Composite filter device

Abstract

The present invention provides a composite filter device that can suppress the generation of ripples in the passband of other bandpass filters connected in common. The composite filter device includes: a ladder filter (10) having at least one series-arm resonator including a first series-arm resonator (S1) and at least one shunt-arm resonator including a first shunt-arm resonator (P1); and at least one bandpass filter (11, 12). One end of the ladder filter (10) and the at least one bandpass filter (11, 12) are connected in common to each other. The first series-arm resonator (S1) is arranged closest to the common terminal (13) among the series-arm resonators (S1 to S5), and the first shunt-arm resonator (P1) is arranged closest to the common terminal (13) among the shunt-arm resonators (P1 to P4). When the duty ratio of the IDT of the first series-arm resonator (S1) is set as Sa, the duty ratio of the IDT of the first shunt-arm resonator (P1) is set as Pa, and the duty ratios of the IDTs of the remaining series-arm resonators (S2 to S5) and shunt-arm resonators (P2 to P4) are set as Ta, any one of the following formulas (1), (2), and (3) is satisfied. Sa < Pa < Ta... Formula (1) Ta < Sa < Pa... Formula (2) Pa < Ta < Sa... Formula (3).

Description

Technical Field

[0001] The present invention relates to a composite filter device that has at least one bandpass filter and a trapezoidal filter connected together. Background Technology

[0002] Previously, composite filter devices were used for the IF band of mobile communication devices such as smartphones. In composite filter devices, one end of multiple bandpass filters is connected to each other. In the composite filter device described in Patent Document 1 below, one end of a trapezoidal filter and other bandpass filters is connected to each other. This trapezoidal filter has a series arm resonator and a parallel arm resonator that include an elastic wave resonator.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-81068 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the composite filter device described in Patent Document 1, although a surface leakage wave is utilized, ripple caused by Rayleigh waves appears outside the passband. When this ripple is located within the passband of another bandpass filter with a common connection, the other bandpass filters suffer from increased loss and degraded performance within the passband.

[0008] The purpose of this invention is to provide a composite filter device capable of suppressing the generation of ripple in the passband of other bandpass filters with common connections.

[0009] Technical solutions for solving the problem

[0010] The composite filter device according to the present invention includes: a ladder filter having at least one series-arm resonator including a first series-arm resonator and at least one shunt-arm resonator including a first shunt-arm resonator, wherein the series-arm resonator and the shunt-arm resonator are surface acoustic wave (SAW) resonators having IDT electrodes; and at least one band-pass filter. One end of the ladder filter and one end of the at least one band-pass filter are connected to each other at a common terminal. The first series-arm resonator is arranged closest to the common terminal among the series-arm resonators of the ladder filter, and the first shunt-arm resonator is arranged closest to the common terminal among the shunt-arm resonators of the ladder filter. When the duty ratios of the IDT electrodes of the first series-arm resonator, the first shunt-arm resonator, the remaining series-arm resonators, and the shunt-arm resonators are set as Sa, Pa, Ta, respectively, any one of the following formulas (1), (2), and (3) is satisfied.

[0011] Sa < Pa < Ta... Formula (1)

[0012] Ta < Sa < Pa... Formula (2)

[0013] Pa < Ta < Sa... Formula (3)

[0014] Advantages of the Invention

[0015] In the composite filter device according to the present invention, it is possible to suppress the generation of ripples in the passband of other band-pass filters connected in common. Description of the Drawings

[0016] Figure 1 is a circuit diagram of the composite filter device according to the first embodiment of the present invention.

[0017] Figure 2 is a schematic top view showing the electrode structure of the surface acoustic wave resonator used in the first embodiment of the present invention.

[0018] Figure 3 (a) is a front cross-sectional view of the surface acoustic wave resonator used in the first embodiment, Figure 3 (b) is a front cross-sectional view showing a modified example of the surface acoustic wave resonator.

