Elastic wave filters and multiplexers

Abstract

This invention provides an elastic wave filter that increases out-of-band attenuation and a multiplexer that improves isolation characteristics. [Solution] The longitudinally coupled resonator type elastic wave filter 3 has a first region A that includes the IDT electrode 6A at one end to the central IDT electrode 6E in the direction in which the n (9) IDT electrodes 6A to 6I are arranged, and a second region B that includes the IDT electrode 6E in the central IDT electrode 6I in the direction in which the n (9) IDT electrodes are arranged. One of the first (second) comb-shaped electrodes 7A (7B) of adjacent IDT electrodes is connected to the signal potential, and the other first (second) comb-shaped electrode 7A (7B) is connected to the reference potential, and in the first (second) region A (region B), all of the first (second) comb-shaped electrodes 7A (7B) connected to the reference potential are connected to the first (second) reference potential wiring 9A (9B).

Description

Technical Field

[0001] The present invention relates to an elastic wave filter and a multiplexer.

[0002] Conventionally, elastic wave filters have been widely used as filters for mobile phones and the like. Patent Document 1 below discloses an example of an elastic wave filter. This elastic wave filter has a vertically coupled resonator section. The vertically coupled resonator section has three or more IDT (Interdigital Transducer) electrodes. Each IDT electrode has a pair of comb-shaped electrodes. One of the comb-shaped electrodes in the IDT electrode is connected to a signal potential, and the other comb-shaped electrode is connected to a ground potential. The comb-shaped electrodes of some of the plurality of IDT electrodes are connected to the ground potential via the same wiring. The comb-shaped electrodes of the remaining IDT electrodes are connected to the ground potential via wiring different from the above wiring.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The elastic wave filter described in Patent Document 1 is used, for example, in a multiplexer such as a duplexer together with other filter devices. However, in the above elastic wave filter, it is difficult to sufficiently increase the out-of-band attenuation amount. Therefore, when the above elastic wave filter is used in a multiplexer, it is difficult to sufficiently increase the isolation characteristics.

[0005] An object of the present invention is to provide an elastic wave filter capable of increasing the out-of-band attenuation amount. Another object of the present invention is to provide a multiplexer capable of improving the isolation characteristics. [Means for solving the problem]

[0006] The elastic wave filter according to the present invention comprises a longitudinally coupled resonator elastic wave filter having n IDT electrodes, and a first reference potential wiring and a second reference potential wiring connected to a reference potential, respectively, when the number of IDT electrodes is an odd number of 7 or more, wherein the longitudinally coupled resonator elastic wave filter has a first region including the IDT electrode at one end to the central IDT electrode in the direction in which the n IDT electrodes are arranged, and a second region including the IDT electrode at the central end to the IDT electrode in the direction in which the n IDT electrodes are arranged, and each IDT electrode includes a first comb-shaped electrode and a second comb-shaped electrode that are interlocked with each other, and in each IDT electrode, one of the first comb-shaped electrode and the second comb-shaped electrode is connected to a signal potential and the other is connected to a reference potential. In the first region, one of the adjacent IDT electrodes is connected to a signal potential, and the other first comb electrode is connected to a reference potential. In the first region, all of the multiple first comb electrodes connected to the reference potential are connected to the first reference potential wiring. The multiple second comb electrodes connected to the reference potential include the second comb electrode connected to the first reference potential wiring, and the second comb electrode connected to the second reference potential wiring. In the second region, the multiple first comb electrodes connected to the reference potential include the first comb electrode connected to the first reference potential wiring, and the first comb electrode connected to the second reference potential wiring. All of the multiple second comb electrodes connected to the reference potential are connected to the second reference potential wiring.

[0007] The multiplexer according to the present invention comprises a plurality of filter devices, wherein at least one of the filter devices is an elastic wave filter configured according to the present invention. [Effects of the Invention]

[0008] The elastic wave filter according to the present invention can increase out-of-band attenuation. The multiplexer according to the present invention can improve isolation characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram of a duplexer according to the first embodiment of the present invention. [Figure 2] This is a schematic plan view of a longitudinally coupled resonator type elastic wave filter according to a first embodiment of the present invention. [Figure 3] This is a schematic diagram of a longitudinally coupled resonator type elastic wave filter in the first embodiment of the present invention. [Figure 4] This is a schematic diagram of the longitudinally coupled resonator type elastic wave filter in the first comparative example. [Figure 5] This is a schematic diagram of the longitudinally coupled resonator type elastic wave filter in the second comparative example. [Figure 6] This figure shows the isolation characteristics in the duplexer of the first embodiment of the present invention, the first comparative example, and the second comparative example. [Figure 7] This figure shows the attenuation frequency characteristics of the transmit filters in the first embodiment and the second comparative example of the present invention. [Figure 8] This figure shows the attenuation frequency characteristics of the receiving filters in the first embodiment and the second comparative example of the present invention. [Figure 9] This is a magnified view of the area around the passband of the transmit filter in Figure 8. [Figure 10] This is a schematic diagram of a multiplexer according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0010] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0011] Note that each embodiment described in this specification is exemplary, and it is pointed out that partial replacement or combination of configurations is possible between different embodiments.

