WO2023248815A1

WO2023248815A1 - Elastic wave filter and communication device

Info

Publication number: WO2023248815A1
Application number: PCT/JP2023/021366
Authority: WO
Inventors: 直史笠松
Original assignee: 京セラ株式会社
Priority date: 2022-06-22
Filing date: 2023-06-08
Publication date: 2023-12-28

Abstract

In the present invention, the frequency characteristics of an elastic wave filter are improved. This elastic wave filter has a first elastic wave resonator. The width of the frequency band of the first elastic wave resonator is represented as Δf, a band ranging from a first end point indicating the frequency at the high-frequency end of a passband of the elastic wave filter to a second end point indicating a frequency exactly Δf higher than the first end point is referred to as a first band, and a band ranging from a third end point indicating the frequency at the low-frequency end of the passband of the elastic wave filter to a fourth end point indicating a frequency exactly Δf lower than the third end point is referred to as a second band. Spuriousness of the first elastic wave resonator is located outside of the frequency band of the first elastic wave resonator and is located either in the passband of the elastic wave filter, in the first band, or in the second band. The elastic wave filter further has an element connected in parallel or in series to the first elastic wave resonator. The element is a capacitor or an inductor.

Description

Elastic wave filters and communication devices

One aspect of the present disclosure relates to an elastic wave filter.

Patent Document 1 below discloses a configuration example of an elastic wave filter.

International Publication No. 2019/009271

An elastic wave filter according to an aspect of the present disclosure is an elastic wave filter having a first elastic wave resonator, in which the width of the frequency band of the first elastic wave resonator is expressed as Δf, and the elastic wave filter passes through the elastic wave filter. A band extending from a first end point indicating a frequency at the end of the high frequency side of the band to a second end point indicating a frequency higher than the first end point by Δf is referred to as a first band, and the band extends through the passage of the elastic wave filter. A band extending from a third end point indicating a frequency at the end of the low frequency side of the band to a fourth end point indicating a frequency lower by Δf than the third end point is referred to as a second band, and the first elastic wave resonance The child spurious is located outside the frequency band of the first elastic wave resonator and within either the pass band, the first band, or the second band of the elastic wave filter. The elastic wave filter further includes an element connected in parallel or series to the first elastic wave resonator, and the element is a capacitor or an inductor.

1 is a diagram illustrating the basic configuration of an elastic wave filter of Embodiment 1. FIG. 3 is a diagram showing an example of the configuration of an elastic wave resonator in the elastic wave filter of Embodiment 1. FIG. FIG. 2 is a diagram schematically showing an example of frequency characteristics of an elastic wave filter according to one aspect of the present disclosure. FIG. 3 is a diagram schematically showing an example of frequency characteristics of a first elastic wave resonator according to one aspect of the present disclosure. 2 is a diagram showing a first configuration example of an elastic wave filter according to the basic configuration of FIG. 1. FIG. 2 is a diagram showing a second configuration example of an elastic wave filter according to the basic configuration of FIG. 1. FIG. 2 is a diagram showing a third configuration example of an elastic wave filter according to the basic configuration of FIG. 1. FIG. FIG. 3 is a diagram showing a fourth configuration example of an elastic wave filter according to the basic configuration of FIG. 1; It is a figure which shows an example of the phase characteristic and impedance characteristic of the 1st elastic wave resonator in the elastic wave filter based on the 1st example of a structure. It is a figure which shows an example of the phase characteristic and impedance characteristic of the 1st elastic wave resonator in the elastic wave filter based on the 2nd example of a structure. It is a figure which shows an example of the phase characteristic and impedance characteristic of the 1st elastic wave resonator in the elastic wave filter based on the 3rd example of a structure. It is a figure which shows an example of the phase characteristic and impedance characteristic of the 1st elastic wave resonator in the elastic wave filter based on the 4th example of a structure. FIG. 7 is a diagram showing another example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter according to the first configuration example. FIG. 3 is a diagram for explaining a change in phase characteristics of a first elastic wave resonator in an elastic wave filter according to a first configuration example. FIG. 7 is a diagram for explaining a change in phase characteristics of a first elastic wave resonator in an elastic wave filter according to a second configuration example. FIG. 7 is a diagram for explaining a change in phase characteristics of the first elastic wave resonator according to a third configuration example. It is a figure for explaining the change of the phase characteristic of the 1st elastic wave resonator concerning the 4th example of composition. 3 is a diagram illustrating a schematic configuration of a communication device in Embodiment 2. FIG.

[Embodiment 1]
Embodiment 1 will be described below. For convenience of explanation, components having the same functions as the components (components) described in Embodiment 1 are given the same reference numerals in each of the subsequent embodiments, and the description thereof will not be repeated. For the sake of brevity, descriptions of known technical matters will be omitted as appropriate. Each component, each material, and each numerical value described in this specification is merely an example unless there is a contradiction. Therefore, for example, unless there is a particular contradiction, the positional relationship and connection relationship of each component is not limited to the example shown in each figure. Further, each figure is not necessarily shown to scale.

(Basic configuration of elastic wave filter)
FIG. 1 illustrates the basic configuration of an elastic wave filter 100 according to a first embodiment. In the first embodiment, an elastic wave filter 100 as a ladder type filter is illustrated. However, as is clear to those skilled in the art, the elastic wave filter according to one aspect of the present disclosure is not limited to the ladder type filter.

The elastic wave filter 100 may have at least one elastic wave resonator including a first elastic wave resonator. Therefore, for example, the elastic wave filter 100 may include a plurality of elastic wave resonators. In other words, the elastic wave filter 100 may further include a second elastic wave resonator different from the first elastic wave resonator. In the example of FIG. 1, the elastic wave filter 100 has three elastic wave resonators 1.

As shown in FIG. 1, the elastic wave filter 100 may include, as the elastic wave resonator 1, an elastic wave resonator (series resonator) located in the series arm SL. In the example of FIG. 1, the elastic wave filter 100 includes a series resonator 1S-1 and a series resonator 1S-2. In this specification, the series resonator 1S-1 and the series resonator 1S-2 are also generically referred to as the series resonator 1S.

The series arm SL may be connected to the input terminal Pin and the output terminal Pout. In the example of FIG. 1, the series resonator 1S-1 is the series resonator on the side closer to the input terminal Pin (the series resonator on the input side), and the series resonator 1S-2 is the series resonator on the side closer to the output terminal Pout. (series resonator on the output side).

