Multiplexer, high-frequency front-end circuitry and communication device

Abstract

Multiplexer (1), comprising: a common port (Port1), a first port (Port12) and a second port (Port22), a first filter (12, 12A) arranged on a first path connecting the common terminal and the first terminal, and a second filter (22) arranged on a second path connecting the common terminal and the second terminal, wherein the second filter (22) has a passband frequency higher than a passband frequency of the first filter (12, 12A), wherein the first filter (12, 12A) two or more series resonators (121s-125s) arranged on the first path, and comprising one or more parallel resonator(s) (121p-124p) arranged on a path connecting the first path and mass, Each of the two or more series resonators and the one or more parallel resonators comprises an IDT electrode (32a, 32b) and a reflector (32c) formed on a substrate (320) comprising a piezoelectric layer (327), wherein the IDT electrode comprises a pair of comb-tooth electrodes (32a, 32b), Each of the pair of comb-tooth electrodes contained in each of the two or more series resonators is formed by several electrode fingers (322a, 323a, 322b, 323b) arranged such that they extend in a direction orthogonal to a propagation direction of an elastic wave, and a busbar electrode (321a, 321b) that connects the first ends of the several electrode fingers together, a direction (D) that connects the other ends of the electrode fingers, intersecting the propagation direction of the elastic wave, the IDT electrode, which is included in each of the two or more series resonators, comprises at least one of a first electrode finger (322b2) and a second electrode finger (322b1) from the multiple electrode fingers, wherein each first electrode finger (322b2) has a width that is larger at the other end than at a middle section, each second electrode finger (322b1) has a width that is smaller at the other end than at a middle section, or that is identical at both, the other end and the middle section, and a ratio of the number of second electrode fingers to the number of multiple electrode fingers encompassed in a series resonator (121s) that is closest to the common port (Port1) by the two or more series resonators is higher than a ratio of the number of second electrode fingers to the number of multiple electrode fingers encompassed in each of the other one or more series resonator(s) of the two or more series resonators (122s-125s).

Description

TECHNICAL FIELD

[0001] The invention relates to a multiplexer, a radio frequency (RF) front-end circuit, and a communication device. STATE OF THE ART

[0002] In recent years, band separators for splitting (separating) an RF signal into frequency bands have been widely used in communications devices, such as mobile phone terminals, so that a single terminal supports multiple frequency bands and multiple radio systems, i.e., so-called multi-band and multi-mode operation. A configuration has been proposed for such a band separator in which two duplexers are combined into a quadplexer, each duplexer comprising a transmit filter and a receive filter (see, for example, JP 2012-028896 A).

[0003] An acoustic wave resonator according to US 2011 / 0 215 883 A1 comprises a piezoelectric substrate and first and second comb-shaped electrodes provided on the piezoelectric substrate and interdigitated with each other. The first comb-shaped electrode comprises a first busbar and first electrode fingers extending in a direction that is not perpendicular to a direction in which the first busbar extends. The second comb-shaped electrode comprises a second busbar and second electrode fingers extending from the second busbar and interdigitated with the first electrode fingers in an interdigitated region.

[0004] In an acoustic wave element according to WO 2015 / 064 238 A1, a first imaginary line connects end portions of a plurality of first electrode fingers in an IDT electrode on the side of a second bus bar, and a second imaginary line connects end portions of a plurality of second electrode fingers in the IDT electrode on the side of a first bus bar, wherein ranges 2° < θA ≤ 10° and 2° < θB ≤ 10° are provided, with an inclination angle θA formed by the first imaginary line and the propagation direction and an inclination angle θB formed by the second imaginary line and the propagation direction. SUMMARY OF THE INVENTIONTechnical Problem

[0005] In a multiplexer, such as a quadplexer, having the above configuration, paths passing through each filter are interconnected, and accordingly, the characteristics of one filter may influence the characteristics of another. Therefore, the characteristics of one filter that do not affect one filter may become a factor affecting the characteristics of another. Specifically, a stopband ripple (a ripple generated in a stopband) of one filter has no influence on the characteristics in the passband of one filter. However, if the frequency at which the stopband ripple is generated lies within the passband of another filter, this may become a factor that increases a ripple in the passband (a passband ripple) of the other filter.

[0006] The present invention has been made to solve the above-described problem, and an object of the invention is to provide a multiplexer, an RF front-end circuit, and a communication device capable of suppressing ripple in a passband. Problem solving

[0007] To achieve the above-described object, a multiplexer according to one aspect of the present invention includes a common terminal, a first terminal, and a second terminal, a first filter arranged on a first path connecting the common terminal and the first terminal, and a second filter arranged on a second path connecting the common terminal and the second terminal, wherein the second filter has a passband frequency higher than a passband frequency of the first filter. The first filter includes two or more series resonators arranged on the first path and one or more parallel resonators arranged on a path connecting the first path and ground.Each of the two or more series resonators and the one or more parallel resonators includes an IDT electrode and a reflector formed on a substrate including a piezoelectric layer, the IDT electrode including a pair of comb-tooth electrodes. Each of the pair of comb-tooth electrodes included in each of the two or more series resonators is formed by a plurality of electrode fingers arranged to extend in a direction orthogonal to a propagation direction of an elastic wave, and a busbar electrode connecting one of the ends of the plurality of electrode fingers to each other. A direction connecting other ends of the plurality of electrode fingers to each other crosses the propagation direction of the elastic wave.The IDT electrode included in each of the two or more series resonators comprises at least one of a first electrode finger and a second electrode finger among the plurality of electrode fingers, each first electrode finger having a width that is larger at the other end than at a middle portion, and each second electrode finger having a width that is smaller at the other end than at a middle portion or that is identical at both the other end and the middle portion.A ratio of the number of the second electrode fingers to the number of the plurality of electrode fingers included in one series resonator among the two or more series resonators that is closest to the common terminal is higher than a ratio of the number of the second electrode fingers to the number of the plurality of electrode fingers included in each of the other one or more series resonators among the two or more series resonators.

[0008] In a single-port resonator formed using a piezoelectric layer and employing surface acoustic waves, a so-called transverse mode ripple is generated between a resonant frequency and an anti-resonant frequency, which can degrade the transmission characteristic in the passband. To counteract this, a so-called slanted IDT is used, in which a direction intersecting the ends of electrode fingers constituting a comb-tooth electrode of an IDT electrode crosses a propagation direction of an elastic wave. In addition, to further reduce insertion loss in the passband, so-called varying fingers are used in conjunction with the slanted IDT. Each varying finger has a width that is larger at one end of the finger than at a middle portion of the finger.

[0009] The present inventor has discovered the following as a result of serious consideration. In the first single-port filter comprising a skewed IDT and varying fingers and using surface acoustic waves, when a ratio of the number of varying fingers to the total number of electrode fingers included in a series resonator closest to a common terminal of the first filter is lower than a ratio of the number of varying fingers to the total number of electrode fingers included in each of the other series resonators, ripple in the passband of the second filter can be suppressed.Accordingly, ripple in the passband of the second filter can be suppressed without deteriorating the filter characteristics of the first filter, compared with a case where the proportion of the varying fingers is the same in all series resonators constituting the first filter.

[0010] The number of first electrode fingers included in the series resonator closest to the common terminal of the two or more series resonators may be smaller than the number of first electrode fingers included in each of the other one or more series resonators.

