Multiplexer

Abstract

To provide a multiplexer that suppresses damage to longitudinally coupled resonator type elastic wave filters without increasing their size. [Solution] The duplexer 10, which is a multiplexer, comprises a transmit filter 1A and a receive filter 1B that share a piezoelectric substrate. The resonators located closest to the common connection terminal 2 of both filters are a series arm resonator S5 and a first longitudinally coupled resonator type elastic wave filter 3, respectively. In each IDT electrode of the resonator, if the region where adjacent electrode fingers overlap in the direction orthogonal to the electrode fingers is defined as the crossing region, then the dimension along the electrode finger extension direction of the crossing region is the crossing width. In the transmit filter 1A, the product of the number of electrode fingers and the crossing width in the IDT electrode of the series arm resonator S5 is defined as C1, and in the receive filter 1B, the sum of the products of the number of electrode fingers and the crossing width in each of the multiple IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3 is defined as TC2.

Description

Technical Field

[0001] The present invention relates to a multiplexer including an elastic wave resonator.

[0002] Conventionally, multiplexers have been widely used as filters for mobile phones, etc. Patent Document 1 below discloses an example of a duplexer. In this duplexer, a transmission filter and a reception filter are commonly connected to an antenna terminal. The transmission filter is a ladder type filter. In the transmission filter, due to the circuit configuration, the series arm resonator is located closest to the antenna terminal side. The reception filter is a longitudinally coupled resonator filter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the duplexer described in Patent Document 1, the impedance characteristics in the passband of the transmission filter in the reception filter, as seen from the antenna terminal, are close to the short side. Therefore, signals may leak from the transmission filter to the reception filter. In this case, the signals flow into the longitudinally coupled resonator filter as the reception filter, that is, the longitudinally coupled resonator type elastic wave filter. Due to this, the longitudinally coupled resonator filter is likely to be damaged.

[0005] On the other hand, in the reception filter, when a series arm resonator is arranged closer to the antenna terminal side than the longitudinally coupled resonator type elastic wave filter, the impedance characteristics can be made closer to the open side. In this case, it is difficult for signals to leak from the transmission filter to the reception filter. However, since the series arm resonator is required, the multiplexer needs to be made larger.

[0006] The object of the present invention is to provide a multiplexer that can suppress damage to a longitudinally coupled resonator type elastic wave filter without increasing its size. [Means for solving the problem]

[0007] In one broad aspect of the multiplexer according to the present invention, a common connection terminal and a transmit filter and a receive filter commonly connected to the common connection terminal are provided, the transmit filter and the receive filter each have a resonator, the resonator of the transmit filter and the resonator of the receive filter share a piezoelectric substrate, the resonator of the transmit filter located closest to the common connection terminal in the circuit configuration is a series arm resonator, the resonator of the receive filter located closest to the common connection terminal in the circuit configuration is a longitudinally coupled resonator type elastic wave filter, the series arm resonator of the transmit filter has an IDT electrode including a plurality of electrode fingers, and the longitudinally coupled resonator type elastic wave filter of the receive filter has a plurality of electrode fingers each The vertically coupled resonator type elastic wave filter and the series arm resonator each have multiple IDT electrodes, and when the direction in which the multiple electrode fingers extend is defined as the electrode finger extension direction and the direction perpendicular to the electrode finger extension direction is defined as the electrode finger orthogonal direction, the region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction is the intersection region, and the dimension of the intersection region along the electrode finger extension direction is the intersection width, and in the transmitting filter, the product of the number of the multiple electrode fingers and the intersection width in the IDT electrode of the series arm resonator is C1, and in the receiving filter, the sum of the products of the number of the multiple electrode fingers and the intersection width in each of the multiple IDT electrodes of the vertically coupled resonator type elastic wave filter is TC2. <C1である。

[0008] In another broad aspect of the multiplexer according to the present invention, a common connection terminal is provided, and a transmit filter and a receive filter are commonly connected to the common connection terminal, the transmit filter and the receive filter each have a resonator, the resonator of the transmit filter and the resonator of the receive filter share a piezoelectric substrate, the resonator of the transmit filter located closest to the common connection terminal in the circuit configuration is a series arm resonator, the resonator of the receive filter located closest to the common connection terminal in the circuit configuration is a longitudinally coupled resonator type elastic wave filter, the series arm resonator of the transmit filter has an IDT electrode including a plurality of electrode fingers, the longitudinally coupled resonator type elastic wave filter of the receive filter has a plurality of IDT electrodes each including a plurality of electrode fingers, and the capacitance of the longitudinally coupled resonator type elastic wave filter in the receive filter is smaller than the capacitance of the series arm resonator in the transmit filter. [Effects of the Invention]

[0009] According to the multiplexer of the present invention, damage to longitudinally coupled resonator type elastic wave filters can be suppressed without increasing the size. [Brief explanation of the drawing]

[0010] [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 duplexer according to the first embodiment of the present invention. [Figure 3] This is a schematic plan view showing a first longitudinally coupled resonator type elastic wave filter and a second longitudinally coupled resonator type elastic wave filter of a receiving filter according to a first embodiment of the present invention. [Figure 4] This is a schematic plan view showing a series arm resonator of a transmitting filter in the first embodiment of the present invention. [Figure 5] This is the circuit diagram of the duplexer for the first comparative example. [Figure 6]This is a Smith chart showing the impedance characteristics of the transmit filter in the receive filter in the passband, as viewed from the common connection terminal, for the first comparative example. [Figure 7] The second comparative example is a Smith chart showing the impedance characteristics of the transmit filter in the receive filter in the passband, as viewed from the common connection terminal. [Figure 8] This is a Smith chart showing the impedance characteristics in the passband of the transmit filter in the receive filter, as viewed from a common connection terminal, according to the first embodiment of the present invention. [Figure 9] This is a schematic plan view of the duplexer in the first comparative example. [Figure 10] This figure shows the power consumption of the series arm resonator located closest to the common connection terminal in the circuit configuration of the transmitting filter, and the power consumption of the first longitudinally coupled resonator type elastic wave filter of the receiving filter, in the first embodiment of the present invention, the first comparative example, and the second comparative example. [Figure 11] This figure shows the attenuation frequency characteristics of the transmitting filter in the first embodiment, the first comparative example, and the second comparative example of the present invention. [Figure 12] This figure shows the attenuation frequency characteristics of the receiving filter in the first embodiment, the first comparative example, and the second comparative example of the present invention. [Figure 13] This is a schematic diagram of a multiplexer according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0011] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0012] It should be noted that the embodiments described herein are illustrative, and that partial substitution or combination of configurations is possible between different embodiments.

[0013] Figure 1 is a circuit diagram of a duplexer according to the first embodiment of the present invention.

[0014] The duplexer 10 is a multiplexer according to the first embodiment of the present invention. More specifically, the duplexer 10 includes a transmission filter 1A, a reception filter 1B, an inductor L1, and a common connection terminal 2. The common connection terminal 2 is an antenna terminal. The antenna terminal is a terminal connected to an antenna. Note that the common connection terminal 2 does not necessarily have to be an antenna terminal.

[0015] The transmission filter 1A and the reception filter 1B are commonly connected to the common connection terminal 2. The inductor L1 is connected between the common connection terminal 2 and the reference potential. However, the inductor L1 does not necessarily have to be provided.

