Longitudinal coupling resonator type elastic wave filter and elastic wave filter

Abstract

Provided is a longitudinal-coupled resonator type elastic wave filter that does not result in a large size and that is capable of increasing the attenuation amount on the high frequency side of the passband. A longitudinal-coupled resonator type elastic wave filter (1) includes a plurality of IDT electrodes (2 to 6) including a first IDT electrode and a second IDT electrode, and a first second reflector (7, 8), the IDT electrodes (2 to 6) have signal side comb electrodes (2a, 3b, 4a, 5b, 6a) and ground side comb electrodes (2b, 3a, 4b, 5a, 6b), the signal side comb electrodes (3b, 5b) of the IDT electrodes (3, 5) corresponding to the first IDT electrode are electrically connected to at least one of the first second reflector (7, 8), the IDT electrodes (2, 6) corresponding to the second IDT electrode are disposed between the IDT electrodes (3, 5) and the first second reflector (7, 8), the signal side comb electrodes (3b, 5b) of the IDT electrodes (3, 5) are connected to one of an input terminal and an output terminal, and the signal side comb electrodes (2a, 6a) of the IDT electrodes (2, 6) are connected to the other of the input terminal and the output terminal.

Description

TECHNICAL FIELD

[0001] The present application relates to a longitudinal-coupled resonator type elastic wave filter having a plurality of IDT electrodes and first and second reflectors, and an elastic wave filter including the longitudinal-coupled resonator type elastic wave filter. BACKGROUND

[0002] In the past, in a longitudinal-coupled resonator type elastic wave filter, a configuration in which a bridge capacitance is connected is known. For example, in Patent Document 1 described below, by connecting a bridge capacitance, the attenuation near the high frequency side of the passband of the filter is made close to the passband. Therefore, the attenuation characteristic of the high frequency side of the passband is improved.

[0003] The bridge capacitance described above is connected in parallel with the longitudinal-coupled resonator type elastic wave filter between the input terminal and the output terminal of the longitudinal-coupled resonator type elastic wave filter.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: International Publication No. 2005 / 101657 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the case where the bridge capacitance described above is provided, it is necessary to constitute the bridge capacitance on the chip surface. Therefore, the area of the chip surface increases by the amount of the bridge capacitance provided. Therefore, there is a problem that the longitudinal-coupled resonator type elastic wave filter is caused to be large-sized.

[0009] An object of the present application is to provide a longitudinal-coupled resonator type elastic wave filter and an elastic wave filter which do not cause a large size and which are capable of improving the attenuation characteristic of the high frequency side of the passband.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] The longitudinal-coupled resonator type elastic wave filter of the present application is provided with: a plurality of IDT electrodes including a first IDT electrode and a second IDT electrode; and a first reflector and a second reflector disposed on both sides of the plurality of IDT electrodes in an elastic wave propagation direction, the plurality of IDT electrodes each having a signal-side comb electrode connected to a signal-side potential and a ground-side comb electrode connected to a ground-side potential, the signal-side comb electrode of the first IDT electrode being electrically connected to at least one of the first reflector and the second reflector, the second IDT electrode being disposed between the first IDT electrode and at least one of the first reflector and the second reflector to which the signal-side comb electrode of the first IDT electrode is connected, the signal-side comb electrode of the first IDT electrode being connected to one of an input terminal and an output terminal, and the comb electrode of the second IDT electrode connected to the signal-side potential being connected to the other of the input terminal and the output terminal.

[0012] Effects of the Invention

[0013] According to the present application, it is possible to provide a longitudinal-coupled resonator type elastic wave filter and an elastic wave filter which do not cause a large size and which can improve the attenuation characteristic on the high frequency side of a passband. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a circuit diagram of a longitudinal-coupled resonator type elastic wave filter of the first embodiment of the present application.

[0015] Figure 2 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of the first embodiment of the present application.

[0016] Figure 3 is a circuit diagram showing a composite filter device having a longitudinal-coupled resonator type elastic wave filter of the first embodiment of the present application.

[0017] Figure 4 is a graph showing the attenuation amount-frequency characteristic of the receive filter of Example 1 and Comparative Example 1.

[0018] Figure 5 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of the second embodiment of the present application.

[0019] Figure 6 is a graph showing the attenuation amount-frequency characteristic of the receive filter of Example 2 and Comparative Example 2.

