KR102457196B1 - Filter and multiplexer - Google Patents

Abstract

A filter with excellent attenuation outside the passband is provided.
A ladder filter including a parallel arm resonator (15) and a parallel arm resonator (16), a group of resonators (17, 18) connected in series with the ladder type filter, and a ground connected to the parallel arm resonator (15) a terminal B1, a ground terminal B2 provided independently of the ground terminal B1, connected to the parallel arm resonator 16, and a ground terminal B3 connected to the resonator groups 17 and 18; Node N1 on the signal path R1 connecting the parallel arm resonator 16 and the ground terminal B2, and the node N2 on the signal path R2 connecting the resonator groups 17 and 18 and the ground terminal B3. ), and between the node N1 and the ground terminal B2 on the signal path R1, or between the node N2 and the ground terminal B3 on the signal path R2. Includes inductors.

Description

FILTER AND MULTIPLEXER

The present invention relates to filters and multiplexers.

Conventionally, a bandpass filter provided on a piezoelectric substrate and in which a ladder filter including a first parallel arm resonator and a second parallel arm resonator and a longitudinal coupling resonator filter are connected in series is known (eg, For example, Patent Document 1).

The filter of Patent Document 1 has a first ground terminal connected to the first parallel arm resonator, a second ground terminal connected to the second parallel arm resonator, and a third ground terminal connected to the longitudinal coupling resonator type filter.

The first ground terminal and the second ground terminal are not connected to each other on the piezoelectric substrate, and the second ground terminal and the third ground terminal are connected to each other on the piezoelectric substrate. In other words, on the piezoelectric substrate, the first ground terminal and the second ground terminal are independent, and the second ground terminal and the third ground terminal are common.

According to the filter of Patent Document 1, since the influence of parasitic inductance is reduced by making the first and second ground terminals independent, the attenuation characteristics at the low end of the pass band can be sharpened. have. In addition, since the ground potential of the longitudinally coupled resonator filter is stabilized by making the second ground terminal and the third ground terminal common, the amount of attenuation outside the pass band (eg, isolation when configuring a multiplexer with other filters) is greatly increased. can do.

Japanese Patent Laid-Open No. 2017-85262

However, in the conventional filter, the amount of attenuation outside the pass band may not be sufficient.

Accordingly, the present invention provides a bandpass filter in which a ladder filter and a longitudinally coupled resonator filter are connected in series, and provides a filter having an excellent amount of attenuation outside the passband.

In order to achieve the above object, a filter according to an aspect of the present invention includes a ladder filter including a first parallel arm resonator and a second parallel arm resonator, a longitudinally coupled resonator filter connected in series with the ladder filter, and , a first ground terminal connected to the first parallel arm resonator, a second ground terminal provided independently of the first ground terminal, and connected to the second parallel arm resonator, and the longitudinal coupling resonator type filter A third ground terminal connected to the first node on a first signal path connecting the second parallel arm resonator and the second ground terminal, and a second signal path connecting the longitudinally coupled resonator filter and a third ground terminal a third signal path connected to a second node, and a connection between the first node and the second ground terminal on the first signal path, or between the second node and the third ground terminal on the second signal path included inductors.

In addition, the multiplexer according to an aspect of the present invention includes a first filter and a second filter whose ends are connected to each other, wherein the first filter is the above filter, and the center of the pass band of the first filter The frequency is higher than the center frequency of the passband of the second filter.

According to the filter described above, since the first ground terminal is provided independently from the second ground terminal and the third ground terminal, the attenuation characteristic at the low end of the pass band can be sharpened like the conventional filter.

Further, the second parallel arm resonator and the longitudinally coupled resonator type filter are connected to each other on the ground side with an inductor interposed therebetween. Here, the inductor is an equivalent expression of the inductance component of the signal path connecting the first node and the second node, and may be substantially negligible.

