Multiplexer

A multiplexer includes: a filter located on a surface of a substrate and including first series and parallel resonators and a first wiring line; and another filter located on another surface of another substrate and including second series and parallel resonators and a second wiring line, each of first resonators among the second series and parallel resonators overlapping with the first series and parallel resonators, and/or the first wiring line, each of second resonators other than the first resonators among the second series and parallel resonators overlapping with none of the first series and parallel resonators and the first wiring line, when capacitances of series and parallel resonators in first basic sections including the first resonators are represented by Cs1 and Cp1, and capacitances of series and parallel resonators in second basic sections not including the first resonators are represented by Cs2 and Cp1, Cp1/Cs1 being less than Cp2/Cs2.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2018-028685, filed on Feb. 21, 2018, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to a multiplexer.

BACKGROUND

It has been known to mount two substrates having filters formed thereon so that the surfaces having the filters formed thereon face each other across an air gap, as disclosed in, for example, Japanese Patent Application Publication No. 2007-67617 (hereinafter, referred to as Patent Document 1). Patent Document 1 describes that the two filters are arranged so as to overlap in plan view and that two filters are arranged so as not to overlap in plan view.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a multiplexer including: a first substrate having a first surface; a second substrate having a second surface, the second surface facing the first surface across an air gap; a first filter located on the first surface and including one or more first series resonators and one or more first parallel resonators, the one or more first series resonators being connected in series through at least a part of a first wiring line between a common terminal and a first terminal, the one or more first parallel resonators being connected in parallel through at least a part of the first wiring line between the common terminal and the first terminal; and a second filter located on the second surface and including one or more second series resonators and one or more second parallel resonators, the one or more second series resonators being connected in series through at least a part of a second wiring line between the common terminal and a second terminal, the one or more second parallel resonators being connected in parallel through at least a part of the second wiring line between the common terminal and the second terminal, in each of one or more first resonators among the one or more second series resonators and the one or more second parallel resonators, at least a part of a corresponding first resonator of the one or more first resonators and/or at least a part of a second wiring line adjacent to the corresponding first resonator overlapping with at least a part of the one or more first series resonators, at least a part of the one or more first parallel resonators, and/or at least a part of the first wiring line in plan view, in each of one or more second resonators other than the one or more first resonators among the one or more second series resonators and the one or more second parallel resonators, a corresponding second resonator of the one or more second resonators and a second wiring line adjacent to the corresponding second resonator overlapping with none of the one or more first series resonators, the one or more first parallel resonators, and the first wiring line in plan view, when the one or more second series resonators and the one or more second parallel resonators are expressed by an equivalent circuit composed of basic sections mirror-symmetrically connected, electrostatic capacitance values of a series resonator and a parallel resonator in one or more first basic sections including the one or more first resonators are respectively represented by Cs1and Cp1, and electrostatic capacitance values of a series resonator and a parallel resonator in one or more second basic sections including the one or more second resonators and not including the one or more first resonators are respectively represented by Cs2and Cp2, at least one of ratios Cp1/Cs1being less than at least one of ratios Cp2/Cs2.

DETAILED DESCRIPTION

When two filters are arranged so as to overlap, the filters interfere with each other, and the isolation characteristic thereby deteriorates. When two filters are arranged so as not to overlap, the size reduction is difficult.

Hereinafter, a description will be given of embodiments of the present disclosure with reference to the accompanying drawings.

First Embodiment

FIG. 1is a circuit diagram of a multiplexer in accordance with a first embodiment. As illustrated inFIG. 1, a transmit filter50is connected between a common terminal Ant and a transmit terminal Tx. A receive filter52is connected between the common terminal Ant and a receive terminal Rx. The passband of the transmit filter50and the passband of the receive filter52do not overlap with each other. The transmit filter50outputs signals in the transmit band to the common terminal Ant among high-frequency signals input to the transmit terminal Tx, and suppresses signals with other frequencies. The receive filter52outputs signals in the receive band to the receive terminal Rx among high-frequency signals input to the common terminal Ant, and suppresses signals with other frequencies.

The transmit filter50is a ladder-type filter, and includes series resonators S11through S14and parallel resonators P11through P13. The series resonators S11through S14are connected in series between the common terminal Ant and the transmit terminal Tx. The parallel resonators P11through P13are connected in parallel between the common terminal Ant and the transmit terminal Tx. The receive filter52is a ladder-type filter, and includes series resonators S21through S24and parallel resonators P21through P23. The series resonators S21through S24are connected in series between the common terminal Ant and the receive terminal Rx. The parallel resonators P21through P23are connected in parallel between the common terminal Ant and the receive terminal Rx.

FIG. 2is a cross-sectional view of the multiplexer in accordance with the first embodiment. As illustrated inFIG. 2, a substrate20is mounted on a substrate10. The substrate10has a support substrate10aand a piezoelectric substrate10b. The support substrate10ais, for example, a sapphire substrate, a spinel substrate, an alumina substrate, a crystal substrate, or a silicon substrate. The piezoelectric substrate10bis, for example, a lithium tantalate substrate or a lithium niobate substrate. The piezoelectric substrate10bis bonded on the upper surface of the support substrate10a. The bonded surface between the piezoelectric substrate10band the support substrate10ahas a planar surface, and is flat. The substrate10is a piezoelectric substrate, and may not be necessarily bonded on the support substrate.

An acoustic wave resonator12and wiring lines14are located on the upper surface of the substrate10. Terminals18are located on the lower surface of the substrate10. The terminals18are foot pads for connecting the acoustic wave resonators12and22to an external device. A via wiring line16penetrating through the substrate10is provided. The via wiring line16electrically connects the wiring line14and the terminal18. The wiring lines14, the via wiring line16, and the terminals18are formed of a metal layer such as, for example, a copper layer, an aluminum layer, or a gold layer. The terminals18include the common terminal Ant, the transmit terminal Tx, the receive terminal Rx, and a ground terminal.

The acoustic wave resonators22and wiring lines24are located on the lower surface of the substrate20. The substrate20is, for example, a sapphire substrate, a spinel substrate, an alumina substrate, a glass substrate, a crystal substrate, or a silicon substrate. The wiring line24is formed of a metal layer such as, for example, a copper layer, an aluminum layer, or a gold layer. The wiring line14of the substrate10and the wiring line24of the substrate20are bonded together through a bump26. The upper surface of the substrate10and the lower surface of the substrate20face each other across an air gap28.

