JP2012034067A - Acoustic wave filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter device that is a bandstop-type acoustic wave filter device having a stop band in a pass band and whose insertion loss in the pass band is small.SOLUTION: An acoustic wave filter device 1 includes: first and second series arm acoustic wave resonators S1 and S2 that are electrically connected in parallel to each other between a first inductor L1 and a second inductor L2; a first parallel arm 13a that electrically connects a connection point among the first inductor L1 and the first and second series arm acoustic wave resonators S1 and S2 to a ground potential and is provided with a first parallel arm acoustic wave resonator P1; and a second parallel arm 13b that electrically connects a connection point among the second inductor L2 and the first and second series arm acoustic wave resonators S1 and S2 to a ground potential and is provided with a second parallel arm acoustic wave resonator P2.

Description

  The present invention relates to an elastic wave filter device. In particular, the present invention relates to a band-stop type elastic wave filter device having a stop band in a pass band.

  In recent years, terrestrial digital broadcasting has become widespread. In terrestrial digital broadcasting, one channel is divided into 13 segments, and one segment arranged at the center of one channel is used for a mobile terminal such as a mobile phone. Broadcast using this one segment is so-called one-segment broadcasting. The frequency band of one-segment broadcasting is 470 MHz to 770 MHz. On the other hand, the transmission band of the mobile phone varies depending on the method and the communication company, but for example, a band of 824 MHz to 830 MHz, 898 MHz to 924 MHz, or the like is used.

  In this way, when a call and a 1Seg broadcast are received and recorded at the same time on a mobile phone whose call transmission band is close to the one-seg broadcast frequency band, the received video of the 1Seg broadcast is There is a risk of disturbance. As a method for suppressing the disturbance of the received video, there is a method using a band rejection filter having a pass band including the frequency band of one-segment broadcasting and having a stop band that matches the transmission band of the mobile phone in the pass band. Conceivable.

  As a specific example of such a band rejection filter, for example, a band rejection surface acoustic wave filter disclosed in Patent Document 1 below can be cited. FIG. 13 shows an equivalent circuit diagram of the band rejection type surface acoustic wave filter described in Patent Document 1. In FIG.

  As shown in FIG. 13, in the surface acoustic wave filter 100, a plurality of inductors 104 and 105 are connected in series in a series arm 103 that electrically connects an input end 101 and an output end 102. The serial arm 103 and the ground potential are electrically connected by a plurality of parallel arms 107a to 107d. Each parallel arm 107a to 107d is provided with a parallel arm surface acoustic wave resonator 108a to 108d.

  In the surface acoustic wave filter 100, a low band stop band of 824 MHz to 830 MHz is formed by the resonance points of the parallel arm surface acoustic wave resonators 108 a to 108 c, and 898 is defined by the resonance point of the parallel arm surface acoustic wave resonator 108 d. A stop band on the high frequency side of ˜924 MHz is formed.

WO2008 / 072439 A1 Publication

  However, the surface acoustic wave filter 100 has a problem that the insertion loss in the portion located on the low band side of the pass band is lower than the low band stop band.

  The present invention has been made in view of the above points, and an object thereof is a band-stop type elastic wave filter device having a stop band in the pass band, and a surface acoustic wave filter having a small insertion loss in the pass band. To provide an apparatus.

  An elastic wave filter device according to the present invention includes an input end, an output end, a series arm, first and second inductors, first and second series arm elastic wave resonators, and a first parallel arm. And a second parallel arm. The serial arm electrically connects the input end and the output end. The first and second inductors are connected in series at the series arm. The first and second series arm acoustic wave resonators are electrically connected in parallel to each other between the first inductor and the second inductor. The first parallel arm electrically connects the connection point between the first inductor and the first and second series arm elastic wave resonators to the ground potential. The first parallel arm is provided with a first parallel arm elastic wave resonator. The second parallel arm electrically connects the connection point between the second inductor and the first and second series arm elastic wave resonators and the ground potential. The second parallel arm is provided with a second parallel arm elastic wave resonator.

