filter

Abstract

The present invention provides a filter having a narrow passband and a small difference in the frequency temperature coefficient between the low-frequency side and the high-frequency side of the passband. The filter comprises: a parallel resonator (P2), one end of which is connected to a path between an input terminal and an output terminal, and the other end of which is grounded, the parallel resonator (P2) having a resonant frequency (fr12) of an attenuation electrode (40) forming the low-frequency side of the passband; and a parallel resonator (P3), one end of which is connected to a path, and the other end of which is grounded, the parallel resonator (P3) having a resonant frequency (fr13) of an attenuation electrode (41) forming the high-frequency side of the passband.

Description

Technical Field

[0001] This invention relates to filters. Background Technology

[0002] In wireless communication devices such as smartphones, filters utilize elastic wave resonators. As a filter, a trapezoidal filter is known, which has a series resonator connected in series with the path between the input and output terminals, and a parallel resonator connected at one end to the path and the other end to ground. It is known that, in addition to the series and parallel resonators, connecting a resonator and an inductor in series between the path and ground can suppress spurious emissions (e.g., Patent Document 1). Furthermore, a bandpass filter is also known, which has two resonant lines, each having a capacitor and a resonant element (e.g., Patent Document 2).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2023-7678

[0004] Patent Document 2: Japanese Patent Application Publication No. 2008-278360

[0005] The temperature coefficient of frequency (TCF) on the low-frequency side of the passband of a filter is small compared to the TCF on the high-frequency side. Furthermore, depending on the application of the filter, there are sometimes filters with narrow passbands. Summary of the Invention

[0006] The present invention was made in view of the above-mentioned problems, and its object is to provide a filter with a narrow passband and a small difference in TCF between the low-frequency side and the high-frequency side of the passband.

[0007] The present invention is a filter comprising: a first elastic wave resonator, one end of which is connected to a path between an input terminal and an output terminal and the other end is grounded, the first elastic wave resonator having a first resonant frequency of an attenuation electrode forming a low-frequency side of the passband; and a second elastic wave resonator, one end of which is connected to the path and the other end is grounded, the second elastic wave resonator having a second resonant frequency of an attenuation electrode forming a high-frequency side of the passband.

[0008] In the above structure, the difference between the frequency temperature coefficient of the high-frequency side and the frequency temperature coefficient of the low-frequency side of the passband is less than 10 ppm / ℃.

[0009] In the above structure, the second elastic wave resonator can be configured such that it is divided into multiple resonators connected in series with each other.

[0010] In the above structure, the capacitance of the second elastic wave resonator can be configured such that it is smaller than the capacitance of the first elastic wave resonator.

[0011] In the above structure, the filter can be configured to have a plurality of the first elastic wave resonators.

[0012] In the above structure, the filter may be configured such that it has a third elastic wave resonator connected in series with the path and has a first anti-resonance frequency, wherein the difference between the first anti-resonance frequency and the second anti-resonance frequency of the first elastic wave resonator is less than ±1.0% relative to the second anti-resonance frequency.

[0013] In the above structure, the filter may be configured such that it has a fourth elastic wave resonator connected in series with the path and has a third anti-resonance frequency, wherein the difference between the third anti-resonance frequency and the fourth anti-resonance frequency of the second elastic wave resonator is less than ±1.0% relative to the fourth anti-resonance frequency.

[0014] In the above structure, the filter can be configured such that a fifth elastic wave resonator with matched impedance is connected at one end to the path and the other end is grounded.

[0015] In the above structure, the first elastic wave resonator and the second elastic wave resonator may have comb-shaped electrodes disposed on a piezoelectric layer formed of the same piezoelectric material, or have a lower electrode and an upper electrode sandwiched between piezoelectric layers formed of the same piezoelectric material.

[0016] In the above structure, the first elastic wave resonator and the second elastic wave resonator may be configured such that they have comb-shaped electrodes disposed on a common piezoelectric layer, or have a lower electrode and an upper electrode sandwiched between the common piezoelectric layer.

[0017] The present invention is a filter comprising: a first elastic wave resonator having its two ends connected to a path between an input terminal and an output terminal, the first elastic wave resonator having a first anti-resonant frequency of an attenuation pole forming a low-frequency side of the passband; and a second elastic wave resonator having its two ends connected to the path, the second elastic wave resonator having a second anti-resonant frequency of an attenuation pole forming a high-frequency side of the passband.

[0018] According to the present invention, a filter with a narrow passband and a small difference in TCF between the low-frequency and high-frequency sides of the passband can be obtained. Attached Figure Description

[0019] Figure 1 This is the circuit diagram of the filter in Example 1.

[0020] Figure 2 This is a plan view of the filter in Example 1.

[0021] Figure 3 (a) is a cross-sectional view of the filter of Example 1. Figure 3 (b) is a plan view of the parallel resonator of Example 1. Figure 3 (c) is a cross-sectional view showing another example of the piezoelectric layer of Example 1.

[0022] Figure 4 (a) and Figure 4 (b) is a graph showing the simulation results of the pass characteristics of the filter of Embodiment 1, as well as the series resonator and the parallel resonator.

[0023] Figure 5 This is a graph showing the simulation results of the pass characteristics of the filters in Comparative Example 1 and Comparative Example 2.

[0024] Figure 6 (a) and Figure 6 (b) is a graph showing the simulation results of the temperature characteristics of the filter in Example 1.

[0025] Figure 7 (a) is a circuit diagram of the filter of Modification 1 of Example 1. Figure 7 (b) is a graph showing the simulation results of the pass characteristics of the filter of variant 1 of embodiment 1, as well as the series resonator and the parallel resonator.

[0026] Figure 8 (a) is a circuit diagram of the filter of Modification 2 of Example 1. Figure 8 (b) is a graph showing the simulation results of the pass characteristics of the filter of variant 2 of embodiment 1, as well as the series resonator and the parallel resonator.

[0027] Figure 9 (a) is a graph showing the simulation results of the filter's pass characteristics when the capacitance of the parallel resonator is varied in Modification 2 of Example 1. Figure 9 (b) is a graph showing the simulation results of the pass-through characteristics of the parallel resonator.

[0028] Figure 10 (a) is a graph showing the simulation results of the pass-through characteristics of the filter of Embodiment 1, as well as the series resonator and the parallel resonator. Figure 10 (b) is a graph showing the simulation results of the absolute values ​​of the admittance |Y| for the series resonator and the parallel resonator.

[0029] Figure 11 (a) and Figure 11 (b) is a cross-sectional view of the case where the elastic wave resonator of Example 1 is a piezoelectric thin film resonator.