[0011] With this configuration, the proportion of varying fingers in the series resonator closest to the common terminal of the first filter is lower than the proportion of varying fingers in each of the other one or more series resonators. Furthermore, the number of varying fingers included in the series resonator closest to the common terminal of the first filter is smaller than the number of varying fingers included in each of the other one or more series resonators. Accordingly, ripple in the passband of the second filter can be effectively suppressed even when electrode parameters, such as the number of pairs and a cut width, vary between the individual IDT electrodes constituting each series resonator.

[0012] The IDT electrode of the series resonator closest to the common terminal of the two or more series resonators may omit the first electrode fingers, and the IDT electrode of each of the other one or more series resonators may include the first electrode fingers.

[0013] Accordingly, ripple in the passband of the second filter can be suppressed most effectively.

[0014] The first filter may have a ladder filter structure formed by the two or more series resonators and the one or more parallel resonators.

[0015] Accordingly, ripple in the passband of the second filter can be suppressed while maintaining a low-loss characteristic of the first filter.

[0016] The first filter may further comprise a longitudinally coupled filter structure arranged on the first path.

[0017] Accordingly, adaptation to required filter properties, for example attenuation gain, is possible.

[0018] The substrate may include the piezoelectric layer including a main surface on which the IDT electrode is formed, a high acoustic velocity supporting substrate through which a bulk wave propagates at a acoustic velocity higher than a acoustic velocity of an elastic wave propagating through the piezoelectric layer, and a low acoustic velocity layer through which a bulk wave propagates at a acoustic velocity lower than a acoustic velocity of an elastic wave propagating through the piezoelectric layer, wherein the low acoustic velocity layer is disposed between the high acoustic velocity supporting substrate and the piezoelectric layer.

[0019] Accordingly, a quality factor of each resonator formed on the substrate including the piezoelectric layer can be maintained at a large value.

[0020] The multiplexer may be formed by a first duplexer and a second duplexer, wherein the first duplexer comprises two filters including the first filter and the second duplexer comprises two filters including the second filter.

[0021] Accordingly, in the multiplexer including the plurality of duplexers, ripple in the passband can be suppressed.

[0022] The first filter may have a passband that is an uplink frequency band in Band 3 of Long Term Evolution (LTE), and the second filter may have a passband that is an uplink frequency band in Band 1 of LTE.

[0023] In a case where the first filter has a passband that is an uplink frequency band in LTE Band 3, and the second filter has a passband that is an uplink frequency band in LTE Band 1, ripple in the passband of the second filter is likely to increase. Therefore, if the series resonator closest to the common terminal of the first filter is configured to satisfy the aforementioned condition, an increase in ripple will be effectively suppressed.

[0024] A high-frequency front-end circuit according to one aspect of the present invention comprises the aforementioned multiplexer and an amplification circuit connected to the multiplexer.

[0025] Accordingly, a high-frequency front-end circuit capable of suppressing ripple in a passband can be provided.

[0026] A communication device according to one aspect of the present invention comprises a radio frequency signal processing circuit that processes a radio frequency signal transmitted and received by an antenna element, and the aforementioned radio frequency front-end circuit that transmits the radio frequency signal between the antenna element and the radio frequency signal processing circuit.

[0027] Accordingly, a communication device capable of suppressing ripple in a passband can be provided. Advantageous effects of the invention

[0028] A multiplexer or the like according to the invention is capable of suppressing ripple in a passband. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a configuration diagram of a quadplexer according to a first embodiment. Fig.Figure 2 is a diagram describing frequency bands associated with Band 1 and Band 3. Fig. 3 is a circuit configuration diagram of a filter according to the first embodiment. Fig. 4 includes a plan view and a cross-sectional view schematically showing a resonator of the filter according to the first embodiment. Fig. 5A is a plan view of an IDT electrode of a filter on a low frequency side according to an example. Fig. 5B is a plan view of an IDT electrode of a filter on a low frequency side according to a comparative example. Fig. 6A is a graph showing a passband characteristic of a filter on a high frequency side according to the example in comparison with the comparative example. Fig.6B is a graph showing a passband characteristic of the filter on the low frequency side according to the example in comparison with the comparative example. Fig. 7 is a diagram conceptually showing a factor of generating a ripple in a pass band of a filter on a high frequency side in the comparative example. Fig. 8A is a graph showing a resonance characteristic of a series resonator of the filter on the low frequency side according to the example in comparison with the comparative example. Fig. 8B is a graph showing a reflection characteristic of the series resonator of the filter on the low frequency side according to the example in comparison with the comparative example. Fig. 9 is a circuit configuration diagram of a filter according to a modification example of the first embodiment. Fig.10 is a configuration diagram of a high-frequency front-end circuit according to a second embodiment. DESCRIPTION OF EMBODIMENTS

[0029] Hereinafter, embodiments of the present invention will be described in detail using an example and the drawings. Each embodiment described below includes general or specific examples. The values, shapes, materials, elements, and the arrangement and connection configuration of the elements described in the following embodiments are examples and do not limit the present invention. Of the elements described in the following embodiments, an element not recited in an independent claim is described as an optional element. The sizes or proportions of the elements depicted in the drawings are not always exact. In the individual figures, elements that are substantially the same are denoted by the same reference numerals, and repetitive descriptions are omitted or simplified.In the following embodiments, “connected” includes not only “directly connected” but also “electrically connected with another element or the like arranged therebetween.” First embodiment

[0030] In this embodiment, a quadplexer is described as an example of a multiplexer. 1. Basic configuration of the multiplexer

[0031] Fig. 1 is a configuration diagram of a quadplexer 1 according to an embodiment. Fig. 1 also shows an antenna element 2 connected to a common port, Port1, of the quadplexer 1. The quadplexer 1 is a multiplexer (band splitter) that includes multiple filters (here, four filters 11, 12, 21, and 22) covering different passbands, and a common port, Port1, that serves as the antenna-side connection for the multiple filters.

[0032] Specifically, the quadplexer 1 comprises as in Fig.1 shows the common port Port1, four individual ports Port11, Port12, Port21 and Port22 and the four filters 11, 12, 21 and 22.

[0033] The common port Port1 is provided for the four filters 11, 12, 21, and 22 and is connected to these filters 11, 12, 21, and 22 in the quadplexer 1. Furthermore, the common port Port1 is connected to the antenna element 2 outside the quadplexer 1. That is, the common port Port1 also serves as an antenna port of the quadplexer 1.

[0034] The individual ports Port11, Port12, Port21, and Port22 are provided in this order for the four filters 11, 12, 21, and 22, respectively, and are connected to the corresponding filter in the quadplexer 1. Furthermore, the individual ports Port11, Port12, Port21, and Port22 are connected to an RF signal processing circuit (Radio Frequency Integrated Circuit (RFIC), not shown) with an amplification circuit or the like (not shown) arranged therebetween outside the quadplexer 1.

[0035] The filter 11 is arranged on a path connecting the common port Port1 and the single port Port11. In this embodiment, the filter 11 serves as a receive filter having a passband that is a downlink frequency band (receive band) in Band 3 of Long Term Evolution (LTE).

[0036] The filter 12 is arranged on a path connecting the common port Port1 and the single port Port12. In this embodiment, the filter 12 serves as a transmission filter having a passband that is an uplink frequency band (transmission band) in Band 3 of LTE. In this embodiment, the filter 12 corresponds to a first filter arranged on a first path connecting the common port Port1 and a first port (here, the single port Port12).

