JP2012147175A - Acoustic wave demultiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic wave demultiplexer that compactly suppresses IMD generation.SOLUTION: An acoustic wave demultiplexer 1 includes: a transmission filter section 20 connected between an antenna terminal 10 and a transmission side signal terminal 11; and a reception filter section 13 connected between the antenna terminal 10 and reception side signal terminals 12a, 12b. The transmission filter 20 has: a series arm 21 connecting the antenna terminal 10 and the transmission side signal terminal 11; a plurality of series arm resonators S1-S4 connected in series on the series arm 21; a plurality of parallel arms 22a-22c connecting the series arm 21 to a ground potential; and parallel arm resonators P1-P3 arranged on the plurality of parallel arms 22a-22c, respectively. The first parallel arm resonator P1 of the plurality of parallel arm resonators P1-P3 which is nearest to the antenna terminal 10 has a higher resonant frequency than the other parallel arm resonators P2, P3.

Description

  The present invention relates to an elastic wave duplexer. In particular, the present invention relates to an acoustic wave duplexer that includes a transmission filter unit and a reception filter unit, and the transmission filter unit includes a ladder-type filter unit.

  2. Description of the Related Art Conventionally, for example, elastic wave demultiplexers using elastic waves such as surface acoustic waves and boundary acoustic waves have been used for communication devices such as mobile phones. This elastic wave duplexer is a non-linear device. For this reason, there exists a problem that an intermodulation distortion (IMD: Inter Modulation Distortion) is easy to generate in an elastic wave splitter.

  In recent years, mobile phone systems are required to widen the occupied bandwidth in order to realize high-speed communication. However, increasing the occupied bandwidth tends to increase the noise level. For this reason, when IMD occurs in the elastic wave demultiplexer, there is a problem that the sensitivity of the received signal deteriorates. For this reason, conventionally, various measures for suppressing the occurrence of IMD in filter devices have been proposed.

  For example, in Patent Document 1 below, in a ladder-type elastic wave duplexer, the area is increased by dividing the series arm resonator or parallel arm resonator closest to the antenna terminal without changing the capacitance. It has been proposed. By doing so, the power consumption per unit area of the series arm resonator or the parallel arm resonator closest to the antenna terminal can be reduced. Therefore, occurrence of IMD can be suppressed.

JP 2007-074698 A

  However, as described in Patent Document 1, when the series arm resonator and the parallel arm resonator are divided, the series arm resonator and the parallel arm resonator are increased in size. Accordingly, there is a problem that it is difficult to reduce the size of the elastic wave duplexer.

  The present invention has been made in view of such a point, and an object of the present invention is to provide an elastic wave duplexer that is small in size and in which generation of IMD is suppressed.

  The elastic wave duplexer according to the present invention includes an antenna terminal, a transmission-side signal terminal and a reception-side signal terminal, a transmission filter unit, and a reception filter unit. The transmission filter unit is connected between the antenna terminal and the transmission-side signal terminal. The reception filter unit is connected between the antenna terminal and the reception side signal terminal. The transmission filter unit includes a series arm, a plurality of series arm resonators, a plurality of parallel arms, and a parallel arm resonator. The serial arm connects the antenna terminal and the transmission side signal terminal. The plurality of series arm resonators are connected in series in the series arm. Each of the plurality of parallel arms connects the series arm and the ground potential. The parallel arm resonator is provided in each of the plurality of parallel arms. Of the plurality of parallel arm resonators, the resonance frequency of the first parallel arm resonator closest to the antenna terminal is higher than the resonance frequency of the other parallel arm resonators.

  In the present invention, “near” and “far” do not indicate a short physical distance but a short electrical distance. Therefore, “closest to the antenna terminal” means closest to the electric circuit.