[0030] Figure 12(a) is the circuit diagram of the filter in Example 2. Figure 12 (b) is a graph showing the simulation results of the pass characteristics of the filter of Embodiment 2, as well as the series resonator and the parallel resonator.

[0031] Figure 13 This is the circuit diagram of the duplexer in Example 3.

[0032] Label Explanation

[0033] 11, 11a~11i: Resonator; 15: Path; 20: Support substrate; 21: Boundary layer; 22: Temperature compensation film; 23, 23a: Piezoelectric layer; 24: Metal film; 25: Wiring; 26: Pad; 30: IDT; 31: Comb electrode; 32: Electrode finger; 33: Busbar; 34: Reflector; 35: Cross region; 40: Attenuator; 41: Attenuator; 51: Lower electrode; 52: Upper electrode; 53: Gap; 54: Resonant region; 60: Transmit filter; 62: Receive filter; 100, 110, 120, 200: Filter; 300: Duplexer. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0035]

Example 1

[0036] Figure 1 This is a circuit diagram of filter 100 in Embodiment 1. (As shown...) Figure 1 As shown, the filter 100 includes: series resonators S1 to S5, which are connected in series with path 15 between input terminal Tin and output terminal Tout; and parallel resonators P1 to P4, one end of which is connected to path 15 and the other end is connected to ground terminal Tg. The series resonators S1 to S5 and the parallel resonators P1 to P4 are elastic wave resonators, each having a piezoelectric layer and electrodes for exciting elastic waves through the piezoelectric layer.

[0037] Series resonators S1-S5 and parallel resonators P1-P4 are each divided into multiple resonators 11 in series. The resonators divided from series resonator S1 are designated as resonators 11a. Similarly, the resonators divided from series resonators S2-S5 and parallel resonators P1-P4 are designated as resonators 11b-11i. Series resonator S1 is divided into 3 resonators 11a, series resonator S2 into 4 resonators 11b, series resonator S3 into 4 resonators 11c, series resonator S4 into 3 resonators 11d, and series resonator S5 into 3 resonators 11e. Parallel resonator P1 is divided into 2 resonators 11f, parallel resonator P2 into 2 resonators 11g, parallel resonator P3 into 6 resonators 11h, and parallel resonator P4 into 2 resonators 11i. The combined capacitance of parallel resonator P3 is smaller than that of parallel resonators P1, P2 and P4.

[0038] In each of the series resonators S1-S5 and the parallel resonators P1-P4, the average spacing D of the electrode fingers 32 of the divided resonators 11 is approximately the same, and adjacent resonators 11 share a common busbar 33. That is, the series resonator S1 is divided into three resonators 11a, therefore the average spacing D of the electrode fingers 32 of the three resonators 11a is approximately the same, and adjacent resonators 11a share a common busbar 33. Regarding the electrode fingers 32 and the busbar 33, in Figure 3 The explanation will be provided in (b).

[0039] Figure 2 This is a plan view of the filter 100 in Embodiment 1. Figure 3 (a) is a cross-sectional view of the filter 100 of Embodiment 1. Figure 3 (b) is a plan view of the parallel resonator P2 in Example 1. Figure 3 As shown in (a), a piezoelectric layer 23 is provided on the support substrate 20. A temperature compensation film 22 is provided between the support substrate 20 and the piezoelectric layer 23. A boundary layer 21 is provided between the support substrate 20 and the temperature compensation film 22.

[0040] like Figure 2 and Figure 3As shown in (a), series resonators S1 to S5 and parallel resonators P1 to P4 are disposed on the piezoelectric layer 23. The series resonators S1 to S5 and the parallel resonators P1 to P4 are divided into multiple resonators 11 in series. Wiring 25 and pads 26 are disposed on the support substrate 20. Wiring 25 connects the series resonators S1 to S5 and the parallel resonators P1 to P4. Furthermore, wiring 25 connects the series resonators S1, S5 and the parallel resonators P1 to P4 to the pads 26. The pads 26 are electrically connected to the input terminal Tin, the output terminal Tout, and the ground terminal Tg. Wiring 25 and pads 26 are metal layers such as gold, copper, or aluminum.

[0041] like Figure 3 As shown in (b), the two resonators 11g constituting the parallel resonator P2 each have an IDT (Interdigital Transducer) 30 and a reflector 34. The IDT 30 and the reflector 34 are formed by a metal film 24 on the piezoelectric layer 23 (see reference). Figure 3 (a) is formed. The IDT 30 has a pair of opposing comb electrodes 31. The comb electrodes 31 have multiple electrode fingers 32 and a bus bar 33 connected to the multiple electrode fingers 32. The comb electrodes 31 of one of the two resonators 11g in their respective IDT 30 share one bus bar 33.

[0042] A pair of comb electrodes 31 have electrode fingers 32 alternately arranged in at least a portion of the intersection region 35 where the electrode fingers 32 intersect. In the intersection region 35, the elastic wave primarily excited by the plurality of electrode fingers 32 propagates mainly in the arrangement direction of the electrode fingers 32. The spacing of the electrode fingers 32 of one of the comb electrodes 31 is approximately the wavelength λ of the elastic wave. The average spacing D of the plurality of electrode fingers 32 is approximately twice the wavelength λ. The average spacing D of the electrode fingers 32 can be calculated by dividing the length of the arrangement direction of the electrode fingers 32 of the IDT 30 by the number of electrode fingers 32. The reflector 34 reflects the elastic wave (surface acoustic wave) excited by the electrode fingers 32 of the IDT 30. Thus, the elastic wave is confined within the intersection region 35 of the IDT 30.

[0043] The average spacing D of the electrode fingers 32 of the two resonators 11g is approximately the same. The length L of the busbar 33 shared by the two resonators 11g in the length direction of the electrode fingers 32 is greater than 0.3λ and less than 2.0λ. Furthermore, in Figure 3 In (b), a parallel resonator P2 is shown, but the series resonators S1 to S5 and the parallel resonators P1, P3, and P4 have the same structure except for the number of segments.

[0044] The supporting substrate 20 is, for example, a sapphire substrate, alumina substrate, silicon substrate, spinel substrate, crystal substrate, quartz substrate, or silicon carbide substrate. The piezoelectric layer 23 is, for example, a single-crystal lithium tantalate (LiTaO3) layer or a single-crystal lithium niobate (LiNbO3) layer, such as a rotary Y-cut X-propagation lithium tantalate layer or a rotary Y-cut X-propagation lithium niobate layer. When the rotary Y-cut X-propagation lithium tantalate layer is 36° or more and 60° or less, the elastic wave is dominated by the SH (Shear Horizontal) wave. The piezoelectric layer 23 can also be a rotary Y-cut X-propagation lithium tantalate layer with a rotation angle of 36° or more and 48° or less. The thickness of the piezoelectric layer 23 is 1λ or less.

