Elastic wave filter

Abstract

To reduce the dependence of the attenuation amount of an elastic wave filter on the frequency in an attenuation bandwidth.SOLUTION: The elastic wave filter includes: at least one serial arm; and a plurality of parallel arms for connecting electrically different positions and a reference potential part together, the parallel arms having a first parallel arm, the first parallel arm having a first elastic wave resonator and an addition circuit connected to the first elastic wave resonator in parallel, and the addition circuit being one of a first addition circuit and a second addition circuit. The first addition circuit includes: a first inductor; a first capacitor connected to the first inductor in parallel; and a second inductor serially connected to the first inductor and the first capacitor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One aspect of the present disclosure relates to an acoustic wave filter. [Background technology]

[0002] Patent Document 1 listed below discloses an example of the configuration of an acoustic wave filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2017-005390 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to reduce the frequency dependence of attenuation in the attenuation band of an acoustic wave filter. [Means for solving the problem]

[0005] An acoustic wave filter according to an aspect of the present disclosure includes a signal path that passes a signal in a pass band, and includes at least one series arm, which is connected in series with each other if there are multiple series arms, and a plurality of parallel arms that connect positions of the signal path that are different electrical positions with respect to the at least one series arm and a reference potential section, the plurality of parallel arms including a first parallel arm, the first parallel arm including a first acoustic wave resonator and an additional circuit connected in parallel to the first acoustic wave resonator, the additional circuit being a first additional circuit or a second additional circuit, the first additional circuit including a first inductor, a first capacitor connected in parallel to the first inductor, and a second inductor connected in series to the first inductor and the first capacitor, and the second additional circuit including a third inductor, a second capacitor connected in series to the third inductor, and a fourth inductor connected in parallel to the third inductor and the second capacitor. Effect of the Invention

[0006] According to one aspect of the present disclosure, it is possible to reduce the frequency dependence of attenuation in an attenuation band of an acoustic wave filter. [Brief description of the drawings]

[0007] [Figure 1] 1 is a circuit diagram illustrating an example of a basic configuration of an acoustic wave filter according to a first embodiment of the present invention. [Diagram 2] 1 is a circuit diagram illustrating an example of a basic configuration of an acoustic wave filter according to a first embodiment of the present invention. [Diagram 3] 1 is a circuit diagram illustrating an acoustic wave filter of Comparative Example 1. FIG. [Figure 4] 1 is a graph illustrating an example of characteristics of an acoustic wave filter according to an embodiment of the present disclosure. [Diagram 5] 5 is a graph showing an enlarged view of a part of FIG. 4. [Figure 6] 1 is a circuit diagram illustrating an example of a basic configuration of an acoustic wave filter according to a second embodiment of the present invention. [Figure 7] 1 is a circuit diagram illustrating an example of a basic configuration of an acoustic wave filter according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a circuit diagram illustrating an acoustic wave filter of Comparative Example 2. [Figure 9] 1 is a graph illustrating an example of characteristics of an acoustic wave filter according to an embodiment of the present disclosure. [Figure 10] 10 is a graph showing an enlarged view of a part of FIG. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Embodiment 1] The first embodiment will be described below. For convenience of explanation, components having the same functions as those described in the first embodiment will be given the same reference numerals in the following embodiments, and the explanations will not be repeated. For simplicity, explanations of well-known technical matters will be omitted as appropriate. Each component, material, and numerical value described in this specification is merely an example, unless otherwise stated. Therefore, for example, unless otherwise stated, the positional relationship and connection relationship of each component are not limited to the examples in each figure. In addition, each figure is not necessarily drawn to scale.

[0009] (Basic structure of elastic wave filters) 1 and 2 are circuit diagrams illustrating an example of a basic configuration of an acoustic wave filter 100 according to a first embodiment. In the first embodiment, the acoustic wave filter 100 is illustrated as a ladder-type filter. However, as will be apparent to those skilled in the art, an acoustic wave filter according to an aspect of the present disclosure is not limited to a ladder-type filter. In FIGS. 1 and 2, the configurations of the additional circuits AC1 and AC2 are different from each other, but the other configurations are the same.

[0010] The acoustic wave filter 100 may have at least one series arm. Accordingly, the acoustic wave filter 100 may have a plurality of series arms. When the acoustic wave filter 100 has a plurality of series arms, the plurality of series arms may be connected in series to each other. In the example of FIG. 1, the acoustic wave filter 100 has three series arms SL-2, SL-4, and SL-6 that are connected in series to each other. In this specification, the series arms SL-2, SL-4, and SL-6 are also collectively referred to as series arms SL.

[0011] 1, the acoustic wave filter 100 may have an acoustic wave resonator (series resonator) located in the series arm SL. In the example of Fig. 1, the acoustic wave filter 100 has series resonators IS-2, IS-4, and IS-6 located in series arms SL-2, SL-4, and SL-6, respectively. In this specification, the series resonators IS-2, IS-4, and IS-6 are also collectively referred to as the series resonators IS.

[0012] At least one series arm may be connected to an input terminal Pin and an output terminal Pout. In the example of Fig. 1, the series arm SL-2 is the series arm SL closer to the input terminal Pin, and the series arm SL-6 is the series arm SL closer to the output terminal Pout. The acoustic wave filter 100 may have a series arm SL on the input terminal Pin side of the series arm SL-2. The acoustic wave filter 100 may have a series arm SL on the output terminal Pout side of the series arm SL-6.

