multiplexer

Abstract

A multiplexer (1) is provided with a first filter (10) and a second filter (50) having a passband on a lower frequency side than the passband of the first filter (10). The longitudinal coupling elastic wave resonator (13) of the first filter (10) has an IDT electrode group (30) including a plurality of IDT electrodes (31 to 37). The IDT electrode group (30) has an asymmetric shape with reference to a center line (CL) passing through the center (Cl) of the IDT electrode group (30) and orthogonal to the elastic wave propagation direction (D1). From the longitudinal coupling elastic wave resonator (13), the IDT electrodes (32, 34, 36) connected to the first path (rl) on the side of the common terminal (Tc) have a total average of electrode finger spacings (pt) smaller and a total of electrode finger numbers (pn) fewer than the IDT electrodes (31, 33, 35, 37) connected to the first path (rl) on the side of the first terminal (Tl).

Description

TECHNICAL FIELD

[0001] The present application relates to a multiplexer provided with a filter having a longitudinally-coupled elastic wave resonator. BACKGROUND

[0002] Conventionally, a multiplexer provided with a plurality of filters is known. As one example of such a multiplexer, a multiplexer provided with a filter having a longitudinally-coupled elastic wave resonator is disclosed in Patent Literature 1. In this multiplexer, by providing the longitudinally-coupled elastic wave resonator in an asymmetric configuration to thereby generate a first-order resonance mode, steepness on a low frequency side of a passband is improved using the first-order resonance mode.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: International Publication No. 2010 / 035372 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] For example, in a case where one of the plurality of filters has the above-described longitudinally-coupled elastic wave resonator and another filter has a passband lower in frequency than that of the one filter, due to the first-order resonance mode generated in the longitudinally-coupled elastic wave resonator, sometimes the insertion loss of the passband of the another filter can decrease.

[0008] The present application has been achieved in order to solve the above-described problem, and aims to suppress a decrease in insertion loss of a passband of another filter in a multiplexer provided with one filter and another filter.

[0009] TECHNICAL SOLUTION FOR SOLVING THE PROBLEM

[0010] To achieve the above object, one embodiment of the present application relates to a multiplexer including a common terminal, a first terminal, and a second terminal, a first filter provided on a first path connecting the common terminal and the first terminal and having a passband of a first frequency band, and a second filter provided on a second path connecting the common terminal and the second terminal and having a passband of a frequency band lower than the first frequency band, the first filter having a longitudinal-coupled elastic wave resonator having an IDT electrode group including a plurality of IDT electrodes arranged along an elastic wave propagation direction, the IDT electrode group having an asymmetric shape with reference to a center line passing through the center of the IDT electrode group and orthogonal to the elastic wave propagation direction, and the total average of the electrode finger pitches of the IDT electrodes connected to the first path on the common terminal side being smaller than the total average of the electrode finger pitches of the IDT electrodes connected to the first path on the first terminal side, and the total sum of the electrode finger pairs of the IDT electrodes connected to the first path on the common terminal side being smaller than the total sum of the electrode finger pairs of the IDT electrodes connected to the first path on the first terminal side.

[0011] Effects of Invention

[0012] According to the present application, it is possible to suppress a decrease in the insertion loss of the passband of the other filter in a multiplexer having one filter and the other filter. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a circuit configuration view of a multiplexer according to an embodiment.

[0014] Figure 2 is a schematic view of a longitudinal-coupled elastic wave resonator of a first filter included in a multiplexer according to an embodiment.

[0015] Figure 3 is a schematic view of a configuration of IDT electrodes of the longitudinal-coupled elastic wave resonator shown in Figure 2

[0016] Figure 4 is a view showing the electrode finger pitches and the electrode finger pairs of the IDT electrodes of the longitudinal-coupled elastic wave resonator of an example according to an embodiment.

[0017] Figure 5 is a circuit configuration view of a multiplexer according to a comparative example.

[0018] Figure 6 is a schematic view of a longitudinal-coupled elastic wave resonator of a first filter included in a multiplexer according to a comparative example.

[0019] Figure 7 ​FIG. 1 is a diagram showing an electrode finger pitch and an electrode finger pair number of an IDT electrode of a longitudinal coupling elastic wave resonator of a comparative example.

[0020] Figure 8 FIG. 2 is a graph showing a pass characteristic of a first filter in the embodiment and the comparative example.

[0021] Figure 9 FIG. 3 is a graph showing a pass characteristic of a second filter in the embodiment and the comparative example.

[0022] Figure 10 FIG. 4 is a graph showing a resonance mode of a single body of a longitudinal coupling elastic wave resonator in the embodiment and the comparative example.

[0023] Figure 11 FIG. 5 is a graph showing an impedance characteristic of the single body of the longitudinal coupling elastic wave resonator observed from the common terminal side in a frequency band including a pass band of the second filter.

[0024] Figure 12 FIG. 6 is a graph showing an impedance characteristic of the single body of the longitudinal coupling elastic wave resonator observed from the common terminal side in a pass band of the first filter. DETAILED DESCRIPTION

[0025] Hereinafter, the embodiment of the present application will be described in detail using the embodiment and the accompanying drawings. In addition, the embodiment described below shows a general or specific example. The numerical value, shape, material, constituent element, arrangement of constituent elements, and connection method, and the like shown in the embodiment below are one example, and the gist is not limited to the present application. For the constituent elements not recited in the independent claim among the constituent elements in the embodiment below, the constituent elements are described as arbitrary constituent elements. Furthermore, the size or size ratio of the constituent elements shown in the drawings is not necessarily strict. Furthermore, in each drawing, the same reference numerals are attached to substantially the same structures, and sometimes the repeated description is omitted or simplified. Furthermore, in the embodiment below, the so-called "connection" includes not only the case of direct connection but also the case of electrically connecting via other elements and the like.

