Acoustic wave filter, duplexer, communication module, and communication apparatus

In an acoustic wave filter, a notch resonator is connected in series or parallel with a plurality of acoustic wave resonators connected in a ladder shape. The notch resonator has a main resonant frequency that is substantially equal to a sub-resonant frequency of the acoustic wave resonators. With this configuration, the occurrence of sub-resonant responses in filter characteristics can be suppressed, resulting in an improvement in communication characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-281959 filed on Oct. 31, 2008, the entire contents of which are incorporated herein by reference.

FIELD

The embodiment disclosed in the present application relates to an acoustic wave filter, a duplexer, a communication module, and a communication apparatus.

BACKGROUND

A high frequency circuit for mobile phones is provided with a filter or a duplexer. The filter or the duplexer often includes acoustic wave resonators such as a surface acoustic wave resonator, a love wave resonator, a boundary acoustic wave resonator, and a film bulk acoustic resonator.

FIG. 1Ais a plan view schematically illustrating an exemplary structure of the surface acoustic wave resonator.FIG. 1Bis a cross-sectional view taken along a line Z-Z inFIG. 1A. In the surface acoustic wave resonator illustrated inFIGS. 1A and 1B, a pair of comb-shaped electrodes102are formed on a surface of a piezoelectric substrate101. On both sides of the comb-shaped electrodes102, grating reflectors103aand103bare provided.

FIG. 2Ais a plan view schematically illustrating an exemplary structure of the love wave resonator.FIG. 2Bis a cross-sectional view taken along a line Z-Z inFIG. 2A. The love wave resonator illustrated inFIGS. 2A and 2Bis obtained by depositing a first dielectric104on the surface acoustic wave resonator including the piezoelectric substrate101, the comb-shaped electrodes102, and the grating reflectors103aand103b.Patent Document 1 (JP 2004-112748 A) discloses the love wave resonator as illustrated inFIGS. 2A and 2B.

FIG. 3Ais a plan view schematically illustrating an exemplary structure of the boundary acoustic wave resonator.FIG. 3Bis a cross-sectional view taken along a line Z-Z inFIG. 3A. The boundary acoustic wave resonator illustrated inFIGS. 3A and 3Bis obtained by depositing the first dielectric104and a second dielectric105on the surface acoustic wave resonator including the piezoelectric substrate101, the comb-shaped electrodes102, and the grating reflectors103aand103b.Patent Document 2 (JP 10(1998)-549008 A) discloses the boundary acoustic wave resonator as illustrated inFIGS. 3A and 3B.

FIG. 4Ais a plan view schematically illustrating an exemplary structure of the film bulk acoustic resonator.FIG. 4Bis a cross-sectional view taken along a line Z-Z inFIG. 4A. In the film bulk acoustic resonator illustrated inFIGS. 4A and 4B, an upper electrode202, a lower electrode203, and a piezoelectric film204are formed on a substrate201. The piezoelectric film204is sandwiched between the upper electrode202and the lower electrode203. An excitation portion206is a region where the upper electrode202and the lower electrode203face each other. A through hole205, an air gap, and the like are provided below the excitation portion206.

FIG. 5illustrates exemplary admittance characteristics of the acoustic wave resonators illustrated inFIGS. 1 to 4in the vicinity of a main resonant frequency. The acoustic wave resonators illustrated inFIGS. 1 to 4have double resonance characteristics with a main resonant frequency (fr0) and a main antiresonant frequency (fa0). The main resonant frequency (fr0) and the main antiresonant frequency (fa0) have values close to each other.

FIG. 6Ais a circuit diagram of a ladder-type filter in which any of the acoustic wave resonators illustrated inFIGS. 1 to 4are connected in a ladder shape. Connecting acoustic wave resonators300in a ladder shape as illustrated inFIG. 6achieves a ladder-type filter having bandpass characteristics in which high frequency components and low frequency components are suppressed as illustrated inFIG. 6B.