A circular electrode32is located in the periphery of the upper surface of the substrate10. A sealing portion30is located on the substrate10so as to surround the substrate20. The sealing portion30is bonded on the circular electrode32. The sealing portion30is made of a metal such as solder or an insulating material such as resin. A lid34is located on the upper surfaces of the substrate20and the sealing portion30. The lid34is, for example, a metal plate made of kovar or an insulator plate. A protective film36is provided so as to cover the sealing portion30and the lid34. The protective film36is, for example, a metal film made of nickel or an insulating film.

FIG. 3Ais a plan view of the acoustic wave resonator12in the first embodiment, andFIG. 3Bis a cross-sectional view of the acoustic wave resonator22in the first embodiment. As illustrated inFIG. 3A, the acoustic wave resonator12is a surface acoustic wave resonator. An Interdigital Transducer (IDT)40and reflectors42are formed on the piezoelectric substrate10bof the substrate10. The IDT40includes a pair of comb-shaped electrodes40afacing each other. The comb-shaped electrode40aincludes a plurality of electrode fingers40band a bus bar40cconnecting the electrode fingers40b. The reflectors42are located at both sides of the IDT40. The IDT40excites a surface acoustic wave on the substrate10. The IDT40and the reflectors42are formed of, for example, an aluminum film or a copper film. A protective film or a temperature compensation film may be formed on the substrate10so as to cover the IDT40and the reflectors42.

The electrostatic capacitance value of the surface acoustic wave resonator is the electrostatic capacitance value between a pair of the comb-shaped electrodes40a, and is substantially proportional to the product of the aperture length along which the electrode fingers40bof a pair of the comb-shaped electrodes40aoverlap with each other and the number of pairs of the electrode fingers40b.

As illustrated inFIG. 3B, the acoustic wave resonator22is a piezoelectric thin film resonator. A piezoelectric film46is located on the substrate20. A lower electrode44and an upper electrode48are located so as to sandwich the piezoelectric film46. An air gap45is formed between the lower electrode44and the substrate20. The region where the lower electrode44and the upper electrode48face each other across at least a part of the piezoelectric film46is a resonance region47. The lower electrode44and the upper electrode48in the resonance region47excite the acoustic wave in the thickness extension mode in the piezoelectric film46. The lower electrode44and the upper electrode48are formed of a metal film such as, for example, a ruthenium film. The piezoelectric film46is, for example, an aluminum nitride film.

The electrostatic capacitance value of the piezoelectric thin film resonator is the electrostatic capacitance value between the lower electrode44and the upper electrode48, and is substantially proportional to the value obtained by dividing the area of the resonance region47by the film thickness of the piezoelectric film46.

The acoustic wave resonators12and22include electrodes exciting the acoustic wave. Thus, the acoustic wave resonators12and22are covered with the air gap28so as not to prevent the excitation of the acoustic wave.

The transmit filter50inFIG. 1is located on the upper surface of the substrate10. The series resonators S11through S14and the parallel resonators P11through P13are the acoustic wave resonators12. The receive filter52is located on the lower surface of the substrate20. The series resonators S21through S24and the parallel resonators P21through P23are the acoustic wave resonators22. The series resonators S11and S12and the parallel resonator P11, which are included in a part54, of the transmit filter50overlap with the series resonators S21and S22and the parallel resonator P21, which are included in the part54, of the receive filter52in plan view. The series resonators S13and S14and the parallel resonators P12and P13, which are included in a part56, of the transmit filter50overlap with none of the acoustic wave resonators22of the receive filter52. The series resonators S23and S24and the parallel resonators P22and P23, which are included in the part56, of the receive filter52overlap with none of the acoustic wave resonators12of the transmit filter50.

Signals in the receive band input from the transmit terminal Tx are suppressed by the transmit filter50. When the transmit filter50and the receive filter52overlap with each other in the part54, signals leak from the transmit filter50to the receive filter52through the air gap28. Accordingly, as indicated by an arrow58inFIG. 1, signals in the receive band leak from the transmit terminal Tx to the receive terminal Rx. Thus, the isolation characteristic deteriorates. The isolation characteristic is improved by arranging the transmit filter50and the receive filter52so that the transmit filter50and the receive filter52do not overlap with each other in plan view. However, this structure increases the size of the multiplexer. The size of the multiplexer can be reduced by arranging the transmit filter50and the receive filter52so that the transmit filter50and the receive filter52overlap with each other in plan view. However, this structure deteriorates the isolation characteristic. Thus, the transmit filter50and the receive filter52are arranged so that a part of the transmit filter50overlaps with a part of the receive filter52in plan view. This structure reduces deterioration in the isolation characteristic and reduces the size.

Simulation

Simulated was a preferred relationship between the electrostatic capacitances of the series resonator and the parallel resonator when a part of the transmit filter50overlaps with a part of the receive filter52in plan view. In the simulation, the acoustic wave resonators12and22assumed for Long Term Evolution (LTE) Band7 (transmit band: 2500 MHz to 2570 MHz, receive band: 2620 MHz to 2690 MHz) were used.

FIG. 4illustrates an equivalent circuit in the simulation. As illustrated inFIG. 4, an inductor L is electrically connected between the common terminal Ant and a ground. The inductor L is a matching circuit. To equivalently express the structure in which the transmit filter50and the receive filter52overlap with each other in plan view, it was determined that capacitors C1and C2were electrically connected between the transmit filter50and the receive filter52. The capacitor C1is electrically connected between a node between the series resonators S11and S12and a node between the series resonators S21and S22. The capacitor C2is electrically connected between a node between the series resonators S12and S13and a node between the series resonators S22and S23. Each of the capacitors C1and C2was assumed to have an electrostatic capacitance value of 0.1 pF.

The transmit filter50and the receive filter52were divided into basic sections, and the electrostatic capacitance ratio between the series resonator and the parallel resonator was varied.FIG. 5is a circuit diagram illustrating an equivalent circuit of a filter in the simulation. As illustrated inFIG. 5, a filter51is connected between terminals T1and T2. The filter51corresponds to each of the transmit filter50and the receive filter52.

The filter51is divided into six sections, which are basic sections61through66. The basic sections61and62are mirror-symmetrically connected with respect to a line71. The basic sections62and63are mirror-symmetrically connected with respect to a line72. In the same manner, the basic sections63and64are mirror-symmetrically connected with respect to a line73, the basic sections64and65are mirror-symmetrically connected with respect to a line74, and the basic sections65and66are mirror-symmetrically connected with respect to a line75. When the filter51is divided into the above basic sections, the series resonator S2is divided in series into series resonators S2aand S2b. The series resonator S3is divided in series into series resonators S3aand S3b. The parallel resonator P1is divided in parallel into resonators P1aand P1b. The parallel resonator P2is divided in parallel into parallel resonators P2aand P2b. The parallel resonator P3is divided in parallel into parallel resonators P3aand P3b. In the example ofFIG. 1, the basic section corresponding to the part54(that is, the basic section where the transmit filter50and the receive filter52overlap with each other) is the basic sections61through63. The basic section corresponding to the part56(that is, the basic section where the transmit filter50and the receive filter52do not overlap) is the basic sections64through66. InFIG. 1, the parallel resonators P12and P22are included in the part56, but the series resonators S12and S22are included in the part54. Thus, the basic section63was determined to be included in the part54.

