Elastic wave filter, high frequency module, and multiplexer

Abstract

The filter (10) includes a series resonator (S2) or a longitudinally coupled resonator (D1) configured on the path connecting the first input / output terminal (110) and the second input / output terminal (120), and a plurality of parallel resonators (P2 and P3) respectively connected between the above path and ground. The second parallel resonator (P2) and the first parallel resonator (P3) of the plurality of parallel resonators (P2 and P3) are connected in parallel without passing through other resonators. The IDT electrode of the first parallel resonator (P3) has a plurality of different electrode finger spacings. The average of all electrode finger spacings of the IDT electrode of the first parallel resonator (P3) is greater than the average of all electrode finger spacings of the IDT electrode of the second parallel resonator (P2).

Description

Technical Field

[0001] This invention relates to elastic wave filters, high-frequency modules, and multiplexers. Background Technology

[0002] Previously, an elastic wave filter with parallel resonators that are divided in parallel was disclosed (e.g., Patent Document 1). By making the resonant frequencies of the parallel resonators that are divided in parallel different, the transition band from the passband to the stopband is steep, and an elastic wave filter with a narrow passband can be realized.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 11-312951 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] An elastic wave resonator is inductive in the frequency band between its resonant frequency and anti-resonant frequency, and capacitive in the frequency bands lower than the resonant frequency and higher than the anti-resonant frequency. Therefore, in the frequency band between the respective resonant frequencies of the parallel resonators that are divided in parallel as described in Patent Document 1, one parallel resonator is capacitive and the other parallel resonator is inductive, thus generating LC resonance in the aforementioned frequency band.

[0008] In recent years, for communication devices such as portable telephone terminals, in order to handle multiple frequency bands and multiple wireless modes in a single terminal (i.e., multi-band and multi-mode), multiplexers (demultiplexers) are widely used to separate (demultiplex) high-frequency signals according to each frequency band. Multiple filters are connected together in the multiplexer. When the aforementioned LC resonance occurs in a certain elastic wave filter in the multiplexer, the impedance of that elastic wave filter in the passband of the other filters connected to it sometimes approaches 50Ω. This leads to a problem where the attenuation of the elastic wave filter in the attenuation band corresponding to the passband of the other filters deteriorates.

[0009] Therefore, the object of the present invention is to provide an elastic wave filter, etc., with a high steepness of the transition band from the passband to the stopband and the ability to suppress the degradation of the attenuation amount of the attenuation band corresponding to the passband of other filters when connected together with other filters.

[0010] means for solving problems

[0011] An elastic wave filter according to one aspect of the present invention comprises: a first input / output terminal; a second input / output terminal; a series resonator or a longitudinally coupled resonator disposed on a path connecting the first input / output terminal and the second input / output terminal; and a plurality of parallel resonators respectively connected between the aforementioned path and ground. The first and second parallel resonators are connected in parallel without passing through other resonators. The first and second parallel resonators each have an IDT electrode composed of a plurality of electrode fingers extending in a direction intersecting the elastic wave propagation direction and arranged parallel to each other. The IDT electrode of the first parallel resonator has a plurality of different electrode finger spacings, and the average of all electrode finger spacings of the IDT electrode of the first parallel resonator is greater than the average of all electrode finger spacings of the IDT electrode of the second parallel resonator.

[0012] One aspect of the high-frequency module of the present invention includes: the above-described elastic wave filter; and an amplifier connected to a first input / output terminal.

[0013] One embodiment of the multiplexer of the present invention includes: a common terminal; the aforementioned elastic wave filter; and a first filter having a third input / output terminal and a fourth input / output terminal, the passband of which is different from that of the elastic wave filter, and the common terminal being connected to the second input / output terminal and the fourth input / output terminal.

[0014] Invention Effects

[0015] According to the elastic wave filter of the present invention, the transition band from the passband to the stopband is steep, and the degradation of the attenuation amount of the attenuation band corresponding to the passband of other filters when connected together with other filters is suppressed. Attached Figure Description

[0016] Figure 1 This is a structural diagram illustrating an example of a multiplexer implemented in this way.

[0017] Figure 2 This is a diagram used to illustrate the distribution of electrode finger spacing in the comparative example.

[0018] Figure 3 This is a coordinate graph showing the impedance characteristics of the first and second parallel resonators in the comparative example.

[0019] Figure 4 This is a diagram used to illustrate the distribution of electrode finger spacing in the embodiments.

[0020] Figure 5 This is a coordinate graph showing the impedance characteristics of the first parallel resonator and the second parallel resonator in the embodiment.

[0021] Figure 6This is a Smith chart showing the impedance characteristics observed from the first input and output terminals of the elastic wave filter in the embodiments and comparative examples.