[0037] The filter 21 is arranged on a path connecting the common port Port1 and the single port Port21. In this embodiment, the filter 21 serves as a receive filter having a passband that is a downlink frequency band (receive band) in Band 1 of LTE.

[0038] The filter 22 is arranged on a path connecting the common port Port1 and the single port Port22. In this embodiment, the filter 22 serves as a transmission filter having a passband that is an uplink frequency band (transmission band) in Band 1 of LTE. In this embodiment, the filter 22 corresponds to a second filter arranged on a second path connecting the common port Port1 and a second port (here, the single port Port22).

[0039] The filter 11 and the filter 12 form an asymmetric duplexer 10 (first duplexer) having a passband that is band 3 of LTE. The filter 21 and the filter 22 form an asymmetric duplexer 20 (second duplexer) having a passband that is band 1 of LTE. That is, the quadplexer 1 according to this embodiment has a configuration in which the common terminal Port1 serves as a common terminal (antenna terminal) of the duplexer 10 having a passband that is band 3 of LTE and a common terminal (antenna terminal) of the duplexer 20 having a passband that is band 1 of LTE. In this embodiment, a signal path passing through the duplexer 10 and a signal path passing through the duplexer 20 are connected to each other at a node N. That is, node N is a point where these two signal paths meet.A description will now be given of the frequency bands allocated to Band 1 and Band 3 of LTE, which are passbands of the quadplexer 1 according to this embodiment. Hereinafter, a range of a frequency band "A or more to B or less" will be simply referred to as "A - B."

[0040] Fig. Figure 2 is a diagram describing the frequency bands assigned to Band 1 and Band 3. Hereinafter, "LTE band" is simply referred to as "Band," and the receive band (Rx) and transmit band (Tx) of each band are simply written using the band name followed by a symbol representing the receive band or transmit band. For example, the receive band (Rx) of Band 1 is referred to as "Band 1 Rx."

[0041] As in Fig.As shown in Figure 2, in Band 1, 1920–1980 MHz are assigned to the transmission band, and 2110–2170 MHz are assigned to the reception band. In Band 3, 1710–1785 MHz are assigned to the transmission band, and 1805–1880 MHz are assigned to the reception band. Accordingly, filters 11, 12, 21, and 22 must have filtering characteristics for passing the transmission band or the reception band of the corresponding band and attenuating the other band, as indicated by the solid lines in Fig. 2 is displayed.

[0042] As described above, the quadplexer 1 includes the filter 12 (first filter) on the low frequency side and the filter 22 (second filter) on the high frequency side. The filter 22 has a passband frequency higher than the passband frequency of the filter 12. The quadplexer 1 is formed by the duplexer 10 (first duplexer) including two filters including the filter 12 (filters 11 and 12 in this embodiment) and the duplexer 20 (second duplexer) including two filters including the filter 22 (filters 21 and 22 in this embodiment).

[0043] The passbands of the two duplexers 10 and 20 are not limited to the combination of band 3 and band 1. For example, a combination of band 25 and band 66 or a combination of band 3 and band 7 can be used. In the quadplexer 1, an impedance element for impedance matching, such as an inductor, can be connected on a path connecting the individual filters 11, 12, 21, and 22 and node N, or on a path connecting node N and the common terminal Port1. 2. Basic filter configurations

[0044] Next, a description is given of the basic configurations of each of the filters 11, 12, 21, and 22. Here, the basic configuration of filter 12 (first filter), which has a passband of band 3 Tx, is described as an example.

[0045] Fig. 3 is a circuit configuration diagram of the filter 12. As shown in Fig.3, the filter comprises 12 series resonators 121s to 125s, parallel resonators 121p to 124p and an inductor 121L.

[0046] The series resonators 121s to 125s are connected in series, in this order, from the common terminal Port1 side on the first path (series arm) connecting the common terminal Port1 and the single terminal Port12. The parallel resonators 121p to 124p are connected in parallel on a path (parallel arm) connecting individual connection points of the series resonators 121s to 125s and a reference terminal (ground). Specifically, the parallel resonators 121p to 123p are connected to the reference terminal with the inductor 121L interposed therebetween, while the parallel resonator 124p is directly connected to the reference terminal. With this connection configuration of the series resonators 121s to 125s and the parallel resonators 121p to 124, the filter 12 serves as a ladder passband filter.

[0047] As described above, the filter 12 (first filter) has a ladder filter structure formed by two or more series resonators arranged on the first path (in this embodiment, the five series resonators 121s to 125s) and one or more parallel resonators (in this embodiment, the four parallel resonators 121p to 124p arranged on the path(s) connecting the first path and the reference terminal (ground)).

[0048] The number of series resonators and the number of parallel resonators of the filter 12 are not limited to five and four, respectively. The number of series resonators can be at least two, and the number of parallel resonators can be at least one.

[0049] Parallel resonators 121p to 123p can be directly connected to the reference terminal without the inductor 121L being interposed, and parallel resonator 124p can be connected to the reference terminal with an inductor interposed therebetween. Impedance elements, such as an inductor and a capacitor, can be inserted or connected to the series arm or the parallel arm.

[0050] In Fig. 3, the parallel resonators 121p to 123p are connected to a common reference terminal (ground), and the parallel resonator 124p is connected to a single reference terminal. The common reference terminal and the single reference terminal are not limited to this and can be appropriately selected, for example, according to limitations in the mounting layout of the filter 12.

[0051] In addition, a parallel resonator may be connected to a node of the series resonator 121s closest to the common terminal Port1, the node being arranged between the series resonator 121s and the common terminal Port1, or to a node of the series resonator 125s among the series resonators 121s to 125s forming a ladder filter structure, the node being closest to the single terminal Port12, the node being arranged between the series resonator 125s and the single terminal Port12. 3. Basic structures of resonators

[0052] Next, the basic structures of the individual resonators (series resonators and parallel resonators) that constitute the filter 12 (first filter) will be described. In this embodiment, each resonator is a surface acoustic wave (SAW) resonator.

[0053] The configurations of the other filters 11, 21, and 22 are not limited to the configuration described above and can be designed according to the required filter characteristics, etc. In particular, the filters 11, 21, and 22 do not necessarily have a ladder filter structure and can, for example, have a longitudinally coupled filter structure. Furthermore, the individual resonators constituting the filters 11, 21, and 22 are not limited to SAW resonators and can, for example, be bulk acoustic wave (AWA) resonators. Furthermore, the filters 11, 21, and 22 can be configured without using resonators and can, for example, be LC resonant filters or dielectric filters.

[0054] Fig. 4 includes a plan view and a cross-sectional view schematically showing a resonator of the low-frequency side filter 12 according to this embodiment. Fig.4 includes a schematic plan view and a schematic cross-sectional view showing the structure of the series resonator 121s of the plurality of resonators constituting the filter 12. The Fig. The series resonator 121s shown in Fig. 4 is used to describe a typical structure of the above-described multiple resonators, and the number and lengths of the electrode fingers constituting one electrode are not limited to those shown in Fig. 4 shown.

[0055] As shown in the top view in Fig.As shown in Figure 4, the series resonator 121s includes a pair of comb-tooth electrodes 32a and 32b that oppose each other, and reflectors 32c arranged in a propagation direction of an elastic wave with respect to the pair of comb-tooth electrodes 32a and 32b. The pair of comb-tooth electrodes 32a and 32b constitute an interdigital transducer (IDT) electrode. Due to limitations in packaging layout, one of the pair of reflectors 32c may not necessarily be provided.