[0045] The temperature compensation film 22 has a temperature coefficient of elasticity with a sign opposite to that of the temperature coefficient of elasticity of the piezoelectric layer 23. For example, the temperature coefficient of elasticity of the piezoelectric layer 23 is negative, while the temperature coefficient of elasticity of the temperature compensation film 22 is positive. The temperature compensation film 22 is an insulating film with silicon oxide (SiO2) as its main component, for example, a silicon oxide film with no additives or containing additive elements such as fluorine, and for example, it is polycrystalline or amorphous. When the temperature compensation film 22 is a silicon oxide film, the sound speed of the bulk wave propagating in the temperature compensation film 22 is slower than the sound speed of the bulk wave propagating in the piezoelectric layer 23.

[0046] The velocity of sound of the bulk wave in boundary layer 21 is faster than that of the bulk wave in temperature compensation film 22. Boundary layer 21 is, for example, a polycrystalline or amorphous film such as alumina, aluminum nitride, silicon, silicon nitride, or silicon carbide. By providing boundary layer 21, the dominant mode elastic wave can be encapsulated in piezoelectric layer 23 and temperature compensation film 22, and unwanted waves such as bulk waves can be attenuated using boundary layer 21.

[0047] Figure 3 (c) is a cross-sectional view showing another example of the piezoelectric layer 23 of Embodiment 1. Figure 2 and Figure 3 In example (a), the following case is illustrated: a piezoelectric layer 23 is provided on the support substrate 20, and the series resonators S1-S5 and the parallel resonators P1-P4 share the same piezoelectric layer 23. That is, the case where the IDT 30 of each of the series resonators S1-S5 and the parallel resonators P1-P4 is provided on the same piezoelectric layer 23 is illustrated. However, it is also possible to... Figure 3 As shown in (c), a plurality of piezoelectric layers 23 are disposed on the support substrate 20, and at least a portion of the elastic wave resonators of the series resonators S1 to S5 and the parallel resonators P1 to P4 are disposed on different piezoelectric layers 23 from other elastic wave resonators. The plurality of piezoelectric layers 23 may be formed of lithium tantalate or lithium niobate with the same Y-cut angle.

[0048] [Simulation 1]

[0049] The pass characteristics of filter 100 in Example 1 were simulated. The simulation conditions are as follows.

[0050] Support substrate 20: Sapphire substrate

[0051] Boundary layer 21: An alumina layer with a thickness of 8.0 μm

[0052] Temperature compensation film 22: a silicon oxide film with a thickness of 0.40 μm.

[0053] Piezoelectric layer 23: A 0.50 μm thick lithium tantalate layer with 42° Y-cut X-propagation.

[0054] Metal film 24: A laminate of a titanium film with a thickness of 0.05 μm and an aluminum film with a thickness of 0.07 μm.

[0055] Series resonator S1: resonant frequency fr1 is 2313.3MHz, anti-resonant frequency fa1 is 2413.7MHz.

[0056] Series resonator S2: resonant frequency fr2 is 2324.2MHz, anti-resonant frequency fa2 is 2424.5MHz.

[0057] Series resonator S3: resonant frequency fr3 is 2340.5MHz, anti-resonant frequency fa3 is 2441.6MHz.

[0058] Series resonator S4: resonant frequency fr4 is 2364.0MHz, anti-resonant frequency fa4 is 2465.7MHz.

[0059] Series resonator S5: resonant frequency fr5 is 2323.6MHz, anti-resonant frequency fa5 is 2423.9MHz.

[0060] Parallel resonator P1: resonant frequency fr11 is 2678.7MHz, anti-resonant frequency fa11 is 2788.2MHz.

[0061] Parallel resonator P2: resonant frequency fr12 is 2301.7MHz, anti-resonant frequency fa12 is 2401.8MHz.

[0062] Parallel resonator P3: resonant frequency fr13 is 2360.7MHz, anti-resonant frequency fa13 is 2462.5MHz.

[0063] Parallel resonator P4: resonant frequency fr14 is 2297.1MHz, anti-resonant frequency fa14 is 2395.9MHz.

[0064] Figure 4 (a) and Figure 4(b) is a graph showing the simulation results of the pass-through characteristics of the filter 100 of Embodiment 1 and the series resonators S1 to S5 and the parallel resonators P1 to P4. Figure 4 (b) shows Figure 4 The passband characteristics of series resonators S1-S5 and parallel resonators P1-P4 near the passband (a). Figure 4 (a) and Figure 4 In (b), the horizontal axis represents frequency, and the vertical axis represents attenuation. Figure 4 In (a), the pass characteristic of filter 100 is set to F.

[0065] like Figure 4 (a) and Figure 4 As shown in (b), the filter 100 of Embodiment 1 has a passband of 2320MHz to 2345MHz. Parallel resonators P2 and P4 have resonant frequencies fr12 and fr14 between the low-frequency end of the passband and the attenuation electrode 40 on the low-frequency side of the passband. Parallel resonator P3 has a resonant frequency fr13 between the high-frequency end of the passband and the attenuation electrode 41 on the high-frequency side of the passband. Parallel resonator P1 has a resonant frequency fr11 at a position significantly away from the attenuation electrode 41 towards the high-frequency side. Series resonators S1 to S5 have anti-resonant frequencies fa1 to fa5 at positions away from the attenuation electrode 41 towards the high-frequency side.

[0066] Thus, the passband Pass is formed by the resonant frequencies fr12 and fr14 of the parallel resonators P2 and P4, and the resonant frequency fr13 of the parallel resonator P3. That is, the attenuation electrode 40 on the low-frequency side of the passband Pass is formed by the resonant frequencies fr12 and fr14 of the parallel resonators P2 and P4, and the attenuation electrode 41 on the high-frequency side is formed by the resonant frequency fr13 of the parallel resonator P3. From the viewpoint that the attenuation electrode 40 is formed by the resonant frequencies fr12 and fr14, the ratio of the absolute value of the difference between the resonant frequencies fr2 and fr14 and the frequency f1 of the attenuation electrode 40 to the frequency f1 of the attenuation electrode 40 (|(fr12, fr14 - f1)| / f1) is preferably 2% or less. Similarly, from the viewpoint that the attenuation electrode 41 is formed by the resonant frequency fr13, the ratio of the absolute value of the difference between the resonant frequency fr13 and the frequency f2 of the attenuation electrode 41 to the frequency f2 of the attenuation electrode 41 (|(fr13 - f2)| / f2) is preferably 2% or less.