When a series resonator S with an electrostatic capacitance value of Cs is divided in series into a resonator Sa with an electrostatic capacitance value of Csa and a resonator Sb with an electrostatic capacitance value of Csb, Cs=(Csa×Csb)/(Csa+Csb). When a parallel resonator P with an electrostatic capacitance value of Cp is divided in parallel into a resonator Pa with an electrostatic capacitance value of Cpa and a resonator Pb with an electrostatic capacitance value of Cpb, Cp=Cpa+Cpb.

FIG. 6illustrates the electrostatic capacitances of samples A through E in the simulation. The electrostatic capacitance values of the series resonator and the parallel resonator in each of the basic sections61through66were represented by Cs and Cp, respectively. The samples A through C correspond to comparative examples, and the samples D and E indicated by hatching correspond to the embodiment. As illustrated inFIG. 6, in the sample C, each of Cs and Cp in each of the basic sections61through66is 1 pF. The ratio Cp/Cs is 1, and Cp×Cs is 1 pF2. The geometric mean of the ratios Cp/Cs of the basic sections61through66is 1, and Cp×Cs is 1 pF2. The geometric mean of the ratios Cp/Cs is obtained by multiplying the ratios Cp/Cs of the basic sections61through66and then obtaining the sixth root of the product.

In the sample A, in each of the basic sections61through63of the part54, Cs is 1/√{square root over (1.3)} pF, Cp is √{square root over (1.3)} pF, Cp/Cs is 1.3, and Cp×Cs is 1 pF2. In each of the basic sections64through66of the part56, Cs is VU pF, Cp is √{square root over (1.3)} pF, Cp/Cs is 1/√{square root over (1.3)}, and Cp×Cs is 1 pF2. The geometric mean of the ratios Cp/Cs of the basic sections61through66is 1, and the geometric mean of the products Cp×Cs of the basic sections61through66is 1 pF2. In the sample B, in each of the basic sections61through63, Cs is 1/√{square root over (1.1)} pF, Cp is √{square root over (1.1)} pF, and Cp/Cs is 1.1. In each of the basic sections64through66, Cs is √{square root over (1.1)} pF, Cp is 1/√{square root over (1.1)} pF, and Cp/Cs is 1/1.1.

In the sample D, in each of the basic sections61through63, Cs is 1/√{square root over (0.9)} pF, Cp is √{square root over (0.9)} pF, and Cp/Cs is 0.9. In each of the basic sections64through66, Cs is √{square root over (0.9)} pF, Cp is 1/√{square root over (0.9)} pF, and Cp/Cs is 1/√{square root over (0.9)}. In the sample E, in each of the basic sections61through63, Cs is 1/√{square root over (0.7)} pF, Cp is √{square root over (0.7)} pF, and Cp/Cs is 0.7. In each of the basic sections64through66, Cs is √{square root over (0.7)} pF, Cp is 1/√{square root over (0.7)} pF, and Cp/Cs is 1/0.7.

The reason why the geometric mean of the ratios Cp/Cs in the basic sections61through66is made to be the same among the samples A through E will be described.FIG. 7is a graph of attenuation versus a capacitance ratio Cp/Cs in one basic section in the simulation. As illustrated inFIG. 7, as Cp/Cs increases, the attenuation at 1880 MHz increases. As seen above, the filter characteristics depend on Cp/Cs. Thus, not to change the filter characteristics, the geometric mean of the ratios Cp/Cs of the basic sections61through66was made to be the same, which is 1 pF2, among the samples A through E.

FIG. 8AandFIG. 8Billustrate transmission characteristics and isolation characteristics in the simulation, respectively.FIG. 8Aillustrates the transmission characteristics of the transmit filter50and the receive filter52in the multiplexer.FIG. 8Billustrates the isolation characteristics from the transmit terminal Tx to the receive terminal Rx. A transmit band76and a receive band78of LTE Band7 are indicated. The simulation is not completely optimized for LTE Band7.

As illustrated inFIG. 8A, the transmission characteristics in the passbands of the transmit filter50and the receive filter52are almost the same among the samples A through E. This is because the geometric mean of the ratios Cp/Cs was made to be the same among the samples A through E. The attenuation in the receive band78of the transmit filter50of the sample E is the greatest, followed by the samples D, C, B, and A. The attenuation of the samples D and E is greater than the attenuation of the samples A through C. The attenuation in the transmit band76of the receive filter52of the sample E is the greatest, followed by the samples D, C, B, and A. As illustrated inFIG. 8B, the isolation characteristic of the sample E is the best, followed by the samples D, C, B, and A. The isolation characteristics of the samples D and E are better than the isolation characteristics of the samples A through C.

FIG. 9AthroughFIG. 9Cillustrate the isolation characteristics in the simulation.FIG. 9Ais an enlarged view near the transmit band76and the receive band78inFIG. 8B.FIG. 9BandFIG. 9Care enlarged views of ranges68and69inFIG. 9A, respectively.

As illustrated inFIG. 9A, the isolation characteristics in the transmit band76and the receive band78of the sample E are the best, followed by the samples D, C, B, and A. As illustrated inFIG. 9B, in the range68(around the frequency at which the isolation is the worst at the transmit band76side), the worst value of the isolation of the sample E is better than the worst value of the isolation of the sample C by 4.3 dB. As illustrated inFIG. 9C, in the range69(around the frequency at which the isolation is the worst at the receive band78side), the isolation of the sample E is better than the isolation of the sample C by 4.9 dB.

The geometric mean of the ratios Cp/Cs of the basic sections61through66were configured to be 0.8, 1.0, and 1.2, and the worst value of the isolation was simulated at the transmit band76side and the receive band78side.FIG. 10AandFIG. 10Billustrate the worst values of the isolation at the transmit band side and the receive band side with respect to the ratios Cp/Cs of the basic sections64through66in the simulation.

As illustrated inFIG. 10AandFIG. 10B, as the geometric mean of the ratios Cp/Cs of the basic sections61through66increases, the isolation improves. In addition, as the ratios Cp/Cs in the basic sections64through66of the part56increase, the isolation improves. The sample of which the ratios Cp/Cs in the basic sections64through66are large is the sample of which the ratios Cp/Cs in the basic sections61through63are relatively small.