  In a specific aspect of the elastic wave filter device according to the present invention, the first series arm elastic wave resonator and the second series arm elastic wave resonator have different resonance frequencies and antiresonance frequencies. According to this configuration, the steepness of the filter characteristics in the transition band between the stop band and the pass band can be enhanced.

  In another specific aspect of the acoustic wave filter device according to the present invention, the parallel arm that electrically connects the portion between the second inductor and the output end and the ground potential is not provided. According to this configuration, the amount of attenuation in the stop band can be further increased.

  In another specific aspect of the acoustic wave filter device according to the present invention, the first inductor is provided closer to the input end than the second inductor. The elastic wave filter device further includes third and fourth series arm elastic wave resonators, a third parallel arm, and a fourth parallel arm. The third and fourth series arm elastic wave resonators are electrically connected in parallel between the first inductor and the input end. The third parallel arm electrically connects the connection point between the input end and the third and fourth series arm elastic wave resonators and the ground potential. The third parallel arm is provided with a third parallel arm elastic wave resonator. The fourth parallel arm electrically connects the connection point between the first inductor and the third and fourth series arm elastic wave resonators and the ground potential. The fourth parallel arm is provided with a fourth parallel arm elastic wave resonator. According to this configuration, the attenuation characteristic in the stop band can be further improved, and the pass band can be widened.

In still another specific aspect of the elastic wave filter device according to the present invention, each of the first and second series arm elastic wave resonators and the first and second parallel arm elastic wave resonators includes a piezoelectric substrate, And an IDT electrode formed on the piezoelectric substrate. The piezoelectric substrate is composed of a 55 ° rotated Y-cut X-propagating LiNbO ₃ substrate. According to this structure, it can suppress that a ripple generate | occur | produces in a pass band.

  In still another specific aspect of the acoustic wave filter device according to the present invention, the duty ratio of at least one IDT electrode of the IDT electrodes of the first and second series arm acoustic wave resonators is 0.3 to 0. Within the range of .5. According to this configuration, it is possible to reduce ripples caused by Rayleigh waves that are generated on the lower side of the stop band in the pass band.

  In still another specific aspect of the surface acoustic wave filter device according to the present invention, the surface acoustic wave filter device is a surface acoustic wave filter device using surface acoustic waves.

  In still another specific aspect of the elastic wave filter device according to the present invention, the elastic wave filter device is a boundary acoustic wave filter device using boundary acoustic waves.

  In the present invention, the first and second series arm elastic wave resonators are electrically connected in parallel. For this reason, the electrical resistance of the first and second series arm elastic wave resonators can be reduced. Therefore, the insertion loss in the pass band can be reduced.

1 is an equivalent circuit diagram of a surface acoustic wave filter device according to an embodiment of the present invention. 1 is a schematic side view of a surface acoustic wave filter device according to an embodiment of the present invention. 1 is a schematic perspective view of a surface acoustic wave chip according to an embodiment of the present invention. It is the typical top view to which a part of surface acoustic wave chip in one embodiment of the present invention was expanded. 5 is a graph showing insertion loss characteristics of the surface acoustic wave filter device according to Example 1 and the surface acoustic wave filter device according to the comparative example. In FIG. 5, the solid line represents the insertion loss characteristic of the surface acoustic wave filter device according to the first embodiment, and the broken line represents the insertion loss characteristic of the surface acoustic wave filter device according to the comparative example. It is an equivalent circuit diagram of a surface acoustic wave filter device according to a comparative example. It is the typical top view which expanded a part of surface acoustic wave filter chip in a comparative example. 6 is a graph showing insertion loss characteristics of the surface acoustic wave device according to the second embodiment and the surface acoustic wave device according to the first embodiment. In FIG. 8, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the second embodiment. 6 is a graph showing insertion loss characteristics of the surface acoustic wave device according to Example 3 and the surface acoustic wave device according to Example 1. In FIG. 9, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the third embodiment. 6 is a graph showing insertion loss characteristics of the surface acoustic wave device according to Example 4 and the surface acoustic wave device according to Example 1. In FIG. 10, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the fourth embodiment. 10 is a schematic cross-sectional view in which a part of a surface acoustic wave filter chip according to Modification 1 is enlarged. 10 is an enlarged schematic cross-sectional view of a part of a surface acoustic wave filter chip according to Modification 2. FIG. 2 is an equivalent circuit diagram of a band rejection type surface acoustic wave filter described in Patent Document 1. FIG.