[0026] (Embodiment)

[0027] [1. Structure of multiplexer]

[0028] Reference Signs Figure 1 The basic structure of the multiplexer to which the embodiment relates will be described.

[0029] Figure 1 FIG. 1 is a circuit structure diagram of a multiplexer 1 to which the embodiment relates. In addition, an antenna element 9 is also shown in FIG. 1. Figure 1

[0030] ​The multiplexer 1 is a splitter or a combiner having a plurality of filters. The multiplexer 1 has a first filter 10 as one filter and a second filter 50 as another filter. The first filter 10 is a filter having a first frequency band as a passband. The second filter 50 is a filter having a frequency band on a lower frequency side than the first frequency band as a passband.

[0031] The multiplexer 1 has a common terminal Tc, a first terminal T1, and a second terminal T2 in addition to the first filter 10 and the second filter 50.

[0032] The common terminal Tc is a common terminal connected to the first filter 10 and the second filter 50. Specifically, the common terminal Tc is connected to one end of the first filter 10 via a node n0 between the common terminal Tc and the first filter 10, and is further connected to one end of the second filter 50 via the node n0. Further, the common terminal Tc is connected to the antenna element 9 outside the multiplexer 1. The common terminal Tc is also an antenna terminal of the multiplexer 1. An inductor L1 for matching is connected between the node n0 and a ground.

[0033] The first terminal T1 is connected to the other end of the first filter 10. Further, the first terminal T1 is an input and output terminal connected to an RF signal processing circuit (not shown) via an amplifying circuit or the like (not shown) outside the multiplexer 1.

[0034] The second terminal T2 is connected to the other end of the second filter 50. Further, the second terminal T2 is an input and output terminal connected to the RF signal processing circuit (not shown) via the amplifying circuit or the like (not shown) outside the multiplexer 1.

[0035] The first filter 10 is arranged on a first path r1 connecting the common terminal Tc and the first terminal T1. The first filter 10 is, for example, a reception filter having a downlink frequency band (reception band) as a passband, and is set to have a higher passband than the second filter 50.

[0036] The second filter 50 is arranged on a second path r2 connecting the common terminal Tc and the second terminal T2. The second filter 50 is, for example, a transmission filter having an uplink frequency band (transmission band) as a passband. Each of the first filter 10 and the second filter 50 is required to have a characteristic of passing a signal of a frequency of its own frequency band and attenuating a signal of a frequency of an opposite frequency band outside the own frequency band.

[0037] The first filter 10 has a first circuit 11, a longitudinally-coupled elastic wave resonator 13, and a second circuit 12. The first circuit 11, the longitudinally-coupled elastic wave resonator 13, and the second circuit 12 are connected in series in this order from the common terminal Tc toward the first terminal T1.

[0038] The first circuit 11 is a band-pass filter including a series arm resonator S1 and a parallel arm resonator P1 as elastic wave resonators. The series arm resonator S1 is arranged on the first path r1 between the common terminal Tc and the longitudinal coupling elastic wave resonator 13, and is connected to one end of the longitudinal coupling elastic wave resonator 13. In the first path r1, the series arm resonator S1 is disposed closer to the common terminal Tc than the parallel arm resonator P1. The parallel arm resonator P1 is connected to a path that links a node n1 between the series arm resonator S1 and the longitudinal coupling elastic wave resonator 13 in the first path r1 and a reference terminal (ground). Specifically, one end of the parallel arm resonator P1 is connected to the node n1, and the other end is connected to the reference terminal. In addition, the parallel arm resonator P1 also functions as a matching element that matches the longitudinal coupling elastic wave resonator 13 and the series arm resonator S1.

[0039] The second circuit 12 is a band-pass filter including a series arm resonator S2 and a parallel arm resonator P2 as elastic wave resonators. The series arm resonator S2 is arranged on the first path r1 between the longitudinal coupling elastic wave resonator 13 and the first terminal T1, and is connected to the other end of the longitudinal coupling elastic wave resonator 13. In the first path r1, the series arm resonator S2 is disposed closer to the longitudinal coupling elastic wave resonator 13 than the parallel arm resonator P2. The parallel arm resonator P2 is connected to a path that links a node n2 between the series arm resonator S2 and the first terminal T1 in the first path r1 and a reference terminal (ground). Specifically, one end of the parallel arm resonator P2 is connected to the node n2, and the other end is connected to the reference terminal.

[0040] In addition, each of the first circuit 11 and the second circuit 12 is not limited to including one series arm resonator and one parallel arm resonator, and can include two or more series arm resonators and two or more parallel arm resonators. Furthermore, an inductor can be provided between the parallel arm resonator and the reference terminal.

[0041] Figure 2 FIG. 13 is a schematic view showing the longitudinal coupling elastic wave resonator 13 of the first filter 10 included in the multiplexer 1. In addition, in FIG. 13, electrodes and wiring lines are shown by solid lines. Figure 2

[0042] The longitudinal coupling elastic wave resonator 13 includes a plurality of surface acoustic wave (SAW) resonators. The surface acoustic wave resonator includes a substrate 320 and an IDT (Inter Digital Transducer) electrode provided on the substrate 320, which will be described later.

[0043] ​The longitudinal coupling elastic wave resonator 13 has an IDT electrode group 30 including a plurality of IDT electrodes arranged along an elastic wave propagation direction Dl. The IDT electrode group 30 of the present embodiment includes seven IDT electrodes 31, 32, 33, 34, 35, 36, 37 which are odd numbers. Further, the longitudinal coupling elastic wave resonator 13 has a plurality of reflectors 41, 42. The plurality of reflectors 41, 42 are arranged on both outer sides of the IDT electrode group 30 in the elastic wave propagation direction Dl so as to sandwich the IDT electrode group 30.