[0016] The multiplexer according to the present invention is not limited to a duplexer. The multiplexer according to the present invention may have at least one filter device other than the transmission filter and the reception filter.

[0017] 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 Band12. Therefore, the passband of the transmission filter 1A is 699 MHz to 716 MHz as the transmission band of Band12. The passband of the reception filter 1B is 729 MHz to 746 MHz as the reception band of Band12. Note that the passbands of the transmission filter 1A and the reception filter 1B are not limited to the above values.

[0018] As shown in FIG. 1, the transmission filter 1A is a ladder-type filter. Specifically, the transmission filter 1A includes a plurality of series-arm resonators and a plurality of parallel-arm resonators, an inductor L2, and a first signal terminal 5A. The plurality of series-arm resonators and the plurality of parallel-arm resonators are both piezoelectric resonators.

[0019] The multiple series-arm resonators are specifically series-arm resonators S1, S2, S3, S4, and S5. In the circuit configuration, the series-arm resonators S1, S2, S3, S4, and S5 are arranged in this order from the first signal terminal 5A. An inductor L2 is connected between the first signal terminal 5A and series-arm resonator S1.

[0020] The multiple parallel arm resonators are specifically parallel arm resonators P1, P2, P3, and P4. Each parallel arm resonator is connected to a reference potential. More specifically, the duplexer 10 has multiple reference potential terminals 6. The reference potential terminals 6 are terminals connected to a reference potential. Each parallel arm resonator is connected to a reference potential via the reference potential terminals 6.

[0021] More specifically, a parallel arm resonator P1 is connected between the connection point between series arm resonators S1 and S2 and the reference potential terminal 6. A parallel arm resonator P2 is connected between the connection point between series arm resonators S2 and S3 and the reference potential terminal 6. A parallel arm resonator P3 is connected between the connection point between series arm resonators S3 and S4 and the reference potential terminal 6. A parallel arm resonator P4 is connected between the connection point between series arm resonators S4 and S5 and the reference potential terminal 6.

[0022] On the other hand, the receiving filter 1B has a first longitudinally coupled resonator type elastic wave filter 3, a second longitudinally coupled resonator type elastic wave filter 4, and a second signal terminal 5B. In terms of circuit configuration, the first longitudinally coupled resonator type elastic wave filter 3 and the second longitudinally coupled resonator type elastic wave filter 4 are arranged between the common connection terminal 2 and the second signal terminal 5B. Note that the circuit configurations of the transmitting filter 1A and the receiving filter 1B are not limited to those described above.

[0023] In the following, elastic wave resonators, series arm resonators, parallel arm resonators, and longitudinally coupled resonator type elastic wave filters may be collectively referred to as resonators.

[0024] Figure 2 is a schematic plan view of a duplexer according to the first embodiment. In Figure 2, each resonator is shown by a schematic diagram of a rectangle with two diagonals. This schematic diagram includes both the IDT (Interdigital Transducer) electrode and the reflector, which will be described later. The same applies to schematic plan views other than Figure 2.

[0025] The duplexer 10 has a piezoelectric substrate 7. The piezoelectric substrate 7 is a piezoelectric substrate. The piezoelectric substrate 7 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 7 may also be a laminated substrate including a piezoelectric layer.

[0026] A common connection terminal 2, a first signal terminal 5A, a second signal terminal 5B, and a plurality of reference potential terminals 6 are provided on the piezoelectric substrate 7. Each of the above terminals is configured as an electrode pad. However, each of the above terminals may also be configured as wiring.

[0027] In the duplexer 10, the resonator of the transmitting filter 1A and the resonator of the receiving filter 1B share the piezoelectric substrate 7. More specifically, the multiple resonators in the duplexer 10 are formed by providing multiple IDT electrodes on the same piezoelectric substrate 7. The configuration of the resonators is described in more detail below.

[0028] Figure 3 is a schematic plan view showing the first longitudinally coupled resonator type elastic wave filter and the second longitudinally coupled resonator type elastic wave filter of the receiving filter in the first embodiment.

[0029] The first longitudinally coupled resonator type elastic wave filter 3 has a piezoelectric substrate 7 and five IDT electrodes. Specifically, the five IDT electrodes in the first longitudinally coupled resonator type elastic wave filter 3 are IDT electrode 8A, IDT electrode 8B, IDT electrode 8C, IDT electrode 8D, and IDT electrode 8E. However, the number of IDT electrodes in the first longitudinally coupled resonator type elastic wave filter 3 is not limited to five. The first longitudinally coupled resonator type elastic wave filter 3 may have multiple IDT electrodes, such as three, seven, or nine.

[0030] The IDT electrode 8A of the first longitudinally coupled resonator type elastic wave filter 3 has a pair of busbars and a plurality of electrode fingers. The pair of busbars are specifically a first busbar 16 and a second busbar 17. The first busbar 16 and the second busbar 17 face each other. The plurality of electrode fingers are specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first busbar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second busbar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interlocked with each other.

[0031] In the IDT electrode 8A, the first busbar 16 and the multiple first electrode fingers 18 are connected to a reference potential. On the other hand, the second busbar 17 and the multiple second electrode fingers 19 are connected to a signal potential.

[0032] In the following, the first busbar 16 and the second busbar 17 may be collectively referred to simply as "busbars." The first electrode finger 18 and the second electrode finger 19 may be collectively referred to simply as "electrode finger." The direction in which multiple electrode fingers extend is defined as the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is defined as the electrode finger orthogonal direction.

[0033] The IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3, other than IDT electrode 8A, also have a pair of busbars and multiple electrode fingers, similar to IDT electrode 8A. The direction orthogonal to the electrode fingers of each IDT electrode in the first longitudinally coupled resonator type elastic wave filter 3 is the same. In each IDT electrode, one busbar is connected to the signal potential and the other busbar is connected to the reference potential.

[0034] 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. The multiple IDT electrodes in the first longitudinally coupled resonator type elastic wave filter 3 are aligned in the direction of elastic wave propagation. Specifically, the multiple IDT electrodes are arranged in the order of IDT electrode 8A, IDT electrode 8B, IDT electrode 8C, IDT electrode 8D, and IDT electrode 8E in the direction of elastic wave propagation.

[0035] In this embodiment, the first busbars and multiple first electrode fingers of IDT electrodes 8A, 8C, and 8E are connected to a reference potential. The second busbars and multiple second electrode fingers of IDT electrodes 8A, 8C, and 8E are connected to a signal potential. Specifically, these second busbars and multiple second electrode fingers are connected to an output potential.

[0036] The first busbars and multiple first electrode fingers of IDT electrodes 8B and 8D are connected to the signal potential. Specifically, these first busbars and multiple first electrode fingers are connected to the input potential. The second busbars and multiple second electrode fingers of IDT electrodes 8B and 8D are connected to the reference potential.

[0037] When the IDT electrode 8A is viewed from a direction perpendicular to the electrode fingers, the region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap is the intersection region F. This intersection region F is a region of the piezoelectric substrate 7 defined based on the configuration of the IDT electrode 8A. However, the intersection region F can also be said to be a region possessed by the IDT electrode 8A in order to show the configuration of the IDT electrode 8A. In the first longitudinally coupled resonator type elastic wave filter 3, each of the five IDT electrodes has an intersection region F. Hereafter, the dimension of the intersection region F along the electrode finger extension direction will be defined as the intersection width. The intersection widths of multiple intersection regions F in the first longitudinally coupled resonator type elastic wave filter 3 are the same.