  Hereinafter, a preferred embodiment in which the present invention is implemented will be described by taking a surface acoustic wave filter device 1 using surface acoustic waves as shown in FIG. 1 as an example. However, the surface acoustic wave filter device 1 is merely an example. The elastic wave filter device according to the present invention is not limited to the surface acoustic wave filter device 1.

  The surface acoustic wave filter device 1 of the present embodiment includes a wide pass band including a frequency band of 470 MHz to 770 MHz, a low frequency side stop band of 824 MHz to 830 MHz, and a high frequency side stop band of 898 MHz to 924 MHz. This is a double trap type surface acoustic wave filter device.

  FIG. 1 is an equivalent circuit diagram of the surface acoustic wave filter device according to this embodiment. First, the circuit configuration of the surface acoustic wave filter device 1 will be described with reference to FIG.

  As shown in FIG. 1, the surface acoustic wave filter device 1 includes an input end 10 and an output end 11. The input end 10 and the output end 11 are electrically connected by a series arm 12. A plurality of inductors L1 to L3 are connected to the series arm 12 in series. In the present embodiment, the third inductor L3 is directly connected to the input terminal 10. The second inductor L2 is directly connected to the output terminal 11. The first inductor L1 is connected between the second inductor L2 and the third inductor L3.

  In the series arm 12, the first and second series arm surface acoustic wave resonators S1 and S2 are electrically connected between the first inductor L1 and the second inductor L2. The first and second series arm surface acoustic wave resonators S1 and S2 are electrically connected in parallel to each other. In the present embodiment, the first series arm surface acoustic wave resonator S1 and the second series arm surface acoustic wave resonator S2 are designed to have different resonance frequencies and antiresonance frequencies.

  On the other hand, in the series arm 12, the third and fourth series arm surface acoustic wave resonators S3 and S4 are electrically connected between the first inductor L1 and the third inductor L3. The third and fourth series arm surface acoustic wave resonators S3 and S4 are electrically connected in parallel to each other. In the present embodiment, the third series arm surface acoustic wave resonator S3 and the fourth series arm surface acoustic wave resonator S4 are designed so that the resonance frequency and the antiresonance frequency are equal to each other.

  The connection point 12a between the first inductor L1 and the first and second series arm surface acoustic wave resonators S1 and S2 and the ground potential are electrically connected by the first parallel arm 13a. . The first parallel arm 13a is provided with a first parallel arm surface acoustic wave resonator P1.

  The connection point 12b between the second inductor L2 and the first and second series arm surface acoustic wave resonators S1 and S2 and the ground potential are electrically connected by the second parallel arm 13b. . The second parallel arm 13b is provided with a second parallel arm surface acoustic wave resonator P2.

  The connection point 12c between the third inductor L3 and the third and fourth series arm surface acoustic wave resonators S3 and S4 and the ground potential are electrically connected by the third parallel arm 13c. . The third parallel arm 13c is provided with a third parallel arm surface acoustic wave resonator P3.

  The connection point 12d between the first inductor L1 and the third and fourth series arm surface acoustic wave resonators S3 and S4 and the ground potential are electrically connected by the fourth parallel arm 13d. . The fourth parallel arm 13d is provided with a fourth parallel arm surface acoustic wave resonator P4.

  In the present embodiment, as described above, the second inductor L2 is directly connected to the output terminal 11, and the portion between the second inductor L2 and the output terminal 11 and the ground potential are electrically connected. There are no connected parallel arms.

  FIG. 2 is a schematic side view of the surface acoustic wave filter device according to this embodiment. FIG. 3 is a schematic perspective view of the surface acoustic wave chip according to the present embodiment. FIG. 4 is a schematic plan view in which a part of the surface acoustic wave chip in the present embodiment is enlarged. In FIG. 3, the resonator is schematically shown as a rectangle with X inside.