The elastic wave filter 100 may include, as the elastic wave resonator 1, an elastic wave resonator (parallel resonator) located in the parallel arm PL. In the example of FIG. 1, the elastic wave filter 100 has a parallel resonator 1P. The parallel arm PL may extend from between the series resonator 1S-1 and the series resonator 1S-2, and may be connected to the ground terminal GND via the parallel resonator 1P.

In FIG. 1, a case is illustrated in which the series resonator 1S-1 is the first elastic wave resonator. However, as is clear from each description below, the first elastic wave resonator may be any one of the at least one elastic wave resonator 1 included in the elastic wave filter 100. Therefore, as described later, the parallel resonator 1P may be the first elastic wave resonator.

The elastic wave filter 100 may further include an element EL connected in parallel or series to the first elastic wave resonator. In the example of FIG. 1, element EL is connected in parallel to series resonator 1S-1. As discussed in more detail below, element EL may be a capacitor or an inductor. A plurality of variations of the elastic wave filter according to the basic configuration shown in FIG. 1 will be described later.

As an example, element EL may be embodied by a discrete component. As another example, the element EL may be realized by electrode wiring on the piezoelectric layer 2 described below. As yet another example, the acoustic wave filter 100 may have a multilayer substrate including a dielectric layer and a conductor layer. In this case, the element EL may be embodied by an electrode pattern within the multilayer substrate.

(Example of configuration of elastic wave resonator)
FIG. 2 shows an example of the configuration of the elastic wave resonator 1 in the elastic wave filter 100. In FIG. 2, the laminated structure of the elastic wave resonator 1 is schematically shown. In the following description, for convenience, the orthogonal coordinate system (xyz coordinate system) shown in FIG. 2 will be introduced. The x direction in the example of the first embodiment is the propagation direction of the elastic wave propagating within the piezoelectric layer 2 in the elastic wave filter 100. On the other hand, the y direction is an example of a direction intersecting the x direction. The z direction is the thickness direction of each member of the elastic wave resonator 1. In the following description, the positive direction in the z direction is assumed to be an upward direction. Therefore, the negative direction in the z direction is downward.

The elastic wave filter 100 may include (i) a support substrate 5 and (ii) a piezoelectric layer 2 located on the support substrate 5. The support substrate 5 and the piezoelectric layer 2 may be common to at least one elastic wave resonator 1. The elastic wave resonator 1 may include an IDT (Interdigital Transduce) electrode 3 located on the piezoelectric layer 2 . Each of the at least one acoustic wave resonator 1 may have an individual IDT electrode 3 .

The support substrate 5 supports each part of the acoustic wave filter 100. As an example, the support substrate 5 may be a Si substrate. The piezoelectric layer 2 may be made of a single crystal material having piezoelectricity. For example, the material of the piezoelectric layer 2 may be lithium tantalate (also referred to as LiTaO ₃ :LT) or lithium niobate (also referred to as LiNbO ₃ :LN). As an example, the piezoelectric layer 2 may be an LT layer.

The IDT electrode 3 may include, for example, a conductive layer made of metal. As an example, the metal may be Al. The IDT electrode 3 may further include a protective layer covering the conductive layer. As an example, the material of the protective layer may be TEOS (Tetraethyl Orthosilicate). The IDT electrode 3 may include a first bus bar and a second bus bar (not shown) that face each other in the y direction.

The IDT electrode 3 includes (i) a plurality of first electrode fingers 32a connected to the first bus bar, and (ii) a plurality of second electrode fingers 32b connected to the second bus bar. good. The first electrode finger 32a may extend from the first bus bar toward the second bus bar in the y direction. The second electrode finger 32b may extend from the second bus bar toward the first bus bar in the y direction. Therefore, the second electrode finger 32b may be inserted into each of the plurality of first electrode fingers 32a in the y direction.

As shown in FIG. 2, the first electrode fingers 32a and the second electrode fingers 32b may be alternately and repeatedly positioned on the piezoelectric layer 2 at approximately constant intervals in the x direction. In this specification, the first electrode finger 32a and the second electrode finger 32b are also generically referred to as electrode fingers 32. In this specification, the electrode finger pitch of the IDT electrode 3 is expressed as p. p may be, for example, the pitch (repetition interval) between the centers of two adjacent electrode fingers 32 in the x direction. As an example, p may be set equal to the half value (λ/2) of the wavelength λ of the elastic wave excited by the IDT electrode 3. In this case, λ may be defined as twice the length of p. Therefore, in the first embodiment, a case where λ=2p is exemplified.

Furthermore, in this specification, the length of the electrode finger 32 in the x direction is referred to as the width w of the electrode finger 32. w may be set as appropriate, for example, depending on the electrical characteristics required of the elastic wave resonator 1. As an example, w may be set according to p. In this specification, the ratio (w/p) of the width of the electrode finger to the pitch of the electrode finger is referred to as the duty of the electrode finger. By changing the duty, the frequency characteristics of the elastic wave resonator 1 can be controlled. Therefore, by changing the Duty, the frequency characteristics of the elastic wave filter 100 can be controlled.

However, the frequency characteristics of the elastic wave resonator 1 can also be controlled by changing either w or p. In this specification, a case will be illustrated later in which the frequency characteristics of the elastic wave resonator 1 are controlled by changing p.

In this specification, the thickness of the piezoelectric layer 2 is expressed as T. Embodiment 1 exemplifies a case where the piezoelectric layer 2 is sufficiently thin, that is, a case where T is sufficiently small. As an example, T may be less than or equal to λ. In this case, the IDT electrode 3 can excite plate waves (Lamb waves) as elastic waves. As an example, the IDT electrode 3 can excite an A1 Lamb wave as a plate wave.

(Schematic example of attenuation characteristics of elastic wave filter)
FIG. 3 schematically shows an example of frequency characteristics (more specifically, attenuation characteristics) of an elastic wave filter (eg, elastic wave filter 100) according to one aspect of the present disclosure. In the graph of FIG. 3, the horizontal axis (Frequency) indicates frequency (unit: Hz), and the vertical axis (transmission) indicates attenuation (unit: dB). The amount of attenuation can also be read as the amount of transmission. Therefore, the attenuation characteristic can also be read as the transmission characteristic.

In this specification, the passband of an elastic wave filter refers to a frequency band from a low frequency side cutoff frequency to a high frequency side cutoff frequency. In the attenuation characteristic of the elastic wave filter 100, there are -3 dB attenuation points on each of the low frequency side and the high frequency side with respect to the peak frequency indicating the frequency at the minimum attenuation amount of 0 dB.