[0044] Each of the IDT electrodes 31 to 37 includes a pair of first comb-shaped electrodes ca and a second comb-shaped electrode cb which oppose each other. The first comb-shaped electrodes ca have a comb shape including a plurality of electrode fingers fa which are parallel to each other and bus bar electrodes which connect one ends of the plurality of electrode fingers fa to each other. The second comb-shaped electrodes cb have a comb shape including a plurality of electrode fingers fb which are parallel to each other and bus bar electrodes which connect one ends of the plurality of electrode fingers fb to each other. The bus bar electrodes each extend along the elastic wave propagation direction Dl. The electrode fingers fa and the electrode fingers fb extend in an orthogonal direction D2 to the elastic wave propagation direction Dl, are alternately and oppositely arranged in the orthogonal direction D2, and oppose each other in the elastic wave propagation direction Dl.

[0045] The plurality of IDT electrodes 31 to 37, that is, the IDT electrode group 30 has an asymmetric shape with reference to a center line CL which passes through a center Cl of the IDT electrode group 30 and is orthogonal to the elastic wave propagation direction Dl. The center Cl of the IDT electrode group 30 is a position which is in the middle of the cross width in the orthogonal direction D2 and is in the middle of the electrode fingers which are the most distal to each other among the electrode fingers fa, fb constituting the IDT electrode group 30 in the elastic wave propagation direction Dl. The asymmetric configuration can be achieved by making the electrode parameters of each of the IDT electrodes 31 to 37 different with reference to the center line CL.

[0046] For example, the asymmetric configuration can be achieved by making at least one of the average pitch, the number of electrode fingers, and the duty of the plurality of electrode fingers fa, fb constituting the IDT electrodes different.

[0047] In addition, the so-called pitch is the distance between the centers of adjacent electrode fingers fa, fb in the elastic wave propagation direction D1. Furthermore, the so-called average pitch is a value obtained by dividing the sum of all the pitches in the corresponding IDT electrode by (the number of electrode fingers - 1). In an IDT electrode having a plurality of (three or more) electrode fingers, the average pitch can be derived as follows. For example, in the IDT electrode 37, the average pitch can be derived by dividing the distance between the centers of the electrode finger at one end of the IDT electrode 37 and the electrode finger at the other end in the elastic wave propagation direction D1 by "the number of electrode fingers constituting the IDT electrode 37 - 1". In addition, if the gap between adjacent electrode fingers fa, fb constituting the IDT electrode is assumed to be, for example, "inter-electrode finger gap" (see Figure 3 ), "the number of electrode fingers constituting the IDT electrode 37 - 1" means "the number of inter-electrode finger gaps".

[0048] The number of electrode fingers and the number of electrode finger pairs have a relationship of "the number of electrode fingers = the number of electrode finger pairs x 2 + 1". For example, if the number of electrode finger pairs is 7 pairs, the number of electrode fingers is 15, and if the number of electrode finger pairs is 10 pairs, the number of electrode fingers is 21. In addition, in the case where the number of electrode fingers is an even number, the number of electrode finger pairs is expressed using a decimal point of 0.5, for example, if the number of electrode finger pairs is 6.5 pairs, the number of electrode fingers is 14, and if the number of electrode finger pairs is 9.5 pairs, the number of electrode fingers is 20.

[0049] The IDT electrode group 30 of the present embodiment has different average pitches and different numbers of electrode finger pairs in the elastic wave propagation direction D1 on both sides of the center line CL, that is, in the two regions divided with the center line CL as a reference. In addition, there is a case where the center line CL is not on the electrode fingers fa, fb.

[0050] For example, the IDT electrode group 30 has different average pitches and different numbers of electrode finger pairs in the IDT electrodes 31, 32, 33 on one side and the IDT electrodes 35, 36, 37 on the other side in the elastic wave propagation direction D1, with the IDT electrode 34 located in the center as a reference. Specifically, the IDT electrode 33 and the IDT electrode 35 have different average pitches and different numbers of electrode finger pairs, the IDT electrode 32 and the IDT electrode 36 have different average pitches and different numbers of electrode finger pairs, and the IDT electrode 31 and the IDT electrode 37 have different average pitches and different numbers of electrode finger pairs.

[0051] Further, the IDT electrodes 31, 33, 35, 37 are connected to the first path r1 on the side of the first terminal T1 as viewed from the longitudinal coupling elastic wave resonator 13. Specifically, after the first comb electrodes ca of the respective IDT electrodes 31, 33, 35, 37 are led out by the lead-out wiring and wired, the IDT electrodes are connected to the second circuit 12 on the first path r1. The second comb electrodes cb are led out by the lead-out wiring and connected to the ground (for example, a ground electrode).

[0052] On the other hand, the IDT electrodes 32, 34, 36 are connected to the first path r1 on the side of the common terminal Tc as viewed from the longitudinal coupling elastic wave resonator 13. Specifically, after the first comb electrodes ca of the respective IDT electrodes 32, 34, 36 are led out by the lead-out wiring and wired, the IDT electrodes are connected to the first circuit 11 on the first path r1. The second comb electrodes cb are led out by the lead-out wiring and connected to the ground. The number of the IDT electrodes connected to the first path r1 on the side of the common terminal Tc as viewed from the longitudinal coupling elastic wave resonator 13 is smaller than the number of the IDT electrodes connected to the first path r1 on the side of the first terminal T1.

[0053] In the present embodiment, among the plurality of IDT electrodes 31 to 37, the total average of the electrode finger pitches of the IDT electrodes 32, 34, 36 connected to the first path r1 on the side of the common terminal Tc as viewed from the longitudinal coupling elastic wave resonator 13 is smaller than the total average of the electrode finger pitches of the IDT electrodes 31, 33, 35, 37 connected to the first path r1 on the side of the first terminal T1, and the total sum of the electrode finger pairs is smaller. Further, the so-called electrode finger pitch is the distance between the centers of the adjacent electrode fingers fa, fb in the elastic wave propagation direction D1. Furthermore, the so-called total average of the electrode finger pitches can be derived by dividing the sum of the distances between the centers of the electrode finger at one end and the electrode finger at the other end in each of the IDT electrodes 31 to 37 by the sum of the number of the electrode finger gaps (refer to FIG. 2) in each of the IDT electrodes. Figure 3 ).