  Next, a physical configuration of the surface acoustic wave filter device 1 according to the present embodiment will be described with reference mainly to FIGS.

  As shown in FIG. 2, the surface acoustic wave filter device 1 includes a wiring board 20. A surface acoustic wave chip 22 is flip-chip mounted on the wiring board 20 via bumps 21. The surface acoustic wave chip 22 is sealed with a resin layer 25 formed on the wiring substrate 20.

  The wiring board 20 can be composed of, for example, a high-temperature fired ceramic multilayer board (HTCC). In the present embodiment, the inductors L1 to L3 shown in FIG. 1 are formed by the wiring 20a formed in the wiring board 20. The inductors L1 to L3 may be configured by, for example, a chip inductor.

  As shown in FIG. 3, the surface acoustic wave chip 22 includes a piezoelectric substrate 23 and an electrode 24 formed on the piezoelectric substrate 23. In the present embodiment, the piezoelectric substrate 23 and the electrode 24 allow the first to fourth series arm surface acoustic wave resonators S1 to S4, the first to fourth parallel arm surface acoustic wave resonators P1 to P4, and the wiring. Etc. are configured. Specifically, as shown in FIG. 4, the electrode 24 includes an IDT electrode 24 a configured by a pair of comb-shaped electrodes that are interleaved with each other. Each of the first to fourth series arm surface acoustic wave resonators S1 to S4 and the first to fourth parallel arm surface acoustic wave resonators P1 to P4 is constituted by the IDT electrode 24a and the piezoelectric substrate 23. Yes.

The piezoelectric substrate 23 is not particularly limited, for example, quartz, LiTaO ₃ or the substrate can be formed of LiNbO ₃ substrates, such as 55 ° rotated Y-cut X-propagation LiNbO ₃ substrate.

  The electrode 24 is, 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, Ti, Cr, and It can be formed of an alloy containing one or more metals selected from the group consisting of Pd. Moreover, the electrode 24 may be comprised by the laminated body of the some conductive layer which consists of the said metal and alloy, for example.

  Moreover, it is preferable that the duty ratio of at least one of the IDT electrodes 24a constituting the first and second series arm elastic wave resonators S1 and S2 is in the range of 0.3 to 0.5.

  The graph shown by the solid line in FIG. 5 is a graph showing the insertion loss characteristic of Example 1 having the same configuration as that of the surface acoustic wave filter device 1 according to this embodiment. Detailed design parameters in Example 1 are shown in Table 1 below.

  In the first embodiment, a wide pass band including a frequency band of 470 MHz to 770 MHz is formed by the LC circuit configured by the capacitances of the resonators S1 to S3, P1 to P3 and the inductors L1 to L3. . Further, the anti-resonance frequency of the second and third series arm surface acoustic wave resonators S2 and S3 and the resonance of the first and fourth parallel arm surface acoustic wave resonators P1 and P4 are blocked on the high frequency side. It is located in the band (898 MHz to 924 MHz) or in the vicinity thereof. For this reason, the antiresonance points of the second and third series arm surface acoustic wave resonators S2 and S3 and the resonance points of the first and fourth parallel arm surface acoustic wave resonators P1 and P4 are included in the passband. A high-side stop band (898 MHz to 924 MHz) is formed. Further, the anti-resonance frequency of the first series arm surface acoustic wave resonator S1 and the resonance frequencies of the second and third parallel arm surface acoustic wave resonators P2 and P3 are in the low-band stop band (824 MHz to 830 MHz). Or it is located in the vicinity. For this reason, the low-band stopband (by the anti-resonance point of the first series arm surface acoustic wave resonator S1 and the resonance points of the second and third parallel arm surface acoustic wave resonators P2 and P3 in the passband. 824 MHz to 830 MHz).

  In the first embodiment, the first and second series arm surface acoustic wave resonators S1 and S2 have different resonance frequencies and antiresonance frequencies. On the other hand, the third and fourth series arm surface acoustic wave resonators S3 and S4 have substantially the same resonance frequency and anti-resonance frequency.