The high frequency side cutoff frequency (fcut1 in FIG. 3) is the frequency of the −3 dB attenuation point on the high frequency side of the passband of the elastic wave filter. fcut1 can also be expressed as the frequency at the end of the high frequency side of the passband. The low frequency side cutoff frequency (fcut2 in FIG. 3) is the frequency of the −3 dB attenuation point on the low frequency side. fcut2 can also be expressed as the frequency at the lower frequency side end of the passband. Therefore, the passband of the elastic wave filter is a band extending from fcut2 to fcut1.

In this specification, the width of the frequency band of the first elastic wave resonator is expressed as Δf. The definition of Δf will be described later. In this specification, the band extending from the first end point to the second end point is referred to as a first band. The first end point may be a point indicating the frequency at the end of the high frequency side of the passband of the elastic wave filter (ie, fcut1). The second end point may point to a frequency that is +Δf higher than the first starting point (ie, fcut1+Δf).

Furthermore, in this specification, the band from the third end point to the fourth end point is referred to as a second band. The third end point may be a point indicating the frequency at the lower frequency side end of the passband of the elastic wave filter (ie, fcut2). The fourth endpoint may be a point pointing to a frequency that is Δf lower than the third endpoint (ie, fcut2−Δf).

As shown in FIG. 3, in the elastic wave filter according to one aspect of the present disclosure, the spurious of the first elastic wave resonator is located within a band extending from the fourth end point (fcut2-Δf) to the second end point (fcut1+Δf). I can do it. In other words, the spurious of the first elastic wave resonator may be located within the pass band, within the first band, or within the second band of the elastic wave filter.

(Schematic example of phase characteristics of the first elastic wave resonator)
FIG. 4 schematically shows an example of frequency characteristics (more specifically, phase characteristics) of the first elastic wave resonator according to one aspect of the present disclosure. The vertical axis (Phase) in the graph of FIG. 4 represents the phase (hereinafter simply referred to as "phase") of the impedance of the first elastic wave resonator (unit: degrees). FIG. 4 shows the phase characteristics of the first elastic wave resonator before being connected to the element EL (that is, the phase characteristics of the first elastic wave resonator alone).

As shown in FIG. 4, the width of the frequency band of the first elastic wave resonator may be determined as Δf=|fa−fr|. fr is the resonant frequency of the first elastic wave resonator, and fa is the anti-resonant frequency of the first elastic wave resonator. In this way, the frequency band of the first elastic wave resonator may range from fr to fa. In the first embodiment, a case where fr<fa is illustrated. In the example of FIG. 4, the frequency band of the first elastic wave resonator is located on the lower frequency side than the above-mentioned second band.

In this specification, the magnitude (absolute value) of the impedance of the first elastic wave resonator is expressed as |Z|. In the following description, the magnitude of impedance will be simply abbreviated as impedance unless there is a particular contradiction. In this specification, fr is defined as the frequency at which the impedance is minimum. On the other hand, fa is determined as the frequency at which the impedance is maximum. An example of a graph showing the impedance characteristics of the first elastic wave resonator will be described later.

As shown in FIG. 4, the phase peak of the first elastic wave resonator is generally located within the frequency band of the first elastic wave resonator. On the other hand, the spurious of the first elastic wave resonator is generally located outside the frequency band of the first elastic wave resonator. As described in FIG. 3 above, the spurious of the first elastic wave resonator can be located within the pass band, the first band, or the second band of the elastic wave filter. In the example of FIG. 4, the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter.

(Each configuration example of elastic wave filter)
FIG. 5 shows a first configuration example of an elastic wave filter according to the basic configuration of FIG. The elastic wave filter shown in FIG. 5 is referred to as an elastic wave filter 100-1. The first elastic wave resonator in the elastic wave filter 100-1 may be a series resonator (eg, series resonator 1S-1).

The elastic wave filter 100-1 may include a capacitor CP connected in parallel to the first elastic wave resonator (eg, series resonator 1S-1) as an element EL. Therefore, the elastic wave filter 100-1 may include a first unit UN1 configured by connecting a series resonator, which is a first elastic wave resonator, and a capacitor CP in parallel. As will be described later, in the elastic wave filter 100-1, the spurious of the first elastic wave resonator may be located within the first band.

FIG. 6 shows a second configuration example of an elastic wave filter according to the basic configuration of FIG. 1. The elastic wave filter shown in FIG. 6 is referred to as an elastic wave filter 100-2. In the elastic wave filter 100-2 as well, the first elastic wave resonator may be a series resonator (eg, series resonator 1S-1).

The elastic wave filter 100-2 may include an inductor LP connected in parallel to the first elastic wave resonator (eg, series resonator 1S-1) as an element EL. Therefore, the elastic wave filter 100-2 may include a second unit UN2 configured by connecting a series resonator, which is a first elastic wave resonator, and an inductor LP in parallel. Elastic wave filter 100-2 is another configuration example of elastic wave filter 100-1. As described later, in the elastic wave filter 100-2, the spurious of the first elastic wave resonator may be located within the second band.

FIG. 7 shows a third configuration example of an elastic wave filter according to the basic configuration of FIG. 1. The elastic wave filter shown in FIG. 7 is referred to as an elastic wave filter 100-3. The first elastic wave resonator in the elastic wave filter 100-3 may be a parallel resonator (eg, parallel resonator 1P).

The elastic wave filter 100-3 may have an inductor LS connected in series to the first elastic wave resonator (eg, parallel resonator 1P) as an element EL. Therefore, the elastic wave filter 100-3 may include a third unit UN3 configured by connecting a parallel resonator, which is a first elastic wave resonator, and an inductor LS in series. As described later, in the elastic wave filter 100-3, the spurious of the first elastic wave resonator may be located within the first band.

FIG. 8 shows a fourth configuration example of an elastic wave filter according to the basic configuration of FIG. 1. The elastic wave filter shown in FIG. 8 is referred to as an elastic wave filter 100-4. In the elastic wave filter 100-4 as well, the first elastic wave resonator may be a parallel resonator (eg, parallel resonator 1P).