  In a specific aspect of the elastic wave duplexer according to the present invention, each of the plurality of parallel arm resonators includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate. The IDT electrode of the first parallel arm resonator has a pitch of electrode fingers smaller than each IDT electrode of the parallel arm resonators other than the first parallel arm resonator of the plurality of parallel arm resonators, or a duty ratio Is small, or the pitch of the electrode fingers is narrow and the duty ratio is small. In this case, the resonance frequency of the first parallel arm resonator can be made higher than the resonance frequencies of the other parallel arm resonators without increasing the size of the first parallel arm resonator. Therefore, both downsizing and suppression of occurrence of IMD can be achieved.

  In another specific aspect of the elastic wave duplexer according to the present invention, each of the plurality of parallel arm resonators includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate. Thinning weighting is applied to the IDT electrodes of the first parallel arm resonator. With this configuration, it is possible to more effectively suppress the occurrence of IMD without increasing the size of the elastic wave duplexer.

  In another specific aspect of the elastic wave duplexer according to the present invention, a capacitor is connected in parallel to the first parallel arm resonator. With this configuration, it is possible to more effectively suppress the occurrence of IMD without increasing the size of the elastic wave duplexer.

In still another specific aspect of the elastic wave branching filter according to the present invention, when the transmission filter unit has a pass band of f _Tx1 or more and f _Tx2 or less, and the reception filter unit has a pass band of f _Rx1 or more and f _Rx2 or less. The attenuation band in the vicinity of the low band side of the pass band of the transmission filter section is in the frequency band between 2f _Tx1 -f _Rx1 and 2f _Tx2 -f _Rx2 .

  In still another specific aspect of the elastic wave duplexer according to the present invention, each of the series arm resonators closest to the antenna terminal among the plurality of series arm resonators and the first parallel arm resonator is one. It is comprised by the elastic wave resonator of this.

  According to the present invention, it is possible to provide an elastic wave duplexer that is small and suppresses the occurrence of IMD.

1 is a schematic circuit diagram of an elastic wave duplexer according to a first embodiment. 1 is a schematic cross-sectional view of a surface acoustic wave resonator. 1 is a schematic cross-sectional view of a boundary acoustic wave resonator. It is a schematic circuit diagram of an elastic wave duplexer according to a first comparative example. It is a graph showing the reflection characteristic (solid line) of the 1st parallel arm resonator which concerns on 1st Embodiment, and the reflection characteristic (dashed line) of the 1st parallel arm resonator which concerns on a 1st comparative example. It is a graph showing IMD (solid line) of the elastic wave duplexer which concerns on 1st Embodiment, and IMD (broken line) of the elastic wave duplexer which concerns on a 1st comparative example. It is a graph showing the passage characteristic from a transmission side signal terminal to an antenna terminal in a 1st embodiment and the 1st comparative example. It is a graph showing the passage characteristic from an antenna terminal to a receiving side signal terminal in a 1st embodiment and the 1st comparative example. It is a graph showing the isolation characteristic from a transmission side signal terminal to a reception side signal terminal in 1st Embodiment and a 1st comparative example. It is a schematic plan view of the IDT electrode of the first parallel arm resonator according to the second embodiment. It is a graph showing each reflection characteristic of the 1st-3rd parallel arm resonator in 3rd Embodiment. It is a graph showing each reflection characteristic of the 1st-3rd parallel arm resonator in a 2nd comparative example. It is a graph showing IMD (solid line) of the elastic wave duplexer which concerns on 3rd Embodiment, and IMD (broken line) of the elastic wave duplexer which concerns on a 2nd comparative example. It is a graph showing the passage characteristic from a transmission side signal terminal to an antenna terminal in a 3rd embodiment and the 2nd comparative example. It is a graph showing the passage characteristic from an antenna terminal to a receiving side signal terminal in a 3rd embodiment and the 2nd comparative example. It is a graph showing the isolation characteristic from a transmission side signal terminal to a reception side signal terminal in 3rd Embodiment and a 2nd comparative example.