  As a comparative example of the surface acoustic wave filter device of Example 1, a surface acoustic wave filter device 200 shown in FIG. 6 was prepared. The surface acoustic wave filter device 200 according to the comparative example includes a series arm surface acoustic wave resonator S201, S202 and inductors L201 to L203 in a series arm 203 that electrically connects an input end 201 and an output end 202. They are alternately connected in series. The serial arm 203 and the ground potential are electrically connected by the parallel arms 204a to 204f. Each parallel arm 204a to 204f is provided with parallel arm surface acoustic wave resonators P201 to P206. Also in this comparative example, a surface acoustic wave chip 210 (see FIG. 7) mounted on a wiring board is provided as in the above embodiment. As shown in FIG. 7, the resonators S <b> 201, S <b> 202, P <b> 201 to P <b> 206 are formed on the surface acoustic wave chip 210. Specifically, the resonators S <b> 201, S <b> 202, P <b> 201 to P <b> 206 are configured by a piezoelectric substrate 211 and an electrode 212 that constitute the surface acoustic wave chip 210. Detailed design parameters in the comparative example are shown in Table 2 below.

  In this comparative example, a high-band stop band (898 MHz to 924 MHz) is formed by the resonance points of the parallel arm surface acoustic wave resonators P201 and P203 to P205. Further, a low-band stop band (824 MHz to 830 MHz) is formed by the antiresonance points of the series arm surface acoustic wave resonators S201 and S202 and the resonance points of the parallel arm surface acoustic wave resonators P202 and P206.

  The insertion loss characteristic of the surface acoustic wave filter device 200 according to the comparative example is shown by a broken line in FIG.

  As shown in FIG. 5, the amount of attenuation in Example 1 is larger in both the high-frequency stopband and the low-frequency stopband than in the comparative example. This reason is considered to be due to the following reasons. That is, in the comparative example, an electric signal that matches the resonance frequency of the parallel arm surface acoustic wave resonator P202 is directly applied to the output end 202 via the parallel arm surface acoustic wave resonator P206 that is directly connected to the output end 202. It is considered that the attenuation amount in the low-band stop band (824 MHz to 830 MHz) is reduced due to leakage. On the other hand, in the first embodiment, since there is no parallel arm surface acoustic wave resonator directly connected to the output end 11, an electrical signal in the frequency band of the low-frequency stopband may leak to the output end 11. As a result, in Example 1, it is considered that the attenuation amount in the lower-band stop band is larger in Example 1 than in the comparative example.

  On the other hand, in the first embodiment, the low band side stop band is formed by three resonators in the first embodiment because the attenuation amount of the low band side stop band can be increased for the above reason. Accordingly, the high-band stop band uses five resonators, and more resonators are used than in the comparative example in which the high-band stop band is formed by four resonators. As a result, in Example 1, it is considered that the amount of attenuation in the high-band stop band is larger than that in the comparative example.

  3 and 7, it can be seen that the series arm surface acoustic wave resonators S3 and S4 having the same function and the series arm surface acoustic wave resonator S201 can have substantially the same size. It can also be seen that the series arm surface acoustic wave resonators S1 and S2 having the same function and the series arm surface acoustic wave resonator S202 can have substantially the same size. That is, in order to widen the pass band, it is necessary to form a relatively large capacity in the series arm. However, in Example 1, the comparative example is configured by one series arm surface acoustic wave resonator. However, it is composed of two series arm surface acoustic wave resonators electrically connected in parallel to each other. For this reason, the area per resonator can be halved. Since the total number of resonators that form the stop band does not change even if the number of parallel arm surface acoustic wave resonators is reduced by the number of series arm surface acoustic wave resonators, the attenuation is equal or greater. Characteristics can be realized. Therefore, in the first embodiment, the surface acoustic wave filter device 1 can be further downsized, as is apparent from the comparison between FIGS. 3 and 7.

  Further, as in the first embodiment, by connecting two series arm surface acoustic wave resonators electrically in parallel, each series arm surface acoustic wave is provided rather than a case where one series arm surface acoustic wave resonator is provided. The crossing width in the resonator can be reduced. For this reason, the resistance loss in each series arm surface acoustic wave resonator can be reduced. As a result, as shown in FIG. 5, it is possible to reduce the insertion loss in the frequency band of 470 MHz to 770 MHz in the pass band. Specifically, in Example 1, the insertion loss in the frequency band is smaller by 0.25 dB than in the comparative example.