The elastic wave filter 100-4 may have a capacitor CS connected in series to the first elastic wave resonator (eg, parallel resonator 1P) as an element EL. Therefore, the elastic wave filter 100-4 may include a fourth unit UN4 configured by connecting a parallel resonator, which is a first elastic wave resonator, and a capacitor CS in series. Elastic wave filter 100-4 is another configuration example of elastic wave filter 100-3. As will be described later, in the elastic wave filter 100-4, the spurious of the first elastic wave resonator may be located within the second band.

(Frequency characteristics of the first elastic wave resonator in each elastic wave filter)
Next, an example of the frequency characteristics of the first elastic wave resonator in each of the above elastic wave filters will be described. In each example described below, the design conditions for the first elastic wave resonator are:
・p (electrode finger pitch of IDT electrode): 1.26 μm
・Duty of IDT electrode: 0.7
・Number of electrode fingers of IDT electrode: 150
・Intersection width of electrode fingers of IDT electrode: 61.2 μm
It is. However, in the example of FIG. 13 described later, different design conditions may be applied.

The elastic wave filters of each example are designed to have T (thickness of the piezoelectric layer) = 0.48 μm. According to the above design conditions, λ=2.52 μm. Therefore, for each example elastic wave filter, T is smaller than λ.

In addition, in each example of the elastic wave filter, the first elastic wave resonator is designed so that fa=4835.1 MHz. The horizontal axis of each graph shown below indicates the normalized frequency fn. fn is given as the frequency f divided by fa. Therefore, the horizontal axis of each graph shown below may be read as f.

It should be noted that, unlike the example of FIG. 4 described above, the frequency characteristics shown below are the frequency characteristics of the first elastic wave resonator in a state connected to the element EL in the elastic wave filter. That is, it should be noted that the frequency characteristics shown below are not the frequency characteristics of the first elastic wave resonator in a state before being connected to the element EL (the frequency characteristics of the first elastic wave resonator alone). Therefore, fr and fa in each of the following descriptions are the resonant frequency and anti-resonant frequency of the first elastic wave resonator in a state connected to the element EL, respectively, unless otherwise specified.

FIG. 9 shows an example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter 100-1. In FIG. 9, reference numeral 900A indicates the phase characteristic of the first elastic wave resonator in the elastic wave filter 100-1, and reference numeral 900B indicates the impedance characteristic of the first elastic wave resonator. In the example of FIG. 9, the capacitance of the capacitor CP is also expressed as CP. In FIG. 9, characteristics corresponding to various values of CP are shown. The case of CP=0.0 pF corresponds to the case where the elastic wave filter 100-1 does not have a capacitor CP (comparative example).

As shown in FIG. 9, in the elastic wave filter 100-1 (that is, a configuration in which a capacitor is connected in parallel to a series resonator that is a first elastic wave resonator), fr is independent of the value of CP. , was confirmed to be almost constant. Furthermore, when the elastic wave filter 100-1 includes the capacitor CP, it was confirmed that fa tends to decrease compared to the comparative example (CP=0.0 pF).

FIG. 10 shows an example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter 100-2. In FIG. 10, the reference numeral 1000A indicates the phase characteristic of the first elastic wave resonator in the elastic wave filter 100-2, and the reference numeral 1000B indicates the impedance characteristic of the first elastic wave resonator. In the example of FIG. 10, the inductance of the inductor LP is also expressed as LP. In FIG. 10, each characteristic corresponding to various values of LP is shown. The case of LP=0.0 nH corresponds to the case where the elastic wave filter 100-2 does not have an inductor LP (comparative example).

As shown in FIG. 10, in the elastic wave filter 100-2 (that is, the configuration in which the inductor is connected in parallel to the series resonator that is the first elastic wave resonator), fr is independent of the value of LP. It was confirmed that it is almost constant. Furthermore, when the elastic wave filter 100-2 includes the inductor LP, it was confirmed that fa tends to increase compared to the comparative example (LP=0.0 nH).

FIG. 11 shows an example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter 100-3. In FIG. 11, reference numeral 1100A indicates the phase characteristic of the first elastic wave resonator in the elastic wave filter 100-3, and reference numeral 1100B indicates the impedance characteristic of the first elastic wave resonator. In the example of FIG. 11, the inductance of the inductor LS is also expressed as LS. In FIG. 11, characteristics corresponding to various values of LS are shown. The case of LS=0.0 nH corresponds to the case where the elastic wave filter 100-3 does not have an inductor LS (comparative example).

As shown in FIG. 11, in the elastic wave filter 100-3 (that is, the configuration in which the inductor is connected in series with the parallel resonator that is the first elastic wave resonator), fa is independent of the value of LS. It was confirmed that it is almost constant. Furthermore, when the elastic wave filter 100-3 includes the inductor LS, it was confirmed that fr tends to decrease compared to the comparative example (LS=0.0 nH).

FIG. 12 shows an example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter 100-4. In FIG. 12, reference numeral 1200A indicates the phase characteristic of the first elastic wave resonator in the elastic wave filter 100-4, and reference numeral 1200B indicates the impedance characteristic of the first elastic wave resonator. In the example of FIG. 12, the capacitance of the capacitor CS is also expressed as CS. The case of CS=0.0 pF corresponds to the case where the elastic wave filter 100-4 does not have the capacitor CS (comparative example).

As shown in FIG. 12, in the elastic wave filter 100-4 (that is, a configuration in which a capacitor is connected in series with a parallel resonator that is a first elastic wave resonator), fa is independent of the value of CS. It was confirmed that it is almost constant. Furthermore, when the elastic wave filter 100-4 includes the capacitor CS, it was confirmed that fr tends to increase compared to the comparative example (CS=0.0 pF).

As mentioned above, the frequency characteristics of the first elastic wave resonator in the elastic wave filter depend on (i) the type of element EL connected to the first elastic wave resonator, and (ii) the first elastic wave It may change depending on at least one of the connection manner between the resonator and the element EL. Therefore, for example, the first elastic wave resonator connected to the element EL may be redesigned according to the required specifications of the elastic wave filter. Hereinafter, with reference to FIG. 13, an example of redesigning the first elastic wave resonator will be described.

FIG. 13 shows another example of the phase characteristics and impedance characteristics of the first elastic wave resonator in the elastic wave filter 100-1. In the example of FIG. 13, it is assumed that the first elastic wave resonator in the elastic wave filter 100-1 has been redesigned (changed in design) from the first elastic wave resonator in the example of FIG. In FIG. 13, reference numeral 1300A is a diagram paired with the above-mentioned reference numeral 900A, and reference numeral 1300B is a diagram paired with the above-mentioned reference numeral 900B.