[0056] The comb-tooth electrode 32a is formed in a comb-tooth shape and is composed of a plurality of electrode fingers 322a and a plurality of offset electrode fingers 323a that are parallel to each other, and a busbar electrode 321a that connects one end of the plurality of electrode fingers 322a and one end of the plurality of offset electrode fingers 323a. The comb-tooth electrode 32b is formed in a comb-tooth shape and is composed of a plurality of electrode fingers 322b and a plurality of offset electrode fingers 323b that are parallel to each other, and a busbar electrode 321b that connects one end of the plurality of electrode fingers 322b and one end of the plurality of offset electrode fingers 323b. The plurality of electrode fingers 322a and 322b and the plurality of offset electrode fingers 323a and 323b are formed to extend in a direction orthogonal to the propagation direction of the elastic wave (X-axis direction).The electrode fingers 322a and the offset electrode fingers 323b face each other in the aforementioned orthogonal direction, and the electrode fingers 322b and the offset electrode fingers 323a face each other in the aforementioned orthogonal direction.

[0057] A direction D connecting the other ends of the plurality of electrode fingers 322a (the end portions of the plurality of electrode fingers 322a not connected to the busbar electrode 321a) intersects the propagation direction of the elastic wave (X-axis direction) at a predetermined angle. Likewise, a direction D connecting the other ends of the plurality of electrode fingers 322b (the end portions of the plurality of electrode fingers 322b not connected to the busbar electrode 321b) intersects the propagation direction of the elastic wave (X-axis direction) at the predetermined angle. With this shape, the individual IDT electrodes constituting the series resonators 121s to 125s and the parallel resonators 121p to 124p are so-called skewed IDTs in which the propagation direction of the elastic wave intersects a direction in which the plurality of electrode fingers are arranged.

[0058] In a single-port resonator formed using a piezoelectric layer and using surface acoustic waves, a so-called transverse mode ripple is generated between a resonant frequency and an anti-resonant frequency, which can degrade the transmission characteristic in the passband. To counteract this, the filter 12 according to this embodiment employs a skewed IDT as the IDT electrode of each resonator.

[0059] The pair of reflectors 32c is arranged in the aforementioned direction D relative to the pair of comb-tooth electrodes 32a and 32b. Specifically, the pair of reflectors 32c is arranged such that the pair of comb-tooth electrodes 32a and 32b are located therebetween in the aforementioned direction D. Each reflector 32c is formed by a plurality of reflection electrode fingers extending parallel to each other and reflector busbar electrodes connecting the plurality of reflection electrode fingers. In the pair of reflectors 32c, the reflector busbar electrodes are formed along the aforementioned direction D.

[0060] The pair of reflectors 32c, which has the configuration described above, is capable of confining standing waves of propagating elastic waves within the resonator (here, the series resonator 121s) without allowing the waves to leak out. Accordingly, the resonator is capable of allowing an RF signal within the passband determined by the electrode spacing, the number of pairs, the cut width, and so on of the pair of comb-tooth electrodes 32a and 32b to propagate therethrough with low loss, and is capable of strongly attenuating an RF signal outside the passband.

[0061] The IDT electrode formed by the plurality of electrode fingers 322a and 322b, the plurality of offset electrode fingers 323a and 323b, and the bus bar electrodes 321a and 321b has a multi-layer structure including an adhesive layer 324 and a main electrode layer 325, as shown in the cross-sectional view in Fig.4. The cross-sectional structure of the reflectors 32c is the same as that of the IDT electrode, and therefore no description thereof will be given below.

[0062] The adhesion layer 324 is a layer for increasing adhesion between a piezoelectric layer 327 and the main electrode layer 325 and is made of, for example, Ti. The adhesion layer 324 has a layer thickness of, for example, 12 nm.

[0063] The main electrode layer 325 consists, for example, of Al containing 1% Cu. The main electrode layer 325 has a layer thickness of, for example, 162 nm.

[0064] A protective layer 326 is formed to cover the IDT electrode. The protective layer 326 is a layer for protecting the main electrode layer 325 from the external environment, adjusting the frequency-temperature characteristics, and increasing moisture resistance. It is, for example, a thin layer containing silicon dioxide as a main component. The protective layer 326 has a layer thickness of, for example, 25 nm.

[0065] The materials of the adhesive layer 324, the main electrode layer 325, and the protective layer 326 are not limited to the aforementioned materials. The IDT electrode does not necessarily have to have the aforementioned multilayer structure. The IDT electrode may be made of a metal such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or an alloy, or may be formed by multiple multilayer bodies made of the aforementioned metal or alloy. The protective layer 326 does not necessarily have to be formed.

[0066] The IDT electrode and the reflectors 32c are arranged on a main surface of a substrate 320, which will be described below. The multilayer structure of substrate 320 will be described below.

[0067] As in the lower part of Fig. 4, the substrate 320 includes a high acoustic velocity supporting substrate 329, a low acoustic velocity thin layer 328, and the piezoelectric layer 327, and has a structure in which the high acoustic velocity supporting substrate 329, the low acoustic velocity thin layer 328, and the piezoelectric layer 327 are laminated in this order.

[0068] The piezoelectric layer 327 is a thin piezoelectric layer having a main surface on which the IDT electrode and the reflectors 32c are arranged. The piezoelectric layer 327 is made of, for example, a 50° Y-cut X-propagation piezoelectric LiTaO3 single crystal or piezoelectric ceramics (a lithium tantalate single crystal cut along a plane having a normal as the central axis, which is the Y-axis rotated 50° around the X-axis, or ceramics through which a surface acoustic wave propagates in the X-axis direction). The thickness of the piezoelectric layer 327 is 3.5 λ or less when the wavelength of an elastic wave determined by the electrode spacing of the IDT electrode is represented by λ and is, for example, 600 nm.

[0069] The high acoustic velocity supporting substrate 329 is a substrate for supporting the low acoustic velocity thin layer 328, the piezoelectric layer 327, and the IDT electrode. The high acoustic velocity supporting substrate 329 is a substrate through which a bulk wave propagates at a sound velocity higher than the sound velocity of an elastic wave, such as a surface acoustic wave or a boundary wave, propagating through the piezoelectric layer 327, and acts to confine a surface acoustic wave within a portion where the piezoelectric layer 327 and the low acoustic velocity thin layer 328 are laminated to each other, and prevent the surface acoustic wave from leaking under the high acoustic velocity supporting substrate 329.The high acoustic velocity supporting substrate 329 is, for example, a silicon substrate and has a thickness of, for example, 125 µm. The high acoustic velocity supporting substrate 329 may be composed of any of (1) aluminum nitride, silicon carbide, silicon nitride, silicon, sapphire, or a piezoelectric body, for example, lithium tantalate, lithium niobate, or crystal; (2) various types of ceramics, for example, alumina (aluminum oxide), zirconia, cordierite, mullite, steatite, or forsterite; (3) magnesium diamond; (4) material containing one of the aforementioned materials as a main component; and (5) material containing a mixture of the aforementioned materials as a main component.