FIG. 7illustrates the principle on which the bandpass characteristics of the ladder-type filter are obtained. InFIG. 7, a solid line indicates the bandpass characteristics obtained when the acoustic wave resonator alone is connected in series (hereinafter, referred to as a series resonator). The series resonator forms a low pass filter having a turnover frequency between a resonant frequency (frs) and an antiresonant frequency (fas). InFIG. 7, a dashed line indicates the bandpass characteristics obtained when the acoustic wave resonator alone is connected in parallel (hereinafter, referred to as a parallel resonator). The parallel resonator forms a high pass filter having a turnover frequency between a resonant frequency (frp) and an antiresonant frequency (fap). The resonant frequency (frs) of the series resonator and the antiresonant frequency (fap) of the parallel resonator are set to be substantially equal to each other. The ladder-type filter, which includes the series resonators and the parallel resonators, has the bandpass characteristics as illustrated inFIG. 6Bas a result that the characteristics indicated by the solid line and the characteristics indicated by the dashed line inFIG. 7are synthesized.

Since the resonance phenomena of the acoustic wave resonator occur due to mechanical vibrations, they often include not only main resonance (main antiresonance) but also several kinds of sub-resonance (sub-antiresonance) corresponding to various vibration modes.

FIG. 8illustrates exemplary admittance characteristics of the acoustic wave resonator.FIG. 8illustrates frequency characteristics in a wide frequency band including sub-resonant frequencies. As illustrated inFIG. 8, in a frequency band away from the main resonant frequency (fr0) and the main antiresonant frequency (fa0), a sub-resonant frequency (fr1) and a sub-antiresonant frequency (fa1) exist. Further, in a frequency band away from the sub-resonant frequency (fr1) and the sub-antiresonant frequency (fa1), a sub-resonant frequency (fr2) and a sub-antiresonant frequency (fa2) exist. The number of occurrences of the sub-resonance (sub-antiresonance) varies depending on the type of the acoustic wave resonator. Further, a frequency interval between the sub-resonance and the main resonance varies depending on the type of the acoustic wave resonator. Even in the acoustic wave resonators of the same type, however, the number of occurrences of the sub-resonance (sub-antiresonance) and the frequency interval between the sub-resonance and the main resonance may vary depending on the material, film thickness, and the like of the acoustic wave resonator.

As described above, since the acoustic wave resonator produces the sub-resonance, the filter using the acoustic wave resonators accordingly has passbands formed based on the sub-resonance.

FIG. 9illustrates exemplary bandpass characteristics of the ladder-type filter using the acoustic wave resonators in a wide frequency band. As illustrated inFIG. 9, the ladder-type filter using the acoustic wave resonators has not only a main passband (referred to as a main resonant response) formed due to the main resonance, but also passbands (referred to as sub-resonant responses) formed due to the sub-resonance. While the acoustic wave resonator generally is specified to suppress frequency components in frequency bands other than the main passband formed due to the main resonance (hereinafter, referred to as suppression specifications), the suppression specifications may not be met due to the sub-resonant responses as illustrated inFIG. 9.

SUMMARY

An acoustic wave filter disclosed in the present application includes acoustic wave resonators. The filter includes a notch resonator connected in series or parallel with the acoustic wave resonators. The notch resonator has a main resonant frequency that is substantially equal to a sub-resonant frequency of the acoustic wave resonators.

Additional objects and advantages of the invention (embodiment) will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

DESCRIPTION OF EMBODIMENT(S)

A duplexer disclosed in the present application includes: an antenna terminal connected to an antenna; a reception circuit that is connected to the antenna terminal and receives a reception signal from the antenna via the antenna terminal; a transmission circuit that is connected to the antenna terminal and transmits a transmission signal to the antenna via the antenna terminal; and a notch resonator connected to the antenna terminal. The reception circuit and the transmission circuit have acoustic wave resonators, and the notch resonator has a main resonant frequency that is substantially equal to a sub-resonant frequency of the acoustic wave resonators.