The reference waveform in FIG. 13 is equivalent to the waveform in FIG. 9 when CS=0.0 pF. That is, in the case of the reference waveform in FIG. 13, the first elastic wave resonator is before redesign. The reference waveform in FIG. 13 corresponds to the comparative example in FIG. In the example of FIG. 13, except for the comparative example, CP=0.3 pF.

The legend "c2" in FIG. 13 represents a redesign that increases the capacitance of the first elastic wave resonator by 0.6 times. In the example shown in FIG. 13, by changing the number of electrode fingers of the IDT electrode in the first acoustic wave resonator from 150 to 90, it is possible to redesign the capacitance of the first acoustic wave resonator to increase it by 0.6. being done.

Furthermore, the legend "p2" in FIG. 13 represents a redesign in which the electrode finger pitch (p) of the IDT electrode in the first acoustic wave resonator is changed from 1.26 μm to 1.215 μm. In this redesign, p is multiplied by about 0.964.

FIG. 13 shows that the magnitude of spurious can be reduced by redesigning the first acoustic wave resonator to reduce its capacitance. According to the elastic wave filter 100-1, a part of the capacitance value of the first elastic wave resonator before redesign can be compensated for by the capacitor CP. Therefore, according to the elastic wave filter 100-1, such redesign can be applied. As is clear to those skilled in the art, such redesign can also be applied to the elastic wave filter 100-4.

As described above, when the element EL is a capacitor, the magnitude of the spurious of the first acoustic wave resonator can be reduced by the capacitor. Therefore, for example, even if the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter, the magnitude of the spurious can be reduced by the capacitor. From this, the first elastic wave resonator may be a series resonator or a parallel resonator, and the element EL may be a capacitor connected in series or in parallel to the first elastic wave resonator. It's fine.

FIG. 13 further shows that the frequency characteristics of the first acoustic wave resonator can be generally shifted by redesigning to change p. For example, fa and fr can be increased by redesigning p to be smaller. Conversely, fa and fr can also be decreased by redesigning to increase p.

(Example of change in phase characteristics of the first elastic wave resonator in each elastic wave filter)
Next, various examples of changes in the phase characteristics of the first elastic wave resonator in each elastic wave filter will be described. FIG. 14 is a diagram for explaining changes in the phase characteristics of the series resonator, which is the first elastic wave resonator, in the elastic wave filter 100-1. Reference numeral 1400A in FIG. 14 shows the phase characteristics of the first elastic wave resonator before connecting the capacitor CP (the phase characteristics of the first elastic wave resonator alone), and the phase characteristics of the first elastic wave resonator after connecting the capacitor CP. is shown schematically. Reference numeral 1400B in FIG. 14 schematically shows the phase characteristics of the redesigned first acoustic wave resonator after the capacitor CP is connected.

In the example indicated by reference numeral 1400A, the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter both before and after the capacitor CP is connected. Specifically, the spurious of the first elastic wave resonator is located near the above-mentioned first end point within the passband of the elastic wave filter.

However, as described above, after the capacitor CP is connected, the magnitude of the spurious of the first acoustic wave resonator can be reduced compared to before the capacitor CP is connected. In addition, after connecting the capacitor CP, fa can be reduced compared to before connecting the capacitor CP. In the following, for convenience, fa before the element EL is connected will be expressed as fa0. fa0 in the example of FIG. 14 indicates fa before the capacitor CP is connected. On the other hand, fa after connecting the capacitor CP in the example 1400A is expressed as fa_cp. Furthermore, fa of the redesigned first acoustic wave resonator after connecting the capacitor CP is expressed as fa_cp'.

As described above, in the elastic wave filter 100-1, fa_cp can become lower than fa0 due to the connection of the capacitor CP. Therefore, as an example, the first elastic wave resonator may be redesigned so that fa_cp' matches fa0. In this case, due to the redesign of the first acoustic wave resonator, fa_cp' becomes higher than fa_cp.

According to the redesign, the frequency characteristics of the first elastic wave resonator can be shifted to the high frequency side. Therefore, compared to the example with reference numeral 1400A, the spurious of the first elastic wave resonator can be shifted to the higher frequency side. Therefore, as shown in the example at 1400B, the spurious of the first acoustic wave resonator can be located within the first band.

As mentioned above, when the first elastic wave resonator in the elastic wave filter is a series resonator and the element EL is a capacitor connected in parallel to the first elastic wave resonator, The spurious of one acoustic wave resonator may be located within the first band.

FIG. 15 is a diagram for explaining changes in the phase characteristics of the series resonator, which is the first elastic wave resonator, in the elastic wave filter 100-2. Reference numeral 1500A in FIG. 15 shows the phase characteristics of the first elastic wave resonator before the inductor LP is connected (the phase characteristics of the first elastic wave resonator alone), and the phase characteristics of the first elastic wave resonator after the inductor LP is connected. is shown schematically. Reference numeral 1500B in FIG. 15 schematically shows the phase characteristics of the redesigned first acoustic wave resonator after the inductor LP is connected.

In the example indicated by reference numeral 1500A, the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter both before and after the inductor LP is connected. Specifically, the spurious of the first elastic wave resonator is located near the above-mentioned third end point within the passband of the elastic wave filter.

As shown in the example at 1500A, after the inductor LP is connected, the magnitude of the spurious of the first acoustic wave resonator may increase compared to before the inductor LP is connected. This behavior is due to the duality between the frequency characteristics of the inductor and the frequency characteristics of the capacitor. Furthermore, as described above, after the inductor LP is connected, fa can increase compared to before the inductor LP is connected.

fa0 in the example of FIG. 15 indicates fa before the inductor LP is connected. In the example of FIG. 15, fa after the inductor LP is connected in the example of code 1500A is expressed as fa_lp. Furthermore, fa of the redesigned first acoustic wave resonator after the inductor LP is connected is expressed as fa_lp'.

As described above, in the elastic wave filter 100-2, fa_lp can become higher than fa0 due to the connection of the inductor LP. Therefore, as an example, the first elastic wave resonator may be redesigned so that fa_lp' matches fa0. In this case, due to the redesign of the first acoustic wave resonator, fa_lp' becomes lower than fa_lp.

According to the redesign, the frequency characteristics of the first elastic wave resonator can be shifted to the lower frequency side. Therefore, compared to the example with reference numeral 1500A, the spurious of the first elastic wave resonator can be shifted to the lower frequency side. Therefore, as shown in the example at 1500B, the spurious of the first acoustic wave resonator can be located within the second band.