[0020] Figure 7 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of the third embodiment of the present application.

[0021] Figure 8 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of a fourth embodiment of the present application.

[0022] Figure 9 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of a fifth embodiment of the present application. DETAILED DESCRIPTION

[0023] Hereinafter, a specific embodiment of the present application will be described with reference to the drawings, whereby the present application will become clear.

[0024] Note that each embodiment described in this specification is an exemplary content, and it is foreseen that partial substitution or combination of structures can be made between different embodiments.

[0025] Figure 1 is a circuit diagram of a longitudinal-coupled resonator type elastic wave filter of a first embodiment of the present application. Also Figure 2 is a schematic circuit diagram of the longitudinal-coupled resonator type elastic wave filter.

[0026] As Figure 1 shown, the longitudinal-coupled resonator type elastic wave filter 1 has a plurality of IDT electrodes 2 to 6. The IDT electrodes 2 to 6 are arranged along an elastic wave propagation direction. Here, the elastic wave propagation direction is a direction orthogonal to an extension direction of electrode fingers of the IDT electrodes 2 to 6.

[0027] A first reflector 7 and a second reflector 8 are provided on both sides of the elastic wave propagation direction of a region where the IDT electrodes 2 to 6 are provided.

[0028] Thus, the longitudinal-coupled resonator type elastic wave filter 1 is a 5IDT type longitudinal-coupled resonator type elastic wave filter having five IDT electrodes 2 to 6.

[0029] The longitudinal-coupled resonator type elastic wave filter 1 is a reception filter of Band 20. Thus, a reception band is 791 MHz to 821 MHz.

[0030] An input terminal 9 is a portion connected to an antenna terminal. An output terminal 10 is a reception terminal, and outputs a received signal.

[0031] The IDT electrodes 2 to 6 each have a pair of comb electrodes 2a, 2b to 6a, 6b. Taking the IDT electrode 2 as an example, the comb electrode 2a has a plurality of first electrode fingers 2al. The comb electrode 2b has a plurality of second electrode fingers 2bl. The plurality of first electrode fingers 2al and the plurality of second electrode fingers 2bl are alternately inserted with each other. A direction orthogonal to an extension direction of the first electrode fingers 2al and the second electrode fingers 2bl is the above-described elastic wave propagation direction.

[0032] The comb electrodes 3a, 3b to 6a, 6b of the IDT electrodes 3 to 6 also have the same configuration as the comb electrodes 2a, 2b.

[0033] The first reflector 7 and the second reflector 8 have a configuration in which both ends of a plurality of electrode fingers are short-circuited. That is, the first reflector 7 and the second reflector 8 are grating type reflectors.

[0034] In the longitudinal-coupled resonator type elastic wave filter 1, the comb electrodes 2a of the IDT electrode 2, the comb electrodes 4a of the IDT electrode 4, and the comb electrodes 6a of the IDT electrode 6 are connected to the input terminal 9. That is, the comb electrodes 2a, 4a, 6a are connected to a signal side potential. On the other hand, the comb electrodes 2b, 4b, 6b are commonly connected and connected to a ground side potential. Therefore, the comb electrodes 2a, 4a, 6a are signal side comb electrodes in the IDT electrodes 2, 4, 6, and the comb electrodes 2b, 4b, 6b become ground side comb electrodes.

[0035] On the other hand, the comb electrodes 3b, 5b of the IDT electrodes 3, 5 are commonly connected and connected to the output terminal 10. The comb electrodes 3a, 5a are commonly connected and connected to a ground side potential. Therefore, in the IDT electrodes 3, 5, the comb electrodes 3b, 5b are signal side comb electrodes, and the comb electrodes 3a, 5a are ground side comb electrodes.

[0036] The longitudinal-coupled resonator type elastic wave filter 1 is characterized by the following 1) to 4). 1) The signal side comb electrodes 3b, 5b of the IDT electrodes 3, 5, which correspond to the first IDT electrodes, are connected to the first reflector 7 and the second reflector 8. 2) The IDT electrodes 2, 6, which correspond to the second IDT electrodes, are respectively arranged between the IDT electrodes 3, 5, which correspond to the first IDT electrodes, and the first reflector 7 and the second reflector 8. 3) The signal side comb electrodes 3b, 5b of the IDT electrodes 3, 5, which correspond to the first IDT electrodes, are connected to the output terminal 10. 4) The signal side comb electrodes 2a, 6a of the IDT electrodes 2, 6, which correspond to the second IDT electrodes, are connected to the input terminal 9. Thereby, the attenuation characteristic on the high frequency side of the passband is improved. These features become clear by showing the characteristics of the specific embodiment 1 and the comparative example 1.