As described above, the samples D and E in which the ratios Cp/Cs of the basic sections61through63are configured to be less than the ratios Cp/Cs of the basic sections64through66improve the isolation characteristic compared to the samples A through C without deteriorating the transmission characteristic in the passband. This is because signals in the receive band input from the transmit terminal Tx can be suppressed by the basic sections64through66by making the ratios Cp/Cs in the basic sections64through66of the part56of the transmit filter50greater than the ratios Cp/Cs in the basic sections61through63of the part54. This is also because signals in the transmit band leaking to the receive filter52in the basic sections61through63are suppressed in the basic sections64through66by making the ratios Cp/Cs in the basic sections64through66of the part56of the receive filter52greater than the ratios Cp/Cs in the basic sections61through63of the part54.

A method of equivalently dividing series resonators and parallel resonators connected as desired into basic sections will be described.FIG. 11AandFIG. 11Bare circuit diagrams illustrating a method of combining series resonators and parallel resonators connected as desired. As illustrated inFIG. 11A, series resonators S1-1, S1-2, S2-1, and S2-2are connected in series between the terminals T1and T2. Parallel resonators P1-1and P1-2are connected in series between a node N1between the series resonators S1-2and S2-1and a ground. A parallel resonator P1-3is connected between a node N2and a ground.

As illustrated inFIG. 11B, the series resonators S1-1and S1-2are equivalently combined into a composite series resonator Sm1. The series resonators S2-1and S2-2are equivalently combined into a composite series resonator Sm2. The parallel resonators P1-1through P1-3are equivalently combined into a composite parallel resonator Pm1. The electrostatic capacitance value Cms1of the composite series resonator Sm1is expressed by Cms1=(Cs11×Cs12)/(Cs11+Cs12) with use of the electrostatic capacitance value Cs11of the series resonator S1-1and the electrostatic capacitance value Cs12of the series resonator S1-2. The electrostatic capacitance value of the composite series resonator Sm2is calculated in the same manner. The electrostatic capacitance value Cmp1of the composite parallel resonator Pm1is expressed by Cmp1=Cp13+(Cp11×Cp12)/(Cp11+Cp12) with use of the respective electrostatic capacitance values Cp11through Cp13of the parallel resonators P1-1through P1-3.

FIG. 12AthroughFIG. 12Care diagrams for describing a method of dividing a filter into basic sections. As illustrated inFIG. 12A, by combining the series resonators and the parallel resonators, composite series resonators Sm1through Sm3and composite parallel resonators Pm1and Pm2are alternately connected.

As illustrated inFIG. 12B, the composite series resonator sandwiched between the composite parallel resonators inFIG. 12Ais divided in series at the ratio of the electrostatic capacitance values of the composite parallel resonators located at both sides of the composite series resonator. For example, the composite series resonator Sm2is sandwiched between the composite parallel resonators Pm1and Pm2. The electrostatic capacitance values of the composite series resonator Sm2and the composite parallel resonators Pm1and Pm2are respectively represented by Cms2, Cmp1, and Cmp2. The electrostatic capacitance values of divided series resonators Sd2aand Sd2bformed by dividing in series the composite series resonator Sm2are respectively represented by Cds2aand Cds2b. In this case, Cds2a=Cms2×(Cmp1+Cmp2)/Cmp2and Cds2b=Cms2×(Cmp1+Cmp2)/Cmp1. The composite series resonator Sm3is also divided in series into divided series resonators Sd3aand Sd3b. Since the composite parallel resonator is not connected to one side of the composite series resonator Sm1, the composite series resonator Sm1is not divided, but is referred to as a divided series resonator Sd1.

Then, as illustrated inFIG. 12C, the composite parallel resonator sandwiched between the divided series resonators inFIG. 12Bis divided in parallel at the ratio of the electrostatic capacitance values of the divided series resonators located at both sides of the composite parallel resonator. For example, the composite series resonator Sm1is sandwiched between the divided series resonators Sd1and Sd2a. The electrostatic capacitance values of divided parallel resonators Pd1aand Pd1bformed by dividing in parallel the composite parallel resonator Pm1are respectively represented by Cdp1aand Cdp1b. In this case, Cdp1a=Cmp1×Cds1/(Cds1+Cds2a) and Cdp1b=Cmp1×Cds2a/(Cds1+Cds2a). The composite parallel resonator Pm2is sandwiched between the divided series resonators Sd2band Sd3a. The electrostatic capacitance values of divided parallel resonators Pd2aand Pd2bformed by dividing in parallel the composite parallel resonator Pm2are respectively represented by Cdp2aand Cdp2b. In this case, Cdp2a=Cmp2×Cds2b/(Cds2b+Cds3a) and Cdp2b=Cmp2×Cds3a/(Cds2b+Cds3a).

As described above, the series resonator and the parallel resonator connected as desired can be equivalently expressed by the basic section.

FIG. 13is a plan view illustrating the upper surface of the substrate10in the first embodiment. InFIG. 13, the sizes of the acoustic wave resonators12are exaggerated. As illustrated inFIG. 13, the acoustic wave resonators12and the wiring lines14are located on the substrate10. The via wiring lines16and the bumps26are coupled to the wiring lines14. Pads Pa1, Pt1, Pr1, and Pg1are respectively coupled to the common terminal Ant, the transmit terminal Tx, the receive terminal Rx, and the ground terminal through the via wiring lines16. Between the pads Pa1and Pt1, the series resonators S11through S14are connected in series and the parallel resonators P11through P13are connected in parallel through the wiring lines14. The series resonators S11through S14and the parallel resonators P11through P13form the transmit filter50.

FIG. 14is a plan view transparently illustrating the lower surface of the substrate20in the first embodiment as viewed from above. InFIG. 14, the sizes of the acoustic wave resonators22are exaggerated. As illustrated inFIG. 14, the acoustic wave resonators22and the wiring lines24are located on the substrate20. The bumps26are connected to the wiring lines24. Pads Pa2, Pr2, and Pg2are respectively coupled to the common terminal Ant, the receive terminal Rx, and the ground terminal through the bumps26, the wiring lines14, and the via wiring lines16. Between the pads Pa2and Pr2, the series resonators S21through S24are connected in series and the parallel resonators P21through P23are connected in parallel through the wiring lines24. The series resonators S21through S24and the parallel resonators P21through P23form the receive filter52.