[0019] Figure 4 is a graph showing the filter characteristics of the ladder filter when the duty ratio of the first series-arm resonator in the ladder filter is 0.5 or 0.425.

[0020] Figure 5This is a graph showing the Rayleigh wave return loss characteristics of other bandpass filters with common connections when the duty cycle of the first series arm resonator in the trapezoidal filter is varied from 0.5 to 0.425.

[0021] Figure 6 (a) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the first series arm resonator is removed from the trapezoidal filter. Figure 6 (b) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the second series arm resonator is removed from the trapezoidal filter. Figure 6 (c) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the third series arm resonator is removed from the trapezoidal filter.

[0022] Figure 7 Figure (a) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the first parallel arm resonator is removed from the trapezoidal filter. Figure 7 (b) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the second parallel arm resonator is removed from the trapezoidal filter. Figure 7 (c) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the third parallel arm resonator is removed from the trapezoidal filter.

[0023] Figure 8 (a) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the fourth series arm resonator is removed from the trapezoidal filter. Figure 8 (b) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the fifth series arm resonator is removed from the trapezoidal filter. Figure 8 (c) is a graph showing the return loss characteristics of the trapezoidal filter and the return loss characteristics when the fourth parallel arm resonator is removed from the trapezoidal filter.

[0024] Figure 9 (a) is a detailed illustration of the structure that shifts the Rayleigh wave response caused by the first parallel arm resonator P1 and the Rayleigh wave response caused by the first series arm resonator S1 to the lower frequency side of the passband of other bandpass filters. Figure 9 (b) is a detailed illustration of the structure that shifts the Rayleigh wave response caused by the first parallel arm resonator P1 and the Rayleigh wave response caused by the first series arm resonator S1 toward the higher frequency side of the passband of other bandpass filters. Figure 9(c) is a detailed illustration of the structure that shifts the Rayleigh wave response caused by the first parallel arm resonator P1 toward the lower frequency side of the passband of other bandpass filters and shifts the Rayleigh wave response caused by the first series arm resonator S1 toward the higher frequency side of that passband. Detailed Implementation

[0025] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0026] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0027] Figure 1 This is a circuit diagram of a composite filter device according to the first embodiment of the present invention. In the composite filter device 1, one end of the trapezoidal filter 10 and other bandpass filters 11, 12, ... are connected to each other via a common terminal 13. The common terminal 13 is connected, for example, to an antenna terminal.

[0028] The trapezoidal filter 10 has a series arm connecting a common terminal 13 and a terminal 14. In this series arm, resonators S1 to S5 of the first to fifth series arms are connected in series. A first parallel arm resonator P1 is connected between the node between the first and second series arm resonators S1 and S2 and the ground potential. A second parallel arm resonator P2 is connected between the node between the second and third series arm resonators S2 and the ground potential. A third parallel arm resonator P3 is connected between the node between the third and fourth series arm resonators S3 and the ground potential. A fourth parallel arm resonator P4 is connected between the node between the fourth and fifth series arm resonators S4 and the ground potential.

[0029] The first series arm resonator S1 to the fifth series arm resonator S5 and the first parallel arm resonator P1 to the fourth parallel arm resonator P4 all contain elastic wave resonators.

[0030] The circuit structures of other bandpass filters 11 and 12 are not limited to this. They can be trapezoidal filters or bandpass filters that include longitudinally coupled resonator type elastic wave filters, etc.

[0031] However, the passbands of bandpass filters 11 and 12 are different from those of trapezoidal filter 10.

[0032] In this embodiment, the trapezoidal filter 10 is a Band 1 Tx filter with a passband of 1920MHz to 1980MHz. Furthermore, the bandpass filter 11 is a Band 32 filter with a passband of 1452MHz to 1496MHz.

[0033] The electrode structure of the elastic wave resonator constituting the first series arm resonator S1 to the fifth series arm resonator S5 and the first parallel arm resonator P1 to the fourth parallel arm resonator P4 is shown in the figure. Figure 2 .