[0054] [2. Configuration of IDT electrodes of longitudinal coupling elastic wave resonator]

[0055] Next, the configuration of the IDT electrodes of the longitudinal coupling elastic wave resonator 13 will be described.

[0056] Figure 3 is a plan view and a cross-sectional view schematically showing the configuration of the IDT electrodes 31 to 37 of the longitudinal coupling elastic wave resonator 13. This figure is a figure in which the configuration of the IDT electrodes is simplified, and the number of electrode fingers, the length, and the like included in the IDT electrodes are different from Figure 3 .

[0057] The longitudinally coupled elastic wave resonator 13 is formed of a substrate 320, an electrode layer 325 and a dielectric layer 326. The substrate 320 is piezoelectric. The electrode layer 325 constitutes each IDT electrode 31 to 37 formed on the substrate 320. The dielectric layer 326 is disposed on the substrate 320 to cover each IDT electrode 31 to 37.

[0058] The substrate 320 is, for example, a LiNbO3 substrate (lithium niobate substrate) with a cut angle of 127.5°. When Rayleigh waves are used as elastic waves propagating within the substrate 320, the cut angle of the substrate 320 is preferably 120°±20° or 300°±20°.

[0059] The electrode layer 325 has a structure in which multiple metal layers are stacked. For example, the electrode layer 325 is formed by stacking Ti layer, Al layer, Ti layer, Pt layer and NiCr layer sequentially from top to bottom.

[0060] The dielectric layer 326 is, for example, a film mainly composed of silicon dioxide (SiO2). The dielectric layer 326 is provided for purposes such as adjusting the frequency and temperature characteristics of the IDT electrodes 31-37, protecting the electrode layer 325 from external environmental damage, or improving moisture resistance.

[0061] Figure 4 This is a diagram showing the electrode finger spacing pt and the number of electrode finger pairs pn of the IDT electrodes 31-37 of the longitudinally coupled elastic wave resonator 13, which is an example of an embodiment.

[0062] exist Figure 4 In (a), the average spacing of the electrode fingers fa and fb and the number of electrode finger pairs pn for each IDT electrode 31-37 are shown. Figure 4 As shown in (a), IDT electrodes 31-37 are based on the central IDT electrode 34 (or center line CL), and are composed of different average spacings and electrode indexes pn in IDT electrodes 31-33 and IDT electrodes 35-37, thus forming an asymmetrical shape.

[0063] exist Figure 4 In (b), the total average of the electrode finger spacing pt and the sum of the electrode finger pairs pn for IDT electrodes 32, 34, and 36 are shown, as are the total average of the electrode finger spacing pt and the sum of the electrode finger pairs pn for IDT electrodes 31, 33, 35, and 37. Figure 4From the longitudinal coupling elastic wave resonator 13, the IDT electrodes 32, 34, 36 connected to the first path r1 on the common terminal Tc side and the IDT electrodes 31, 33, 35, 37 connected to the first path r1 on the first terminal T1 side are compared. The total average of the electrode finger pitches pt is smaller, and the total sum of the electrode finger numbers pn is smaller. In addition, the respective crossing widths of the IDT electrodes 31 to 37 are the same, and the respective duty ratios of the IDT electrodes 31 to 37 are the same.

[0064] [3. Comparison between the embodiment and the comparative example]

[0065] The multiplexer 1 of the embodiment having the above-described structure is described while being compared with the comparative example.

[0066] Figure 5 is a circuit configuration diagram of the multiplexer 101 of the comparative example. The multiplexer of the comparative example 101 has a first filter 110 and a second filter 150. Further, the first filter 110 of the comparative example has a first circuit 111, a longitudinal coupling elastic wave resonator 113, and a second circuit 112. However, the longitudinal coupling elastic wave resonator 113 of the comparative example has a different structure from the longitudinal coupling elastic wave resonator 13 of the embodiment.

[0067] Figure 6 is a schematic diagram showing the longitudinal coupling elastic wave resonator 113 of the first filter 110 that the multiplexer 101 of the comparative example has. The longitudinal coupling elastic wave resonator 113 of the comparative example has an IDT electrode group 130 including a plurality of IDT electrodes arranged along an elastic wave propagation direction D1. The IDT electrode group 130 of the comparative example includes a plurality of IDT electrodes 131, 132, 133, 134, 135, 136, 137. Further, the longitudinal coupling elastic wave resonator 113 has a plurality of reflectors 41, 42.

[0068] The IDT electrodes 132, 134, 136 of the comparative example are connected to the first path r1 on the first terminal T1 side as viewed from the longitudinal coupling elastic wave resonator 113. On the other hand, the IDT electrodes 131, 133, 135, 137 are connected to the first path r1 on the common terminal Tc side as viewed from the longitudinal coupling elastic wave resonator 113. As viewed from the longitudinal coupling elastic wave resonator 113, the number of IDT electrodes connected to the first path r1 on the common terminal Tc side is larger than the number of IDT electrodes connected to the first path r1 on the first terminal T1 side.

[0069] Figure 7 is a graph showing the electrode finger pitches pt and the electrode finger numbers pn of the IDT electrodes 131 to 137 of the longitudinal coupling elastic wave resonator 113 of the comparative example.

[0070] In Figure 7In (a) of FIG. 10, the average interval of the electrode fingers fa, fb of each of the IDT electrodes 131 to 137 and the number of pairs of electrode fingers pn are shown. As shown in (a) of FIG. 10, the IDT electrodes 131 to 137 are composed of different average intervals and the number of pairs of electrode fingers pn in the IDT electrodes 131 to 133 and the IDT electrodes 135 to 137, with the IDT electrode 134 at the center (or the center line CL) as a reference, and become asymmetric shapes. Figure 7 In (a) of FIG. 10, the average interval of the electrode fingers fa, fb of each of the IDT electrodes 131 to 137 and the number of pairs of electrode fingers pn are shown. As shown in (a) of FIG. 10, the IDT electrodes 131 to 137 are composed of different average intervals and the number of pairs of electrode fingers pn in the IDT electrodes 131 to 133 and the IDT electrodes 135 to 137, with the IDT electrode 134 at the center (or the center line CL) as a reference, and become asymmetric shapes.