FIG. 15is a plan view of the multiplexer in accordance with the first embodiment. The acoustic wave resonators22and the wiring lines24of the substrate20are superimposed on the substrate10. The region where the acoustic wave resonator12and the wiring line14overlap with the acoustic wave resonator22and the wiring line24is indicated by a bold line55. As illustrated inFIG. 15, a part of the parallel resonator P11of the transmit filter50overlaps with a part of the series resonator S21of the receive filter52in plan view. A part of the series resonator S11overlaps with a part of the parallel resonator P21in plan view. A part of the series resonator S12overlaps with a part of the parallel resonator P22in plan view. A part of the parallel resonator P12overlaps with a part of the series resonator S22in plan view.

When the acoustic wave resonator12(or22) connected to the wiring line14(or24) that connects the acoustic wave resonator12(or22) to the next acoustic wave resonator12(or22) and overlaps with the acoustic wave resonator22(or12) and/or the wiring line24(or14) is determined to be included in the part54(i.e., when the wiring line is taken into consideration), the parallel resonators P11and P12and the series resonators S11through S13overlap with the acoustic wave resonator22and/or the wiring line24. In the same manner, the parallel resonators P21and P22and the series resonators S21through S23overlap with the acoustic wave resonator12and/or the wiring line14. Thus, in both the transmit filter50and the receive filter52, the basic sections61through65are included in the part54, and the basic section66is included in the part56. Thus, the ratio Cp/Cs in the basic section66is configured to be greater than the ratios Cp/Cs in the basic sections61through65. This configuration improves the isolation characteristic.

When the wiring line14is not taken into consideration and the acoustic wave resonator12(or22) overlapping with the acoustic wave resonator22(or12) is determined to be included in the part54, the parallel resonators P11and P12and the series resonators S11and S12overlap with the acoustic wave resonator22. In the same manner, the parallel resonators P21and P22and the series resonators S21and S22overlap with the acoustic wave resonator12. Accordingly, in both the transmit filter50and the receive filter52, the basic sections61through64are included in the part54, and the basic sections65and66are included in the part56. Thus, the ratios Cp/Cs in the basic sections65and66are configured to be greater than the ratios Cp/Cs in the basic sections61through64. This configuration improves the isolation characteristic.

FIG. 16is a plan view of a multiplexer in accordance with a first variation of the first embodiment. As illustrated inFIG. 16, a part of the parallel resonator P11of the transmit filter50overlaps with a part of the series resonator S21of the receive filter52in plan view. A part of the series resonator S11overlaps with a part of the parallel resonator P21in plan view. A part of the series resonator S12overlaps with a part of the series resonator S22in plan view.

When the part54is determined taking into consideration the wiring line14(or24) to the next acoustic wave resonator12(or22), the parallel resonator P11and the series resonators S11and S12overlap with the acoustic wave resonator22and/or the wiring line24. Thus, in the transmit filter50, the basic sections61through63are included in the part54, and the basic sections64through66are included in the part56. Thus, the ratios Cp/Cs in the basic sections64through66are configured to be greater than the ratios Cp/Cs in the basic sections61through63. This configuration improves the isolation characteristic.

In the receive filter52, the parallel resonators P21and P22and the series resonators S21and S22overlap with the acoustic wave resonator12and/or the wiring line14. Accordingly, in the receive filter52, the basic sections61through64are included in the part54, and the basic sections65and66are included in the part56. Thus, the ratios Cp/Cs in the basic sections65and66are configured to be greater than the ratios Cp/Cs in the basic sections61through64. This configuration improves the isolation characteristic.

When the part54is determined without taking into consideration the wiring line14, the parallel resonator P11and the series resonators S11and S12overlap with the acoustic wave resonator22. In the same manner, the parallel resonator P21and the series resonators S21and S22overlap with the acoustic wave resonator12. Accordingly, in both the transmit filter50and the receive filter52, the basic sections61through63are included in the part54, and the basic sections64through66are included in the part56. Thus, the ratios Cp/Cs in the basic sections64through66are configured to be greater than the ratios Cp/Cs in the basic sections61through63. This configuration improves the isolation characteristic.

FIG. 17is a plan view of a multiplexer in accordance with a second variation of the first embodiment. As illustrated inFIG. 17, a part of the parallel resonator P11of the transmit filter50overlaps with a part of the series resonator S21of the receive filter52in plan view. A part of the series resonator S11overlaps with a part of the parallel resonator P21in plan view.

When the part54is determined taking into consideration the wiring line, the parallel resonator P11and the series resonators S11and S12overlap with the acoustic wave resonator22and/or the wiring line24. The parallel resonators P21and P22and the series resonators S21and S22overlap with the acoustic wave resonator12and/or the wiring line14. Accordingly, as in the case ofFIG. 16, in the transmit filter50, the ratios Cp/Cs in the basic sections64through66are configured to be greater than the ratios Cp/Cs in the basic sections61through63. In the receive filter52, the ratios Cp/Cs in the basic sections65and66are configured to be greater than the ratios Cp/Cs in the basic sections61through64. This configuration improves the isolation characteristic.

When the part54is determined without taking into consideration the wiring line14, the parallel resonator P11and the series resonator S11overlap with the acoustic wave resonators22. In the same manner, the parallel resonator P21and the series resonator S22overlap with the acoustic wave resonators12. Accordingly, in both the transmit filter50and the receive filter52, the basic sections61and62are included in the part54, and the basic sections63through66are included in the part56. Thus, the ratios Cp/Cs in the basic sections63through66are configured to be greater than the ratios Cp/Cs in the basic sections61and62. This configuration improves the isolation characteristic.

First Method of Determining in which Part54or56Each Basic Section is Included

Next, an exemplary method of determining in which part54or56each of the basic sections61through66is included will be described. A case where a series resonator between parallel resonators is divided in series will be described.FIG. 18AthroughFIG. 18Care circuit diagrams illustrating a first method of determining in which part54or56each basic section is included. As illustrated inFIG. 18A, the series resonator S2is divided in series into the series resonators S2-1through S2-3. Among the series resonators S2-1through S2-3, the series resonator S2-1is included in the part54. That is, the series resonator S2-1overlaps with the acoustic wave resonator of another filter. The series resonators S2-2and S2-3are included in the part56. That is, the series resonators S2-2and S2-3do not overlap with any acoustic wave resonator of another filter.

As illustrated inFIG. 18B, the series resonators S2-2and S2-3(indicated by a bold dotted line inFIG. 18A) within the part56are combined into a series resonator S2-23. The series resonator S2-23is included in the part56.

As illustrated inFIG. 18C, when a filter is equivalently divided into the basic sections61through66, the series resonator S2is divided into the series resonator S2-1of the basic section62and the series resonator S2-23of the basic section63. In the series resonator S2, the series resonator S2-1in the part54and the series resonators S2-2and S2-3in the part56are not combined. Thus, the basic section62including the series resonator S2-1is determined to be included in the part54, and the basic section63including the series resonators S2-2and S2-3is determined to be included in the part56. Thus, the basic sections61and62are determined to be included in the part54, and the basic sections63through66are determined to be included in the part56.