[0013] At least one series arm may constitute a signal path that passes a signal in a pass band. In the example of Fig. 1, the three series arms SL function as signal paths that pass a signal in a pass band defined by the acoustic wave filter 100 between the input terminal Pin and the output terminal Pout.

[0014] The acoustic wave filter 100 may have a plurality of parallel arms. In the example of Fig. 1, the acoustic wave filter 100 has four parallel arms: a parallel arm PL-1, a parallel arm PL-3, a parallel arm PL-5, and a parallel arm PL-7. In this specification, the parallel arms PL-1, PL-3, PL-5, and PL-7 are also collectively referred to as parallel arms PL.

[0015] The parallel arms may connect the reference potential unit to positions that are different from each other in electrical position with respect to at least one series arm of the signal path. In the example of FIG. 1, the first end of each of the four parallel arms PL is connected to the signal path at the node NN1, the node NN3, the node NN5, and the node NN7. Meanwhile, the second end of each of the four parallel arms PL is connected to the ground terminal GD-1, the ground terminal GD-3, the ground terminal GD-5, and the ground terminal GD-7. The node NN1, the node NN3, the node NN5, and the node NN7 are located between the input terminal Pin, the series arm SL-2, the series arm SL-4, the series arm SL-6, and the output terminal Pout, respectively, and are at different electrical positions from each other. The ground terminal GD-1, the ground terminal GD-3, the ground terminal GD-5, and the ground terminal GD-7 function as the reference potential unit. In this specification, the ground terminals GD-1, GD-3, GD-5, and GD-7 are also collectively referred to as ground terminals GD.

[0016] The multiple parallel arms may have a first parallel arm. In the example of Fig. 1, the four parallel arms PL have a parallel arm PL-1 as the first parallel arm.

[0017] The first parallel arm may include a first acoustic wave resonator and an additional circuit connected in parallel to the first acoustic wave resonator. In the example of Fig. 1, the parallel arm PL-1 includes an acoustic wave resonator Res1 and an additional circuit AC1 connected in parallel to the acoustic wave resonator Res1. In the example of Fig. 2, the parallel arm PL-1 includes an acoustic wave resonator Res1 and an additional circuit AC2 connected in parallel to the acoustic wave resonator Res1.

[0018] The additional circuit may be a first additional circuit or a second additional circuit. The first additional circuit may include a first inductor, a first capacitor connected in parallel to the first inductor, and a second inductor connected in series to the first inductor and the first capacitor. In the example of FIG. 1, the additional circuit AC1 includes an inductor L11, a capacitor C11 connected in parallel to the inductor L11, and an inductor L12 connected in series to the inductor L11 and the capacitor C11. The second additional circuit may include a third inductor, a second capacitor connected in series to the third inductor, and a fourth inductor connected in parallel to the third inductor and the second capacitor. In the example of FIG. 2, the additional circuit AC2 includes an inductor L13, a capacitor C12 connected in series to the inductor L13, and an inductor L14 connected in parallel to the inductor L13 and the capacitor C12.

[0019] As shown below, the additional circuit AC1 and the additional circuit AC2 can be substantially equivalent as circuits. The resonance angular frequency ω1r and the anti-resonance angular frequency ω1a of the additional circuit AC1 are expressed by the following formula (1). The resonance angular frequency ω2r and the anti-resonance angular frequency ω2a of the additional circuit AC2 are expressed by the following formula (2). ω1r=[(L11+L12) / (C11·L11·L12)] 1 / 2 ω1a=(L11 C11) -1 / 2 ...Formula (1) ω2r=(L13 C12) -1 / 2 ω2a=1 / [C12·(L13+L14)] 1 / 2 ...Formula (2) L11: Inductance of inductor L11 L12: Inductance of inductor L12 C11: Capacitance of capacitor C11 L13: Inductance of inductor L13 L14: Inductance of inductor L14 C12: Capacitance of capacitor C12

[0020] When the following condition (3) is satisfied, the resonant angular frequency ω1r is equal to the resonant angular frequency ω2r, and the anti-resonant angular frequency ω1a is equal to the anti-resonant angular frequency ω2a. In other words, the additional circuit AC1 and the additional circuit AC2 are substantially equivalent as circuits. L11=L14 2 / (L13+L14) L12 = L13 L14 / (L13 + L14) C11 = C12 [(L13 + L14) L14] 2 ...Condition (3)

[0021] This condition (3) is equivalent to the following condition (4). L13 = L12 (L11 + L12) / L11 L14=L11+L12 C12=C11·[L11 / (L11+L12)] 2 ...Condition (4)

[0022] In this case, the following relationship holds: C12 / C11=[L11 / (L12+L13)] =[L14 / (L13+L14)]<1 This relationship means that the capacitance C12 of the additional circuit AC2 is smaller than the capacitance C11 of the additional circuit AC1. Because the resonant angular frequency ω1r of the additional circuit AC1 and the resonant angular frequency ω2r of the additional circuit AC2 are equal, the inductance of the entire additional circuit AC1 is smaller than the inductance of the entire additional circuit AC2. Due to this difference in inductance, the additional circuit AC1 is easier to miniaturize than the additional circuit AC2. This is because increasing the inductance leads to longer wiring length, which in turn leads to larger circuits.