Thereby, series resonance by the combined capacitance of the second parallel arm resonator and the longitudinally coupled resonator type filter and the second inductor occurs. The attenuation pole generated by the series resonance shifts toward the low frequency side as compared with the case where the second inductor is not provided. As a result, attenuation in the target frequency band on the low-frequency side outside the passband is effectively improved.

Since the second inductor is commonly connected to the second parallel arm resonator and the longitudinally coupled resonator type filter, it is possible to reduce the size of the device compared to the case where separate inductors are connected to the second parallel arm resonator and the longitudinally coupled resonator type filter.

In addition, since the second inductor is connected between the first node and the second ground terminal, the ground potential of the longitudinally coupled resonator filter is unstable compared to the case where the second inductor is connected between the second node and the third ground terminal. hard to lose As a result, the attenuation in the target frequency band is stably improved.

According to the above filter, attenuation in the target frequency band on the low frequency side outside the passband is improved together with the steep attenuation characteristic at the low end of the passband. Therefore, by combining the above filter and another filter having a lower passband center frequency to form a multiplexer, a multiplexer excellent in isolation between bands is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a circuit diagram which shows an example of the structure of the multiplexer which concerns on embodiment.
2 is a plan view and a cross-sectional view schematically showing an example of the structure of an IDT (InterDigital Transducer) electrode.
3 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate of the multiplexer according to the embodiment.
4 is a plan view schematically showing an example of electrode arrangement on a piezoelectric substrate of a multiplexer according to Comparative Example 1. FIG.
5 is a circuit diagram showing an example of the configuration of a multiplexer according to Comparative Example 2. FIG.
6 is a plan view schematically showing an example of electrode arrangement on a piezoelectric substrate of a multiplexer according to Comparative Example 2. FIG.
7 is a circuit diagram showing an example of the configuration of a multiplexer according to Comparative Example 3. FIG.
8 is a plan view schematically showing an example of electrode arrangement on a piezoelectric substrate of a multiplexer according to Comparative Example 3. FIG.
9 is a plan view schematically showing an example of electrode arrangement on a piezoelectric substrate of a multiplexer according to a modification.
10 is a graph showing an example of an isolation characteristic between terminals (Tx, Rx) of a multiplexer.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail using embodiment and drawings. In addition, all embodiments described below represent generic or specific examples. Numerical values, shapes, materials, constituent elements, arrangement of constituent elements, connection form, etc. shown in the following embodiments are examples and are not intended to limit the present invention. In addition, in the following embodiment, "connected" includes not only the case of direct connection with a wiring conductor, but also the case of electrically connecting via other circuit elements.

A multiplexer according to the embodiment will be described with an example of a duplexer including a transmission filter and a reception filter.

1 is a circuit diagram showing an example of the configuration of a multiplexer 1 according to an embodiment. As shown in FIG. 1 , the multiplexer 1 includes terminals Ant, Tx, and Rx, a reception filter 10 and a transmission filter 20 . The terminal Ant is connected to the antenna element 30 .

The reception filter 10 is a filter circuit having a predetermined reception frequency band as a pass band, and is connected to a terminal Ant and a terminal Rx. One end and the other end of the reception filter 10 may be directly connected to the terminals Ant and Rx, respectively, or may be connected through other circuit elements not shown.

In the reception filter (10), a ladder type resonator filter is constituted by serial arm resonators (13 and 14) and parallel arm resonators (15 and 16). Further, a longitudinally coupled resonator type filter is constituted by the resonator groups 17 and 18 connected in parallel to each other. Each of the resonator groups 17 and 18 has five IDT electrodes juxtaposed in the propagation direction of the elastic wave. The ladder type resonator filter and the longitudinally coupled resonator type filter are connected in series.

One end of the parallel arm resonator 15 is connected to the ground B1. The node N1 on the signal path R1 connecting the parallel arm resonator 16 and the ground B2 and the node N2 on the signal path R2 connecting the resonator groups 17 and 18 and the ground B3 are It is connected by a signal path R3.