[0034] In the elastic wave resonator, reflectors 8 and 9 are arranged on both sides of the elastic wave propagation direction of the IDT electrode 7. This constitutes a single-port elastic wave resonator.

[0035] Figure 3 (a) is a front cross-sectional view of the elastic wave resonator according to the first embodiment. The aforementioned IDT electrode 7 and reflectors 8 and 9 are disposed on the piezoelectric substrate 2, which serves as the piezoelectric layer. The piezoelectric substrate 2 comprises a LiTaO3 substrate. However, the piezoelectric substrate 2 may also comprise other piezoelectric single crystals.

[0036] Figure 3 (b) is a front cross-sectional view illustrating a modified example of an elastic wave resonator. In this modified example, an IDT electrode 7 and reflectors 8 and 9 are provided on a composite piezoelectric substrate 5. In the composite piezoelectric substrate 5, a low-velocity layer 4 and a piezoelectric layer 2A are stacked on a support substrate 3 containing Si or the like. The piezoelectric layer 2A contains LiTaO3 and LiNbO3, and its thickness is set to 10λ or less when the wavelength determined by the electrode finger spacing of the IDT electrode 7 is set to λ. Preferably, it is 5λ or less. The low-velocity layer 4 contains a low-velocity material in which the velocity of the propagating bulk wave is lower than the velocity of the bulk wave propagating in the piezoelectric layer 2A. Examples of such low-velocity materials include silicon oxide, glass, silicon oxynitride, tantalum oxide, and compounds in which fluorine, carbon, and boron are added to silicon oxide, as well as media with the above materials as the main components.

[0037] In addition to Si, the support substrate 3 can also contain various dielectrics and piezoelectrics. Preferably, the support substrate 3 contains a hypersonic material.

[0038] High-velocity acoustic materials are defined as materials in which the speed of sound propagating in bulk is higher than the speed of sound propagating in elastic waves within the piezoelectric layer 2A. Examples of such high-velocity acoustic materials include alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) films or diamond, media primarily composed of the above materials, and media primarily composed of mixtures of the above materials, among many other materials.

[0039] In the composite piezoelectric substrate 5, due to the aforementioned stacked structure, elastic waves are effectively confined within the piezoelectric layer 2A. This improves the Q value.

[0040] In addition, as the support substrate 3, instead of using a structure with a support substrate containing a high acoustic velocity material, a structure in which a high acoustic velocity member 3b is laminated on the substrate 3a may be employed. The high acoustic velocity member 3b contains the above-described high acoustic velocity material. In this case, the substrate 3a may also contain materials other than the high acoustic velocity material. As such materials, various dielectrics and semiconductors can be used.

[0041] The composite filter device 1 is characterized as follows.

[0042] In the ladder filter 10, the series arm resonator closest to the common terminal 13 is the first series arm resonator S1, and the shunt arm resonator closest to the common terminal 13 is the first shunt arm resonator P1. Here, the duty ratio of the IDT electrode of the first series arm resonator S1 is set as Sa, the duty ratio of the IDT electrode of the first shunt arm resonator P1 is set as Pa, and the duty ratios of the IDT electrodes of the remaining second series arm resonator S2 to fifth series arm resonator S5 and second shunt arm resonator P2 to fourth shunt arm resonator P4 are set as Ta. In this case, any one of the following equations (1), (2), and (3) is satisfied.

[0043] Sa < Pa < Ta... Equation (1)

[0044] Ta < Sa < Pa... Equation (2)

[0045] Pa < Ta < Sa... Equation (3)

[0046] In the composite filter device 1, since the duty ratios of the surface acoustic wave resonators of the ladder filter 10 satisfy any one of equations (1) to (3), generation of ripples in the passband of the bandpass filter 11 can be suppressed. As a result, deterioration of the loss in the passband of the bandpass filter 11 can be suppressed, and the filter characteristics can be improved.

[0047] This will be described in more detail.