  Further, in Example 1, the steepness of the filter characteristics in the transient band between the low-band stop band and the pass band located on the lower band side than the low-band stop band is greater than that of the comparative example. Has been increased. This is considered to be due to the following reasons. That is, in Example 1, the resonance frequency and the anti-resonance frequency are different between the first series arm surface acoustic wave resonator S1 and the second series arm surface acoustic wave resonator S2. For this reason, the other of the first and second series arm surface acoustic wave resonators S1 and S2 functions as a capacitor at one resonance frequency. Therefore, the frequency interval between the resonance frequency and the anti-resonance frequency of each of the first and second series arm surface acoustic wave resonators S1 and S2 becomes narrow. Therefore, it is considered that the steepness of the filter characteristics in the transient band is enhanced by positioning the anti-resonance frequency in the transient band between the pass band and the stop band.

  The pass band can be widened by increasing at least one of the duty ratio, the cross width, and the logarithm of at least one series arm surface acoustic wave resonator. That is, in this embodiment, the bandwidth of the pass band can be adjusted by adjusting at least one of the duty ratio, the cross width, and the logarithm of the series arm surface acoustic wave resonator.

  Hereinafter, this effect will be described in detail based on specific examples.

  8 shows a surface acoustic wave device according to Example 2 in which the duty ratio of the series arm surface acoustic wave resonator S4 is increased from 0.395 to 0.495, as shown in Table 3 below. It is a graph showing the insertion loss characteristic with the surface acoustic wave apparatus which concerns. In FIG. 8, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the second embodiment. As shown in FIG. 8, the passband of Example 2 in which the duty ratio of the series arm surface acoustic wave resonator S <b> 4 is large is wider than that of Example 1 on the low frequency side.

  9 shows a surface acoustic wave device according to Example 3 in which the cross width of the series arm surface acoustic wave resonator S4 is increased from 59.1 μm to 70.0 μm as shown in Table 4 below. It is a graph showing the insertion loss characteristic with the surface acoustic wave apparatus which concerns. In FIG. 9, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the third embodiment. As shown in FIG. 9, the third example in which the cross width of the series arm surface acoustic wave resonators S <b> 4 is large has a wider pass band on the lower frequency side than the first example.

  10 shows a surface acoustic wave device according to Example 4 in which the logarithm of the series arm surface acoustic wave resonator S4 is increased from 68 to 80 pairs, and the surface acoustic wave according to Example 1 as shown in Table 5 below. It is a graph showing the insertion loss characteristic with a wave apparatus. In FIG. 10, the solid line represents the insertion loss characteristic in the first embodiment, and the broken line represents the insertion loss characteristic in the fourth embodiment. As shown in FIG. 10, the passband of the fourth embodiment in which the logarithm of the series arm surface acoustic wave resonator S <b> 4 is larger than that of the first embodiment is lower.

  As described above, by increasing at least one of the duty ratio, the cross width, and the logarithm of at least one series arm surface acoustic wave resonator, the pass band can be broadened by changing the duty ratio, the cross width. This is considered to be because the capacitance of the series arm surface acoustic wave resonator in which at least one of the logarithms is increased is increased.

  In the second embodiment, the position of the anti-resonance frequency of the series arm surface acoustic wave resonator can be finely adjusted. Therefore, the attenuation amount in the high-band stop band is larger than that in the first embodiment. In the third and fourth embodiments, the area of the series arm surface acoustic wave resonator S4 is larger than that of the first embodiment, whereas in the second embodiment, the series arm surface acoustic wave resonator S4 is larger than that of the first embodiment. The area of is not large. For this reason, in Example 2, it is possible to further improve the attenuation amount of the high-band stop band while suppressing an increase in the size of the apparatus.

However, when a 55 ° rotated Y-cut X-propagating LiNbO ₃ substrate is used as the piezoelectric substrate 23, if the duty ratio is excessively increased, ripples are likely to be generated in the pass band, so the duty ratio is 0.3 to 0.5. It is preferable that it is the range of these.

