Multiplexer and radio frequency (RF) front-end module

Abstract

Multiplexer (1A), comprising - a common connection (15), - a first connection (16), - a second connection (17), - a first filter (11) arranged on a channel connecting the common terminal (15) and the first terminal (16), and - a second filter (12) arranged on a channel connecting the common terminal (15) and the second terminal (17), the second filter (12) having higher passband frequencies than the first filter (11), wherein: - the second filter (12) comprises an elastic wave filter including a plurality of interdigital transducers (IDTs) (211, 212, 213, 214, 215) arranged along a propagation direction of elastic waves, - each of the plurality of IDTs (211, 212, 213, 214, 215) includes a pair of IDT electrodes (211a, 211b, 212a, 212b, 213a, 213b, 214a, 214b, 215a, 215b) facing each other, - among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b) included in the plurality of IDTs (211, 212, 213, 214, 215), first IDT electrodes (212b, 214b) are connected to the common terminal side of the common terminal (15) and the second terminal (17), and second IDT electrodes (211b, 213b, 215b) are connected to the second terminal side of the common terminal (15) and the second terminal (17), - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) are each formed on a surface of a piezoelectric substrate (326), and each has a plurality of electrode fingers (222b) arranged side by side in the propagation direction of elastic waves, - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) have different main center distances of the electrode fingers, and - at least one of the second IDT electrodes (211b, 213b, 215b) has a maximum main center-to-center distance of the electrode fingers among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b).

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a multiplexer containing a plurality of filters and a radio frequency (RF) front-end module containing the multiplexer. BACKGROUND OF THE INVENTION

[0002] For several years, mobile phones have been required to be able to handle multiple frequency bands and multiple wireless systems, i.e., multi-band and multi-mode. For this purpose, a multiplexer that divides a radio frequency (RF) signal into multiple wireless carrier frequencies is placed directly below a single antenna. One of several bandpass filters used in the multiplexer is an elastic wave filter with a low-loss characteristic within the passband and a steep passband characteristic around the passband.

[0003] For example, a filter containing a longitudinally coupled elastic wave filter with five interdigital transducers (IDTs), as disclosed in WO 2013 / 069225 A1, can be used as an elastic wave filter. In this elastic wave filter, the five IDTs are arranged along a propagation direction of elastic waves on a piezoelectric substrate.

[0004] In the elastic wave filter disclosed in WO 2013 / 069225 A1, among the five IDTs, a first IDT electrode, a third IDT electrode, and a fifth IDT electrode are commonly connected to an input-side terminal (unbalanced terminal), and a second IDT electrode and a fourth IDT electrode are connected to another output-side terminal (balanced terminal). In an embodiment according to WO 2013 / 069225 A1, the center-to-center pitch of electrode fingers of the first and fifth IDT electrodes is about 1.0582 µm, the center-to-center pitch of electrode fingers of the second and fourth IDT electrodes is about 1.0569 µm, and the center-to-center pitch of electrode fingers of the third IDT electrode is about 1.0612 µm. Therefore, an IDT electrode having the maximum electrode finger center-to-center distance (the third IDT electrode in the aforementioned embodiment of WO 2013 / 069225 A1) is connected to the input-side terminal.

[0005] To process multibands as described above, a multiplexer containing multiple filters is used. However, it has been found that if an elastic wave filter with the electrode finger pitches described above is used as one of the multiplexer's filters, the passband characteristics of another filter in the same multiplexer may degrade.

[0006] A multimode elastic wave device according to US 2014 / 0049341 A1 comprises first to fifth IDT electrodes between a pair of reflectors, wherein both the average of the electrode finger pitches in the first IDT electrode and the average of the electrode finger pitches in the fifth IDT electrode are smaller than both the average of the electrode finger pitches in the second IDT electrode and the average of the electrode finger pitches in the fourth IDT electrode. SUMMARY OF THE INVENTION

[0007] The invention is based on the object of suppressing the deterioration of the passband characteristics of another filter of the same multiplexer in cases where an elastic wave filter is used in a multiplexer.

[0008] According to embodiments of the present invention, a multiplexer includes: a common terminal, a first terminal, a second terminal, a first filter arranged on a channel connecting the common terminal and the first terminal, and a second filter arranged on a channel connecting the common terminal and the second terminal, wherein the second filter has higher passband frequencies than the first filter. The second filter is an elastic wave filter and includes a plurality of interdigital transducers (IDTs) arranged along a propagation direction of elastic waves. Each of the plurality of IDTs includes a pair of IDT electrodes facing each other.Among the plurality of IDT electrodes included in the plurality of IDTs, first IDT electrodes are connected to the common terminal side of the common terminal and the second terminal, and second IDT electrodes are connected to the second terminal side of the common terminal and the second terminal. The first IDT electrodes and the second IDT electrodes are each formed on a surface of a piezoelectric substrate, and each has a plurality of electrode fingers arranged side by side in the elastic wave propagation direction. The first IDT electrodes and the second IDT electrodes have different main pitches of the electrode fingers. At least one of the second IDT electrodes among the plurality of IDT electrodes has a maximum main pitch of the electrode fingers.

[0009] By allowing at least one of the second IDT electrodes to have the maximum electrode finger center-to-center pitch, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the frequency passband of the first filter can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0010] At least one of the first IDT electrodes among the plurality of IDT electrodes may have a minimum main center-to-center distance of the electrode fingers.