[0048] Figure 4 is a diagram showing the filter characteristics of the ladder filter 10 in the case where the duty ratio of the first series arm resonator S1 is 0.425 and in the case where the duty ratio of the first series arm resonator S1 is 0.5. The dashed line shows the result in the case where the duty ratio = 0.5, and the solid line shows the case where the duty ratio = 0.425.

[0049] In addition, corresponding to the amount of change in the duty ratio, the wavelength and the crossover width determined by the electrode finger pitch of the IDT electrode are adjusted, and the characteristics are adjusted.

[0050] By Figure 4It is clear that even if the duty cycle is changed from 0.5 to 0.425, the filter characteristics of the two are almost identical, and there will be no degradation of insertion loss or attenuation characteristics in the filter characteristics caused by the change in duty cycle.

[0051] Furthermore, when the LiTaO3 substrate is used as a piezoelectric substrate, the response caused by the Rayleigh wave occurs at a position 0.76 times the resonant frequency fr.

[0052] Table 1 below shows the cross width of the IDT electrodes and the number of electrode finger pairs for the first series arm resonator S1 with a duty cycle of 0.5 and 0.425. As shown in Table 1, in the first series arm resonator S1, the relationship between the duty cycle and the wavelength determined by the electrode finger spacing is the opposite. Furthermore, this relationship is preferably also true between multiple series arm resonators or multiple parallel arm resonators.

[0053] [Table 1]

[0054] wavelength 1.9237 1.9387 Cross width 25.4 30.6 The number of electrode fingers 160 160

[0055] Figure 5 The waveform of the Rayleigh wave response, i.e., the return loss characteristics, is shown when the duty cycle is varied from 0.5 to 0.425 as described above. Figure 5 The solid line shows the result when the duty cycle is 0.425, and the dashed line shows the result when the duty cycle is 0.5.

[0056] By changing the duty cycle of the first series arm resonator S1 from 0.5 to 0.425, the response induced by the Rayleigh wave shifts from 1447.2 MHz to 1429.8 MHz. That is, the response induced by the Rayleigh wave shifts to the lower frequency side. The invention of this application utilizes the shifting of the frequency position of the response induced by the Rayleigh wave by changing the duty cycle of the IDT electrode in this way.

[0057] Figure 6 (a)~ Figure 6 (c) Figure 7 (a)~ Figure 7 (c) and Figure 8 (a)~ Figure 8 The solid line in (c) is a diagram showing the return loss characteristics of the Rayleigh wave response when any one of the resonators is removed from the ladder filter 10. Figure 6 of (a), Figure 6 (b) and Figure 7 The dashed line in (a) shows the return loss characteristics of the ladder filter 10 itself.

[0058] Figure 6The solid line in (a) shows the return loss characteristics of the filter after removing the first series arm resonator S1. Figure 6 The solid line in (b) shows the return loss characteristics of the filter after removing the second series arm resonator S2. Figure 6 The solid line in (c) shows the return loss characteristics of the filter with the third series arm resonator S3 removed.

[0059] Figure 7 The solid line in (a) shows the return loss characteristics of the filter after removing the first parallel arm resonator P1. Figure 7 The solid line in (b) shows the return loss characteristics of the filter without the second parallel arm resonator P2. Figure 7 The solid line in (c) shows the return loss characteristics of the filter with the third parallel arm resonator P3 removed.

[0060] Figure 8 The solid line in (a) shows the return loss characteristics of the filter after removing the fourth series arm resonator S4. Figure 8 The solid line in (b) shows the return loss characteristics of the filter after removing the fifth series arm resonator S5. Figure 8 The solid line in (c) shows the return loss characteristics of the filter with the fourth parallel arm resonator P4 removed.

[0061] In addition, as a method for removing each series arm resonator or each parallel arm resonator, the series arm resonator is set to short circuit and the parallel arm resonator is set to open circuit.

