Patent Application
20230283262
The present invention relates to an acoustic wave filter including first, second, and third acoustic wave resonators connected in series, and a composite filter device.
Hitherto, various acoustic wave filters including multiple acoustic wave resonators have been proposed. In an acoustic wave filter disclosed in Japanese Unexamined Patent Application Publication No. 09-205343 below, multiple resonators having the same electrode finger pitch and connected in series are provided. According to Japanese Unexamined Patent Application Publication No. 09-205343, a series arm resonator is split into multiple resonators connected in series, thus enhancing electric power handling capability.
Deterioration of electric power handling capability of an acoustic wave resonator is caused by a large displacement in a frequency range from a resonant frequency to an anti-resonant frequency during power application. In particular, local heat generation due to high voltage at the anti-resonant frequency causes electrochemical migration, thus lowering the electric power handling capability.
According to Japanese Unexamined Patent Application Publication No. 09-205343, the series arm resonator is split into multiple resonators connected in series to improve the electric power handling capability, but the electric power handling capability is still insufficient. In particular, in recent years, as demand for higher frequency has increased, a distance between electrode fingers has been shortened, which requires further improvement in the electric power handling capability.
Preferred embodiments of the present invention provide acoustic wave filters and composite filter devices that each can achieve enhanced electric power handling capability.
In a broad aspect of an acoustic wave filter according to a preferred embodiment of the present invention, the acoustic wave filter includes an input end, an output end, and a series arm connecting the input end and the output end. The series arm includes n acoustic wave resonators connected in series in an order of first, second, to nth acoustic wave resonators, where n is a natural number. Each of the n acoustic wave resonators includes multiple electrode fingers. The n acoustic wave resonators include an mth acoustic wave resonator, where m is a natural number of 1<m<n. The mth acoustic wave resonator is interposed between the first and nth acoustic wave resonators. An electrode finger pitch of the mth acoustic wave resonator is smallest among electrode finger pitches of the n acoustic wave resonators.
In another broad aspect of an acoustic wave filter according to a preferred embodiment of the present invention, the acoustic wave filter includes an input end, an output end, a series arm connecting the input end and the output end, and a parallel arm connecting the series arm and a ground potential. The parallel arm includes n acoustic wave resonators connected in series in an order of first, second, to nth acoustic wave resonators, where n is a natural number. Each of the n acoustic wave resonators includes multiple electrode fingers. The n acoustic wave resonators include an mth acoustic wave resonator, where m is a natural number of 1<m<n. The mth acoustic wave resonator is interposed between the first and nth acoustic wave resonators. An electrode finger pitch of the mth acoustic wave resonator is largest among electrode finger pitches of the n acoustic wave resonators.
A composite filter device according to a preferred embodiment of the present invention includes an acoustic wave filter according to another preferred embodiment of the present invention and at least one band-pass filter with a pass band different from a pass band of the acoustic wave filter. One end of the acoustic wave filter and one end of the at least one band-pass filter are connected in common.
Acoustic wave filters and composite filter devices according to preferred embodiments of the present invention can achieve enhanced electric power handling capability.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Hereinafter, specific preferred embodiments of the present invention will be described with reference to the drawings to clarify the present invention.
It should be noted that the preferred embodiments described herein are merely examples, and partial replacement or combination of elements or features is possible between different preferred embodiments.
The composite filter device 1 includes a common terminal 4 that is connected to an antenna. An inductor L1 for impedance adjustment is connected between the common terminal 4 and a ground potential.
An acoustic wave filter 2 according to the first preferred embodiment of the present invention is connected between the common terminal 4 and a transmission terminal 5. The acoustic wave filter 2 is a transmission filter. Therefore, the transmission terminal 5 is an input end, and the common terminal 4 is an output end.
An acoustic wave filter 3 as a reception filter is connected between the common terminal 4 and a reception terminal 6.
In the acoustic wave filter 2, series arm resonators S1 to S5 are provided in a series arm connecting the transmission terminal 5 and the common terminal 4. In multiple parallel arms connecting the series arm and the ground potential, parallel arm resonators P1 to P4 are provided.
The parallel arm resonator P1 is connected between a connection point between the series arm resonator S1 and the series arm resonator S2 and the ground potential. The parallel arm resonator P2 is connected between a connection point between the series arm resonator S2 and the series arm resonator S3 and the ground potential. Ground potential side end portions of the parallel arm resonators P1 and P2 are connected in common to the ground potential. The parallel arm resonator P3 is connected between a connection point between the series arm resonator S3 and the series arm resonator S4 and the ground potential. The parallel arm resonator P4 is connected between a connection point between the series arm resonator S4 and the series arm resonator S5 and the ground potential. Ground potential side end portions of the parallel arm resonator P3 and the parallel arm resonator P4 are connected in common to the ground potential via an inductor L3.
