Acoustic wave filters and multiplexers

Abstract

This invention provides an elastic wave filter that can reduce the power consumption of the additional circuitry. [Solution] The elastic wave filter 1 comprises a filter circuit 10 provided in a first path r1 connecting an input terminal T1 and an output terminal T2, and an additional circuit 20 provided in a second path r2 connected in parallel with the first path r1. The filter circuit 10 has a plurality of series arm resonators S1 to S4 provided in the first path r1. On both outer sides of the series arm resonators S2 to S4 are provided a first node n1 and a second node n2, which are connection points between the first path r1 and the second path r2, with the first node n1 being located closer to the input terminal T1 than the second node n2. The series arm resonator S2, located closer to the output terminal T2 than the first node n1, has one or more IDT electrodes 11, and the electrode finger pitch pf of the IDT electrode connected to the first node n1 is smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators S1, S3, and S4.

Description

Technical Field

[0001] The present invention relates to an elastic wave filter and a multiplexer including the elastic wave filter.

Background Art

[0002] Conventionally, an elastic wave filter including a plurality of elastic wave resonators has been known. As an example of this type of elastic wave filter, Patent Document 1 discloses an elastic wave filter including a filter circuit having a predetermined frequency band as a pass band and an additional circuit (cancellation circuit) connected in parallel to the filter circuit. Each of the filter circuit and the additional circuit is constituted by an elastic wave resonator having an IDT (InterDigital Transducer) electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the elastic wave filter disclosed in Patent Document 1, there is a problem that the power consumption of the additional circuit increases. For example, when the power consumption of the additional circuit increases, the electrode fingers of the IDT electrodes included in the additional circuit may be blown.

[0005] The present invention has been made to solve the above problems, and provides an elastic wave filter and the like that can reduce the power consumption of the additional circuit.

Means for Solving the Problems

[0006] An elastic wave filter according to one aspect of the present invention comprises an input terminal and an output terminal, a filter circuit provided in a first path connecting the input terminal and the output terminal, and an additional circuit provided in a second path connected in parallel with at least a portion of the first path, wherein the additional circuit has a longitudinally coupled elastic wave resonator, and the filter circuit has a plurality of series arm resonators provided in the first path and one or more parallel arm resonators provided in a path connecting the first path and ground, and each of the plurality of series arm resonators and the one or more parallel arm resonators has an IDT electrode and is arranged in the first path On both outer sides of the one or more series arm resonators, there are first and second nodes which are connection points between the first path and the second path, the first node is located closer to the input terminal than the second node, and a predetermined series arm resonator among the plurality of series arm resonators that is connected to the first node and located closer to the output terminal than the first node is composed of one or more IDT electrodes, and the electrode finger pitch of the IDT electrode connected to the first node is smaller than the electrode finger pitch of the IDT electrodes of the other series arm resonators excluding the predetermined series arm resonator.

[0007] An elastic wave filter according to one aspect of the present invention comprises an input terminal and an output terminal, a filter circuit provided in a first path connecting the input terminal and the output terminal, and an additional circuit provided in a second path connected in parallel with at least a portion of the first path, wherein the additional circuit has a longitudinally coupled elastic wave resonator, the filter circuit has a plurality of series arm resonators provided in the first path, and one or more parallel arm resonators provided in a path connecting the first path and ground, each of the plurality of series arm resonators and the one or more parallel arm resonators has an IDT electrode, and on both sides of the one or more series arm resonators arranged in the first path, A first node and a second node are provided, which are connection points between the first path and the second path. The first node is located on the input terminal side of the second node and is situated between two adjacent series arm resonators on the first path. Of the two series arm resonators, a predetermined series arm resonator located on the output terminal side of the first node is composed of one or more IDT electrodes. The electrode finger pitch of the IDT electrode connected to the first node is smaller than the electrode finger pitch of the IDT electrode of the series arm resonator connected to the first node and located on the input terminal side of the first node.

[0008] A multiplexer according to one aspect of the present invention comprises the above-described elastic wave filter and another filter having a circuit different from the filter circuit. [Effects of the Invention]

[0009] According to the elastic wave filter and the like of the present invention, the power consumption of the additional circuit can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit diagram showing the filter circuit and additional circuit of the elastic wave filter according to Embodiment 1. [Figure 2] These are schematic plan and cross-sectional views of the electrode configuration of the elastic wave resonator in the filter circuit. [Figure 3]This is a schematic plan view showing the electrode configuration of the longitudinally coupled elastic wave resonator in the additional circuit. [Figure 4] This figure shows the electrode parameters of the IDT electrode of the elastic wave filter in Embodiment 1. [Figure 5] This figure shows the electrode parameters of the IDT electrode of the elastic wave filter in the comparative example. [Figure 6] This is a schematic diagram showing the resonant frequency of the series arm resonator included in the filter circuit. [Figure 7] This figure shows the power consumption of the additional circuits for the elastic wave filters in Embodiment 1 and the Comparative Example. [Figure 8] This figure shows the attenuation outside the passband of the elastic wave filters in Embodiment 1 and the comparative example. [Figure 9] This figure shows a part of the IDT electrode in the filter circuit of modified example 1 of Embodiment 1. [Figure 10] This figure shows a part of the IDT electrode in the additional circuit of modified example 1 of Embodiment 1. [Figure 11] This figure shows the electrode parameters of the IDT electrode in a modified example 1 of Embodiment 1. [Figure 12] This is a circuit diagram showing the filter circuit and additional circuit of an elastic wave filter according to a modified example 2 of Embodiment 1. [Figure 13] This is a circuit diagram showing the filter circuit and additional circuit of an elastic wave filter according to a modified example 3 of Embodiment 1. [Figure 14] This is a circuit diagram of the multiplexer according to Embodiment 2. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the embodiments and the drawings. Note that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangements and connection forms of components shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components not described in the independent claims are described as optional components. Also, the sizes or size ratios of the components shown in the drawings are not necessarily precise. In each figure, substantially the same configurations are denoted by the same reference numerals, and duplicate descriptions may be omitted or simplified. Further, in the following embodiments, "connected" includes not only cases of direct connection but also cases of electrical connection via other elements or the like.

[0012] (Embodiment 1) [Configuration of the surface acoustic wave filter] The configuration of the surface acoustic wave filter according to Embodiment 1 will be described with reference to FIGS. 1 to 4.

[0013] FIG. 1 is a circuit configuration diagram showing a filter circuit 10 and an additional circuit 20 of a surface acoustic wave filter 1 according to Embodiment 1.

[0014] As shown in FIG. 1, the surface acoustic wave filter 1 includes a filter circuit 10 and an additional circuit 20. The surface acoustic wave filter 1 also includes an input terminal T1 and an output terminal T2.

[0015] The input terminal T1 is a terminal to which a high-frequency signal is input. For example, the input terminal T1 is connected to an RF signal processing circuit (not shown) via an amplifier circuit or the like (not shown). The output terminal T2 is a terminal from which a high-frequency signal is output. For example, the output terminal T2 is connected to an antenna element (not shown).

[0016] The filter circuit 10 is located on a first path r1 connecting the input terminal T1 and the output terminal T2. The filter circuit 10 is a circuit that uses a predetermined frequency band as its passband, as defined by the communication standard. The elastic wave filter 1, including the filter circuit 10, is, for example, a transmit filter that uses the upfrequency band (transmitting band) as its passband.