[0062] Depend on Figure 6 (a)~ Figure 8 As can be clearly seen from (c), when the first series arm resonator S1, which is the series arm resonator closest to the common terminal 13, is removed, and when the first parallel arm resonator P1, which is the parallel arm resonator closest to the common terminal 13, is removed, the frequency position of the Rayleigh wave response has a large influence, while the frequency position of the Rayleigh wave response has a small influence in the case of other resonators.

[0063] As described above, by changing the duty cycle of the first series arm resonator S1 and the first parallel arm resonator P1, the frequency position of the response caused by the Rayleigh wave can be significantly changed. Moreover, in this invention, when the duty cycle of the IDT electrode of the first series arm resonator S1 is set to Sa, the duty cycle of the IDT electrode of the first parallel arm resonator P1 is set to Pa, and the duty cycles of the IDT electrodes of the remaining second series arm resonators S2 to the fifth series arm resonator S5 and the second parallel arm resonators P2 to the fourth parallel arm resonator P4 are set to Ta, any one of the aforementioned equations (1) to (3) is satisfied. Thus, the filter characteristics of the bandpass filter 11 can be improved by the following methods [1] to [3].

[0064] [1] In the first embodiment, when the duty cycle Sa of the IDT electrode of the first series arm resonator S1 is reduced, as previously stated, the frequency position of the response caused by the Rayleigh wave shifts to the lower frequency side. Similarly, when the duty cycle Pa of the IDT electrode of the first parallel arm resonator P1 is reduced, the response caused by the Rayleigh wave also shifts to the lower frequency side. Therefore, as Figure 9 As shown in (a), at a lower frequency side than the passband of the bandpass filter 11, the Rayleigh wave response caused by the first series arm resonator S1 and the Rayleigh wave response caused by the first parallel arm resonator P1 can be shifted out of the passband below the passband of the bandpass filter 11. In the trapezoidal filter 10, the resonant frequency of the series arm resonator becomes higher than the resonant frequency of the parallel arm resonator. Therefore, when the Rayleigh wave response is shifted out of the passband of the bandpass filter 11, the duty cycle Sa of the IDT electrode of the first series arm resonator S1 becomes smaller than the duty cycle Pa of the IDT electrode of the first parallel arm resonator P1. Therefore, if Sa < Pa < Ta, then as Figure 9 As shown in (a), it can suppress the generation of ripple in the passband of the bandpass filter 11 and improve the filter characteristics of the bandpass filter 11.

[0065] [2] In the second method, such as Figure 9 As shown in (b), the Rayleigh wave responses caused by the first series arm resonator S1 and the first parallel arm resonator P1 are shifted outwards from the high-frequency passband of the bandpass filter 11, towards the higher frequency side. Therefore, it is sufficient to set Ta < Sa < Pa.

[0066] [3] In the third method, such as Figure 9As shown in (c), the Rayleigh wave response caused by the first series arm resonator S1 is shifted to the higher frequency side of the passband of the larger bandpass filter 11, and the Rayleigh wave response caused by the first parallel arm resonator P1 is shifted to the lower frequency side of the passband of the larger bandpass filter 11. In this case, Pa < Ta < Sa.

[0067] As described above, in this invention, since the duty cycles of the first series arm resonator S1 and the first parallel arm resonator P1 have a significant impact on the frequency position of the response caused by the Rayleigh wave in the trapezoidal filter 10, they are configured to satisfy the above equations (1), (2), or (3). This causes the ripple caused by the Rayleigh wave to shift outside the passband of the bandpass filter 11. Therefore, it is possible to improve the filter characteristics of the bandpass filter 11, which serves as a common connection to other bandpass filters.

[0068] Furthermore, in the above embodiment, the passband of bandpass filter 11 is shown as another bandpass filter passband. However, in order to improve the filter characteristics in the passbands of other bandpass filters with common connection, the duty cycle of the IDT electrode of the first series arm resonator S1 and the duty cycle of the IDT electrode of the first parallel arm resonator P1 can be configured to satisfy any one of the above equations (1) to (3) in order to improve the filter characteristics in the passbands of bandpass filter 12 and other bandpass filters with common connection.