Inductor L1 is disposed between node N1 and ground B2 on signal path R1, and inductor L2 is disposed between node N2 and ground B3 on signal path R2. The ground-side ends of all the IDT electrodes included in the resonator groups 17 and 18 are connected to the ground B3 through the inductor L2. Grounds B1, B2 and B3 are terminals for external connection and have parasitic inductance.

The inductors L1 and L2 may have an equivalent inductance component of the corresponding wiring, or may be an inductance component of a discrete component. The inductance of the inductor L1 is greater than the inductance of the inductor L2. The inductance of the inductor L2 may be small enough to be substantially negligible. On the other hand, although an inductance component exists in other wirings, the illustration is omitted because it is not an essential part of the present invention.

The transmission filter 20 is a ladder-type resonator filter comprising series arm resonators 21, 22, 23, 24 and 25 and parallel arm resonators 26, 27, 28 and 29. The ground-side end of the parallel-arm resonator 26 is connected to the ground B4, and the ground-side ends of the parallel-arm resonators 27, 28 and 29 are connected to the ground B5. Grounds B4 and B5 are terminals for external connection and have parasitic inductance components.

Next, the basic structure of the IDT electrode will be described.

2 is a plan view and a cross-sectional view schematically showing an example of the basic structure of the IDT electrode 50 . The structure of the IDT electrode 50 shown in FIG. 2 constitutes series arm resonators 13 and 14, parallel arm resonators 15 and 16, and resonator groups 17 and 18 in the reception filter 10. applied to each IDT electrode. On the other hand, the example of FIG. 2 is for explaining the basic structure of the IDT electrode 50, and the number and length of electrode fingers constituting the electrode is not limited to the example of FIG.

The IDT electrode 50 is composed of a pair of comb-tooth-shaped electrodes 50a and 50b facing each other. The comb-tooth-shaped electrode 50a is composed of a plurality of electrode fingers 51a parallel to each other and a bus bar electrode 52a connecting the plurality of electrode fingers 51a. The comb-toothed electrode 50b is composed of a plurality of electrode fingers 51b parallel to each other and a bus bar electrode 52b connecting the plurality of electrode fingers 51b. The electrode fingers 51a and 51b are formed to extend in a direction perpendicular to the X-axis direction, which is the propagation direction of the elastic wave, and are arranged to engage with each other.

The parameters defining the shape and size of the IDT electrode 50 are referred to as electrode parameters. As an example of the electrode parameter, the wavelength (λ), which is the repetition period in the X-axis direction of the electrode finger 51a or the electrode finger 51b, and the cross width, which is the length at which the electrode fingers 51a and 51b overlap when viewed in the X-axis direction. (L), the line width (W) of the electrode fingers (51a, 51b), and the space width (S) between the adjacent electrode fingers (51a, 51b) are mentioned.

The number of pairs equal to 1/2 of the number of electrode fingers combined with the electrode fingers 51a and 51b, the pitch (W+S) which is the repetition period of the electrode fingers combined with the electrode fingers 51a and 51b, and the duty ratio that is the ratio of the line width to the pitch W/(W+S) is also an example of an electrode parameter.

The electrode fingers 51a and 51b and the busbar electrodes 52a and 52b are constituted by an electrode layer 53 formed on the piezoelectric substrate 59 .

As an example, the electrode layer 53 may be composed of a metal such as copper or aluminum or an alloy thereof, and the piezoelectric substrate 59 may be composed of a piezoelectric layer containing lithium tantalate or lithium niobate. The electrode layer 53 may be formed on the piezoelectric substrate 59 through an adhesive layer (not shown). The electrode layer 53 may be covered with a protective layer 54 .