[0023] The parallel arms may have a second parallel arm different from the first parallel arm. In the example of Fig. 1, the four parallel arms PL have three second parallel arms, namely, parallel arm PL-3, parallel arm PL-5, and parallel arm PL-7.

[0024] The second parallel arm may include a second acoustic wave resonator and an inductor connected in parallel to the second acoustic wave resonator. In the example of FIG. 1, the parallel arm PL-3 includes an acoustic wave resonator Res3 and an inductor L3 connected in parallel to the acoustic wave resonator Res3. The parallel arm PL-5 includes an acoustic wave resonator Res5 and an inductor L5 connected in parallel to the acoustic wave resonator Res5. The parallel arm PL-7 includes an acoustic wave resonator Res7 and an inductor L7 connected in parallel to the acoustic wave resonator Res7. In this specification, the acoustic wave resonators Res1, Res3, Res5, and Res7 are also collectively referred to as acoustic wave resonators Res.

[0025] The resonant frequency of the second acoustic wave resonator may be located in the attenuation band. The amount of attenuation in the attenuation band can be reduced. The resonant frequencies fr of the acoustic wave resonators Res3, Res5, and Res7 may be located in the attenuation band A2 shown in FIG. 4. All of the resonant frequencies fr of the acoustic wave resonators Res3, Res5, and Res7 may be located in the attenuation band A2. On the other hand, some of the resonant frequencies fr of the acoustic wave resonators Res3, Res5, and Res7 may be located in the attenuation band A2.

[0026] Each of the parallel arms may include an elastic wave resonator and an inductor connected in parallel to the elastic wave resonator. In the example of FIG. 1, the parallel arm PL-1 includes an elastic wave resonator Res1, and an inductor L11 and an inductor L12 connected in parallel to the elastic wave resonator Res1. The parallel arm PL-3 includes an elastic wave resonator Res3 and an inductor L3 connected in parallel to the elastic wave resonator Res3. The parallel arm PL-5 includes an elastic wave resonator Res5 and an inductor L5 connected in parallel to the elastic wave resonator Res5. The parallel arm PL-7 includes an elastic wave resonator Res7 and an inductor L7 connected in parallel to the elastic wave resonator Res7.

[0027] Each of the parallel arms may have an elastic wave resonator, and the first elastic wave resonator may have the highest resonance frequency among the elastic wave resonators in the parallel arms. In the example of Fig. 1, each of the four parallel arms PL has an elastic wave resonator Res. The elastic wave resonator Res1 may have the highest resonance frequency among the four elastic wave resonators Res.

[0028] The acoustic wave filter may have an attenuation band in the vicinity of the high frequency side of the high frequency end of the pass band. By positioning the attenuation band in the vicinity of the high frequency side of the high frequency end of the pass band, the boundary region between the pass band and the attenuation band can be clarified. As shown in FIG. 4 described later, the acoustic wave filter 100 of the first embodiment may have an attenuation band A2 in the vicinity of the high frequency side of the high frequency end f1 of the pass band A1. In this specification, the vicinity of the high frequency side of the high frequency end f1 of the pass band A1 refers to a range from the high frequency end f1 of the pass band A1 to a difference Δf (=|fr-fa|) between the resonance frequency fr and the anti-resonance frequency fa of the series resonator IS.

[0029] The bandwidth of the attenuation band may be set to be at least twice the frequency difference between the resonance frequency and the anti-resonance frequency of the first acoustic wave resonator. As shown in Fig. 4, the acoustic wave filter 100 of the first embodiment has an attenuation band A2. The bandwidth wf of the attenuation band A2 can be defined as the frequency difference (=|f3-f2|) between the low frequency end f2 and the high frequency end f3 of the attenuation band A2 (wf=|f3-f2|). The bandwidth wf may be set to be at least twice the frequency difference (=|fr1-fa1|) between the resonance frequency fr1 and the anti-resonance frequency fa1 of the acoustic wave resonator Res1 (wf≧2·|fr1-fa1|).

[0030] Comparative Example 1 Fig. 3 is a circuit diagram illustrating an elastic wave filter 100x of Comparative Example 1. As shown in Fig. 3, in the elastic wave filter 100x, the additional circuit AC1 of the elastic wave filter 100 of Fig. 1 is changed to an inductor L1. The inductor L1 may be referred to as the additional circuit of the elastic wave filter 100x. Other configurations of the elastic wave filter 100x of Comparative Example 1 are similar to those of the elastic wave filter 100 illustrated in Fig. 1, and therefore detailed description thereof will be omitted.

[0031] (Example of acoustic wave filter characteristics) Fig. 4 illustrates graphs TCH1 and ICH1 showing an example of characteristics of an acoustic wave filter according to an embodiment of the present disclosure, Fig. 5 illustrates an enlarged view of a portion of the frequency range of the graphs TCH1 and ICH1 in Fig. 4.

[0032] Graph TCH1 represents the attenuation characteristics of the acoustic wave filters of Embodiment 1 and Comparative Example 1. Graph G1 represented by a solid line represents the attenuation characteristics of the acoustic wave filter of Embodiment 1, and graph G0 represented by a dashed line represents the attenuation characteristics of the acoustic wave filter of Comparative Example 1.

