Bipolar Transistor). The gate (or base), which is the 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 the ground via an inductor. Further, a DC bias voltage (DC bias current) is supplied to the gate (or base) of the above-mentioned amplifying transistor. With the above structure, the low-noise amplifier 2 supplies a DC bias voltage (DC bias current) to the gate (or base), thereby amplifying the high-frequency signal that has passed through the surface acoustic wave filter 1 and outputting it to the output terminal 140. In addition, the input impedance of the low-noise amplifier 2 becomes capacitive and high impedance.

[0077] One end of the inductor 31 is connected to the input / output terminal 120 of the surface acoustic wave filter 1, and the other end is connected to the input terminal 130 of the low-noise amplifier 2. It is a circuit element for achieving impedance matching between the surface acoustic wave filter 1 and the low-noise amplifier 2. In addition, the inductor 31 is not an essential component of the high-frequency module 100 according to the present embodiment.

[0078] The surface acoustic wave filter 1 is a band-pass type filter (band-pass filter), and includes series arm resonators 11, 12, 13, and 14, shunt arm resonators 21, 22, 23, and 24, an inductor 34, and input / output terminals 110 and 120.

[0079] The series arm resonators 11 to 14 are surface acoustic wave resonators each including a surface acoustic wave resonator, and are arranged in 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 is composed of only the series arm resonator 11 to form one series arm resonator (surface acoustic wave resonator). The series arm resonator 12 is composed of only the series arm resonator 12 to form one series arm resonator (surface acoustic wave resonator). The series arm resonator 13 is composed of only the series arm resonator 13 to form one series arm resonator (surface acoustic wave resonator). The series arm resonators 11 to 14 are each an example of a first surface acoustic wave resonator and, in addition, an example of a first series arm resonator.

[0080] The series arm resonators 11 to 14 are sequentially connected in order of the series arm resonators 11, 12, 13, and 14 starting from the input / output terminal 110.

[0081] The parallel-arm resonators 21 to 23 are each an elastic-wave resonator including an elastic-wave oscillator, and are connected between the above-described series-arm path and the ground. The parallel-arm resonator 21 is connected between the connection point of the series-arm resonators 11 and 12 and the ground. The parallel-arm resonator 22 is connected between the connection point of the series-arm resonators 12 and 13 and the ground. The parallel-arm resonator 23 is connected between the connection point of the series-arm resonators 13 and 14 and the ground. The parallel-arm resonator 21 forms one parallel-arm resonator (elastic-wave resonator) only with the parallel-arm resonator 21, the parallel-arm resonator 22 forms one parallel-arm resonator (elastic-wave resonator) only with the parallel-arm resonator 22, and the parallel-arm resonator 23 forms one parallel-arm resonator (elastic-wave resonator) only with the parallel-arm resonator 23.

[0082] The parallel-arm resonators 24 and the inductor 34 connected in series with each other are elastic-wave resonators including elastic-wave oscillators, and form 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 the ground. More specifically, the parallel-arm resonator 24 is connected to the series-arm path connecting the input / output terminals 110 and 120, and the inductor 34 is connected to the ground. The parallel-arm resonator 24 is an example of the second elastic-wave resonator, the inductor 34 is an example of the first inductor, and the parallel-arm resonator 20 is an example of the first parallel-arm resonator.

[0083] 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 with the parallel-arm resonator 24, the resonance frequency frp20 of the parallel-arm resonator 20 is shifted to the lower-frequency side with respect to the resonance frequency frp24 of the parallel-arm resonator 24. That is, by connecting the inductor 34 in series with 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.

[0084] The series-arm resonators 11 to 14 and the parallel-arm resonators 21 to 24 are formed on the same piezoelectric substrate 70. Thereby, the elastic-wave filter 1 can be miniaturized. In addition, not all of the elastic-wave oscillators included in the elastic-wave filter 1 may 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. Accordingly, compared with the case where each elastic-wave oscillator is formed on a different piezoelectric substrate, the elastic-wave filter 1 can be miniaturized.

[0085] In addition, each of the series-arm resonators 11 to 14 and the shunt-arm resonators 21 to 23 (surface acoustic wave resonators) has only one surface acoustic wave resonator, but each of the series-arm resonators 11 to 14 and the shunt-arm resonators 21 to 23 may also be any of the following resonators, for example: (1) a resonator composed of a surface acoustic wave resonator and a circuit including at least one of a capacitor and an inductor connected in parallel with the surface acoustic wave resonator; (2) a resonator composed of a surface acoustic wave resonator and a circuit including at least one of a capacitor and an inductor connected in series with the surface acoustic wave resonator; (3) a resonator composed of a plurality of surface acoustic wave resonators connected in parallel; and (4) a resonator composed of a plurality of surface acoustic wave resonators connected in series.

[0086] In addition, the surface acoustic wave filter 1 according to the present embodiment only needs to include at least one of the series-arm resonators 11 to 14 and the shunt-arm resonator 20, and may not have other surface acoustic wave resonators. In addition, the surface acoustic wave filter 1 according to the present embodiment may include at least one of a longitudinal coupling resonator, a capacitor, and an inductor in addition to the series-arm resonator and the shunt-arm resonator that constitute the ladder-type filter.

[0087] [2 Structure of Surface Acoustic Wave Resonator]

[0088] Next, the structures of the surface acoustic wave resonators (series-arm resonators and shunt-arm resonators) that constitute the surface acoustic wave filter 1 are illustrated.

[0089] Figure 2A FIGS. are a top view and a cross-sectional view schematically showing a first example of the surface acoustic wave resonators that constitute the surface acoustic wave filter 1 according to the embodiment. In the figure, the basic structures of the plurality of surface acoustic wave resonators that constitute the surface acoustic wave filter 1 are illustrated. In addition, Figure 2A The surface acoustic wave resonator 60 shown is used to illustrate the typical structure of the surface acoustic wave resonator that constitutes the surface acoustic wave filter 1, and the number and length of the electrode fingers that constitute the electrodes are not limited thereto.