[0022] Figure 7 This is a coordinate graph showing the return loss characteristics observed from the first input and output terminals of the elastic wave filter in the embodiments and comparative examples.

[0023] Figure 8 This is a coordinate graph showing the filter characteristics of the elastic wave filter in the embodiments and comparative examples. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described in detail using the accompanying drawings. It should be noted that the embodiments described below are all inclusive or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of constituent elements, and connection methods shown in the following embodiments are examples and are not intended to limit the present invention. Constituent elements in the following embodiments not described in the independent claims are described as arbitrary constituent elements. Furthermore, the sizes or size ratios of the constituent elements shown in the drawings are not strict. Also, in the figures, substantially identical structures are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified. Furthermore, in the following embodiments, "connection" includes not only direct connections but also electrical connections via other elements.

[0025] (Implementation Method)

[0026] [1. Structure of a multiplexer]

[0027] Figure 1 This is a structural diagram illustrating an example of the multiplexer 50 implemented in this way. Figure 1 The diagram also shows an antenna element ANT connected to a common terminal 150 of the multiplexer 50, and an amplifier 20 connected to the input / output terminals 110 of the filter 10 constituting the multiplexer 50. The antenna element ANT is, for example, a multi-band antenna conforming to communication standards such as LTE (Long Term Evolution). The amplifier 20 is, for example, a low-noise amplifier that amplifies the high-frequency received signal from the antenna element ANT. The filter 10 and the amplifier 20 constitute a high-frequency module 30.

[0028] The multiplexer 50 is a demultiplexing / multiplexing circuit that uses an elastic wave filter. The multiplexer 50 has a common terminal 150, a filter 10 and a filter 40, and the common terminal 150 is connected to the input / output terminals 120 of the filter 10 and the input / output terminals 140 of the filter 4.

[0029] Common terminal 150 is commonly disposed on filters 10 and 40, and is connected to filters 10 and 40 inside multiplexer 50. Additionally, common terminal 150 is connected to antenna element ANT outside multiplexer 50. That is, common terminal 150 is also an antenna terminal of multiplexer 50.

[0030] Filter 10 has input / output terminals 110 and 120, and filter 40 has input / output terminals 130 and 140. Input / output terminal 110 is an example of a first input / output terminal, input / output terminal 120 is an example of a second input / output terminal, input / output terminal 130 is an example of a third input / output terminal, and input / output terminal 140 is an example of a fourth input / output terminal. For example, filter 10 is a receiving filter, in which case input / output terminal 110 becomes an output terminal and input / output terminal 120 becomes an input terminal. For example, filter 40 is a transmitting filter, in which case input / output terminal 130 becomes an input terminal and input / output terminal 140 becomes an output terminal.

[0031] Filter 10 is an elastic wave filter connected together with filter 40 in multiplexer 50. Filter 10 includes series resonators or longitudinally coupled resonators, as well as multiple parallel resonators. Here, filter 10 includes series resonators S1 and S2 and longitudinally coupled resonator D1 as series resonators or longitudinally coupled resonators, and parallel resonators P1, P2, and P3 as multiple parallel resonators. It should be noted that filter 10 may also omit both series resonators and longitudinally coupled resonators. For example, filter 10 may omit either series resonator S1 or S2. For example, filter 10 may also be a trapezoidal filter without longitudinally coupled resonator D1. In addition, filter 10 only needs to have at least parallel resonators P2 and P3 as multiple parallel resonators, but it may omit parallel resonator P1.

[0032] Series resonator S1 is a series resonator disposed on the path connecting input / output terminal 110 and input / output terminal 120, specifically disposed between input / output terminal 120 and longitudinally coupled resonator D1. Series resonator S2 is a series resonator disposed on the path connecting input / output terminal 110 and input / output terminal 120, specifically disposed between input / output terminal 110 and longitudinally coupled resonator D1. Longitudinally coupled resonator D1 is a longitudinally coupled resonator disposed on the path connecting input / output terminal 110 and input / output terminal 120, specifically disposed between series resonator S1 and series resonator S2. For example, longitudinally coupled resonator D1 is a seven-electrode longitudinally coupled resonator.