[0038] The first longitudinally coupled resonator type elastic wave filter 3 has a pair of reflectors. Specifically, the pair of reflectors are reflector 9A and reflector 9B. More specifically, reflectors 9A and reflector 9B are provided on the piezoelectric substrate 7 so as to sandwich a plurality of IDT electrodes in the direction of elastic wave propagation and face each other. Reflector 9A has a pair of reflector busbars and a plurality of reflector electrode fingers 15. Specifically, the pair of reflector busbars are reflector busbar 13 and reflector busbar 14. Both ends of each reflector electrode finger 15 are short-circuited by reflector busbar 13 and reflector busbar 14. Reflector 9B is configured similarly to reflector 9A.

[0039] The second longitudinally coupled resonator type elastic wave filter 4 shares a piezoelectric substrate 7 with the first longitudinally coupled resonator type elastic wave filter 3. Similar to the first longitudinally coupled resonator type elastic wave filter 3, the second longitudinally coupled resonator type elastic wave filter 4 has five IDT electrodes and a pair of reflectors. Specifically, the five IDT electrodes in the second longitudinally coupled resonator type elastic wave filter 4 are IDT electrode 8F, IDT electrode 8G, IDT electrode 8H, IDT electrode 8I, and IDT electrode 8J. The pair of reflectors are specifically reflector 9C and reflector 9D. Note that the number of IDT electrodes in the second longitudinally coupled resonator type elastic wave filter 4 is not limited to five.

[0040] Each IDT electrode of the second longitudinally coupled resonator type elastic wave filter 4, like each IDT electrode of the first longitudinally coupled resonator type elastic wave filter 3, has a pair of busbars and multiple electrode fingers, and has an intersection region F. In reflectors 9C and 9D, both ends of multiple reflector electrode fingers are short-circuited by a pair of reflector busbars.

[0041] The first longitudinally coupled resonator type elastic wave filter 3 and the second longitudinally coupled resonator type elastic wave filter 4 each have a single-stage configuration. The first longitudinally coupled resonator type elastic wave filter 3 is connected to the second longitudinally coupled resonator type elastic wave filter 4. This constitutes a two-stage longitudinally coupled resonator type elastic wave filter. However, in this specification, a single-stage longitudinally coupled resonator type elastic wave filter is referred to as a single longitudinally coupled resonator type elastic wave filter. Therefore, in the present invention, the first longitudinally coupled resonator type elastic wave filter 3 and the second longitudinally coupled resonator type elastic wave filter 4 are separate resonators.

[0042] The receiving filter 1B may have a plurality of second longitudinally coupled resonator type elastic wave filters 4. In this case, the plurality of second longitudinally coupled resonator type elastic wave filters 4 may be connected to each other. When the receiving filter 1B has a first longitudinally coupled resonator type elastic wave filter 3 and at least one second longitudinally coupled resonator type elastic wave filter 4, the first longitudinally coupled resonator type elastic wave filter 3 is located closest to the common connection terminal 2 in the circuit configuration. However, the receiving filter 1B does not necessarily have to have a second longitudinally coupled resonator type elastic wave filter 4.

[0043] Figure 4 is a schematic plan view showing the series arm resonators of the transmitting filter in the first embodiment.

[0044] The series arm resonator S5 shares a piezoelectric substrate 7 with the resonator of the receiving filter 1B. The series arm resonator S5 has one IDT electrode 8 and a pair of reflectors. The pair of reflectors are specifically reflector 9E and reflector 9F.

[0045] The IDT electrode 8 of the series arm resonator S5 has a pair of busbars and multiple electrode fingers, and has an intersection region F, similar to each IDT electrode of the first longitudinally coupled resonator type elastic wave filter 3 shown in Figure 3. In the reflectors 9E and 9F of the series arm resonator S5, both ends of the multiple reflector electrode fingers are short-circuited by a pair of reflector busbars.

[0046] As shown in Figure 1, each of the multiple series arm resonators other than the series arm resonator S5, and the multiple parallel arm resonators, also has one IDT electrode and one pair of reflectors. In this embodiment, both the multiple series arm resonators and the multiple parallel arm resonators are elastic wave resonators.

[0047] In addition, the electrode finger extension direction, the electrode finger orthogonal direction, and the crossover width are similarly defined for each IDT electrode and each crossover region F in the first longitudinally coupled resonator type elastic wave filter 3, the second longitudinally coupled resonator type elastic wave filter 4, and the series arm resonator S5.

[0048] In the resonators of the transmitting filter 1A and the receiving filter 1B, each IDT electrode and each reflector may be made of a multilayer metal film, or they may be made of a single layer metal film.

[0049] In this embodiment, the series arm resonator S5 is the resonator located closest to the common connection terminal 2 in the circuit configuration of the transmitting filter 1A. The first longitudinally coupled resonator type elastic wave filter 3 is the resonator located closest to the common connection terminal 2 in the circuit configuration of the receiving filter 1B.

[0050] In the following, C1 is defined as the product of the number of electrode fingers and the crossover width at the IDT electrode 8 of the series-arm resonator S5 shown in Figure 4. Note that when the number of electrode fingers at the IDT electrode 8 of the series-arm resonator S5 is N1 and the crossover width in the crossover region F is A1, then C1 = N1 × A1.

[0051] On the other hand, for each of the plurality of IDT electrodes of the first vertically coupled resonator type elastic wave filter 3 shown in FIG. 3, let the value obtained by summing the product of the number of electrode fingers and the crossover width be TC2. In the present embodiment, in the plurality of IDT electrodes of the first vertically coupled resonator type elastic wave filter 3, the crossover widths are the same. Therefore, when the sum of the number of electrode fingers of the plurality of IDT electrodes of the first vertically coupled resonator type elastic wave filter 3 is N2 and the crossover width of each crossover region F in the first vertically coupled resonator type elastic wave filter 3 is A2, TC2 = N2 × A2.

[0052] The features of the present embodiment are as follows. 1) In the circuit configuration of the transmission filter 1A, the resonator located closest to the common connection terminal 2 side is the series arm resonator S5, and in the circuit configuration of the reception filter 1B, the resonator located closest to the common connection terminal 2 side is the first vertically coupled resonator type elastic wave filter 3. 2) TC2 < C1. As a result, without increasing the size of the duplexer 10, breakage of the first vertically coupled resonator type elastic wave filter 3 can be suppressed. This will be shown below by comparing the present embodiment with the first comparative example and the second comparative example.

[0053] The first comparative example is different from the first embodiment in that, as shown in FIG. 5, the reception filter 101B has a series arm resonator S101. The first comparative example is also different from the first embodiment in that the series arm resonator S101 is the resonator located closest to the common connection terminal 2 side in the circuit configuration of the reception filter 101B. Furthermore, the first comparative example is also different from the first embodiment in that TC2 > C1.

[0054] The second comparative example is different from the first embodiment in that TC2 > C1. Note that the circuit configuration of the second comparative example is the same as the circuit configuration of the first embodiment.