[0011] By allowing at least one of the first IDT electrodes to have the minimum electrode finger pitch as described above, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the passband of the first filter can be shifted to a higher-frequency side of the passband of the first filter, which lies within the lower-frequency side stopband of the second filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0012] According to embodiments of the present invention, a multiplexer includes a common terminal, a first terminal, a second terminal, a first filter arranged on a channel connecting the common terminal and the first terminal, and a second filter arranged on a channel connecting the common terminal and the second terminal, the second filter having higher passband frequencies than the first filter. The second filter is an elastic wave filter and includes a plurality of interdigital transducers (IDTs) arranged along a propagation direction of elastic waves. Each of the plurality of IDTs includes a pair of IDT electrodes facing each other.Among the plurality of IDT electrodes included in the plurality of IDTs, first IDT electrodes are connected to the common terminal side of the common terminal and the second terminal, and second IDT electrodes are connected to the second terminal side of the common terminal and the second terminal. The first IDT electrodes and the second IDT electrodes are each formed on a surface of a piezoelectric substrate, and each has a plurality of electrode fingers arranged side by side in the elastic wave propagation direction. The first IDT electrodes and the second IDT electrodes have different main pitches of the electrode fingers. A total average of pitches of the electrode fingers included in the first IDT electrodes is less than a total average of pitches of the electrode fingers included in the second IDT electrodes.

[0013] By setting the overall average pitch of the electrode fingers included in the first IDT electrodes smaller than the overall average pitch of the electrode fingers included in the second IDT electrodes, the position of an unnecessary wave that causes a large return loss of the second filter and appears in the frequency passband of the first filter can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0014] According to embodiments of the present invention, a multiplexer includes: a common terminal, a first terminal, a second terminal, a first filter arranged on a channel connecting the common terminal and the first terminal, and a second filter arranged on a channel connecting the common terminal and the second terminal, wherein the second filter has higher passband frequencies than the first filter. The second filter is an elastic wave filter and includes a plurality of interdigital transducers (IDTs) arranged along a propagation direction of elastic waves. Each of the plurality of IDTs includes a pair of IDT electrodes facing each other.Among the plurality of IDT electrodes included in the plurality of IDTs, first IDT electrodes are connected to the common terminal side of the common terminal and the second terminal, and second IDT electrodes are connected to the second terminal side of the common terminal and the second terminal. The first IDT electrodes and the second IDT electrodes are each formed on a surface of a piezoelectric substrate, and each has a plurality of electrode fingers arranged side by side in the elastic wave propagation direction. The first IDT electrodes and the second IDT electrodes have different main center-to-center pitches of the electrode fingers. When an average of center-to-center pitches of the electrode fingers of each of the IDT electrodes is obtained, an IDT electrode having a maximum average is one of the second IDT electrodes.

[0015] By obtaining the average of the center-to-center pitches of the electrode fingers of each of the IDT electrodes by configuring an IDT electrode having the maximum average pitch as one of the second IDT electrodes, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the frequency passband of the first filter can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0016] When the average of the center-to-center distances of the electrode fingers of each of the IDT electrodes is obtained, an IDT electrode having a minimum average may be one of the first IDT electrodes.

[0017] By configuring an IDT electrode having the minimum average as one of the first IDT electrodes, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the passband of the first filter can be shifted to a higher-frequency side of the passband of the first filter, which is within the lower-frequency side stopband of the second filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0018] A circuit element different from the second filter may be connected between the first IDT electrodes and the common terminal.

[0019] Even if a circuit element other than the second filter is connected between the first IDT electrodes and the common terminal, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the frequency passband of the first filter can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0020] The second filter may include an odd number of three or more IDTs, and the number of first IDT electrodes may be smaller than the number of second IDT electrodes.

[0021] According to the present invention, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the passband of the first filter can be easily shifted to a higher frequency side. When an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0022] The second filter can contain five or more IDTs.

[0023] According to the invention, the frequency passband of both the first filter and the second filter can be widened.

[0024] The first filter and the second filter can both be receive filters.

[0025] According to the present invention, it is possible to provide a multiplexer including a plurality of reception filters which, when an elastic wave filter is used, can suppress the deterioration of passband characteristics of another filter in the same multiplexer.

[0026] If the first filter is connected to the common terminal, the second filter can be connected to the common terminal.

[0027] According to the present invention, even if an unnecessary wave that causes a large return loss of the second filter occurs in the passband of the first filter, the unnecessary wave can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter in the same multiplexer can be suppressed.

[0028] According to embodiments of the present invention, a radio frequency (RF) front-end module includes the multiplexer described above.

[0029] By allowing at least one of the second IDT electrodes to have the maximum electrode finger center-to-center pitch in a multiplexer of an RF front-end module as described above, the position of an unnecessary wave that causes a large return loss of the second filter and occurs in the frequency passband of the first filter can be removed from the passband of the first filter. Accordingly, when an elastic wave filter is used in an RF front-end module, the deterioration of the passband characteristics of another filter in the same RF front-end module can be suppressed.

[0030] The present invention can suppress, when an elastic wave filter is used in a multiplexer or an RF front-end module, the deterioration of passband characteristics of another filter in the same multiplexer or the same RF front-end module.