[0033] Parallel resonators P2 and P3 of the multiple parallel resonators in filter 10 are connected in parallel without passing through other resonators. Parallel resonator P1 is a parallel resonator connected between a node on the path connecting series resonator S1 and longitudinally coupled resonator D1 and ground. Parallel resonator P3 is an example of a first parallel resonator connected between a middle node on the path connecting series resonator S2 and input / output terminal 110 and ground. Parallel resonator P2 is an example of a second parallel resonator connected between a middle node on the path connecting series resonator S2 and input / output terminal 110 and ground, and connected in parallel with parallel resonator P3. A node refers to the connection point between components or between a component and a terminal. The node connected to parallel resonator P2 is the same node as the node connected to parallel resonator P3, and parallel resonators P2 and P3 are connected in parallel without passing through other resonators. For example, parallel resonators P2 and P3 can be segmented resonators, or they can be combined to form a single resonator. The passband and attenuation band of filter 10 are formed by series resonators S1 and S2, parallel resonators P1, P2, and P3, and a longitudinally coupled resonator D1. For example, the anti-resonance frequencies of parallel resonators P2 and P3 are designed to be located within the passband of filter 10, and the resonant frequencies of parallel resonators P2 and P3 are designed to be located near the attenuation poles of the low-frequency side of that passband. For example, filter 10 is a receive filter that uses LTE Band 8Rx (925-960MHz) as its passband.

[0034] Each resonator has an IDT electrode composed of multiple electrode fingers that extend in a direction intersecting the elastic wave propagation direction and are arranged parallel to each other. The IDT electrode of each resonator is formed on a substrate having a piezoelectric layer (a piezoelectric substrate). For example, the piezoelectric substrate is a Y-cut LiNbO3 substrate, and each resonator is a Rayleigh wave type surface acoustic wave element. Alternatively, a reflector can be formed on the piezoelectric substrate, arranged adjacent to the IDT electrode in the elastic wave propagation direction.

[0035] When the distance between adjacent electrode fingers in the direction of elastic wave propagation (specifically, the distance between the center lines of the electrode fingers) is defined as the electrode finger spacing, the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings. Consequently, the parallel resonator P3 generates multiple resonant points and has multiple resonant frequencies. Furthermore, the average of all electrode finger spacings of the IDT electrodes of the parallel resonator P3 is greater than the average of all electrode finger spacings of the IDT electrodes of the parallel resonator P2. Therefore, the average frequency of the multiple resonant frequencies of the parallel resonator P3 is less than the average frequency of the multiple resonant frequencies of the parallel resonator P2. The average of all electrode finger spacings of the IDT electrodes is obtained by dividing the distance between the centers of the electrode fingers at both ends of the IDT electrode in the direction of elastic wave propagation by the value obtained by subtracting 1 from the number of electrode fingers of the IDT electrode.

[0036] For example, if the electrode finger spacing of the IDT electrodes of the parallel resonator P2 is fixed, the average frequency of the multiple resonant frequencies of the parallel resonator P3 is less than the resonant frequency of the parallel resonator P2. Hereinafter, examples with multiple different electrode finger spacings for the IDT electrodes of the parallel resonator P3 will be described as embodiments, and examples with fixed electrode finger spacing for the IDT electrodes of the parallel resonator P3 will be described as comparative examples.

[0037] Filter 40 is an example of a first filter having input / output terminals 130 and 140 and a passband different from that of filter 10. For example, the passband of filter 40 is located on a lower frequency side than the passband of filter 10. Filter 40 can be an elastic wave filter or an LC filter. For example, filter 40 is a transmit filter that uses LTE Band 8Tx (880-915MHz) as its passband.

[0038] It should be noted that the number of filters connected to the common terminal 150 in the multiplexer 50 can also be more than three. Alternatively, the multiplexer 50 can also consist of only multiple transmitting filters, or only multiple receiving filters.

[0039] [2. Comparative Example]

[0040] Next, a comparative example with a fixed electrode finger spacing of the IDT electrodes of the parallel resonator P3 will be described.

[0041] Table 1 shows the parameters of the parallel resonators P1, P2, and P3 in the comparative example.

[0042] [Table 1]

[0043] Parallel resonators Average spacing Spacing distribution electrostatic capacitor P1 1.6778μm fixed 3.06pF P2 1.6759μm fixed 1.17pF P3 1.6892μm fixed 0.51pF

[0044] As shown in Table 1, in the comparative examples, the average spacing between all the IDT electrodes of the parallel resonator P1 is 1.6778 μm, the distribution of the electrode spacing is fixed, and the capacitance of the parallel resonator P1 is 3.06 pF. The average spacing between all the IDT electrodes of the parallel resonator P2 is 1.6759 μm, the distribution of the electrode spacing is fixed, and the capacitance of the parallel resonator P2 is 1.17 pF. The average spacing between all the IDT electrodes of the parallel resonator P3 is 1.6892 μm, the distribution of the electrode spacing is fixed, and the capacitance of the parallel resonator P3 is 0.51 pF.

[0045] Figure 2 This is a diagram used to illustrate the distribution of electrode finger spacing in the comparative example. Figure 2 The bottom side shows a top view of the parallel resonator P3 in the comparative example. Figure 2 Above, a coordinate graph showing the electrode finger spacing of the IDT electrodes of the parallel resonator P3 in the comparative example is shown. For example, when the number of electrode fingers of the IDT electrodes of the parallel resonator P3 is 42, the electrode finger spacing becomes 41. Figure 2 In the diagram, t1 to t41 represent the spacing between 41 electrode fingers.