The piezoelectric substrate 59 may consist of one piezoelectric layer, or may be a laminated substrate having at least a part of piezoelectricity. The laminated substrate having piezoelectric properties at least in part includes a support substrate, a high-sonic film formed on the support substrate, the bulk wave sound velocity propagating faster than the acoustic wave sound velocity propagating through the piezoelectric thin film, and the high-sonic velocity film is laminated on the piezoelectric thin film. It may be a laminated body composed of a low sound velocity film having a propagating bulk wave sound velocity lower than that of the propagating bulk wave sound velocity and a piezoelectric thin film laminated on the low sound velocity film. Further, the support substrate may be a high-sonic-velocity support substrate such as a silicon substrate that serves both as a high-sonic film and a support substrate.

Next, an example of the electrode arrangement of the multiplexer 1 formed on the piezoelectric substrate will be described.

3 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate 59 of the multiplexer 1 . As shown in FIG. 3 , each resonator of the multiplexer 1 is constituted by an IDT electrode formed in a correspondingly marked area on the piezoelectric substrate 59 . Further, on the piezoelectric substrate 59, terminals (Ant, Tx, Rx, B1, B2, B3, B4, and B5), which are electrode structures for external connection, and wiring connecting the resonators and wiring connecting the resonators and terminals An electrode that functions as

The bus bar electrode on the ground side of the IDT electrodes constituting the resonator groups 17 and 18 and the ground terminal B3 are connected via a three-dimensional wiring 19 . The ground terminal B1 is provided independently from the ground terminals B2 and B3.

Inductors L1 and L2 are the inductance components of the corresponding wiring. Specifically, the inductor L1 is an inductance component of the wiring connecting the node N1 and the ground terminal B2. The inductor L2 is an inductance component of the wiring connecting the node N2 and the ground terminal B3.

The inductance component of the inductor L1 is greater than the inductance component of the inductor L2. Specifically, since the wiring connecting the node N1 and the ground terminal B2 is composed of a wiring that is intentionally wrapped in a serpentine, the inductance component of the inductor L1 is large. On the other hand, since the wiring connecting the node N2 and the ground terminal B3 is composed of a wiring having a planar pattern having no meandering portion, the inductance component of the inductor L2 is negligible. small.

The electrode parameters of the parallel arm resonators 15 and 16 are set as follows as an example. The number of pairs of the parallel arm resonators 15 and 16 is 63 and 67 pairs, respectively, and the crossing widths are 71 μm and 91 μm, respectively.

The capacitance of a resonator is mainly proportional to the product of the number of pairs and the cross width. The capacitance of the parallel arm resonators 15 and 16 is 2.1 pF and 2.8 pF, respectively, and the capacitance of the parallel arm resonator 16 is greater than the capacitance of the parallel arm resonator 15 .

According to the multiplexer 1 configured as described above, since the ground terminal B1 is provided independently from the ground terminals B2 and B3, the attenuation characteristic at the low end of the pass band can be steeply similar to the conventional filter. have.

Further, the parallel arm resonator 16 and the resonator groups 17 and 18 are connected to each other through a signal path R3 on the ground side.

As a result, series resonance by the combined capacitance of the parallel arm resonator 16 and the resonator groups 17 and 18 and the inductor L1 occurs. The damping pole generated by the series resonance shifts toward the low frequency side compared to the case where the inductor L1 is not provided. As a result, attenuation in the transmission frequency band on the low-frequency side outside the passband is effectively improved.

Since the inductor L1 is commonly connected to the parallel arm resonator 16 and the resonator groups 17 and 18, compared to the case where individual inductors are connected to the parallel arm resonator 16 and the resonator groups 17 and 18, , it becomes possible to miniaturize the device.

In addition, since the attenuation pole is shifted using the inductor L1 connected between the node N1 and the ground terminal B2, the inductance of the inductor L2 connected between the node N2 and the ground terminal B3 is reduced. no need to make it big Since the inductance of the inductor L2 is not increased, the ground potential of the resonator groups 17 and 18 is unlikely to become unstable. As a result, the attenuation in the transmission frequency band is stably improved.