[0031] Further details, features and advantages of the invention will become apparent from the following purely exemplary and non-limiting description of embodiments in conjunction with the drawing comprising nine drawing figures. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a circuit diagram of a communication device including a multiplexer according to a first embodiment. Fig. 1B is a graph illustrating the insertion loss (passband characteristics) of the multiplexer according to the first embodiment. Fig.2 is a circuit diagram illustrating a multiplexer according to the first embodiment, which includes a first filter and a second filter. Fig. 3 is a schematic plan view showing the second filter of the Fig. 2 illustrated multiplexer. Fig. 4 (a) is a plan view and Fig. 4 (b) is a sectional view schematically showing an IDT of the second filter according to Fig. 2 show. Fig. 5 is a schematic plan view illustrating a second filter of a multiplexer according to a comparative example. Fig. 6A and Fig. 6B shows the insertion loss in the frequency passband of the first filter. Fig. 7A and Fig. 7B show the return loss of the second filter in the frequency passband of the first filter. Fig.8 is a circuit diagram of an RF front-end module including a multiplexer according to the first embodiment. Fig. 9 is a schematic plan view illustrating the configuration of a second filter side of a multiplexer according to a second embodiment. DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below illustrate broad or concrete examples. The reference numerals, shapes, materials, elements, and the arrangement and connections of the elements are only examples and should not be construed as limiting the present invention. Among the elements in the following embodiments, elements not described in independent claims are described as arbitrary elements. The sizes or proportions of elements illustrated in the drawings are not necessarily exact. First Embodiment 1. Overall configuration of the multiplexer

[0033] Fig. 1A is a circuit diagram of a communication device 9 including a multiplexer 1 according to a first embodiment. Fig.1B is a graph illustrating the insertion loss (passband characteristics) of the multiplexer 1 according to the embodiment.

[0034] As in Fig. As illustrated in Figure 1A, the communication device 9 includes the multiplexer 1 and a radio frequency integrated circuit (RFIC) 4, which is a radio frequency (RF) signal processing circuit. The multiplexer 1 is connected to an antenna device 2 with a common antenna terminal 15 therebetween.

[0035] Fig. 1A illustrates, as an example of the multiplexer 1, a quadplexer applied to band 25 (transmit passband: about 1850 MHz to about 1915 MHz, and receive passband: about 1930 MHz to about 1995 MHz) and to band 66 (transmit passband: about 1710 MHz to about 1780 MHz, and receive passband: about 2110 MHz to about 2200 MHz) of Long-Term Evolution (LTE).

[0036] The multiplexer 1 contains transmitting-side filters 101 and 103, receiving-side filters 102 and 104, a common antenna connection 15, Transmitting input terminals 106 and 108 and receiving output terminals 107 and 109. Lead wires from each of the transmitting-side filters 101 and 103 and the receiving-side filters 102 and 104 are bundled and connected to the common antenna terminal 15.

[0037] The transmitting-side filters 101 and 103 are band-pass filters that receive a transmission wave generated by the RFIC 4 through the transmission input terminals 106 and 108, respectively, filter the transmission wave using their respective transmission passbands, and output the filtered transmission waves to the common antenna terminal 15.

[0038] The receiving-side filters 102 and 104 are band-pass filters that receive a reception wave input from the common antenna terminal 15, filter the reception wave using their respective reception passbands, and output the filtered reception waves to the reception output terminals 107 and 109, respectively.

[0039] Now any two in the Fig. The filters contained in the multiplexer 1 shown in Figure 1A will be described in more detail. The two filters are referred to as the first filter 11 and the second filter 12.

[0040] Fig. Fig. 2 is a circuit diagram illustrating a multiplexer 1A including the first filter 11 and the second filter 12.

[0041] As in Fig.As illustrated in Figure 2, the first filter 11 is arranged on a channel connecting the common antenna terminal 15 and a first terminal 16. The second filter 12 is arranged on a channel connecting the common antenna terminal 15 and a second terminal 17. The second filter 12 is connected to the common antenna terminal 15 at least when the first filter 11 is connected to the common antenna terminal 15 and performs filtering.

[0042] The second filter 12 has higher passband frequencies than the first filter 11. For example, in the embodiment, the first filter 11 is described as a filter having a receive passband of band 25 (band 25 Rx), and the second filter 12 is described as a filter having a receive passband of band 66 (band 66 Rx). 2. Structure of IDTs of the second filter

[0043] Fig.3 is a schematic plan view illustrating the second filter 12 of the multiplexer 1A.

[0044] The second filter 12 is a longitudinally coupled elastic wave filter and includes a plurality of IDTs 211, 212, 213, 214, and 215. Note that the first filter 11 may be a ladder filter including series resonators and parallel resonators, or a longitudinally coupled elastic wave filter.

[0045] Before describing the second filter 12, the structure of the IDTs 211 to 215 of the second filter 12 will be described using an IDT 22 common to the IDTs 211 to 215.

[0046] Fig. 4 (a) is a plan view and Fig.4 (b) is a sectional view schematically illustrating the IDT 22. Note that the IDT 22 is used here to describe the typical structure of an elastic wave filter, and the number and length of electrode fingers configuring each electrode are not limited to those of the IDT 22.

[0047] The IDT 22 includes interdigital transducer (IDT) electrodes 22a and 22b, which are essentially comb-shaped.

[0048] As in Fig.As illustrated in Figure 4(a), the pair of IDT electrodes 22a and 22b facing each other is formed on a piezoelectric substrate 326. The IDT electrode 22a includes a plurality of electrode fingers 222a extending parallel to each other and a bus bar electrode 221a connecting the plurality of electrode fingers 222a. The IDT electrode 22b includes a plurality of electrode fingers 222b extending parallel to each other and a bus bar electrode 221b connecting the plurality of electrode fingers 222b. The plurality of electrode fingers 222a and 222b are formed along a direction intersecting a propagation direction of elastic waves. That is, the electrode fingers 222a and 222b are formed adjacent to each other in the propagation direction of elastic waves.

[0049] The IDT electrodes 22a and 22b, each including the plurality of electrode fingers 222a and 222b and the bus bar electrodes 221a and 221b, have a multi-layer structure including an adhesion layer 323 and a main electrode layer 324, as shown in Fig. 4 (b) illustrates.

[0050] The adhesion layer 323 is a layer for improving the adhesion between the piezoelectric substrate 326 and the main electrode layer 324, and Ti, for example, is used as a material of the adhesion layer 323. The adhesion layer 323 has a film thickness of about 12 nm, for example.