An inductor L2 is connected between the transmission terminal 5 and the ground potential.
In the acoustic wave filter 2, each of the series arm resonators S1 to S5 and the parallel arm resonators P1 to P4 has a structure in which an acoustic wave resonator is split into multiple acoustic wave resonators connected in series in order to enhance the electric power handling capability. That is, each of the resonators includes multiple split resonators. To be more specific, of the series arm resonators S1 to S5, the series arm resonator S1 includes acoustic wave resonators S1a to S1d, the series arm resonator S2 includes acoustic wave resonators S2a to S2e, the series arm resonator S3 includes acoustic wave resonators S3a to S3d, the series arm resonator S4 includes acoustic wave resonators S4a to S4c, and the series arm resonator S5 includes acoustic wave resonators S5a to S5d.
Each of the parallel arm resonators P1 to P3 has a structure in which three acoustic wave resonators are connected in series, and the parallel arm resonator P4 has a structure in which two acoustic wave resonators are connected in series.
As illustrated in
As illustrated in
One feature of the acoustic wave filter 2 is that electrode finger pitches of the acoustic wave resonators S4a to S4c are different in the series arm resonator S4. To be more specific, the acoustic wave resonator S4a corresponds to a first acoustic wave resonator, the acoustic wave resonator S4b corresponds to a second acoustic wave resonator, and the acoustic wave resonator S4c corresponds to a third acoustic wave resonator. Hereinafter, the acoustic wave resonator S4a will be described as the first acoustic wave resonator S4a, the acoustic wave resonator S4b will be described as the second acoustic wave resonator S4b, and the acoustic wave resonator S4c will be described as the third acoustic wave resonator S4c. An average electrode finger pitch of the second acoustic wave resonator S4b is smallest among average electrode finger pitches of the first to third acoustic wave resonators S4a to S4c, and the second acoustic wave resonator S4b is physically interposed between the first acoustic wave resonator S4a and the third acoustic wave resonator S4c.
The number of acoustic wave resonators is not limited to three. A characteristic series arm resonator according to a preferred embodiment of the present invention only needs to include n (n is a natural number) acoustic wave resonators. The n acoustic wave resonators only need to be connected in series in an order of first, second, . . . , and nth acoustic wave resonators. Further, the n acoustic wave resonators only need to include an mth acoustic wave resonator (m is a natural number of 1<m<n), and an electrode finger pitch of the mth acoustic wave resonator only needs to be smallest among electrode finger pitches of the n acoustic wave resonators. In the present preferred embodiment, n=3 and m=2.
Preferably, the n acoustic wave resonators are disposed on an input end side in the series arm.
As illustrated in
A resonant frequency of the second acoustic wave resonator S4b is located outside a pass band. To be more specific, the resonant frequency of the second acoustic wave resonator S4b is located in a frequency band higher than the pass band. The first to third acoustic wave resonators S4a, S4b, and S4c satisfy the following relationship: a capacitance of second acoustic wave resonator S4b=number of pairs of electrode fingers x intersecting width<capacitances of first and third acoustic wave resonators S4a and S4c. In this case, areas of the first and third acoustic wave resonators S4a and S4c, which generate large amounts of heat, are larger than when the first to third acoustic wave resonators have the same resonant frequency and the same capacitance. Therefore, a heat generation density is lowered and the electric power handling capability can be enhanced. Further, attenuation in the frequency band higher than the pass band can be improved without degrading attenuation in the pass band.
In the present preferred embodiment, the electrode finger pitch P in the second acoustic wave resonator S4b is smallest among the electrode finger pitches in the first to third acoustic wave resonators S4a to S4c.
Therefore, the acoustic wave filter 2 can achieve effectively enhanced electric power handling capability. A reason for this is as follows. In the series arm resonator S4, the first to third acoustic wave resonators S4a to S4c are connected in series. Since the electrode finger pitch of the second acoustic wave resonator S4b is smallest, power consumption, that is, an amount of heat generation, in the second acoustic wave resonator S4b is smallest among the first to third acoustic wave resonators S4a to S4c. Therefore, by physically interposing the second acoustic wave resonator S4b, which is less likely to generate heat, between the first and third acoustic wave resonators S4a and S4c, power consumption per unit area in the series arm resonator S4 can be reduced, thus enhancing the electric power handling capability.
No circuit elements other than the first to third acoustic wave resonators S4a to S4c are connected between the first and third acoustic wave resonators S4a and S4c and the second acoustic wave resonator S4b. Further, wires connecting the first and third acoustic wave resonators S4a and S4c to the second acoustic wave resonator S4b are not connected to the ground potential. Therefore, heat dissipation from the second acoustic wave resonator S4b tends to be insufficient. In such a case, preferred embodiments of the present invention is particularly suitable. Here, multiple wires connecting acoustic wave resonators are collectively referred to as a connection node. Similar to the above, a preferred embodiment of the present invention is particularly suitable when no circuit elements other than the n acoustic wave resonators are connected to the connection node connecting the n acoustic wave resonators, and the connection node is not connected to the ground potential.