[0033] In the graph TCH1, the horizontal axis (Frequency) indicates frequency (unit: GHz), and the vertical axis (Transmission) indicates attenuation (unit: dB). Attenuation can also be interpreted as a passing amount. Therefore, attenuation characteristics can also be interpreted as passing characteristics.

[0034] Graph ICH1 represents the impedance characteristics of the additional circuit of the elastic wave filter of Embodiment 1 and Comparative Example 1. Here, the inductor L1 of Comparative Example 1 is used as the additional circuit of Comparative Example 1. The solid line represents the impedance characteristics of the additional circuit of Embodiment 1, and the dashed line represents the impedance characteristics of the additional circuit of the elastic wave filter of Comparative Example 1.

[0035] In the graph ICH1, the horizontal axis (Frequency) indicates frequency (unit: GHz), and the vertical axis (|X|) indicates the absolute value of impedance (unit: Ω). In the following description, unless otherwise stated, the absolute value of impedance is simply abbreviated to impedance. In this specification, the resonant frequency fr is defined as the frequency at which the impedance is minimum. On the other hand, the anti-resonant frequency fa is defined as the frequency at which the impedance is maximum.

[0036] 4 and 5 show a pass band A1 and an attenuation band A2 of an elastic wave filter. In this specification, the pass band of an elastic wave filter refers to a frequency band from a low-frequency cutoff frequency f0 to a high-frequency cutoff frequency f1. In the attenuation characteristics of an elastic wave filter, there are −3 dB attenuation points on both the low-frequency side and the high-frequency side with respect to a peak frequency indicating a frequency at which the minimum attenuation is 0 dB.

[0037] The low-frequency cutoff frequency f0 is the frequency of the -3 dB attenuation point on the low-frequency side of the pass band. The high-frequency cutoff frequency f1 is the frequency of the -3 dB attenuation point on the high-frequency side of the pass band of the elastic wave filter. The low-frequency cutoff frequency f0 can also be expressed as the frequency at the low-frequency end of the pass band, or the low-frequency end. The high-frequency cutoff frequency f1 can also be expressed as the frequency at the high-frequency end of the pass band A1, or the high-frequency end. In this specification, the attenuation band of the acoustic wave filter is a frequency range in which the amount of attenuation is greater than a certain level on the higher frequency side of the pass band A1. More specifically, the attenuation band A2 is a frequency range that is wider than the difference Δf (=|fr1-fa1|) between the resonance frequency fr1 and the anti-resonance frequency fa1 of the acoustic wave resonator Res1 from the vicinity of the high frequency end f1 of the pass band A1 on the higher frequency side and in which the amount of attenuation is greater than a certain level.

[0038] Here, as an example of the first embodiment, the capacitance of the capacitor C11 of the additional circuit AC1 is 0.53 pF, the inductance values ​​of the inductors L11 and L12 are 0.34 nH and 0.227 nH, and the inductance ratio γ is 0.6. Also, the inductance value of the inductor L1 (additional circuit) of the first comparative example is 0.365 nH. The inductance ratio γ is expressed as "γ = L11 / (L11 + L12)" and represents the ratio of the inductance L11 to the total amount of the inductances L11 and L12. In other words, the inductances L11 and L12 and the inductance ratio γ have a relationship of "L12 = L11 (1 - γ) / γ".

[0039] 4 and 5, in the attenuation band A2, the through-put amount in the embodiment 1 is generally smaller than the through-put amount in the comparative example 1. That is, the through-put peaks P1, P2, and P3 in the embodiment 1 are reduced more than those in the comparative example 1, and the attenuation characteristics in the attenuation band A2 are good. The reason for this will be explained below.

[0040] 4, the impedance |X| of the additional circuits of the first embodiment and the first comparative example is the same at the frequency f0 at the low-frequency end of the passband A1. The impedance of the additional circuits of the first embodiment and the first comparative example is maximum at the anti-resonance frequencies fa1 and fa0, and is minimum at the resonant frequencies fr1 and fr0, respectively.

[0041] The anti-resonant frequency fa1 of the additional circuit of the first embodiment is closer to the high frequency end f1 of the pass band A1 than the anti-resonant frequency fa0 of the additional circuit of the first comparative example. Therefore, within the range from the low frequency end f2 of the attenuation band A2 to the resonance frequencies fr1 and fr0, the impedance of the additional circuit of the first embodiment is smaller than the impedance of the additional circuit of the first comparative example. As a result, the attenuation in the attenuation band A2 is reduced in the first embodiment compared to the first comparative example. As described above, the heights of the peaks P1, P2, and P3 are lower in the first embodiment than in the first comparative example. This is because the additional circuit is connected in parallel to the acoustic wave resonator Res1, and therefore the reduction in the impedance of the additional circuit leads to an increase in the attenuation in the signal path connecting the input terminal Pin to the output terminal Pout.

[0042] As described above, in the first embodiment, by connecting the additional circuit AC1 or the additional circuit AC2 in parallel to the first acoustic wave resonator in the first parallel arm, it is possible to reduce the frequency dependency of the attenuation in the attenuation band A2.

[0043] [Embodiment 2] The following describes the second embodiment. For ease of explanation, components having the same functions as those described in the first embodiment are given the same reference numerals, and the explanation thereof will not be repeated.