[0090] The surface acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0091] As Figure 2A shown in (a) of, a pair of comb-shaped electrodes 60a and 60b facing each other are formed on the piezoelectric substrate 50. 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).

[0092] In addition, if Figure 2A As shown in FIG. 5( b ), the IDT electrode 54 composed of a plurality of electrode fingers 61 a and 61 b and bus bar electrodes 62 a and 62 b has a laminated structure of an adhesion layer 540 and a main electrode layer 542 .

[0093] The adhesion layer 540 is used to improve the adhesion between the piezoelectric substrate 50 and the main electrode layer 542. For example, Ti is used. For example, Al containing 1% Cu is used as the main electrode layer 542. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a dielectric film primarily composed of silicon dioxide, for example, to protect the main electrode layer 542 from external environmental influences, adjust the frequency-temperature characteristics, and improve moisture resistance.

[0094] 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 need not have the aforementioned multilayer structure. For example, the IDT electrode 54 may be composed of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd. Furthermore, the IDT electrode 54 may be composed of multiple stacks composed of the aforementioned metals or alloys. Furthermore, the protective layer 55 may not be formed.

[0095] Next, the stacked structure of the piezoelectric substrate 50 will be described.

[0096] like Figure 2A As shown in (c), the piezoelectric substrate 50 includes a high-acoustic-velocity support substrate 51, a low-acoustic-velocity film 52, and a piezoelectric film 53. The high-acoustic-velocity support substrate 51, the low-acoustic-velocity film 52, and the piezoelectric film 53 are sequentially stacked. The piezoelectric substrate 50 is an example of the piezoelectric substrate 70 of the elastic wave filter 1.

[0097] The piezoelectric film 53 comprises, for example, a θ° Y-cut X-propagation LiTaO3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut with the X-axis as the center axis and an axis rotated θ° from the Y-axis as the normal, and a single crystal or ceramic in which surface acoustic waves propagate in the X-axis direction). The material and cut angle θ of the piezoelectric single crystal used for the piezoelectric film 53 can be appropriately selected according to the required specifications of each filter.

[0098] The high acoustic velocity supporting 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 supporting substrate 51 is also a substrate in which the acoustic velocity of the bulk wave in the high acoustic velocity supporting 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 confine the surface acoustic wave in the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated without leaking to below the high acoustic velocity supporting substrate 51. As the material of the high acoustic velocity supporting substrate 51, for example, piezoelectric bodies 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 alumina, 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.

[0099] 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 supporting substrate 51. According to this structure and the property that the energy of the elastic wave is essentially concentrated in the medium with low acoustic velocity, the leakage of the surface acoustic wave energy outside the piezoelectric film 53 can be 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.

[0100] In addition, according to the above lamination structure of the piezoelectric substrate 50, compared with the conventional structure in which a piezoelectric substrate is used as a single layer, the Q value 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.

[0101] In addition, the high acoustic velocity supporting substrate 51 may also have a structure in which a supporting substrate and a high acoustic velocity film in which the acoustic velocity of the bulk wave propagated is higher than that of the surface wave, the boundary wave, and other elastic waves propagating in the piezoelectric film 53 are laminated. In this case, the same material as that of the high acoustic velocity supporting substrate 51 can be used as the material of the high acoustic velocity film. In addition, as the material of the supporting substrate, for example, piezoelectric bodies 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, etc., 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.

[0102] In addition, in this specification, the so-called "main component of the material" refers to a component that accounts for more than 50% by weight in the material. The above-mentioned main component may exist in any state of single crystal, polycrystal, and amorphous, or in a state where they are mixed.

[0103] Figure 2B It is a cross-sectional view schematically showing a second example of the elastic wave resonator constituting the elastic wave filter 1 according to the embodiment. In Figure 2A In the shown elastic wave resonator 60, an example is shown in which the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53, but the substrate on which the IDT electrode 54 is formed may also be as Figure 2B shown as a single-layer piezoelectric single crystal substrate 57 including a piezoelectric body layer.

[0104] 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 on the IDT electrode 54. The piezoelectric single crystal substrate 57 is an example of the piezoelectric substrate 70 of the elastic wave filter 1.

[0105] The above-mentioned piezoelectric film 53 and piezoelectric single crystal substrate 57 may also appropriately change the lamination structure, material, cutting angle, and thickness according to the requirements and characteristics of the elastic wave filter. Even for an elastic wave resonator using a LiTaO3 piezoelectric substrate or the like having a cutting angle other than the above-mentioned cutting angle, the same effect as that of the elastic wave resonator 60 using the above-mentioned piezoelectric film 53 can be obtained.

[0106] In addition, the substrate on which the IDT electrode 54 is formed may also have a structure in which a support substrate, an energy confinement layer, and a piezoelectric film are laminated in sequence. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film uses a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic, for example. The support substrate is a substrate that supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

[0107] The energy confinement layer includes one or more layers, and the velocity of the bulk acoustic wave propagating in at least one of its layers is greater than the velocity of the elastic wave propagating near the piezoelectric film. For example, the energy confinement layer may also have a laminated structure of a low-velocity layer and a high-velocity layer. The low-velocity layer is a film in which the velocity of the bulk wave in the low-velocity layer is lower than the velocity of the elastic wave propagating in the piezoelectric film. The high-velocity layer is a film in which the velocity of the bulk wave in the high-velocity layer is higher than the velocity of the elastic wave propagating in the piezoelectric film. In addition, the support substrate may be used as the high-velocity layer.

[0108] Alternatively, the energy confinement layer may be an acoustic impedance layer having a structure in which low acoustic impedance layers having relatively low acoustic impedance and high acoustic impedance layers having relatively high acoustic impedance are alternately stacked.

[0109] Here, electrode parameters of IDT electrode 54 constituting elastic wave resonator 60 will be described.