[0067] Series resonator S1 and parallel resonator P1 are configured for impedance matching. Series resonators S2 and S5 are configured to ensure attenuation in the attenuation domain at higher frequencies than the passband and to improve the insertion loss of the passband. Series resonators S3 and S4 are configured to make the attenuation characteristics (skirt characteristics) between the passband and the attenuation domain steeper.

[0068] Next, the pass characteristics of the filters in Comparative Example 1 and Comparative Example 2 were simulated. Like typical trapezoidal filters, the attenuation poles on the low-frequency side of the passband are formed by the resonant frequency of the parallel resonator, and the attenuation poles on the high-frequency side are formed by the anti-resonant frequency of the series resonator. The simulation conditions are as follows.

[0069] Compare the conditions of Example 1

[0070] Series resonator S1: resonant frequency is 2456.5MHz, anti-resonant frequency is 2556.7MHz.

[0071] Series resonator S2: resonant frequency is 2381.5MHz, anti-resonant frequency is 2479.2MHz.

[0072] Series resonator S3: resonant frequency is 2347.7MHz, anti-resonant frequency is 2444.8MHz.

[0073] Series resonator S4: resonant frequency 2328.8MHz, anti-resonant frequency 2425.6MHz

[0074] Series resonator S5: resonant frequency 2364.2MHz, anti-resonant frequency 2461.7MHz

[0075] Parallel resonator P1: resonant frequency is 2366.5MHz, anti-resonant frequency is 2464.7MHz.

[0076] Parallel resonator P2: resonant frequency is 2247.9MHz, anti-resonant frequency is 2342.9MHz.

[0077] Parallel resonator P3: resonant frequency is 2227.9MHz, anti-resonant frequency is 2322.3MHz.

[0078] Parallel resonator P4: resonant frequency is 2239.2MHz, anti-resonant frequency is 2333.1MHz.

[0079] Other simulation conditions are the same as in Simulation 1.

[0080] Compare the conditions of Example 2

[0081] Series resonator S1: resonant frequency is 2402.6MHz, anti-resonant frequency is 2501.8MHz

[0082] Series resonator S2: resonant frequency is 2329.2MHz, anti-resonant frequency is 2425.6MHz

[0083] Series resonator S3: resonant frequency is 2296.1MHz, anti-resonant frequency is 2392.0MHz.

[0084] Series resonator S4: resonant frequency 2277.7MHz, anti-resonant frequency 2373.6MHz

[0085] Series resonator S5: resonant frequency is 2312.3MHz, anti-resonant frequency is 2408.5MHz.

[0086] Parallel resonator P1: resonant frequency is 2366.5MHz, anti-resonant frequency is 2364.6MHz

[0087] Parallel resonator P2: resonant frequency is 2247.9MHz, anti-resonant frequency is 2342.9MHz.

[0088] Parallel resonator P3: resonant frequency is 2227.9MHz, anti-resonant frequency is 2322.3MHz.

[0089] Parallel resonator P4: resonant frequency is 2239.2MHz, anti-resonant frequency is 2333.1MHz.

[0090] Other simulation conditions are the same as in Simulation 1.

[0091] Figure 5 This is a graph showing the simulation results of the pass characteristics of the filters in Comparative Example 1 and Comparative Example 2. Figure 5 In the diagram, the horizontal axis represents frequency, and the vertical axis represents attenuation. For example... Figure 5 As shown, Comparative Example 1 has a passband of 2300MHz to 2400MHz. Comparative Example 2 has a passband of 2300MHz to 2350MHz, and its passband width is about half that of Comparative Example 1. The passband of Comparative Example 1 has good flatness and low insertion loss. On the other hand, the passband of Comparative Example 2 has poor flatness and high insertion loss. Thus, when the attenuation electrode 40 on the low-frequency side of the passband is formed by the resonant frequencies of the parallel resonators P1 to P4, and the attenuation electrode 41 on the high-frequency side is formed by the anti-resonant frequencies of the series resonators S1 to S5, if the bandwidth of the passband is to be narrowed, the flatness of the passband will deteriorate and the insertion loss will increase. This is believed to be caused by the deviation between the resonant frequencies of the series resonators S1 to S5 and the anti-resonant frequencies of the parallel resonators P1 to P4 located within the passband.

[0092] On the other hand, in Embodiment 1, the attenuation electrode 40 on the low-frequency side of the passband is formed by the resonant frequencies fr12 and fr14 of the parallel resonators P2 and P4, and the attenuation electrode 41 on the high-frequency side is formed by the resonant frequency fr13 of the parallel resonator P3. In this case, as... Figure 4As in (a), even if the bandwidth of the passband is narrowed, the flatness of the passband can be suppressed.

[0093] [Simulation 2]

[0094] The temperature characteristics of filter 100 in Example 1 were simulated. The temperature of filter 100 was set to 85°C, 25°C, and -20°C. The simulation conditions outside these points were the same as in Simulation 1.

[0095] Figure 6 (a) and Figure 6 (b) is a graph showing the simulation results of the temperature characteristics of the filter 100 of Example 1. Figure 6 (b) is to Figure 6 A magnified view of the passband near Pass (a). Figure 6 (a) and Figure 6 In (b), the horizontal axis represents frequency, and the vertical axis represents attenuation. For example... Figure 6 (a) and Figure 6 As shown in (b), on both the low-frequency and high-frequency sides of the passband, the frequency characteristic shifts towards the low-frequency side as the temperature increases. For example, with an attenuation of 10 dB, the temperature coefficient of frequency (TCF) on the low-frequency side of the passband is approximately -5 ppm / ℃, while the TCF on the high-frequency side is approximately -8 ppm / ℃. Therefore, the difference in TCF between the low-frequency and high-frequency sides is approximately -3 ppm / ℃.

[0096] It is known that the temperature characteristics at the resonant frequency and the temperature characteristics at the anti-resonant frequency differ in an elastic wave resonator. The TCF of the series resonators S1 to S5 at the anti-resonant frequency is approximately -20 ppm / ℃. Therefore, in a typical trapezoidal filter, where the resonant frequency of the parallel resonators forms the attenuation electrode on the low-frequency side of the passband, and the anti-resonant frequency of the series resonators forms the attenuation electrode on the high-frequency side, the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband is considered to be approximately -15 ppm / ℃. Therefore, by forming the attenuation electrode 40 on the low-frequency side and the attenuation electrode 41 on the high-frequency side of the passband using the resonant frequencies fr12 to fr14 of the parallel resonators P2 to P4, as in Example 1, the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband can be reduced.