A communication module disclosed in the present application includes the above-described acoustic wave filter or the above-described duplexer. In the acoustic wave filter, the acoustic wave resonators can be connected in a ladder shape. In the acoustic wave filter, the notch resonator can be connected in series to an input terminal or an output terminal. In the acoustic wave filter, the notch resonator can be connected in parallel to an input terminal or an output terminal. In the duplexer, the notch resonator can be connected in parallel to the antenna terminal.

Configuration of an acoustic wave filter

An acoustic wave filter according to the present embodiment is characterized by connecting a notch resonator, thereby suppressing sub-resonant responses. The notch resonator is an acoustic wave resonator that resonates at a main resonant frequency or a main antiresonant frequency. The main resonant frequency or the main antiresonant frequency is substantially equal to a sub-resonant frequency or a sub-antiresonant frequency of acoustic wave resonators included in the acoustic wave filter.

For ease of explanation of the principle, a description will be given of a filter that uses acoustic wave resonators having only one frequency band in which sub-resonance occurs.

FIG. 10Ais a circuit diagram of a ladder-type filter in which a plurality of acoustic wave resonators1are connected in a ladder shape.FIG. 10Bis a circuit diagram of a series notch resonator2.FIG. 10Cillustrates exemplary bandpass characteristics of the ladder-type filter and the series notch resonator in a wide frequency band. InFIG. 10C, a solid line indicates the bandpass characteristics of the ladder-type filter, and a dashed line indicates the bandpass characteristics of the series notch resonator.FIG. 11Ais a circuit diagram of a ladder-type filter obtained by connecting the series notch resonator illustrated inFIG. 10Bto the ladder-type filter illustrated inFIG. 10A.FIG. 11Billustrates bandpass characteristics of a conventional ladder-type filter and the ladder-type filter illustrated inFIG. 11A. InFIG. 11B, a solid line indicates the bandpass characteristics of the conventional ladder-type filter, and a dashed line indicates the bandpass characteristics of the ladder-type filter illustrated inFIG. 11A.

As illustrated inFIG. 10C, the series notch resonator2illustrated inFIG. 10Bhas a main antiresonant frequency that is set close to a sub-resonant response frequency of the ladder-type filter illustrated inFIG. 10A. A surface acoustic wave resonator, a love wave resonator, or a boundary acoustic wave resonator used as the series notch resonator2has a main resonant frequency and a main antiresonant frequency that can be adjusted according to the film thickness, width, period, and the like of a comb-shaped electrode. Further, a film bulk acoustic resonator has a main resonant frequency and a main antiresonant frequency that can be adjusted according to the film thickness and the like of an upper electrode, a lower electrode, and a piezoelectric film.

For example,FIG. 11Aillustrates a ladder-type filter obtained by connecting the series notch resonator2illustrated inFIG. 10Bto an output terminal3of the ladder-type filter illustrated inFIG. 10A. The ladder-type filter illustrated inFIG. 11Ahas its sub-resonant response suppressed as shown in the bandpass characteristics indicated by the dashed line inFIG. 11B. As indicated by A inFIG. 11B, the suppression characteristics (dashed line) of the series notch resonator2vary slightly in the vicinity of a sub-resonant frequency and a sub-antiresonant frequency as compared with the characteristics (solid line) of the ladder-type filter in which the series notch resonator2is not connected. However, the variation in the suppression characteristics indicated by A is so small that it has no adverse effect on the performance of the filter. Note here that an input/output impedance of the filter may be shifted by connecting the series notch resonator2to the ladder-type filter. Thus, in order to allow the filter to have an input/output impedance of a desired value, it is preferable to adjust a capacitance or the like of the acoustic wave resonators1included in the filter.