[0046] In the comparative example, the IDT electrodes of the parallel resonator P3 do not have multiple different electrode finger spacings; the electrode finger spacing becomes fixed. (See Table 1 and...) Figure 2 As shown, the electrode finger spacing from t1 to t41 is all 1.6892 μm. Furthermore, as shown in Table 1, the average electrode finger spacing of the IDT electrodes of the parallel resonator P3 is greater than the average electrode finger spacing of the IDT electrodes of the parallel resonator P2. Therefore, the resonant frequency of the parallel resonator P3 is lower than the resonant frequency of the parallel resonator P2.

[0047] Figure 3 This is a coordinate graph showing the impedance characteristics of the parallel resonators P2 and P3 in the comparative example. Figure 3 In the diagram, the solid line represents the impedance characteristics of the parallel resonator P3, and the dashed line represents the impedance characteristics of the parallel resonator P2.

[0048] As described above, in the comparative example, the average spacing between all the electrode fingers of the IDT electrodes of the parallel resonator P3 is greater than the average spacing between all the electrode fingers of the IDT electrodes of the parallel resonator P2. Therefore, the resonant frequency of the parallel resonator P3 is lower than the resonant frequency of the parallel resonator P2. An elastic wave resonator is inductive in the frequency band between its resonant and anti-resonant frequencies, and capacitive in the frequency bands lower than the resonant frequency and higher than the anti-resonant frequency. In the passband (e.g., Band 8Tx) of the filter 40, located on the low-frequency side of the passband of the filter 10, the parallel resonator P2 is capacitive, and the parallel resonator P3 is inductive. That is, in Figure 3 In the frequency band shown by the dashed box, parallel resonator P2 becomes capacitive and parallel resonator P3 becomes inductive, generating LC resonance. When LC resonance is generated in filter 10 of multiplexer 50, the impedance of filter 10 in the passband of filter 40, which is connected to filter 10, sometimes approaches 50Ω (i.e., the return loss in the passband of filter 40 increases), resulting in a problem of deterioration in the attenuation of filter 10 in the attenuation band corresponding to the passband of filter 40.

[0049] Therefore, in the embodiment, the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings.

[0050] [3. Example]

[0051] Next, an embodiment with multiple different electrode finger spacings for the IDT electrodes of the parallel resonator P3 will be described.

[0052] Table 2 shows the parameters of the parallel resonators P1, P2, and P3 in the embodiment.

[0053] [Table 2]

[0054] Parallel resonators Average spacing Spacing distribution electrostatic capacitor P1 1.6778μm fixed 3.06pF P2 1.6759μm fixed 1.17pF P3 1.6975μm different 0.51pF

[0055] As shown in Table 2, in this embodiment, the average spacing of all the electrode fingers of the IDT electrodes of the parallel resonator P1 is 1.6778 μm, the distribution of the electrode finger spacing of the IDT electrodes of the parallel resonator P1 is fixed, and the electrostatic capacitance of the parallel resonator P1 is 3.06 pF. The average spacing of all the electrode fingers of the IDT electrodes of the parallel resonator P2 is 1.6759 μm, the distribution of the electrode finger spacing of the IDT electrodes of the parallel resonator P2 is fixed, and the electrostatic capacitance of the parallel resonator P2 is 1.17 pF. The average spacing of all the electrode fingers of the IDT electrodes of the parallel resonator P3 is 1.6975 μm, the distribution of the electrode finger spacing of the IDT electrodes of the parallel resonator P3 is different (i.e., the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings), and the electrostatic capacitance of the parallel resonator P3 is 0.51 pF.

[0056] Figure 4 This is a diagram illustrating the distribution of electrode finger spacing in the embodiments. Figure 4 The lower side shows a top view of the parallel resonator P3 in the embodiment. Figure 4 The upper side shows a coordinate graph representing the electrode finger spacing of the IDT electrodes of the parallel resonator P3 in the embodiment. For example, when the number of electrode fingers of the IDT electrodes of the parallel resonator P3 is 42, the electrode finger spacing becomes 41. Figure 4 In the figure, 41 electrode finger spacings are shown from t1 to t41.