[0110] The wavelength of the elastic wave resonator is composed of Figure 2A The repetition period of the multiple electrode fingers 61a or 61b of the IDT electrode 54 shown in (b) is defined by the wavelength λ. Furthermore, the electrode finger pitch is ½ the wavelength λ and is defined as (W + S), where the line width of the electrode fingers 61a and 61b that constitute the comb-shaped electrodes 60a and 60b, respectively, is W, and the spacing between adjacent electrode fingers 61a and 61b is S. Furthermore, the duty ratio 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 of each electrode finger 61a or 61b to the sum of the line width and spacing, and is defined as W / (W + S). Furthermore, the crossover width of the IDT electrode 54 is the length of the overlapping electrode fingers when viewing the electrode fingers 61a and 61b from the direction of elastic wave propagation (the X-axis direction).

[0111] In the IDT electrode 54 , when the spacing between adjacent electrode fingers is not constant, the electrode finger pitch of the IDT electrode 54 is defined by the average electrode finger pitch of the IDT electrode 54 . Assuming the total number of electrode fingers 61 a and 61 b included in the IDT electrode 54 is Ni, and the center-to-center distance between the electrode fingers at one end and the electrode fingers at the other end of the IDT electrode 54 in the direction of elastic wave propagation is Di, the average electrode finger pitch of the IDT electrode 54 is defined as Di / (Ni–1).

[0112] also, Figure 2C : is a cross-sectional view schematically showing a third example of the elastic wave resonator constituting the elastic wave filter 1 according to the embodiment. Figure 2C , a bulk acoustic wave resonator is shown as the elastic wave resonator of the elastic 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. The support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are stacked in this order.

[0113] The support substrate 65 is a substrate that supports the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68, and is, for example, a silicon substrate. Furthermore, the support substrate 65 has a cavity in the area in contact with 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 elastic wave filter 1.

[0114] 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, for example, Al containing 1% Cu.

[0115] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 mainly contains, for example, at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz, and LiBO (lithium borate).

[0116] The bulk acoustic wave resonator constituting the above-described stacked structure generates resonance by applying electrical energy between the lower electrode 66 and the upper electrode 68, thereby inducing bulk acoustic waves within the piezoelectric layer 67. The bulk acoustic waves generated by the 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, the bulk acoustic wave resonator is a resonator that utilizes bulk acoustic waves.

[0117] [3 Resonance Characteristics and Pass Characteristics of Elastic Wave Filter 1]

[0118] First, the basic operating principle of a ladder-type bandpass filter composed of one series-arm resonator and one parallel-arm resonator will be described.

[0119] 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 becomes the low-frequency side stopband. Further, if the frequency is further increased, the impedance of the parallel-arm resonator becomes high near the anti-resonance frequency fap, and the impedance of the series-arm resonator approaches 0 near the resonance frequency frs. Thereby, in the vicinity of the anti-resonance frequency fap to the resonance frequency frs, it becomes a signal passband in the signal path as the series-arm path. Thereby, a passband 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 reaches the vicinity of the anti-resonance frequency fas, the impedance of the series-arm resonator becomes high, becoming the high-frequency side stopband.

[0120] Further, in each of the series-arm resonator and the parallel-arm resonator, in a frequency band lower than the resonance frequency, the impedance of the resonator shows capacitive (C-type), and in a frequency band higher than the resonance frequency and lower than the anti-resonance frequency, the impedance of the resonator shows inductive (L-type). Further, in a frequency band higher than the anti-resonance frequency, the impedance of the resonator shows capacitive.

[0121] Alternatively, when the resonance bandwidth is wider than the desired passband width, the anti-resonance frequency of the parallel-arm resonator is higher than the high-frequency end of the passband, and the resonance frequency of the series-arm resonator is lower than the low-frequency end of the passband. A resonator in which at least a part of the frequency range from the resonance frequency to the anti-resonance frequency, i.e., the resonance band, overlaps with the passband of the surface acoustic wave filter 1 is defined as a resonator contributing to the formation of the passband of the surface acoustic wave filter 1.

[0122] Next, the impedance characteristics and the transmission characteristics of the surface acoustic wave filter 1 will be described.

[0123] Figure 3A It is a graph showing the transmission characteristics in the frequency band near the passband of the surface acoustic wave filter 1 according to the embodiment and the impedance characteristics of the parallel-arm resonator 20. Figure 3B It is a graph showing the impedance characteristics of the wide-area parallel-arm resonator 20 according to the embodiment.

[0124] As Figure 3AAs shown, the resonance frequency frp24 of the parallel-arm resonator 24 is within the above-mentioned passband. On the other hand, the resonance frequency frp20 of the parallel-arm resonator 20 is below the low-frequency end of the passband of the SAW filter 1, and the anti-resonance frequency fap20 of the parallel-arm resonator 20 is above the high-frequency end of the above-mentioned passband. In addition, the frequency difference Δfa between the anti-resonance frequency fap20 and the high-frequency end of the above-mentioned passband is smaller than the frequency difference Δfr between the resonance frequency frp20 and the low-frequency end of the above-mentioned passband.

[0125] In addition, although not shown in Figure 3A , at least one resonance frequency among the series-arm resonators 11 to 14 is within the above-mentioned passband, and at least one anti-resonance frequency among the parallel-arm resonators 21 to 23 is within the above-mentioned passband. Accordingly, the insertion loss of the ladder-type SAW filter 1 can be reduced.

[0126] In a ladder-type SAW filter, by making the resonance frequency of the series-arm resonator and the anti-resonance frequency of the parallel-arm resonator be within the passband, low-loss and steep pass characteristics can be achieved. Therefore, in the passband, the impedance of the SAW filter tends to be at least capacitive. Therefore, in the case of connecting a capacitive circuit such as the low-noise amplifier 2 having a capacitive input impedance to the SAW filter, by disposing an inductive matching circuit between the capacitive circuit and the SAW filter, impedance matching of both can be achieved with a reference impedance.