[0097] [Variation Example 1]

[0098] Figure 7 (a) is a circuit diagram of filter 110 of variant 1 of embodiment 1. Figure 7As shown in (a), in a variation of Example 1 of Embodiment 1, it includes: a series resonator S11 connected in series with path 15 between input terminal Tin and output terminal Tout; and parallel resonators P11 and P12, one end of which is connected to path 15 and the other end of which is connected to ground terminal Tg. The series resonator S11 and the parallel resonators P11 and P12 are elastic wave resonators for exciting elastic waves in a piezoelectric layer, and similarly have an IDT 30 and a reflector 34 as in Embodiment 1.

[0099] The pass characteristics of filter 110 in variant 1 of Example 1 were simulated. The simulation conditions are as follows.

[0100] Series resonator S11: resonant frequency fr21 is 2340.5MHz, anti-resonant frequency fa21 is 2441.6MHz.

[0101] Parallel resonator P11: Resonant frequency fr31 is 2301.7MHz, anti-resonant frequency fa31 is 2401.8MHz.

[0102] Parallel resonator P12: resonant frequency fr32 is 2360.7MHz, anti-resonant frequency fa32 is 2462.5MHz.

[0103] Other simulation conditions are the same as in Simulation 1.

[0104] Figure 7 (b) is a graph showing the simulation results of the pass-through characteristics of filter 110, series resonator S11, and parallel resonators P11 and P12 in a modified example of embodiment 1. Figure 7 In (b), the horizontal axis represents frequency, and the vertical axis represents attenuation. Figure 7 In (b), the pass characteristic of filter 110 is set to F. For example... Figure 7 As shown in (b), the filter 110 of Modification 1 of Embodiment 1 has a passband Pass of 2320MHz to 2345MHz. The parallel resonator P11 has a resonant frequency fr31 near the frequency of the attenuation electrode 40 on the low-frequency side of the passband Pass. The parallel resonator P12 has a resonant frequency fr32 near the frequency of the attenuation electrode 41 on the high-frequency side of the passband Pass. The series resonator S11 has an anti-resonant frequency fa21 located away from the attenuation electrode 41 towards the high-frequency side.

[0105] Thus, it is also possible to have two parallel resonators P11 and P12 connected in path 15 between the input terminal Tin and the output terminal Tout. In this case, the attenuation pole 40 is made visible by the resonant frequency fr31 of the parallel resonator P11, and the attenuation pole 41 is made visible by the resonant frequency fr32 of the parallel resonator P12, thereby forming a passband Pass with narrow bandwidth and suppression of flatness degradation.

[0106] [Variation Example 2]

[0107] Figure 8 (a) is a circuit diagram of filter 120 of variant 2 of embodiment 1. Figure 8 As shown in (a), in a variation 2 of Embodiment 1, it includes: series resonators S21 and S22, which are connected in series with path 15 between input terminal Tin and output terminal Tout; and parallel resonators P21 to P23, one end of which is connected to path 15 and the other end is connected to ground terminal Tg. The series resonators S21 and S22 and the parallel resonators P21 to P23 are elastic wave resonators for piezoelectric layer-excited elastic waves, and similarly have IDT 30 and reflector 34 as in Embodiment 1.

[0108] The pass characteristics of filter 120 in variation 2 of Example 1 were simulated. The simulation conditions are as follows.

[0109] Series resonator S21: resonant frequency fr41 is 2340.5MHz, anti-resonant frequency fa41 is 2441.6MHz.

[0110] Series resonator S22: resonant frequency fr42 is 2364.0MHz, anti-resonant frequency fa42 is 2465.7MHz.

[0111] Parallel resonator P21: resonant frequency fr51 is 2301.7MHz, anti-resonant frequency fa51 is 2401.8MHz.

[0112] Parallel resonator P22: resonant frequency fr52 is 2360.7MHz, anti-resonant frequency fa52 is 2462.5MHz.

[0113] Parallel resonator P23: resonant frequency fr53 is 2297.1MHz, anti-resonant frequency fa53 is 2395.9MHz.

[0114] Other simulation conditions are the same as in Simulation 1.

[0115] Figure 8(b) is a graph showing the simulation results of the pass-through characteristics of filter 120, series resonators S21, S22, and parallel resonators P21-P23 in variant 2 of embodiment 1. Figure 8 In (b), the horizontal axis represents frequency, and the vertical axis represents attenuation. Figure 8 In (b), the pass characteristic of filter 120 is set to F. For example... Figure 8 As shown in (b), the filter 120 of variation 2 of embodiment 1 has a passband Pass of 2320MHz to 2345MHz. Parallel resonators P21 and P23 have resonant frequencies fr51 and fr53 near the frequency of the attenuation electrode 40 on the low-frequency side of the passband Pass. Parallel resonator P22 has a resonant frequency fr52 near the frequency of the attenuation electrode 41 on the high-frequency side of the passband Pass. Series resonators S21 and S22 have anti-resonant frequencies fa41 and fa42 at positions away from the attenuation electrode 41 on the high-frequency side.

[0116] Thus, it is also possible to have three parallel resonators P21 to P23 connected in path 15 between the input terminal Tin and the output terminal Tout. In this case, the attenuation electrode 40 is brought into play by the resonant frequencies fr51 and fr53 of the parallel resonators P21 and P23, and the attenuation electrode 41 is brought into play by the resonant frequency fr52 of the parallel resonator P22, thereby forming a passband. This also allows for the formation of a passband with narrow bandwidth and suppression of flatness degradation. Furthermore, compared to variant 1 of embodiment 1, the flatness of the passband is improved, and insertion loss can be reduced.

[0117] According to Example 1, as Figure 1 Thus, parallel resonators P2 (the first elastic wave resonator) and P3 (the second elastic wave resonator) are connected, each with one end connected to path 15 and the other end grounded. Figure 4 (a) and Figure 4 As in (b), the parallel resonator P2 (the first elastic wave resonator) has a resonant frequency fr12 (the first resonant frequency) of the attenuation electrode 40 on the low-frequency side that forms the passband. The parallel resonator P3 (the second elastic wave resonator) has a resonant frequency fr13 (the second resonant frequency) of the attenuation electrode 41 on the high-frequency side that forms the passband. Thus, a passband with narrow bandwidth and good flatness can be formed. Furthermore, as... Figure 6 (a) and Figure 6 As in (b), the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband can be reduced. Therefore, even with temperature changes, changes in the passband width can be suppressed.