[0057] In this embodiment, the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings. Specifically, the different electrode finger spacings of the IDT electrodes of the parallel resonator P3 are not regular, and adjacent electrode finger spacings in the IDT electrodes of the parallel resonator P3 are different. Figure 4 The diagram shows that the electrode finger spacings t1 to t41 are not regularly different; for example, the electrode finger spacing t1 is different from the electrode finger spacing t2, the electrode finger spacing t2 is different from the electrode finger spacing t3, and so on, as is the electrode finger spacing t40 and the electrode finger spacing t41, indicating that adjacent electrode finger spacings are different. Therefore, multiple resonant points are generated in the parallel resonator P3, and the parallel resonator P3 has multiple resonant frequencies. Furthermore, as shown in Table 2, the average of all electrode finger spacings of the IDT electrodes of the parallel resonator P3 is greater than the average of all electrode finger spacings of the IDT electrodes of the parallel resonator P2. Therefore, the average frequency of the multiple resonant frequencies of the parallel resonator P3 is less than the resonant frequency of the parallel resonator P2.

[0058] Furthermore, as shown in Table 2, the electrostatic capacitance of parallel resonator P3 is smaller than that of parallel resonator P2. Electrostatic capacitance is a value proportional to parameters such as the logarithm of the IDT electrodes, the cross width, and the duty ratio. Therefore, by adjusting these parameters, the electrostatic capacitance of parallel resonator P3 can be made smaller than that of parallel resonator P2. For example, the product of the cross width of the IDT electrodes of parallel resonator P3 and the value of subtracting 1 from the number of electrode fingers of that IDT electrode is less than the product of the cross width of the IDT electrodes of parallel resonator P2 and the value of subtracting 1 from the number of electrode fingers of that IDT electrode. The cross width refers to the length of the overlapping portion of multiple electrode fingers when viewed from the direction of elastic wave propagation. Figure 4 The length in L is represented by L.

[0059] Figure 5 This is a coordinate graph showing the impedance characteristics of the parallel resonators P2 and P3 in the embodiment. Figure 5In the diagram, the solid line represents the impedance characteristics of the parallel resonator P3, and the dashed line represents the impedance characteristics of the parallel resonator P2.

[0060] As described above, in this embodiment, since the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings, multiple resonant points are generated in the parallel resonator P3. On the other hand, an anti-resonant point is generated based on the average of all the electrode finger spacings of the IDT electrodes of the parallel resonator P3. Furthermore, since the average of all the electrode finger spacings of the IDT electrodes of the parallel resonator P3 is greater than the average of all the electrode finger spacings of the IDT electrodes of the parallel resonator P2, the average frequency of the multiple resonant frequencies of the parallel resonator P3 is lower than the resonant frequency of the parallel resonator P2. When an elastic wave resonator has multiple resonant frequencies, the frequency band between the highest resonant frequency and the anti-resonant frequency becomes inductive, and the frequency band lower than the highest resonant frequency becomes capacitive. By adjusting the average of all the electrode finger spacings, the anti-resonant frequency can be made to the desired frequency, and by making the electrode finger spacings different, the frequency band where the parallel resonator P3 becomes inductive can be narrowed. Therefore, even when parallel resonators P2 and P3 are connected in parallel, LC resonance is difficult to achieve, and the impedance of filter 10 in the passband of filter 40, which is connected to filter 10, is close to 50Ω. That is, the return loss in the passband of filter 40 can be reduced. Therefore, the degradation of the attenuation of filter 10 in the attenuation band corresponding to the passband of filter 40 when connected to filter 40 can be suppressed.

[0061] like Figure 5 As shown, the difference between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 is less than the difference between the anti-resonant frequency of the parallel resonator P3 and the anti-resonant frequency of the parallel resonator P2. Specifically, the highest resonant frequency of the parallel resonator P3 is the same as the resonant frequency of the parallel resonator P2. This further narrows the frequency band that generates LC resonance and further reduces the return loss in the passband of the filter 40. It should be noted that "same" can be incomplete or approximately the same. For example, even if the highest resonant frequency of the parallel resonator P3 deviates from the resonant frequency of the parallel resonator P2 by a few percent, these frequencies are still considered to be the same. Furthermore, "difference" refers to the value obtained by subtracting the smaller value from the larger one.

[0062] [4. Comparison between the Example and the Comparative Example]

[0063] Next, the embodiments and comparative examples are compared to illustrate that, in the embodiments, it is possible to suppress the degradation of the attenuation amount of the attenuation band of the filter 10 corresponding to the passband of the filter 40 when it is connected together with the filter 40.

[0064] Figure 6 This is a Smith chart showing the impedance characteristics observed from the input / output terminals 110 of filter 10 in the embodiments and comparative examples. Figure 6 In the diagram, solid lines represent the impedance characteristics in the embodiments, and dashed lines represent the impedance characteristics in the comparative examples.

[0065] like Figure 6 As shown, in the comparative example, the impedance observed from the input / output terminal 110 of the filter 10 in the passband (880-915MHz) of the filter 40 is close to 50Ω. In contrast, in the embodiment, the impedance observed from the input / output terminal 110 of the filter 10 in the passband of the filter 40 is made to be far away from 50Ω.