[0051] For example, Al containing 1% Cu is used as the material for the main electrode layer 324. The main electrode layer 324 has a film thickness of approximately 162 nm.

[0052] A protective layer 325 is formed to cover the IDT electrodes 22a and 22b. The protective layer 325 is a layer for protecting the main electrode layer 324 from the external environment, adjusting the frequency-temperature characteristics, and improving moisture resistance. The protective layer 325 is, for example, a film containing silicon dioxide as a main component.

[0053] The piezoelectric substrate 326 is made of, for example, a piezoelectric LiTaO 3 -Single crystal, a piezoelectric LiNbO 3 -Single crystal with a specific cutting angle or made of piezoelectric ceramic.

[0054] The design parameters of the IDT 22 will now be described. The wavelength of a surface acoustic wave (SAW) resonator is defined by a repetition center distance λ of the plurality of electrode fingers 222a and 222b, which have the wavelengths shown in part (b) of Fig.4. The overlap width L of the IDT electrodes 22a and 22b is as shown in part (a) of Fig. 4 illustrates an overlapping electrode finger length in the case where the electrode fingers 222a of the IDT electrode 22a and the electrode fingers 222b of the IDT electrode 22b are viewed from the elastic wave propagation direction. A metallization ratio D is a line width occupancy rate of the plurality of electrode fingers 222a and 222b, which is the ratio of the line width of the electrode fingers 222a and 222b to the sum of the line width and the space width of the electrode fingers 222a and 222b. Specifically, the metallization ratio D is defined as W / (W+S), where W is the line width of the electrode fingers 222a and 222b that configure the IDT electrodes 22a and 22b, and S is the space width between the adjacent electrode fingers 222a and electrode fingers 222b. 3. Configuration of the second filter according to an embodiment

[0055] As described above, the second filter 12 is a longitudinally coupled elastic wave filter and includes the plurality of IDTs 211 to 215 as shown in Fig. 3. The second filter 12 further includes reflectors 220 and 221, a first port 230, and a second port 240, the first port 230 being arranged on the common antenna terminal 15 side, as viewed from the plurality of IDTs 211 to 215, consisting of the common antenna terminal 15 and the second terminal 17. The second port 240 is arranged on the second terminal 17 side, as viewed from the plurality of IDTs 211 to 215, consisting of the common antenna terminal 15 and the second terminal 17.

[0056] For example, when an RF signal is input from the common antenna terminal 15 to the second filter 12, a potential difference arises between the common antenna terminal 15 and a reference terminal (ground), which in turn deforms the piezoelectric substrate 326, thereby generating a surface acoustic wave. By approximately matching the center-to-center pitch λ of the electrode fingers of each of the IDTs 211 to 215 to the wavelength of the passband, an RF signal having a passable frequency component can be passed using the second filter 12.

[0057] The IDT 211 of the second filter 12 includes a pair of IDT electrodes 211a and 211b facing each other. Similarly, the IDTs 212 to 215 each have pairs of IDT electrodes 212a and 212b, 213a and 213b, 214a and 214b, and 215a and 215b facing each other. The IDTs 211 to 215 are arranged sequentially along the elastic wave propagation direction in such a way that they are longitudinally coupled. That is, the IDTs 212 and 214 are arranged to sandwich the IDT 213 in the propagation direction, and the IDTs 211 and 215 are arranged to sandwich the IDTs 212 to 214 in the propagation direction. The reflectors 220 and 221 are arranged to sandwich the IDTs 211 to 215 in the propagation direction.

[0058] IDTs 212 and 214 are connected in parallel between the first port 230 and the reference terminal (ground). Specifically, IDT electrodes 212a and 214a are connected to the reference terminal. IDT electrodes 212b and 214b are connected to the common antenna terminal 15 side, consisting of the common antenna terminal 15 and the second terminal 17, with the first port 230 interposed therebetween.

[0059] IDTs 211, 213, and 215 are connected in parallel between the second port 240 and the reference terminal. Specifically, IDT electrodes 211a, 213a, and 215a are connected to the reference terminal. IDT electrodes 211b, 213b, and 215b are connected to the second terminal 17 side of the common antenna terminal 15 and the second terminal 17, with the second port 240 interposed therebetween.

[0060] In this way, in the second filter 12, among the plurality of IDTs 211 to 215, first IDT electrodes 212b and 214b are connected to the common antenna terminal 15 side, and second IDT electrodes 211b, 213b, and 215b are connected to the second terminal 17 side. That is, the connection destination of the first IDT electrodes 212b and 214b is the common antenna terminal 15, and the connection destination of the second IDT electrodes 211b, 213b, and 215b is the second terminal 17.

[0061] Table 1 shows the design parameters (electrode finger main pitch λm, overlap width L, number N of IDT pairs and metallization ratio D) of the IDTs 211 to 215. Table 1 IDT 211b IDT 212b IDT 213b IDT 214b IDT 215b Electrode finger main center distance λm (µm) λ1 1.850 λ2 1.838 (minimum) λ3 1.854 (maximum) λ4 1.838 (minimum) λ5 1.850 Overlap width L (µm) 40 40 40 40 40 Number N of pairs 21,5 19 9,5 19 21,5 Metallization ratio D 0,6 0,6 0,6 0,6 0,6 Connected to the second connection common antenna connection second connection common antenna connection second connection

[0062] The center-to-center spacing of the electrode fingers of the reflectors 220 and 221 is approximately 1.855 µm and is thus larger than the main center-to-center spacings λ1 to λ5 of the electrode fingers of the IDTs 211 to 215.