FIG. 12Ais a circuit diagram of a ladder-type filter in which the plurality of acoustic wave resonators1are connected in a ladder shape.FIG. 12Bis a circuit diagram of a parallel notch resonator12.FIG. 12Cillustrates exemplary bandpass characteristics of the ladder-type filter and the parallel notch resonator in a wide frequency band. InFIG. 12C, a solid line indicates the bandpass characteristics of the ladder-type filter, and a dashed line indicates the bandpass characteristics of the parallel notch resonator.FIG. 13Ais a circuit diagram of a ladder-type filter obtained by connecting the parallel notch resonator12illustrated inFIG. 12Bto the ladder-type filter illustrated inFIG. 12A.FIG. 13Billustrates bandpass characteristics of a conventional ladder-type filter and the ladder-type filter illustrated inFIG. 13A. InFIG. 13B, a solid line indicates the bandpass characteristics of the conventional ladder-type filter, and a dashed line indicates the bandpass characteristics of the ladder-type filter illustrated inFIG. 13A.

As illustrated inFIG. 12C, the parallel notch resonator12illustrated inFIG. 12Bhas a main resonant frequency that is set close to a sub-resonant response frequency of the ladder-type filter illustrated inFIG. 12A. A surface acoustic wave resonator, a love wave resonator, or a boundary acoustic wave resonator used as the parallel notch resonator12has a main resonant frequency and a main antiresonant frequency that can be adjusted according to the film thickness, width, period, and the like of a comb-shaped electrode. Further, a film bulk acoustic resonator has a main resonant frequency and a main antiresonant frequency that can be adjusted according to the film thickness and the like of an upper electrode, a lower electrode, and a piezoelectric film.

For example,FIG. 13Aillustrates a ladder-type filter obtained by connecting the parallel notch resonator12illustrated inFIG. 12Bto an output terminal3of the ladder-type filter illustrated inFIG. 12A. The ladder-type filter illustrated inFIG. 13Ahas its sub-resonant response suppressed as shown in the bandpass characteristics indicated by the dashed line inFIG. 13B. As indicated by B inFIG. 13B, the suppression characteristics of the parallel notch resonator12vary slightly in the vicinity of a sub-resonant frequency and a sub-antiresonant frequency as compared with the bandpass characteristics of the ladder-type filter in which the parallel notch resonator12is not connected. However, the variation in the suppression characteristics is so small that it has no adverse effect on the performance of the filter. Note here that an input/output impedance of the filter may be shifted by connecting the parallel notch resonator12. Thus, in order to allow the filter to have an input/output impedance of a desired value, it is preferable to adjust a capacitance or the like of acoustic wave resonators11included in the filter.

In each of the above-described ladder-type filters, although the notch resonator is connected to the output terminal of the filter, the notch resonator may be connected to an input terminal of the filter, which results in the same effect. Further, the notch resonator may be connected not only to the input terminal but also to various portions of the filter, which results in the same effect. In each of the above-described ladder-type filters, although one notch resonator is connected, two or more notch resonators may be connected, which results in the same effect.

FIG. 14Ais a circuit diagram of a ladder-type filter in which a series notch resonator22is connected between a series resonator21and a parallel resonator23.FIG. 14Bis a circuit diagram of a ladder-type filter in which the series notch resonator22is connected between series resonators21aand21b.FIG. 14Cis a circuit diagram of a ladder-type filter in which the series notch resonator22is connected between parallel resonators23aand23b.FIG. 14Dis a circuit diagram of a ladder-type filter in which the series notch resonator22is connected in parallel with the series resonator21.FIG. 14Eis a circuit diagram of a ladder-type filter in which the series notch resonator22is connected in parallel with the plurality of series resonators21aand21b.As illustrated inFIGS. 14A to 14E, the series notch resonator22may be connected to any portion of the ladder-type filter, thereby suppressing sub-resonant responses. In the circuit of the ladder-type filter of the present embodiment, a resonator whose both ends are connected to a signal line S (seeFIG. 14A, for example) is defined as a “series resonator”, and a resonator whose both ends are connected between the signal line S and a ground line G is defined as a “parallel resonator”.