[0127] In contrast, according to the structure of the SAW filter 1 according to the present embodiment, it is highly likely that at least one of the resonance frequency frp24 and the anti-resonance frequency fap24 of the parallel-arm resonator 24 formed on the same piezoelectric substrate 70 as the series-arm resonators 11 to 14 and the parallel-arm resonators 21 to 23 forming the passband is within the passband. However, by connecting an inductor 34 in series with the parallel-arm resonator 24, the resonance bandwidth of the parallel-arm resonator 20 is expanded, and the above-mentioned passband is adjusted to be between the resonance frequency frp20 and the anti-resonance frequency fap20 of the parallel-arm resonator 20. Thereby, the impedance of the parallel-arm resonator 20 in the above-mentioned passband becomes inductive, and impedance matching of the above-mentioned capacitive circuit and the SAW filter 1 can be achieved without disposing an inductive matching circuit between the above-mentioned capacitive circuit and the SAW filter 1. In addition, by making the anti-resonance frequency fap20 having a high impedance be closer to the above-mentioned passband than the resonance frequency frp20 having 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. Furthermore, as Figure 3BAs shown, the parallel-arm resonator 20 has a high impedance in the DC (direct current) region. Thus, it is possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the surface acoustic wave filter 1 side. Therefore, there is no need to serially arrange a capacitor for DC cut-off in the path connecting the input terminals of the surface acoustic wave filter 1 and the amplification transistors of the low-noise amplifier 2. Therefore, it is possible to provide a low-loss and small-sized surface acoustic wave filter 1 with reduced matching loss and insertion loss on both sides.

[0128] Figure 4 is an admittance diagram showing the impedance characteristics of the surface acoustic wave filter 1 according to the embodiment. As Figure 4 shown in (a) of, the impedance of the passband on the input / output terminal 110 side observed from the node B (the connection node of the series-arm resonator 14 and the parallel-arm resonator 20) ( Figure 4 the thick solid line in (a) of) is located near the reference impedance. That is, the impedance of the surface acoustic wave filter without the parallel-arm resonator 20 is located near the reference impedance. In the state where the parallel-arm resonator 20 is not attached, when the 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 surface acoustic wave filter and the low-noise amplifier 2 deviates from the reference impedance.

[0129] In contrast, as Figure 4 shown in (b) of, the impedance of the passband on the input / output terminal 110 side observed from the node A (input / output terminal 120) ( Figure 4 the thick solid line in (b) of) has the inductive impedance of the parallel-arm resonator 20 added to the impedance at the node B, and thus moves counterclockwise on the constant-conductance circle, and therefore becomes inductive and low impedance.

[0130] Accordingly, it is possible to make the impedance of the high-frequency module 100 having a structure in which the surface acoustic wave filter 1 having an inductive impedance and the low-noise amplifier 2 having a capacitive impedance are connected approach the reference impedance. Therefore, it is possible to reduce the matching loss of the surface acoustic wave filter 1 and the high-frequency module 100.

[0131] In addition, in the surface acoustic wave filter 1 according to the present embodiment, the first parallel-arm resonator (parallel-arm resonator 20) is connected closest to the input / output terminal 120 among the plurality of parallel-arm resonators.

[0132] Accordingly, the resonator showing an inductive impedance in the passband is arranged closest to the input terminal 130 of the low-noise amplifier 2 showing a capacitive impedance, so that the impedance matching between the surface acoustic wave filter 1 and the low-noise amplifier 2 can be made to coincide with high efficiency and high precision.

[0133] In addition, the first parallel-arm resonator may not be connected closest to the input / output terminals 120 among the plurality of parallel-arm resonators, and may be connected to a node on the series-arm path from the input / output terminals 110 to the series-arm resonator 14.

[0134] [Structure of the surface acoustic wave filter 1A according to Modification 1]

[0135] Figure 5 FIG. 3 is a circuit configuration diagram of the surface acoustic wave filter 1A according to Modification 1 of the embodiment. As shown in this figure, the surface acoustic wave filter 1A according to Modification 1 is a band-pass filter (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. Compared with the surface acoustic wave filter 1 according to the embodiment, the structure of the parallel-arm resonator 20A is different. Hereinafter, for the surface acoustic wave filter 1A according to this modification, the description of the same structure as that of the surface acoustic wave filter 1 according to the embodiment will be omitted, and the description will be centered on the different structure.

[0136] The parallel-arm resonator 24 and the inductor 34 connected in series with each other are surface acoustic wave resonators including surface acoustic wave resonators, 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 the 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 the ground. The parallel-arm resonator 24 is an example of a second surface 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.

[0137] 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 with the parallel-arm resonator 24, the resonance frequency frp20A of the parallel-arm resonator 20A is shifted to the lower frequency side with respect to the resonance frequency frp24 of the parallel-arm resonator 24. That is, by connecting the inductor 34 in series with 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.

[0138] The resonant frequency fpr24 of the parallel arm resonator 24 lies within the aforementioned passband. Meanwhile, the resonant frequency fpr20A of the parallel arm resonator 20A lies below the low-frequency end of the passband of the elastic wave filter 1A, while the antiresonant frequency fap20A of the parallel arm resonator 20A lies above the high-frequency end of the passband. Furthermore, the frequency difference Δfa between the antiresonant frequency fap20A and the high-frequency end of the passband is smaller than the frequency difference Δfr between the resonant frequency fpr20A and the low-frequency end of the passband.

[0139] Thus, by connecting the inductor 34 in series with the parallel arm resonator 24, the resonant bandwidth of the parallel arm resonator 20A is expanded, and the passband is adjusted to lie between the resonant frequency frap20A and the antiresonant frequency fap20A of the parallel arm resonator 20A. Consequently, the impedance of the parallel arm resonator 20A in the passband becomes inductive, enabling impedance matching between the capacitive circuit connected to the elastic wave filter 1A and the elastic wave filter 1A without providing an inductive matching circuit between the capacitive circuit and the elastic wave filter 1A. Furthermore, by positioning the antiresonant frequency fap20A, which has high impedance, closer to the passband than the resonant frequency frap20A, which has low impedance, signals in the passband can be transmitted from the input / output terminal 110 to the input / output terminal 120 with low loss. Furthermore, the parallel arm resonator 20A has high impedance in the DC (direct current) region. This prevents the DC bias voltage (DC bias current) supplied to low-noise amplifier 2 from leaking toward elastic wave filter 1A, eliminating the need for a DC cut capacitor between elastic wave filter 1A and low-noise amplifier 2. Consequently, a low-loss and compact elastic wave filter 1A can be provided, with both reduced matching loss and insertion loss.