(First and second modifications)
FIG. 11 is a schematic cross-sectional view in which a part of the surface acoustic wave chip in Modification 1 is enlarged. FIG. 12 is a schematic cross-sectional view in which a part of the surface acoustic wave chip in Modification 2 is enlarged.

  In the above embodiment, the surface acoustic wave filter device 1 using a surface acoustic wave has been described. However, in the present invention, the surface acoustic wave filter device may be, for example, a boundary acoustic wave device using a boundary acoustic wave. In this case, for example, as shown in FIG. 11, the acoustic wave chip 22 is formed on the piezoelectric substrate 23 and has a dielectric layer 26 made of a dielectric such as silicon oxide or silicon nitride. Further, as shown in FIG. 12, for example, a dielectric layer 27 is formed on the dielectric layer 26 made of silicon oxide or the like, which is made of silicon nitride or the like and has a higher sound speed than the dielectric layer 26. May be. In other words, the acoustic wave chip 22 may be a so-called two-medium type boundary acoustic wave chip or a so-called three-medium type boundary acoustic wave chip.

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave filter apparatus 10 ... Input end 11 ... Output end 12 ... Series arm 12a-12d ... Connection point 13a ... 1st parallel arm 13b ... 2nd parallel arm 13c ... 3rd parallel arm 13d ... 4th Parallel arm 20 ... Wiring substrate 20a ... Wiring 21 ... Bump 22 ... Surface acoustic wave chip 23 ... Piezoelectric substrate 24 ... Electrode 24a ... IDT electrode 25 ... Resin layer 26 ... Dielectric layer 27 ... Dielectric layers L1-L3 ... Inductor S1 S4 ... Series arm surface acoustic wave resonators P1-P4 ... Parallel arm surface acoustic wave resonators

Claims (8)

An input end;
An output end;
A series arm electrically connecting the input end and the output end;
First and second inductors connected in series in the series arm;
Between the first inductor and the second inductor, first and second series arm acoustic wave resonators electrically connected in parallel with each other;
A connection point between the first inductor and the first and second series arm elastic wave resonators is electrically connected to a ground potential, and a first parallel arm elastic wave resonator is provided. A first parallel arm that is
A connection point between the second inductor and the first and second series arm elastic wave resonators is electrically connected to a ground potential, and a second parallel arm elastic wave resonator is provided. A second parallel arm,
An elastic wave filter device.   2. The acoustic wave filter device according to claim 1, wherein the first series arm acoustic wave resonator and the second series arm acoustic wave resonator have different resonance frequencies and antiresonance frequencies.   3. The acoustic wave filter device according to claim 1, wherein a parallel arm that electrically connects a portion between the second inductor and the output end and a ground potential is not provided. 4. The first inductor is provided closer to the input end than the second inductor,
Third and fourth series arm acoustic wave resonators electrically connected in parallel between the first inductor and the input end;
A connection point between the input end and the third and fourth series arm elastic wave resonators is electrically connected to a ground potential, and a third parallel arm elastic wave resonator is provided. A third parallel arm;
A connection point between the first inductor and the third and fourth series arm elastic wave resonators is electrically connected to a ground potential, and a fourth parallel arm elastic wave resonator is provided. A fourth parallel arm,
The elastic wave filter device according to any one of claims 1 to 3, further comprising: Each of the first and second series arm elastic wave resonators and the first and second parallel arm elastic wave resonators includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate. And
The acoustic wave filter device according to any one of claims 1 to 4, wherein the piezoelectric substrate is configured by a 55 ° rotation Y-cut X-propagating LiNbO ₃ substrate.   6. The acoustic wave filter according to claim 5, wherein a duty ratio of at least one of the IDT electrodes of the first and second series arm acoustic wave resonators is in a range of 0.3 to 0.5. 7. apparatus.   The surface acoustic wave filter device according to claim 1, which is a surface acoustic wave filter device using surface acoustic waves.   The elastic wave filter apparatus as described in any one of Claims 1-6 which is a boundary acoustic wave filter apparatus using a boundary acoustic wave.

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