[0017] The additional circuit 20 is a cancellation circuit having a cancellation component with the same amplitude and out of phase as the filter circuit 10. The additional circuit 20 is provided in the second path r2, which is connected in parallel to at least a portion of the first path r1. By adding the additional circuit 20 to the filter circuit 10, it is possible to improve the out-of-passband attenuation characteristics of the filter circuit 10.

[0018] Next, the connection relationships of each elastic wave resonator included in the filter circuit 10 and the add-on circuit 20 will be described.

[0019] As shown in Figure 1, the filter circuit 10 includes series arm resonators S1, S2, S3, and S4, which are elastic wave resonators, as well as parallel arm resonators P1, P2, P3, and P4.

[0020] The series-arm resonators S1 to S4 are arranged on the first path r1 connecting the input terminal T1 and the output terminal T2. The series-arm resonators S1 to S4 are connected in series in this order from the input terminal T1 to the output terminal T2.

[0021] The parallel arm resonators P1 to P4 are arranged on paths connecting each node between the series arm resonators S1 to S4, which are aligned on the first path r1, to ground (reference terminal). Specifically, of the parallel arm resonators P1 to P4, the parallel arm resonator P1, which is closest to the input terminal T1, has one end connected to the node between the input terminal T1 and the series arm resonator S1, and the other end connected to ground. The parallel arm resonator P2 has one end connected to the node between the series arm resonators S1 and S2 (the first node n1, described later). The parallel arm resonator P3 has one end connected to the node between the series arm resonators S2 and S3. The parallel arm resonator P4 has one end connected to the node between the series arm resonators S3 and S4. The other ends of the parallel arm resonators P2, P3, and P4 are connected to ground by a common wiring.

[0022] Thus, the filter circuit 10 has a π-type ladder filter structure consisting of four series arm resonators S1 to S4 arranged on the first path r1, and four parallel arm resonators P1 to P4 arranged on the path connecting the first path r1 and ground. Note that the number of series arm resonators and parallel arm resonators constituting the filter circuit 10 is not limited to four each; it is sufficient to have two or more series arm resonators and one or more parallel arm resonators. In addition, an inductor may be provided between the parallel arm resonators and ground.

[0023] Each elastic wave resonator may be a single resonator composed of one IDT electrode, or it may be a plurality of segmented resonators composed of multiple IDT electrodes. The plurality of segmented resonators may be a plurality of segmented resonators connected in series with each other, or a plurality of segmented resonators connected in parallel with each other.

[0024] Multiple segmented resonators connected in series refer to elastic wave resonators in which the connection nodes between adjacent segmented resonators connected in series are not connected to anything other than those adjacent segmented resonators. For example, no other elements are connected between adjacent segmented resonators, and the connection nodes between adjacent segmented resonators are not connected to ground, etc.

[0025] On both sides of the series arm resonators S2, S3, and S4 arranged in the first path r1, there are first nodes n1 and second nodes n2, which are connection points between the first path r1 and the second path r2. The first node n1 is located closer to the input terminal T1 than the second node n2. In other words, the second node n2 is located closer to the output terminal T2 than the first node n1.

[0026] In this example, a first node n1 is located on a first path r1 between series arm resonators S1 and S2, and a second node n2 is located on a first path r1 between series arm resonator S4 and output terminal T2. In other words, the first node n1 is located between two adjacent series arm resonators S1 and S2 on the first path r1, and the second node n2 is located between series arm resonator S4 and output terminal T2.

[0027] The locations where the first node n1 and the second node n2 are provided are not limited to those described above. As described above, if the first node n1 is provided between series arm resonators S1 and S2, the second node n2 may be provided between series arm resonators S2 and S3 or between series arm resonators S3 and S4. For example, if the first node n1 is provided between the input terminal T1 and the series arm resonator S1, the second node n2 may be provided between series arm resonators S1 and S2, between series arm resonators S2 and S3, between series arm resonators S3 and S4, or between series arm resonator S4 and the output terminal T2. For example, if the first node n1 is provided between series arm resonators S2 and S3, the second node n2 may be provided between series arm resonators S3 and S4 or between series arm resonator S4 and the output terminal T2. For example, if the first node n1 is located between the series arm resonators S3 and S4, the second node n2 may be located between the series arm resonator S4 and the output terminal T2.

[0028] One end of the additional circuit 20 is connected to the first node n1, and the other end of the additional circuit 20 is connected to the second node. The additional circuit 20 has a longitudinally coupled elastic wave resonator 25 having multiple IDT electrodes, and a capacitive element 28.

[0029] The longitudinally coupled elastic wave resonator 25 is located on the second path r2 connecting the first node n1 and the second node n2. The capacitive element 28 is located on the second path r2 connecting the longitudinally coupled elastic wave resonator 25 and the second node n2. In other words, the capacitive element 28 is located on the output terminal T2 side as viewed from the longitudinally coupled elastic wave resonator 25.

[0030] Next, the IDT electrodes and other components of each elastic wave resonator in the filter circuit 10 and the add-on circuit 20 will be described.

[0031] Figure 2 shows a schematic plan view and cross-sectional view of the electrode configuration of the elastic wave resonator 15 of the filter circuit 10.

[0032] The elastic wave resonator 15 shown in Figure 2 is formed from a piezoelectric substrate 100, an electrode 110, and a protective film 113, and comprises an IDT electrode 11 composed of these components, and a plurality of reflectors 12. The elastic wave resonator 15 is a surface acoustic wave (SAW) resonator composed of the IDT electrode 11, the plurality of reflectors 12, and the piezoelectric substrate 100. Note that the elastic wave resonator 15 shown in Figure 2 is for illustrating a typical structure, and the number and length of the electrode fingers constituting the electrode are not limited to this.

[0033] As shown in the cross-sectional view of Figure 2, the electrodes 110 that make up the IDT electrode 11 and the multiple reflectors 12 have a laminated structure consisting of an adhesion layer 111 and a main electrode layer 112.

[0034] The adhesion layer 111 is a layer for improving the adhesion between the piezoelectric substrate 100 and the main electrode layer 112, and for example, Ti is used as the material.

[0035] For the main electrode layer 112, for example, aluminum containing 1% copper is used as the material.

[0036] The protective film 113 is formed to cover the electrode 110. The protective film 113 is a layer intended to protect the main electrode layer 112 from the external environment, adjust the frequency-temperature characteristics, and improve moisture resistance, and is, for example, a film mainly composed of silicon dioxide (SiO2).

[0037] The materials constituting the adhesion layer 111, the main electrode layer 112, and the protective film 113 are not limited to those described above. Furthermore, the electrode 110 does not have to be in the laminated structure described above. The electrode 110 may be composed of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or it may be composed of multiple laminates made of the above metals or alloys. Also, the protective film 113 may not be formed.

[0038] As the material for the piezoelectric substrate 100, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials mainly composed of the above materials can be used.

[0039] The piezoelectric substrate 100 may be a substrate having a piezoelectric layer in at least a portion of it, or it may be a laminated structure having a piezoelectric layer. For example, the piezoelectric substrate 100 may have a structure comprising a high-sonic-velocity support substrate, a low-sonic-velocity film, and a piezoelectric layer, in which the high-sonic-velocity support substrate, the low-sonic-velocity film, and the piezoelectric layer are laminated in this order.