As illustrated inFIG. 18AthroughFIG. 18C, the series resonator S2between the adjacent parallel resonators P1and P2is divided into the series resonators S2-1through S2-3, and among the series resonators S2-1through S2-3, the series resonator S2-1is included in the part54, and the series resonators S2-2and S2-3are included in the part56. In this case, when the series resonator S2is divided into the series resonator S2ain the basic section62and the series resonator S2bin the basic section63(seeFIG. 5), the series resonator S2may be divided so that the series resonators S2aand S2bcorrespond to the series resonators S2-1and S2-23.

Second Method of Determining in which Part54or56Each Basic Section is Included

A case where a parallel resonator between series resonators is divided in parallel will be described.FIG. 19AthroughFIG. 19Care circuit diagrams illustrating a second method of determining in which part54or56each basic section is included. As illustrated inFIG. 19A, the parallel resonator P2is divided into parallel resonators P2-1through P2-3. The parallel resonators P2-2and P2-3are connected in series. The parallel resonator P2-1is connected in parallel to the parallel resonators P2-2and P2-3. The parallel resonator P2-1is included in the part54. The parallel resonators P2-2and P2-3are included in the part56.

As illustrated inFIG. 19B, the parallel resonators P2-2and P2-3(indicated by a bold dotted line inFIG. 19A) are equivalently combined into a parallel resonator P2-23. The parallel resonator P2-23is included in the part56.

As illustrated inFIG. 19C, when a filter is equivalently divided into the basic sections61through66, the parallel resonator P2is divided into the parallel resonator P2-1in the basic section63and the parallel resonator P2-23in the basic section64. In the parallel resonator P2, the parallel resonator P2-1in the part54and the parallel resonators P2-2and P2-3in the part56are not combined. Thus, the basic section63including the parallel resonator P2-1is determined to be included in the part54, and the basic section64including the parallel resonators P2-2and P2-3is determined to be included in the part56. Accordingly, the basic sections61through63are determined to be included in the part54, and the basic sections64through66are determined to be included in the part56.

As illustrated inFIG. 19AthroughFIG. 19C, the parallel resonator P2between the adjacent series resonators S2and S3is divided into the parallel resonators P2-1through P2-3. Among the parallel resonators P2-1through P2-3, the parallel resonator P2-1is included in the part54, and the parallel resonators P2-2and P2-3are included in the part56. In this case, when the parallel resonator P2is divided into the parallel resonator P2ain the basic section63and the parallel resonator P2bin the basic section64(seeFIG. 5), the parallel resonator P2may be divided so that the parallel resonators P2aand P2bcorrespond to the parallel resonators P2-1and P2-23.

Third Method of Determining in which Part54or56Each Basic Section is Included

A case where a parallel resonator between series resonators is divided in parallel will be described.FIG. 20AthroughFIG. 20Care circuit diagrams illustrating a third method of determining in which part54or56each basic section is included. As illustrated inFIG. 20A, a circuit is the same as the circuit illustrated inFIG. 19A. The parallel resonators P2-1and P2-2are included in the part54. The parallel resonator P2-3is included in the part56.

As illustrated inFIG. 20B, one or some of the parallel resonators P2-2and P2-3that are divided in series are included in the part54, and the remaining parallel resonator is included in the part56. In this case, the parallel resonator P2-3is determined to be included in the part54.

As illustrated inFIG. 20C, the parallel resonators P2-1through P2-3are combined, and thereafter, as with the same method as the method illustrated inFIG. 12Athrough FIG.12C, the filter is divided into the basic sections61through66. Since the parallel resonator P2is included in the part54, the basic sections61through64are determined to be included in the part54, and the basic sections65and66are determined to be included in the part56.

As illustrated inFIG. 20AthroughFIG. 20C, when the parallel resonator P2between the adjacent series resonators S2and S3is divided in parallel, one parallel resonator of the parallel-divided resonators is further divided into the parallel resonators P2-2and P2-3, and the parallel resonators P2-2and P2-3are included in different parts54and56, it is determined that both the parallel resonators P2-2and P2-3are included in the part54. In this case, it may be determined that the parallel resonators P2-2and P2-3are included in the part56.

Fourth Method of Determining in which Part54or56Each Basic Section is Included

FIG. 21AthroughFIG. 21Care circuit diagrams illustrating a fourth method of determining in which part54or56each basic section is included. As illustrated inFIG. 21A, a circuit is the same as the circuit illustrated inFIG. 19A. The series resonators S1through S3and the parallel resonator P1are included in the part54. A series resonator S4and the parallel resonators P2-1through P3are included in the part56. As described above, the series resonator S3is included in the part54, but the parallel resonator P3is included in the part56.

As illustrated inFIG. 21B, when the parallel resonator of the parallel resonator and the series resonator that are alternately connected is included in the part56, the series resonator S3is determined to be included in the part56.

As illustrated inFIG. 21C, the parallel resonators P2-1through P2-3are combined, and thereafter, the filter is divided into the basic sections61through66by the same method as the method illustrated inFIG. 12AthroughFIG. 12C. Since the series resonator S2is included in the part54, the basic sections61through63are determined to be included in the part54, and the basic sections64through66are determined to be included in the part56.

As illustrated inFIG. 21AthroughFIG. 21C, when the adjacent series resonators S2and S3are included in the part54and the parallel resonator P2between the series resonators S2and S3is included in the part56, the series resonator S3may be determined to be included in the part56. In this case, the parallel resonator P2and the series resonator S3may be determined to be included in the part54.

Fifth Method of Determining in which Part54or56Each Basic Section is Included

A case where a part of the wiring line is included in the part54will be described.FIG. 22AthroughFIG. 22Bare circuit diagrams illustrating a fifth method of determining in which part54or56each basic section is included. As illustrated inFIG. 22A, a circuit is the same as the circuit illustrated inFIG. 18A. Among the series resonators S2-1through S2-3formed by dividing the series resonator S2, the series resonator S2-1is included in the part54, and the series resonators S2-2and S2-3are included in the part56. A wiring line14abetween the series resonators S2-2and S2-3is included in the part54. That is, the wiring line14abetween the series resonators S2-2and S2-3overlaps with the acoustic wave resonator of another filter.

As illustrated inFIG. 22B, it is determined that the series resonators S2-2and S2-3and the wiring line14aare determined to be included in the part56. Thereafter, the filter is divided into the basic sections61through66in the same manner asFIG. 18BandFIG. 18C.