[0012] Figure 1 is a circuit diagram of a duplexer according to a first embodiment of the present invention.

[0013] The duplexer 10 is a multiplexer according to a first embodiment of the present invention. Specifically, the duplexer 10 includes a reception filter 1A, a transmission filter 1B, and a common connection terminal 2. The reception filter 1A and the transmission filter 1B are commonly connected to the common connection terminal 2. The reception filter 1A is a surface acoustic wave filter according to an embodiment of the present invention.

[0014] Note that the multiplexer according to the present invention is not limited to a duplexer. For example, the multiplexer according to the present invention may have three or more filter devices. At least one filter device in the multiplexer may be a surface acoustic wave filter according to the present invention.

[0015] In this specification, it is assumed that the passband of the multiplexer or the filter device is a band defined by a standard such as a communication band. The communication band of the duplexer 10 is Band28. Therefore, the passband of the reception filter 1A is 758 MHz to 803 MHz as the reception band of Band28. The passband of the transmission filter 1B is 703 MHz to 748 MHz as the transmission band of Band28. However, the passbands of the reception filter 1A and the transmission filter 1B are not limited to the above.

[0016] As shown in FIG. 1, the reception filter 1A includes a longitudinally coupled resonator type surface acoustic wave filter 3, a plurality of surface acoustic wave resonators, a first signal terminal 4A and a second signal terminal 4B, a first reference potential wiring 9A and a second reference potential wiring 9B, a first reference potential terminal 12A, and a second reference potential terminal 12B. The plurality of surface acoustic wave resonators specifically include a plurality of series arm resonators and a plurality of parallel arm resonators.

[0017] The first reference potential wiring 9A and the second reference potential wiring 9B are wirings connected to the reference potential, respectively. The first reference potential terminal 12A and the second reference potential terminal 12B are terminals connected to the reference potential, respectively. The first reference potential wiring 9A is connected to the first reference potential terminal 12A. Therefore, the first reference potential wiring 9A is connected to the reference potential via the first reference potential terminal 12A. The second reference potential wiring 9B is connected to the second reference potential terminal 12B. Therefore, the second reference potential wiring 9B is connected to the reference potential via the second reference potential terminal 12B.

[0018] On the other hand, the transmission filter 1B is a ladder-type filter. Specifically, the transmission filter 1B includes a plurality of series-arm resonators, a plurality of parallel-arm resonators, a third signal terminal 4C, and a fourth signal terminal 4D. In the following, the elastic wave resonator, the series-arm resonator, the parallel-arm resonator, and the vertically-coupled resonator type elastic wave filter may be collectively referred to as resonators.

[0019] The first signal terminal 4A of the reception filter 1A and the fourth signal terminal 4D of the transmission filter 1B are connected to the common connection terminal 2. The common connection terminal 2 is an antenna terminal. The antenna terminal is connected to an antenna. Note that the common connection terminal 2 does not necessarily have to be an antenna terminal.

[0020] In the present embodiment, the common connection terminal 2, the second signal terminal 4B, the third signal terminal 4C, the first reference potential terminal 12A, and the second reference potential terminal 12B are configured as electrode pads. On the other hand, the first signal terminal 4A and the fourth signal terminal 4D are configured as wirings. However, each of the above terminals may be configured as an electrode pad or may be configured as a wiring.

[0021] In the reception filter 1A, a vertically-coupled resonator type elastic wave filter 3 is connected between the first signal terminal 4A and the second signal terminal 4B. Hereinafter, the specific configuration of the vertically-coupled resonator type elastic wave filter 3 will be shown.

[0022] Figure 2 is a schematic plan view of a longitudinally coupled resonator type elastic wave filter in the first embodiment. In Figure 2, the first reference potential wiring 9A is shown by a dashed line. The second reference potential wiring 9B is shown by a broken line. In Figure 2, each region described later is shown by a broken or double-dash line. The same applies to the schematic diagrams of the longitudinally coupled resonator type elastic wave filter described later.