[0118] In variation 1 of Example 1, the same applies, such as Figure 7 (a) and Figure 7 As in (b), the parallel resonator P11 (the first elastic wave resonator) has a resonant frequency fr31 (the first resonant frequency) of the attenuation electrode 40 on the low-frequency side forming the passband. The parallel resonator P12 (the second elastic wave resonator) has a resonant frequency fr32 (the second resonant frequency) of the attenuation electrode 41 on the high-frequency side forming the passband. This is also true in variation 2 of embodiment 1, as... Figure 8 (a) and Figure 8 As in (b), the parallel resonator P21 (the first elastic wave resonator) has a resonant frequency fr51 (first resonant frequency) of the attenuation electrode 40 on the low-frequency side of the passband. The parallel resonator P22 (the second elastic wave resonator) has a resonant frequency fr52 (second resonant frequency) of the attenuation electrode 41 on the high-frequency side of the passband. Thus, in modifications 1 and 2 of Embodiment 1, a passband with narrow bandwidth and good flatness can also be formed, and the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband can be reduced.

[0119] Furthermore, in Example 1, as Figure 6 As in (b), the difference between the TCF on the high-frequency side and the TCF on the low-frequency side of the passband is 10 ppm / ℃ or less. Therefore, even with temperature variations, changes in the passband width can be suppressed. From the viewpoint of suppressing changes in the passband width, the difference between the TCF on the high-frequency side and the TCF on the low-frequency side of the passband is preferably 8 ppm / ℃ or less, more preferably 6 ppm / ℃ or less, and even more preferably 4 ppm / ℃ or less.

[0120] Furthermore, in Example 1, as Figure 1 In this way, the parallel resonator P3 (the second elastic wave resonator) is divided into multiple resonators 11h connected in series with each other. Therefore, the combined capacitance of the parallel resonator P3 is smaller than the capacitance of the parallel resonator P3 when it is not divided into multiple resonators.

[0121] Here, the effect of reducing the capacitance of the parallel resonator P3 is explained. Figure 8 The pass characteristics of filter 120 in the modified example 2 of embodiment 1 shown in (a) were simulated when the capacitance of parallel resonator P22 was changed to three levels (reference capacitance, half the reference capacitance, and twice the reference capacitance). Figure 9 (a) is a graph showing the simulation results of the pass characteristics of filter 120 when the capacitance of parallel resonator P22 is varied in Modification 2 of Embodiment 1. Figure 9 Figure (b) is a graph showing the simulation results of the throughput characteristics of the parallel resonator P22. Figure 9 (a) and Figure 9In (b), the horizontal axis represents frequency and the vertical axis represents attenuation.

[0122] like Figure 9 As shown in (b), regarding the throughput characteristics of the parallel resonator P22, the smaller the capacitance of the parallel resonator P22, the more severe the attenuation of the resonant frequency, but the steepness increases. Figure 9 As shown in (a), the smaller the capacitance of the parallel resonator P22, the greater the steepness of the resonant frequency. Therefore, the smaller the capacitance of the parallel resonator P22, the greater the steepness of the attenuation characteristics (skirt characteristics) of the attenuation domain from the passband to the high-frequency side.

[0123] Therefore, in Embodiment 1, by dividing the parallel resonator P3 (the second elastic wave resonator) into multiple resonators 11h connected in series, the skirt characteristic of the filter 100 can be made steep. From the viewpoint of making the skirt characteristic steep, the number of divisions when dividing the parallel resonator P3 into multiple resonators 11h is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. When the combined capacitance decreases, the attenuation of the attenuation electrode 41 deteriorates, so the number of divisions is preferably 8 or less, more preferably 7 or less, and even more preferably 6 or less.

[0124] Furthermore, from the viewpoint of making the skirt characteristic of the filter 100 steeper, the combined capacitance of the parallel resonator P3 (the second elastic wave resonator) is preferably smaller than the capacitance (combined capacitance) of the parallel resonator P2 (the first elastic wave resonator), more preferably 3 / 4 or less, and even more preferably 1 / 2 or less.

[0125] Furthermore, in Example 1, as Figure 1 and Figure 4 As in (a), there are multiple parallel resonators P2 and P4, which have resonant frequencies fr12 and fr14 of the attenuation electrode 40 forming the low-frequency side of the passband. The same applies in variation 2 of embodiment 1, as... Figure 8 (a) and Figure 8 As in (b), multiple parallel resonators P21 and P23 are provided, which have resonant frequencies fr51 and fr53 of the attenuation electrode 40 forming the low-frequency side of the passband. This improves the steepness of the skirt characteristic of the attenuation domain from the passband towards the low-frequency side. The skirt characteristic on the low-frequency side is largely determined by the parallel resonators and is less susceptible to the influence of series resonators. Therefore, to improve the steepness of the skirt characteristic on the low-frequency side, it is preferable that the attenuation electrode 40 is formed by multiple parallel resonators P2 and P4.

[0126] Furthermore, in Embodiment 1, the series resonator S5 (the third elastic wave resonator) having an anti-resonance frequency fa5 (the first anti-resonance frequency) is connected in series with path 15 between the input terminal Tin and the output terminal Tout. The ratio of the difference between the anti-resonance frequency fa5 and the anti-resonance frequency fa12 (the second anti-resonance frequency) of the parallel resonator P2 (the first elastic wave resonator) relative to the anti-resonance frequency fa12 ((fa5-fa12) / fa12) is ±1.0% or less. Regarding the resulting effect, using... Figure 10 (a) and Figure 10 (b) will be explained.

[0127] Figure 10 (a) is a graph showing the simulation results of the pass-through characteristics of the filter 100 of Embodiment 1 and the series resonators S1-S5 and the parallel resonators P1-P4. Figure 10 Figure (b) is a graph showing the simulation results of the absolute values ​​of the admittances |Y| for the series resonators S1-S5 and the parallel resonators P1-P4. Figure 10 In (a), the horizontal axis represents frequency, and the vertical axis represents attenuation. Figure 10 In (b), the horizontal axis represents frequency, and the vertical axis represents the absolute value of admittance |Y|. The simulation conditions are the same as in Simulation 1.

[0128] like Figure 10 (a) and Figure 10 As shown in (b), the attenuation pole 40 of the low-frequency side of the passband Pass is formed by the resonant frequencies fr12 and fr14 of the parallel resonators P2 and P4, and the anti-resonant frequencies fa12 and fa14 are located in the attenuation domain, which is higher than the passband Pass. Therefore, the attenuation of the filter in the attenuation domain sometimes deteriorates according to the anti-resonant frequencies fa12 and fa14. Therefore, by making the anti-resonant frequency fa5 of the series resonator S5 close to the anti-resonant frequency fa12, the attenuation degradation of the filter caused by the anti-resonant frequency fa12 is suppressed. That is, the ratio of the difference between the anti-resonant frequency fa5 and the anti-resonant frequency fa12 to the anti-resonant frequency fa12 ((fa5-fa12) / fa12) is ±1.0% or less. Thus, the attenuation degradation of the filter caused by the anti-resonant frequency fa12 can be suppressed.