[0071] In (a) of FIG. 10, the average interval of the electrode fingers fa, fb of each of the IDT electrodes 131 to 137 and the number of pairs of electrode fingers pn are shown. As shown in (a) of FIG. 10, the IDT electrodes 131 to 137 are composed of different average intervals and the number of pairs of electrode fingers pn in the IDT electrodes 131 to 133 and the IDT electrodes 135 to 137, with the IDT electrode 134 at the center (or the center line CL) as a reference, and become asymmetric shapes. Figure 7 In (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 and the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 131, 133, 135, 137 are shown. As shown in (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 are larger than those of the IDT electrodes 131, 133, 135, 137. Figure 7 In (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 and the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 131, 133, 135, 137 are shown. As shown in (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 are larger than those of the IDT electrodes 131, 133, 135, 137.

[0072] That is, in the comparative example, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 131, 133, 135, 137 connected to the common terminal Tc side are larger than those of the IDT electrodes 132, 134, 136 connected to the first terminal Tl side. In contrast, in the embodiment, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 32, 34, 36 connected to the common terminal Tc side are smaller than those of the IDT electrodes 31, 33, 35, 37 connected to the first terminal Tl side.

[0073] Figure 8 is a graph showing the pass characteristics of the first filter 10, 110 in the embodiment and the comparative example. Figure 9 is a graph showing the pass characteristics of the second filter 50, 150 in the embodiment and the comparative example. In Figure 8 and Figure 9 In (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 and the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 131, 133, 135, 137 are shown. As shown in (b) of FIG. 10, the total average of the electrode finger intervals pt and the total sum of the number of pairs of electrode fingers pn of the IDT electrodes 132, 134, 136 are larger than those of the IDT electrodes 131, 133, 135, 137.

[0074] As shown in (a) of FIG. 10, the IDT electrodes 131 to 137 are composed of different average intervals and the number of pairs of electrode fingers pn in the IDT electrodes 131 to 133 and the IDT electrodes 135 to 137, with the IDT electrode 134 at the center (or the center line CL) as a reference, and become asymmetric shapes. Figure 8As shown, on the low frequency side of the passband of the 1st filter 10, 110, the drop in the insertion loss is small in both the embodiment and the comparative example. For example, at a frequency of 859 MHz, the insertion loss is 1.62 dB in both the embodiment and the comparative example.

[0075] However, as shown in the comparative example, a ripple occurs near 851.4 MHz on the high frequency side compared to the passband of the 2nd filter 150. Therefore, the insertion loss on the high frequency side of the passband of the 2nd filter 150 drops. For example, the insertion loss at a frequency of 849 MHz becomes 2.05 dB. Figure 9

[0076] In this regard, in the embodiment, a ripple does not occur near a frequency of 851.4 MHz, and a ripple occurs, for example, at a frequency (omitted from the drawing) that is higher than the attenuation slope on the high frequency side of the passband. That is, in the embodiment, the ripple moves to the high frequency side, and thus the drop in the insertion loss on the high frequency side of the passband of the 2nd filter 50 can be suppressed. For example, the insertion loss at a frequency of 849 MHz becomes 1.94 dB.

[0077] Here, the difference in the insertion loss of the 2nd filter 50 and 150 due to the difference in the structure of the 1st filter 10 and 110 will be described.

[0078] Figure 10 is a drawing showing the resonance modes of the single body of the longitudinal-coupled elastic wave resonator in the embodiment and the comparative example. In Figure 10 , as the resonance modes generated by each longitudinal-coupled elastic wave resonator 13, 113, a second-order resonance mode m2, a first-order resonance mode ml, a zero-order resonance mode mo, and an IDT-IDT inter-resonance mode mi are shown. These resonance modes are generated by the current distribution generated in the longitudinal-coupled elastic wave resonator.

[0079] The first-order resonance mode ml is generated by providing a plurality of IDT electrodes in an asymmetric shape in the elastic wave propagation direction Dl. In the embodiment and the comparative example, by forming an attenuation pole generated by the resonance frequency of this first-order resonance mode ml in a frequency band between the passband of the 2nd filter and the passband of the 1st filter, the steepness of the attenuation slope on the low frequency side of the passband of the 1st filter 10 and 110 is improved.

[0080] However, in the comparative example, a ripple generated by the first-order resonance mode ml occurs near the high frequency side of the passband of the 2nd filter 150 (see Figure 9 ). Therefore, the insertion loss on the high frequency side of the passband of the 2nd filter 150 drops.

[0081] ​In contrast, the first-order resonance mode ml of the embodiment is generated at a higher frequency than the first-order resonance mode ml of the comparative example. As shown in Figure 10 the first-order resonance mode ml of the comparative example is generated near a frequency of 851.4 MHz, in contrast, the first-order resonance mode ml of the embodiment is generated near a frequency of 852.2 MHz. Therefore, the ripple generated by the first-order resonance mode ml of the embodiment occurs at a higher frequency than the comparative example. Therefore, in the embodiment, the first-order resonance mode ml generated by the longitudinal-coupling elastic wave resonator 13 has less adverse effect on the passband of the second filter 50 than the comparative example.

[0082] Here, the return loss that can be generated by the longitudinal-coupling elastic wave resonator 13, 113 is further described.