[0140] [5. Configuration of Filter Circuit 3 and High-Frequency Module 100B According to Modification 2]

[0141] Figure 6A This is a circuit diagram of a filter circuit 3 and a high-frequency module 100B according to Modification 2 of the embodiment. As shown in this figure, high-frequency module 100B includes a filter circuit 3, a low-noise amplifier 2, and an inductor 31. High-frequency module 100B according to this modification differs from high-frequency module 100 according to the embodiment only in that the elastic wave filter 1 is replaced with filter circuit 3. The following description of high-frequency module 100B according to this modification focuses on filter circuit 3, which differs from high-frequency module 100 according to the embodiment.

[0142] The filter circuit 3 includes a parallel arm resonator 20 , filter units 40A, 40B, and 40C, a switch circuit 80 , and input / output terminals 111 , 112 , 113 , and 120 .

[0143] The parallel-arm resonator 20 is an elastic-wave resonator including a parallel-arm resonator element 24 and an inductor 35 that are connected in series with 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 the ground. The parallel-arm resonator element 24 is an example of a second elastic-wave resonator element, 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.

[0144] 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 element 24 has a resonance frequency frp24 and an anti-resonance frequency fap24. By connecting the inductor 35 in series with the parallel-arm resonator element 24, the resonance frequency frp20 of the parallel-arm resonator 20 is shifted to the lower frequency side with respect to the resonance frequency frp24 of the parallel-arm resonator element 24. That is, by connecting the inductor 35 in series with the parallel-arm resonator element 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 element 24.

[0145] The filter section 40A is an example of an elastic-wave filter section, one end of which is connected to the selection terminal 80b of the switch circuit 80, and the other end of which is connected to the input / output terminal 111. The filter section 40A has a circuit structure of the elastic-wave filter 1 according to the embodiment except for the parallel-arm resonator 20, and includes series-arm resonator elements 11, 12, 13, and 14, and parallel-arm resonator elements 21, 22, and 23. That is, the filter section 40A and the parallel-arm resonator 20 separated by the switch circuit 80 have the same circuit structure as the elastic-wave filter 1 according to the embodiment.

[0146] The filter section 40B is an example of a first filter section, one end of which is connected to the selection terminal 80c of the switch circuit 80, and the other end of which is connected to the input / output terminal 112. The filter section 40B has at least any one of an elastic-wave resonator element, an inductor, and a capacitor. The filter section 40B and the parallel-arm resonator 20 (first parallel-arm resonator) are connected by the switch circuit 80, thereby forming a band-pass type first filter.

[0147] One end of the filter section 40C is connected to the selection terminal 80d of the switch circuit 80, and the other end of which is connected to the input / output terminal 113. The filter section 40C has at least any one of an elastic-wave resonator element, an inductor, and a capacitor. The filter section 40C and the parallel-arm resonator 20 (first parallel-arm resonator) are connected by the switch circuit 80, thereby forming a band-pass filter.

[0148] All the surface acoustic wave resonators (series arm resonators 11 to 14 and shunt arm resonators 21 to 23) included in the filter section 40A and the shunt arm resonators 24 included in the shunt arm resonator 20 are formed on the same piezoelectric substrate 70. Accordingly, the filter circuit 3 can be miniaturized.

[0149] In addition, when the filter sections 40B and 40C include surface acoustic wave resonators, the surface acoustic wave resonators included in the filter sections 40B and 40C may also be formed on the piezoelectric substrate 70.

[0150] 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 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. One end of the switch 181 is connected to the common terminal 80a, and the other end is connected to the selection terminal 80b. One end of the switch 183 is connected to the common terminal 80a, and the other end is connected to the selection terminal 80c. One end of the switch 185 is connected to the common terminal 80a, and the other end is connected to the selection terminal 80d. One end of the switch 182 is connected to the connection point between the other end of the switch 181 and the selection terminal 80b, and the other end is connected to the ground. One end of the switch 184 is connected to the connection point between the other end of the switch 183 and the selection terminal 80c, and the other end is connected to the ground. One end of the switch 186 is connected to the connection point between the other end of the switch 185 and the selection terminal 80d, and the other end is connected to the ground.

[0151] In the above structure, 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 turned on, the switches 182, 183, and 185 are turned off, and the filter section 40A and the shunt arm resonator 20 are connected. In addition, 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 turned on, and the switches 184, 181, and 185 are turned off. In addition, 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 turned on, and the switches 186, 181, and 183 are turned off.

[0152] In addition, in the filter circuit 3 according to this modification example, the filter section 40C may be omitted, and in this case, the input / output terminal 113, the selection terminal 80d, the switches 185, and 186 may also be omitted.

[0153] Figure 6B It is a diagram schematically showing the pass characteristics of each filter of the filter circuit 3 and the impedance characteristics of the parallel arm resonator 20 according to the second modification of the embodiment. As shown in this diagram, there are successively from the high-frequency side a passband formed by the filter section 40A and the parallel arm resonator 20, a passband formed by the filter section 40B and the parallel arm resonator 20, and a passband formed by the filter section 40C and the parallel arm resonator 20.

[0154] In addition, the high and low of the frequencies of the above three passbands are not limited to the above order, and in addition, at least a part of the above three passbands may overlap.

[0155] As Figure 6B shown, the resonance frequency frp20 of the parallel arm resonator 20 is below the low-frequency end of the passband on the lowest-frequency side among the above three passbands, and the anti-resonance frequency fap20 of the parallel arm resonator 20 is above the high-frequency end of the passband on the highest-frequency side among the above three passbands.