[0129] Therefore, in Embodiment 1, by making the ratio of the difference between the anti-resonance frequency fa5 of the series resonator S5 and the anti-resonance frequency fa12 of the parallel resonator P2 to the anti-resonance frequency fa12 less than ±1.0%, the attenuation degradation caused by the anti-resonance frequency fa12 of the parallel resonator P2 can be suppressed. From the viewpoint of suppressing attenuation degradation, the ratio of the difference between the anti-resonance frequency fa5 and the anti-resonance frequency fa12 to the anti-resonance frequency fa12 is preferably less than ±0.8%, more preferably less than ±0.6%, and even more preferably less than ±0.4%.

[0130] Furthermore, in Embodiment 1, the resonant frequencies fr2, fr3, and fr5 of the series resonators S2, S3, and S5 are located in the passband. This reduces losses in the passband.

[0131] Furthermore, in Embodiment 1, the series resonator S4 (fourth elastic wave resonator) having an anti-resonant frequency fa4 (third anti-resonant frequency) is connected in series with path 15 between the input terminal Tin and the output terminal Tout. The difference between the anti-resonant frequency fa4 and the anti-resonant frequency fa13 (fourth anti-resonant frequency) of the parallel resonator P3 (second elastic wave resonator) is ±1.0% or less relative to the anti-resonant frequency fa13. Therefore, for the same reason as above, it is possible to suppress the degradation of filter attenuation caused by the anti-resonant frequency fa13 (see reference). Figure 10 (a) and Figure 10 (b)). From the viewpoint of suppressing the deterioration of attenuation, the ratio of the difference between the anti-resonance frequency fa4 and the anti-resonance frequency fa13 to the anti-resonance frequency fa13 is preferably ±0.8% or less, more preferably ±0.6% or less, and even more preferably ±0.4% or less.

[0132] Furthermore, in Example 1, as Figure 1 As shown, a parallel resonator P1 (the fifth elastic wave resonator) is used for impedance matching. One end of the parallel resonator P1 is connected to path 15, and the other end is grounded. This allows for the suppression of waveform disturbances through the characteristic waveform.

[0133] Furthermore, in Example 1 and its variations, such as Figure 3 (a) to Figure 3 As illustrated in (c), the series resonators S1 to S5 and the parallel resonators P1 to P4 are surface acoustic wave resonators having a piezoelectric layer 23 and a comb-shaped electrode 31 disposed on the piezoelectric layer 23. However, this is not a limitation; for example, it could also be a piezoelectric thin film resonator. Figure 11 (a) and Figure 11 (b) is a cross-sectional view of the case where the elastic wave resonator in Example 1 is a piezoelectric thin film resonator. Additionally, in Figure 11 (a) and Figure 11 In (b), parallel resonators P2 and P3 in series resonators S1 to S5 and parallel resonators P1 to P4 are illustrated, but the other series resonators S1 to S5 and parallel resonators P1 and P4 have the same structure.

[0134] like Figure 11 (a) and Figure 11 As shown in (b), a piezoelectric layer 23a and a lower electrode 51 and an upper electrode 52 sandwiching at least a portion of the piezoelectric layer 23a are provided on the support substrate 20. A gap 53 is formed between the lower electrode 51 and the support substrate 20. The region sandwiching the piezoelectric layer 23a and where the lower electrode 51 and the upper electrode 52 face each other is a resonant region 54. In the resonant region 54, the lower electrode 51 and the upper electrode 52 excite elastic waves to the piezoelectric layer 23a. The lower electrode 51 and the upper electrode 52 are, for example, metal films including a ruthenium film. The piezoelectric layer 23a is, for example, an aluminum nitride layer, a zinc oxide layer, a single-crystal lithium tantalate layer, or a single-crystal lithium niobate layer. An acoustic reflection film that reflects elastic waves may also be provided instead of the gap 53.

[0135] Thus, the series resonators S1 to S5 and the parallel resonators P1 to P4 can be any of the surface acoustic wave resonators and piezoelectric thin film resonators. In any case, the series resonators S1 to S5 and the parallel resonators P1 to P4 all have piezoelectric layers 23 and 23a and electrodes (comb electrode 31 or lower electrode 51 and upper electrode 52) for exciting elastic waves on the piezoelectric layers.

[0136] Parallel resonators P2 and P3 (the first elastic wave resonator and the second elastic wave resonator) can be connected as follows: Figure 3 In the case of (a), where a comb-shaped electrode 31 is provided on a shared piezoelectric layer 23, it is also possible to... Figure 3 (c) refers to the case where comb-shaped electrodes 31 are provided on each piezoelectric layer 23 formed of the same piezoelectric material. As a result, the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband can be reduced.

[0137] Furthermore, the parallel resonators P2 and P3 (the first elastic wave resonator and the second elastic wave resonator) can be as follows: Figure 11 As in (a), there is a lower electrode 51 and an upper electrode 52 sandwiched together by a common piezoelectric layer 23a. Alternatively, it can be as follows: Figure 11 (b) describes a case where a lower electrode 51 and an upper electrode 52 are sandwiched between different piezoelectric layers 23a formed of the same piezoelectric material. This reduces the difference between the TCF on the low-frequency side and the TCF on the high-frequency side of the passband.

[0138] The wavelength of the elastic wave excited in the piezoelectric thin-film resonator is approximately twice the thickness of the piezoelectric layer. In Example 1, the resonant frequency fr12 of the parallel resonator P2 is smaller than the resonant frequency fr13 of the parallel resonator P3; therefore, the thickness T1 of the piezoelectric layer 23a of the parallel resonator P2 is larger than the thickness T2 of the piezoelectric layer 23a of the parallel resonator P3. Similarly, the thickness of the piezoelectric layer 23a of the parallel resonator P4 is larger than the thickness T2 of the piezoelectric layer 23a of the parallel resonator P3.

[0139] The wavelength of the elastic wave excited in the surface acoustic wave resonator is approximately twice the average spacing D of the electrode fingers 32. Therefore, the average spacing D of the electrode fingers 32 in the parallel resonator P2 is larger than that in the parallel resonator P3 (refer to...). Figure 3 (a)). Similarly, for the parallel resonator P4, the average spacing D of the electrode fingers 32 of the parallel resonator P4 is larger than that of the parallel resonator P3.

[0140]

Example 2

[0141] In Example 1 and its variations, the attenuation poles on both the low-frequency and high-frequency sides of the passband are formed by the resonant frequency of the parallel resonator. However, it is also possible that the attenuation poles on both the low-frequency and high-frequency sides of the passband are formed by the anti-resonant frequency of the series resonator. Therefore, in Example 2, the case where the attenuation poles on both the low-frequency and high-frequency sides of the passband are formed by the anti-resonant frequency of the series resonator will be described.

