JP2010109417A - Ladder type filter and duplexer with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ladder type filter high in steepness of passband upper-side filter characteristics and excelling in VSWR characteristics, and to provide a duplexer with the same. <P>SOLUTION: The ladder type filter includes: a plurality of serial arm resonators each having an IDT electrode 30; a parallel arm resonator arranged on a parallel arm 13; and capacitors C1, C2 connected in parallel to partial serial arm resonators S2a, S2b, S3c within the plurality of serial arm resonators. Cross-width weighting is applied to the IDT electrodes 30 of the serial arm resonators S2a, S2b, S3c with the capacitors C1, C2 connected in parallel thereto to form a plurality of maximum points maximizing the cross width in the elastic wave propagation direction. Cross-width weighting is applied to IDT electrodes 40 of serial arm resonators S1a, S1b, S2c, S3a, d3b to which no capacitor is connected in parallel thereto to form only one maximum point maximizing the cross width in the elastic wave propagation direction. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a ladder-type filter, and more particularly to a ladder-type filter having an acoustic wave resonator subjected to cross width weighting and a duplexer including the same.

  Conventionally, for example, in Patent Document 1 and Patent Document 2 below, it has been proposed to perform cross width weighting on a resonator having an IDT electrode. Specifically, Patent Document 1 discloses a resonator having a structure schematically shown in FIG. As shown in FIG. 12, the resonator 100 disclosed in Patent Document 1 is provided with an IDT electrode 101 constituted by a pair of comb electrodes interleaved with each other, and provided on both sides of the IDT electrode 101 in the surface acoustic wave propagation direction. Grating reflectors 102 and 103 are provided. In the resonator 100, the IDT electrode 101 is subjected to cross width weighting so that the cross width of the electrode finger 101a of the IDT electrode 101 increases from both sides in the surface acoustic wave propagation direction toward the center. In Patent Document 1, by applying such cross width weighting to the IDT electrode 101, spurious due to Rayleigh waves in the case of using the longitudinal mode, the transverse mode, and the Love wave type surface acoustic wave can be suppressed. It is described that the Q value can be increased.

  On the other hand, in Patent Document 2, when the cross width weighting is applied to the IDT electrode so that there is one maximum point as in the resonator 100 shown in FIG. 12, good resonance characteristics can be obtained, but the power durability is high. It has been pointed out that it tends to be low. In view of this problem, Patent Document 2 proposes that the IDT electrode is subjected to cross width weighting in which a plurality of maximum points appear.

FIG. 13 is a schematic plan view of a resonator disclosed in Patent Document 2. As shown in FIG. As shown in FIG. 13, in the resonator 200 disclosed in Patent Document 2, the IDT electrode 201 has a crossing width so that the crossing width of the electrode finger 201a of the IDT electrode 201 is maximum. Weighting is applied. As in the IDT electrode 201, by applying cross width weighting to the IDT electrode so that there are a plurality of maximum points, the Q value at the antiresonance frequency can be increased and the power durability can be improved.
Japanese Patent No. 2645674 WO2007 / 108269 A1

  In recent years, high frequency filters using resonators and the like have been used in portable information terminals that use a plurality of high frequency bands, such as mobile phone terminals, for the purpose of preventing data from intermingling. From the viewpoint of surely preventing data from being mixed, good frequency characteristics are also demanded for such a high-frequency filter. For this reason, it is also conceivable to configure a high-frequency filter using a resonator having an IDT electrode subjected to cross width weighting disclosed in Patent Document 1 and Patent Document 2 described above.

  However, for example, when a ladder-type filter is configured by using a resonator having a single maximum point or a plurality of resonators having a maximum point, high steepness of the filter characteristic on the high passband side and good VSWR characteristics It was difficult to achieve both.

  An object of the present invention is to provide a ladder type filter having a high steepness in the filter characteristics on the high side of the passband and a good VSWR characteristic, and a duplexer including the same.