[0070] The low acoustic velocity thin layer 328 is a thin layer through which a bulk wave propagates at a sound velocity lower than the sound velocity of an elastic wave propagating through the piezoelectric layer 327, and is disposed between the piezoelectric layer 327 and the high acoustic velocity supporting substrate 329. With this structure and a property that essentially concentrates energy in a medium through which an elastic wave propagates at a low acoustic velocity, leakage of surface acoustic wave energy from the IDT electrode to the outside is suppressed. The low acoustic velocity thin layer 328 is a thin layer containing, for example, silicon dioxide as a main component.The thickness of the low acoustic velocity thin layer 328 is 2 λ or less when the wavelength of an elastic wave represented by the electrode spacing of the IDT electrode by λ is, for example, 670 nm.

[0071] According to the multilayer structure of the substrate 320 described above, a Q factor at a resonant frequency and an anti-resonant frequency can be significantly increased compared to a prior art structure in which a piezoelectric substrate is used as a single layer. That is, a SAW resonator with a high Q factor can be configured, and thus a low insertion loss filter can be configured using the SAW resonator.

[0072] The high-acoustic-velocity supporting substrate 329 may comprise a multilayer structure including a support substrate and a thin high-acoustic-velocity layer through which a bulk wave propagates at a sound velocity higher than the sound velocity of an elastic wave, such as a surface acoustic wave or boundary wave, propagating through the piezoelectric layer 327. In this case, the support substrate may be made of sapphire or a piezoelectric body, such as lithium tantalate, lithium niobate, or crystal; various types of ceramics, such as alumina, magnesium, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric body, such as glass; semiconductors, such as silicon or gallium nitride; a resin substrate; or the like.The high acoustic velocity thin film may be composed of various high acoustic velocity materials, such as aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC thin film, or diamond, a medium containing one of the aforementioned materials as a main component, or a medium containing a mixture of the aforementioned materials as a main component.

[0073] In this embodiment, the IDT electrode constituting the filter 12 is formed on the substrate 320 comprising the piezoelectric layer 327. Alternatively, the substrate on which the IDT electrode is formed may be a piezoelectric substrate formed of the piezoelectric layer 327 as a single layer. In this case, the piezoelectric substrate is made of, for example, a piezoelectric single crystal of LiTaO3 or another piezoelectric single crystal of LiNbO3 or the like.

[0074] The substrate on which the IDT electrode constituting the filter 12 is formed may have either a single-layer structure formed of a single piezoelectric layer or a multi-layer structure in which a piezoelectric layer is laminated on a support surface, as long as the substrate includes a piezoelectric layer.

[0075] The piezoelectric layer 327 according to this embodiment uses a LiTaO3 single crystal with a 50° Y-cut and X-propagation, but the cut angle of the single crystal material is not limited to this. That is, the multilayer structure, material, and thickness can be appropriately changed according to the required passband characteristic of an elastic wave filter device. A similar effect can also be achieved in a SAW filter using a LiTaO3 piezoelectric substrate or a LiNbO3 piezoelectric substrate having a cut angle other than the aforementioned.

[0076] Now, the electrode parameters of IDT electrodes forming SAW resonators are described.

[0077] The wavelength of the SAW resonator is defined as a wavelength λ, which is a repetition period of a plurality of electrode fingers 322a or 322b constituting the IDT electrode arranged in the central part of Fig. 4. The electrode pitch is half the wavelength λ and is defined as (W + S), where W represents a line width of each of the electrode fingers 322a and 322b, which respectively form the comb-tooth electrodes 32a and 32b, and S represents a pitch width between the adjacent electrode fingers 322a and 322b. A cross-sectional width L of the pair of comb-tooth electrodes 32a and 32b is a length over which the electrode fingers 322a and 322b cross each other in the direction D, as shown in the upper part of Fig.4. The electrode metallization ratio of each resonator is an occupancy of the line widths of the plurality of electrode fingers 322a and 322b, that is, a ratio of the line widths of the plurality of electrode fingers 322a and 322b to the sum of the line widths and space widths, and is defined as W / (W + S).

[0078] Table 1 shows the details of the electrode parameters (wavelength λ, cut width L, number of pairs M, and electrode metallization ratio R) of the series resonators 121s to 125s and the parallel resonators 121p to 124p constituting the filter 12 according to the example and the comparative example. [Table 1] Series resonator 121s Series resonator 122s Series resonator 123s Series resonator 124s Series resonator 125s Wavelength λ (µm) 2,1445 2,1694 2,1646 2,1678 2,1420 Cutting line width L (µm) 18,7 20,1 18,0 33,0 17,6 Number of pairs M 140 190 128 107 150 Electrode metallization ratio R 0,5 0,5 0,5 0,5 0,5 Parallel resonator 121p Parallel resonator 122p Parallel resonator 123p Parallel resonator 124p Wavelength λ (µm) 2,2508 2,2507 2,2398 2,2506 Cutting width L (µm) 80,0 82,0 32,8 48,8 Number of pairs M 60 38 108 113 Electrode metallization ratio R 0,5 0,5 0,5 0,5

[0079] In the example and the comparison example, the series resonators and parallel resonators are each formed by a skewed IDT. Alternatively, only the series resonators can be formed by a skewed IDT.

[0080] In the example and the comparative example, each of the series resonators and parallel resonators includes offset electrode fingers. Alternatively, not every resonator necessarily needs to include offset electrode fingers. 4. Resonator structure, varying between example and comparison example

[0081] The electrode parameters of the individual resonators shown in Table 1 are identical in the example and the comparative example, and are common to the individual series resonators 121s to 125s and parallel resonators 121p to 124p. In contrast, a description will be given below of a case where, in the filter 12 according to the example, the resonator structure varies between the series resonator 121s and the other series resonators 122s to 125s.

[0082] Fig. 5A is a plan view of the IDT electrode of the filter 12 on the low frequency side according to the example. Fig.5B is a plan view of the IDT electrode of a low-frequency side filter according to the comparative example.

[0083] As in Fig. 5A, in the filter 12 on the low frequency side according to the example, in the series resonator 121s which is closest to the common terminal Port1 among the series resonators 121s to 125s, the electrode fingers 322a and 322b (322b1 in Fig. 5A) and the offset electrode fingers 323a (323a1 in Fig. 5A) and Fig.323b, which form the pair of comb-tooth electrodes 32a and 32b, are not so-called varying fingers. A varying finger is, among a plurality of electrode fingers, an electrode finger that has a width that is larger at the end portion not connected to the busbar electrode than at the middle portion of the electrode finger. That is, the plurality of electrode fingers 322a and 322b that form the series resonator 121s are second electrode fingers, each of which has a width that is smaller at the end portion than at the middle portion, or that is identical at both the end portion and the middle portion.

[0084] On the other hand, in the other series resonators 122s to 125s, the electrode fingers 322a and 322b (322b2 with an end portion 322d in Fig. 5A) and the offset electrode fingers 323a (323a2 with an end portion 323d in Fig. 5A) and Fig.323b, which form the pair of comb-tooth electrodes 32a and 32b, are called varying fingers. That is, the plurality of electrode fingers 322a and 322b, which form the series resonators 122s to 125s, are first electrode fingers, each of which has a width that is larger at the end portion than at the middle portion.

[0085] In contrast, in the filter 12 on the low frequency side according to the comparative example, in each series resonator 121s to 125s, the electrode fingers 322a and 322b (322b2 with an end portion 322d in Fig. 5B) and the offset electrode fingers 323a (323a2 with an end portion 323d in Fig. 5B) and Fig.323b, which form the pair of comb-tooth electrodes 32a and 32b, are called varying fingers. That is, the plurality of electrode fingers 322a and 322b, which form the series resonators 121s and 125s, are first electrode fingers (varying fingers), each of which has a width that is larger at the end portion than at the middle portion.