[0055] The design parameters of the first embodiment, the first comparative example, and the second comparative example were as shown in Tables 1 to 3. The reference numerals 8A to 8J and 9A to 9F described in Tables 1 to 3 correspond to the reference numerals of the IDT electrodes and reflectors used in this specification

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] As shown in Table 1, in the first embodiment, in the first longitudinally coupled resonator type elastic wave filter 3 of the receiving filter 1B, the crossover width A2 of each IDT electrode is 66 μm. The number of electrode fingers of the IDT electrode 8A is 26. Therefore, the product of the number of electrode fingers of the IDT electrode 8A and the crossover width A2 is 1716 [fingers·μm].

[0060] Similarly, the products of the number of electrode fingers and the crossover width A2 at IDT electrodes 8B, 8C, 8D, and 8E are 2706 [fibers·μm], 2970 [fibers·μm], 2574 [fibers·μm], and 1452 [fibers·μm], respectively. Therefore, the sum of the products of the number of electrode fingers and the crossover width A2 at each of the multiple IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3, TC2, is 11418 [fibers·μm].

[0061] Furthermore, when the design parameters shown in Table 1 are used, as described above, the crossover width A2 of all IDT electrodes is the same in the first longitudinally coupled resonator type elastic wave filter 3. In this case, TC2 can be expressed as TC2 = N2 × A2. That is, in the first embodiment, the above value TC2 can also be expressed as 173 [electrodes] × 66 [μm] = 11418 [electrodes·μm].

[0062] As shown in Table 3, in the first embodiment, the product C1 of the number of electrode fingers N1 and the crossover width A1 at the IDT electrode 8 of the series arm resonator S5 of the transmitting filter 1A is 181 [fingers] × 76 [μm] = 13756 [fingers·μm]. Therefore, in the first embodiment, TC2 <C1である。

[0063] On the other hand, as shown in Tables 1 and 3, in the first comparative example and the second comparative example, TC2 = 15224 [particles·μm] and C1 = 11946 [particles·μm]. Therefore, in the first comparative example and the second comparative example, TC2 > C1.

[0064] The impedance characteristics were compared in the first embodiment, the first comparative example, and the second comparative example. Specifically, these impedance characteristics are those in the passband of the transmitting filter in the receiving filter, as viewed from the common connection terminal. These impedance characteristics are shown using a Smith chart. In this Smith chart, the closer the impedance is to the short side, the easier it is for the signal to leak from the transmitting filter to the receiving filter. Conversely, the closer the impedance is to the open side, the less likely it is for the signal to leak from the transmitting filter to the receiving filter.

[0065] Figure 6 is a Smith chart showing the impedance characteristics in the passband of the transmit filter in the receive filter, as viewed from the common connection terminal, for the first comparative example. Figure 7 is a Smith chart showing the impedance characteristics in the passband of the transmit filter in the receive filter, as viewed from the common connection terminal, for the second comparative example. Figure 8 is a Smith chart showing the impedance characteristics in the passband of the transmit filter in the receive filter, as viewed from the common connection terminal, for the first embodiment.

[0066] As shown in Figure 6, in the first comparative example, the impedance is located on the open side compared to the second comparative example shown in Figure 7. Therefore, signal leakage from the transmitting filter 1A to the receiving filter 101B shown in Figure 5 is less likely. In the first comparative example, due to the circuit configuration of the receiving filter 101B, the series arm resonator S101 is the resonator located closest to the common connection terminal 2. As a result, the impedance is located on the open side.

[0067] On the other hand, as shown in Figure 7, in the second comparative example, the impedance is located on the short-circuit side compared to the first comparative example shown in Figure 6. Therefore, signal leakage from the transmitting filter to the receiving filter is more likely. In the second comparative example, the receiving filter does not have a series arm resonator. Therefore, the second comparative example does not achieve the same effect as the first comparative example.

[0068] Note that the circuit configuration of the second comparative example is the same as the circuit configuration of the first embodiment. Nevertheless, in the first embodiment shown in Figure 8, the impedance is located on the open side compared to the second comparative example shown in Figure 7. Therefore, signal leakage from the transmitting filter 1A to the receiving filter 1B shown in Figure 1 is less likely. Thus, when the duplexer 10 is operating, the power consumption of the first longitudinally coupled resonator type elastic wave filter 3 in the receiving filter 1B can be reduced. Consequently, the first longitudinally coupled resonator type elastic wave filter 3 is less likely to be damaged.

[0069] Figure 9 is a schematic plan view of the first comparative example duplexer.

[0070] As is clear from comparing Figure 9 and Figure 2, the area of ​​the piezoelectric substrate 107 in the first comparative example is larger than the area of ​​the piezoelectric substrate 7 in the first embodiment. This is because the number of resonators in the first comparative example is greater than the number of resonators in the first embodiment. Specifically, the series arm resonator S101 is not provided in the first embodiment, while the series arm resonator S101 is provided in the first comparative example.

[0071] Conventionally, as in the second comparative example, when the circuit configuration of the receiving filter did not include a series arm resonator on the common connection terminal side compared to the first longitudinally coupled resonator type elastic wave filter, the impedance was located on the short-circuit side, as shown in Figure 7. Therefore, in order to bring the impedance closer to the open-circuit side, it was necessary to include a series arm resonator S101 and increase the size of the duplexer, as shown in the first comparative example in Figure 9.

[0072] In contrast to these, in the first embodiment shown in Figure 2, damage to the first longitudinally coupled resonator type elastic wave filter 3 can be suppressed without increasing the size of the duplexer 10. Specifically, in the first comparative example related to this comparison, the area of ​​the piezoelectric substrate 107 shown in Figure 9 is 1 mm × 1.4 mm. On the other hand, in the first embodiment, the area of ​​the piezoelectric substrate 7 shown in Figure 2 is 1 mm × 1.3 mm. Therefore, in the first embodiment, the duplexer 10 can be made 7% smaller than in the first comparative example. The reason for obtaining the above effect will be explained below.

[0073] In an elastic wave resonator, capacitance is proportional to the product of the number of electrode fingers and the crossover width of the IDT electrode. On the other hand, the smaller the capacitance, the larger the impedance, for example, at frequencies lower than the resonant frequency. That is, in an elastic wave resonator, the smaller the product of the number of electrode fingers and the crossover width of the IDT electrode, the larger the impedance. A similar trend is observed in longitudinally coupled resonator elastic wave filters. Specifically, in a longitudinally coupled resonator elastic wave filter, the smaller the sum of the product of the number of electrode fingers and the crossover width of each of the multiple IDT electrodes, the larger the impedance, for example, at frequencies outside the band used as the passband.

[0074] In the first embodiment, TC2 < C1. That is, the value TC2 obtained by summing the products of the number of electrode fingers and the crossover width A2 for each of the plurality of IDT electrodes of the first vertically coupled resonator type elastic wave filter 3 is smaller than the product C1 of the number of electrode fingers N1 and the crossover width A1 of the IDT electrode 8 of the series arm resonator S5. Therefore, in the first embodiment, the value TC2 of the first vertically coupled resonator type elastic wave filter 3 is relatively small. Thus, in the first vertically coupled resonator type elastic wave filter 3, for example, the impedance is relatively large at frequencies outside the band used as the passband of the receiving filter 1B. More specifically, in the first vertically coupled resonator type elastic wave filter 3 of the receiving filter 1B, the impedance is relatively large in the passband of the transmitting filter 1A.