[0037] Figure 3 is a circuit diagram showing a composite filter device 11 having the longitudinal-coupled resonator type elastic wave filter 1 of the first embodiment of the present application.

[0038] The composite filter device 11 has an antenna terminal 12. The antenna terminal 12 is connected to an antenna. A receiving filter 13 is connected between the antenna terminal 12 and the output terminal 10. A transmitting filter 15 is connected between the antenna terminal 12 and the transmitting terminal 14. The composite filter device 11 is a duplexer with a receiving filter 13 and a transmitting filter 15.

[0039] It should be noted that, in addition to the receiving filter 13 and the transmitting filter 15, one or more other bandpass filters can also be connected to the composite filter device 11. That is, the composite filter device 11 can also be a multiplexer or a tripod.

[0040] The receiving filter 13 has series arm resonators S1 and S2 connected in series with the longitudinally coupled resonator type elastic wave filter 1. Additionally, a parallel arm resonator P1 is connected between the connection point between the series arm resonators S1 and S2 and the ground potential. The receiving filter 13 is the elastic wave filter of the present invention. However, the elastic wave filter of the present invention is not limited to a receiving filter.

[0041] As Example 1, a longitudinally coupled resonator type elastic wave filter 1 of the first embodiment is constructed. For comparison, a longitudinally coupled resonator type elastic wave filter of Comparative Example 1 is constructed in the same manner as in Example 1, except that the first reflector 7 and the second reflector 8 are not electrically connected to the comb electrodes 3b and 5b on the signal side of the IDT electrodes 3 and 5, and the first reflector 7 and the second reflector 8 are set to a floating state.

[0042] Figure 4 The attenuation-frequency characteristics of the receiving filters of Embodiment 1 and Comparative Example 1, which include the longitudinally coupled resonator type elastic wave filter described in Embodiment 1 and Comparative Example 1 above, are shown. Figure 4 The solid line in the figure shows the attenuation-frequency characteristic of the receiving filter of Example 1, and the dashed line shows the attenuation-frequency characteristic of Comparative Example 1.

[0043] Depend on Figure 4 As can be seen, compared with Comparative Example 1, according to Example 1, a larger attenuation was achieved in the high-frequency range of 830MHz to 855MHz in the passband. Therefore, the attenuation characteristics in the high-frequency range of the passband were effectively improved. It should be noted that... Figure 4 In this context, frequency range A is the passband of the transmitting side of Band 20. Therefore, according to Embodiment 1, it can be seen that a receiving filter for Band 20 can be provided that sufficiently ensures the attenuation in the passband of the transmitting side of Band 20.

[0044] As described above, in Embodiment 1, the amount of attenuation on the high frequency side of the passband is improved, which is considered to be due to the increase in the capacitance generated between the input terminal 9 and the output terminal 10. Note that the capacitance here refers to the capacitance of the characteristic impedance generated by providing the wiring on the piezoelectric substrate, and the capacitance generated between adjacent multiple IDT electrodes.

[0045] In the present application, it is considered that the above-mentioned capacitance component is formed by connecting the wiring on the signal side of the first IDT electrodes, i.e., the IDT electrodes 3, 5 in the present embodiment, which are not adjacent to the first reflector 7 and the second reflector 8, to the first reflector 7 and the second reflector 8. Thereby, it is considered that the attenuation is close to the passband, and the amount of attenuation on the high frequency side of the passband near the passband is increased.

[0046] As described above, in the present application, by the above-mentioned electrical connection configuration, the above-mentioned capacitance component is utilized, and therefore, it is not necessary to additionally provide a capacitor for constituting a bridging capacitance on the piezoelectric substrate. Therefore, it does not lead to a large size and the attenuation characteristic on the high frequency side of the passband can be improved.

[0047] In the first embodiment, the comb electrodes 3b, 5b on the signal side of the IDT electrodes 3, 5 as the first IDT electrodes are commonly connected to the first reflector 7 and the second reflector 8, and connected to the output terminal 10. However, the present application is not limited to such a connection configuration. Hereinafter, the second to fifth embodiments will be described.