[0086] That is, in the filter 12 according to the example, on the low-frequency side, the series resonator 121s closest to the common terminal Port1 is formed by the second electrode fingers, while the other series resonators 122s to 125s are formed by the first electrode fingers (variable fingers). In contrast, in the filter according to the comparative example, on the low-frequency side, each of the series resonators is formed by the first electrode fingers (variable fingers).

[0087] A description will be given below of an effect achieved in the quadplexer 1 according to the example having the above-described configuration in comparison with the quadplexer according to the comparative example. 5. Comparison of properties of the quadplexer according to the example and the comparative example

[0088] Fig. Figure 6A is a graph showing the passband characteristics of the filter 22 on the high frequency side according to the example in comparison with the comparative example. Specifically, Fig. 6A shows the pass characteristic of the path passing through filter 22 on the high-frequency side (the filter for Band 1 Tx), and more specifically, it shows the insertion loss, which is a ratio of the strength of a signal output from the common terminal Port1 to the strength of a signal input to the individual terminal Port22. As can be seen from Fig.6A, in the example the ripple in the passband (here in band 1 Tx) is reduced compared to the comparison example (the section of Fig. 6A) is suppressed.

[0089] Fig. Figure 6B is a graph showing the passband characteristics of the filter 12 on the low frequency side (the filter for Band 3 Tx) according to the example compared with the comparative example. Specifically, Fig. 6B shows the passband characteristics of the path passing through filter 12 on the low-frequency side (the filter for Band 3 Tx), and more specifically, it shows the insertion loss, which is a ratio of the strength of a signal output from the common terminal Port1 to the strength of a signal input to the individual terminal Port12. As shown in Fig.6B, the insertion loss in the passband of the filter 12 in the example and the comparative example is the same, and no difference is seen.

[0090] That is, in the quadplexer 1 according to the example, compared with the quadplexer according to the comparative example, the ripple in the passband of the filter 22 on the high frequency side is reduced, while the low loss characteristic in the passband of the filter 12 on the low frequency side is maintained.

[0091] The following are reasons for the above.

[0092] Fig. Fig. 7 is a diagram conceptually showing a factor of generating a ripple in the passband of the filter 22 on the high frequency side in the comparative example. Part (a) of Fig.Fig. 7 is a graph schematically showing the reflection characteristics of each reflector 32c constituting a resonator, and specifically showing the frequency characteristic of the reflection coefficient. Part (b) of Fig. Figure 7 is a graph schematically showing the resonance characteristic of the resonator, and specifically showing the frequency characteristics of the impedance (so-called impedance characteristic) of the resonator. Part (c) of Fig. 7 is a diagram describing the frequency relationship between band 1 and band 3, similar to Fig. 2, and schematically shows, with solid lines, the filter characteristics required for the individual filters 11, 12, 21, and 22. The reflector 32c is designed to have a high reflection coefficient in a predetermined band encompassing the resonant frequency of the resonator, so that a surface acoustic wave propagating thereto is retained therein without leaking outward.

[0093] In this case, as described in part (a) of Fig. 7, fluctuations in the reflection coefficient in which the reflection coefficient repeatedly increases and decreases resulting from the reflector 32c occur in the band around the predetermined band where the reflection coefficient is high (the section A in Fig. 7).

[0094] In the SAW resonator, as described in part (b) of Fig. 7, the fluctuations in the reflection coefficient cause a ripple in the impedance characteristic (the section B in Fig. 7) on the high frequency side of the resonance property (that is, the high frequency side of both a resonance frequency fr and an anti-resonance frequency fa).

[0095] Generally, in a filter having a ladder filter structure, a resonant frequency frs of a series resonator and an anti-resonant frequency fap of a parallel resonator are set to be substantially equal to each other, and accordingly, a bandpass filter is formed in which frs and fap serve as a center frequency of the passband. Therefore, when a SAW resonator is used as a series resonator in the ladder filter structure, a stopband ripple (a ripple generated in the stopband) resulting from the reflector 32c is generated in the stopband on the high-frequency side of the bandpass filter.

[0096] Such stopband ripple is not so critical in a single filter. However, in a multiplexer comprising multiple filters, if a frequency at which a stopband ripple is generated by one of the filters is within the passband of another of the filters, the stopband ripple causes an increase in a ripple in the passband of the other filter (passband ripple).

[0097] In this embodiment, when the electrode fingers constituting the IDT electrode of the series resonator 121s of the filter 12 for band 3 Tx are the first electrode fingers (varying fingers), similarly to the electrode fingers constituting the IDT electrode of the other series resonators 122s to 125s as in the comparative example, a ripple of the series resonator 121s in band 1 Tx is generated (see parts (b) and (c) of Fig.7). Therefore, in the comparative example, a ripple is generated in the passband in the path passing through the filter 22 on the high frequency side (the filter for band 1 Tx), although the filter 12 on the low frequency side (the filter for band 3 Tx) is kept low loss.

[0098] In contrast, in the example, the electrode fingers constituting the IDT electrode of the series resonator 121s of the filter 12 for band 3 Tx are the second electrode fingers (non-varying fingers), which are different from the electrode fingers constituting the IDT electrodes of the other series resonators 122s to 125s. Accordingly, ripple in the passband in the path passing through the filter 22 (the filter for band 1 Tx) can be suppressed. This will be explained below with reference to Fig. 8A and Fig. 8B.

[0099] Fig.8A is a graph showing the resonance characteristic of the series resonator 121s of the filter 12 on the low frequency side according to the example in comparison with the comparative example. Fig. Figure 8B is a graph showing the reflection characteristic of the series resonator 121s of the filter 12 on the low frequency side according to the example in comparison with the comparative example. Specifically, Fig. 8A shows the resonance characteristic of the series resonator 121s formed by the first electrode fingers (varying fingers) according to the comparative example (dashed line) and the resonance characteristic of the series resonator 121s formed by the second electrode fingers according to the example (solid line). Fig.Figure 8B shows the reflection characteristic of the series resonator 121s formed by the first electrode fingers (variable fingers) according to the comparative example (dashed line) and the reflection characteristic of the series resonator 121s formed by the second electrode fingers according to the example (solid line). The reflection characteristic is shown as return loss, which is a ratio of the strength of a signal output to the common terminal Port1 to the strength of a signal input to the filter 12 via the common terminal Port1.

[0100] When the resonator has the multilayer structure comprising the IDT electrode, the piezoelectric layer 327, the low acoustic velocity thin film 328 and the high acoustic velocity supporting substrate 329 and the skewed IDT structure, a favorable quality characteristic of the resonator is achieved in the configuration comprising varying fingers (comparative example) as shown in Fig. 8A. However, in the configuration comprising varying fingers (the comparative example), a stopband ripple increases on the high frequency side of the anti-resonance frequency as in Fig. 8B. In contrast, in the configuration not including varying fingers (the example), stopband ripple on the high-frequency side of the anti-resonance frequency is suppressed compared to the comparative example.