[0023] The longitudinally coupled resonator type elastic wave filter 3 has a piezoelectric substrate 5 and a plurality of IDT electrodes. Alternatively, the duplexer 10 can be said to have the piezoelectric substrate 5 on which the longitudinally coupled resonator type elastic wave filter 3 is constructed. The piezoelectric substrate 5 is a piezoelectric substrate. The piezoelectric substrate 5 is a substrate made solely of piezoelectric material. Examples of piezoelectric materials include lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate). The piezoelectric substrate 5 may also be a laminated substrate including a piezoelectric layer.

[0024] In this embodiment, all resonators of the receiving filter 1A and transmitting filter 1B shown in Figure 1 share a piezoelectric substrate 5. The piezoelectric substrate 5 is provided with the terminals shown in Figure 1. More specifically, the piezoelectric substrate 5 is provided with a common connection terminal 2, a first signal terminal 4A, a second signal terminal 4B, a third signal terminal 4C, a fourth signal terminal 4D, a first reference potential terminal 12A, and a second reference potential terminal 12B. However, each resonator may have its own separate piezoelectric substrate 5. Multiple terminals may be provided on different piezoelectric substrates 5.

[0025] As shown in Figure 2, the longitudinally coupled resonator type elastic wave filter 3 has nine IDT electrodes. The nine IDT electrodes are provided on a piezoelectric substrate 5. Specifically, the nine IDT electrodes of the longitudinally coupled resonator type elastic wave filter 3 are IDT electrode 6A, IDT electrode 6B, IDT electrode 6C, IDT electrode 6D, IDT electrode 6E, IDT electrode 6F, IDT electrode 6G, IDT electrode 6H, and IDT electrode 6I. The longitudinally coupled resonator type elastic wave filter 3 has a single-stage configuration.

[0026] Furthermore, the number of IDT electrodes in the longitudinally coupled resonator type elastic wave filter 3 is not limited to 9. In the present invention, the longitudinally coupled resonator type elastic wave filter 3 only needs to have n IDT electrodes when n is an odd number of 7 or more. More specifically, in the present invention, n is any odd number of 7 or more, and in the first embodiment, n=9. However, in the present invention, n may be an odd number such as 7 or 11.

[0027] The IDT electrode 6A of the longitudinally coupled resonator type elastic wave filter 3 has a pair of comb-shaped electrodes. Specifically, the pair of comb-shaped electrodes are a first comb-shaped electrode 7A and a second comb-shaped electrode 7B. The first comb-shaped electrode 7A has a first busbar 16 and a plurality of first electrode fingers 18. One end of each of the plurality of first electrode fingers 18 is connected to the first busbar 16. The second comb-shaped electrode 7B has a second busbar 17 and a plurality of second electrode fingers 19. One end of each of the plurality of second electrode fingers 19 is connected to the second busbar 17.

[0028] The first comb-shaped electrode 7A and the second comb-shaped electrode 7B are arranged such that the first busbar 16 and the second busbar 17 face each other. The multiple first electrode fingers 18 and the multiple second electrode fingers 19 are interlocked with each other. Therefore, the first comb-shaped electrode 7A and the second comb-shaped electrode 7B are interlocked with each other.

[0029] In the following, the first comb-shaped electrode 7A and the second comb-shaped electrode 7B may be collectively referred to simply as the comb-shaped electrode. The first electrode finger 18 and the second electrode finger 19 may be collectively referred to simply as the electrode finger. The direction in which the multiple electrode fingers extend is called the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is called the electrode finger orthogonal direction. The first busbar 16 is located on one side in the electrode finger extension direction, and the second busbar 17 is located on the other side.

[0030] In the longitudinally coupled resonator type elastic wave filter 3, all IDT electrodes other than IDT electrode 6A also have a pair of comb-shaped electrodes, similar to IDT electrode 6A. The direction orthogonal to the electrode fingers of each IDT electrode in the longitudinally coupled resonator type elastic wave filter 3 is the same.

[0031] When an AC voltage is applied to each IDT electrode, elastic waves are excited. The direction of elastic wave propagation at each IDT electrode is parallel to the direction perpendicular to the electrode fingers. The nine IDT electrodes in the longitudinally coupled resonator type elastic wave filter 3 are aligned in the direction of elastic wave propagation. Specifically, in the direction in which the nine IDT electrodes are aligned, IDT electrodes 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, and 6I are arranged in this order.