[0066] Figure 7 This is a coordinate graph showing the return loss characteristics observed from the input / output terminals 110 of filter 10 in the embodiments and comparative examples. Figure 7 In the diagram, the solid line represents the return loss characteristics in the embodiment, and the dashed line represents the return loss characteristics in the comparative example.

[0067] like Figure 7 As shown, in the comparative example, the maximum return loss observed from the input / output terminal 110 of filter 10 in the passband of filter 40 (880-915MHz: the frequency band between mark 1 and mark 2) increases to 22.6dB. In contrast, in the embodiment, the maximum return loss observed from the input / output terminal 110 of filter 10 in the passband of filter 40 can be reduced to 1.8dB. Since amplifier 20, which acts as a low-noise amplifier, is connected to the input / output terminal 110 of filter 10, which serves as a receiving filter, as in the comparative example, when the return loss observed from the input / output terminal 110 of filter 10 in the passband of filter 40 is large, the noise generated by the transmitted signal from filter 40 is also amplified by amplifier 20, and the receiving sensitivity deteriorates. However, in the embodiment, the return loss is small, and good receiving sensitivity can be achieved.

[0068] Figure 8 This is a coordinate graph showing the filter characteristics of filter 10 in the embodiments and comparative examples. Solid lines represent the filter characteristics in the embodiments, and dashed lines represent the filter characteristics in the comparative examples.

[0069] like Figure 8As shown, in the comparative example, the minimum attenuation value of the attenuation band of the filter 10 corresponding to the passband of the filter 40 is 51.9 dB. In contrast, in the embodiment, the minimum attenuation value of the attenuation band of the filter 10 corresponding to the passband of the filter 40 can be increased to 58.0 dB.

[0070] [5. Summary]

[0071] As described above, the filter 10 includes input / output terminals 110 and 120, series resonators or longitudinally coupled resonators (here, series resonators S1 and S2 and longitudinally coupled resonator D1) arranged on the path connecting the input / output terminals 110 and 120, and a plurality of parallel resonators (here, parallel resonators P1, P2, and P3) respectively connected between the aforementioned path and ground. Parallel resonators P3 and P2 are connected in parallel without passing through other resonators. Parallel resonators P2 and P3 each have an IDT electrode composed of multiple electrode fingers extending in a direction intersecting the elastic wave propagation direction and arranged parallel to each other. The IDT electrode of parallel resonator P3 has multiple different electrode finger spacings, and the average of all electrode finger spacings of the IDT electrode of parallel resonator P3 is greater than the average of all electrode finger spacings of the IDT electrode of parallel resonator P2.

[0072] Because the IDT electrodes of the parallel resonator P3 have multiple different electrode finger spacings, multiple resonant points are generated in the parallel resonator P3, resulting in multiple resonant frequencies. Furthermore, since the average frequency of the multiple resonant frequencies of the parallel resonator P3 is less than the average frequency of more than one resonant frequency of the parallel resonator P2, and compared to the case with a fixed electrode finger spacing, the low-frequency end of the inductive band of the parallel resonator P3 is located on the high-frequency side, thus narrowing the inductive band of the parallel resonator P3. Therefore, even when the parallel resonators P2 and P3 are connected in parallel, it is difficult to generate LC resonance, and the impedance of filter 10 in the passband of filter 40, which is connected together with filter 10, can be suppressed to approach 50Ω. That is, the return loss in the passband of filter 40 can be reduced. Therefore, the degradation of the attenuation amount in the attenuation band of filter 10 corresponding to the passband of filter 40 when connected together with filter 40 can be suppressed. Furthermore, since the parallel resonators P2 and P3, which are connected in parallel without other resonators (e.g., in parallel splitting), have different resonant frequencies, the transition band from the passband to the stopband is steep, enabling the realization of a narrow passband elastic wave filter. It should be noted that when the parallel resonators P2 and P3 are connected in parallel via other resonators (e.g., series resonators), their interaction is reduced, and the steepness cannot be sufficiently increased.

[0073] It should be noted that this effect is achieved by having the IDT electrodes of the parallel resonator P3, which is connected in parallel, have multiple different electrode finger spacings. However, even if the IDT electrodes of the non-parallel resonators (such as the parallel resonator P1) have multiple different electrode finger spacings, the above effect will not be achieved.

[0074] For example, the electrostatic capacitance of parallel resonator P3 can also be smaller than that of parallel resonator P2. Specifically, the product of the cross width of the IDT electrode of parallel resonator P3 and the value of minus 1 from the number of electrode fingers of the IDT electrode can also be smaller than the product of the cross width of the IDT electrode of parallel resonator P2 and the value of minus 1 from the number of electrode fingers of the IDT electrode.