FIG. 15Ais a circuit diagram of a ladder-type filter in which a parallel notch resonator32is connected between series resonators31aand31b.FIG. 15Bis a circuit diagram of a ladder-type filter in which the parallel notch resonator32is connected between a parallel resonator33and a ground line G.FIG. 15Cis a circuit diagram of a ladder-type filter in which the parallel notch resonator32is connected between the parallel resonator33and a signal line S.FIG. 15Dis a circuit diagram of a ladder-type filter in which the parallel notch resonator32is connected between a node between a plurality of parallel notch resonators33aand33bon a ground line G side and the ground line G.FIG. 15Eis a circuit diagram of a ladder-type filter in which the parallel notch resonator32is connected between a node between the plurality of parallel notch resonators33aand33bon a signal line S side and the signal line S. As illustrated inFIGS. 15A to 15E, the parallel notch resonator32may be connected to any portion of the ladder-type filter, thereby suppressing sub-resonant responses.

The method for suppressing sub-resonant responses of the present invention is not limited to use in the above-described ladder-type filters, but is applicable to any types of acoustic wave filters. For example, the method also is applicable to a double-mode filter (unbalanced output filter) using surface acoustic waves, love waves or boundary acoustic waves as illustrated inFIG. 16A. In the double-mode filter illustrated inFIG. 16A, an input comb-shaped electrode43ais connected to an input terminal41, and output comb-shaped electrodes43band43care connected to an output terminal42. The input comb-shaped electrode43aand the output comb-shaped electrodes43band43care arranged in parallel, and reflectors44aand44bare arranged in parallel with the output comb-shaped electrodes43band43c.

The method for suppressing sub-resonant responses of the present invention is also applicable to a piezoelectric thin film double-mode filter (balanced output filter) as illustrated inFIG. 16B.FIG. 16Bis a cross-sectional view of the piezoelectric thin film double-mode filter. In the double-mode filter illustrated inFIG. 16B, a first resonance portion and a second resonance portion are laminated. In the first resonance portion, a dielectric film48ais sandwiched between a pair of piezoelectric films47aand47b.In the second resonance portion, a dielectric film48bis sandwiched between a pair of piezoelectric films47cand47d.An input terminal45is connected to a junction between the first resonance portion and the second resonance portion. An output terminal46ais connected to the piezoelectric film47aon the first resonance portion side. An output terminal46bis connected to the piezoelectric film47don the second resonance portion side.

In both the balanced output double-mode filter and the unbalanced output double-mode filter illustrated inFIGS. 16A and 16B, the series notch resonator (seeFIG. 10B, for example) or the parallel notch resonator (seeFIG. 12, for example) may be connected to the input terminal or the output terminal, thereby suppressing sub-resonant responses.

Configuration of a duplexer

FIG. 17Ais a circuit diagram of a duplexer. The duplexer includes a transmission filter56, a reception filter53, and a matching circuit52. When a notch resonator is connected to the transmission filter56or the reception filter53, the duplexer has its sub-resonant responses suppressed. As illustrated inFIG. 17B, when a series notch resonator57is connected to an antenna terminal51, the duplexer has its sub-resonant responses suppressed. As illustrated inFIG. 17C, when a parallel notch resonator58is connected to the antenna terminal51, the duplexer has its sub-resonant responses suppressed. Each of the notch resonators57and58has a main resonant frequency that can be made substantially equal to a sub-resonant frequency of the transmission filter56or a sub-resonant frequency of the reception filter53.

FIG. 18Ais a circuit diagram illustrating an example of the duplexer illustrated inFIG. 17C. A transmission filter96and a reception filter93inFIG. 18Aare 4-pole ladder-type filters using love wave resonators. A matching circuit92is a circuit in which inductors L and a capacitor C are connected in a π-shape. A parallel notch resonator97is connected to an antenna terminal91. The parallel notch resonator97is a love wave resonator. The period of a comb-shaped electrode of the parallel notch resonator97is adjusted so that the parallel notch resonator97has a main resonant frequency that is substantially equal to a sub-resonant frequency of the reception filter93.