[0032] The longitudinally coupled resonator type elastic wave filter 3 has a pair of reflectors. Specifically, the pair of reflectors are reflector 8A and reflector 8B. More specifically, reflectors 8A and 8B are provided on the piezoelectric substrate 5 so as to sandwich nine IDT electrodes in the elastic wave propagation direction and face each other. Each IDT electrode and each reflector may be made of a multilayer metal film or a single layer metal film.

[0033] Figure 3 is a schematic diagram of a longitudinally coupled resonator type elastic wave filter in the first embodiment. In Figure 3, each IDT electrode and each reflector is shown as a schematic rectangle. In Figure 3, each IDT electrode is hatched. In Figure 3, the fact that wiring is connected to the upper part of the IDT electrode in Figure 3 indicates that wiring is connected to the first comb-shaped electrode of the IDT electrode. On the other hand, in Figure 3, the fact that wiring is connected to the lower part of the IDT electrode in Figure 3 indicates that wiring is connected to the second comb-shaped electrode of the IDT electrode. The same applies to schematic diagrams other than Figure 3.

[0034] In the following, the order in which the nine IDT electrodes are arranged will be designated as the number of each IDT electrode, with IDT electrode 6A being numbered 1. The numbers of IDT electrodes 6A, 6C, 6E, 6G, and 6I are odd. On the other hand, the numbers of IDT electrodes 6B, 6D, 6F, and 6H are even.

[0035] In each IDT electrode, one of the first comb-shaped electrode and the second comb-shaped electrode is connected to the signal potential, and the other is connected to the reference potential. Specifically, in the first IDT electrode 6A, the first comb-shaped electrode is connected to the reference potential, and the second comb-shaped electrode is connected to the signal potential. In the other odd-numbered IDT electrodes, the first comb-shaped electrode is connected to the reference potential, and the second comb-shaped electrode is connected to the signal potential. More specifically, in the odd-numbered IDT electrodes, the second comb-shaped electrode is connected to the signal potential on the second signal terminal 4B side.

[0036] On the other hand, in the even-numbered IDT electrodes, the first comb-shaped electrode is connected to the signal potential, and the second comb-shaped electrode is connected to the reference potential. More specifically, in the even-numbered IDT electrodes, the first comb-shaped electrode is connected to the signal potential on the first signal terminal 4A side.

[0037] In the longitudinally coupled resonator type elastic wave filter 3, one of the odd-numbered IDT electrodes is adjacent to one of the even-numbered IDT electrodes. Of the adjacent IDT electrodes, the first comb electrode of one is connected to the signal potential, and the first comb electrode of the other is connected to the reference potential.

[0038] A first reference potential wiring 9A, schematically shown by a dashed line, and a second reference potential wiring 9B, schematically shown by a dashed line, are provided on the piezoelectric substrate 5. The first reference potential wiring 9A and the second reference potential wiring 9B are connected to a reference potential. In the longitudinally coupled resonator type elastic wave filter 3, the comb-shaped electrode connected to the reference potential is connected to one of the first reference potential wiring 9A and the second reference potential wiring 9B.

[0039] The first reference potential wiring 9A is not connected to the second reference potential wiring 9B. The first reference potential terminal 12A is not connected to the second reference potential terminal 12B. In other words, in the receiving filter 1A as an elastic wave filter, the path through which the first reference potential wiring 9A is connected to the reference potential and the path through which the second reference potential wiring 9B is connected to the reference potential are different from each other.

[0040] As shown in Figure 3, the longitudinally coupled resonator type elastic wave filter 3 has a first region A and a second region B. Specifically, the first region A is the region that includes the IDT electrode 6A at one end to the central IDT electrode 6E in the direction in which the nine IDT electrodes are arranged. The second region B is the region that includes the IDT electrode 6E in the direction in which the nine IDT electrodes are arranged to the other end to the IDT electrode 6I.

[0041] In the first region A, the first comb-shaped electrodes connected to the reference potential are the first comb-shaped electrodes IDT electrode 6A, IDT electrode 6C, and IDT electrode 6E. All of these first comb-shaped electrodes are connected to the first reference potential wiring 9A.

[0042] In the first region A, the second comb-shaped electrodes connected to the reference potential are the second comb-shaped electrodes of IDT electrodes 6B and 6D. The second comb-shaped electrode of IDT electrode 6B is connected to the first reference potential wiring 9A. The second comb-shaped electrode of IDT electrode 6D is connected to the second reference potential wiring 9B. Thus, the second comb-shaped electrodes connected to the reference potential include the second comb-shaped electrode connected to the first reference potential wiring 9A and the second comb-shaped electrode connected to the second reference potential wiring 9B.