[0069] Even in this case, it is equally possible to improve the filter characteristics of other bandpass filters with common connections.

[0070] Furthermore, in this invention, since the duty cycle is adjusted, the aforementioned filter characteristics can be improved with almost no impact on the insertion loss and attenuation characteristics of other bandpass filters and trapezoidal filters in the common connection.

[0071] Furthermore, in the above embodiment, the common terminal 13 is the side connected to the antenna terminal, but in this invention, the common terminal can also be the output terminal. That is, when the trapezoidal filter 10 is a receiving filter, the common terminal 13 becomes an input terminal; when the trapezoidal filter 10 is a transmitting filter, the common terminal 13 becomes an output terminal. In either case, this invention can suppress the generation of ripple in the passband of other bandpass filters.

[0072] Explanation of reference numerals in the attached figures

[0073] 1: Composite filter device;

[0074] 2: Piezoelectric substrate;

[0075] 2A: Piezoelectric layer;

[0076] 3: Support base plate;

[0077] 3a: Substrate;

[0078] 3b: Hypersonic components;

[0079] 4: Low-sound-velocity layer;

[0080] 5: Composite piezoelectric substrate;

[0081] 7: IDT electrode;

[0082] 8, 9: Reflectors;

[0083] 10: Trapezoidal filter;

[0084] 11, 12: Bandpass filters;

[0085] 13: Common terminal;

[0086] 14: terminal;

[0087] P1~P4: The first to fourth parallel arm resonators;

[0088] S1~S5: Series arm resonators from the 1st to the 5th.

Claims

1. A composite filter device, comprising: A trapezoidal filter having at least one series arm resonator including a first series arm resonator and at least one parallel arm resonator including a first parallel arm resonator, wherein the series arm resonator and the parallel arm resonator are elastic wave resonators with IDT electrodes; and At least one bandpass filter, wherein one end of the trapezoidal filter and the at least one bandpass filter are connected to each other at a common terminal. The first series arm resonator is positioned closest to the common terminal among the series arm resonators of the trapezoidal filter, and the first parallel arm resonator is positioned closest to the common terminal among the parallel arm resonators of the trapezoidal filter. When the duty cycles of the IDT electrodes of the first series arm resonator, the first parallel arm resonator, the remaining series arm resonators, and the parallel arm resonators are set to Sa, Pa, and Ta respectively, any one of the following equations (1), (2), and (3) is satisfied. Sa < Pa < Ta… Equation (1) Ta < Sa < Pa… Equation (2) Pa < Ta < Sa… (3) 2. The composite filter device according to claim 1, wherein, The first series arm resonator and the first parallel arm resonator each have a piezoelectric layer and an IDT electrode disposed on the piezoelectric layer, wherein the piezoelectric layer comprises a LiTaO3 substrate.

3. The composite filter device according to claim 1, wherein, The first series arm resonator and the first parallel arm resonator each have a piezoelectric layer, an IDT electrode disposed on the piezoelectric layer, and a high-velocity acoustic component stacked on the surface of the piezoelectric layer opposite to the IDT electrode. The high-velocity acoustic component comprises a high-velocity acoustic material in which the velocity of a propagating volume wave is higher than the velocity of an elastic wave propagating in the piezoelectric layer.

4. The composite filter device according to claim 3, wherein, It also includes: a low-velocity layer, stacked between the high-velocity component and the piezoelectric layer, comprising a low-velocity material in which the velocity of the propagating volume wave is lower than the velocity of the volume wave propagating in the piezoelectric layer.

5. The composite filter device according to any one of claims 1 to 4, wherein, In the multiple series-arm resonators, the duty cycle is inversely related to the wavelength determined by the distance between the electrode fingers.

6. The composite filter device according to any one of claims 1 to 4, wherein, In the plurality of parallel arm resonators, the magnitude of the duty cycle is inversely related to the magnitude of the wavelength determined by the distance between the electrode fingers.

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