[0156] Accordingly, it is highly possible that at least one of the resonance frequency frp24 and the anti-resonance frequency fap24 of the parallel arm resonator 24 formed on the same piezoelectric substrate 70 as the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 forming the passband is within the passband. However, by serially connecting the inductor 35 to the parallel arm resonator 24, the resonance bandwidth of the parallel arm resonator 20 is expanded, and the above three passbands are adjusted to be between the resonance frequency frp20 and the anti-resonance frequency fap20 of the parallel arm resonator 20. Thereby, the impedance in the above three passbands of the parallel arm resonator 20 becomes inductive, and impedance matching between the low-noise amplifier 2 (capacitive circuit) connected to the input / output terminal 120 and the filter circuit 3 can be achieved without providing an inductive matching circuit between the low-noise amplifier 2 and the filter circuit 3. In addition, the parallel arm resonator 20 has a high impedance in the DC (direct current) region. Thereby, leakage of the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 to the filter circuit 3 side can be prevented, and thus it is not necessary to serially arrange a DC cutoff capacitor in the path connecting the filter circuit 3 and the low-noise amplifier 2. Therefore, a low-loss and small-sized filter circuit 3 and a high-frequency module 100B can be provided.

[0157] [6 Effects, etc.]

[0158] As described above, the surface acoustic wave filter 1 according to the present embodiment includes a series arm resonator 14 disposed in a series arm path connecting input / output terminals 110 and 120, and a shunt arm resonator 20 connected between the series arm path and ground. The series arm resonator 14 is a first surface acoustic wave resonator, and the shunt arm resonator 20 includes a shunt arm resonator 24 and an inductor 34 connected in series between the series arm path and ground. The series arm resonator 14 and the shunt arm resonator 24 are formed on the same piezoelectric substrate 70. The resonance frequency frp20 of the shunt arm resonator 20 is equal to or lower than the lower frequency end of the passband of the surface acoustic wave filter 1, and the anti-resonance frequency fap20 of the shunt arm resonator 20 is equal to or higher than the upper frequency end of the passband. The frequency difference Δfa between the anti-resonance frequency fap20 and the upper frequency end of the passband is less than the frequency difference Δfr between the resonance frequency frp20 and the lower frequency end of the passband.

[0159] Accordingly, it is highly likely that at least one of the resonance frequency frp24 and the anti-resonance frequency fap24 of the shunt arm resonator 24 formed on the same piezoelectric substrate 70 as the series arm resonator 14 forming the passband is within the passband. However, by connecting the inductor 34 in series with the shunt arm resonator 24, the resonance bandwidth of the shunt arm resonator 20 is expanded, and the passband is adjusted to be between the resonance frequency frp20 and the anti-resonance frequency fap20 of the shunt arm resonator 20. As a result, the impedance of the shunt arm resonator 20 in the passband becomes inductive, and it is possible to match the impedance of the capacitive circuit and the surface acoustic wave filter 1 without providing an inductive matching circuit between the low-noise amplifier 2 having a capacitive impedance connected to the surface acoustic wave filter 1 and the surface acoustic wave filter 1. In addition, by making the anti-resonance frequency fap20 having a high impedance closer to the passband than the resonance frequency frp20 having a low impedance, it is possible to transmit the signal in the passband from the input / output terminal 110 to the input / output terminal 120 with low loss. Furthermore, since the shunt arm resonator 20 has a 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 surface acoustic wave filter 1 side. Therefore, it is not necessary to serially arrange a DC cut-off capacitor in the path connecting the surface acoustic wave filter 1 and the low-noise amplifier 2. Therefore, it is possible to provide a low-loss and small-sized surface acoustic wave filter 1 with reduced matching loss and insertion loss.

[0160] In addition, for example, in the surface acoustic wave filter 1, the resonance frequency frp24 of the shunt arm resonator 24 is within the passband.

[0161] Based on this, although the resonance bandwidth of the parallel arm resonator 24 is expected to be smaller than the above-mentioned passband, the resonance bandwidth of the parallel arm resonator 20 can be expanded by connecting the inductor 34 in series with the parallel arm resonator 24. As a result, the impedance of the parallel arm resonator 20 in the above-mentioned passband can be made inductive using a small parallel arm resonator 24.

[0162] Furthermore, for example, in the elastic wave filter 1 , all the elastic wave resonators included in the elastic wave filter 1 are formed on the piezoelectric substrate 70 .

[0163] This allows the elastic wave filter 1 to be miniaturized.

[0164] For example, the elastic 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.

[0165] Thus, parallel arm resonator 20 , which exhibits inductive impedance in the passband, is arranged closest to input terminal 130 of low-noise amplifier 2 , which exhibits capacitive impedance, among the plurality of parallel arm resonators. This allows impedance matching between elastic wave filter 1 and low-noise amplifier 2 to be achieved efficiently and accurately.

[0166] Furthermore, for example, in the elastic wave filter 1 , the parallel arm resonator 24 is connected to the series arm path, and the inductor 34 is connected to the ground.

[0167] Thus, when the parallel arm resonator 24 and the series arm resonator 14 are formed on a single piezoelectric substrate 70, the wiring connecting the parallel arm resonator 24 and the series arm resonator 14, as well as the wiring connecting the parallel arm resonator 24 and the inductor 34, can be shortened. Consequently, the elastic wave filter 1 can have low loss.

[0168] Furthermore, for example, in the elastic wave filter 1A according to Modification 1, the parallel arm resonator 24 is connected to the ground, and the inductor 34 is connected to the series arm path.