  The ladder filter according to the present invention includes an input end, an output end, a plurality of series arm resonators, a parallel arm resonator, and a capacitor. The plurality of series arm resonators are connected in series with each other in a series arm connecting the input end and the output end. Each of the plurality of series arm resonators has an IDT electrode. The parallel arm resonator is provided on the parallel arm that connects the series arm and the ground potential. Each of the series arm resonator and the parallel arm resonator includes an elastic wave resonator. The capacitor is connected in parallel to a part of the plurality of series arm resonators. The IDT electrode of the series arm resonator to which the capacitors are connected in parallel is subjected to cross width weighting so that a plurality of maximum points where the cross width is maximum are formed in the elastic wave propagation direction. The IDT electrodes of the series arm resonators to which capacitors are not connected in parallel are subjected to cross width weighting so that only one local maximum point having a maximum cross width is formed in the elastic wave propagation direction.

  In a specific aspect of the ladder filter according to the present invention, the IDT electrode of the series arm resonator to which the capacitor is connected in parallel has two maximum points where the cross width is maximum in the elastic wave propagation direction. Cross width weighting is applied as described above.

  In another specific aspect of the ladder filter according to the present invention, the parallel arm resonator includes an IDT electrode, and the IDT electrode of the parallel arm resonator has a maximum crossing width that is maximum in the elastic wave propagation direction. Cross width weighting is applied so that only one point is formed. According to this configuration, when the IDT electrode of the parallel arm resonator is used as an IDT electrode that is subjected to cross width weighting so that a plurality of local maximum points having a maximum cross width are formed in the elastic wave propagation direction. As compared with, the VSWR characteristics in the receiving filter can be further improved.

  The duplexer according to the present invention includes the ladder filter according to the present invention.

  In a specific aspect of the duplexer according to the present invention, the duplexer further includes an antenna terminal, a transmission filter and a reception filter connected to the antenna terminal, and the transmission filter includes a ladder filter. According to this configuration, it is possible to improve the VSWR characteristic in the reception-side filter while enhancing the steepness of the filter characteristic on the high-pass band side on the transmission side.

  In the ladder filter according to the present invention, the IDT electrode of the series arm resonator to which the capacitors are connected in parallel has a crossing width so that a plurality of maximum points having a maximum crossing width are formed in the elastic wave propagation direction. The IDT electrodes of series arm resonators that are weighted but do not have capacitors connected in parallel have a crossover width so that only one local maximum point is formed in the elastic wave propagation direction. Since the weighting is performed, the steepness of the filter characteristic on the high passband side can be increased and the VSWR characteristic can be improved.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a circuit diagram of the duplexer of the present embodiment. As shown in FIG. 1, the duplexer 1 includes a transmission-side filter 11 mounted on the transmission-side filter chip 20 and a reception-side filter 12 mounted on the reception-side filter chip 21. The reception-side filter 12 is provided between the antenna terminal 10 and the first and second reception-side signal terminals 18a and 18b. On the other hand, the transmission filter 11 is provided between the antenna terminal 10 and the transmission signal terminal 17.

  The transmission-side filter 11 includes an input end 15 connected to the antenna terminal 10 and an output end 16 connected to the transmission-side signal terminal 17. The input end 15 and the output end 16 are connected by a series arm 9. The series arm 9 is provided with a plurality of series arm resonators S1 to S3 connected in series with each other. Each series arm resonator S1 to S3 includes one series arm resonator or a plurality of series arm resonators connected in series with each other. That is, the series arm 9 is provided with a plurality of series arm resonators connected in series with each other. This series arm resonator is an elastic wave resonator.

  Specifically, in the present embodiment, the first series arm resonator S1 directly connected to the input end 15 is configured by two series arm resonators S1a and S1b connected in series with each other. . A capacitor is not connected in parallel to the series arm resonators S1a and S1b.

  The second series arm resonator S2 connected to the subsequent stage of the first series arm resonator S1 includes three series arm resonators S2a to S2c connected in series. A capacitor C1 is connected in parallel to the series arm resonators S2a and S2b among the three series arm resonators S2a to S2c constituting the second series arm resonator S2. On the other hand, no capacitor is connected in parallel to the series arm resonator S2c.

  The third series arm resonator S3 connected between the second series arm resonator S2 and the output end 16 is constituted by three series arm resonators S3a to S3c connected in series with each other. Yes. A capacitor is not connected in parallel to the series arm resonators S3a and S3b among the three series arm resonators S3a to S3c constituting the third series arm resonator S3. On the other hand, a capacitor C2 is connected in parallel to the series arm resonator S3c. An inductor L5 is further connected in parallel to the series arm resonator S3c.