[0083] Figure 11 is a graph showing the impedance characteristic of the individual longitudinal-coupling elastic wave resonator 13, 113 viewed from the common terminal Tc side in a frequency band including the passband of the second filter. In Figure 11 , the impedance characteristic in a frequency of 814 MHz to 852 MHz including the passband of the second filter 50, 150 and the frequency band in which the first-order resonance mode ml is generated is shown. In addition, in the graph, the position of 849 MHz is shown by a mark Ml, and the position of 852 MHz is shown by a mark M2.

[0084] As shown in Figure 11 , in the comparative example, the impedance characteristic is away from the outer circumferential circle of the Smith chart and approaches the reference impedance (for example, 50 Ω) on the inner side. The reason for this is because, in the comparative example, the total average of the electrode finger pitch pt of the IDT electrode connected to the common terminal Tc side is large and the total sum of the electrode finger pairs pn is large compared to the first terminal Tl side, so the resonance frequency of the first-order resonance mode ml is low, and the ripple is close to the passband of the second filter 150. Therefore, for example, near a frequency of 851 MHz, the impedance of the longitudinal-coupling elastic wave resonator 113 approaches the reference impedance, and the return loss of the longitudinal-coupling elastic wave resonator 113 viewed from the common terminal Tc side becomes large.

[0085] In the embodiment, however, the impedance characteristic is shifted outward from the reference impedance, in the vicinity of the outer circumference. The reason for this is that, in the embodiment, the total average of the electrode finger pitch pt of the IDT electrodes connected to the common terminal Tc side is small and the total sum of the electrode finger number pn is small compared to the first terminal Tl side, so the first-order resonance mode ml is shifted to the high frequency side, and the ripple is shifted to the high frequency side from the passband of the second filter 50. Therefore, in the frequency range of 849 MHz to 852 MHz, the impedance of the longitudinal coupled elastic wave resonator 13 is shifted from the reference impedance, and the return loss of the longitudinal coupled elastic wave resonator 13 viewed from the common terminal Tc side is reduced. That is, the reduction in the insertion loss of the passband of the second filter 50 can be suppressed.

[0086] At this time, even if only the total average of the electrode finger pitch pt is reduced, the resonance mode ml is shifted to the high frequency side. However, impedance mismatch occurs between the IDT electrodes 32, 34, 36 connected to the common terminal Tc side and the IDT electrodes 31, 33, 35, 37 connected to the first terminal Tl side, and the insertion loss of the passband of the first filter 10 is reduced. Therefore, the total sum of the electrode finger number pn is changed, and the reduction in the insertion loss is suppressed.

[0087] In addition, the electrode finger number pn of the IDT electrodes of the longitudinal coupled elastic wave resonator 13 is determined by the bandwidth of the passband of the first filter 10, so it is difficult to greatly change the electrode finger number pn, but by reducing the electrode finger number pn on the common terminal Tc side and increasing the electrode finger number pn on the first terminal Tl side, the total sum of the electrode finger number pn can be adjusted. Thus, the reduction in the insertion loss of the passband of the second filter 50 can be suppressed without greatly changing the bandwidth of the passband of the first filter 10.

[0088] Further, preferably, in the first filter 10 of the multiplexer 1, a parallel arm resonator Pl is connected on the common terminal Tc side of the longitudinal coupled elastic wave resonator 13.

[0089] Figure 12 is a graph showing the impedance characteristic of the individual longitudinal coupled elastic wave resonator 13 viewed from the common terminal Tc side in the passband of the first filter 10. In Figure 12 , the impedance characteristic in the frequency range of 859 MHz to 894 MHz, which is the passband of the first filter 10, 110, is shown.

[0090] As Figure 12As shown, if the longitudinal-coupling elastic wave resonator 13 is observed as a single body, the impedance characteristic moves to the high-impedance side compared to the comparative example, and in addition, the low-frequency band side of the passband moves capacitively away from the reference impedance (50 Ω). Therefore, if it is the longitudinal-coupling elastic wave resonator 13 alone, the impedance of the longitudinal-coupling elastic wave resonator 13 becomes high in the passband of the 1st filter 10, and it becomes easy to generate an insertion loss.

[0091] Therefore, by connecting the parallel-arm resonator P1 having inductance on the common terminal Tc side of the longitudinal-coupling elastic wave resonator 13, the impedance of the low-frequency band side of the passband of the 1st filter 10 is made close to the reference impedance. Thereby, it is possible to suppress a decrease in the insertion loss of the passband of the 1st filter 10. In addition, it is preferable that the parallel-arm resonator P1 be connected directly to the longitudinal-coupling elastic wave resonator 13 without passing through other elastic wave resonators between the parallel-arm resonator P1 and the longitudinal-coupling elastic wave resonator 13.

[0092] (SUMMARY)

[0093] As described above, the multiplexer 1 according to the present embodiment has the common terminal Tc, the 1st terminal T1, and the 2nd terminal T2, the 1st filter 10 provided on the 1st path r1 connecting the common terminal Tc and the 1st terminal T1 and having a 1st frequency band as a passband, and the 2nd filter 50 provided on the 2nd path r2 connecting the common terminal Tc and the 2nd terminal T2 and having a frequency band on a lower frequency side than the 1st frequency band as a passband. The 1st filter 10 has the longitudinal-coupling elastic wave resonator 13. The longitudinal-coupling elastic wave resonator 13 has the IDT electrode group 30 including a plurality of IDT electrodes 31 to 37 arranged along an elastic wave propagation direction D1. The IDT electrode group 30 has an asymmetric shape with reference to a center line CL passing through a center C1 of the IDT electrode group 30 and orthogonal to the elastic wave propagation direction D1. Among the plurality of IDT electrodes 31 to 37, a total average of electrode finger pitches pt of the IDT electrodes 32, 34, 36 connected to the 1st path r1 on the common terminal Tc side is smaller than a total average of electrode finger pitches pt of the IDT electrodes 31, 33, 35, 37 connected to the 1st path r1 on the 1st terminal T1 side, and a total sum of electrode finger numbers pn of the IDT electrodes 32, 34, 36 connected to the 1st path r1 on the common terminal Tc side is smaller than a total sum of electrode finger numbers pn of the IDT electrodes 31, 33, 35, 37 connected to the 1st path r1 on the 1st terminal T1 side.