The acoustic wave filter 3 is a ladder filter including series arm resonators S11 to S15 and parallel arm resonators P11 to P14. Also in the acoustic wave filter 3, although not limited, the series arm resonators S11 to S15 and the parallel arm resonators P11 to P14 include acoustic wave resonators. In the acoustic wave filter 3 as a reception filter, an inductor L4 is connected between the parallel arm resonator P14 and the ground potential. An inductor L5 is connected between the reception terminal 6 and the ground potential.
A circuit configuration of the acoustic wave filter 3 is not limited, and may be any other band-pass filter other than the ladder filter. The acoustic wave filter 3 may be a band-pass filter other than the acoustic wave filter.
Next,
In Example 1, for the first and third acoustic wave resonators S4a and S4c, wavelengths determined by the electrode finger pitches of the IDT electrodes were set to 1.5374 μm, and wavelengths determined by the electrode finger pitches of the reflectors were also set to the same value. For the second acoustic wave resonator S4b, a wavelength determined by the electrode finger pitch was set to about 1.5297 μm, and a wavelength determined by the electrode finger pitch of the reflectors was also set to the same value.
In Comparative Example 1, a wavelength determined by the electrode finger pitch for the second acoustic wave resonator S4b was set to be equal to the wavelengths determined by the electrode finger pitches for the first and third acoustic wave resonators S4a and S4c, that is, 1.5374 μm. Other configurations of Comparative Example 1 were the same as those of Example 1.
In
Therefore, the acoustic wave filter 2 can achieve effectively enhanced electric power handling capability as compared with existing acoustic wave filters.
As illustrated in
The second acoustic wave resonator P3b is interposed between the first acoustic wave resonator P3a and the third acoustic wave resonator P3c in a Y direction orthogonal to an acoustic wave propagation direction X.
In the acoustic wave filter of the second preferred embodiment, the third parallel arm resonator P3 is configured as described above, and other configurations are the same as those of Comparative Example 1 described above. That is, a series arm resonator S4 is the same as that of Comparative Example 1 described above.
It will be described with reference to
In Example 2, for the first and third acoustic wave resonators P3a and P3c, wavelengths determined by electrode finger pitches were about 1.5858 μm. That is, the electrode finger pitch is about 0.7929 (=about 1.5858/2) μm. The same pitch was used for reflectors.
On the other hand, for the second acoustic wave resonator P3b, a wavelength determined by an electrode finger pitch was set to about 1.5866 μm, that is, an electrode finger pitch was set to about 0.7933 μm, and the electrode finger pitch for reflectors was also set to the same value.
In Comparative Example 2, for the first to third acoustic wave resonators P3a to P3c, electrode finger pitches were all the same, that is, wavelengths determined by the electrode finger pitches were 1.5858 μm. Other configurations of Comparative Example 2 were the same as those of Example 2.
In
As is clear from
The resonant frequencies and the anti-resonant frequencies of the first to third acoustic wave resonators S4a to S4c are as shown in Table 1 below.
The resonant frequencies and the anti-resonant frequencies of the first to third acoustic wave resonators P3a to P3c in the parallel arm resonator P3 are as shown in Table 2 below.
The number of acoustic wave resonators is not limited to three. Also in the second preferred embodiment, the series arm resonator only needs to include n (n is a natural number) acoustic wave resonators. In the parallel arm, n acoustic wave resonators only need to be connected in series in an order of first, second, . . . , and nth acoustic wave resonators. Further, the n acoustic wave resonators only need to include an mth acoustic wave resonator (m is a natural number of 1<m<n), and an electrode finger pitch of the mth acoustic wave resonator only needs to be largest among electrode finger pitches of the n acoustic wave resonators. In the present preferred embodiment, n=3 and m=2.
As illustrated in
In the acoustic wave filter 32, series arm resonators S1 to S5 are provided in a series arm connecting the transmission terminal 5 and the common terminal 4. Parallel arm resonators P1 to P4 are connected between the series arm and the ground potential. A difference from the acoustic wave filter 2 of the first preferred embodiment is that each of the series arm resonators S1 to S5 is a single acoustic wave resonator and is not split into multiple acoustic wave resonators. Similarly, each of the parallel arm resonators P1 to P4 is a single acoustic wave resonator in the acoustic wave filter 32.
In the acoustic wave filter 32, which is a ladder filter, the series arm resonators S2 to S4 correspond to first to third acoustic wave resonators.