[0044] (Basic structure of elastic wave filters) 6 and 7 are circuit diagrams illustrating an example of a basic configuration of an acoustic wave filter 100a according to a second embodiment. In the first embodiment, the acoustic wave filter 100a is illustrated as a ladder-type filter. However, as will be apparent to those skilled in the art, an acoustic wave filter according to an aspect of the present disclosure is not limited to a ladder-type filter. Although the configurations of the additional circuits AC1 and AC2 are different between FIG. 6 and FIG. 7, the other configurations are the same.

[0045] The acoustic wave filter 100a may have at least one series arm. Accordingly, the acoustic wave filter 100a may have a plurality of series arms. When the acoustic wave filter 100a has a plurality of series arms, the plurality of series arms may be connected in series to each other. In the example of FIG. 6, the acoustic wave filter 100a has four series arms SL-1, SL-3, SL-5, and SL-7 that are connected in series to each other. In this specification, the series arms SL-1, SL-3, SL-5, and SL-7 are also collectively referred to as series arms SL.

[0046] As shown in Fig. 6, the acoustic wave filter 100a may have an acoustic wave resonator (series resonator) located in the series arm SL. In the example of Fig. 6, the acoustic wave filter 100a has series resonators IS-1, IS-3, IS-5, and IS-7 located in the series arms SL-1, SL-3, SL-5, and SL-5, respectively. In this specification, the series resonators IS-1, IS-3, IS-5, and IS-7 are also collectively referred to as the series resonators IS.

[0047] At least one series arm may be connected to an input terminal Pin and an output terminal Pout. In the example of Fig. 6, the series arm SL-1 is the series arm SL closer to the input terminal Pin, and the series arm SL-7 is the series arm SL closer to the output terminal Pout. The acoustic wave filter 100a may have a series arm SL between the input terminal Pin and the series arm SL-1. The acoustic wave filter 100a may have a series arm SL between the series arm SL-7 and the output terminal Pout.

[0048] At least one series arm may form a signal path that passes a signal in a pass band. In the example of Fig. 6, the series arms SL-1, SL-3, SL-5, and the series resonator IS-7 function as a signal path that passes a signal in a pass band defined by the acoustic wave filter 100a.

[0049] The acoustic wave filter may have an attenuation band in the vicinity of the high frequency side of the high frequency end of the pass band. By positioning the attenuation band in the vicinity of the high frequency side of the high frequency end of the pass band, the boundary region between the pass band and the attenuation band can be clarified. As shown in FIG. 6 described later, the acoustic wave filter 100a of the second embodiment may have an attenuation band A2 in the vicinity of the high frequency side of the high frequency end f1 of the pass band A1. In this specification, the vicinity of the high frequency side of the high frequency end f1 of the pass band A1 refers to a range from the high frequency end f1 of the pass band A1 to a difference Δf (=|fr-fa|) between the resonance frequency fr and the anti-resonance frequency fa of the series resonator IS.

[0050] The acoustic wave filter 100a may have a plurality of parallel arms. In the example of Fig. 6, the acoustic wave filter 100a has three parallel arms, namely, a parallel arm PL-2, a parallel arm PL-4, and a parallel arm PL-6. In this specification, the parallel arms PL-2, PL-4, and PL-6 are also collectively referred to as a parallel arm PL.

[0051] The parallel arms may connect the reference potential unit to positions that are different in electrical position with respect to at least one series arm of the signal path. In the example of FIG. 6, the first end of each of the three parallel arms PL is connected to the signal path at the node NN2, the node NN4, and the node NN6. Meanwhile, the second end of each of the three parallel arms PL is connected to the ground terminal GD-2, the ground terminal GD-4, and the ground terminal GD-6. The node NN2, the node NN4, and the node NN6 are located between the series arm SL-1, the series arm SL-3, the series arm SL-5, and the output terminal Pout, respectively, and are at different electrical positions from each other. The ground terminal GD-2, the ground terminal GD-4, and the ground terminal GD-6 function as the reference potential unit. In this specification, the ground terminal GD-2, the ground terminal GD-4, and the ground terminal GD-6 are also collectively referred to as the ground terminal GD.

[0052] The multiple parallel arms may have a first parallel arm and a second parallel arm. In the example of Fig. 6, the three parallel arms PL have a parallel arm PL-2 as the first parallel arm, and parallel arms PL-4 and PL-6 as the second parallel arms.

[0053] The first parallel arm may have a first acoustic wave resonator. The second parallel arm may have a second acoustic wave resonator. In the example of FIG. 6, the parallel arm PL-2 has an acoustic wave resonator Res2 as the first acoustic wave resonator. The parallel arms PL-4 and PL-6 have acoustic wave resonators Res4 and Res6 as the second acoustic wave resonators, respectively. The resonant frequency of the second acoustic wave resonator may be higher than the resonant frequency of the first acoustic wave resonator. The resonant frequency of the acoustic wave resonator Res2 may be higher than the resonant frequencies of the acoustic wave resonators Res4 and Res6. That is, a plurality of parallel arms PL may have acoustic wave resonators Res, and among them, the acoustic wave resonator Res2 of the parallel arm PL-2 may have the highest resonant frequency.