[0063] The electrode finger main pitches λm shown in Table 1 are the pitches of the electrode fingers at the center of the IDT electrodes 211b to 215b, respectively. For example, in the case of the IDT electrode 211b, the main pitch λm is a pitch formed by electrode fingers occupying at least 50% of all the electrode fingers of the IDT electrode 211b. In a longitudinally coupled elastic wave filter, the electrode finger pitch at two ends of the IDT electrode 211b may be made smaller than that at its center to adjust the coupling degree to the adjacently positioned IDT electrode 212b. Thus, the electrode finger pitch λ has different values ​​for the center and the two ends of the IDT electrode 211b in the elastic wave propagation direction, viewed from the entire IDT electrode 211b.Therefore, in the embodiment, the electrode finger pitches λ of the IDT electrodes 211b to 215b can be compared based on the main pitches λm.

[0064] In the embodiment underlying Table 1, the electrode finger main center distances λm have the following relationship: (λ2=λ4)<(λ1=λ5)<λ3

[0065] The electrode finger main pitches λ2 and λ4 of the first IDT electrodes 212b and 214b connected to the common antenna terminal 15 are different from the electrode finger main pitches λ1, λ3 and λ5 of the second IDT electrodes 211b, 213b and 215b connected to the second terminal 17.

[0066] Among the main pitches λ1 to λ5 of the plurality of IDT electrodes 211b to 215b, the electrode finger main pitch λ3 of the second IDT electrode 213b connected to the second terminal 17 is the maximum. Among the main pitches λ1 to λ5, the main pitches λ2 and λ4 of the IDT electrodes 212b and 214b connected to the common antenna terminal 15 are the minimum.

[0067] In the embodiment, the overall average pitch λ of the electrode fingers included in the first IDT electrodes 212b and 214b is smaller than the overall average pitch λ of the electrode fingers included in the second IDT electrodes 211b, 213b, and 215b. The overall average pitch λ of the electrode fingers can be obtained by calculating the weighted average of the electrode finger pitches λ, including those at the center and two ends of each IDT electrode. In the embodiment, the overall average pitch of the electrode finger fingers of the first IDT electrodes 212b and 214b is about 1.789 μm, and the overall average pitch of the electrode finger fingers of the second IDT electrodes 211b, 213b, and 215b is about 1.819 μm.

[0068] In the embodiment, when the average of the electrode finger pitches λ of each of the IDT electrodes 211b to 215b is obtained, an IDT electrode having the maximum average is one of the second IDT electrodes 211b, 213b, and 215b. The average of plural electrode finger pitches λ is a value obtained for each IDT electrode by calculating the weighted average of the electrode finger pitches λ, including those at the center and the two ends of the IDT electrode. In the embodiment, an IDT electrode having the maximum average is the IDT electrode 213b, and IDT electrodes having the minimum average are the IDT electrodes 212b and 214b. 4. Configuration of the second filter according to a comparative example

[0069] Fig. 5 is a schematic plan view illustrating a second filter 552 of a multiplexer according to a comparative example.

[0070] As in Fig. 5, the second filter 552 includes a plurality of IDTs 511 to 515, the reflectors 220 and 221, the first port 230, and the second port 240.

[0071] The IDT 511 has a pair of IDT electrodes 511a and 511b facing each other. Similarly, the IDTs 512 to 515 each have pairs of IDT electrodes 512a and 512b, 513a and 513b, 514a and 514b, and 515a and 515b facing each other. The IDTs 511 to 515 are arranged sequentially along the elastic wave propagation direction in such a way that they are longitudinally coupled.

[0072] IDTs 511, 513, and 515 are connected in parallel between the first port 230 and a reference terminal (ground). Specifically, IDT electrodes 511a, 513a, and 515a are connected to the reference terminal. IDT electrodes 511b, 513b, and 515b, on the other hand, are connected to the common antenna terminal 15, with the first port 230 interposed therebetween.

[0073] IDTs 512 and 514 are connected in parallel between second port 240 and the reference terminal. Specifically, IDT electrodes 512a and 514a are connected to the reference terminal. IDT electrodes 512b and 514b, on the other hand, are connected to second terminal 17, with second port 240 sandwiched between them.

[0074] In the second filter 552 according to the comparative example, among the plurality of IDTs 511 to 515, first IDT electrodes 511b, 513b, and 515b are connected to the common antenna terminal 15, and second IDT electrodes 512b and 514b are connected to the second terminal 17.

[0075] Table 2 lists the design parameters of the IDTs 511 to 515 according to the comparison example. Table 2 IDT 511b IDT 512b IDT 513b IDT 514b IDT 515b Electrode finger main center distance λm (µm) λ1 1.833 λ2 1.817 (minimum) λ3 1.926 (maximum) λ4 1.817 (minimum) λ5 1.833 Overlap width L (µm) 43 43 43 43 43 Number N of pairs 16,5 11 11,15 11 16,5 Metallization ratio D 0,6 0,6 0,6 0,6 0,6 Connected to the common antenna connection second connection common antenna connection second connection common antenna connection

[0076] The center-to-center spacing of the electrode fingers of the reflectors 220 and 221 is approximately 1.861 µm and is thus larger than the electrode finger main center-to-center spacing λ1 of the IDT 511 and smaller than the electrode finger main center-to-center spacing λ3 of the IDT 513.

[0077] In the comparative example underlying Table 2, the electrode finger main center distances λm have the following relationship: (λ2+λ4)<(λ1+λ5)<λ3

[0078] The size relationship among the electrode finger main pitches λm according to the comparative example is the same as that of the above-described embodiment, but in the comparative example, the IDT electrodes 511b, 513b, and 515b are connected to the common antenna terminal 15, and the IDT electrodes 512b and 514b are connected to the second terminal 17. 5. Frequency characteristics of the embodiment and the comparative example

[0079] The frequency characteristics of the multiplexer according to the above-described embodiment and the comparative example are described below.