  Hereinafter, a preferred embodiment in which the present invention is implemented will be described by taking the elastic wave duplexer 1 shown in FIG. 1 as an example. However, the elastic wave duplexer 1 is merely an example. The present invention is not limited to the elastic wave duplexer 1 at all. The elastic wave duplexer according to the present invention may be, for example, an elastic wave triplexer.

  FIG. 1 is a schematic circuit diagram of an elastic wave duplexer 1 of the present embodiment. The elastic wave duplexer 1 shown in FIG. 1 is a kind of duplexer. Specifically, the elastic wave duplexer 1 is a duplexer for UMTS-BAND8. For this reason, the transmission frequency band of the elastic wave duplexer 1 is 880 MHz to 915 MHz, and the reception frequency band is 925 MHz to 960 MHz.

  The elastic wave duplexer 1 includes an antenna terminal 10 connected to an antenna, a transmission-side signal terminal 11, and first and second reception-side signal terminals 12a and 12b. A reception filter section 13 is connected between the antenna terminal 10 and the first and second reception signal terminals 12a and 12b. On the other hand, a transmission filter unit 20 is connected between the antenna terminal 10 and the transmission-side signal terminal 11. An inductor L1 as an impedance matching circuit is connected between a connection point between the transmission filter unit 20 and the reception filter unit 13, a connection point between the antenna terminal 10 and the ground potential.

  In the present embodiment, the reception filter unit 13 is configured by a longitudinally coupled resonator type acoustic wave filter unit. The reception filter unit 13 is a so-called balanced filter unit having a balanced-unbalanced conversion function. Accordingly, balanced signals are output from the first and second receiving signal terminals 12a and 12b. Note that the reception filter unit 13 may use, for example, a surface acoustic wave or a boundary acoustic wave.

  The transmission filter unit 20 is a so-called ladder-type elastic wave filter unit. The transmission filter unit 20 has a series arm 21. In the series arm 21, a plurality of series arm resonators S1 to S4 are connected in series. In the present embodiment, among the plurality of series arm resonators S1 to S4, the series arm resonators S2 and S3 are configured by two elastic wave resonators connected in series with each other. The series arm resonator S1 closest to the antenna terminal 10 is composed of one elastic wave resonator. In the present embodiment, the capacitor C2 is connected in parallel to the series arm resonator S2.

  The transmission filter unit 20 is provided with a plurality of parallel arms 22a to 22c. Each of the plurality of parallel arms 22a to 22c connects the serial arm 21 and the ground potential. Parallel arm resonators P1 to P3 are provided in each of the plurality of parallel arms 22a to 22c. An inductor L2 is connected between the connection point between the parallel arm 22a and the parallel arm 22b and the ground potential. On the other hand, an inductor L3 is connected between the parallel arm resonator P3 and the ground potential.

  The elastic wave resonators constituting each of the plurality of parallel arm resonators P1 to P3 and the plurality of series arm resonators S1 to S4 are the surface acoustic wave resonator 30 shown in FIG. 2 or the boundary acoustic wave shown in FIG. The resonator 40 is configured.

  The surface acoustic wave resonator 30 includes a piezoelectric substrate 31 and an IDT electrode 32 provided on the piezoelectric substrate 31. The surface acoustic wave resonator 30 may further include a dielectric layer provided on the piezoelectric substrate 31 so as to cover the IDT electrode 32. This dielectric layer can be formed of, for example, silicon oxide or silicon nitride.

  The boundary acoustic wave resonator 40 includes a piezoelectric substrate 41, an IDT electrode 42 provided on the piezoelectric substrate 41, and a first dielectric layer 43 provided on the piezoelectric substrate 41 so as to cover the IDT electrode 42. And a second dielectric layer 44 that is provided on the first dielectric layer 43 and has a sound velocity faster than that of the first dielectric layer 43. Note that the second dielectric layer 44 is not essential, and the boundary acoustic wave resonator may be composed of only the piezoelectric substrate, the IDT electrode, and the first dielectric layer.