[0054] The anti-resonance frequency of the second acoustic wave resonator may be located near the high frequency side of the high frequency end of the pass band. The anti-resonance frequencies of the acoustic wave resonator Res4 and the acoustic wave resonator Res6 may be located near the high frequency side of the high frequency end f1 of the pass band A1. In this specification, the vicinity of the high frequency side of the high frequency end f1 of the pass band A1 refers to a range from the high frequency end f1 of the pass band A1 to a difference Δf (=|fr-fa|) between the resonance frequency fr and the anti-resonance frequency fa of the series resonator IS.

[0055] The second parallel arm may include a second acoustic wave resonator and an additional circuit connected in series to the second acoustic wave resonator. In the example of Fig. 6, the parallel arm PL-4 includes an acoustic wave resonator Res4 and an additional circuit AC1-4 connected in series to the acoustic wave resonator Res4. The parallel arm PL-6 includes an acoustic wave resonator Res6 and an additional circuit AC1-6 connected in series to the acoustic wave resonator Res6. In the example of Fig. 7, the parallel arm PL-4 includes an acoustic wave resonator Res4 and an additional circuit AC2-4 connected in series to the acoustic wave resonator Res4. The parallel arm PL-6 includes an acoustic wave resonator Res6 and an additional circuit AC2-6 connected in series to the acoustic wave resonator Res6.

[0056] The additional circuit may include a first additional circuit or a second additional circuit. The first additional circuit may include a first inductor, a first capacitor connected in parallel to the first inductor, and a second inductor connected in series to the first inductor and the first capacitor. In the example of FIG. 6, the additional circuit AC1-4 includes an inductor L41, a capacitor C41 connected in parallel to the inductor L41, and an inductor L42 connected in series to the inductor L41 and the capacitor C41. The additional circuit AC1-6 includes an inductor L61, a capacitor C61 connected in parallel to the inductor L61, and an inductor L62 connected in series to the inductor L61 and the capacitor C61.

[0057] The second additional circuit may include a third inductor, a second capacitor connected in series to the third inductor, and a fourth inductor connected in parallel to the third inductor and the second capacitor. In the example of Fig. 7, the additional circuit AC2-4 includes an inductor L43, a capacitor C42 connected in series to the inductor L43, and an inductor L44 connected in parallel to the inductor L43 and the capacitor C42. The additional circuit AC2-6 includes an inductor L63, a capacitor C62 connected in series to the inductor L63, and an inductor L64 connected in parallel to the inductor L63 and the capacitor C62.

[0058] As shown in the first embodiment, the additional circuit AC1 and the additional circuit AC2 can be made substantially equivalent as circuits. Moreover, the additional circuit AC1 can be made smaller in size more easily than the additional circuit AC2.

[0059] 6 and 7, both the parallel arms PL-4 and PL-6 have either the additional circuit AC1 or the additional circuit AC2. Alternatively, the parallel arm PL-4 may have the additional circuit AC1, and the parallel arm PL-6 may have the additional circuit AC2. Conversely, the parallel arm PL-4 may have the additional circuit AC2, and the parallel arm PL-6 may have the additional circuit AC1.

[0060] Comparative Example 2 Fig. 8 is a circuit diagram of an elastic wave filter 100y of Comparative Example 2. As shown in Fig. 8, in the elastic wave filter 100y, the additional circuits AC1-4 and AC1-6 of the elastic wave filter 100a of Fig. 6 are changed to inductors L4 and L6, respectively. The inductors L4 and L6 may be referred to as the additional circuits of the elastic wave filter 100x. The other configuration of the elastic wave filter 100y of Comparative Example 2 is similar to that of the elastic wave filter 100a illustrated in Fig. 6, and therefore detailed description thereof will be omitted.

[0061] (Examples of characteristics of each elastic wave filter) Fig. 9 illustrates graphs TCH2 and ICH2 showing an example of characteristics of an acoustic wave filter according to an embodiment of the present disclosure, and Fig. 10 illustrates an enlarged view of a portion of the frequency range of the graphs TCH2 and ICH2 in Fig. 9.

[0062] Graph TCH2 represents the attenuation characteristics of the elastic wave filters of Embodiment 2 and Comparative Example 2. Graph G1 represented by a solid line represents the attenuation characteristics of the elastic wave filter of Embodiment 2, and graph G0 represented by a dashed line represents the attenuation characteristics of the elastic wave filter of Comparative Example 2.

[0063] Graph ICH2 shows the impedance characteristics of the additional circuit of the elastic wave filter of Embodiment 2 and Comparative Example 2. Here, the inductor L4 of Comparative Example 2 is used as the additional circuit of Comparative Example 2. The solid line graph shows the impedance characteristics of the additional circuit of Embodiment 2, and the dashed line graph shows the impedance characteristics of the additional circuit of the elastic wave filter of Comparative Example 2. Graph ICH2 also shows the impedance-frequency characteristics of the series resonators IS-3 and IS-5.

[0064] 9 shows a pass band A1 and an attenuation band A2 of the acoustic wave filter. The pass band A1 and the attenuation band A2 are defined as described in the first embodiment.