[0040] As shown in the plan view of Figure 2, the IDT electrode 11 of the filter circuit 10 has a pair of comb-shaped electrodes 11A and 11B that face each other.

[0041] In this plan view, a predetermined direction along the main surface 100a of the piezoelectric substrate 100 is called the first direction d1, and a direction along the main surface 100a of the piezoelectric substrate 100 and intersecting the first direction d1 is called the second direction d2. The first direction d1 is the direction of elastic wave propagation of the elastic wave resonator 15. In this embodiment, the first direction d1 and the second direction d2 are orthogonal.

[0042] The comb-shaped electrode 11A is composed of a plurality of electrode fingers 11a arranged to extend in a second direction d2, and a busbar electrode 11c connecting one end of each of the plurality of electrode fingers 11a. The comb-shaped electrode 11B is composed of a plurality of electrode fingers 11b arranged to extend in a second direction d2, and a busbar electrode 11c connecting one end of each of the plurality of electrode fingers 11b. The plurality of electrode fingers 11a and 11b are arranged alternately in a first direction d1 with a predetermined electrode finger pitch pf. The electrode finger pitch pf of the IDT electrode 11 is the distance between the centers of adjacent electrode fingers 11a and 11b in the first direction d1.

[0043] The electrode finger pitch pf is the average pitch of multiple electrode fingers 11a and 11b. The electrode finger pitch pf is calculated, for example, by dividing the distance between the centers of the two electrode fingers located at the outermost end of the IDT electrode 11 in the first direction d1 by "total number of electrode fingers - number of IDT electrodes". In this example, the number of IDT electrodes is 1. In other words, the electrode finger pitch pf in the IDT electrode 11 is derived by (Equation 1) shown below.

[0044] Electrode finger pitch = (distance between the centers of the two electrode fingers located at the outermost end of the IDT electrode in the first direction) / (total number of electrode fingers - number of IDT electrodes) ... (Equation 1)

[0045] When an elastic wave resonator is composed of multiple segmented resonators, the electrode finger pitch pf is calculated by determining the distance between the centers of the two electrode fingers located at the outermost end of the IDT electrode in each of the segmented resonators, and then dividing the sum of these distances by "total number of electrode fingers - number of segmented resonators". In other words, the electrode finger pitch pf in multiple segmented resonators is derived by (Equation 2) shown below.

[0046] Electrode finger pitch = (Calculate the distance between the centers of the two electrode fingers located at the outermost end of the IDT electrode in each of the multiple divided resonators, and sum the calculated distances between the centers) / (Total number of electrode fingers - Number of divided resonators) ... (Equation 2)

[0047] Furthermore, "total number of electrode fingers - number of IDT electrodes" and "total number of electrode fingers - number of divided resonators" can also be considered as the total number of gaps created by adjacent electrode fingers in an IDT electrode.

[0048] The reflector 12 is positioned on both sides of the IDT electrode 11 in the first direction d1. The plurality of reflectors 12 consists of one reflector 12 located on the negative side of the first direction d1 as viewed from the IDT electrode 11, and the other reflector 12 located on the positive side of the first direction d1. The reflector 12 consists of a plurality of reflective electrode fingers 12a arranged to extend in the second direction d2, and a busbar electrode 12c connecting one end of the plurality of reflective electrode fingers 12a.

[0049] Figure 3 is a schematic plan view showing the electrode configuration of the longitudinally coupled elastic wave resonator 25 of the additional circuit 20.

[0050] The longitudinally coupled elastic wave resonator 25 shown in Figure 3 is formed from a piezoelectric substrate 100, electrodes 110, and a protective film 113, and comprises a plurality of IDT electrodes 31 and 32 and a plurality of reflectors 37 composed of these components. In other words, the longitudinally coupled elastic wave resonator 25 is a resonator composed of IDT electrodes 31 and 32, reflectors 37, and a piezoelectric substrate 100. Note that the longitudinally coupled elastic wave resonator 25 shown in Figure 3 is for illustrating a typical structure, and the number and length of electrode fingers constituting the electrodes are not limited thereto. The cross-sectional structure of the electrodes constituting the IDT electrodes 31 and 32 and the reflectors 37 is the same as the cross-sectional view in Figure 2.

[0051] The longitudinally coupled elastic wave resonator 25 has a plurality of IDT electrodes 31 and 32. The plurality of IDT electrodes 31 and 32 are arranged in this order along a first direction d1 (e.g., the direction of elastic wave propagation). The additional circuit 20 also has a plurality of reflectors 37. The plurality of reflectors 37 are located on both sides of the plurality of IDT electrodes 31 and 32, sandwiching them in the first direction d1.

[0052] As shown in Figure 3, each IDT electrode 31 and 32 of the longitudinally coupled elastic wave resonator 25 has a comb-like shape. IDT electrode 31 has a pair of comb-like electrodes 31A and 31B facing each other. IDT electrode 32 has a pair of comb-like electrodes 32A and 32B facing each other.

[0053] Each of the comb-shaped electrodes 31A and 32A consists of a plurality of electrode fingers 36a arranged to extend in a second direction d2, and a busbar electrode 36c connecting one end of each of the plurality of electrode fingers 36a. Each of the comb-shaped electrodes 31B and 32B consists of a plurality of electrode fingers 36b arranged to extend in a second direction d2, and a busbar electrode 36c connecting one end of each of the plurality of electrode fingers 36b. The plurality of electrode fingers 36a and 36b are arranged alternately in a first direction d1 with a predetermined electrode finger pitch pc. The electrode finger pitch pc of the IDT electrodes 31 and 32 is the distance between the centers of adjacent electrode fingers 36a and 36b in the first direction d1.

[0054] The electrode finger pitch pc is the average pitch of multiple electrode fingers 36a and 36b. The electrode finger pitch pc is calculated, for example, by adding the distance between the centers of the two electrode fingers located at the outermost end of IDT electrode 31 and the distance between the centers of the two electrode fingers located at the outermost end of IDT electrode 32, and dividing the result by "total number of electrode fingers - number of IDT electrodes". In this example, the number of IDT electrodes is 2. In other words, the electrode finger pitch pc in the longitudinally coupled elastic wave resonator 25 is derived by (Equation 3) shown below.

[0055] Electrode finger pitch = (Calculate the distance between the centers of the two electrode fingers located at the outermost end of each IDT electrode in the first direction, and sum the calculated distances between the centers) / (Total number of electrode fingers - Number of IDT electrodes) ... (Equation 3)

[0056] The IDT electrode 31 is connected to the first node n1 via a second path r2 on the input terminal T1 side as viewed from the longitudinally coupled elastic wave resonator 25. The IDT electrode 32 is connected to the second node n2 via a second path r2 on the output terminal T2 side as viewed from the longitudinally coupled elastic wave resonator 25 and a capacitive element 28.

[0057] The high-frequency signal input to input terminal T1 is output from output terminal T2 via filter circuit 10. The additional circuit 20 cancels out unwanted waves outside the passband of filter circuit 10 by multiplying them with waves of opposite phase and same amplitude, thereby suppressing the output of unwanted waves from elastic wave filter 1.

[0058] [Electrode parameters of IDT electrodes, etc.] The electrode parameters of IDT electrodes 11, 31, and 32 will be explained.