  At least one parallel arm is connected between the series arm 9 and the ground potential. Specifically, in the present embodiment, a plurality of parallel arms 13a to 13c are connected between the series arm 9 and the ground potential.

  Parallel arm resonators P1 to P3 are provided in each of the plurality of parallel arms 13a to 13c. Each parallel arm resonator P <b> 1 to P <b> 3 includes one parallel arm resonator or a plurality of parallel arm resonators connected in series to each other. This parallel arm resonator is an elastic wave resonator.

  Specifically, the first parallel arm 13a is connected between a connection point between the first series arm resonator S1 and the second series arm resonator S2 and the ground potential. The first parallel arm 13a is provided with a first parallel arm resonator P1 and an inductor L1 that are connected in series with each other. The first parallel arm resonator P1 is composed of two parallel arm resonators P1a and P1b connected in series with each other.

  On the other hand, the second parallel arm 13b is connected between a connection point between the second series arm resonator S2 and the third series arm resonator S3 and the ground potential. The second parallel arm 13b is provided with a second parallel arm resonator P2 and an inductor L2 that are connected in series with each other. The second parallel arm resonator P2 is composed of two parallel arm resonators P2a and P2b connected in series with each other.

  The first parallel arm 13a and the second parallel arm 13b are connected to each other and connected to the ground potential via the inductor L3. Note that each of the inductor L3 and the inductors L1, L2, L4, and L5 may be constituted by an inductance component obtained by a wiring pattern or a coil pattern, or may be constituted by separate inductor chips.

  The third parallel arm 13c is connected between a connection point between the third series arm resonator S3 and the output terminal 16 and the ground potential. The third parallel arm 13c is provided with a third parallel arm resonator P3 and an inductor L4 that are connected in series with each other. The third parallel arm resonator P3 includes two parallel arm resonators P3a and P3b connected in series with each other.

  The feature of this embodiment is that each of the plurality of series arm resonators S1a, S1b, S2a to S2c, S3a to S3c has an IDT electrode, and the series arm resonators S2a and S2b in which capacitors are connected in parallel. In S3c, cross width weighting is performed so that a plurality of local maximum points are formed in the IDT electrode, and in the series arm resonators S1a, S1b, S2c, S3a, S3b in which capacitors are not connected in parallel, Cross width weighting is performed so that only one local maximum point is formed on the IDT electrode. In the following description, series arm resonators S2a, S2b, and S3c to which capacitors C1 or C2 are connected in parallel are collectively referred to as series arm resonators Sx, and series arm resonators S1a in which no capacitors are connected in parallel are used. , S1b, S2c, S3a, and S3b are collectively referred to as a series arm resonator Sy.

  The capacitor of the present embodiment may be a capacitor composed of a pair of comb-tooth electrodes formed on a piezoelectric substrate, or a capacitor composed of a pair of capacitance extraction electrodes formed on a piezoelectric substrate. Alternatively, an external capacitor may be used.

FIG. 2 is a schematic plan view of a series arm resonator Sx in which capacitors are connected in parallel, and FIG. 3 is a schematic cross-sectional view of a part of the series arm resonator Sx along the elastic wave propagation direction. As shown in FIG. 3, the series arm resonator Sx includes a piezoelectric substrate 35, an electrode 36, an intermediate film 37, and an upper layer film 38. The piezoelectric substrate 35 is configured by a substrate made of an appropriate piezoelectric material such as LiNbO ₃ or LiTaO ₃ . The piezoelectric substrate 35 can be composed of, for example, a LiNbO ₃ substrate having a cut angle of 126.0 °.

  The electrode 36 is formed on the piezoelectric substrate 35. The electrode 36 constitutes an IDT electrode 30 and first and second grating reflectors 31 and 32 described later. The electrode 36 can be made of an appropriate electrode material such as Al, Pt, Au, or Cu. The electrode 36 can also be configured by a conductive film stack in which a plurality of conductive films are stacked. For example, the electrode 36 can be configured by a laminated film in which a NiCr film, a Pt film, a Ti film, an Al film, and a Ti film are laminated in this order from the piezoelectric substrate 35 side.