[0043] In the second region B, the first comb-shaped electrodes connected to the reference potential are the first comb-shaped electrodes of IDT electrodes 6E, 6G, and 6I. The first comb-shaped electrodes of IDT electrodes 6E and 6G are connected to the first reference potential wiring 9A. The first comb-shaped electrode of IDT electrode 6I is connected to the second reference potential wiring 9B. Thus, the plurality of first comb-shaped electrodes connected to the reference potential include the first comb-shaped electrode connected to the first reference potential wiring 9A and the first comb-shaped electrode connected to the second reference potential wiring 9B.

[0044] In the second region B, the second comb electrodes connected to the reference potential are the second comb electrodes of IDT electrode 6F and IDT electrode 6H. All of these second comb electrodes are connected to the second reference potential wiring 9B.

[0045] The features of this embodiment are that it has the following configurations 1) to 4): 1) In the first region A, all of the multiple first comb-shaped electrodes connected to the reference potential are connected to the first reference potential wiring 9A. 2) In the first region A, the multiple second comb-shaped electrodes connected to the reference potential include a second comb-shaped electrode connected to the first reference potential wiring 9A and a second comb-shaped electrode connected to the second reference potential wiring 9B. 3) In the second region B, the multiple first comb-shaped electrodes connected to the reference potential include a first comb-shaped electrode connected to the first reference potential wiring 9A and a first comb-shaped electrode connected to the second reference potential wiring 9B. 4) In the second region B, all of the multiple second comb-shaped electrodes connected to the reference potential are connected to the second reference potential wiring 9B.

[0046] The longitudinally coupled resonator type elastic wave filter 3 in the receiving filter 1A, which acts as an elastic wave filter, has the configurations described in 1) to 4) above, thereby increasing the out-of-band attenuation of the receiving filter 1A. This improves the isolation characteristics of the duplexer 10. The details of this will be explained below, along with the details of the circuit configuration in this embodiment.

[0047] As shown in Figure 1, the receiving filter 1A includes a longitudinally coupled resonator type elastic wave filter 3, a plurality of elastic wave resonators, a first signal terminal 4A and a second signal terminal 4B, and inductors L1 and L2. The longitudinally coupled resonator type elastic wave filter 3 is connected between the first signal terminal 4A and the second signal terminal 4B. The signal received from the common connection terminal 2 is input to the first signal terminal 4A and output from the second signal terminal 4B after passing through each element of the receiving filter 1A.

[0048] The multiple elastic wave resonators in the receiving filter 1A specifically include multiple series arm resonators and multiple parallel arm resonators. More specifically, the multiple series arm resonators in the receiving filter 1A are series arm resonator S1, series arm resonator S2, and series arm resonator S3. Series arm resonator S1 is connected between the first signal terminal 4A and the longitudinally coupled resonator type elastic wave filter 3. Series arm resonators S2 and S3 are connected in series with each other between the longitudinally coupled resonator type elastic wave filter 3 and the second signal terminal 4B.

[0049] The multiple parallel arm resonators in the receiving filter 1A are more specifically parallel arm resonators P1 and P2. Parallel arm resonator P1 is connected between the connection point between the series arm resonator S1 and the longitudinally coupled resonator type elastic wave filter 3 and the reference potential. Parallel arm resonator P2 is connected between the connection point between the series arm resonators S2 and S3 and the reference potential. Parallel arm resonator P1 is connected to the first reference potential terminal 12A. The first reference potential terminal 12A is connected to inductor L1. On the other hand, parallel arm resonator P2 is connected to the second reference potential terminal 12B. The second reference potential terminal 12B is connected to inductor L2. Inductors L1 and L2 are connected to the reference potential.

[0050] The parallel arm resonator P1 is connected to the first reference potential wiring 9A. The first reference potential wiring 9A is connected to the inductor L1 via the first reference potential terminal 12A. Therefore, the comb-shaped electrodes of some of the multiple IDT electrodes and the parallel arm resonator P1 are commonly connected to the reference potential via the inductor L1.

[0051] On the other hand, the parallel arm resonator P2 is connected to the second reference potential wiring 9B. The second reference potential wiring 9B is connected to the inductor L2 via the second reference potential terminal 12B. Therefore, among all the IDT electrodes in the longitudinally coupled resonator type elastic wave filter 3, the comb-shaped electrodes of some of the IDT electrodes and the parallel arm resonator P2 are commonly connected to the reference potential via the inductor L2.