[0059] Figure 4 shows the electrode parameters of the IDT electrodes 11, 31, and 32 of the elastic wave filter 1 of Embodiment 1. Figure 5 shows the electrode parameters of the IDT electrodes of the elastic wave filter of the comparative example.

[0060] The basic structure of the comparative example's elastic wave filter is almost the same as that of the elastic wave filter 1 of Embodiment 1 shown in Figures 1 to 3.

[0061] The electrode parameters of Embodiment 1 and the Comparative Example are common in the following respects. For example, the crossover width of each IDT electrode of the series arm resonators S1 to S4 and the longitudinally coupled elastic wave resonator 25 is the same in Embodiment 1 and the Comparative Example. Also, the logarithm, duty cycle, and offset gap of each IDT electrode are the same in Embodiment 1 and the Comparative Example. Furthermore, Embodiment 1 and the Comparative Example are common in that the electrode finger pitch pc of the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 is larger than the electrode finger pitch pf of the IDT electrode 11 of the series arm resonators S1 to S4. Furthermore, Embodiment 1 and the Comparative Example are common in that the crossover width of the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 is smaller than the crossover width of the IDT electrode 11 of the series arm resonators S1 to S4. The crossover width is the length over which the electrode fingers 11a and 11b (or electrode fingers 36a and 36b) overlap when the IDT electrode 11 is viewed from a first direction d1.

[0062] Figures 4 and 5 show the electrode parameters of one of the multiple divided resonators that make up a series arm resonator. For example, in the series arm resonator S2, the electrode parameters of one divided resonator are "crossover width 30 × logarithm 251.5", and three of these same divided resonators are connected in series. Similarly, in the series arm resonator S4, the electrode parameters of one divided resonator are "crossover width 36 × logarithm 240", and two of these divided resonators are connected in series.

[0063] This embodiment differs from the comparative example in the following respects. For example, in the comparative example, the electrode finger pitch pf of the IDT electrode 11 is larger for the series arm resonator S2 than for the series arm resonator S1, but in Embodiment 1, the electrode finger pitch pf of the IDT electrode 11 is smaller for the series arm resonator S2 than for the series arm resonator S1.

[0064] In other words, in this embodiment, among the multiple series arm resonators S1 to S2 arranged in the first path r1, the series arm resonator S2 connected to the first node n1 and located closer to the output terminal T2 than the first node n1 has a smaller electrode finger pitch pf of the IDT electrode 11 than the series arm resonator S1 connected to the first node n1 and located closer to the input terminal T1 than the first node n1. More specifically, the series arm resonator S2 connected to the first node n1 and located closer to the output terminal T2 than the first node n1 has the smallest electrode finger pitch pf of the IDT electrode 11 among the multiple series arm resonators S1 to S4.

[0065] In this way, by reducing the electrode finger pitch pf of the IDT electrode 11 of the series arm resonator S2, which is connected to the first node n1 and located on the output terminal T2 side of the first node n1, it is possible to suppress an increase in the power consumption of the additional circuit 20.

[0066] Figure 6 is a schematic diagram showing the resonant frequency and other parameters of the series arm resonator S2 included in the filter circuit 10.

[0067] Here, we will explain using a series arm resonator S2 connected to the first node n1 and located on the output terminal T2 side of the first node n1 as an example. In the following explanation, the series arm resonator before changing the electrode parameters of the IDT electrode 11 will be referred to as series arm resonator S2a, and the series arm resonator after the change will be referred to as series arm resonator S2b.

[0068] For example, as shown in Figure 6, if the anti-resonance frequency fa of the series arm resonator S2a is located near the maximum frequency of the passband of the filter circuit 10, the impedance of the series arm resonator S2a at the maximum frequency is high, making it difficult for the signal at the maximum frequency to be transmitted to the series arm resonator S2a. As a result, the above signal is transmitted from the first node n1 before the series arm resonator S2a to the second path r2. Consequently, the current flowing through the add-on circuit 20 increases, and the power consumption of the add-on circuit 20 increases.

[0069] In contrast, the series arm resonator S2b shown in Figure 6 reduces the electrode finger pitch pf of the IDT electrode 11 to shorten the wavelength of the series arm resonator S2b, shifting the anti-resonance frequency fa of the series arm resonator S2b to the higher frequency side. As a result, the impedance of the series arm resonator S2b at the maximum frequency of the passband becomes lower, making it easier for the signal at the maximum frequency to be transmitted to the series arm resonator S2b side. Consequently, it is possible to suppress the current flowing through the additional circuit 20 from becoming excessively large and to reduce the power consumption of the additional circuit 20.

[0070] In the elastic wave filter 1 of this embodiment, among the multiple series arm resonators S1 to S4, a predetermined series arm resonator (e.g., S2) connected to the first node n1 and located on the output terminal T2 side of the first node n1 is composed of one or more IDT electrodes. The electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 is smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators (e.g., S1, S3, S4) excluding the predetermined series arm resonator S2.

[0071] As described above, by making the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 of the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators S1, S3, and S4, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0072] Furthermore, in the elastic wave filter 1 of this embodiment, of the two series arm resonators S1 and S2, a predetermined series arm resonator S2 located on the output terminal T2 side of the first node n1 is composed of one or more IDT electrodes 11. The electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 is smaller than the electrode finger pitch pf of the IDT electrode 11 of the series arm resonator S1 connected to the first node n1 and located on the input terminal T1 side of the first node n1.

[0073] As described above, by making the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 of the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrode 11 of the series arm resonator S1 located closer to the input terminal T1 than the first node n1, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0074] In this embodiment, if a predetermined series arm resonator S2 connected to the first node n1 and located on the output terminal T2 side of the first node n1 is composed of multiple series divided resonators, the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 is derived as follows. The electrode finger pitch pf is calculated, for example, by dividing the distance between the centers in the first direction of the two electrode fingers located at the outermost end of the IDT electrode 11 connected to the first node n1 by "total number of electrode fingers of the IDT electrode connected to the first node - number of IDT electrodes connected to the first node". In this example, the number of IDT electrodes connected to the first node n1 is 1. In other words, the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 is derived by (Equation 4) shown below.

[0075] Electrode finger pitch = (distance between the centers in the first direction of the two electrode fingers located at the outermost ends of the IDT electrode connected to the first node) / (total number of electrode fingers of the IDT electrode connected to the first node - number of IDT electrodes connected to the first node) ... (Equation 4)

[0076] [Effects, etc.] The effects of the elastic wave filter 1 of Embodiment 1 will be explained with reference to Figures 7 and 8. First, the power consumption of the additional circuit 20 will be explained.

[0077] Figure 7 shows the power consumption of the additional circuit 20 of the elastic wave filter in Embodiment 1 and the comparative example.

[0078] Figure 7 shows the ratio of the power consumption of the additional circuit 20 to the power consumption of a predetermined series arm resonator. The predetermined series arm resonator is the series arm resonator with the highest power consumption among the multiple series arm resonators S1 to S4. The predetermined series arm resonator may be the series arm resonator S2 connected to the first node n1 on the output terminal T2 side, or it may be other series arm resonators S1, S3, and S4 different from the series arm resonator S2.

[0079] Power consumption is the power consumption at the maximum frequency of the passband of the elastic wave filter. Furthermore, power consumption is the power consumption per unit area of ​​each elastic wave resonator, and is calculated based on the electrical elements such as the elastic wave resonators, the electrode parameters of the wiring connected to the electrical elements, and the power input to the elastic wave filter. Electrode parameters include data such as the conductor material, length, width, and height. The area is calculated, for example, by the distance between the centers of the two electrode fingers located at the outermost end of the IDT electrode in the first direction d1 multiplied by the crossing width.