As mentioned above, when the first elastic wave resonator in the elastic wave filter is a series resonator and the element EL is an inductor connected in parallel to the first elastic wave resonator, The spurious of one acoustic wave resonator may be located within the second band.

FIG. 16 is a diagram for explaining changes in the phase characteristics of the parallel resonator, which is the first elastic wave resonator, in the elastic wave filter 100-3. Reference numeral 1600A in FIG. 16 indicates the phase characteristics of the first elastic wave resonator before the inductor LS is connected (the phase characteristics of the first elastic wave resonator alone), and the phase characteristics of the first elastic wave resonator after the inductor LS is connected. is shown schematically. Reference numeral 1600B in FIG. 16 schematically shows the phase characteristics of the redesigned first acoustic wave resonator after the inductor LS is connected.

In the example indicated by reference numeral 1600A, the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter both before and after the inductor LS is connected. Specifically, the spurious of the first elastic wave resonator is located near the first end point within the passband of the elastic wave filter.

As can be understood from the above description regarding FIG. 15, after the inductor LS is connected, the magnitude of the spurious of the first acoustic wave resonator may increase compared to before the inductor LS is connected. Further, after connecting the inductor LS, fr may decrease compared to before connecting the inductor LS. In the following, for convenience, fr before the element EL is connected will be expressed as fr0. fr0 in the example of FIG. 16 indicates fr before the inductor LS is connected. On the other hand, fr after the inductor LS is connected in the example 1600A is written as fr_ls. Furthermore, fr of the redesigned first acoustic wave resonator after the inductor LS is connected is expressed as fr_ls'.

As described above, in the elastic wave filter 100-3, fr_ls can become lower than fr0 due to the connection of the inductor LS. Therefore, as an example, the first elastic wave resonator may be redesigned so that fr_ls' matches fr0. In this case, fr_ls' becomes higher than fr_ls due to the redesign of the first elastic wave resonator.

According to the redesign, the frequency characteristics of the first elastic wave resonator can be shifted to the high frequency side. Therefore, compared to the example with reference numeral 1600A, the spurious of the first elastic wave resonator can be shifted to the higher frequency side. Therefore, as shown in the example at 1600B, the spurious of the first acoustic wave resonator can be located within the first band.

As mentioned above, when the first elastic wave resonator in the elastic wave filter is a parallel resonator and the element EL is an inductor connected in series with the first elastic wave resonator, The spurious of one acoustic wave resonator may be located within the first band.

FIG. 17 is a diagram for explaining changes in the phase characteristics of the parallel resonator, which is the first elastic wave resonator, in the elastic wave filter 100-4. Reference numeral 1700A in FIG. 17 shows the phase characteristics of the first elastic wave resonator before connecting the capacitor CS (the phase characteristics of the first elastic wave resonator alone), and the phase characteristics of the first elastic wave resonator after connecting the capacitor CS. is shown schematically. Reference numeral 1700B in FIG. 17 schematically shows the phase characteristics of the redesigned first acoustic wave resonator after connecting the capacitor CS.

In the example indicated by reference numeral 1700A, the spurious of the first elastic wave resonator is located within the passband of the elastic wave filter both before and after the capacitor CS is connected. Specifically, the spurious of the first elastic wave resonator is located near the third end point within the passband of the elastic wave filter.

As described above, after the capacitor CS is connected, the magnitude of the spurious of the first acoustic wave resonator can be reduced compared to before the capacitor CS is connected. Furthermore, after connecting the capacitor CS, fr may increase compared to before connecting the capacitor CS. fr0 in the example of FIG. 17 indicates fr before capacitor CS is connected. In the example of FIG. 17, fr after the capacitor CS is connected in the example of 1700A is expressed as fr_cs. Furthermore, fr of the redesigned first acoustic wave resonator after connecting the capacitor CS is expressed as fr_cs'.

As described above, in the elastic wave filter 100-4, fr_cs can become higher than fr0 due to the connection of the capacitor CS. Therefore, as an example, the first elastic wave resonator may be redesigned so that fr_cs' matches fr0. In this case, fr_cs' becomes lower than fr_cs due to the redesign of the first elastic wave resonator.

According to the redesign, the frequency characteristics of the first elastic wave resonator can be shifted to the lower frequency side. Therefore, compared to the example with reference numeral 1700A, the spurious of the first elastic wave resonator can be shifted to the lower frequency side. Therefore, as shown in the example at 1700B, the spurious of the first acoustic wave resonator can be located within the second band.

As mentioned above, when the first elastic wave resonator in the elastic wave filter is a parallel resonator and the element EL is a capacitor connected in series to the first elastic wave resonator, The spurious of one acoustic wave resonator may be located within the second band.

As is clear from the descriptions of FIGS. 14 to 17, the first elastic wave resonator in the elastic wave filter may be connected in parallel or in series with the element EL. Element EL may then be a capacitor or an inductor. Thereby, the spurious position of the first elastic wave resonator can be set according to the required specifications of the elastic wave filter. Therefore, according to one aspect of the present disclosure, the frequency characteristics of the elastic wave filter can be improved.

For example, as shown in FIGS. 14 to 17, the spurious of the first elastic wave resonator can be located within the pass band, the first band, or the second band of the elastic wave filter. Moreover, the spurious of the first elastic wave resonator can also be located outside the frequency band of the first elastic wave resonator.

Therefore, as an example, the passband of the elastic wave filter may be located between the resonant frequency of the first elastic wave resonator and the spurious of the first elastic wave resonator (e.g., see reference numeral 1600B in FIG. 16). . As another example, the passband of the elastic wave filter may be located between the anti-resonance frequency of the first elastic wave resonator and the spurious of the first elastic wave resonator (see e.g. 1400B in FIG. 14). ).

As understood from these, the passband of the elastic wave filter does not need to include either the resonant frequency or the anti-resonant frequency of the first elastic wave resonator (for example, see reference numeral 1400B in FIG. 14). ).

In the examples shown in FIGS. 14 to 17, the passband of the elastic wave filter is located on the higher frequency side than the frequency band of the first elastic wave resonator. However, as is clear to those skilled in the art, the passband of the elastic wave filter may be located on the lower frequency side than the frequency band of the first elastic wave resonator. Therefore, for example, the spurious of the first elastic wave resonator may also be located on the lower frequency side than the frequency band of the first elastic wave resonator.