[0075] As a result, the impedance in the passband of the transmitting filter 1A in the receiving filter 1B as seen from the common connection terminal 2 in the duplexer 10 is located on the open side. Thereby, when the duplexer 10 operates, the power consumption of the first vertically coupled resonator type elastic wave filter 3 in the receiving filter 1B can be reduced.

[0076] As described above, even if the series arm resonator is not arranged closer to the common connection terminal 2 than the first vertically coupled resonator type elastic wave filter 3, the power consumption of the first vertically coupled resonator type elastic wave filter 3 can be reduced. Therefore, without increasing the size of the duplexer 10, it is possible to make the first vertically coupled resonator type elastic wave filter 3 less likely to be damaged.

[0077] In the first embodiment, the fact that the power consumption of the first vertically coupled resonator type elastic wave filter 3 can be reduced will be specifically shown below.

[0078] In the first embodiment, the first comparative example, and the second comparative example, the power consumption in the first vertically coupled resonator type elastic wave filter of the receiving filter was compared. In addition, in the first embodiment, the first comparative example, and the second comparative example, the power consumption of the series arm resonator located closest to the common connection terminal side in terms of the circuit configuration of the transmitting filter was compared.

[0079] In the circuit configuration of the transmitting filter, the series arm resonator located closest to the common connection terminal is the series arm resonator S5, as shown in Figures 1 and 5. Therefore, in the following, this series arm resonator may be simply referred to as the series arm resonator S5.

[0080] In this comparison, the power consumption of the first longitudinally coupled resonator type elastic wave filter 3 and the series arm resonator S5 was calculated by simulation. Specifically, this simulation was performed when power was applied to the first signal terminal 5A of the transmitting filter 1A at the highest frequency in the passband of the transmitting filter 1A.

[0081] Figure 10 shows the power consumption of the series arm resonator located closest to the common connection terminal in the circuit configuration of the transmitting filter, and the power consumption of the first longitudinally coupled resonator type elastic wave filter of the receiving filter, in the first embodiment, the first comparative example, and the second comparative example.

[0082] As described above, in the circuit configuration of the receiving filter, the first longitudinally coupled resonator type elastic wave filter 3 is the resonator located closest to the common connection terminal 2. In a comparison of duplexers with such circuit configurations, the power consumption of the first longitudinally coupled resonator type elastic wave filter 3 is lower in the first embodiment than in the second comparative example. Therefore, in the first embodiment, the first longitudinally coupled resonator type elastic wave filter 3 is less likely to be damaged.

[0083] Of the first embodiment, the first comparative example, and the second comparative example, the power consumption of the first longitudinally coupled resonator type elastic wave filter 3 in the first comparative example is the lowest. This is because, in the first comparative example, the series arm resonator S101 is located closer to the common connection terminal 2 than the first longitudinally coupled resonator type elastic wave filter 3 in the circuit configuration of the receiving filter 101B shown in Figure 5.

[0084] More specifically, in the first comparative example, even if a signal leaks from the transmitting filter 1A to the receiving filter 101B, the largest power is applied to the series arm resonator S101, which is located closest to the common connection terminal 2, due to the circuit configuration of the receiving filter 101B. Therefore, in the first comparative example, the power consumption of the first longitudinally coupled resonator type elastic wave filter 3 is reduced due to the circuit configuration. However, as mentioned above, the duplexer becomes larger in the first comparative example.

[0085] As shown in Figure 10, in the first embodiment, the power consumption of the series arm resonator S5 is lower than in the first comparative example. This is because in the first embodiment, the product C1 of the number of electrode fingers N1 and the crossover width A1 of the series arm resonator S5 is larger than in the first comparative example.

[0086] More specifically, in the series arm resonator S5, the larger the product C1, the larger the capacitance. In the series arm resonator S5, the larger the capacitance, the smaller the impedance, for example, at frequencies lower than the resonant frequency. That is, in the first embodiment, the impedance in the series arm resonator S5 is smaller than in the first comparative example, and therefore the power consumption of the series arm resonator S5 is smaller. Consequently, in the first embodiment, the series arm resonator S5 is less likely to be damaged.

[0087] In the first embodiment, both the transmitting filter 1A and the receiving filter 1B are less likely to be damaged. Therefore, in the first embodiment, the power withstand capability of the duplexer 10 can be increased compared to the first and second comparative examples.

[0088] In addition, in the first embodiment, the low impedance of the series arm resonator S5 allows for good impedance matching on the common connection terminal 2 side.

[0089] More specifically, in the first comparative example shown in Figure 5, the resonator located closest to the common connection terminal 2 in the circuit configuration of the receiving filter 101B is the series arm resonator S101. In this case, by increasing the impedance of the series arm resonator S5, which is located closest to the common connection terminal 2 in the circuit configuration of the transmitting filter 1A, impedance matching on the common connection terminal 2 side is improved. In contrast, in the first embodiment, the series arm resonator S101 is not provided. In this case, by decreasing the impedance of the series arm resonator S5, impedance matching on the common connection terminal 2 side is improved.

[0090] Therefore, in the first embodiment, both the effect of increasing the power withstand capability of the duplexer 10 and the effect of improving impedance matching on the common connection terminal 2 side can be obtained.

[0091] Furthermore, the attenuation frequency characteristics of the transmitting filter and the receiving filter were compared in the first embodiment, the first comparative example, and the second comparative example.

[0092] Figure 11 shows the attenuation frequency characteristics of the transmitting filter in the first embodiment, the first comparative example, and the second comparative example. Figure 12 shows the attenuation frequency characteristics of the receiving filter in the first embodiment, the first comparative example, and the second comparative example. In Figure 11, the double arrow W1 indicates the passband of the transmitting filter. In Figure 12, the double arrow W2 indicates the passband of the receiving filter.

[0093] As shown in Figure 11, the insertion loss of the transmit filter in the first embodiment is smaller than that of the transmit filter in the second comparative example. Specifically, in the first embodiment, the maximum absolute value of the insertion loss in the passband of the transmit filter is 1.28 dB. In the second comparative example, the maximum absolute value of the insertion loss in the passband of the transmit filter is 1.43 dB. Note that the insertion loss of the transmit filter is equivalent in the first embodiment and the first comparative example.

[0094] As shown in Figure 12, the insertion loss of the receiving filter in the first embodiment is smaller than that of the receiving filter in the first comparative example. Specifically, in the first embodiment, the maximum absolute value of the insertion loss in the passband of the receiving filter is 1.55 dB. In the first comparative example, the maximum absolute value of the insertion loss in the passband of the receiving filter is 1.75 dB. In the second comparative example, the maximum absolute value of the insertion loss in the passband of the receiving filter is 1.56 dB. Therefore, the insertion loss of the receiving filter is almost the same in the first embodiment and the second comparative example.

[0095] As described above, in the first embodiment, insertion loss can be reduced in both the transmit filter and the receive filter. This is for the following reasons.

[0096] In the first embodiment shown in Figure 1, as described above, signal leakage from the transmitting filter 1A to the receiving filter 1B can be suppressed. This reduces the insertion loss of the transmitting filter 1A.

[0097] Furthermore, in the first embodiment, the series arm resonator S101 shown in Figure 5 is not provided. This avoids the increase in insertion loss that would occur if the series arm resonator S101 were provided. In addition, in the first embodiment, the crossover width A2 of each IDT electrode in the first longitudinally coupled resonator type elastic wave filter 3 is narrower than in the first comparative example. As a result, the electrical resistance of each IDT electrode is lower in the first embodiment. Therefore, the insertion loss due to the first longitudinally coupled resonator type elastic wave filter 3 is small in the receiving filter 1B. Consequently, the insertion loss of the receiving filter 1B can be reduced in the first embodiment.