The piezoelectric substrates 31 and 41 can be composed of, for example, a LiNbO ₃ substrate, a LiTaO ₃ substrate, a quartz substrate, or the like. The IDT electrodes 32 and 42 are, for example, a metal selected from the group consisting of Al, Pt, Au, Ag, Cu, Ni, Ti, Cr, and Pd, or Al, Pt, Au, Ag, Cu, Ni, and Ti. , Cr and Pd can be used to form an alloy containing one or more metals selected from the group consisting of Cr and Pd. Further, the IDT electrodes 32 and 42 may be constituted by a laminated body of a plurality of conductive layers made of the above metals or alloys, for example. The first dielectric layer 43 can be formed of, for example, silicon oxide. The second dielectric layer 44 can be formed of, for example, silicon nitride.

  In the present embodiment, among the plurality of parallel arm resonators P1 to P3, the first parallel arm resonator P1 closest to the antenna terminal 10 is configured by one elastic wave resonator. A capacitor C1 (capacitance: 0.30 pF) is connected in parallel to the first parallel arm resonator P1. On the other hand, capacitors are not connected in parallel to the other parallel arm resonators P2 and P3. Thereby, the resonance frequency of the first parallel arm resonator P1 is set higher than the resonance frequencies of the other parallel arm resonators P2 and P3. Specifically, in the present embodiment, the resonance frequency of the first parallel arm resonator P1 is 867.2 MHz. The resonance frequency of the second parallel arm resonator P2 is 866.5 MHz. The resonance frequency of the third parallel arm resonator P3 is 865.0 MHz.

As described above, the elastic wave duplexer is a non-linear device, and therefore IMD is likely to occur. For example, when a signal having a frequency that matches the difference between the frequency twice the transmission signal and the frequency of the reception signal is input from the antenna, an IMD having the same frequency as that of the reception signal is generated by intermodulation with the transmission signal. In the case of an elastic wave duplexer for UMTS-BAND8, 2f _Tx1 −f _Rx1 and 2f when the pass band of the transmission filter unit is f _Tx1 or more and f _Tx2 or less and the pass band of the reception filter unit is f _Rx1 or more and f _Rx2 or less. The frequency band between _Tx2- f _Rx2 (hereinafter referred to as “2Tx-Rx band”) is 835 MHz to 870 MHz. When an interference wave is input to this frequency band and power consumption due to the interference wave increases in the elastic wave duplexer, an IMD is generated in the pass band of the reception filter unit.

  In the present embodiment, the resonance frequencies of the first to third parallel arm resonators P1 to P3 are in the 2Tx-Rx band (835 MHz to 870 MHz), and form an attenuation band near the pass band of the transmission filter unit 20. is doing. For this reason, if the power consumption due to the interference wave increases in the first to third parallel arm resonators P1 to P3, a large IMD may occur. In particular, since the parallel arm resonator P1 is closest to the antenna terminal 10, the power consumption of the interference wave is increased. Even if an IMD occurs in the other parallel arm resonators P2 and P3, it is greatly attenuated until it is transmitted to the reception filter unit 13. However, since the parallel arm resonator P1 is close to the reception filter unit 13, it does not attenuate so much. And transmitted to the reception filter unit 13.

  However, in this embodiment, among the plurality of parallel arm resonators P1 to P3, the resonance frequency of the first parallel arm resonator P1 closest to the antenna terminal 10 is the resonance frequency of the other parallel arm resonators P2 and P3. Is higher than. For this reason, generation | occurrence | production of IMD can be suppressed. Hereinafter, this effect will be described in detail based on specific examples.

  As a comparative example (first comparative example) of the elastic wave duplexer 1 of the present embodiment, as shown in FIG. 4, no capacitor is connected in parallel to the first parallel arm resonator P101 closest to the antenna terminal. Except for the above, an elastic wave duplexer 100 having substantially the same configuration as the elastic wave duplexer 1 is given. In the elastic wave duplexer 100, the resonance frequency of the first parallel arm resonator P101 is 864.8 MHz. The resonance frequency of the second parallel arm resonator is 866.5 MHz. The resonance frequency of the third parallel arm resonator is 865.0 MHz. For this reason, the 2nd parallel arm resonator has the highest resonance frequency among the 1st-3rd parallel arm resonators.