An intermediate film 37 is formed on the portion of the upper surface of the piezoelectric substrate 35 where the electrode 36 is not formed. The upper surface of the intermediate film 37 and the upper surface of the electrode 36 are substantially flush. By this intermediate film 37, the upper surface of the piezoelectric substrate 35 on which the electrode 36 is formed is made flat. The intermediate film 37 can be formed of an appropriate insulating material such as SiO ₂ or SiN.

The electrode 36 and the intermediate film 37 are covered with an upper film 38. The upper layer film 38 can be formed of an appropriate insulating material such as SiO ₂ or SiN. Further, the upper layer film 38 may be composed of a stacked body of a plurality of insulating films. The upper layer film 38 can be constituted by, for example, a stacked body of insulating films in which a SiO ₂ film and a SiN film are stacked in this order from the piezoelectric substrate 35 side. Note that the upper layer film 38 is preferably formed of a material having frequency temperature characteristics opposite to the frequency temperature characteristics of the piezoelectric substrate 35. According to this configuration, the frequency temperature characteristic of the series arm resonator Sx can be improved.

  As shown in FIG. 2, the series arm resonator Sx includes an IDT electrode 30 formed by an electrode 36, and first and second grating reflectors 31 and 32. The first and second grating reflectors 31 and 32 are disposed on both sides of the IDT electrode 30 in the elastic wave propagation direction. In the present embodiment, the series arm resonator Sx is a resonator using a surface acoustic wave excited by the IDT electrode 30. However, the series arm resonator Sx may be a resonator using an elastic wave other than the surface acoustic wave, for example, a boundary acoustic wave.

  The IDT electrode 30 includes first and second comb electrodes 33 and 34. Each of the first and second comb electrodes 33 and 34 includes a plurality of electrode fingers 33a and 34a extending in parallel with each other. The plurality of electrode fingers 33a and the plurality of electrode fingers 34a are interleaved with each other.

  In this embodiment, the IDT electrode 30 is subjected to cross width weighting so that a plurality of maximum points where the cross widths of the electrode fingers 33a and the electrode fingers 34a are maximum are formed in the surface acoustic wave propagation direction. . Specifically, the IDT electrode 30 is subjected to cross width weighting so that two maximum points where the cross width is maximum are formed in the surface acoustic wave propagation direction. Therefore, the first envelope A, which is a virtual line formed by connecting the tips of the plurality of electrode fingers 34a, and the second virtual line formed by connecting the tips of the plurality of electrode fingers 33a. Each of the envelopes B includes first peak portions A1 and B1 and second peak portions A2 and B2 that protrude toward the tip side of the electrode fingers. The crossing region H1 surrounded by the first and second envelopes A and B has a shape in which two substantially rhombic regions are connected. The first and second envelopes A and B may be in contact with each other or may be isolated from each other as shown in FIG.

  FIG. 4 shows a schematic plan view of a series arm resonator Sy with no capacitors connected in parallel. The series arm resonator Sy has substantially the same configuration as the series arm resonator Sx except for the applied cross width weighting. Therefore, members having substantially the same function as the constituent members of the series arm resonator Sx are referred to by the same reference numerals, and description thereof is omitted. In the description of the series arm resonator Sy, FIG. 3 is commonly referred to.

  Similarly to the series arm resonator Sx in which the capacitor is connected in parallel, the series arm resonator Sy in which the capacitor is not connected in parallel also has the piezoelectric substrate 35, the electrode 36, the intermediate film 37, and the upper layer film 38. It has.

  As shown in FIG. 4, the series arm resonator Sy includes the IDT electrode 40 constituted by the electrode 36 shown in FIG. 3, and the first and the first provided on both sides of the IDT electrode 40 in the surface acoustic wave propagation direction. 2 grating reflectors 41 and 42. In the present embodiment, the series arm resonator Sy is a resonator that uses a surface acoustic wave excited by the IDT electrode 40. However, the series arm resonator Sy may be a resonator using an elastic wave other than the surface acoustic wave, for example, a boundary acoustic wave.