[0052] However, the circuit configuration of the receiving filter 1A, which is an elastic wave filter according to the present invention, is not limited to the above. For example, inductors L1 and L2 do not necessarily have to be provided. The elastic wave filter according to the present invention only needs to have a longitudinally coupled resonator type elastic wave filter 3 and a first reference potential wiring 9A and a second reference potential wiring 9B.

[0053] The transmitting filter 1B includes a plurality of series arm resonators and a plurality of parallel arm resonators, a third signal terminal 4C and a fourth signal terminal 4D, and inductors L3 and L4.

[0054] The series arm resonators in the transmitting filter 1B are, more specifically, series arm resonators S11a, S11b, S12a, S12b, S13, and S14. These series arm resonators are connected in series between the third signal terminal 4C and the fourth signal terminal 4D. More specifically, in the circuit configuration, they are arranged in the order of series arm resonators S11a, S11b, S12a, S12b, S13, and S14, starting from the third signal terminal 4C side.

[0055] The multiple parallel arm resonators in the transmitting filter 1B are, more specifically, parallel arm resonators P11, P12, P13, and P14. Parallel arm resonator P11 is connected between the third signal terminal 4C and the reference potential. Parallel arm resonator P12 is connected between the connection point between series arm resonators S11b and S12a and the reference potential. Parallel arm resonator P13 is connected between the connection point between series arm resonators S12b and S13 and the reference potential. Parallel arm resonator P14 is connected between the connection point between series arm resonators S13 and S14 and the reference potential.

[0056] Parallel arm resonators P11, P12, and P13 are commonly connected to inductor L3. Parallel arm resonator P14 is connected to inductor L4. Inductors L3 and L4 are connected to a reference potential. However, the circuit configuration of the transmitting filter 1B is not limited to the above.

[0057] As described above, the duplexer 10 of this embodiment can improve isolation characteristics. The details of this effect are shown below by comparing this embodiment with the first comparative example and the second comparative example.

[0058] The circuit configurations of the first and second comparative examples differ from the first embodiment only in the configuration of the wiring connecting the longitudinally coupled resonator type elastic wave filter or parallel arm resonator in the receiving filter to the reference potential. As shown in Figure 4, the receiving filter in the first comparative example has a reference potential wiring 109. The reference potential wiring 109 is connected to the reference potential. The reference potential wiring 109 is connected to all comb-shaped electrodes connected to the reference potential.

[0059] The reference potential wiring 109 is connected to both the parallel arm resonators P1 and P2, as shown with reference to Figure 1. As shown in Figure 4, the reference potential wiring 109 is connected to the reference potential via both inductors L1 and L2.

[0060] As shown in Figure 5, the receiving filter in the second comparative example has a first reference potential wiring 109A and a second reference potential wiring 109B. The first reference potential wiring 109A and the second reference potential wiring 109B are connected to a reference potential. The first reference potential wiring 109A is connected to the reference potential via an inductor L1. The second reference potential wiring 109B is connected to the reference potential via an inductor L2.

[0061] All first comb electrodes connected to the reference potential are connected to the first reference potential wiring 109A. The plurality of second comb electrodes connected to the reference potential include a second comb electrode connected to the first reference potential wiring 109A and a second comb electrode connected to the second reference potential wiring 109B. Specifically, the second comb electrode of IDT electrode 6B is connected to the first reference potential wiring 109A. The second comb electrodes of IDT electrodes 6D, 6F, and 6H are connected to the second reference potential wiring 109B.

[0062] The first reference potential wiring 109A shown in Figure 5 is connected to the parallel arm resonator P1 shown with reference to Figure 1. The second reference potential wiring 109B shown in Figure 5 is connected to the parallel arm resonator P2 shown with reference to Figure 1.

[0063] The isolation characteristics were compared in the first embodiment, the first comparative example, and the second comparative example. In the first embodiment, the first comparative example, and the second comparative example, the passband of the transmit filter was 703MHz to 748MHz. The passband of the receive filter was 758MHz to 803MHz.

[0064] Figure 6 shows the isolation characteristics of the duplexer in the first embodiment, the first comparative example, and the second comparative example.

[0065] As shown in Figure 6, enclosed by a dashed line, the isolation characteristics in the first embodiment are improved compared to the first and second comparative examples.