[0080] As shown in Figure 7, in Embodiment 1, the power consumption ratio of the additional circuit 20 is 1 / 4 compared to the comparative example. Thus, in Embodiment 1, the power consumption of the additional circuit 20 can be reduced compared to the comparative example.

[0081] Next, we will explain the attenuation of the elastic wave filter outside the passband.

[0082] Figure 8 shows the attenuation outside the passband of the elastic wave filters in Embodiment 1 and the comparative example.

[0083] Figure 8 shows the isolation characteristics of the elastic wave filter 1, which is a transmitting filter, in the opposite band. In this example, the transmitting bandwidth of the elastic wave filter 1 is 1710MHz-1785MHz, and the opposite band in which attenuation is required for the elastic wave filter 1 is 1805MHz-1880MHz. As shown in Figure 8, the elastic wave filter 1 is able to secure sufficient attenuation in the opposite band. Thus, in Embodiment 1, it is possible to secure attenuation in the attenuation band which is outside the passband, and to reduce the power consumption of the additional circuit 20.

[0084] [Modification 1 of Embodiment 1] The elastic wave filter 1 of the first modified embodiment will be described with reference to Figures 9 to 11. In the first modified embodiment, an example will be described in which the offset gap of the IDT electrode is larger in the additional circuit 20 than in the filter circuit 10.

[0085] Figure 9 shows a portion of the IDT electrode 11 of the filter circuit 10 in modified example 1 of Embodiment 1. Figure 10 shows a portion of the IDT electrodes 31 and 32 of the additional circuit 20 in modified example 1 of Embodiment 1. Figure 11 shows the electrode parameters of the IDT electrodes 11, 31 and 32 in modified example 1 of Embodiment 1.

[0086] Figure 9 shows the offset gap g1 of the IDT electrode 11 of the filter circuit 10. The offset gap g1 of the IDT electrode 11 is the distance between the tip of the electrode finger 11b and the busbar electrode 11c opposite the tip of the electrode finger 11b. The tip of the electrode finger 11b is the end opposite to the end of the electrode finger 11b that is connected to the busbar electrode 11c. Note that the offset gap g1 is also the distance between the tip of the electrode finger 11a and the busbar electrode 11c opposite the tip of the electrode finger 11a (not shown).

[0087] Figure 10 shows the offset gap g2 of the IDT electrode 31 of the additional circuit 20. The offset gap g2 of the IDT electrode 31 is the distance between the tip of the electrode finger 36b and the busbar electrode 36c opposite the tip of the electrode finger 36b. The tip of the electrode finger 36b is the end opposite to the end of the electrode finger 36b that is connected to the busbar electrode 36c. Note that the offset gap g2 is also the distance between the tip of the electrode finger 36a and the busbar electrode 36c opposite the tip of the electrode finger 36a (not shown).

[0088] In modified example 1, the offset gap g2 of the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 is larger than the offset gap g1 of the IDT electrode 11 of the series arm resonator S2.

[0089] With this configuration, the electric field strength between the tip of the electrode finger and the busbar electrode is lower for IDT electrodes 31 and 32 than for IDT electrode 11. This prevents the electrode fingers 36a and 36b of IDT electrodes 31 and 32 from melting.

[0090] [Modification 2 of Embodiment 1] The elastic wave filter 1 of the modified example 2 of Embodiment 1 will be described with reference to Figure 12. In modified example 2, an example in which the series arm resonator S2 is a longitudinally coupled elastic wave resonator will be described.

[0091] Figure 12 is a circuit diagram showing the filter circuit 10 and the additional circuit 20 of the elastic wave filter 1 according to a modified example 2 of Embodiment 1.

[0092] As shown in Figure 12, the elastic wave filter 1 comprises a filter circuit 10 and an additional circuit 20. The elastic wave filter 1 also comprises an input terminal T1 and an output terminal T2. The configuration of the additional circuit 20, input terminal T1, and output terminal T2 is the same as in Embodiment 1.

[0093] The filter circuit 10 includes series arm resonators S1, S2, S3, and S4, which are elastic wave resonators, and parallel arm resonators P1, P2, P3, and P4. The configuration of the series arm resonators S1, S3, and S4, and the parallel arm resonators P1, P2, P3, and P4 is the same as in Embodiment 1.

[0094] In the modified example 2, the series arm resonator S2, which is connected to the first node n1 and located closer to the output terminal T2 than the first node n1, is composed of a longitudinally coupled elastic wave resonator.

[0095] Among the multiple series arm resonators, the IDT electrode of the series arm resonator S2, which is connected to the first node n1 and located closer to the output terminal T2 than the first node n1, is composed of multiple IDT electrodes.

[0096] Figure 12 shows, as an example, three IDT electrodes, IDT1, IDT2, and IDT3. IDT1, IDT2, and IDT3 are arranged in this order along the first direction. IDT1 and IDT3, which are positioned odd-numbered in the first direction, are connected to the series arm resonator S3, which is located closer to the output terminal T2 than the series arm resonator S2. IDT2, which is positioned even-numbered in the first direction, is connected to the first node n1, which is located closer to the input terminal T1 than the series arm resonator S2.

[0097] In this modified example, the electrode finger pitch pf of the IDT electrode (IDT2) connected to the first node n1 among the multiple IDT electrodes (IDT1, IDT2, and IDT3) that constitute the predetermined series arm resonator S2 is smaller than the electrode finger pitch pf of the other series arm resonators S1, S3, and S4, excluding the predetermined series arm resonator S2.

[0098] As described above, by making the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrodes of the other series arm resonators S1, S3, and S4 excluding the series arm resonator S2, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0099] Alternatively, as described above, by making the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrode of the series arm resonator S1 which is connected to the first node n1 and located closer to the input terminal T1 than the first node n1, the current flowing from upstream to the series arm resonator S2 can be increased and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0100] The electrode finger pitch pf of IDT2 connected to the first node n1 is derived as follows. The electrode finger pitch pf is calculated, for example, by dividing the distance between the centers of the two electrode fingers located at the outermost end of IDT2 in the first direction by "total number of electrode fingers of IDT electrodes connected to the first node - number of IDT electrodes connected to the first node". In this example, the number of IDT electrodes connected to the first node n1 is 1. In other words, the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 is derived by (Equation 5) shown below.

[0101] Electrode finger pitch = (distance between the centers in the first direction of the two electrode fingers located at the outermost ends of the IDT electrode connected to the first node) / (total number of electrode fingers of the IDT electrode connected to the first node - number of IDT electrodes connected to the first node) ... (Equation 5)

[0102] [Modification 3 of Embodiment 1] The elastic wave filter 1 of Modification 3 of Embodiment 1 will be described with reference to Figure 13. In Modification 3, an example in which the series arm resonator S2 is a longitudinally coupled elastic wave resonator will be described.

[0103] Figure 13 is a circuit diagram showing the filter circuit 10 and the additional circuit 20 of the elastic wave filter 1 according to a modified example 3 of Embodiment 1.