[0142] Figure 12 (a) is a circuit diagram of filter 200 in Example 2. Figure 12 As shown in (a), in Embodiment 2, it includes: series resonators S31 and S32, which are connected in series with path 15 between input terminal Tin and output terminal Tout; and parallel resonator P31, one end of which is connected to path 15 and the other end is grounded. The series resonators S31, S32 and the parallel resonator P31 are elastic wave resonators for piezoelectric layer-excited elastic waves, and similarly have IDT30 and reflector 34 as in Embodiment 1.

[0143] The pass characteristics of filter 200 in Example 2 were simulated. The simulation conditions are as follows.

[0144] Series resonator S31: Resonant frequency fr61 is 2191.5MHz, anti-resonant frequency fa61 is 2288.5MHz.

[0145] Series resonator S32: resonant frequency fr62 is 2260.3MHz, anti-resonant frequency fa62 is 2359.2MHz.

[0146] Parallel resonator P31: Resonant frequency fr71 is 2257.3MHz, anti-resonant frequency fa71 is 2356.4MHz.

[0147] Other simulation conditions are the same as in Simulation 1.

[0148] Figure 12 (b) is a graph showing the simulation results of the pass-through characteristics of the filter 200 of Embodiment 2, as well as the series resonators S31, S32 and the parallel resonator P31. Figure 12 In (b), the horizontal axis represents frequency, and the vertical axis represents attenuation. Figure 12 In (b), the pass characteristic of filter 200 is set to F. For example... Figure 12 As shown in (b), the filter 200 of Embodiment 2 has a passband Pass of 2320MHz to 2345MHz. The series resonator S31 has an anti-resonant frequency fa61 near the frequency of the attenuation electrode 40 on the low-frequency side of the passband Pass. The series resonator S32 has an anti-resonant frequency fa62 near the frequency of the attenuation electrode 41 on the high-frequency side of the passband Pass. The parallel resonator P31 has a resonant frequency fr71 located away from the attenuation electrode 40 towards the low-frequency side.

[0149] According to Example 2, as Figure 12 As in (a), it has a series resonator S31 (first elastic wave resonator) and a series resonator S32 (second elastic wave resonator), each with its two ends connected to path 15 respectively. Figure 12 As in (b), the series resonator S31 (the first elastic wave resonator) has an anti-resonance frequency fa61 (the first anti-resonance frequency) of the attenuation electrode 40 on the low-frequency side of the passband Pass. The series resonator S32 (the second elastic wave resonator) has an anti-resonance frequency fa62 (the second anti-resonance frequency) of the attenuation electrode 41 on the high-frequency side of the passband Pass. Thus, a passband Pass with narrow bandwidth and good flatness can be formed. Furthermore, since both the low-frequency and high-frequency sides of the passband Pass are formed by series resonators, the difference between the TCF of the low-frequency side and the TCF of the high-frequency side of the passband Pass can be reduced. Therefore, even with temperature changes, changes in the passband width can be suppressed. Furthermore, the series resonators S31 and S32 and the parallel resonator P31 can also be... Figure 11 (a) and Figure 11 (b) such a piezoelectric thin film resonator.

[0150]

Example 3

[0151] Figure 13 This is the circuit diagram of the duplexer 300 in Example 3. (As shown...) Figure 13As shown, a transmit filter 60 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 62 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 60 allows signals in the transmit frequency band of the high-frequency signal input from the transmit terminal Tx to be transmitted to the common terminal Ant as transmit signals, and suppresses signals of other frequencies. The receive filter 62 allows signals in the receive frequency band of the high-frequency signal input from the common terminal Ant to be received to the receive terminal Rx as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 60 and the receive filter 62 can be a filter of Embodiment 1 and its variations, as well as Embodiment 2. A duplexer is illustrated as a multiplexer, but a tripplexer or quadplexer can also be used.

[0152] The embodiments of the present invention have been described in detail above, but the present invention is not limited to this specific embodiment and can be modified and altered in various ways within the scope of the spirit of the present invention as described in the claims.

Claims

1. A filter having: A first elastic wave resonator, one end of which is connected to the path between the input and output terminals, and the other end grounded, has a first resonant frequency of an attenuating electrode forming the low-frequency side of the passband; and A second elastic wave resonator, one end of which is connected to the path and the other end is grounded, has a second resonant frequency of the attenuation pole that forms the high-frequency side of the passband.

2. The filter according to claim 1, wherein, The difference between the frequency temperature coefficient of the high-frequency side and the frequency temperature coefficient of the low-frequency side of the passband is less than 10 ppm / ℃.

3. The filter according to claim 1 or 2, wherein, The second elastic wave resonator is divided into multiple resonators connected in series with each other.

4. The filter according to claim 3, wherein, The capacitance of the second elastic wave resonator is smaller than that of the first elastic wave resonator.

5. The filter according to claim 1 or 2, wherein, The filter has multiple of the first elastic wave resonators.

6. The filter according to claim 1 or 2, wherein, The filter has a third elastic wave resonator connected in series with the path and has a first anti-resonance frequency. The difference between the first anti-resonance frequency and the second anti-resonance frequency of the first elastic wave resonator is less than ±1.0% relative to the second anti-resonance frequency.

7. The filter according to claim 1 or 2, wherein, The filter has a fourth elastic wave resonator connected in series with the path and has a third anti-resonance frequency. The difference between the third anti-resonance frequency and the fourth anti-resonance frequency of the second elastic wave resonator is less than ±1.0% relative to the fourth anti-resonance frequency.

8. The filter according to claim 1 or 2, wherein, The filter has a fifth elastic wave resonator with matched impedance, one end of which is connected to the path and the other end is grounded.

9. The filter according to claim 1 or 2, wherein, The first elastic wave resonator and the second elastic wave resonator have comb-shaped electrodes disposed on a piezoelectric layer formed of the same piezoelectric material, or have a lower electrode and an upper electrode sandwiched between piezoelectric layers formed of the same piezoelectric material.

10. The filter according to claim 1 or 2, wherein, The first elastic wave resonator and the second elastic wave resonator have comb-shaped electrodes disposed on a common piezoelectric layer, or have a lower electrode and an upper electrode sandwiched between the common piezoelectric layer.

11. A filter having: A first elastic wave resonator, whose two ends are connected to the path between the input terminal and the output terminal, the first elastic wave resonator having a first anti-resonant frequency of the attenuating electrode forming the low-frequency side of the passband; and A second elastic wave resonator, whose two ends are connected to the path, has a second anti-resonant frequency of the attenuating pole that forms the high-frequency side of the passband.

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