[0048] In the second to fifth embodiments, the IDT electrodes 3, 5 as the first IDT electrodes are commonly connected to the first reflector 7 and the second reflector 8, and connected to the output terminal 10. Figure 2 The circuit configuration is also shown in a schematic circuit diagram.

[0049] Figure 5 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of the second embodiment of the present application. In the longitudinal-coupled resonator type elastic wave filter 21 of the second embodiment, five IDT electrodes 2 to 6 are arranged in the elastic wave propagation direction. Further, the first reflector 7 and the second reflector 8 are arranged on both sides of the region where the IDT electrodes 2 to 6 are provided. In the longitudinal-coupled resonator type elastic wave filter 21, the IDT electrodes 2, 6 corresponding to the second IDT electrodes are arranged between the IDT electrodes 3, 5 corresponding to the first IDT electrodes and the first reflector 7 and the second reflector 8. The difference from the first embodiment is that the comb electrodes on the signal side of the IDT electrodes 3, 5 connected to the input terminal 9 are electrically connected to the first reflector 7 and the second reflector 8. That is, the comb electrodes on the signal side of the IDT electrodes 3, 5 are connected to the input terminal 9. The first reflector 7 and the second reflector 8 are also connected to this input terminal 9. The comb electrodes on the signal side of the IDT electrodes 2, 4, 6 are connected to the output terminal 10.

[0050] Thus, in this invention, the comb electrode on the signal side of the first IDT electrode can also be connected to the input terminal 9, and in this case, the comb electrode on the signal side of the second IDT electrode can be connected to the output terminal 10.

[0051] The other structures of the longitudinally coupled resonator type elastic wave filter 21 are the same as those of the longitudinally coupled resonator type elastic wave filter 1.

[0052] The receiving filter of Embodiment 2, which has the above-described longitudinally coupled resonator type elastic wave filter 21, is constructed in the same manner as Embodiment 1. However, in Embodiment 2, in the longitudinally coupled resonator type elastic wave filter 21, the electrode fingers of the IDT electrodes 2 and 6 adjacent to the first reflector 7 and the second reflector 8 are electrode fingers connected to the ground side potential.

[0053] In addition, as a comparative example 2, except that the first reflector 7 and the second reflector 8 of the longitudinally coupled resonator type elastic wave filter in the receiving filter of the above embodiment 2 are not electrically connected to the comb electrodes on the signal side of the IDT electrodes 3 and 5, the same receiving filter as in embodiment 2 is constructed.

[0054] Figure 6 This is a graph showing the attenuation-frequency characteristics of the receiving filters in Example 2 and Comparative Example 2. The solid line shows the results of Example 2, and the dashed line shows the results of Comparative Example 2.

[0055] exist Figure 6 In the diagram, frequency range A shows the passband of the transmit filter for Band 20.

[0056] Depend on Figure 6 As can be seen, in Example 2, compared with Comparative Example 2, the attenuation in the high-frequency passband, especially in the transmission band of Band 20, is also significantly increased. Therefore, as with Example 1, it is clear that this does not result in a larger size and can increase the attenuation in the high-frequency passband.

[0057] However, in relation to Figure 4 In comparison with Example 1, the improvement in attenuation on the high-frequency side of the passband is smaller in Example 2. This is believed to be because the polarity of the electrode fingers of the IDT electrodes 2 and 6 adjacent to the first reflector 7 and the second reflector 8 becomes the ground side potential, thus reducing the effect of bringing the attenuation electrode closer to the passband.

[0058] Figure 7 This is a schematic circuit diagram of a longitudinally coupled resonator type elastic wave filter according to the third embodiment of the present invention.

[0059] The longitudinal-coupled resonator type elastic wave filter 31 has three IDT electrodes 32 to 34. A first reflector 35 and a second reflector 36 are provided on both sides of a region where the IDT electrodes 32 to 34 are provided. In the present application, the number of the plurality of IDT electrodes in the longitudinal-coupled resonator type elastic wave filter is not particularly limited, and a longitudinal-coupled resonator type elastic wave filter of a 3IDT type can also be used.

[0060] Here, the IDT electrode 33 corresponds to a first IDT electrode, and the IDT electrode 32 corresponding to a second IDT electrode is provided between the IDT electrode 33 and the first reflector 35. In addition, the IDT electrode 34 corresponding to a second IDT electrode is provided between the IDT electrode 33 corresponding to a first IDT electrode and the second reflector 36.