[0104] As shown in Figure 13, the elastic wave filter 1 comprises a filter circuit 10 and an additional circuit 20. The elastic wave filter 1 also comprises an input terminal T1 and an output terminal T2. The configuration of the additional circuit 20, input terminal T1, and output terminal T2 is the same as in Embodiment 1.

[0105] The filter circuit 10 includes series arm resonators S1, S2, S3, and S4, which are elastic wave resonators, and parallel arm resonators P1, P2, P3, and P4. The configuration of the series arm resonators S1, S3, and S4, and the parallel arm resonators P1, P2, P3, and P4 is the same as in Embodiment 1.

[0106] In modified example 3, the series arm resonator S2 connected to the first node n1 and located closer to the output terminal T2 than the first node n1 is composed of a longitudinally coupled elastic wave resonator.

[0107] Among the multiple series arm resonators, the IDT electrode of the series arm resonator S2, which is connected to the first node n1 and located closer to the output terminal T2 than the first node n1, is composed of multiple IDT electrodes.

[0108] Figure 13 shows, as an example, three IDT4, IDT5, and IDT6, which are multiple IDT electrodes. IDT4, IDT5, and IDT6 are arranged in this order along the first direction. IDT5, which is positioned in an even position in the first direction, is connected to the series arm resonator S3, which is located on the output terminal T2 side of the series arm resonator S2. IDT4 and IDT6, which are positioned in an odd position in the first direction, are connected to the first node n1, which is located on the input terminal T1 side of the series arm resonator S2.

[0109] In this modified example, the electrode finger pitch pf of the IDT electrodes (IDT4 and IDT6) connected to the first node n1 among the multiple IDT electrodes (IDT4, IDT5 and IDT6) that constitute the predetermined series arm resonator S2 is smaller than the electrode finger pitch pf of the other series arm resonators S1, S3 and S4, excluding the predetermined series arm resonator S2.

[0110] As described above, by making the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrodes of the other series arm resonators S1, S3, and S4 excluding the series arm resonator S2, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0111] Alternatively, as described above, by making the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrode of the series arm resonator S1 which is connected to the first node n1 and located closer to the input terminal T1 than the first node n1, the current flowing from upstream to the series arm resonator S2 can be increased and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, since the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0112] The electrode finger pitch pf of IDT4 and IDT6 connected to the first node n1 is derived as follows. The electrode finger pitch pf is calculated by adding the distance between the centers in the first direction of the two electrode fingers located at the outermost end of IDT4 and the distance between the centers in the first direction of the two electrode fingers located at the outermost end of IDT6, and dividing this value by "total number of electrode fingers of IDT electrodes connected to the first node - number of IDT electrodes connected to the first node". In this example, the number of IDT electrodes connected to the first node n1 is 2. In other words, the electrode finger pitch pf of the IDT electrode connected to the first node n1 among the multiple IDT electrodes constituting the series arm resonator S2 is derived by (Equation 6) shown below.

[0113] Electrode finger pitch = (Calculate the distance between the centers of the two electrode fingers located at the outermost end of each IDT electrode connected to the first node, and sum the calculated distances between the centers) / (Total number of electrode fingers of the IDT electrodes connected to the first node - Number of IDT electrodes connected to the first node) ... (Equation 6)

[0114] (Embodiment 2) The multiplexer according to Embodiment 2 will be described with reference to Figure 14.

[0115] Figure 14 is a circuit diagram of the multiplexer 5 according to Embodiment 2.

[0116] The multiplexer 5 is a demultiplexer or multiplexer equipped with multiple filters. The multiplexer 5 includes an elastic wave filter 1 having a filter circuit 10 and an additional circuit 20, and other filters 50 different from the elastic wave filter 1. The multiplexer 5 also includes a first terminal T10 connected to the elastic wave filter 1, a second terminal T20 connected to both the elastic wave filter 1 and the other filters 50, and a third terminal T30 connected to the other filters 50. The aforementioned input terminal T1 corresponds to the first terminal T10. The output terminal T2 is provided between the filter circuit 10 of the elastic wave filter 1 and node n10, which is the connection point between the elastic wave filter 1 and the other filters 50.

[0117] The basic configuration of the elastic wave filter 1, the other filters 50, the first terminal T10, and the second terminal T20 is the same as in Embodiment 1.

[0118] For example, multiplexer 5 receives high-frequency signals in Band 3 (transmit bandwidth: 1710MHz-1785MHz, receive bandwidth: 1805MHz-1880MHz) as input and output. The transmit bandwidth of elastic wave filter 1 is set to a lower frequency than the receive bandwidth of the other filters 50.

[0119] As described above, a multiplexer 5 including the elastic wave filter 1 can provide a multiplexer in which the power consumption of the additional circuit 20 of the elastic wave filter 1 is suppressed.

[0120] (summary) An example of an elastic wave filter, etc., according to one aspect of this embodiment is provided below.

[0121] The elastic wave filter 1 of Example 1 comprises an input terminal T1 and an output terminal T2, a filter circuit 10 provided in a first path r1 connecting the input terminal T1 and the output terminal T2, and an additional circuit 20 provided in a second path r2 connected in parallel with at least a portion of the first path r1. The additional circuit 20 has a longitudinally coupled elastic wave resonator 25. The filter circuit 10 has a plurality of series arm resonators S1 to S4 provided in the first path r1, and one or more parallel arm resonators P1 to P4 provided in a path connecting the first path r1 and ground. Each of the series arm resonators S1 to S4 and the one or more parallel arm resonators P1 to P4 has an IDT electrode 11. On the outer sides of one or more series arm resonators (e.g., S2 to S4) arranged on the first path r1, there are first nodes n1 and second nodes n2, which are connection points between the first path r1 and the second path r2, with the first node n1 located closer to the input terminal T1 than the second node n2. Of the multiple series arm resonators S1 to S4, a predetermined series arm resonator (e.g., S2) connected to the first node n1 and located closer to the output terminal T2 than the first node n1 is composed of one or more IDT electrodes. The electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 is smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators (e.g., S1, S3, S4), excluding the predetermined series arm resonator S2.

[0122] In this way, by making the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 of the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators S1, S3, and S4, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, because the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0123] The elastic wave filter 1 in Example 2 is the elastic wave filter described in Example 1, wherein the first node n1 may be located between two adjacent series arm resonators (e.g., S1 and S2) on the first path r1.

[0124] According to this, current flows more easily from the first node n1 to the series arm resonator S2 located on the output terminal T2 side, and it is possible to suppress the current flowing from the first node n1 to the additional circuit 20 from becoming excessively large. As a result, the power consumption of the additional circuit 20 can be reduced.

[0125] The elastic wave filter 1 of Example 3 comprises an input terminal T1 and an output terminal T2, a filter circuit 10 provided in a first path r1 connecting the input terminal T1 and the output terminal T2, and an additional circuit 20 provided in a second path r2 connected in parallel with at least a portion of the first path r1. The additional circuit 20 has a longitudinally coupled elastic wave resonator 25. The filter circuit 10 has a plurality of series arm resonators S1 to S4 provided in the first path r1, and one or more parallel arm resonators P1 to P4 provided in a path connecting the first path r1 and ground. Each of the series arm resonators S1 to S4 and the one or more parallel arm resonators P1 to P4 has an IDT electrode 11. On the outer sides of one or more series arm resonators (e.g., S2 to S4) arranged on the first path r1, there are first nodes n1 and second nodes n2, which are connection points between the first path r1 and the second path r2. The first node n1 is located closer to the input terminal T1 than the second node n2, and is situated between two adjacent series arm resonators (e.g., S1 and S2) on the first path r1. Of the two series arm resonators S1 and S2, a predetermined series arm resonator S2 located closer to the output terminal T2 than the first node n1 is composed of one or more IDT electrodes 11. The electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 is smaller than the electrode finger pitch pf of the IDT electrode 11 of the series arm resonator S1 connected to the first node n1 and located closer to the input terminal T1 than the first node n1.