By the way, as described above, the elastic wave filter according to one aspect of the present disclosure may further include a second elastic wave resonator different from the first elastic wave resonator. In addition, the elastic wave filter does not need to have an element (eg, a capacitor or an inductor) connected in parallel or in series with the second elastic wave resonator. Therefore, as an example, the second elastic wave resonator may be any one of the two elastic wave resonators other than the first elastic wave resonator (e.g., series resonance child 1S-2).

As an example, the second elastic wave resonator may be designed so that the spurious of the second elastic wave resonator does not overlap with the spurious of the first elastic wave resonator. Therefore, for example, the second elastic wave resonator is designed so that the spurious of the second elastic wave resonator is not located within the pass band, the first band, or the second band of the elastic wave filter. It's okay to be.

Therefore, as an example, the first elastic wave resonator may be designed to have a higher anti-resonance frequency than the second elastic wave resonator. From this, for example, the first elastic wave resonator may be designed to have the highest anti-resonance frequency among the plurality of elastic wave resonators in the elastic wave filter.

As understood from FIGS. 14 and 17 described above, when the element EL connected in parallel or series with the first acoustic wave resonator is a capacitor, Δf (the first (the width of the frequency band of the elastic wave resonator) may be reduced. Therefore, in this case, Δf may be smaller than the average value of the frequency band widths of the plurality of elastic wave resonators.

On the other hand, as understood from FIGS. 15 and 16 above, when the element EL connected in parallel or series to the first acoustic wave resonator is an inductor, the Δf may increase. Therefore, in this case, Δf can be larger than the average value of the frequency band widths of the plurality of elastic wave resonators.

[Embodiment 2]
FIG. 18 illustrates a schematic configuration of a communication device 151 in the second embodiment. The communication device 151 is an application example of an elastic wave filter according to one aspect of the present disclosure, and performs wireless communication using radio waves. The communication device 151 may include one duplexer 101 as a transmission filter 109 and another duplexer 101 as a reception filter 111. Each of the two duplexers 101 may include an elastic wave filter according to one aspect of the present disclosure. In this way, the communication device 151 may include an elastic wave filter according to one aspect of the present disclosure.

In the communication device 151, a transmission information signal TIS containing information to be transmitted is modulated and frequency-increased (converted to a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and the transmission information signal TIS is converted into a transmission signal. It may be converted to TS. The bandpass filter 155 may remove unnecessary components other than the transmission passband for the TS. Next, the TS after removing unnecessary components may be amplified by the amplifier 157 and input to the transmission filter 109.

The transmission filter 109 may remove unnecessary components outside the transmission passband from the input transmission signal TS. The transmission filter 109 may output the TS from which unnecessary components have been removed to the antenna 159 via an antenna terminal (eg, TCin described above). The antenna 159 may convert the TS, which is an electrical signal input to itself, into a radio wave as a wireless signal, and transmit the radio wave to the outside of the communication device 151.

Additionally, the antenna 159 may convert the received radio waves from the outside into a reception signal RS, which is an electrical signal, and input the RS to the reception filter 111 via the antenna terminal. The reception filter 111 may remove unnecessary components other than the reception passband from the input RS. The reception filter 111 may output the reception signal RS from which unnecessary components have been removed to the amplifier 161. The output RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unnecessary components other than the receiving passband from the amplified RS. The frequency of the RS after unnecessary component removal is lowered and demodulated by the RF-IC 153, and may be converted into a received information signal RIS.

The TIS and RIS may be low frequency signals (baseband signals) containing appropriate information. For example, TIS and RIS may be analog audio signals or digitized audio signals. The passband of the wireless signal may be set as appropriate and may conform to various known standards.

〔summary〕
An elastic wave filter according to aspect 1 of the present disclosure is an elastic wave filter having a first elastic wave resonator, in which the width of the frequency band of the first elastic wave resonator is expressed as Δf, and the elastic wave filter passes through the elastic wave filter. A band extending from a first end point indicating a frequency at the end of the high frequency side of the band to a second end point indicating a frequency higher than the first end point by Δf is referred to as a first band, and the band extends through the passage of the elastic wave filter. A band extending from a third end point indicating a frequency at the end of the low frequency side of the band to a fourth end point indicating a frequency lower by Δf than the third end point is referred to as a second band, and the first elastic wave resonance The child spurious is located outside the frequency band of the first elastic wave resonator and within either the pass band, the first band, or the second band of the elastic wave filter. The elastic wave filter further includes an element connected in parallel or series to the first elastic wave resonator, and the element is a capacitor or an inductor.

In the elastic wave filter according to Aspect 2 of the present disclosure, in Aspect 1, the first elastic wave resonator is a series resonator, the spurious is located within the first band, and the element is , may be a capacitor connected in parallel to the first acoustic wave resonator.

In the elastic wave filter according to aspect 3 of the present disclosure, in aspect 1, the first elastic wave resonator is a parallel resonator, the spurious is located within the first band, and the element is , may be an inductor connected in series with the first elastic wave resonator.

In the elastic wave filter according to Aspect 4 of the present disclosure, in Aspect 1, the first elastic wave resonator is a series resonator, the spurious is located within the second band, and the element is , may be an inductor connected in parallel to the first elastic wave resonator.

In the elastic wave filter according to Aspect 5 of the present disclosure, in Aspect 1, the first elastic wave resonator is a parallel resonator, the spurious is located within the second band, and the element is , may be a capacitor connected in series to the first elastic wave resonator.

In the elastic wave filter according to Aspect 6 of the present disclosure, in Aspect 1, the first elastic wave resonator is a series resonator or a parallel resonator, and the spurious is within the passband of the elastic wave filter. and the element may be a capacitor connected in series or in parallel to the first acoustic wave resonator.

The elastic wave filter according to aspect 7 of the present disclosure is the same as in aspect 1, further comprising a second elastic wave resonator different from the first elastic wave resonator, and the spurious of the second elastic wave resonator is , which is not located within the passband, the first band, or the second band of the elastic wave filter, and is connected in parallel or series to the second elastic wave resonator. It may not have a capacitor or inductor.

An elastic wave filter according to an aspect 8 of the present disclosure, in the aspect 1, includes a plurality of elastic wave resonators including the first elastic wave resonator, the element is a capacitor, and Δf is a plurality of elastic wave resonators. may be smaller than the average width of the frequency band in the elastic wave resonator.