[0066] Specifically, in the first comparative example, the minimum absolute value of isolation in the passband of the transmit filter is small at 59.5. In the second comparative example, the minimum absolute value of isolation in the passband of the transmit filter is 62.3. The isolation characteristics are improved in the second comparative example compared to the first comparative example. In contrast, in the first embodiment, the minimum absolute value of isolation in the passband of the transmit filter is large at 63.1. That is, the isolation characteristics are further improved in the first embodiment compared to the second comparative example.

[0067] The attenuation frequency characteristics of the transmit filter 1B and receive filter 1A in the first embodiment are as follows. The attenuation frequency characteristics of the transmit filter and receive filter in the second comparative example are also shown.

[0068] Figure 7 shows the attenuation frequency characteristics of the transmit filter in the first embodiment and the second comparative example. Figure 8 shows the attenuation frequency characteristics of the receive filter in the first embodiment and the second comparative example. Figure 9 is a magnified view of the area near the passband of the transmit filter in Figure 8. In Figures 7 to 9, the passband of the transmit filter is indicated by W1. In Figures 7 and 8, the passband of the receive filter is indicated by W2.

[0069] As shown in Figure 7, there is no difference in the attenuation frequency characteristics of the transmitting filter between the first embodiment and the second comparative example.

[0070] As shown in Figures 8 and 9, in the first embodiment, the out-of-band attenuation of the receiving filter is greater than in the second comparative example. More specifically, in the passband W1, the attenuation of the receiving filter in the first embodiment is greater than the attenuation of the receiving filter in the second comparative example. This improves the isolation characteristics of the duplexer 10 according to the first embodiment.

[0071] In the first embodiment, an example was shown in which only one filter device in the multiplexer is an elastic wave filter according to the present invention. However, multiple filter devices in the multiplexer may be elastic wave filters according to the present invention.

[0072] In a multiplexer, it is preferable that at least one filter device is an elastic wave filter according to the present invention, and that the passband of at least one elastic wave filter is located at a higher frequency than the passband of at least one other filter device. This makes it possible to more reliably improve the isolation characteristics of the multiplexer. Note that when one passband is located at a higher frequency than the other passband, it means that all frequencies in one passband are higher than all frequencies in the other passband.

[0073] As shown in the first embodiment in Figure 1, it is preferable that the multiple parallel arm resonators include a parallel arm resonator P1 connected to a first reference potential wiring 9A and a parallel arm resonator P2 connected to a second reference potential wiring 9B. This makes it possible to make the frequency of the attenuation pole to which the parallel arm resonator P1 contributes and the frequency of the attenuation pole to which the parallel arm resonator P2 contributes different from each other. This increases the degree of freedom in adjusting the frequency range in the band where the out-of-band attenuation is large, and the magnitude of the attenuation in that band.

[0074] More specifically, in the receiving filter 1A as an elastic wave filter, the path through which the first reference potential wiring 9A is connected to the reference potential and the path through which the second reference potential wiring 9B is connected to the reference potential are different. Therefore, the path through which the parallel arm resonator P1 is connected to the reference potential and the path through which the parallel arm resonator P2 is connected to the reference potential are different. As a result, in the attenuation frequency characteristics of the elastic wave filter, the frequency of the attenuation pole to which the parallel arm resonator P1 contributes and the frequency of the attenuation pole to which the parallel arm resonator P2 contributes are different.

[0075] In this embodiment, the piezoelectric substrate 5 shown in Figure 3 is mounted on a package substrate (not shown) as a chip configured with terminals, wiring, and resonators. The package substrate is provided with inductors L1, L2, L3, and L4 shown in Figure 1. As described above, the first reference potential wiring 9A and the second reference potential wiring 9B are not connected on the piezoelectric substrate 5. Similarly, the first reference potential terminal 12A and the second reference potential terminal 12B are not connected on the piezoelectric substrate 5. However, on the package substrate, the path through which the receiving filter 1A, as an elastic wave filter, is connected to the reference potential may be common.

[0076] For example, the inductor L1 may be provided on the piezoelectric substrate 5. In this case, for example, the first reference potential wiring 9A is connected to the inductor L1. The inductor L1 is connected to the first reference potential terminal 12A. That is, the first reference potential wiring 9A is connected to the first reference potential terminal 12A via the inductor L1. The first reference potential wiring 9A is then connected to the reference potential via the inductor L1 and the first reference potential terminal 12A.

[0077] Similarly, for example, the inductor L2 may be provided on the piezoelectric substrate 5. In this case, for example, the second reference potential wiring 9B is connected to the inductor L2. The inductor L2 is connected to the second reference potential terminal 12B. That is, the second reference potential wiring 9B is connected to the second reference potential terminal 12B via the inductor L2. The second reference potential wiring 9B is then connected to the reference potential via the inductor L2 and the second reference potential terminal 12B.