[0094] In this way, by having the IDT electrodes 31 to 37 have an asymmetric shape, the steepness on the low frequency side of the passband of the first filter 10 can be improved using the attenuation pole generated by the first-order resonance mode ml. Further, by reducing the total average of the electrode finger spacings pt of the electrode fingers fa, fb of the IDT electrodes connected to the common terminal Tc side and reducing the total sum of the electrode finger numbers pn compared to the first terminal Tl side, the first-order resonance mode ml can be shifted to the high frequency side. Thus, the first-order resonance mode ml can be reduced to affect the passband of the second filter 50. That is, the insertion loss drop of the passband of the second filter 50 can be suppressed in the multiplexer 1 having the first filter 10 and the second filter 50.

[0095] Further, it can also be that at least one of the average spacings of the electrode fingers fa, fb and the electrode finger numbers pn of the IDT electrodes are different on both sides of the elastic wave propagation direction Dl of the center line CL, whereby the IDT electrode group 30 has the above-described asymmetric shape.

[0096] In this way, by having at least one of the average spacings of the electrode fingers fa, fb and the electrode finger numbers pn different to achieve an asymmetric shape, the steepness on the low frequency side of the passband of the first filter 10 can be improved using the attenuation pole generated by the first-order resonance mode ml.

[0097] Further, it can also be that the average spacings of the electrode fingers and the electrode finger numbers pn of the IDT electrodes are respectively different on both sides of the elastic wave propagation direction Dl of the center line CL, whereby the IDT electrode group 30 has the above-described asymmetric shape.

[0098] In this way, by having the average spacings of the electrode fingers fa, fb and the electrode finger numbers pn respectively different to achieve an asymmetric shape, the steepness on the low frequency side of the passband of the first filter 10 can be appropriately improved using the attenuation pole generated by the first-order resonance mode ml.

[0099] Further, it can also be that the first filter 10 has a parallel arm resonator Pl connected to the first path rl between the common terminal Tc and the longitudinal coupling elastic wave resonator 13.

[0100] In this way, by connecting the parallel arm resonator Pl, the impedance on the low frequency band side of the passband of the first filter 10 can be made close to the reference impedance. Thus, the insertion loss drop of the passband of the first filter 10 can be suppressed.

[0101] Further, it can also be that the first filter 10 has a series arm resonator S1 connected to the first path r1 between the common terminal Tc and the longitudinal coupling elastic wave resonator 13, and a parallel arm resonator P1 connected to the first path r1, the series arm resonator S1 being disposed on the common terminal Tc side of the parallel arm resonator P1.

[0102] Thus, the impedance in the passband of the first filter 10 can be increased, and the drop in the insertion loss of the passband of the second filter 50 can be suppressed.

[0103] Further, it can also be that the number of the plurality of IDT electrodes 31 to 37 is odd, and the number of the IDT electrodes 32, 34, 36 connected to the common terminal Tc side is less than the number of the IDT electrodes 31, 33, 35, 37 connected to the first terminal T1 side.

[0104] For example, the more the number of the IDT electrodes, the greater the influence of the first order resonance mode ml on the passband of the second filter 50, but by the multiplexer 1 having the above-described structure, the drop in the insertion loss of the passband of the second filter 50 can be suppressed, and the effects of the present application can be appropriately exerted. Further, by increasing the number of the IDT electrodes of the longitudinal coupling elastic wave resonator 13, particularly, by providing seven or more, the cross width of the IDT electrodes can be reduced, for example, and thus the steepness on the low frequency side of the passband of the first filter 10 can be increased. Further, by reducing the number of the IDT electrodes connected to the common terminal Tc side, the sum of the electrode finger numbers pn can also be reduced, and the steepness on the low frequency side of the passband of the first filter 10 can be increased.

[0105] Further, it can also be that the resonance frequency of the first order resonance mode ml generated by the longitudinal coupling elastic wave resonator 13 is in a frequency band between the passband of the second filter 50 and the passband of the first filter 10.

[0106] Thus, the steepness on the low frequency side of the passband of the first filter 10 can be increased while the drop in the insertion loss of the passband of the second filter 50 is suppressed. Particularly, in a case where the transition band as a frequency band between the passband of the first filter 10 and the passband of the second filter is narrow, for example, in a case where the value of (transition band / center frequency) x 100 is 2% or less, the effects can be more appropriately exerted.

[0107] Further, it can also be that the first filter 10 is a reception filter, and the second filter 50 is a transmission filter.

[0108] Thus, the steepness on the low frequency side of the passband of the reception filter can be increased while the drop in the insertion loss of the passband of the transmission filter is suppressed.

[0109] (Other Embodiments)

[0110] The above describes the multiplexer according to the embodiments of the present application, but other embodiments achieved by combining any of the components of the above-described embodiments, modifications of the above-described embodiments and examples made by those skilled in the art without departing from the spirit of the present application, a high-frequency front-end circuit and a communication apparatus including the multiplexer according to the present application are also included in the present application.

[0111] Although the second filter 50 is described as a transmission filter in the above-described embodiments, the second filter 50 can also be a reception filter. In addition, the multiplexer 1 is not limited to the structure having both a transmission filter and a reception filter, and can be a structure having only a transmission filter or only a reception filter.

[0112] In addition, although the multiplexer including two filters is described in the above-described embodiments, the present application can also be applied to a triplexer in which three filters are commonized, a hexaplexer in which six filters are commonized, and the like. That is, the multiplexer can have two or more filters.