  A graph showing the reflection characteristic of the first parallel arm resonator P1 according to the present embodiment is shown by a solid line in FIG. A graph showing the reflection characteristic of the first parallel arm resonator P101 according to the first comparative example is shown by a broken line in FIG.

  FIG. 6 is a graph showing the IMD (solid line) of the elastic wave duplexer 1 according to the present embodiment and the IMD (broken line) of the elastic wave duplexer 100 according to the first comparative example. The IMD of each elastic wave duplexer has a constant difference between the frequency of the received signal and the frequency of the transmitted signal (45 MHz), and a difference between the frequency of the received signal and the frequency of the interference wave signal is also constant (90 MHz). Measurement was performed by changing the frequency of the received signal between 925 MHz and 960 MHz. For example, when the frequency of the reception signal is 925 MHz, the frequency of the transmission signal is 880 MHz, and the frequency of the interference wave signal is 835 MHz. For example, when the frequency of the reception signal is 960 MHz, the frequency of the transmission signal is 915 MHz, and the frequency of the interference wave signal is 870 MHz. In the IMD measurement, the power of the transmission signal at the antenna terminal was +21 dBm, and the power of the jamming signal at the antenna terminal was −15 dBm. And the balun was connected to the 1st and 2nd receiving side signal terminal, and IMD output from the balun was measured.

  FIG. 7 is a graph showing pass characteristics from the transmission-side signal terminal to the antenna terminal in the present embodiment and the first comparative example. FIG. 8 is a graph showing the pass characteristics from the antenna terminal to the reception-side signal terminal in the present embodiment and the first comparative example. FIG. 9 is a graph showing the isolation characteristic from the transmission side signal terminal to the reception side signal terminal in the present embodiment and the first comparative example.

  From the results shown in FIG. 5, the capacitor C1 is connected in parallel to the first parallel arm resonator P1 of this embodiment, so that the resonance frequency of the first parallel arm resonator P1 is the first of the first comparative example. It can be seen that the parallel arm resonator P101 can be shifted to a higher frequency side than the resonance frequency. Therefore, the resonance frequency of the first parallel arm resonator P1 is located near the upper end of the 2Tx-Rx band. In the 2Tx-Rx band, the reflection loss of the first parallel arm resonator P1 is smaller than the reflection loss of the first parallel arm resonator P101.

  Further, as shown in FIG. 6, the resonance frequency of the first parallel arm resonator P101 is shifted by a higher frequency in the elastic wave duplexer 1 in which the resonance frequency of the first parallel arm resonator P1 is shifted by a higher frequency. It can be seen that the IMD characteristics are improved in the high frequency side portion (about 950 MHz to 960 MHz) of the reception frequency band (925 MHz to 960 MHz) than the elastic wave duplexer 100 that is not.

  From this result, the IMD characteristic is improved without increasing the size of the elastic wave duplexer by making the resonance frequency of the first parallel arm resonator P1 higher than the resonance frequency of any of the other parallel arm resonators P2 and P3. I understand that I can do it. This is because in the 2Tx-Rx band, the power loss of the first parallel arm resonator P1 when an interference wave is input is reduced because the reflection loss of the first parallel arm resonator P1 is reduced. It is considered that the occurrence of IMD was suppressed.

  As shown in FIGS. 7 to 9, since the transmission characteristics are the same in this embodiment and the first comparative example, the capacitor C1 is provided to increase the resonance frequency of the first parallel arm resonator P1. It can be seen that the transmission characteristics do not deteriorate even when shifted to the frequency side.