[0061] The comb electrode of the IDT electrode 33 connected to the signal side of the output terminal 10 is connected to the first reflector 35 and the second reflector 36. Therefore, in the present embodiment, it is also possible to improve the attenuation amount on the high frequency side of the passband as in the first embodiment and the second embodiment.

[0062] Figure 8 is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of a fourth embodiment of the present application.

[0063] The longitudinal-coupled resonator type elastic wave filter 41 has three IDT electrodes 42 to 44, a first reflector 45, and a second reflector 46. Therefore, the longitudinal-coupled resonator type elastic wave filter 41 is a longitudinal-coupled resonator type elastic wave filter of a 3IDT type.

[0064] The IDT electrode 44 corresponding to a second IDT electrode is connected between the IDT electrode 43 corresponding to a first IDT electrode and the second reflector 46. Here, the comb electrode of the IDT electrode 43 connected to the output terminal 10, that is, the comb electrode on the signal side is connected to the second reflector 46.

[0065] Therefore, it is possible to improve the attenuation amount on the high frequency side of the passband as in the first embodiment to the third embodiment.

[0066] Note that the first reflector 45 is not connected to the IDT electrode 43 corresponding to a first IDT electrode. In this way, only one of the first reflector 45 and the second reflector 46 can be connected to the comb electrode on the signal side of the first IDT electrode.

[0067] That is, in the present application, it is sufficient that the comb electrode on the signal side of the first IDT electrode is connected to at least one of the first reflector and the second reflector. In this case, it is also possible to improve the attenuation amount on the high frequency side of the passband.

[0068] Figure 9is a schematic circuit diagram of a longitudinal-coupled resonator type elastic wave filter of a fifth embodiment of the present application.

[0069] The longitudinal-coupled resonator type elastic wave filter 51 has two IDT electrodes 52, 53. A first reflector 54 and a second reflector 55 are provided on both sides of a region where the IDT electrodes 52, 53 are provided. In this way, in the present application, the number of the plurality of IDT electrodes 52, 53 can also be an even number.

[0070] The second reflector 55 of the longitudinal-coupled resonator type elastic wave filter 51 is connected to the comb electrodes of the signal side of the IDT electrode 52 on the input terminal 9 side. Therefore, on the input terminal 9 side, the IDT electrode 52 corresponds to the first IDT electrode, and the IDT electrode 53 corresponds to the second IDT electrode. Therefore, it is possible to improve the attenuation amount on the high frequency side of the passband.

[0071] Further, on the output terminal 10 side, the comb electrodes of the signal side of the IDT electrode 53 are connected to the first reflector 54. In this case, on the output terminal 10 side, the IDT electrode 53 corresponds to the first IDT electrode, and the IDT electrode 52 corresponds to the second IDT electrode.

[0072] Therefore, by the above-described electrical connection configuration on the output terminal 10 side, it is possible to improve the attenuation amount on the high frequency side of the passband.

[0073] As described above, in the present application, the number of the plurality of IDT electrodes can be an odd number or an even number. In the case where there are m (m is an even number) IDT electrodes as in the present embodiment, the IDT electrode adjacent to the first reflector among the m IDT electrodes becomes the second IDT electrode, and the IDT electrode located on the side opposite to the first reflector from the second IDT electrode corresponds to the first IDT electrode.

[0074] Further, in the case where there are n (n is an odd number) IDT electrodes, in a configuration in which the n IDT electrodes are arranged from the first reflector side toward the second reflector side, the IDT electrode located at the even number from the first reflector side is the first IDT electrode, and the IDT electrode located at the odd number adjacent to the first reflector and the second reflector becomes the second IDT electrode.

[0075] Explanation of Reference Numerals

[0076] 1, 21, 31, 41, 51... longitudinal-coupled resonator type elastic wave filter;

[0077] 2, 3, 4, 5, 6... IDT electrode;

[0078] 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b... comb electrode;

[0079] 2a1, 2b1... first electrode finger, second electrode finger;

[0080] 7, 8... first reflector, second reflector;

[0081] 9... input terminal;

[0082] 10... output terminal;

[0083] 11... composite filter arrangement;

[0084] 12... antenna terminal;

[0085] 13... receive filter;

[0086] 14... transmit terminal;

[0087] 15... transmit filter;

[0088] 32, 33, 34... IDT electrode;

[0089] 35, 36... first reflector, second reflector;

[0090] 42, 43, 44... IDT electrode;

[0091] 45, 46... first reflector, second reflector;

[0092] 52, 53... IDT electrode;

[0093] 54, 55... first reflector, second reflector;

[0094] P1... parallel arm resonator;

[0095] S1, S2... series arm resonator.