The elastic wave filter according to aspect 9 of the present disclosure is the same as in aspect 1, and includes a plurality of elastic wave resonators including the first elastic wave resonator, the element is an inductor, and Δf is a plurality of elastic wave resonators. may be larger than the average width of the frequency band in the elastic wave resonator.

The elastic wave filter according to aspect 10 of the present disclosure, in any one of aspects 1 to 9, includes a plurality of elastic wave resonators including the first elastic wave resonator, and the elastic wave filter includes a plurality of elastic wave resonators including the first elastic wave resonator, and The resonator may have the highest anti-resonance frequency among the plurality of elastic wave resonators.

The elastic wave filter according to aspect 11 of the present disclosure, in any one of aspects 1 to 10, further includes a piezoelectric layer, and the first elastic wave resonator is located on the piezoelectric layer. If the wavelength λ of the elastic wave excited by the IDT electrode is defined as twice the electrode finger pitch of the IDT electrode, the thickness of the piezoelectric layer is λ The IDT electrode may excite a plate wave as the elastic wave.

In the elastic wave filter according to aspect 12 of the present disclosure, in any one of aspects 1 to 11, the passband of the elastic wave filter includes (i) the resonance frequency of the first elastic wave resonator and the spurious or (ii) between the anti-resonance frequency of the first elastic wave resonator and the spurious.

In the elastic wave filter according to aspect 13 of the present disclosure, in any one of aspects 1 to 12, the passband of the elastic wave filter may be any one of the resonant frequency and the anti-resonant frequency of the first elastic wave resonator. It is not necessary to include .

A communication device according to aspect 14 of the present disclosure may include the elastic wave filter according to any one of aspects 1 to 13.

[Additional notes]
The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to each embodiment described above. That is, the invention according to the present disclosure can be modified in various ways within the scope shown in the present disclosure, and the invention according to the present disclosure also applies to embodiments obtained by appropriately combining technical means disclosed in different embodiments. Included in technical scope. In other words, it should be noted that those skilled in the art can easily make various changes or modifications based on the present disclosure. It should also be noted that these variations or modifications are included within the scope of this disclosure.

1 Elastic wave resonator 1S-1 Series resonator (an example of the first elastic wave resonator)
1S-2 Series resonator (an example of a second elastic wave resonator)
1P parallel resonator (another example of the first elastic wave resonator)
2 Piezoelectric layer 3 IDT electrode 32 Electrode fingers 100, 100-1, 100-2, 100-3, 100-4 Acoustic wave filter 151 Communication device EL element CP Capacitor (element, parallel to the first elastic wave resonator) capacitor connected to)
CS capacitor (element, capacitor connected in series to the first elastic wave resonator)
LP inductor (element, inductor connected in parallel to the first elastic wave resonator)
LS inductor (element, inductor connected in series with the first elastic wave resonator)

Claims

An elastic wave filter having a first elastic wave resonator,
The width of the frequency band of the first elastic wave resonator is expressed as Δf,
A band extending from a first end point indicating a frequency at the end of the high frequency side of the passband of the elastic wave filter to a second end point indicating a frequency higher than the first end point by Δf is referred to as a first band,
A band extending from a third end point indicating a frequency at the low frequency side end of the passband of the elastic wave filter to a fourth end point indicating a frequency lower by Δf with respect to the third end point is referred to as a second band. ,
The spurious of the first elastic wave resonator is
located outside the frequency band of the first elastic wave resonator, and
located within the passband, the first band, or the second band of the elastic wave filter;
The elastic wave filter further includes an element connected in parallel or series to the first elastic wave resonator,
the element is a capacitor or an inductor;
elastic wave filter.
The first elastic wave resonator is a series resonator,
the spurious is located within the first band;
the element is a capacitor connected in parallel to the first acoustic wave resonator;
The elastic wave filter according to claim 1.
The first elastic wave resonator is a parallel resonator,
the spurious is located within the first band;
The element is an inductor connected in series with the first elastic wave resonator.
The elastic wave filter according to claim 1.
The first elastic wave resonator is a series resonator,
the spurious is located within the second band,
The element is an inductor connected in parallel to the first elastic wave resonator.
The elastic wave filter according to claim 1.
The first elastic wave resonator is a parallel resonator,
the spurious is located within the second band,
The element is a capacitor connected in series with the first acoustic wave resonator.
The elastic wave filter according to claim 1.
The first elastic wave resonator is a series resonator or a parallel resonator,
The spurious is located within the passband of the elastic wave filter,
The element is a capacitor connected in series or parallel to the first acoustic wave resonator.
The elastic wave filter according to claim 1.
further comprising a second elastic wave resonator different from the first elastic wave resonator,
The spurious of the second elastic wave resonator is not located within the pass band, the first band, or the second band of the elastic wave filter,
does not have a capacitor or inductor connected in parallel or series with the second acoustic wave resonator;
The elastic wave filter according to claim 1.
It has a plurality of elastic wave resonators including the first elastic wave resonator,
the element is a capacitor;
Δf is smaller than the average value of the frequency band widths of the plurality of elastic wave resonators,
The elastic wave filter according to claim 1.
It has a plurality of elastic wave resonators including the first elastic wave resonator,
the element is an inductor;
Δf is larger than the average value of the frequency band widths of the plurality of elastic wave resonators,
The elastic wave filter according to claim 1.
It has a plurality of elastic wave resonators including the first elastic wave resonator,
The first elastic wave resonator has the highest anti-resonance frequency among the plurality of elastic wave resonators,
The elastic wave filter according to any one of claims 1 to 9.
It further has a piezoelectric layer,
The first acoustic wave resonator has an IDT electrode located on the piezoelectric layer,
When the wavelength λ of the elastic wave excited by the IDT electrode is defined as twice the electrode finger pitch of the IDT electrode, the thickness of the piezoelectric layer is λ or less,
The IDT electrode excites a plate wave as the elastic wave.
The elastic wave filter according to any one of claims 1 to 10.
The pass band of the elastic wave filter is between (i) the resonant frequency of the first elastic wave resonator and the spurious, or (ii) between the anti-resonant frequency of the first elastic wave resonator and the spurious. located between
The elastic wave filter according to any one of claims 1 to 11.
The pass band of the elastic wave filter does not include either the resonant frequency or the anti-resonant frequency of the first elastic wave resonator.
The elastic wave filter according to any one of claims 1 to 12.
A communication device comprising the elastic wave filter according to any one of claims 1 to 13.