[0080] Fig. 6A and Fig. 6B illustrate the insertion loss in the frequency passband of the first filter 11. As an evaluation circuit similar to that shown in Fig. 6A, a circuit that bundles lead wires on one side of the first filter 11 and the second filter 12 is used. As an evaluation circuit corresponding to the comparative example, a circuit is used where the second filter 12 of the embodiment is replaced with the second filter 552 of the comparative example.

[0081] Fig. 6B is a graph illustrating the insertion loss (passband characteristics) in the embodiment and the comparative example from about 1850 MHz to about 2050 MHz. As shown in Fig.6B, in the comparative example, the insertion loss becomes larger near about 1975 MHz, which is within the band of Band 25 Rx.

[0082] In contrast, in the embodiment, compared to the comparative example, the insertion loss becomes smaller near about 1975 MHz. This difference is calculated with reference to the Fig. 7A and Fig. 7B.

[0083] Fig. 7A and Fig. 7B illustrate the return loss of the second filter 12 (or the filter 552) in the frequency passband of the first filter 11. As an evaluation circuit similar to the one shown in Fig.7A, a circuit that does not combine the first filter 11 and the second filter 12 and that includes only the second filter 12 is used. As an evaluation circuit corresponding to the comparative example, a circuit that includes only the second filter 552 of the comparative example is used.

[0084] Fig. Figure 7B is a graph illustrating the return loss in the embodiment and the comparative example from about 1850 MHz to about 2050 MHz. As shown in Fig.As illustrated in Figure 7B, in the comparative example, an unnecessary wave causing a large return loss occurs near about 1975 MHz, which is within the 25 Rx band. This indicates that in the second filter 552 of the comparative example, a signal injected at about 1975 MHz is not sufficiently reflected and is partially absorbed. Because of this unnecessary wave near about 1975 MHz, the insertion loss increases in the region of about 1975 MHz, as shown in Fig. 6B.

[0085] In contrast, in the embodiment, the return loss is small within the 25 Rx band. That is, by changing the electrode finger pitches λ of the IDT electrodes 211b to 215b, the position of an unnecessary wave that causes a large return loss of the second filter 12 and that appears in the frequency passband (25 Rx band) of the first filter 11 is removed from the passband of the first filter 11. Specifically, by increasing the electrode finger main pitches λm of the IDT electrodes 211b, 213b, and 215b connected to the second terminal 17 or decreasing the electrode finger main pitches of the IDT electrodes 212b and 214b connected to the common antenna terminal 15, the position of the above-mentioned unnecessary wave can be shifted to a higher frequency side of the passband of the first filter 11.Accordingly, in the multiplexer 1A using the second filter 12 of the embodiment, an increase in the insertion loss in the passband of the first filter 11 can be suppressed. 6. Conclusion

[0086] The multiplexer 1A according to the embodiment described above includes the common antenna terminal 15, the first terminal 16, the second terminal 17, the first filter 11 arranged on a channel connecting the common antenna terminal 15 and the first terminal 16, and the second filter 12 arranged on a channel connecting the common antenna terminal 15 and the second terminal 17 and having higher passband frequencies than the first filter 11.

[0087] The second filter 12 is an elastic wave filter and includes the plurality of IDTs 211 to 215 arranged along the elastic wave propagation direction. Each of the IDTs 211 to 215 includes a pair of IDT electrodes facing each other. Among the IDT electrodes configuring the IDTs 211 to 215, first IDT electrodes 212b and 214b are connected to the common antenna terminal 15 side, consisting of the common antenna terminal 15 and the second terminal 17, and second IDT electrodes 211b, 213b, and 215b are connected to the second terminal 17 side, consisting of the common antenna terminal 15 and the second terminal 17. The first IDT electrodes 212b and 214b and the second IDT electrodes 211b, 213b and 215b are each formed on the surface of the piezoelectric substrate 326, and each has a plurality of electrode fingers arranged side by side in the elastic wave propagation direction.The first IDT electrodes 212b and 214b and the second IDT electrodes 211b, 213b, and 215b have different main pitches λm among a plurality of electrode fingers arranged adjacent to each other in the elastic wave propagation direction. At least one of the second IDT electrodes 211b, 213b, and 215b has a maximum electrode finger main pitch λm among the plurality of IDT electrodes 211b to 215b.

[0088] With this configuration, the position of an unnecessary wave that causes a large return loss of the second filter 12 and that occurs in the frequency passband of the first filter 11 can be removed from the passband of the first filter 11. Accordingly, when an elastic wave filter is used in the multiplexer 1A, the deterioration of the passband characteristics of another filter in the same multiplexer 1A can be suppressed.

[0089] At least one of the first IDT electrodes 212b and 214b may have a minimum electrode finger main pitch λm among the plurality of IDT electrodes 211b to 215b.

[0090] Accordingly, the position of an unnecessary wave that causes a large return loss of the second filter 12 and that occurs in the passband of the first filter 11 can be shifted to a higher frequency side of the passband of the first filter 11, which is within the lower frequency side stopband of the second filter 12. Accordingly, when an elastic wave filter is used in the multiplexer 1A, the deterioration of the passband characteristics of another filter in the same multiplexer 1A can be suppressed.

[0091] In the multiplexer 1A according to the embodiment, the total average of the center-to-center pitches λ of the electrode fingers included in the first IDT electrodes 212b and 214b is smaller than the total average of the center-to-center pitches λ of the electrode fingers included in the second IDT electrodes 211b, 213b, and 215b.