[0101] In a multiplexer formed by multiple filters (in this embodiment, filters 11, 12, 21, and 22), the characteristics of the series resonator closest to the common terminal Port1 of a filter (in this embodiment, the characteristics of the series resonator 121s of the band 3 Tx filter) influence the characteristics of the other filters (in this embodiment, the band 3 Rx filter, the band 1 Tx filter, and the band 1 Rx filter).

[0102] When the filter 12 (the filter for band 3 Tx) has the multilayer structure comprising the IDT electrode, the piezoelectric layer 327, the low acoustic velocity thin film 328 and the high acoustic velocity supporting substrate 329, and the skewed IDT structure, a low-loss characteristic in the passband of the filter 12 can be achieved by using varying fingers as electrode fingers of the IDT electrode to increase the Q values ​​of individual resonators.

[0103] However, when the frequency at which a stopband ripple is generated in the filter 12 is included in the frequency band of the filter 22 (the filter for band 1 Tx), a ripple is generated in the characteristics in the passband of the filter 22. In contrast, in the example, the proportion of varying fingers in the series resonator 121s, which has the greatest influence on the reflection characteristic of the filter 12, is lower than in the other series resonators 122s to 125s, so the ripple in the passband of the filter 22 is reduced, achieving the low-loss characteristic in the passband of the filter 12. Accordingly, the stopband ripple of the filter 12 can be reduced.Accordingly, in the multiplexer in which the filter on the low frequency side and the filter on the high frequency side are connected to a common terminal, the ripple in the passband of the filter 22 on the high frequency side can be suppressed without deteriorating the filter characteristics of the filter 12 on the low frequency side.

[0104] The multiplexer according to the present invention is not limited to the configuration described above. For example, in the filter 12 according to the example, the ratio of the number of second electrode fingers to the total number of electrode fingers constituting the series resonator 121s closest to the common terminal Port1 may be higher than the ratio of the number of second electrode fingers to the total number of electrode fingers constituting each of the other series resonators 122s to 125s.

[0105] Accordingly, the ripple in the passband of the filter 22 can be suppressed without deteriorating the filter characteristics of the filter 12, compared with a case where the proportion of varying fingers in all of the series resonators 121s to 125s constituting the filter 12 is the same.

[0106] Further, in the filter 12 according to the example, the number of first electrode fingers (varying fingers) in the IDT electrode constituting the series resonator 121s closest to the common terminal Port1 may be smaller than the number of first electrode fingers (varying fingers) in the IDT electrode constituting each of the other series resonators 122s to 125s.

[0107] Accordingly, the ripple in the passband of the filter 22 can be effectively suppressed even if the electrode parameters, such as the number of pairs and a cut width, vary among the individual IDT electrodes constituting the individual series resonators. 6. Filter configurations according to a modified example (modification example)

[0108] In the first embodiment, as an example, a description was given of the configuration of the first filter (in the first embodiment, the filter 12) having only a ladder filter structure. Alternatively, the first filter may have a longitudinally coupled filter structure in addition to the ladder filter structure. In a modified example, a description will be given of a quadplexer with a first filter having such a filter structure. Among several filters included in the quadplexer, the filters other than the first filter have the same configuration as in the first embodiment, and therefore, no description will be given thereof.

[0109] Fig. 9 is a circuit configuration diagram of a filter 12A (first filter) according to the modification example of the first embodiment.

[0110] As in Fig.9, the filter 12A includes series resonators 121s and 122s, parallel resonators 121p and 122p, and a longitudinally coupled resonator 150. That is, the filter 12A is a filter formed by adding the longitudinally coupled resonator 150 to the ladder filter structure.

[0111] The longitudinally coupled resonator 150 has a longitudinally coupled filter structure arranged between the common terminal Port1 and the single terminal Port12. In this embodiment, the longitudinally coupled resonator 150 is arranged between the series resonator 122s and the single terminal Port12 and is formed by nine IDTs and reflectors arranged on both sides of the nine IDTs. The position of the longitudinally coupled resonator 150 is not limited to this. For example, the longitudinally coupled resonator 150 can be arranged between the series resonator 121s and the series resonator 122s, or between the series resonator 121s and the common terminal Port1.

[0112] Also, in the quadplexer including the first filter (in the modification example, the filter 12A) having the above-described configuration, the ripple in the passband can be suppressed by setting the ratio of the number of second electrode fingers to the total number of electrode fingers constituting the series resonator closest to the common terminal Port1 (in this embodiment, the series resonator 121s) to be higher than the ratio of the number of second electrode fingers to the total number of electrode fingers constituting each of the other series resonators as in the first embodiment.

[0113] Furthermore, the filter 12A according to this embodiment, which has a longitudinally coupled filter structure, is adaptable to required filter characteristics, for example, attenuation gain. Second embodiment

[0114] The quadplexers according to the above-described first embodiment and modification example are applicable to an RF front-end circuit and also to a communication device including the RF front-end circuit. In this embodiment, a description will be given of the RF front-end circuit and the communication device.

[0115] Fig. 10 is a configuration diagram of an RF front-end circuit 30 according to the second embodiment. Fig. 10 also shows the individual elements connected to the RF front-end circuit 30 (the antenna element 2, an RF signal processing circuit (RFIC) 3, and a baseband signal processing circuit (BBIC) 4). The RF front-end circuit 30, the RF signal processing circuit 3, and the baseband signal processing circuit 4 form a communication device 40.

[0116] The RF front-end circuit 30 includes the quadplexer 1 according to the first embodiment, a receiving-side switch 13 and a transmitting-side switch 23, a low-noise amplification circuit 14, and a current amplification circuit 24.

[0117] The receiving-side switch 13 is a circuit comprising two select terminals each connected to the individual terminals Port11 and Port21, which are receiving terminals of the quadplexer 1, and a common terminal connected to the low-noise amplifying circuit 14.

[0118] The transmission-side switch 23 is a circuit including two select terminals each connected to the individual terminals Port12 and Port22, which are transmission terminals of the quadplexer 1, and a common terminal connected to the current amplifying circuit 24.

[0119] Each of the receiving-side switch 13 and the transmitting-side switch 23 connects the common terminal and a signal path corresponding to a predetermined band to each other in accordance with a control signal received from a control unit (not shown), and is formed, for example, by a single-pole, double-throw (SPOT) switch. The number of select terminals connected to the common terminal is not limited, and multiple select terminals may be connected. This means that the RF front-end circuit 30 can be compatible with carrier aggregation.

[0120] The low-noise amplification circuit 14 is a reception amplification circuit which amplifies an RF signal (here, an RF reception signal) received via the antenna element 2, the quadplexer 1 and the reception-side switch 13 and outputs the RF signal to the RF signal processing circuit 3.

[0121] The current amplification circuit 24 is a transmission amplification circuit that amplifies an RF signal (here, an RF transmission signal) output from the RF signal processing circuit 3 and outputs the RF signal to the antenna element 2 via the transmission-side switch 23 and the quadplexer 1.

[0122] The RF signal processing circuit 3 performs signal processing, such as down-conversion, on the RF reception signal received by the antenna element 2 through the reception signal path, and outputs a reception signal generated by the signal processing to the baseband signal processing circuit 4. The RF signal processing circuit 3 also performs signal processing, such as up-conversion, on the transmission signal received by the baseband signal processing circuit 4, and outputs an RF transmission signal generated by the signal processing to the current amplification circuit 24. The RF signal processing circuit 3 is, for example, an RFIC.

[0123] The signal generated by the baseband signal processing circuit 4 is used, for example, as an image signal for displaying an image or as a voice signal for telephone calls.