In addition, since the ground-side ends of all the IDT electrodes of the resonator groups 17 and 18 are common, the ground potential of the resonator groups 17 and 18 is more stabilized, and the parasitic inductance component is reduced, thereby attenuating in the transmission frequency band. improvement effect is increased.

In addition, the capacitance of the parallel arm resonators 16 is the largest among the capacitances of the parallel arm resonators 15 and 16 . Accordingly, the combined capacitance of the parallel arm resonator 16 and the resonator groups 17 and 18 is increased, and the inductance component necessary for shifting the attenuation pole to the low frequency side can be reduced. As a result, it is possible to contribute to the miniaturization of the chip.

According to the reception filter 10, attenuation in the transmission frequency band is improved together with the steep attenuation characteristic at the low end of the passband. Therefore, by combining the reception filter 10 and the transmission filter 20 to constitute the multiplexer 1, the multiplexer 1 excellent in isolation between the transmission and reception is obtained.

The effects of the above-described multiplexer 1 and the modified example will be described in comparison with the comparative example.

4 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate 59 of the multiplexer 2 according to Comparative Example 1. As shown in FIG.

Compared with the multiplexer 1, the multiplexer 2 is the same in circuit configuration and differs in that the inductance component of the inductor L1 is smaller.

As shown in Fig. 4, in the multiplexer 2, since the wiring connecting the node N1 and the ground terminal B2 is composed of an electrode having a planar pattern, the inductance component of the inductor L1 is the inductance component of the inductor L2. ) is almost equal to the inductance component of ) and is negligibly small.

5 is a circuit diagram showing an example of the configuration of the multiplexer 3 according to Comparative Example 2. As shown in FIG.

6 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate 59 of the multiplexer 3 .

The multiplexer 3 differs from the multiplexer 1 in that it has an inductor L3 between the parallel arm resonator 16 and the node N1.

5 and 6, in the multiplexer 3, in the reception filter 11, the inductor L3 by the wiring intentionally twisted between the parallel arm resonator 16 and the node N1. ) is provided. Since the length of the wiring corresponding to the inductor L1 is substantially 0, and the wiring corresponding to the inductor L2 is composed of electrodes having a planar pattern, the inductance components of the inductors L1 and L2 are all negligible. small enough to be

7 is a circuit diagram showing an example of the configuration of the multiplexer 4 according to Comparative Example 3. As shown in FIG.

8 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate 59 of the multiplexer 4 .

The multiplexer 4 is different from the multiplexer 1 in that it does not have a signal path connecting the node N1 and the node N2.

7 and 8, in the multiplexer 4, in the reception filter 12, the ground terminals B1, B2, and B3 are all provided independently. In addition, an inductor L4 by wiring intentionally wrapped between the parallel arm resonator 16 and the ground terminal B2 is provided.

9 is a plan view schematically showing an example of electrode arrangement on the piezoelectric substrate 59 of the multiplexer 5 according to the modification.

The multiplexer 5 is the same in circuit configuration as compared with the multiplexer 1 of FIG. 1, and is different in that the inductance component of the inductor L1 is smaller and the inductance component of the inductor L2 is larger.

As shown in Fig. 9, in the multiplexer 5, since the wiring between the node N2 and the ground terminal B3 is composed of a winding wiring intentionally, the inductance component of the inductor L2 is large. In addition, since the wiring connecting the node N1 and the ground terminal B2 is formed of an electrode having a planar pattern, the inductance component of the inductor L1 is negligibly small. Accordingly, in the multiplexer 5, the inductance component of the inductor L2 is larger than the inductance component of the inductor L1.