[0065] Here, as an example of the second embodiment, the capacitance of the capacitor C41 of the additional circuit AC1-4 is 0.3 pF, the inductance values ​​of the inductors L41 and L42 are 3.1 nH and 0.233 nH, and the inductance ratio γ is 0.93 (γ = L41 / (L41 + L42)). The capacitance of the capacitor C61 of the additional circuit AC1-6 is 0.58 pF, the inductance values ​​of the inductors L61 and L62 are 0.72 nH and 0.117 nH, and the inductance ratio γ is 0.86 (γ = L61 / (L61 + L62)). Also, the inductance values ​​of the inductors L4 and L6 of the second comparative example are 3.2 nH and 1.8 nH.

[0066] As shown in the graph TCH2 of Fig. 9 and Fig. 10, in the attenuation band A2, the transmission amount in the second embodiment is relatively stable and the attenuation characteristics are good. In contrast, in the second comparative example, ripples PP are generated, the transmission amount is highly frequency-dependent, and the attenuation characteristics in the attenuation band A2 are not good. The reason for this will be explained below.

[0067] As shown in graph ICH2 of Fig. 10, in Comparative Example 2, in region RR within the attenuation band A2, the impedance of the inductor L4 (additional circuit) crosses with the impedances of the series resonators IS-3 and IS-5 located before and after the inductor L4. It is believed that this impedance crossing causes the ripple PP. The series resonators IS-3 and IS-5 tend to increase from their resonant frequency fr3 toward the anti-resonant frequency fa3, while the additional circuit of Comparative Example 2 tends to decrease from its anti-resonant frequency fa0. For this reason, the impedance of the inductor L4 (additional circuit) is likely to cross with the impedances of the series resonators IS-3 and IS-5 located before and after the inductor L4.

[0068] On the other hand, the impedance characteristic of the additional circuit AC1-4 in the second embodiment is different from that of the inductor L4. That is, in the impedance characteristic of the additional circuit AC1-4, a kind of resonance frequency fr1 (sub-peak) appears on the low-frequency side of the low-frequency end f2 of the attenuation band A2, and an anti-resonance frequency fa2 appears within the attenuation band A2. Therefore, the impedance of the additional circuit AC1-4 tends to increase with frequency between the resonance frequency fr1 and the anti-resonance frequency fa2.

[0069] As a result, the impedance of the additional circuit AC1-4 does not cross the impedance of the series resonators IS-3 and IS-5 in a region where the impedance is relatively low. The impedance of the additional circuit AC1-4 crosses the impedance of the series resonators IS-3 and IS-5 in a region RR1 near the anti-resonance frequency fa3. However, since the impedance is sufficiently large in this region RR1, no ripple is actually generated even if the impedances cross.

[0070] Here, it has been explained that ripples may occur due to the relationship between the impedance of the additional circuit AC1-4 (or inductor L4) and the impedance of the series resonators IS-3 and IS-5 located before and after it. This relationship between inductance and ripple also holds for the additional circuit AC1-6 (or inductor L6) and the series resonators IS-5 and IS-7 located before and after it. In this example, the parameters of the two additional circuits AC1-4 and the additional circuit AC1-6 are set to the same value, and the parameters of the series resonators IS located before and after these additional circuits are set to the same value. For this reason, the impedances of the additional circuits AC1-6, etc. are not shown in the figure.

[0071] As described above, in the second embodiment, by connecting the additional circuit AC1 or the additional circuit AC2 in series to the second acoustic wave resonator in the second parallel arm, it is possible to reduce the frequency dependency of the attenuation in the attenuation band A2.

[0072] 〔summary〕 An acoustic wave filter according to a first aspect of the present disclosure includes a signal path that passes a signal in a pass band, and includes at least one series arm, which is connected in series with each other if there are multiple series arms, and a plurality of parallel arms that connect positions of the signal path that are different electrical positions with respect to the at least one series arm, and a reference potential section, the plurality of parallel arms including a first parallel arm, the first parallel arm including a first acoustic wave resonator and an additional circuit connected in parallel to the first acoustic wave resonator, the additional circuit being a first additional circuit or a second additional circuit, the first additional circuit including a first inductor, a first capacitor connected in parallel to the first inductor, and a second inductor connected in series to the first inductor and the first capacitor, and the second additional circuit including a third inductor, a second capacitor connected in series to the third inductor, and a fourth inductor connected in parallel to the third inductor and the second capacitor.

[0073] An acoustic wave filter according to a second aspect of the present disclosure is the acoustic wave filter of the first aspect, which may have an attenuation band in the vicinity of a higher frequency side of a higher frequency end of the pass band.

[0074] In an acoustic wave filter according to a third aspect of the present disclosure, in the second aspect, a bandwidth of the attenuation band may be equal to or greater than twice the frequency difference between a resonant frequency and an anti-resonant frequency of the first acoustic wave resonator.

[0075] In an acoustic wave filter according to a fourth aspect of the present disclosure, in any one of the first to third aspects, the multiple parallel arms may further include a second parallel arm different from the first parallel arm, the second parallel arm including a second acoustic wave resonator and an inductor connected in parallel to the second acoustic wave resonator, and a resonant frequency of the second acoustic wave resonator may be located in the attenuation band.

[0076] In an acoustic wave filter according to a fifth aspect of the present disclosure, in any one of the first to fourth aspects, each of the parallel arms may include an acoustic wave resonator and an inductor connected in parallel to the acoustic wave resonator.