[0075] Therefore, the anti-resonance point of the parallel resonator P3 is formed on the low-frequency side of the passband of the filter 10. Since the electrostatic capacitance of the parallel resonator P3 is small, the impedance of the anti-resonance point of the parallel resonator P3 becomes larger. Therefore, the degradation of the insertion loss on the low-frequency side of the passband of the filter 10 can be suppressed.

[0076] For example, the difference between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 can be less than the difference between the anti-resonant frequency of the parallel resonator P3 and the anti-resonant frequency of the parallel resonator P2.

[0077] The frequency band between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 overlaps with the inductive frequency band of the parallel resonator P3 and the capacitive frequency band of the parallel resonator P2 (i.e., the frequency band that generates LC resonance). Therefore, by reducing the difference between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2, the frequency band that generates LC resonance can be narrowed, and the return loss in the passband of the filter 40 can be reduced. Therefore, the degradation of the attenuation amount in the attenuation band of the filter 10 corresponding to the passband of the filter 40 when it is connected together with the filter 40 can be suppressed.

[0078] For example, the highest resonant frequency among the multiple resonant frequencies of the parallel resonator P3 can also be the same as the resonant frequency of the parallel resonator P2.

[0079] As described above, since the frequency band between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 is the frequency band that generates LC resonance, by aligning the highest resonant frequency of the parallel resonator P3 with the resonant frequency of the parallel resonator P2, the frequency band that generates LC resonance can be further narrowed, and the return loss in the passband of the filter 40 can be further reduced. Therefore, the degradation of the attenuation amount in the attenuation band of the filter 10 corresponding to the passband of the filter 40 when connected together with the filter 40 can be further suppressed.

[0080] For example, the different spacing patterns of the multiple different electrode fingers of the IDT electrodes of the parallel resonator P3 may not be regular, and the spacing between adjacent electrode fingers in the IDT electrodes of the parallel resonator P3 may be different.

[0081] When ripple is generated between multiple resonant points in the parallel resonator P3, the attenuation of the attenuation band of the filter 10 deteriorates. Conversely, by making the spacing between the multiple electrode fingers of the IDT electrodes of the parallel resonator P3 irregularly different, and by making the spacing between adjacent electrode fingers in the IDT electrodes of the parallel resonator P3 different, the number of resonant points generated in the parallel resonator can be increased, thereby reducing the ripple generated between the resonant points.

[0082] For example, the distance between the electrode fingers of the IDT electrode of the parallel resonator P2 can also be fixed.

[0083] When the IDT electrodes of the parallel resonator P2 have multiple different electrode finger spacings, multiple resonant points are generated in the parallel resonator P2, and these resonant points are generated at higher frequencies compared to when the electrode finger spacing is fixed. This widens the capacitive bandwidth of the parallel resonator P2 (i.e., the bandwidth generating LC resonance). Consequently, the return loss in the passband of the filter 40 increases. Therefore, by setting the electrode finger spacing of the IDT electrodes of the parallel resonator P2 to a fixed value, the return loss in the passband of the filter 40 can be reduced.

[0084] The high-frequency module 30 includes a filter 10 and an amplifier 20 connected to the input / output terminals 110.

[0085] Thus, a high-frequency module 30 is provided that has a high steepness of the transition band from the passband to the stopband and can suppress the degradation of the attenuation amount of the attenuation band of the filter 10 corresponding to the passband of the filter 40 when it is connected together with the filter 40.

[0086] The multiplexer 50 has a common terminal 150, a filter 10, and a filter 40 with input and output terminals 130 and 140 and a passband different from that of the filter 10. The common terminal 150 is connected to the input and output terminals 120 and 140.

[0087] Thus, a multiplexer 50 can be provided that has a steep transition band from the passband to the stopband and can suppress the degradation of the attenuation amount of the attenuation band of the filter 10 corresponding to the passband of the filter 40.

[0088] For example, filter 10 can be a receiving filter and filter 40 can be a transmitting filter, with the passband of filter 10 located on a higher frequency side than the passband of filter 40.

[0089] Therefore, the degradation of the attenuation amount in the low-frequency band of the passband of filter 10 can be suppressed, and the receiving sensitivity of filter 10 can be improved.

[0090] (Other implementation methods)

[0091] The filter 10, high-frequency module 30, and multiplexer 50 of the embodiments of the present invention have been described above. However, the present invention also includes other embodiments implemented by combining any of the constituent elements in the above embodiments, as well as various modifications that can be conceived by those skilled in the art to the above embodiments without departing from the spirit of the present invention.