[0092] In the multiplexer 1A according to the embodiment, when the average of the electrode finger pitches λ of each of the IDT electrodes 211b to 215b is obtained, an IDT electrode having the maximum average is one of the second IDT electrodes 211b, 213b, and 215b.

[0093] With this configuration, the position of an unnecessary wave that causes a large return loss of the second filter 12 and that occurs in the frequency passband of the first filter 11 can be removed from the passband of the first filter 11. Accordingly, when an elastic wave filter is used in the multiplexer 1A, the deterioration of the passband characteristics of another filter in the same multiplexer 1A can be suppressed. Further embodiments

[0094] Although certain specific embodiments of multiplexers 1 and 1A have been described above, the invention is not limited thereto. For example, the described embodiments can be modified as follows without departing from the scope of the invention.

[0095] Fig. Figure 8 is a circuit diagram illustrating a radio frequency (RF) front-end module 8 including a multiplexer 1B. In the Fig. In the RF front-end module 8 illustrated in FIG. 8, two low-noise amplifiers (LNAs) 3 are arranged between the first port 16 and the RFIC 4 and between the second port 17 and the RFIC 4, respectively. To switch the connection state to the antenna device 2, a multiport switch 5 is arranged between the first filter 11 and the common antenna port 15 and between the second filter 12 and the common antenna port 15. The multiport switch 5 is a switch that can switch multiple connections on and off simultaneously. Thanks to the multiport switch 5, when the first filter 11 is connected to the common antenna port 15, that is, when the first filter 11 is processing signals, the second filter 12 can also be connected to the common antenna port 15.

[0096] As in the embodiment described above, in the RF front-end module 8 having such a circuit configuration, when an elastic wave filter is used as part of the multiplexer 1B, the deterioration of the passband characteristics of another filter in the same multiplexer 1B can be suppressed.

[0097] Although an embodiment in which both the first filter 11 and the second filter 12 of the multiplexer 1A are reception filters was described above, the invention is not limited to this configuration, and both filters 11 and 12 may be transmission filters, or one of the filters 11 and 12 may be a reception filter and the other may be a transmission filter. Specifically, a band-pass filter of the 66 Rx band may serve as the second filter 12, and one of the 25 Tx band and the 66 Tx band may serve as the first filter 11. Alternatively, a band-pass filter of the 25 Rx band may serve as the second filter 12, and one of the 66 Tx band and the 25 Tx band may serve as the first filter 11. Alternatively, a bandpass filter of band 25 Tx may serve as the second filter 12, and a bandpass filter of band 66 Tx may serve as the first filter 11.

[0098] Possible modifications within the scope of the inventive concept include, for example, the features described below.

[0099] Fig. 9 is a schematic plan view illustrating the configuration of the second filter 12 side of a multiplexer according to another embodiment.

[0100] In the multiplexer according to this embodiment, a circuit element 350 is connected between the first IDT electrodes 212b and 214b of the second filter 12 and the common antenna terminal 15. Specifically, the circuit element 350, which is different from the second filter 12, is connected in series between the first port 230 and the common antenna terminal 15. The circuit element 350 is, for example, an inductor, a capacitor, a switch, an LC resonator, or an elastic wave resonator. For example, the LC resonator and the elastic wave resonator may be series resonators or parallel resonators, or may be resonators including both a series resonator and a parallel resonator. The circuit element 350 may be provided for the purpose of frequency trapping or impedance matching.In this embodiment, even if the circuit element 350 is connected between the first IDT electrodes 212b and 214b and the common antenna terminal 15 as described above, the position of an unnecessary wave that causes a large return loss of the second filter 12 and that occurs in the frequency passband of the first filter 11 can be removed from the passband of the first filter 11. Accordingly, when an elastic wave filter is used in a multiplexer, the deterioration of the passband characteristics of another filter configured in the same multiplexer can be suppressed.

[0101] In the above-described embodiments, a surface acoustic wave (SAW) filter including IDT electrodes was used as the multiplexers 1 and 1A and the RF front-end module 8. However, each filter configuring the multiplexers 1 and 1A and the RF front-end module 8 may be an elastic wave filter using a boundary acoustic wave. Even in this case, the same advantageous effects as those of the multiplexers 1 and 1A and the RF front-end module 8 according to the above-described embodiments can be achieved.

[0102] The piezoelectric substrate 326 included in the SAW filter may have a multilayer structure in which a high-acoustic-velocity support substrate, a low-acoustic-velocity film, and a piezoelectric film are laminated in this order. The piezoelectric film is made of, for example, a piezoelectric LiTaO 3The piezoelectric film is formed from a 50° Y-cut single crystal with X-propagation, or a piezoelectric ceramic, specifically, a lithium tantalate single crystal cut along a surface having, as a normal, an axis rotated 50° from the Y-axis around the X-axis serving as the central axis, or a ceramic that is a single crystal or ceramic in which a surface acoustic wave propagates in the X-axis direction. The piezoelectric film has a thickness of about 600 nm, for example. The high acoustic velocity support substrate is a substrate that supports the low acoustic velocity film, the piezoelectric film, and the IDT electrodes.The high acoustic velocity support substrate is a substrate where the acoustic velocity of a bulk acoustic wave in the high acoustic velocity support substrate is higher than that of a surface acoustic wave or a boundary acoustic wave propagating in the piezoelectric film. It has the function of confining an elastic wave in a portion where the piezoelectric film and the low acoustic velocity film are laminated, thereby preventing the elastic wave from escaping downward beneath the high acoustic velocity support substrate. The high acoustic velocity support substrate is, for example, a silicon substrate and has a thickness of about 200 μm.The low acoustic velocity film is a film where the acoustic velocity of an elastic wave in the low acoustic velocity film is lower than that of a bulk wave propagating in the piezoelectric film, and is sandwiched between the piezoelectric film and the high acoustic velocity support substrate. With this structure and the characteristic of concentrating energy in a medium where the acoustic velocity of an elastic wave is substantially low, the leakage of SAW energy to the outside of the IDT electrodes is suppressed. The low acoustic velocity film is, for example, a film that has silicon dioxide as a main component and has a thickness of about 670 nm.With this multilayer structure, the Q-factor of a resonance frequency and an anti-resonance frequency can be significantly increased compared to the structure where the piezoelectric substrate 326 is used as a single layer. That is, because a SAW resonator with a high Q-factor can be configured, a filter with low insertion loss can be configured using this SAW resonator.