That is, an electrode finger pitch of the series arm resonator S3, which is the second acoustic wave resonator, is smaller than electrode finger pitches of the series arm resonators S2 and S4, which are the first and third acoustic wave resonators. As illustrated in
In the acoustic wave filter 32, since the series arm resonators S2 to S4 are configured as described above, an amount of heat generated by the series arm resonator S3 is smaller than an amount of heat generated by each of the series arm resonators S2 and S4. Therefore, the amount of heat generation can be reduced in a portion where the series arm resonators S2 to S4 are disposed on the piezoelectric substrate 7, thus enhancing the electric power handling capability.
As described above, preferred embodiments of the present invention are not limited to a structure in which one acoustic wave resonator is split to include first to third acoustic wave resonators connected in series, but can be widely applied to structures including first to third acoustic wave resonators connected in series.
In the composite filter device 31, the acoustic wave filter 33 as a reception filter has a structure in which a longitudinally coupled resonator acoustic wave filter 34 and an acoustic wave resonator 35 are connected. A circuit configuration of the acoustic wave filter 33 is not limited.
The series arm resonator S2 includes an acoustic wave resonator S2a corresponding to a first acoustic wave resonator in the present invention, acoustic wave resonators S2b1 and S2b2 corresponding to second acoustic wave resonators, and a third acoustic wave resonator S2c. The acoustic wave resonators S2b1 and S2b2 are connected in parallel.
The series arm resonators S3 to S5 have a structure in which multiple acoustic wave resonators are connected in series. Parallel arm resonators P1 to P4 also have a structure in which multiple acoustic wave resonators are connected in series. Ground potential side end portions of the parallel arm resonators P3 and P4 are connected in common to the ground potential via an inductor L3.
In the composite filter device 41, in the series arm resonator S2, electrode finger pitches of the second acoustic wave resonators S2b1 and S2b2 are smaller than electrode finger pitches of the first and third acoustic wave resonators S2a and S2c. The electrode finger pitches of the first acoustic wave resonator S2a and the third acoustic wave resonator S2c may be equal or different.
The electrode finger pitches of the second acoustic wave resonators S2b1 and S2b2 may be equal or different. However, the electrode finger pitches of the second acoustic wave resonators S2b1 and S2b2 need to be smaller than the electrode finger pitches of the first and third acoustic wave resonators S2a and S2c as described above.
Since the acoustic wave filter 42 is configured as described above, an amount of heat generated in the series arm resonator S2 can be reduced, thus enhancing the electric power handling capability. That is, the second acoustic wave resonators S2b1 and S2b2, which are less likely to generate heat, are interposed between the first and third acoustic wave resonators S2a and S2c. Therefore, the amount of heat generation can be reduced and the electric power handling capability can be enhanced.
The second acoustic wave resonator, such as the second acoustic wave resonators S2b1 and S2b2, may be split so that multiple acoustic wave resonators are connected in parallel. In this case, the number of divisions may be three or more.
In the first to fourth preferred embodiments, the first and third acoustic wave resonators may also have a structure split so that multiple acoustic wave resonators are connected in parallel.
The composite filter device 41A is otherwise similar to the composite filter device 41 illustrated in
As in the composite filter device 41A, in an acoustic wave filter 42A, the first to third parallel arm resonators may be connected in a parallel arm. Electrode finger pitches of the second acoustic wave resonators P1c1 and P1c2 are larger than electrode finger pitches of the first and third acoustic wave resonators P1b and P1d. The electrode finger pitches of the first acoustic wave resonator P1b and the third acoustic wave resonator P1d may be equal or different. The electrode finger pitches of the acoustic wave resonator P1c1 and the acoustic wave resonator P1c2 may be equal or different. In a preferred embodiment of the present invention, the first to third acoustic wave resonators may be used in the parallel arm resonator as described above.
Note that in the acoustic wave filter 51, instead of the series arm resonators S2 to S4, acoustic wave resonators 52 to 54 of the series arm resonator S1 may be used as the first to third acoustic wave resonators, thus enhancing the electric power handling capability.
That is, in preferred embodiments of the present invention, positions of the first to third acoustic wave resonators connected in series are not limited.
That is, the first to third acoustic wave resonators in preferred embodiments of the present invention are not limited to ladder filters.
That is, a composite filter device according to a preferred embodiment of the present invention can be applied not only to a duplexer including a transmission filter and a reception filter but also to various composite filter devices such as a multiplexer in which the one ends of three or more band-pass filters are connected in common.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-191895 | Nov 2020 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2020-191895 filed on Nov. 18, 2020 and is a Continuation Application of PCT Application No. PCT/JP2021/041750 filed on Nov. 12, 2021. The entire contents of each application are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/041750 | Nov 2021 | US |
| Child | 18196520 | US |