[0126] In this way, by making the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 of the series arm resonator S2 smaller than the electrode finger pitch pf of the IDT electrode 11 of the series arm resonator S1 located closer to the input terminal T1 than the first node n1, the current flowing from upstream to the series arm resonator S2 can be increased, and the current flowing to the additional circuit 20 can be decreased. This reduces the power consumption of the additional circuit 20. Furthermore, because the power consumption of the additional circuit 20 can be reduced, the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20 can be suppressed.

[0127] The elastic wave filter 1 in Example 4 is the elastic wave filter described in Example 3, wherein the electrode finger pitch pf of the IDT electrode 11 connected to the first node n1 among the one or more IDT electrodes 11 described above may be smaller than the electrode finger pitch pf of the IDT electrodes 11 of the other series arm resonators S1, S3, S4, excluding the predetermined series arm resonator S2.

[0128] According to this, current flows more easily from the first node n1 to the series arm resonator S2 located on the output terminal T2 side, and it is possible to suppress the current flowing from the first node n1 to the additional circuit 20 from becoming excessively large. As a result, the power consumption of the additional circuit 20 can be reduced.

[0129] The elastic wave filter 1 in Example 5 is an elastic wave filter described in any of Examples 1 to 4, wherein the additional circuit 20 further includes a capacitive element 28, which may be provided in the second path r2 between the longitudinally coupled elastic wave resonator 25 and the second node n2.

[0130] According to this, for example, it is possible to suppress the instantaneous flow of a large current from the output terminal T2 side to the longitudinally coupled elastic wave resonator 25. This makes it possible to suppress the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20.

[0131] The elastic wave filter 1 in Example 6 is an elastic wave filter described in any of Examples 1 to 5, wherein the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 may have a smaller crossover width than the IDT electrode 11 of the series arm resonator S2, which is connected to the first node n1 and located on the output terminal T2 side of the first node n1.

[0132] According to this, the impedance of the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 can be reduced. This makes it possible to suppress the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32 included in the additional circuit 20.

[0133] The elastic wave filter 1 of Example 7 is an elastic wave filter described in any of Examples 1 to 6, wherein the IDT electrodes 11, 31, and 32 have a pair of comb-shaped electrodes, and each of the pair of comb-shaped electrodes has a plurality of electrode fingers and a busbar electrode connecting one end of the plurality of electrode fingers. An offset gap is provided between the tip of the electrode finger and the busbar electrode opposite the tip of the electrode finger. The offset gap g2 of the IDT electrodes 31 and 32 of the longitudinally coupled elastic wave resonator 25 may be larger than the offset gap g1 of the IDT electrode 11 of the series arm resonator S2 which is connected to the first node n1 and located on the output terminal T2 side of the first node n1.

[0134] This configuration allows for a reduction in the electric field strength between the tip of the electrode finger 36a (or 36b) of the IDT electrodes 31 and 32 and the busbar electrode 36c. This suppresses the melting of the electrode fingers 36a and 36b of the IDT electrodes 31 and 32.

[0135] The multiplexer 5 of Example 8 comprises the elastic wave filter 1 described in any of Examples 1 to 7 and another filter 50 having a circuit different from that of the filter circuit 10.

[0136] This makes it possible to provide a multiplexer 5 in which the attenuation amount in the passband of the other filter 50 is ensured, and the power consumption of the elastic wave filter 1 is suppressed.

[0137] (Other embodiments) Although embodiments of the elastic wave filter and the like according to the present invention have been described above, the present invention also includes other embodiments realized by combining any of the components in the above embodiments, modified examples obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive of without departing from the spirit of the present invention, and high-frequency front-end circuits and communication devices including the elastic wave filter or multiplexer according to the present invention.

[0138] The above example shows a longitudinally coupled elastic wave resonator 25 equipped with two IDT electrodes, but it is not limited to this, and the number of IDT electrodes may be three or more.

[0139] Furthermore, although the above description used a multiplexer containing two filters as an example, the present invention can also be applied to, for example, a triplexer in which the antenna terminals of three filters are shared, or a hexaplexer in which the antenna terminals of six filters are shared. In other words, a multiplexer only needs to have two or more filters.

[0140] Furthermore, the other filters 50 are not limited to the configuration of the filters described above, and can be appropriately designed according to the required filter characteristics, etc. Specifically, the other filters 50 may be a vertically coupled filter structure or a ladder-type filter structure. Also, each resonator constituting the other filters 50 is not limited to SAW resonators, but may be, for example, a BAW (Bulk Acoustic Wave) resonator. Moreover, the other filters 50 may be constructed without using resonators, and may be, for example, an LC resonant filter or a dielectric filter.

[0141] In the above example, the piezoelectric substrate 100 is shown to include a high-sonic-velocity support substrate, a low-sonic-velocity film, and a piezoelectric layer. However, the configurations of the high-sonic-velocity support substrate, the low-sonic-velocity film, and the piezoelectric layer may be as shown below.

[0142] The piezoelectric layer consists of, for example, a θ° Y-cut X-propagating LiTaO3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut by a plane whose normal is an axis rotated θ° from the Y axis in the Z axis direction with the X axis as the central axis, and in which surface acoustic waves propagate in the X axis direction).

[0143] The high-speed sound-relief substrate is a substrate that supports the low-speed sound-relief film, the piezoelectric layer, and the electrode 110. Furthermore, the high-speed sound-relief substrate is a substrate in which the sound velocity of bulk waves within the high-speed sound-relief substrate is faster than the elastic waves of surface waves and boundary waves propagating through the piezoelectric layer, and functions to confine the surface acoustic waves to the portion where the piezoelectric layer and the low-speed sound-relief film are laminated, preventing them from leaking below the high-speed sound-relief substrate.

[0144] A high-speed support substrate is, for example, a silicon substrate. The material for the high-speed support substrate can be, for example, a piezoelectric material such as aluminum nitride, lithium tantalate, lithium niobate, or quartz; a ceramic material such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, or sialon; a dielectric material such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), or diamond; or a semiconductor material such as silicon; or a material mainly composed of the above materials. The spinel mentioned above includes aluminum compounds containing one or more elements selected from Mg, Fe, Zn, Mn, etc., and oxygen. Examples of the spinel mentioned above include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0145] A low-sound-velocity film is a film in which the velocity of bulk waves within the film is lower than the velocity of sound of elastic waves propagating through the piezoelectric layer, and it is placed between the piezoelectric layer and the high-sound-velocity support substrate. Due to this structure and the property that elastic waves concentrate energy in a medium with an inherently low sound velocity, leakage of surface acoustic wave energy outside the IDT electrode is suppressed.

[0146] A low-sonic-velocity film is, for example, a film mainly composed of silicon dioxide (SiO2). The material of the low-sonic-velocity film is not limited to the above, and for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or compounds of silicon oxide to which fluorine, carbon, or boron have been added, or materials mainly composed of the above materials can also be used.