[0169] In addition, for example, the filter circuit 3 according to the second modification includes: a surface acoustic wave filter 1 (or 1A); a first band-pass filter; and a switch circuit 80 having a common terminal 80a, a selection terminal 80b, and a selection terminal 80c, which switches 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 surface acoustic wave filter 1 includes a shunt arm resonator 20 and a filter section 40A, and the first filter includes a shunt arm resonator 20 and a filter section 40B. The shunt arm resonator 20 is connected to the common terminal 80a, the filter section 40A is connected to the selection terminal 80b, and the filter section 40B is connected to the selection terminal 80c. The resonance frequency frp20 is equal to or lower than the lower low-frequency end of the passband of the surface acoustic wave filter 1 and the lower low-frequency end of the passband of the first filter, and the anti-resonance frequency fap20 is equal to or higher than the higher high-frequency end of the passband of the surface acoustic wave filter 1 and the higher high-frequency end of the passband of the first filter.

[0170] Accordingly, there is a high possibility that at least one of the resonance frequency frp24 and the anti-resonance frequency fap24 of the shunt arm resonator 24 formed on the piezoelectric substrate 70 identical to the series arm resonator 14 forming the filter section 40A of the passband is within the passband. However, by connecting an inductor 35 in series with the shunt arm resonator 24, the resonance bandwidth of the shunt arm resonator 20 is expanded, and the passbands of the surface acoustic wave filter 1 and the first filter are adjusted to be between the resonance frequency frp20 and the anti-resonance frequency fap20 of the shunt arm resonator 20. As a result, the impedance in the above two passbands of the shunt arm resonator 20 becomes inductive, and impedance matching between the low-noise amplifier 2 (capacitive circuit) connected to the input / output terminal 120 and the filter circuit 3 can be achieved without providing an inductive matching circuit between the low-noise amplifier 2 and the filter circuit 3. In addition, the shunt arm resonator 20 has a high impedance in the DC (direct current) region. Accordingly, leakage of the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 to the filter circuit 3 side can be prevented, and thus there is no need to serially arrange a capacitor for DC cut-off in the path connecting the filter circuit 3 and the low-noise amplifier 2. Therefore, a filter circuit 3 with low loss and small size can be provided.

[0171] In addition, for example, the high-frequency module 100 according to the embodiment includes a surface acoustic wave filter 1 and a low-noise amplifier 2 having an input terminal 130 connected to an input / output terminal 120.

[0172] Accordingly, it is possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the surface acoustic wave filter 1 side. Therefore, there is no need to serially arrange a capacitor for DC cut-off in the path connecting the surface acoustic wave filter 1 and the low-noise amplifier 2. Thus, it is possible to provide a low-loss and small-sized high-frequency module 100 with reduced matching loss and insertion loss both.

[0173] In addition, for example, in the high-frequency module 100, a capacitor is not serially arranged in the path connecting the input terminal of the amplification transistor included in the low-noise amplifier 2 and the input / output terminal 120.

[0174] Accordingly, it is possible to miniaturize the high-frequency module 100.

[0175] In addition, for example, the high-frequency module 100B according to the second modification includes a filter circuit 3 and a low-noise amplifier 2 whose input terminal 130 is connected to the connection point between the common terminal 80a and the shunt-arm resonator 20.

[0176] Accordingly, it is possible to prevent the DC bias voltage (DC bias current) supplied to the low-noise amplifier 2 from leaking to the filter circuit 3 side. Therefore, there is no need to serially arrange a capacitor for DC cut-off in the path connecting the filter circuit 3 and the low-noise amplifier 2. Thus, it is possible to provide a low-loss and small-sized high-frequency module 100B with reduced matching loss and insertion loss both.

[0177] In addition, for example, in the high-frequency module 100B, a capacitor is not serially arranged in the path connecting the input terminal 130 of the low-noise amplifier 2 and the above connection point.

[0178] Accordingly, it is possible to miniaturize the high-frequency module 100B.

[0179] (Other embodiments)

[0180] As described above, regarding the surface acoustic wave filter, filter circuit, and high-frequency module according to the present invention, embodiments and modifications have been described. However, the present invention is not limited to the above embodiments and modifications. Modifications obtained by making various modifications conceived by those skilled in the art to the above embodiments and modifications within the scope not departing from the gist of the present invention, and various devices incorporating the surface acoustic wave filter, filter circuit, and high-frequency module according to the present invention are also included in the present invention.

[0181] In addition, for example, in the surface acoustic wave filter, filter circuit, and high-frequency module according to the above embodiments and modifications, matching elements such as inductors and capacitors, and switch circuits may be connected between the respective components.

[0182] Hereinafter, the features of the surface acoustic wave filter, filter circuit, and high-frequency module described based on the above-described embodiments and modified examples will be shown.

[0183] <1> A surface acoustic wave filter is a band-pass type surface acoustic wave filter, wherein

[0184] it includes:

[0185] a first series-arm resonator disposed in a series-arm path connecting a first input / output terminal and a second input / output terminal; and

[0186] a first shunt-arm resonator connected between the series-arm path and ground,

[0187] the first series-arm resonator includes a first surface acoustic wave resonator,

[0188] the first shunt-arm resonator includes a second surface acoustic wave resonator and a first inductor connected in series between the series-arm path and ground,

[0189] the first surface acoustic wave resonator and the second surface acoustic wave resonator are formed on the same piezoelectric substrate,

[0190] a first resonance frequency, which is the resonance frequency of the first shunt-arm resonator, is below the low-frequency end of the passband of the surface acoustic wave filter, and a first anti-resonance frequency, which is the anti-resonance frequency of the first shunt-arm resonator, is above the high-frequency end of the passband,

[0191] a frequency difference between the first anti-resonance frequency and the high-frequency end of the passband is smaller than a frequency difference between the first resonance frequency and the low-frequency end of the passband.

[0192] <2>

[0193] The surface acoustic wave filter according to <1>, wherein

[0194] the resonance frequency of the second surface acoustic wave resonator is within the passband.

[0195] <3>

[0196] The surface acoustic wave filter according to <1> or <2>, wherein

[0197] it includes:

[0198] a plurality of series-arm resonators including the first series-arm resonator; and

[0199] a plurality of shunt-arm resonators including the first shunt-arm resonator,

[0200] the plurality of series-arm resonators and the plurality of shunt-arm resonators each include a surface acoustic wave resonator,

[0201] All of the surface acoustic wave resonators included in the surface acoustic wave filter are formed on the piezoelectric substrate.