[0098] Incidentally, in the first embodiment, the relationship TC2 < C1 holds. That is, the value TC2 obtained by summing the products of the number of electrode fingers and the crossover width A2 in each of the plurality of IDT electrodes of the first vertically coupled resonator type elastic wave filter 3 is smaller than the product C1 of the number of electrode fingers N1 and the crossover width A1 in the IDT electrode 8 of the series arm resonator S5. This relationship can also be expressed as the relationship of the electrostatic capacitances in the first vertically coupled resonator type elastic wave filter 3 and the series arm resonator S5.

[0099] Specifically, in an elastic wave resonator such as the series arm resonator S5, the electrostatic capacitance is proportional to the product of the number of electrode fingers and the crossover width in the IDT electrode. In a vertically coupled resonator type elastic wave filter, the electrostatic capacitance is proportional to the value obtained by summing the products of the number of electrode fingers and the crossover width in each of the plurality of IDT electrodes. Therefore, in the first embodiment, the electrostatic capacitance of the first vertically coupled resonator type elastic wave filter 3 is smaller than the electrostatic capacitance of the series arm resonator S5. Thereby, without increasing the size of the duplexer 10, breakage of the first vertically coupled resonator type elastic wave filter 3 can be suppressed.

[0100] Incidentally, the electrostatic capacitance of the resonator is, more specifically, proportional to the duty ratio. That is, the electrostatic capacitance of the resonator is proportional to the value obtained by multiplying the product of the number of electrode fingers and the crossover width in the IDT electrode by the duty ratio. Here, the duty ratio is the ratio of the portion where the electrode fingers cover the piezoelectric substrate in the direction orthogonal to the electrode fingers. For example, the duty ratio in a certain region is the value obtained by dividing the sum of the dimensions along the direction orthogonal to the electrode fingers of the portion where the electrode fingers cover the piezoelectric substrate in the region by the dimension along the direction orthogonal to the electrode fingers of the region.

[0101] However, in the case of a surface acoustic wave filter, in many cases, within one IDT electrode, the duty ratio is generally the same in any region. Similarly, in many cases, between a plurality of IDT electrodes, the duty ratio is generally the same in any region. In this case, when comparing the capacitances between resonators, there is no need to consider the duty ratio. And in the first embodiment, between the series arm resonator S5 and the first vertically coupled resonator type surface acoustic wave filter 3, the duty ratio in any region of any IDT electrode is the same. As described above, since the relationship TC2 < C1 holds, the capacitance of the first vertically coupled resonator type surface acoustic wave filter 3 is smaller than the capacitance of the series arm resonator S5.

[0102] On the other hand, there may be cases where the duty ratio varies for each region within one IDT electrode or between a plurality of IDT electrodes. For example, when the duty ratios in a plurality of regions within one IDT electrode in a surface acoustic wave resonator are different from each other, it can be said that the capacitance of the surface acoustic wave resonator is the combined capacitance obtained by combining the capacitances of all regions. In this case, each of the plurality of regions is a surface acoustic wave resonator, and it may be treated as if a plurality of surface acoustic wave resonators are connected in parallel to each other. That is, the sum of the capacitances in all regions is the capacitance of the above-mentioned surface acoustic wave resonator. Even when the duty ratios in a plurality of regions of a plurality of IDT electrodes in a vertically coupled resonator type surface acoustic wave filter are different from each other, the sum of the capacitances in all regions is the capacitance of the vertically coupled resonator type surface acoustic wave filter.

[0103] In the following, the value obtained by multiplying the product of the number of electrode fingers and the crossover width by the duty cycle may be referred to as the reference value for comparison. When comparing the capacitances of resonators, if a reference value for comparison is used, it should be treated in the same way as capacitance. Specifically, if the duty cycles differ in multiple regions within a single IDT electrode in an elastic wave resonator, the sum of the reference values ​​for comparison in all regions should be treated as the reference value for comparison in that elastic wave resonator. If the duty cycles differ in multiple regions of multiple IDT electrodes in a longitudinally coupled resonator type elastic wave filter, the sum of the reference values ​​for comparison in all regions should be treated as the reference value for comparison in that longitudinally coupled resonator type elastic wave filter.

[0104] For example, let n be a natural number, and assume that the series arm resonator S5, which is an elastic wave resonator, has n regions. In this case, let a be a natural number between 1 and n, and let I1a be the number of electrode fingers in the a-th region of the IDT electrode of the series arm resonator S5, and let da be the duty cycle. In this example, assume that the crossover width of the series arm resonator S5 is A1 in all regions. If B1 is the reference value for comparison in the series arm resonator S5, then B1 can be expressed as B1 = Σ[(I1a × A1) × da] (1 ≤ a ≤ n).

[0105] The number of regions in the series-arm resonator S5 can be the total number of boundaries between regions with different duty cycles plus 1. In the first embodiment, when the duty cycle at the IDT electrode of the series-arm resonator S5 is constant, the number of regions is 1.

[0106] On the one hand, let m be a natural number, and assume that the first longitudinally coupled resonator type elastic wave filter 3 has m regions. In this case, let b be a natural number greater than or equal to 1 and less than or equal to m, and let the number of electrode fingers in the b-th region of the plurality of IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3 be I2b, and the duty ratio be db. In this example, assume that the crossover width of the first longitudinally coupled resonator type elastic wave resonator is A2 in any region. When the comparison reference value in the first longitudinally coupled resonator type elastic wave filter 3 is B2, it can be expressed as B2 = Σ[(I2b × A2) × db] (1 ≤ b ≤ m).

[0107] Note that the number of regions in the first longitudinally coupled resonator type elastic wave filter 3 may be the number obtained by adding 1 to the total number of boundaries of regions with different duty ratios. When the duty ratios in the plurality of IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3 are constant as in the first embodiment, the number of regions is 1.

[0108] When B2 < B1, the capacitance of the first longitudinally coupled resonator type elastic wave filter 3 is smaller than the capacitance of the series arm resonator S5. <着

[0109] Hereinafter, a preferred configuration in the first embodiment will be shown. This configuration can also be applied to the multiplexer according to the present invention other than the first embodiment.

[0110] First, as shown in FIG. 1, the series arm resonator S5 is a resonator located on the side of the most common connection terminal 2 in the circuit configuration of the transmission filter 1A. The first longitudinally coupled resonator type elastic wave filter 3 is a resonator located on the side of the most common connection terminal 2 in the circuit configuration of the reception filter 1B. And, as shown in FIG. 4, the number of a plurality of electrode fingers in the IDT electrode 8 of the series arm resonator S5 is N1. As shown in FIG. 3, the sum of the number of a plurality of electrode fingers in the plurality of IDT electrodes of the first longitudinally coupled resonator type elastic wave filter 3 is N2. When comparing the number N1 and the sum N2 of the number, it is preferable that N2 < N1. Thereby, the power resistance of the transmission filter 1A can be increased, and the insertion loss of the reception filter 1B can be reduced.