[0147] The laminated structure of the piezoelectric substrate 100 allows for a significant increase in the Q factor of the elastic wave resonator at the resonant and anti-resonant frequencies compared to a structure using a single layer of piezoelectric substrate 100. In other words, it is possible to construct a surface acoustic wave resonator with a high Q factor, and using this surface acoustic wave resonator, it becomes possible to construct a filter with low insertion loss.

[0148] Furthermore, the high-sound-velocity support substrate may have a structure in which a support substrate and a high-sound-velocity film are laminated together, the bulk waves propagating through the piezoelectric layer having a higher sound velocity than the elastic waves of the surface waves and boundary waves propagating through the piezoelectric layer.

[0149] In this layered structure, the support substrate material can be a piezoelectric material such as sapphire, lithium tantalate, lithium niobate, or quartz; various ceramics such as alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric material such as glass; or a semiconductor material such as silicon or gallium nitride; or a resin substrate.

[0150] Furthermore, as materials for high-speed films, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; or materials mainly composed of the above materials can be used. Note that the spinel mentioned above includes aluminum compounds containing one or more elements selected from Mg, Fe, Zn, Mn, etc., and oxygen. Examples of the spinel mentioned above include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0151] The materials of each layer exemplified in the above-described laminated structure of the piezoelectric substrate 100 are merely examples and may be changed, for example, depending on the characteristics that are important among the required high-frequency propagation characteristics.

[0152] Furthermore, although the piezoelectric substrate 100 described above is a piezoelectric substrate, the piezoelectric substrate may also be a piezoelectric substrate consisting of a single layer of piezoelectric material. In this case, the piezoelectric substrate may be composed of, for example, a piezoelectric single crystal of LiTaO3 or another piezoelectric single crystal such as LiNbO3. In addition, the piezoelectric substrate 100 on which the IDT electrode is formed may be composed entirely of piezoelectric material, or a structure in which piezoelectric material layers are laminated on a support substrate may be used, as long as it is piezoelectric. Moreover, the cut angle of the piezoelectric substrate 100 according to the above embodiment is not limited. In other words, the laminated structure, material, and thickness may be changed as appropriate depending on the required transmission characteristics of the acoustic wave filter, and similar effects can be achieved even with an acoustic surface wave filter using a LiTaO3 piezoelectric substrate or a LiNbO3 piezoelectric substrate having a cut angle other than the cut angle shown in the above embodiment. [Industrial applicability]

[0153] The present invention can be widely used in communication devices such as mobile phones as a multiplexer, front-end circuit, and communication device having an elastic wave filter. [Explanation of Symbols]

[0154] 1. Elastic wave filter 5 Multiplexer 10 Filter Circuits 11 IDT electrode 11A, 11B comb-shaped electrode 11a, 11b electrode fingers 11c busbar electrode 12 reflector 12a Reflector electrode finger 12c busbar electrode 15 Elastic wave resonator 20 Additional Circuits 25. Longitudinal coupled elastic wave resonator 28 Capacitive elements 31, 32 IDT electrode 31A, 31B, 32A, 32B comb electrode 36a, 36b electrode fingers 36c busbar electrode 37 Reflector 50 Other filters 100 Piezoelectric substrate 100a main surface 110 electrodes 111 Contact layer 112 Main electrode layer 113 Protective film d1 1st direction d2 2nd direction g1, g2 offset gap n1 First node n2 Second node n10 node P1, P2, P3, P4 parallel arm resonators pf, pc electrode finger pitch r1 First route r2 Second route S1, S2, S3, S4 series arm resonators T1 Input Terminal T2 Output Terminal T10 First terminal T20 2nd terminal T30 Third Terminal

Claims

1. Input terminals and output terminals, A filter circuit is provided in the first path connecting the input terminal and the output terminal, An additional circuit provided in a second path connected in parallel with at least a portion of the first path, Equipped with, The aforementioned additional circuit has a longitudinally coupled elastic wave resonator, The filter circuit has a plurality of series arm resonators provided in the first path, and one or more parallel arm resonators provided in the path connecting the first path and ground. Each of the plurality of series-arm resonators and the one or more parallel-arm resonators has an IDT electrode. On both outer sides of one or more series-arm resonators arranged in the first path, a first node and a second node, which are connection points between the first path and the second path, are provided. The first node is located closer to the input terminal than the second node. Of the plurality of series arm resonators, a predetermined series arm resonator connected to the first node and located closer to the output terminal than the first node is composed of one or more IDT electrodes. The electrode finger pitch of the IDT electrode connected to the first node among the one or more IDT electrodes is smaller than the electrode finger pitch of the IDT electrodes of the other series arm resonators, excluding the predetermined series arm resonator. Elastic wave filter.

2. The first node is located between two adjacent series-arm resonators on the first path. The elastic wave filter according to claim 1.

3. Input terminals and output terminals, A filter circuit is provided in the first path connecting the input terminal and the output terminal, An additional circuit provided in a second path connected in parallel with at least a portion of the first path, Equipped with, The aforementioned additional circuit has a longitudinally coupled elastic wave resonator, The filter circuit has a plurality of series arm resonators provided in the first path, and one or more parallel arm resonators provided in the path connecting the first path and ground. Each of the plurality of series-arm resonators and the one or more parallel-arm resonators has an IDT electrode. On both outer sides of one or more series-arm resonators arranged in the first path, a first node and a second node, which are connection points between the first path and the second path, are provided. The first node is located closer to the input terminal than the second node, and is situated between two adjacent series-arm resonators on the first path. Of the two series arm resonators, a predetermined series arm resonator located closer to the output terminal than the first node is composed of one or more IDT electrodes. The electrode finger pitch of the IDT electrode connected to the first node among the one or more IDT electrodes is smaller than the electrode finger pitch of the IDT electrode of the series arm resonator connected to the first node and located closer to the input terminal than the first node. Elastic wave filter.

4. The electrode finger pitch of the IDT electrode connected to the first node among the one or more IDT electrodes is smaller than the electrode finger pitch of the IDT electrodes of the other series arm resonators, excluding the predetermined series arm resonator. The elastic wave filter according to claim 3.

5. The aforementioned additional circuit further includes a capacitive element, The capacitive element is provided in the second path between the longitudinally coupled elastic wave resonator and the second node. The elastic wave filter according to any one of claims 1 to 4.

6. The IDT electrode of the longitudinally coupled elastic wave resonator has a smaller crossover width than the IDT electrode of the series arm resonator, which is connected to the first node and located closer to the output terminal than the first node. The elastic wave filter according to any one of claims 1 to 5.

7. The IDT electrode has a pair of comb-shaped electrodes, Each of the pair of comb-shaped electrodes has a plurality of electrode fingers and a busbar electrode connecting one end of the plurality of electrode fingers, An offset gap is provided between the tip of the electrode finger and the busbar electrode facing the tip of the electrode finger. The offset gap of the IDT electrode of the longitudinally coupled elastic wave resonator is greater than the offset gap of the IDT electrode of the series arm resonator connected to the first node and located closer to the output terminal than the first node. The elastic wave filter according to any one of claims 1 to 6.

8. An elastic wave filter according to any one of claims 1 to 7, Another filter having a circuit different from the aforementioned filter circuit, A multiplexer equipped with the following features.

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