Taking the multiplexer 1 as an example, and for the multiplexers 1, 2, 3, 4 and 5 according to the examples, comparative examples 1, 2 and 3, and modified examples, isolation characteristics between terminals (Tx→Rx) saved The uplink frequency band (814 MHz or more and 849 MHz or less) of Band26 of LTE (registered trademark) (Long Term Evolution) is used as the passband (hereinafter, the transmission band) of the transmission filter 20, and the downlink frequency band (859 MHz or more and 894 MHz) MHz or less) was used as the pass band (hereinafter, the reception band) of the reception filters 10, 11 and 12.

10 is a graph showing an example of an isolation characteristic between terminals (Tx→Rx) of a multiplexer.

As shown in FIG. 10, the minimum value (worst value of isolation) of the insertion loss within the transmission band is 60.7 dB in the Example, 58.6 dB in the modified example, 57.2 dB in Comparative Example 1, 56.3 dB in Comparative Example 2, In Comparative Example 3, it is 53.8 dB.

In the embodiment, by connecting the node N1 and the node N2, the combined capacitance of the parallel arm resonator 16 and the resonator groups 17 and 18 and the attenuation pole generated by the series resonance by the inductor L1 are reduced. It shifted from the vicinity of a reception band to the low frequency side. By shifting the attenuation pole to the low frequency side using the combined capacitance, good isolation was achieved over the entire transmission band while reducing the required inductance component.

In Comparative Example 1, the node N1 and the node N2 are connected, but the inductor L1 is realized as an electrode having a planar pattern, and since the inductance component is substantially negligible, the attenuation pole is set to the low frequency side It cannot be shifted sufficiently. Therefore, compared with the embodiment, the isolation from the mid-range to the high range (831.5 MHz or more and 849 MHz or less) of the transmission band deteriorates.

In Comparative Example 2, the inductor L3 is provided between the parallel arm resonator 16 and the node N1, and the attenuation pole generated by the series resonance of the parallel arm resonator 16 and the inductor L3 is applied to the receiving band. By shifting from the vicinity to the low frequency side, the attenuation of the transmission band was improved.

In Comparative Example 2, the required inductance component becomes larger as the capacitance of the resonator groups 17 and 18 is not used in order to shift the damping pole as compared with the Example. Therefore, it becomes an obstacle to downsizing of an apparatus. Further, since the steepness of the attenuation characteristic deteriorates at the low end of the reception band, the isolation in the vicinity of the high end of the transmission band (849 MHz) deteriorates.

In Comparative Example 3, the ground of the parallel arm resonator 16 and the ground of the resonator groups 17 and 18 were not common, and the inductor L4 was provided between the parallel arm resonator 16 and the ground terminal B2. , by shifting the attenuation pole generated by the series resonance of the parallel arm resonator 16 and the inductor L4 from the vicinity of the reception band to the low frequency side, the attenuation of the transmission band was improved.

In Comparative Example 3, since the ground ends of the resonator groups 17 and 18 are not connected to the ground terminal B2, the parasitic inductance component generated at the ground of the resonator groups 17 and 18 increases. Usually, the more stable the ground potential of the resonator groups 17 and 18, the greater the attenuation in the transmission band. In Comparative Example 3, since the parasitic inductance component increases, the ground potential becomes difficult to stabilize. isolation is deteriorated.

In the modified example, by connecting the node N1 and the node N2, the combined capacitance of the parallel arm resonator 16 and the resonator groups 17 and 18 and the attenuation pole generated by the series resonance by the inductor L2 are reduced. It shifted from the vicinity of a reception band to the low frequency side. In the modified example, the required inductance component was made small by shifting the attenuation pole to the low-frequency side using the combined capacitance as in the example.

In the modified example, the attenuation pole is shifted to the low frequency side by using the inductor L2 connected between the node N2 and the ground terminal B3. The parasitic inductance component increases. Therefore, isolation in the vicinity of the transmission band mid-range (831.5 MHz) deteriorates compared with the embodiment.