[0113] In addition, the second filter 50 is not limited to the above-described filter structure, and can be appropriately designed according to the required filter characteristics and the like. Specifically, the second filter 50 can be a vertically coupled filter structure or a ladder filter structure. In addition, each resonator constituting the second filter 50 is not limited to a SAW resonator, and can be a BAW (Bulk Acoustic Wave) resonator, for example. Further, the second filter 50 can be configured without using a resonator, and can be an LC resonant filter or a dielectric filter, for example.

[0114] In addition, the materials of the electrode layer 325 and the dielectric layer 326 constituting the IDT electrode and the reflector are not limited to the above-described materials. In addition, the IDT electrode can not have the above-described stacked structure. The IDT electrode can include Ti, Al, Cu, Pt, Au, Ag, Pd, and the like, or an alloy, and can further include a plurality of stacked bodies including the above-described metal or alloy.

[0115] Further, in the embodiment, a substrate having piezoelectricity is shown as the substrate 320, and the substrate can also be a piezoelectric substrate including a single layer of a piezoelectric layer. The piezoelectric substrate in this case includes, for example, a piezoelectric single crystal of LiTaO3or another piezoelectric single crystal such as LiNbO3. Further, regarding the substrate 320 on which the IDT electrode is formed, a configuration in which a piezoelectric layer is layered on a support substrate can also be used in addition to a configuration in which the entire substrate includes a piezoelectric layer, as long as the substrate has piezoelectricity. Further, the cut angle of the substrate 320 involved in the above-described embodiment is not limited. That is, the layered configuration, material, and thickness can also be appropriately changed by characteristics and the like according to the requirements of the elastic wave filter, and the same effects can be achieved even if an acoustic surface wave filter using a LiTaO3piezoelectric substrate or a LiNbO3piezoelectric substrate having a cut angle other than the cut angle shown in the above-described embodiment is used.

[0116] Industrial Applicability

[0117] The present application can be widely used as a multiplexer, a front-end circuit, and a communication device that have a filter having a longitudinal-coupled elastic wave resonator in a communication device such as a portable telephone.

[0118] Explanation of Reference Numerals

[0119] 1: multiplexer;

[0120] 9: antenna element;

[0121] 10: first filter;

[0122] 11: first circuit;

[0123] 12: second circuit;

[0124] 13: longitudinal-coupled elastic wave resonator;

[0125] 30: IDT electrode group;

[0126] 31, 32, 33, 34, 35, 36, 37: IDT electrode;

[0127] 41, 42: reflector;

[0128] 50: second filter;

[0129] 320: substrate;

[0130] 325: electrode layer;

[0131] 326: dielectric layer;

[0132] ca, cb: comb-shaped electrode;

[0133] C1: center;

[0134] CL: center line;

[0135] D1: elastic wave propagation direction;

[0136] D2: orthogonal direction;

[0137] fa, fb: electrode fingers;

[0138] L1: inductor;

[0139] m0, m1, m2, mi: resonance mode;

[0140] n0, n1, n2: node;

[0141] pn: electrode finger pair number;

[0142] pt: electrode finger pitch;

[0143] P1, P2: parallel arm resonator;

[0144] r1: 1st path;

[0145] r2: 2nd path;

[0146] S1, S2: series arm resonator;

[0147] Tc: common terminal;

[0148] T1: 1st terminal;

[0149] T2: 2nd terminal.

Claims

1. A multiplexer comprising: a common terminal, a first terminal, and a second terminal; a first filter serving as one filter, provided on a first path connecting the common terminal and the first terminal, and having a first frequency band as a passband; and a second filter serving as another filter, provided on a second path connecting the common terminal and the second terminal, and having a second frequency band lower than the first frequency band as a passband, wherein the first filter has a longitudinal-coupling elastic wave resonator, wherein the longitudinal-coupling elastic wave resonator has an IDT electrode group including a plurality of IDT electrodes arranged along an elastic wave propagation direction, wherein the IDT electrode group has an asymmetric shape with reference to a center line passing through the center of the IDT electrode group and orthogonal to the elastic wave propagation direction, wherein, among the plurality of IDT electrodes, a total average of electrode finger spacings of IDT electrodes connected to the first path on the common terminal side is smaller than a total average of electrode finger spacings of IDT electrodes connected to the first path on the first terminal side, and a total sum of electrode finger numbers of the IDT electrodes connected to the first path on the common terminal side is smaller than a total sum of electrode finger numbers of the IDT electrodes connected to the first path on the first terminal side, as viewed from the longitudinal-coupling elastic wave resonator.

2. The multiplexer according to claim 1, wherein at least one of an average spacing of electrode fingers and a number of electrode fingers of the IDT electrodes is different on both sides of the elastic wave propagation direction of the center line, whereby the IDT electrode group has the asymmetric shape.

3. The multiplexer according to claim 2, wherein the average spacing of electrode fingers and the number of electrode fingers of the IDT electrodes are different on both sides of the elastic wave propagation direction of the center line, respectively, whereby the IDT electrode group has the asymmetric shape.

4. The multiplexer according to any one of claims 1 to 3, wherein the first filter has a shunt arm resonator connected to the first path between the common terminal and the longitudinal-coupling elastic wave resonator.

5. The multiplexer according to any one of claims 1 to 3, wherein the first filter has a series arm resonator and a shunt arm resonator connected to the first path between the common terminal and the longitudinal-coupling elastic wave resonator, and the series arm resonator is provided on the common terminal side than the shunt arm resonator in the first path.

6. The multiplexer according to any one of claims 1 to 3, wherein the number of the plurality of IDT electrodes is odd, and the number of IDT electrodes connected to the common terminal side is smaller than the number of IDT electrodes connected to the first terminal side.

7. The multiplexer according to any one of claims 1 to 3, wherein a resonance frequency of a first-order resonance mode generated by the longitudinal-coupling elastic wave resonator is in a frequency band between the passband of the second filter and the passband of the first filter.

8. The multiplexer according to any one of claims 1 to 3, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first filter is a receive filter, The second filter is a transmit filter.

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