[0202] <4>

[0203] The surface acoustic wave filter according to <1> or <2>, wherein

[0204] comprises:

[0205] a plurality of series-arm resonators including the first series-arm resonator; and

[0206] a plurality of shunt-arm resonators including the first shunt-arm resonator,

[0207] the first shunt-arm resonator is connected closest to the first input / output terminal among the plurality of shunt-arm resonators.

[0208] <5>

[0209] The surface acoustic wave filter according to any one of <1> to <4>, wherein

[0210] the second surface acoustic wave resonator is connected to the series-arm path, and the first inductor is connected to ground.

[0211] <6>

[0212] The surface acoustic wave filter according to any one of <1> to <4>, wherein

[0213] the second surface acoustic wave resonator is connected to ground, and the first inductor is connected to the series-arm path.

[0214] <7>

[0215] A filter circuit comprising:

[0216] the surface acoustic wave filter according to any one of <1> to <6>;

[0217] a band-pass type first filter; and

[0218] a first switch circuit having a common terminal, a first selection terminal, and a second selection terminal, and switching the connection between the common terminal and the first selection terminal and the connection between the common terminal and the second selection terminal,

[0219] the surface acoustic wave filter has the first shunt-arm resonator and a surface acoustic wave filter section,

[0220] the first filter has the first shunt-arm resonator and a first filter section,

[0221] the first shunt-arm resonator is connected to the common terminal,

[0222] The elastic wave filter unit is connected to the first selection terminal.

[0223] The first filter unit is connected to the second selection terminal.

[0224] The first resonant frequency is below the low-frequency end of the passband of the elastic wave filter and the low-frequency end of the passband of the first filter, and the first anti-resonant frequency is above the high-frequency end of the passband of the elastic wave filter and the high-frequency end of the passband of the first filter.

[0225] <8>

[0226] A high-frequency module, comprising:

[0227] The elastic wave filter according to any one of <1> to <6>; and

[0228] The low noise amplifier has an input terminal connected to the first input / output terminal.

[0229] <9>

[0230] The high-frequency module according to <8>,

[0231] No capacitor is arranged in series in a path connecting the input end of the amplifier transistor included in the low-noise amplifier and the first input / output terminal.

[0232] <10>

[0233] A high-frequency module, comprising:

[0234] <7> The filter circuit described; and

[0235] The low-noise amplifier has an input terminal connected to a connection point between the common terminal and the first parallel arm resonator.

[0236] <11>

[0237] The high-frequency module according to <10>,

[0238] No capacitor is arranged in series on the path connecting the input terminal and the connection point.

[0239] Industrial Applicability

[0240] The present invention can be widely used in communication devices such as mobile phones as a low-loss elastic wave filter, a filter circuit, and a high-frequency module applicable to multi-band frequency standards.

Claims

1. An elastic wave filter, which is a bandpass elastic wave filter, wherein: have: a first series arm resonator arranged in a series arm path connecting the first input / output terminal and the second input / output terminal; and a first parallel arm resonator connected between the series arm path and ground; The first series arm resonator includes a first elastic wave resonator. The first parallel arm resonator includes a second elastic wave resonator and a first inductor connected in series between the series arm path and ground. The first elastic wave resonator and the second elastic wave resonator are formed on the same piezoelectric substrate. A first resonance frequency, which is the resonance frequency of the first parallel arm resonator, is below the low-frequency end of the passband of the elastic wave filter, and a first antiresonance frequency, which is the antiresonance frequency of the first parallel arm resonator, is above the high-frequency end of the passband. A frequency difference between the first anti-resonance frequency and a high-frequency end of the passband is smaller than a frequency difference between the first resonant frequency and a low-frequency end of the passband.

2. The elastic wave filter according to claim 1, wherein The resonant frequency of the second elastic wave resonator is within the passband.

3. The elastic wave filter according to claim 1 or 2, wherein have: a plurality of series arm resonators, including the first series arm resonator; and a plurality of parallel arm resonators, including the first parallel arm resonator, The plurality of series arm resonators and the plurality of parallel arm resonators each include an elastic wave resonator. All of the elastic wave resonators included in the elastic wave filter are formed on the piezoelectric substrate.

4. The elastic wave filter according to claim 1 or 2, wherein have: a plurality of series arm resonators, including the first series arm resonator; and 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.

5. The elastic wave filter according to any one of claims 1 to 4, wherein The second elastic wave resonator is connected to the series arm path, and the first inductor is connected to the ground.

6. The elastic wave filter according to any one of claims 1 to 4, wherein The second elastic wave resonator is connected to the ground, and the first inductor is connected to the series arm path.

7. A filter circuit comprising: The elastic wave filter according to any one of claims 1 to 6; a first filter of a bandpass type; and The first switch circuit includes a common terminal, a first selection terminal, and a second selection terminal, and switches between a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal. The elastic wave filter includes the first parallel arm resonator and an elastic 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 elastic wave filter unit is connected to the first selection terminal. The first filter unit is connected to the second selection terminal. The first resonance frequency is below the lower end of the low-frequency side among the lower end of the passband of the elastic wave filter and the lower end of the passband of the first filter, and the first anti-resonance frequency is above the upper end of the high-frequency side among the upper end of the passband of the elastic wave filter and the upper end of the passband of the first filter.

8. A high-frequency module, comprising: The elastic wave filter according to any one of claims 1 to 6; and A low-noise amplifier, the input terminal of which is connected to the first input / output terminal.

9. The high-frequency module according to claim 8, wherein A capacitor is not serially disposed in the path connecting the input terminal of the amplification transistor included in the low-noise amplifier and the first input / output terminal.

10. A high-frequency module, comprising: The filter circuit according to claim 7; and A low-noise amplifier, the input terminal of which is connected to the connection point between the common terminal and the first parallel-arm resonator.

11. The high-frequency module according to claim 10, wherein A capacitor is not serially disposed in the path connecting the input terminal and the connection point.

Images