FIG. 18Billustrates a chip structure of the transmission filter96. In the transmission filter chip illustrated inFIG. 18B, a plurality of acoustic wave filters96dare connected to each other in series or parallel. At both ends of a signal line S, an input terminal96aconnected to a transmission terminal95, and an output terminal96bconnected to the antenna terminal91are provided. A notch resonator96eis connected between the signal line S and a ground terminal96c.With this configuration, the transmission filter96has its sub-resonant responses suppressed.

FIG. 18Cillustrates a chip structure of the reception filter93. In the reception filter chip illustrated inFIG. 18C, a plurality of acoustic wave filters93dare connected to each other in series or parallel. At both ends of a signal line S, an input terminal93aconnected to the matching circuit92, and an output terminal93hconnected to a reception terminal94are provided. The reception filter chip illustrated inFIG. 18Cincludes no notch resonator. In other words, a series notch resonator or a parallel notch resonator may be provided on either an input side (e.g., the reception filter93) or an output side (e.g., the transmission filter96) of the duplexer. For comparison, a conventional duplexer in which no parallel notch resonator is connected to an antenna terminal (no notch resonator is provided on a transmission chip) also is manufactured.

FIG. 19Aillustrates filter characteristics of the conventional duplexer in which no notch resonator is connected and frequency characteristics of the notch resonator alone. V1indicates frequency characteristics of the transmission filter, and V2indicates frequency characteristics of the reception filter. As indicated by V1and V2, the transmission filter and the reception filter have their sub-resonant responses in the vicinity of 2200 to 2400 MHz. V3indicates bandpass characteristics of the parallel notch resonator alone. As indicated by V3, the parallel notch resonator has a main resonant frequency that is substantially equal to the sub-resonant response frequency of the reception filter.

FIG. 19Billustrates the frequency characteristics of the transmission filter in the case where the parallel notch resonator is not connected to the antenna terminal (i.e., the conventional filter), and in the case where the parallel notch resonator is connected to the antenna terminal (e.g., the filter illustrated inFIG. 18A).FIG. 19Cillustrates the frequency characteristics of the reception filter in the case where the parallel notch resonator is not connected to the antenna terminal (i.e., the conventional filter), and in the case where the parallel notch resonator is connected to the antenna terminal (e.g., the filter illustrated inFIG. 18A). When the parallel notch resonator is connected to the antenna terminal, the reception filter has its sub-resonant response suppressed significantly as illustrated inFIG. 19C, and the transmission filter also has its sub-resonant response suppressed slightly as illustrated inFIG. 19B. This is because the notch resonator connected to the antenna terminal of the duplexer can affect not only the reception filter characteristics but also the transmission filter characteristics. Also, it can be seen that connecting the parallel notch resonator has a small influence on a main resonant response of the duplexer.

Configuration of a communication module

FIG. 20illustrates an exemplary communication module including the acoustic wave filter or the duplexer of the present embodiment. As illustrated inFIG. 20, a duplexer62includes a reception filter62aand a transmission filter62b.The reception filter62ais connected with reception terminals63aand63bthat are compatible with balanced output, for example. Further, the transmission filter62bis connected to a transmission terminal65via a power amplifier64. The reception filter62aand the transmission filter62binclude the acoustic wave filter of the present embodiment.

In a receiving operation, the reception filter62areceives reception signals via an antenna terminal61, allows only signals in a predetermined frequency band to pass, and outputs the resultant signals to the outside from the reception terminals63aand63b.In a transmitting operation, the transmission filter62breceives transmission signals that have been input from the transmission terminal65and amplified by the power amplifier64, allows only signals in a predetermined frequency band to pass, and outputs the resultant signals to the outside from the antenna terminal61.

When the acoustic wave filter or the duplexer of the present embodiment is included in the reception filter62aand the transmission filter62bof the communication module, the communication module has its sub-resonant responses suppressed, resulting in an improvement in communication characteristics.