[0111] More specifically, since the number N1 of a plurality of electrode fingers in the IDT electrode 8 of the series arm resonator S5 is large, the electrical resistance of the IDT electrode 8 can be reduced. As a result, the power consumption of the series arm resonator S5 can be reduced. Therefore, the power resistance of the series arm resonator S5 can be increased, and the power resistance of the transmission filter 1A can be increased.

[0112] On the other hand, the total number N2 of a plurality of electrode fingers in the plurality of IDT electrodes of the first vertically coupled resonator type surface acoustic wave filter 3 is small. Here, the capacitance of the first vertically coupled resonator type surface acoustic wave filter 3 is proportional to the product TC2 of the total number N2 and the crossover width A2. Therefore, in the first vertically coupled resonator type surface acoustic wave filter 3, when setting a desired capacitance, the product TC2 of the total number N-2 and the crossover width A2 is adjusted to a desired value. At this time, when the total number N2 is small, the crossover width A2 can be widened. Thereby, in the first vertically coupled resonator type surface acoustic wave filter 3, leakage in the electrode finger extending direction of the surface acoustic wave can be suppressed. Therefore, the insertion loss of the receiving filter 1B can be reduced.

[0113] When the wavelength defined by the electrode finger pitch is λ, it is preferable that the crossover width A2 in the plurality of IDT electrodes of the first vertically coupled resonator type surface acoustic wave filter 3 is 10λ or more. Thereby, leakage in the electrode finger extending direction of the surface acoustic wave can be more reliably suppressed. The electrode finger pitch is the center-to-center distance in the direction orthogonal to the electrode fingers between adjacent electrode fingers. In the first embodiment related to the comparison shown in FIG. 10 and the like, the crossover width A2 is 12.8λ.

[0114] On the other hand, when the crossover width A2 in each IDT electrode of the first vertically coupled resonator type surface acoustic wave filter 3 is too wide, the electrical resistance of each IDT electrode becomes high. However, in the first embodiment, since TC2 < C1, the product TC2 of the total number N2 of a plurality of electrode fingers and the crossover width A2 in the plurality of IDT electrodes of the first vertically coupled resonator type surface acoustic wave filter 3 is small. Therefore, the crossover width A2 can be set to a suitable value.

[0115] In the receiving filter 1B, as shown in Figure 3, the IDT electrodes connected to the input potential in the first longitudinally coupled resonator type elastic wave filter 3 are IDT electrode 8B and IDT electrode 8D. The IDT electrodes connected to the output potential are IDT electrode 8A, IDT electrode 8C, and IDT electrode 8E. Thus, in the first longitudinally coupled resonator type elastic wave filter 3, it is preferable that the number of IDT electrodes connected to the input potential is less than the number of IDT electrodes connected to the output potential. This makes it possible to reduce the insertion loss of the transmitting filter 1A.

[0116] More specifically, in the first embodiment, the impedance in the passband of the transmit filter 1A in the receive filter 1B, as seen from the common connection terminal 2 in the duplexer 10, is located on the open side, as shown in Figure 8. This makes it difficult for signals to leak from the transmit filter 1A to the receive filter 1B. Here, in the circuit configuration of the receive filter 1B, the resonator located closest to the common connection terminal 2 is the first longitudinally coupled resonator type elastic wave filter 3. Therefore, in order to position the above impedance on the open side in the receive filter 1B, the impedance on the common connection terminal 2 side of the first longitudinally coupled resonator type elastic wave filter 3 should be increased.

[0117] In the first longitudinally coupled resonator type elastic wave filter 3, the impedance on the common connection terminal 2 side is greater the fewer the number of IDT electrodes connected to the common connection terminal 2 side. In the first longitudinally coupled resonator type elastic wave filter 3 included in the receiving filter 1B, the part connected to the common connection terminal 2 side is the part connected to the input potential, and the part connected to the second signal terminal 5B side is the part connected to the output potential. Therefore, in the first longitudinally coupled resonator type elastic wave filter 3, the smaller the number of IDT electrodes connected to the input potential, the greater the impedance on the common connection terminal 2 side of the first longitudinally coupled resonator type elastic wave filter 3.

[0118] In the first embodiment, in the first longitudinally coupled resonator type elastic wave filter 3, the number of IDT electrodes connected to the input potential is less than the number of IDT electrodes connected to the output potential. This makes it possible to increase the impedance on the common connection terminal 2 side of the first longitudinally coupled resonator type elastic wave filter 3. As a result, in the impedance characteristics shown in Figure 8, the impedance can be positioned on the open side, making it difficult for signals to leak from the transmitting filter 1A to the receiving filter 1B. Therefore, the insertion loss of the transmitting filter 1A can be reduced.

[0119] As shown in Figure 2, a common connection wiring 12 connected to a common connection terminal 2 is provided on the piezoelectric substrate 7. The series arm resonator S5 of the transmitting filter 1A and the first longitudinally coupled resonator type elastic wave filter 3 of the receiving filter 1B are commonly connected to the common connection wiring 12. Note that the common connection wiring 12 is not necessarily provided. The series arm resonator S5 and the first longitudinally coupled resonator type elastic wave filter 3 may be connected to the common connection terminal 2 by individual wiring.

[0120] However, as shown in Figure 2, it is preferable that the series arm resonator S5 and the first longitudinally coupled resonator type elastic wave filter 3 face each other across the common connection wiring 12 in the direction of electrode finger extension of the series arm resonator S5. This makes it possible to reduce the insertion loss of the transmitting filter 1A.

[0121] More specifically, in the above configuration, the common connection wiring 12 electrically connects the portion of the series arm resonator S5 of the transmitting filter 1A on the common connection terminal 2 side and the portion of the first longitudinally coupled resonator type elastic wave filter 3 of the receiving filter 1B on the common connection terminal 2 side. The common connection wiring 12 is connected to the common connection terminal 2. The common connection terminal 2 is the terminal to which the series arm resonator S5 and the first longitudinally coupled resonator type elastic wave filter 3 are commonly connected. Therefore, the common connection wiring 12 can be said to be electrically part of the common connection terminal 2. Thus, the above configuration corresponds to a configuration in which the length of the wiring connecting the first longitudinally coupled resonator type elastic wave filter 3 and the common connection terminal 2 is very short.

[0122] The shorter the length of the wiring, the smaller the inductance component in the wiring. Therefore, the inductance component is small between the first longitudinally coupled resonator type elastic wave filter 3 and the common connection terminal 2.

[0123] In the Smith chart shown in Figure 8, when the inductance component is large, the impedance is located far enough along the equiresistance lines that it travels counterclockwise. The equiresistance lines refer to the circles in the Smith chart shown in Figure 8. When the inductance component is large, the impedance is located on the short-circuit side in the impedance characteristics shown in Figure 8.

[0124] In contrast, in the configuration shown in Figure 2, the inductance component is small between the first longitudinally coupled resonator elastic wave filter 3 and the common connection terminal 2. Therefore, in this configuration, the impedance characteristic in the passband of the transmitting filter 1A in the receiving filter 1B, as seen from the common connection terminal 2, can be positioned on the open side. This makes it difficult for signals to leak from the transmitting filter 1A to the receiving filter 1B. Consequently, the insertion loss of the transmitting filter 1A can be reduced.

[0125] The receiving filter 1B has the second longitudinally coupled resonator type elastic wave filter 4, and it is preferable that the crossover width A2 in the first longitudinally coupled resonator type elastic wave filter 3 is narrower than the crossover width in the second longitudinally coupled resonator type elastic wave filter 4. Thereby, the insertion loss of the receiving filter 1B can be reduced.