On the other hand, in any of the multiplexers 1, 2, 3, 4, and 5 according to the embodiment, Comparative Examples 1, 2 and 3, and the modified example, the ground terminal B1 is independent from the ground terminals B2 and B3. have. When the ground terminal B1 is shared with the ground terminals B2 and B3, the attenuation pole generated by the parallel arm resonator 15 is also shifted to the low frequency side, and the steepness of the attenuation characteristic at the low frequency side of the reception band is impaired. this can happen According to the multiplexers 1, 2, 3, 4 and 5, such disadvantages can be avoided.

As mentioned above, although the filter and multiplexer which concern on embodiment of this invention were demonstrated, this invention is not limited to each embodiment. As long as it does not deviate from the spirit of the present invention, various modifications that those skilled in the art come up with are added to this embodiment, and forms constructed by combining components from other embodiments are also included within the scope of one or more aspects of the present invention. may be

For example, in the embodiment, an example of a duplexer has been described. However, the present invention is not limited to a duplexer. For example, a diplexer, a triplexer, and a quadplexer that simply demultiplex and multiplex a plurality of signals having different frequency bands. It may be applied to a lexer or the like.

For example, in the embodiment, the second parallel arm resonator and the longitudinally coupled resonator type filter are connected to each other through an inductor on the ground side, and this inductor is connected to the node N1 on the first signal path R1 and the ground terminal ( An example of the inductor L1 between B2) is shown, but is not limited thereto. The inductor may be an inductor L2 between the node N2 on the signal path R2 and the ground terminal B3. Depending on the inductor L2, similarly to the inductor L1, the attenuation outside the pass band can be increased.

INDUSTRIAL APPLICABILITY As a filter and a multiplexer, the present invention can be widely used in communication devices such as mobile phones.

1, 2, 3, 4, 5: Multiplexer
10, 11, 12: receive filter
13, 14: serial arm resonator
15, 16: parallel arm resonator
17, 18: resonator group
19: three-dimensional wiring
20: transmit filter
21, 22, 23, 24, 25: serial arm resonator
26, 27, 28, 29: parallel arm resonator
30: antenna element
50: IDT electrode
50a, 50b: comb-shaped electrodes
51a, 51b: electrode finger
52a, 52b: busbar electrodes
53: electrode layer
54: protective layer
59: piezoelectric substrate
N1, N2: Node
R1, R2, R3: signal path
L1, L2, L3, L4: Inductor
Ant, Tx, Rx, B1, B2, B3, B4, B5: terminals

Claims (6)

A ladder type filter including a first parallel arm resonator and a second parallel arm resonator;
a longitudinally coupled resonator filter connected in series with the ladder filter;
a first ground terminal connected to the first parallel arm resonator;
a second ground terminal provided independently of the first ground terminal and connected to the second parallel arm resonator and a third ground terminal connected to the longitudinally coupled resonator type filter;
A third node connected to a first node on a first signal path connecting the second parallel arm resonator and the second ground terminal and a second node on a second signal path connecting the longitudinally coupled resonator filter and a third ground terminal signal path and
and an inductor connected between the first node and the second ground terminal on the first signal path or between the second node and the third ground terminal on the second signal path. According to claim 1,
wherein the inductor is disposed on the first signal path and is a first inductor connected between the first node and the second ground terminal. 3. The method of claim 2,
a second inductor connected between the second node and the third ground terminal;
an inductance of the first inductor is greater than an inductance of the second inductor. 4. The method according to any one of claims 1 to 3,
The longitudinally coupled resonator filter has a plurality of IDT (InterDigital Transducer) electrodes juxtaposed in the propagation direction of the elastic wave, and all one ends of the plurality of IDT electrodes are connected to the third ground terminal Being a filter. 4. The method according to any one of claims 1 to 3,
The second parallel arm resonator has the largest capacitance among all the parallel arm resonators included in the ladder filter. One end includes a first filter and a second filter connected to each other,
The first filter is the filter according to any one of claims 1 to 3,
and a center frequency of the pass band of the first filter is higher than a center frequency of the pass band of the second filter.

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