  Hereinafter, other examples of preferred embodiments of the present invention will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second Embodiment)
FIG. 10 is a schematic plan view of the IDT electrode of the first parallel arm resonator P1 in the second embodiment.

  In the first embodiment, an example has been described in which the resonance frequency of the first parallel arm resonator P1 is shifted to the high frequency side by connecting the capacitor C1 in parallel to the first parallel arm resonator P1. However, in the present invention, the method for shifting the resonance frequency of the first parallel arm resonator to the high frequency side is not particularly limited.

  For example, the capacitor C1 is not provided, or the capacitor C1 is provided, and the IDT electrode of the first parallel arm resonator P1 is configured by the IDT electrode 50 subjected to thinning weighting as shown in FIG. The resonance frequency of one parallel arm resonator P1 may be shifted to the high frequency side. Even in that case, the occurrence of IMD can be suppressed as in the first embodiment.

  Furthermore, in this embodiment, since it is not necessary to provide the capacitor C1, it is possible to further reduce the size of the elastic wave duplexer compared to the first embodiment.

  Note that thinning weighting is a region in which elastic waves are not excited partially by removing part of the electrode fingers of at least one of the pair of comb-like electrodes constituting the IDT electrode. Is to form. However, when a part of the electrode finger is completely removed, the acoustic velocity of the elastic wave is reduced at that part. Therefore, usually, as shown in FIG. 10, a part of the electrode fingers of one comb-like electrode is cut off from the bus bar and connected to the bus bar of the other comb-like electrode.

(Third embodiment)
In this embodiment, the pitch of the electrode fingers of the IDT electrodes of the first parallel arm resonator P1 is made narrower than the pitch of the electrode fingers of the IDT electrodes of the other parallel arm resonators P2 and P3. An example in which the resonance frequency of the arm resonator P1 is set higher than the resonance frequencies of the other parallel arm resonators P2 and P3 will be described.

  Specifically, in this embodiment, the pitch of the electrode fingers of the IDT electrode of the first parallel arm resonator P1 is 2.237 μm, and the pitch of the electrode fingers of the IDT electrode of the second parallel arm resonator P2 is 2. .238 μm, the pitch of the electrode fingers of the IDT electrodes of the third parallel arm resonator P 3 is 2.244 μm, and the capacitor C 1 is not provided, and the configuration is substantially the same as the first embodiment. It has become. As shown in FIG. 11, in this embodiment, the resonance frequency of the first parallel arm resonator P1 is higher than the resonance frequencies of the other parallel arm resonators P2 and P3.

  As a comparative example (second comparative example) of the present embodiment, the electrode finger pitch of the IDT electrode of the first parallel arm resonator P1 is 2.242 μm, and the IDT electrode electrode of the second parallel arm resonator P2 is used. The finger pitch is 2.234 μm, the electrode finger pitch of the IDT electrode of the third parallel arm resonator P3 is 2.241 μm, and the first to third parallel arm resonators P1 to P1 are shown in FIG. The example which made the resonance frequency of the 2nd parallel arm resonator P2 the highest among P3 is given.

  FIG. 13 is a graph showing an IMD (solid line) of the elastic wave duplexer according to the third embodiment and an IMD (broken line) of the elastic wave duplexer according to the second comparative example. FIG. 14 is a graph showing insertion loss between the transmission-side signal terminal and the antenna terminal in the third embodiment and the second comparative example. FIG. 15 is a graph showing insertion loss between the antenna terminal and the reception-side signal terminal in the third embodiment and the second comparative example. FIG. 16 is a graph showing insertion loss between the transmission side signal terminal and the reception side signal terminal in the third embodiment and the second comparative example.

  As shown in FIG. 13, even when the resonance frequency of the first parallel arm resonator P1 is made higher than the resonance frequencies of the other parallel arm resonators P2 and P3 by adjusting the electrode finger pitch, It can be seen that IMD can be effectively suppressed as in the case of the first embodiment. In addition, from the results shown in FIGS. 14 to 16, the resonance frequency of the first parallel arm resonator P1 is made higher than the resonance frequencies of the other parallel arm resonators P2 and P3 by adjusting the electrode finger pitch. However, it can be seen that the transmission characteristics do not deteriorate.