As illustrated inFIG. 22AandFIG. 22B, when none of the adjacent resonators (the series resonators S2-2and S2-3) overlap with the acoustic wave resonator and the wiring line of another filter, even if a part of the wiring line14abetween the adjacent resonators overlaps with the acoustic wave resonator and/or the wiring line of another filter, the adjacent resonators may be determined to be included in the part56. In this case, both the adjacent resonators may be determined to be included in the part54.

The methods described inFIG. 11AthroughFIG. 12Care considered as the fundamental methods for a method of equivalently dividing the series resonators and the parallel resonators of the transmit filter50and the receive filter52into the basic sections61through66and a method of determining in which part54or56each of the basic sections61through66is included, and the methods described inFIG. 18AthroughFIG. 22Bmay be used as exceptional methods.

As described above, in the first embodiment and the variations thereof, a lower surface (a first surface) of the substrate20(a first substrate) and an upper surface (a second surface) of the substrate10(a second substrate) face each other across the air gap28. The receive filter52(a first filter) is located on the lower surface of the substrate20, and includes one or more series resonators S21through S24(first series resonators) connected in series through at least a part of the wiring line24(a first wiring line) between the common terminal Ant and the receive terminal Rx (a first terminal) and one or more parallel resonators P21through P23(first parallel resonators) connected in parallel through at least a part of the wiring line24between the common terminal Ant and the receive terminal Rx. The transmit filter50(a second filter) is located on the upper surface of the substrate10, and includes one or more series resonators S11through S14(second series resonators) connected in series through at least a part of the wiring line14(a second wiring line) between the common terminal Ant and the transmit terminal Tx (a second terminal) and one or more parallel resonators P11through P13(second parallel resonators) connected in parallel through at least a part of the wiring line14between the common terminal Ant and the transmit terminal Tx.

As illustrated inFIG. 15throughFIG. 17, at least a part of each of one or more first resonators (for example, S11, S12, P11and P12inFIG. 15) among the series resonators S11through S14and the parallel resonator P11through P13overlaps with at least a part of the series resonators S21through S24and the parallel resonators P21through P23in plan view. One or more second resonators (for example, S13, S14, P12and P13inFIG. 15) other than the one or more first resonators among the series resonators S11through S14and the parallel resonators P11through P13overlap with none of the series resonators S21through S24and the parallel resonators P21through P23in plan view.

When the series resonators S11through S14and the parallel resonators P11through P13are expressed by an equivalent circuit composed of basic sections mirror-symmetrically connected, the electrostatic capacitance values of the series resonator and the parallel resonator in one or more first basic sections (for example, the basic sections61through63inFIG. 5) including one or more first resonators (for example, S11, S12, P11and P12inFIG. 15) are represented by Cs1and Cp1, respectively. The electrostatic capacitance values of the series resonator and the parallel resonator in one or more second basic sections (for example, the basic sections64and65inFIG. 5) including one or more second resonators (for example, S13, S14, P12and P13inFIG. 15) and not including one or more first resonators are represented by Cs2and Cp2, respectively. In this case, as illustrated inFIG. 14, at least one of the ratios Cp1/Cs1is configured to be less than at least one of the ratios Cp2/Cs2.

This configuration suppresses signals in the receive band of the transmit filter50in the basic sections64through66of which the ratios Cp2/Cs2are large. Thus, the isolation characteristic is improved. In addition, the ratios Cp1/Cs1of the basic sections61through63are reduced. This configuration enables to set the geometric mean of the ratios Cp/Cs of the transmit filter50so that the desired characteristics of the transmit filter50are achieved.

The maximum value of the ratios Cp1/Cs1of the one or more first resonators is preferably less than the minimum value of the ratios Cp2/Cs2of the one or more second resonators. The geometric mean of the ratios Cp1/Cs1of the one or more first resonators is preferably less than the geometric mean of the ratios Cp2/Cs2of the one or more second resonators.

As described inFIG. 15throughFIG. 17, at least one of each of the one or more first resonators (for example, S11, S12, P11and P12inFIG. 15) may overlap with at least a part of the series resonators S21through S24and/or at least a part of the one or more parallel resonators P11through P13in plan view.

In each of the one or more first resonators, at least a part of a corresponding first resonator and/or at least a part of the wiring line24adjacent to the corresponding first resonator may overlap with at least a part of the series resonators S11through S14, at least a part of the parallel resonators P11through P13, and/or at least a part of the wiring line14in plan view. The one or more second resonators other than the one or more first resonators and/or the wiring line24adjacent to the one or more second resonators may overlap with none of the one or more series resonators S11through S14, the parallel resonator P11through P13, and the wiring line14in plan view.

A wiring line adjacent to a resonator is the wiring line between the resonator and a resonator adjacent to the resonator or the wiring line between the resonator and a terminal. For example, inFIG. 1, the wiring line adjacent to the series resonator S21is a wiring line between the series resonator S21and the common terminal Ant, a wiring line between the series resonators S21and S22, and a wiring line between the series resonator S21and the parallel resonator P21. These wiring lines have electric potentials approximately equal to that of the series resonator S11, and when these wiring lines overlap with the resonator and/or the wiring line on the substrate10in plan view, high-frequency signals interfere with the receive filter52.

As illustrated inFIG. 15throughFIG. 17, one or more second resonators include the series resonator S24, which is closest to the transmit terminal Tx in terms of electric connection among the series resonators S21through S24, and the parallel resonator P23, which is closest to the transmit terminal Tx in terms of electric connection among the parallel resonators P21through P23. This configuration suppresses signals in the receive band in at least the basic section66.

All the one or more first resonators are closer to the common terminal Ant in terms of electric connection than any of the one or more second resonators. This configuration suppresses signals in the receive band in the basic section closer to the transmit terminal Tx. Thus, the isolation characteristic is further improved.

The equivalent circuit composed of the basic sections mirror-symmetrically connected is calculated as follows. As illustrated inFIG. 11AandFIG. 11B, one or more series resonators S1-1, S1-2, S2-1, and S2-2and one or more parallel resonators P1-1through P1-3are combined so that one or more composite series resonators Sm1and Sm2and one or more composite parallel resonators Pm1are alternately connected.