Claims

1. A longitudinally coupled resonator type elastic wave filter, comprising: Multiple IDT electrodes, including a first IDT electrode and a second IDT electrode; and The first reflector and the second reflector are disposed on both sides of the elastic wave propagation direction of the plurality of IDT electrodes. The plurality of IDT electrodes each have a comb-shaped electrode on the signal side connected to the signal side potential and a comb-shaped electrode on the ground side connected to the ground side potential. The comb electrode on the signal side of the first IDT electrode is electrically connected to at least one of the first reflector and the second reflector. A second IDT electrode is disposed between the first IDT electrode and at least one of the first reflector and the second reflector connected to the comb electrode on the signal side of the first IDT electrode. The comb electrode on the signal side of the first IDT electrode is connected to one of the input terminal and the output terminal, and the comb electrode on the signal side of the second IDT electrode is connected to the other of the input terminal and the output terminal.

2. The longitudinally coupled resonator type elastic wave filter according to claim 1, wherein, The first IDT electrode is electrically connected to one of the first reflector and the second reflector.

3. The longitudinally coupled resonator type elastic wave filter according to claim 1, wherein, The first IDT electrode is electrically connected to both the first reflector and the second reflector.

4. The longitudinally coupled resonator type elastic wave filter according to any one of claims 1 to 3, wherein, The second IDT electrode is adjacent to at least one of the first reflector and the second reflector of the comb electrode on the signal side connected to the first IDT electrode. The electrode in the second IDT electrode that is adjacent to the first reflector or the second reflector is connected to the signal side potential.

5. The longitudinally coupled resonator type elastic wave filter according to any one of claims 1 to 3, wherein, The second IDT electrode is adjacent to at least one of the first reflector and the second reflector of the comb electrode on the signal side connected to the first IDT electrode. The electrode in the second IDT electrode that is adjacent to the first reflector or the second reflector is connected to the ground side potential.

6. The longitudinally coupled resonator type elastic wave filter according to any one of claims 1 to 3, wherein, The plurality of IDT electrodes includes n IDT electrodes, wherein the even-numbered IDT electrode located from the first reflector side is the first IDT electrode, and the odd-numbered IDT electrode adjacent to the first reflector and the second reflector is the second IDT electrode, where n is an odd number.

7. The longitudinally coupled resonator type elastic wave filter according to claim 6, wherein, The comb electrode on the signal side of the first IDT electrode is connected to the output terminal, and the comb electrode on the signal side of the second IDT electrode is connected to the input terminal.

8. The longitudinally coupled resonator type elastic wave filter according to claim 6, wherein, The comb electrode on the signal side of the first IDT electrode is connected to the input terminal, and the comb electrode on the signal side of the second IDT electrode is connected to the output terminal.

9. The longitudinally coupled resonator type elastic wave filter according to claim 7 or 8, wherein, The value of n is 5.

10. The longitudinally coupled resonator type elastic wave filter according to claim 7 or 8, wherein, The value of n is 3.

11. The longitudinally coupled resonator type elastic wave filter according to any one of claims 1 to 3, wherein, The plurality of IDT electrodes includes m IDT electrodes, wherein the IDT electrode adjacent to the first reflector among the m IDT electrodes is the second IDT electrode, and the IDT electrode located on the side of the second IDT electrode opposite to the first reflector is the first IDT electrode, wherein m is an even number.

12. The longitudinally coupled resonator type elastic wave filter according to claim 11, wherein, The value of m is 2. The first IDT electrode is connected to the first reflector and is adjacent to the second reflector. The second reflector is connected to the second IDT electrode.

13. An elastic wave filter, wherein, The elastic wave filter has a series arm connecting the input end and the output end. In the series arm, the longitudinally coupled resonator type elastic wave filter according to any one of claims 1 to 12 is connected in series with the series arm resonator. At least one parallel arm resonator is connected between the series arm and the ground potential.

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