[0078] Figure 10 is a schematic diagram of a multiplexer according to the second embodiment.

[0079] The multiplexer 20 of this embodiment has three or more filter devices. Specifically, the multiplexer 20 has a receiving filter 1A, a transmitting filter 1B, a filter device 21C, and at least one other filter device. The receiving filter 1A and the transmitting filter 1B are the same receiving filter and transmitting filter as in the first embodiment.

[0080] The filter device 21C may be, for example, a receiving filter or a transmitting filter. The same applies to filter devices other than the receiving filter 1A, the transmitting filter 1B, and the filter device 21C.

[0081] The multiplexer 20 has a receiving filter 1A as an elastic wave filter according to the present invention. Therefore, similar to the first embodiment, the isolation characteristics can be improved in the multiplexer 20.

[0082] The multiplexer 20 may also have an elastic wave filter according to the present invention other than the receiving filter 1A. In this case, it is preferable that the passband of the elastic wave filter is located at a higher frequency than the passband of, for example, the filter device 21C. This makes it possible to more reliably improve the isolation characteristics. [Explanation of symbols]

[0083] 1A...Receiver filter 1B...Transmit filter 2… Common connection terminal 3…Longitudinal coupled resonator type elastic wave filter 4A~4D…Signal terminals 1 to 4 5… Piezoelectric substrate 6A~6I…IDT electrode 7A, 7B…First and second comb-shaped electrodes 8A,8B…Reflector 9A, 9B... First and second reference potential wiring 10… Duplexa 12A, 12B… First and second reference potential terminals 16, 17… 1st and 2nd bus bars 18, 19… First and second electrode fingers 20…Multiplexer 21C...Filter device 109...Reference potential wiring 109A, 109B… First and second reference potential wiring A, B... First and second regions L1~L4...Inductors P1, P2, P11~P14... Parallel arm resonators S1~S3, S11a, S11b, S12a, S12b, S13, S14... Series arm resonators

Claims

1. When n is set to an odd number of 7 or more, a longitudinally coupled resonator type elastic wave filter having the n IDT electrodes, A first reference potential wiring and a second reference potential wiring, each connected to a reference potential, Equipped with, The longitudinally coupled resonator type elastic wave filter has a first region in the direction in which the n IDT electrodes are aligned, including the IDT electrode at one end and the IDT electrode at the center, and a second region in the direction in which the n IDT electrodes are aligned, including the IDT electrode at the center and the IDT electrode at the other end. Each IDT electrode includes a first comb-shaped electrode and a second comb-shaped electrode that are interposed with each other, and in each IDT electrode, one of the first comb-shaped electrode and the second comb-shaped electrode is connected to a signal potential and the other is connected to a reference potential, and in adjacent IDT electrodes, one of the first comb-shaped electrodes is connected to a signal potential and the other of the first comb-shaped electrodes is connected to a reference potential. In the first region, all of the first comb-shaped electrodes connected to the reference potential are connected to the first reference potential wiring, and the multiple second comb-shaped electrodes connected to the reference potential include the second comb-shaped electrode connected to the first reference potential wiring, and the second comb-shaped electrode connected to the second reference potential wiring. An elastic wave filter in which, in the second region, a plurality of the first comb-shaped electrodes connected to a reference potential include a first comb-shaped electrode connected to a first reference potential wiring and a first comb-shaped electrode connected to a second reference potential wiring, and all of the plurality of the second comb-shaped electrodes connected to a reference potential are connected to the second reference potential wiring.

2. The piezoelectric substrate comprising the longitudinally coupled resonator type elastic wave filter, A first reference potential terminal and a second reference potential terminal are provided on the piezoelectric substrate, Furthermore, The first reference potential wiring is connected to the reference potential via the first reference potential terminal. The elastic wave filter according to claim 1, wherein the second reference potential wiring is connected to the reference potential via the second reference potential terminal.

3. It further includes multiple parallel arm resonators, The elastic wave filter according to claim 1 or 2, wherein the plurality of parallel arm resonators include a parallel arm resonator connected to a first reference potential wiring and a parallel arm resonator connected to a second reference potential wiring.

4. Equipped with multiple filter devices, A multiplexer wherein at least one of the filter devices is an elastic wave filter according to any one of claims 1 to 3.

5. The multiplexer according to claim 4, wherein the passband of at least one of the elastic wave filters is located at a higher frequency than the passband of at least one of the filter devices other than the elastic wave filter.

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