  Similarly, by making the duty ratio of the IDT electrode of the first parallel arm resonator P1 smaller than the duty ratio of the IDT electrodes of the other parallel arm resonators P2 and P3, the resonance frequency of the first parallel arm resonator P1 Can be suppressed even if it is higher than the resonance frequency of the other parallel arm resonators P2 and P3. Further, the pitch of the electrode fingers of the IDT electrodes of the first parallel arm resonator P1 is made narrower than the pitch of the electrode fingers of the IDT electrodes of the other parallel arm resonators P2 and P3, and the first parallel arm resonator P1. By making the duty ratio of the IDT electrode of the other parallel arm resonators P2 and P3 smaller than the duty ratio of the IDT electrode of the other parallel arm resonators P2 and P3, the resonance frequency of the first parallel arm resonator P1 can be reduced. Even when the frequency is higher than the resonance frequency, the occurrence of IMD can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Elastic wave duplexer 10 ... Antenna terminal 11 ... Transmission side signal terminal 12a, 12b ... Reception side signal terminal 13 ... Reception filter part 20 ... Transmission filter part 21 ... Series arm 22a-22c ... Parallel arm 30 ... Surface acoustic wave resonator 40 ... boundary acoustic wave resonators 31, 41 ... piezoelectric substrate 32, 42 ... IDT electrode 43 ... first dielectric layer 44 ... second dielectric layer 50 ... IDT electrodes P1-P3 ... parallel arm resonators S1-S4 ... Series arm resonators L1 to L3 ... Inductors C1, C2 ... Capacitors

Claims (6)

An antenna terminal;
A transmission side signal terminal and a reception side signal terminal;
A transmission filter unit connected between the antenna terminal and the transmission-side signal terminal;
A receiving filter connected between the antenna terminal and the receiving signal terminal;
An elastic wave duplexer comprising:
The transmission filter unit
A series arm connecting the antenna terminal and the transmission side signal terminal;
A plurality of series arm resonators connected in series in the series arm;
A plurality of parallel arms connecting the series arm and a ground potential;
A parallel arm resonator provided in each of the plurality of parallel arms;
Have
An elastic wave duplexer in which a resonance frequency of a first parallel arm resonator closest to the antenna terminal among the plurality of parallel arm resonators is higher than a resonance frequency of other parallel arm resonators. Each of the plurality of parallel arm resonators includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate,
Whether the IDT electrodes of the first parallel arm resonators have electrode finger pitches narrower than the IDT electrodes of the parallel arm resonators other than the first parallel arm resonators of the plurality of parallel arm resonators. The elastic wave duplexer according to claim 1, wherein the duty ratio is small, or the pitch of the electrode fingers is narrow and the duty ratio is small. Each of the plurality of parallel arm resonators includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate,
The elastic wave duplexer according to claim 1 or 2, wherein thinning weighting is applied to an IDT electrode of the first parallel arm resonator.   The elastic wave duplexer according to any one of claims 1 to 3, wherein a capacitor is connected in parallel to the first parallel arm resonator. When the pass band of the transmission filter unit is f _Tx1 or more and f _Tx2 or less, and the pass band of the reception filter unit is f _Rx1 or more and f _Rx2 or less, the attenuation band in the vicinity of the low pass side of the pass band of the transmission filter unit is The elastic wave duplexer according to any one of claims 1 to 4, which is in a frequency band between 2f _Tx1 -f _Rx1 and 2f _Tx2 -f _Rx2 .   Each of the series arm resonator closest to the antenna terminal among the plurality of series arm resonators and the first parallel arm resonator is constituted by one elastic wave resonator. The elastic wave duplexer according to any one of 5 above.

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