[0092] For example, in the above embodiment, an example was described in which the electrostatic capacitance of parallel resonator P3 is smaller than that of parallel resonator P2, but the electrostatic capacitance of parallel resonator P3 may also be larger than that of parallel resonator P2.

[0093] For example, in the above embodiment, an example was described in which the difference between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 is less than the difference between the anti-resonant frequency of the parallel resonator P3 and the anti-resonant frequency of the parallel resonator P2. However, the difference between the highest resonant frequency of the parallel resonator P3 and the resonant frequency of the parallel resonator P2 may also be greater than the difference between the anti-resonant frequency of the parallel resonator P3 and the anti-resonant frequency of the parallel resonator P2.

[0094] For example, in the above embodiment, an example was described in which the different ways of the multiple different electrode finger spacings of the IDT electrodes of the parallel resonator P3 are not regular and the adjacent electrode finger spacings of the IDT electrodes of the parallel resonator P3 are different. However, the above different ways can also be regular. In addition, the adjacent electrode finger spacings of the IDT electrodes of the parallel resonator P3 can also be the same.

[0095] For example, in the above embodiment, an example of a fixed electrode finger spacing of the IDT electrode of the parallel resonator P2 is described, but the IDT electrode of the parallel resonator P2 may also have multiple different electrode finger spacings.

[0096] Industrial availability

[0097] This invention, as an elastic wave filter, high-frequency module, and multiplexer applicable to multi-band systems, can be widely used in communication devices such as portable telephones.

[0098] Explanation of reference numerals in the attached figures

[0099] 10, 40 filters;

[0100] 20 Amplifiers;

[0101] 30 High-frequency modules;

[0102] More than 50 tools;

[0103] 110, 120, 130, 140 input / output terminals;

[0104] 150 common terminals;

[0105] ANT antenna element;

[0106] D1 Longitudinal Coupled Resonator;

[0107] P1, P2, P3 parallel resonators;

[0108] S1 and S2 are series resonators.

Claims

1. An elastic wave filter, comprising: First input / output terminal; Second input / output terminal; A series resonator or a longitudinally coupled resonator, configured on the path connecting the first input / output terminal and the second input / output terminal; and Multiple parallel resonators are connected between the path and ground, respectively. The first and second parallel resonators in the plurality of parallel resonators are connected in parallel without passing through other resonators. The first parallel resonator and the second parallel resonator each have an IDT electrode composed of multiple electrode fingers, which extend in a direction intersecting the direction of elastic wave propagation and are arranged parallel to each other. The IDT electrodes of the first parallel resonator have multiple different electrode finger spacings. The average spacing between all the electrode fingers of the IDT electrodes of the first parallel resonator is greater than the average spacing between all the electrode fingers of the IDT electrodes of the second parallel resonator.

2. The elastic wave filter according to claim 1, wherein, The electrostatic capacitance of the first parallel resonator is smaller than that of the second parallel resonator.

3. The elastic wave filter according to claim 1 or 2, wherein, The product of the cross width of the IDT electrode of the first parallel resonator and the value of subtracting 1 from the number of electrode fingers of the IDT electrode is less than the product of the cross width of the IDT electrode of the second parallel resonator and the value of subtracting 1 from the number of electrode fingers of the IDT electrode.

4. The elastic wave filter according to claim 1 or 2, wherein, The difference between the highest resonant frequency of the first parallel resonator and the resonant frequency of the second parallel resonator is less than the difference between the anti-resonant frequency of the first parallel resonator and the anti-resonant frequency of the second parallel resonator.

5. The elastic wave filter according to claim 4, wherein, The highest resonant frequency among the multiple resonant frequencies of the first parallel resonator is the same as the resonant frequency of the second parallel resonator.

6. The elastic wave filter according to claim 1 or 2, wherein, The different spacing patterns of the multiple different electrode fingers of the IDT electrodes of the first parallel resonator are not regular, and the spacing of adjacent electrode fingers in the IDT electrodes of the first parallel resonator is different.

7. The elastic wave filter according to claim 1 or 2, wherein, The electrode finger spacing of the IDT electrodes of the second parallel resonator is fixed.

8. A high-frequency module, comprising: The elastic wave filter according to any one of claims 1 to 7; and An amplifier that is connected to the first input / output terminal.

9. A multiplexer, comprising: Common terminal; The elastic wave filter according to any one of claims 1 to 7; and The first filter has a third input / output terminal and a fourth input / output terminal, and its passband differs from that of the elastic wave filter. The common terminal is connected to the second input / output terminal and the fourth input / output terminal.

10. The multiplexer according to claim 9, wherein, The elastic wave filter is a receiving filter. The first filter is a transmitting filter. The passband of the first filter is located on the lower frequency side than the passband of the elastic wave filter.

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