[0124] The RF front-end circuit 30 may include another circuit element arranged between the elements described above.

[0125] The RF front-end circuit 30 and the communication device 40 having the above-described configuration are capable of suppressing ripple in the passband using the quadplexer 1 according to the first embodiment.

[0126] The RF front-end circuit 30 may include the quadplexer according to the modification example of the first embodiment instead of the quadplexer 1 according to the first embodiment.

[0127] The communication device 40 may not necessarily include the baseband signal processing circuit (BBIC) 4, depending on the processing scheme for an RF signal. Further embodiments

[0128] The multiplexer, the RF front-end circuit, and the communication device according to the embodiments of the invention have been described above using the embodiments and the modification example. Other embodiments implemented by combining any elements in the above-described embodiments and the modification example, other modification examples implemented by applying various modifications that a person skilled in the art can devise without departing from the spirit of the invention to the above-described embodiments, and various devices including the RF front-end circuit and the communication device according to the invention are also encompassed by the present invention.

[0129] Above, a description of a quadplexer was given as an example of a multiplexer. However, the invention is applicable, for example, to a triplexer comprising three filters connected to a common antenna terminal, or a hexaplexer comprising six filters connected to a common antenna terminal. That is, any multiplexer comprising two or more filters can be applied.

[0130] Furthermore, the configuration of the multiplexer is not limited to a configuration comprising both a transmit filter and a receive filter. A configuration comprising only a transmit filter or only a receive filter can be used. In the first embodiment, a description was given of a case where filter 12 corresponds to the first filter and filter 22 corresponds to the second filter. That is, both the first and second filters are transmission filters in the first embodiment. However, the invention is applicable to any multiplexer in which the stopband ripple of the first filter is within the passband of the second filter, regardless of the use of the first and second filters. Accordingly, at least one of the first and second filters may be a reception filter. Industrial applicability

[0131] The invention can be widely applied as a multiplexer, a front-end circuit and a communication device applicable to a multi-band system for a communication device such as a mobile phone. LIST OF REFERENCE SYMBOLS 1 quadplexer 2 antenna elements 3 RF signal processing circuit (RFIC) 4 baseband signal processing circuit (BBIC) 10, 20 duplexers 11, 12, 12A, 21, 22 filters 13 receiving-side switch 14 low-noise amplification circuit 23 transmission-side switch 24 Current amplification circuit 30 RF front-end circuit 32a, 32b Comb tooth electrode 32c reflector 40 Communication device 121s to 125s series resonator 121p to 124p parallel resonator 121L Inductor 150 longitudinally coupled resonator 320 substrate 321a, 321b busbar electrode 322a, 322b, 322b1, 322b2 electrode fingers 322d, 323d end section 323a, 323a1, 323a2, 323b offset electrode fingers 324 Adhesive layer 325 Main electrode layer 326 protective layer 327 piezoelectric layer 328 thin layer with low speed of sound 329 high speed of sound supporting substrate Port1 shared connection Port11, Port12, Port21, Port22 single port

Claims

[1] Multiplexer (1), comprising: a common port (Port1), a first port (Port12) and a second port (Port22), a first filter (12, 12A) arranged on a first path connecting the common terminal and the first terminal, and a second filter (22) arranged on a second path connecting the common terminal and the second terminal, the second filter (22) having a passband frequency higher than a passband frequency of the first filter (12, 12A), wherein the first filter (12, 12A) two or more series resonators (121s-125s) arranged on the first path, and one or more parallel resonators (121p-124p) arranged on a path connecting the first path and ground, each of the two or more series resonators and the one or more parallel resonators comprises an IDT electrode (32a, 32b) and a reflector (32c) formed on a substrate (320) comprising a piezoelectric layer (327), the IDT electrode comprising a pair of comb-tooth electrodes (32a, 32b), each of the pair of comb-tooth electrodes included in each of the two or more series resonators is formed by a plurality of electrode fingers (322a, 323a, 322b, 323b) arranged to extend in a direction orthogonal to a propagation direction of an elastic wave, and a busbar electrode (321a, 321b) connecting first ends of the plurality of electrode fingers together, a direction (D) connecting other ends of the electrode fingers crosses the propagation direction of the elastic wave, the IDT electrode included in each of the two or more series resonators comprises at least one of a first electrode finger (322b2) and a second electrode finger (322b1) among the plurality of electrode fingers, wherein each first electrode finger (322b2) has a width that is larger at the other end than at a central portion, each second electrode finger (322b1) has a width that is smaller at the other end than at a central portion, or that is identical at both the other end and the central portion, and a ratio of the number of second electrode fingers to the number of the plurality of electrode fingers included in a series resonator (121s) closest to the common terminal (Port1) among the two or more series resonators is higher than a ratio of the number of second electrode fingers to the number of the plurality of electrode fingers included in each of the other one or more series resonators among the two or more series resonators (122s-125s). [2] A multiplexer (1) according to claim 1, wherein the number of first electrode fingers included in the series resonator (121s) of the two or more series resonators closest to the common terminal is smaller than the number of first electrode fingers included in each of the other one or more series resonators (122s-125s). [3] Multiplexer (1) according to claim 1 or 2, wherein the IDT electrode of the series resonator (121s) which is closest to the common terminal of the two or more series resonators does not include the first electrode fingers and the IDT electrode of each of the other one or more series resonators (122s-125s) comprises the first electrode fingers. [4] A multiplexer (1) according to any one of claims 1 to 3, wherein the first filter (12, 12A) has a ladder filter structure formed by the two or more series resonators (121s-125s) and the one or more parallel resonators (121p-124p). [5] Multiplexer (1) according to one of claims 1 to 4, wherein the first filter (12, 12A) further comprises a longitudinally coupled filter structure (150) arranged on the first path. [6] Multiplexer (1) according to one of claims 1 to 5, wherein the substrate comprises: the piezoelectric layer (327) including a main surface on which the IDT electrode is formed, a high sound velocity supporting substrate (329) through which a bulk wave propagates at a sound velocity higher than a sound velocity of an elastic wave propagating through the piezoelectric layer, and a thin layer with a low sound velocity (328) through which a bulk wave propagates at a sound velocity that is lower than a sound velocity of an elastic wave propagating through the piezoelectric layer, wherein the thin layer with a low sound velocity (328) is arranged between the high sound velocity supporting substrate (329) and the piezoelectric layer (327). [7] Multiplexer (1) according to one of claims 1 to 6, which is formed by a first duplexer (10) and a second duplexer (20), wherein the first duplexer (10) comprises two filters (11, 12, 12A) including the first filter (12, 12A) and the second duplexer (20) comprises two filters (21, 22) including the second filter (22). [8] Multiplexer (1) according to one of claims 1 to 7, wherein the first filter (12, 12A) has a passband that is an uplink frequency band in band 3 of Long Term Evolution (LTE), and the second filter (22) has a passband that is an uplink frequency band in band 1 of the LTE. [9] High-frequency front-end circuit (30), comprising: the multiplexer (1) according to one of claims 1 to 8 and an amplification circuit (14, 24) connected to the multiplexer. [10] Communication device (40) comprising: a high-frequency signal processing circuit (3) which processes a high-frequency signal transmitted and received by an antenna element, and the radio frequency front-end circuit (30) according to claim 9, which transmits the radio frequency signal between the antenna element and the radio frequency signal processing circuit (3).

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