Then, as illustrated inFIG. 12AandFIG. 12B, the composite series resonator Sm2, which has a first end to which the composite parallel resonator Pm1(a first composite parallel resonator) with an electrostatic capacitance value of Cmp1is connected, has a second end to which the composite parallel resonator Pm2(a second composite parallel resonator) with an electrostatic capacitance value of Cmp2is connected, and has an electrostatic capacitance value of Cms, is divided in series into the divided series resonator Sd2a, which is closer to the composite parallel resonator Pm1and has an electrostatic capacitance value of Cms×(Cmp1+Cmp2)/Cmp2, and the divided series resonator Sd2b, which is closer to the composite parallel resonator Pm2and has an electrostatic capacitance value of Cms×(Cmp1+Cmp2)/Cmp1. As described above, one or more composite series resonators Sm1through Sm3are divided into one or more divided series resonators Sd1through Sd3b.

Then, the composite parallel resonator Pm1, which has a first end to which the divided series resonator Sd1(a first divided series resonator) with an electrostatic capacitance value of Cds1is connected, has a second end to which the divided series resonator Sd2a(a second divided series resonator) with an electrostatic capacitance value of Cds2is connected, and has an electrostatic capacitance value of Cmp, is divided in parallel into the divided parallel resonator Pd1a, which is closer to the divided series resonator Sd1and has an electrostatic capacitance value of Cmp×Cds1/(Cds1+Cds2), and the divided parallel resonator Pd1b, which is closer to the divided series resonator Sd2aand has an electrostatic capacitance value of Cmp×Cds2/(Cds1+Cds2). As described above, the one or more composite parallel resonators Pm1and Pm2are divided into one or more divided parallel resonators Pd1athrough Pd2b.

As illustrated inFIG. 5, the one or more divided series resonators are determined to be the series resonators in the one or more basic sections61through66, and the one or more divided parallel resonators are determined to be the parallel resonators in the corresponding one of the one or more basic sections61through66. Accordingly, the equivalent circuit composed of the basic sections61through66mirror-symmetrically connected is calculated.

When the second terminal is, the transmit terminal Tx and the second filter is the transmit filter50, the ratio Cp1/Cs1of the basic section63, which is electrically closest to the transmit terminal Tx among the one or more first basic sections (for example, the basic sections61through63) and overlaps with the receive filter52in plan view, is greater than the ratios Cp1/Cs1of the remaining first basic sections61and62. Signals in the receive band are suppressed in the basic section63close to the transmit terminal Tx.

Furthermore, the ratios Cp1/Cs1of the one or more first basic sections61through63decrease at electrically closer distances to the common terminal Ant. Thus, signals in the receive band are suppressed in the basic sections61through63electrically closer to the transmit terminal Tx.

At least a part of each of one or more third resonators (for example, S21, S22, P21and P22inFIG. 15) among the series resonators S21through S24and the parallel resonators P21through P23, overlaps with at least a part of the series resonators S11through S14and/or at least a part of the parallel resonators P11through P13in plan view. One or more fourth resonators (for example, S23, S24and P23inFIG. 15) other than the one or more third resonators among the series resonators S21through S24and the parallel resonators P21through P23overlap with none of the series resonators S11through S14and the parallel resonators P11through P13in plan view.

When the series resonators S11through S14and the parallel resonators P11through P13are expressed by an equivalent circuit composed of the basic sections61through66mirror-symmetrically connected, the electrostatic capacitance values of the series resonator and the parallel resonator in the one or more third basic sections61through63including the one or more third resonators are represented by Cs3and Cp3, respectively. The electrostatic capacitance values of the series resonator and the parallel resonator in the one or more fourth basic sections64through66including the one or more fourth resonators and not including one or more third resonators are represented by Cs4and Cp4, respectively. In this case, at least one of ratios Cp3/Cs3of the third resonators is configured to be less than at least one of ratios Cp4/Cs4of the fourth resonators.

This configuration suppresses signals in the transmit band of the receive filter52in the basic sections64through66of which the ratios Cp4/Cs4are large. Thus, the isolation characteristic is improved. Additionally, the ratios Cp3/Cs3of the basic sections61through63are reduced. This configuration enables to set the overall ratio Cp/Cs of the receive filter52so that the desired characteristics of the receive filter52are achieved.

The maximum value of the ratios Cp3/Cs3of the one or more third resonators is preferably less than the minimum value of the ratios Cp4/Cs4of the one or more fourth resonators. The geometric mean of the ratios Cp3/Cs3of the one or more third resonators is preferably less than the geometric mean of the ratios Cp4/Cs4of the one or more fourth resonators.

It is sufficient if in each of the one or more third resonators, at least a part of a corresponding third resonator of the one or more third resonators and/or at least a part of the wiring line14adjacent to the corresponding third resonator overlaps with at least a part of the series resonators S21through S24, at least a part of the parallel resonators P21through P23, and/or at least a part of the wiring line24in plan view. It is sufficient if the one or more fourth resonators other than the one or more third resonators and/or the wiring line24adjacent to the one or more fourth resonators overlap with none of the one or more series resonators S21through S24, the parallel resonators P21through P23, and the wiring lines14in plan view.

As illustrated inFIG. 15throughFIG. 17, one or more fourth resonators include the series resonator S14, which is closest to the receive terminal Rx in terms of electric connection among the series resonators S11through S14, and the parallel resonator P13, which is closest to the receive terminal Rx in terms of electric connection among the parallel resonators P11through P13. This configuration suppresses signals in the transmit band at least in the basic section66.

All the one or more third resonators are closer to the common terminal Ant in terms of electric connection than any of the one or more fourth resonators. This configuration suppresses signals in the transmit band in the basic section closer to the receive terminal Rx. Therefore, the isolation characteristic is further improved.

When the first terminal is the receive terminal Rx and the first filter is the receive filter52, the ratio Cp1/Cs1of the basic section61, which is electrically closest to the common terminal Ant among the one or more third basic sections (for example, the basic sections61through63) and overlaps with the transmit filter50in plan view, is greater than the ratios Cp1/Cs1of other third basic sections62and63. This configuration suppresses signals in the transmit band in the basic section63close to the common terminal Ant.

Furthermore, the ratios Cp1/Cs1of the one or more third basic sections61through63increase at electrically closer distances to the common terminal Ant. Thus, signals in the transmit band are suppressed in the basic sections61through63electrically closer to the common terminal Ant.

The first embodiment and the variations thereof describe a case where the first filter is the receive filter52and the second filter is the transmit filter50, but the first filter may be the transmit filter50and the second filter may be the receive filter52. The number of the series resonators and the parallel resonators constituting the ladder-type filter can be freely selected. The acoustic wave resonators of the first filter and the second filter may be surface acoustic wave resonators, or piezoelectric thin film resonators. A case where the sealing portion30is located so as to surround the substrate20is described, but the sealing portion30may not be necessarily provided. A duplexer has been described as an example of the multiplexer, but the multiplexer may be a triplexer or a quadplexer. The first filter and the second filter are at least two filters of the multiplexer.