  The IDT electrode 40 includes first and second comb electrodes 43 and 44. Each of the first and second comb electrodes 43 and 44 includes a plurality of electrode fingers 43a and 44a extending in parallel to each other. The plurality of electrode fingers 43a and the plurality of electrode fingers 44a are interleaved with each other.

  In this embodiment, the IDT electrode 40 is subjected to cross width weighting so that only one local maximum point where the cross width between the electrode finger 43a and the electrode finger 44a is maximum is formed in the surface acoustic wave propagation direction. Yes. Therefore, the third envelope C, which is a virtual line formed by connecting the tips of the plurality of electrode fingers 44a, and the fourth line, which is a virtual line formed by connecting the tips of the plurality of electrode fingers 43a. Each of the envelope lines D includes only one peak portion protruding toward the tip side of the electrode finger. And the crossing area | region H2 enclosed by the 3rd and 4th envelopes C and D is a substantially rhombus-shaped area | region. The third and fourth envelopes C and D may be in contact with each other or may be separated from each other as shown in FIG.

  In the present embodiment, the configuration of the parallel arm resonator is not particularly limited. For example, the parallel arm resonator can be configured by an appropriate resonator having an IDT electrode. However, as schematically shown in FIG. 5, the parallel arm resonator is subjected to cross width weighting so that only one local maximum point is formed in the same manner as the series arm resonator Sy in which no capacitor is connected in parallel. The IDT electrode 50 and the first and second grating reflectors 51 and 52 disposed on both sides of the IDT electrode 50 in the surface acoustic wave propagation direction are preferable.

  As described above, in this embodiment, the IDT electrode 30 of the series arm resonator Sx to which the capacitor C1 or C2 is connected in parallel is connected to the electrode finger 33a and the electrode finger 34a in the surface acoustic wave propagation direction. Cross width weighting is performed so that a plurality of maximum points where the cross width becomes maximum is formed, while the IDT electrode 40 of the series arm resonator Sy having no capacitor connected in parallel has a surface acoustic wave propagation direction. , The cross width weighting is performed so that only one maximum point where the cross width between the electrode finger 43a and the electrode finger 44a is maximum is formed. For this reason, as is also supported in the following embodiments, the steepness of the filter characteristics on the high passband side can be improved and the VSWR characteristics can be improved.

  In the present embodiment, the IDT electrode of the parallel arm resonator is also subjected to the cross width weighting so that only one local maximum point having the maximum cross width is formed, similarly to the IDT electrode 40 of the series arm resonator Sy. It has been subjected. Therefore, the IDT electrode of the parallel arm resonator is compared with the case where an IDT electrode weighted so as to form a plurality of maximum points where the cross width is maximum in the elastic wave propagation direction is used. Thus, the VSWR characteristic in the receiving filter 12 can be further improved.

  Hereinafter, the effects of the present embodiment will be described in more detail using specific examples.

(Example)
The duplexer 1 having the configuration shown in FIGS. 1 to 5 is manufactured with the following design parameters. The insertion loss in the transmission side filter 11, the VSWR characteristic on the antenna terminal 10 side, and the VSWR characteristic on the transmission side signal terminal 17 side Each was measured.

Piezoelectric substrate: LiNbO ₃ substrate with a cut angle of 126.0 ° Intermediate film: SiO ₂ film with a thickness of 170 nm Electrode 36: NiCr film (thickness: 10 nm) / Pt film (thickness: 40 nm) / Ti film (thickness: 10 nm) / Al film (thickness: 80 nm) / Ti film (thickness: 10 nm)
Upper layer film 38: From the piezoelectric substrate side, SiO ₂ film (thickness 500 nm) / SiN film (thickness: 30 nm)
Capacitor C1 capacitance: 0.75 pF
Capacitor C2 capacitance: 2.90 pF
Inductance value of the inductor L5: 1.15 nH

  The design parameters of each resonator of the transmission filter 11 were set as shown in Table 1 below. Further, the cross width weighting was performed on all the resonators of the transmission filter 11 so that the minimum cross width / the maximum cross width = 0.2. A resonator having a maximum cross width has a maximum cross width at the center of the IDT electrode in the surface acoustic wave propagation direction and a minimum at both ends. In addition, the crossing width was changed linearly in the surface acoustic wave propagation direction.