The configuration of the communication module illustrated inFIG. 20is an example. The filter of the present invention may be mounted on a communication module in another form, which results in the same effect.

Configuration of a communication apparatus

FIG. 21illustrates an RF block of a mobile phone terminal as an example of a communication apparatus including the acoustic wave filter or the communication module of the present embodiment. The communication apparatus illustrated inFIG. 21is a mobile phone terminal that is compatible with a GSM (Global System for Mobile Communications) communication system and a W-CDMA (Wideband Code Division Multiple Access) communication system. The GSM communication system in the present embodiment is compatible with a 850 MHz band, a 950 MHz band, a 1.8 GHz band, and a 1.9 GHz band. Although the mobile phone terminal includes a microphone, a speaker, a liquid crystal display, and the like in addition to the components illustrated inFIG. 21, they are not illustrated in the figure because they are not necessary for describing the present embodiment. Here, reception filters73a,77,78,79, and80and a transmission filter73binclude the acoustic wave filter of the present embodiment.

First, an antenna switch circuit72selects an LSI to be operated, based on whether the communication system of a reception signal input via an antenna71is W-CDMA or GSM. If the input reception signal conforms to the W-CDMA communication system, the antenna switch circuit72performs switching so that the reception signal is output to a duplexer73. The reception signal input to the duplexer73is limited to a predetermined frequency band by the reception filter73a,and the resultant balanced reception signal is output to an LNA74. The LNA74amplifies the input reception signal, and outputs the amplified reception signal to an LSI76. The LSI76performs demodulation processing for obtaining an audio signal based on the input reception signal, and controls operations of respective units in the mobile phone terminal.

On the other hand, in the case of transmitting a signal, the LSI76generates a transmission signal. A power amplifier75amplifies the generated transmission signal, and outputs the amplified transmission signal to the transmission filter73b.The transmission filter73breceives the transmission signals, and allows only signals in a predetermined frequency band to pass. The transmission filter73boutputs the resultant transmission signals to the outside from the antenna71via the antenna switch circuit72.

If the input reception signal conforms to the GSM communication system, the antenna switch circuit72selects one of the reception filters77to80in accordance with the frequency band of the reception signal, and outputs the reception signal to the selected reception filter. The reception signal is band-limited by the selected one of the reception filters77to80, and the band-limited reception signal is input to an LSI83. The LSI83performs demodulation processing for obtaining an audio signal based on the input reception signal, and controls operations of the respective units in the mobile phone terminal. On the other hand, in the case of transmitting a signal, the LSI83generates a transmission signal. A power amplifier81or82amplifies the generated transmission signal, and outputs the amplified signal to the outside from the antenna71via the antenna switch circuit72.

When the acoustic wave filter or the communication module including the acoustic wave filter of the present embodiment is included in the communication apparatus, the communication apparatus has its sub-resonant responses suppressed, resulting in an improvement in communication characteristics.

Effect etc. of the embodiment

According to the present embodiment, the notch resonator is connected in series or parallel in the acoustic wave filter, so that the occurrence of sub-resonant responses in the filter characteristics can be suppressed, resulting in an improvement in communication characteristics.

According to the present embodiment, it is possible to suppress sub-resonant responses without deteriorating a main resonant response.

The acoustic wave resonators1,93d,and96d,the series resonators21,21a,21b,31a,and31b,and the parallel resonators23,23a,23b,33,33a,and33bin the present embodiment are examples of the acoustic wave resonator of the present invention. The series notch resonators2,22, and57, and the parallel notch resonators12,32,58,96e,and97in the present embodiment are examples of the notch resonator of the present invention. The antenna terminals51,61,71, and91in the present embodiment are examples of the antenna terminal of the present invention. The reception filters53,62a,and93in the present embodiment are examples of the reception circuit of the present invention. The transmission filters56,62b,and96in the present embodiment are examples of the transmission circuit of the present invention.