[0126] More specifically, as described above, in the first embodiment, since TC2 < C1, the capacitance of the first longitudinally coupled resonator type elastic wave filter 3 is small. In this case, in the impedance characteristics in the passband of the receiving filter 1B shown by the Smith chart, the impedance is located higher than 50Ω. In other words, in the Smith chart, the impedance is located on the right side of the center.

[0127] However, in the first embodiment, the receiving filter 1B has the second longitudinally coupled resonator type elastic wave filter 4. In addition, the crossover width A2 in the first longitudinally coupled resonator type elastic wave filter 3 is narrower than the crossover width in the second longitudinally coupled resonator type elastic wave filter 4. Thereby, the deviation of the impedance in the passband of the receiving filter 1B from the center in the Smith chart can be corrected. Specifically, in the Smith chart, the impedance can be located near 50Ω. Thereby, the insertion loss of the receiving filter 1B can be reduced.

[0128] FIG. 13 is a schematic diagram of the multiplexer according to the second embodiment.

[0129] The multiplexer 20 of this embodiment has a common connection terminal 2 and three or more filter devices. Specifically, the multiplexer 20 has a transmission filter 1A, a receiving filter 1B, a filter device 21C, and at least one other filter device. The transmission filter 1A, the receiving filter 1B, the filter device 21C, and the other filter devices are commonly connected to the common connection terminal 2.

[0130] The transmit filter 1A and the receive filter 1B are the same receive filter and transmit filter as in the first embodiment. The filter device 21C may be, for example, a receive filter or a transmit filter. The same applies to filter devices other than the transmit filter 1A, the receive filter 1B, and the filter device 21C.

[0131] In the multiplexer 20 of this embodiment, as in the first embodiment, damage to the first longitudinally coupled resonator type elastic wave filter 3 in the receiving filter 1B can be suppressed without increasing its size. In addition, the insertion loss of the transmitting filter 1A and the receiving filter 1B can be reduced. [Explanation of symbols]

[0132] 1A...Transmit Filter 1B...Receiver filter 2… Common connection terminal 3,4…First and second longitudinally coupled resonator type elastic wave filters 5A, 5B…1st and 2nd signal terminals 6…Reference potential terminal 7. Piezoelectric substrate 8,8A~8J…IDT electrode 9A~9F…Reflector 10… Duplexa 12…Common connection wiring 13, 14… Reflector busbars 15...Reflector electrode finger 16, 17… 1st and 2nd bus bars 18, 19… First and second electrode fingers 20…Multiplexer 21C...Filter device 101B...Receiver filter 107... Piezoelectric substrate F...Cross area L1, L2…Inductors P1~P4... Parallel arm resonators S1~S5, S101...Series arm resonator

Claims

1. Common connection terminal and The transmit filter and receive filter are commonly connected to the aforementioned common connection terminal, Equipped with, The transmitting filter and the receiving filter each have a resonator, and the resonator of the transmitting filter and the resonator of the receiving filter share a piezoelectric substrate. In the circuit configuration of the aforementioned transmitting filter, the resonator located closest to the common connection terminal is a series arm resonator. In the circuit configuration of the receiving filter, the resonator located closest to the common connection terminal is a longitudinally coupled resonator type elastic wave filter. The series arm resonator of the transmitting filter has an IDT electrode including a plurality of electrode fingers, and the longitudinally coupled resonator type elastic wave filter of the receiving filter has a plurality of IDT electrodes, each including a plurality of electrode fingers. In the IDT electrodes of the longitudinally coupled resonator type elastic wave filter and the series arm resonator, when the direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction and the direction perpendicular to the electrode finger extension direction is defined as the electrode finger orthogonal direction, the region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction is the intersection region, and the dimension of the intersection region along the electrode finger extension direction is the intersection width. A multiplexer in which, in the transmitting filter, C1 is the product of the number of electrode fingers and the crossover width at the IDT electrode of the series arm resonator, and in the receiving filter, TC2 is the sum of the products of the number of electrode fingers and the crossover width at each of the multiple IDT electrodes of the longitudinally coupled resonator type elastic wave filter, such that TC2 < C1.

2. Common connection terminal and The transmit filter and receive filter are commonly connected to the aforementioned common connection terminal, Equipped with, The transmitting filter and the receiving filter each have a resonator, and the resonator of the transmitting filter and the resonator of the receiving filter share a piezoelectric substrate. In the circuit configuration of the aforementioned transmitting filter, the resonator located closest to the common connection terminal is a series arm resonator. In the circuit configuration of the receiving filter, the resonator located closest to the common connection terminal is a longitudinally coupled resonator type elastic wave filter. The series arm resonator of the transmitting filter has an IDT electrode including a plurality of electrode fingers, and the longitudinally coupled resonator type elastic wave filter of the receiving filter has a plurality of IDT electrodes, each including a plurality of electrode fingers. A multiplexer in which the capacitance of the longitudinally coupled resonator type elastic wave filter in the receiving filter is smaller than the capacitance of the series arm resonator in the transmitting filter.

3. The multiplexer according to claim 1 or 2, wherein in the transmitting filter, N1 is the number of electrode fingers of the IDT electrode of the series arm resonator, and in the receiving filter, N2 is the total number of electrode fingers of the IDT electrode of the longitudinally coupled resonator type elastic wave filter, and N2 < N1.

4. The receiving filter, in the longitudinally coupled resonator type elastic wave filter, the plurality of IDT electrodes include an IDT electrode connected to an input potential and an IDT electrode connected to an output potential, wherein the number of IDT electrodes connected to an input potential is less than the number of IDT electrodes connected to an output potential, according to any one of claims 1 to 3.

5. The piezoelectric substrate is provided with a common connection wiring that connects the series arm resonator of the transmitting filter and the longitudinally coupled resonator type elastic wave filter of the receiving filter, In the IDT electrode of the series arm resonator, when the direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction, the series arm resonator and the longitudinally coupled resonator type elastic wave filter face each other with the common connection wiring in between, The multiplexer according to any one of claims 1 to 4, wherein the common connection wiring is connected to the common connection terminal.

6. The receiving filter's longitudinally coupled resonator type elastic wave filter is a first longitudinally coupled resonator type elastic wave filter, and the receiving filter further comprises at least one second longitudinally coupled resonator type elastic wave filter other than the first longitudinally coupled resonator type elastic wave filter, the second longitudinally coupled resonator type elastic wave filter having a plurality of IDT electrodes, each including a plurality of electrode fingers. In each of the IDT electrodes of the first longitudinally coupled resonator type elastic wave filter and the second longitudinally coupled resonator type elastic wave filter, when the direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction and the direction perpendicular to the electrode finger extension direction is defined as the electrode finger orthogonal direction, the region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction is the intersection region, and the dimension of the intersection region along the electrode finger extension direction is the intersection width. The multiplexer according to any one of claims 1 to 5, wherein the crossover width in the first longitudinally coupled resonator type elastic wave filter is narrower than the crossover width in the second longitudinally coupled resonator type elastic wave filter.

7. The multiplexer according to any one of claims 1 to 6, further comprising at least one filter device that is commonly connected to the common connection terminal with the transmit filter and the receive filter.

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