  In the resonator having two cross-point maximum points, the cross-width is minimized at the center and both ends in the surface acoustic wave propagation direction of the IDT electrode, and is maximized at a quarter of both ends. In addition, the crossing width was changed linearly in the surface acoustic wave propagation direction.

(Comparative Example 1)
Cross width weighting is applied to all the resonators of the transmission filter 11 so that only one maximum point is formed in which the cross width between the electrode finger 43a and the electrode finger 44a is maximum in the surface acoustic wave propagation direction. In addition, a duplexer having the same configuration as that of the above example except for the capacitances of the capacitors C1 and C2 and the inductance value of the inductor L5 is manufactured as Comparative Example 1, and the insertion loss in the transmission filter 11 and the VSWR on the antenna terminal 10 side are manufactured. Each of the characteristics and the VSWR characteristics on the transmission side signal terminal 17 side were measured. A measurement result is shown in FIGS. 6-8 with the measurement result of an Example.

(Comparative Example 2)
Cross width weighting is applied to all resonators of the transmission filter 11 so that two local maximum points are formed in the direction of surface acoustic wave propagation where the cross widths of the electrode fingers 43a and 44a are maximum. Except for this, a duplexer having the same configuration as that of the above embodiment is manufactured as Comparative Example 2, and the insertion loss in the transmission side filter 11, the VSWR characteristic on the antenna terminal 10 side, and the VSWR characteristic on the transmission side signal terminal 17 side Each was measured. A measurement result is shown in FIGS. 9-11 with the measurement result of an Example.

  Note that the capacitances of the capacitors C1 and C2 and the inductance value of the inductor L5 in Comparative Example 1 are as follows.

Capacitor C1 capacitance: 0.85 pF
Capacitor C2 capacitance: 3.00 pF
Inductance value of the inductor L5: 1.15 nH

  The capacitances of the capacitors C1 and C2 and the inductance value of the inductor L5 in Comparative Example 2 were the same as the capacitances of the capacitors C1 and C2 and the inductance value of the inductor L5 in the example.

  As can be seen from the results shown in FIG. 6, two cross width weights are applied to the resonators to which the capacitors are connected in parallel, while the resonators to which the capacitors are not connected in parallel have the maximum points. The embodiment in which one cross width weighting is applied is steeper in the filter characteristics on the higher passband side than the comparative example 1 in which all resonators are subjected to one cross width weighting with a maximum point. Was high. Specifically, in the frequency band from 1.91 GHz to 1.94 GHz, the frequency interval from the insertion loss of 3.5 dB to 45 dB with respect to the through level of the filter characteristics was 11.6 MHz in Comparative Example 1. On the other hand, in the example, it was 10.6 MHz and 1 MHz smaller. Regarding the VSWR characteristics in the Tx band (1.85 GHz to 1.91 GHz), as can be seen from the results shown in FIG. 7 and FIG. 8, the example and the comparative example 1 were almost the same.

  Further, as can be seen from the results shown in FIG. 9, the steepness of the filter characteristics on the high side of the passband was almost the same in the example and the comparative example 2. Specifically, in the frequency band of 1.91 GHz to 1.94 GHz, the frequency interval from the insertion loss of 3.5 dB to 45 dB with respect to the through level of the filter characteristics is 10.6 MHz in the embodiment. In Comparative Example 2, the frequency was 10.8 MHz. Regarding the VSWR characteristics in the Tx band (1.85 GHz to 1.91 GHz), as can be seen from the results shown in FIG. 10 and FIG. 11, the VSWR characteristics are much higher in the example than in the comparative example 2. I understand.

  From these results, a resonator with a capacitor connected in parallel is weighted with two cross widths, while a resonator without a capacitor connected in parallel is weighted with one cross width. Thus, it is understood that the steepness of the filter characteristic on the high pass band side can be improved without degrading the VSWR characteristic.

  In the above-described embodiment, an example in which the cross point weighting of two maximum points is applied to the IDT electrode 30 of the series arm resonator Sx has been described. However, in the present invention, the cross width weighting applied to the IDT electrode 30 is not particularly limited as long as the weighting is such that a plurality of maximum points are formed. For example, the IDT electrode 30 of the series arm resonator Sx may be subjected to cross width weighting having three or more maximum points.