[0077] In an elastic wave filter according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, each of the multiple parallel arms may have an elastic wave resonator, and the first elastic wave resonator may have a maximum resonant frequency among the elastic wave resonators in the multiple parallel arms.

[0078] An acoustic wave filter according to a seventh aspect of the present disclosure includes a signal path that passes a signal in a pass band, and includes at least one series arm, which is connected in series when there are a plurality of series arms, and a plurality of parallel arms that connect positions in the signal path that are different in electrical position from each other with respect to the at least one series arm and a reference potential unit, and includes an attenuation band near a high frequency side of a high frequency end of the pass band, and the plurality of parallel arms include a first parallel arm and a second parallel arm, and the second parallel arm includes a second acoustic wave resonator and a second parallel arm that is connected between the second acoustic wave resonator and a reference potential unit. and an additional circuit connected in series between the first and second additional circuits, the additional circuit being a first additional circuit or a second additional circuit, the first additional circuit having a first inductor, a first capacitor connected in parallel to the first inductor, and a second inductor connected in series to the first inductor and the first capacitor, and the second additional circuit having a third inductor, a second capacitor connected in series to the third inductor, and a fourth inductor connected in parallel to the third inductor and the second capacitor.

[0079] An elastic wave filter according to an eighth aspect of the present disclosure is similar to the seventh aspect, in that the first parallel arm may have a first elastic wave resonator, and a resonant frequency of the second elastic wave resonator may be higher than a resonant frequency of the first elastic wave resonator.

[0080] An acoustic wave filter according to a ninth aspect of the present disclosure is the acoustic wave filter of the seventh or eighth aspect, wherein an anti-resonant frequency of the second acoustic wave resonator may be located in the vicinity of a high frequency side of a high frequency end of the pass band.

[0081] [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 the above-mentioned embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0082] 100, 100a acoustic wave filter SL (SL-1~SL-7) Series arm IS(IS-1~IS-7) Series resonator PL (PL-1~PL-7) Parallel arm Res(Res1~Res7) Elastic wave resonator AC1 (AC1-2, AC1-4, AC1-6), AC2 (AC2-4, AC2-6) Additional circuit Pin Input terminal Pout Output terminal NN(NN1~NN7) Node GD(GD-1~GD-7) Ground terminal

Claims

1. At least one series arm that constitutes a signal path that passes a signal in a passband and is connected in series to each other when there are a plurality of series arms; a plurality of parallel arms connecting positions of the signal path that are different from each other in electrical position with respect to the at least one series arm and a reference potential portion; The plurality of parallel cups have a first parallel arm, The first parallel arm is A first acoustic wave resonator; an additional circuit connected in parallel to the first acoustic wave resonator, the additional circuit is a first additional circuit or a second additional circuit, The first addition circuit is A first inductor; a first capacitor connected in parallel with the first inductor; a second inductor connected in series with the first inductor and the first capacitor; The second addition circuit is A third inductor; a second capacitor connected in series with the third inductor; a fourth inductor connected in parallel to the third inductor and the second capacitor; Elastic wave filters.

2. 2. The acoustic wave filter according to claim 1, further comprising an attenuation band adjacent to a higher frequency side of a higher frequency end of the pass band.

3. The acoustic wave filter according to claim 2 , wherein a bandwidth of the attenuation band is equal to or greater than twice the frequency difference between a resonant frequency and an antiresonant frequency of the first acoustic wave resonator.

4. The plurality of parallel arms further include a second parallel arm different from the first parallel arm, The second parallel arm is A second acoustic wave resonator; an inductor connected in parallel to the second acoustic wave resonator, The acoustic wave filter according to claim 2 , wherein a resonant frequency of the second acoustic wave resonator is located in the attenuation band.

5. Each of the parallel arms is An elastic wave resonator; an inductor connected in parallel to the acoustic wave resonator; The acoustic wave filter according to claim 1 ,

6. each of the parallel arms includes an elastic wave resonator; The acoustic wave filter according to claim 1 , wherein the first acoustic wave resonator has a maximum resonant frequency among the acoustic wave resonators in the parallel arms.

7. At least one series arm that constitutes a signal path that passes a signal in a passband and is connected in series to each other when there are a plurality of series arms; a plurality of parallel arms connecting positions of the signal path that are different from each other in electrical position with respect to the at least one series arm and a reference potential portion; an attenuation band in the vicinity of the high frequency side of the high frequency end of the pass band; The plurality of parallel arms include a first parallel arm and a second parallel arm, The second parallel arm is A second acoustic wave resonator; an additional circuit connected in series between the second acoustic wave resonator and a reference potential portion, the additional circuit is a first additional circuit or a second additional circuit, The first addition circuit is A first inductor; a first capacitor connected in parallel with the first inductor; a second inductor connected in series with the first inductor and the first capacitor; The second addition circuit is A third inductor; a second capacitor connected in series with the third inductor; a fourth inductor connected in parallel to the third inductor and the second capacitor; Elastic wave filters.

8. the first parallel arm includes a first acoustic wave resonator, The acoustic wave filter according to claim 7 , wherein a resonant frequency of the second acoustic wave resonator is higher than a resonant frequency of the first acoustic wave resonator.

9. The acoustic wave filter according to claim 7 , wherein an anti-resonant frequency of the second acoustic wave resonator is located near a high frequency side of a high frequency end of the pass band.

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