  Each envelope may be constituted by at least one of one or more curved portions and one or more straight portions.

It is an equivalent circuit diagram of the duplexer according to the embodiment. It is a schematic plan view of a series arm resonator in which capacitors are connected in parallel. FIG. 2 is a schematic cross-sectional view of a series arm resonator in which capacitors are connected in parallel. It is a schematic plan view of a series arm resonator in which capacitors are not connected in parallel. It is a schematic plan view of a parallel arm resonator. It is a graph showing the insertion loss of the transmission side filter in an Example and the comparative example 1. FIG. 6 is a graph showing VSWR characteristics on the antenna terminal side in Examples and Comparative Example 1. 6 is a graph showing VSWR characteristics on the transmission side signal terminal side in Examples and Comparative Example 1. It is a graph showing the insertion loss of the transmission side filter in an Example and the comparative example 2. FIG. It is a graph showing the VSWR characteristic by the side of the antenna terminal in an Example and the comparative example 2. FIG. It is a graph showing the VSWR characteristic by the side of the transmission side signal terminal in an Example and the comparative example 2. FIG. 2 is a schematic plan view of a resonator disclosed in Patent Document 1. FIG. 10 is a schematic plan view of a resonator disclosed in Patent Document 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Duplexer 9 ... Series arm 10 ... Antenna terminal 11 ... Transmission side filter 12 ... Reception side filter 13a ... 1st parallel arm 13b ... 2nd parallel arm 13c ... 3rd parallel arm 15 ... Input end 16 ... Output end 17 ... Transmission side signal terminals 18a, 18b ... Reception side signal terminals S1-S3 ... Series arm resonators P1-P3 ... Parallel arm resonators S1a, S1b, S2a, S2b, S2c, S3a, S3b, S3c ... Series arm resonators P1a, P1b, P2a, P2b, P3a, P3b ... Parallel arm resonators C1 and C2 ... Capacitors P1 to P5 ... Inductors H1 and H2 ... Crossover areas A to D ... Envelope 20 ... Transmission filter chip 21 ... Reception filter chip 30 ... IDT electrodes 31, 32 ... grating reflectors 33, 34 ... comb electrodes 33a, 34a ... electrode fingers 35 ... piezoelectric substrate 36 ... electrode 37 ... intermediate film 38 ... Layer film 40 ... IDT electrodes 41 and 42 ... grating reflectors 43 and 44 ... comb electrodes 43a, 44a ... electrode finger 50 ... IDT electrodes 51, 52 ... grating reflectors

Claims (5)

An input end;
An output end;
A plurality of series arm resonators each having an IDT electrode, which are connected in series with each other in a series arm connecting the input end and the output end;
A parallel arm resonator provided on a parallel arm connecting the series arm and a ground potential;
A capacitor connected in parallel to some series arm resonators of the plurality of series arm resonators,
Each of the series arm resonator and the parallel arm resonator comprises an acoustic wave resonator,
The IDT electrode of the series arm resonator to which the capacitor is connected in parallel is subjected to cross width weighting so that a plurality of maximum points where the cross width is maximum are formed in the elastic wave propagation direction,
The IDT electrodes of the series arm resonators to which the capacitors are not connected in parallel are subjected to cross width weighting so that only one local maximum point having a maximum cross width is formed in the elastic wave propagation direction. Ladder type filter.   The IDT electrode of the series arm resonator to which the capacitor is connected in parallel is subjected to cross width weighting so that two maximum points where the cross width is maximum are formed in the elastic wave propagation direction. The ladder type filter according to claim 1.   The parallel arm resonator has an IDT electrode, and the IDT electrode of the parallel arm resonator has a cross width weighting so that only one local maximum point having a maximum cross width is formed in the elastic wave propagation direction. The ladder filter according to claim 1 or 2, wherein the ladder filter is applied.   A duplexer comprising the ladder type filter according to any one of claims 1 to 3.   The duplexer according to claim 4, further comprising: an antenna terminal; and a transmission-side filter and a reception-side filter connected to the antenna terminal, wherein the transmission-side filter includes the ladder type filter.

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