[0103] The present invention can be generally used in a low-loss multiplexer and a low-loss RF front-end module applicable to multi-band and multi-mode frequency standards in a communication device such as a mobile phone.

[0104] Although preferred embodiments of the invention have been described above, it will be understood that variations and modifications will occur to those skilled in the art without departing from the spirit and scope of the invention. The scope of the invention should therefore be determined solely by reference to the following claims.

Claims

[1] Multiplexer (1A), comprising - a common connection (15), - a first connection (16), - a second connection (17), - a first filter (11) arranged on a channel connecting the common terminal (15) and the first terminal (16), and - a second filter (12) arranged on a channel connecting the common terminal (15) and the second terminal (17), the second filter (12) having higher passband frequencies than the first filter (11), wherein: - the second filter (12) comprises an elastic wave filter including a plurality of interdigital transducers (IDTs) (211, 212, 213, 214, 215) arranged along a propagation direction of elastic waves, - each of the plurality of IDTs (211, 212, 213, 214, 215) includes a pair of IDT electrodes (211a, 211b, 212a, 212b, 213a, 213b, 214a, 214b, 215a, 215b) facing each other, - among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b) included in the plurality of IDTs (211, 212, 213, 214, 215), first IDT electrodes (212b, 214b) are connected to the common terminal side of the common terminal (15) and the second terminal (17), and second IDT electrodes (211b, 213b, 215b) are connected to the second terminal side of the common terminal (15) and the second terminal (17), - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) are each formed on a surface of a piezoelectric substrate (326), and each has a plurality of electrode fingers (222b) arranged side by side in the propagation direction of elastic waves, - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) have different main center distances of the electrode fingers, and - at least one of the second IDT electrodes (211b, 213b, 215b) has a maximum main center-to-center distance of the electrode fingers among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b). [2] The multiplexer (1A) according to claim 1, wherein at least one of the first IDT electrodes (212b, 214b) has a minimum main pitch of the electrode fingers among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b). [3] Multiplexer (1A), comprising - a common connection (15), - a first connection (16), - a second connection (17), - a first filter (11) arranged on a channel connecting the common terminal (15) and the first terminal (16), and - a second filter (12) arranged on a channel connecting the common terminal (15) and the second terminal (17), the second filter (12) having higher passband frequencies than the first filter (11), wherein: - the second filter (12) comprises an elastic wave filter including a plurality of interdigital transducers (IDTs) (211, 212, 213, 214, 215) arranged along a propagation direction of elastic waves, - each of the plurality of IDTs (211, 212, 213, 214, 215) includes a pair of IDT electrodes (211a, 211b, 212a, 212b, 213a, 213b, 214a, 214b, 215a, 215b) facing each other, - among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b) included in the plurality of IDTs (211, 212, 213, 214, 215), first IDT electrodes (212b, 214b) are connected to the common terminal side of the common terminal (15) and the second terminal (17), and second IDT electrodes (211b, 213b, 215b) are connected to the second terminal side of the common terminal (15) and the second terminal (17), - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) are each formed on a surface of a piezoelectric substrate (326), and each has a plurality of electrode fingers (222b) arranged side by side in the propagation direction of elastic waves, - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) have different main center distances of the electrode fingers and - an overall average of center-to-center distances of the electrode fingers included in the first IDT electrodes (212b, 214b) is smaller than an overall average of center-to-center distances of the electrode fingers included in the second IDT electrodes (211b, 213b, 215b). [4] Multiplexer (1A), comprising - a common connection (15), - a first connection (16), - a second connection (17), - a first filter (11) arranged on a channel connecting the common terminal (15) and the first terminal (16), and - a second filter (12) arranged on a channel connecting the common terminal (15) and the second terminal (17), the second filter (12) having higher passband frequencies than the first filter (11), wherein: - the second filter (12) comprises an elastic wave filter including a plurality of interdigital transducers (IDTs) (211, 212, 213, 214, 215) arranged along a propagation direction of elastic waves, - each of the plurality of IDTs (211, 212, 213, 214, 215) includes a pair of IDT electrodes (211a, 211b, 212a, 212b, 213a, 213b, 214a, 214b, 215a, 215b) facing each other, - among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b) included in the plurality of IDTs (211, 212, 213, 214, 215), first IDT electrodes (212b, 214b) are connected to the common terminal side of the common terminal (15) and the second terminal (17), and second IDT electrodes (211b, 213b, 215b) are connected to the second terminal side of the common terminal (15) and the second terminal (17), - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) are each formed on a surface of a piezoelectric substrate (326), and each has a plurality of electrode fingers (222b) arranged side by side in the propagation direction of elastic waves, - the first IDT electrodes (212b, 214b) and the second IDT electrodes (211b, 213b, 215b) have different main center distances of the electrode fingers, and - an IDT electrode belonging to the second IDT electrodes (211b, 213b, 215b) has a maximum average of the distances of the electrode fingers among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b). [5] The multiplexer (1A) according to claim 4, wherein an IDT electrode belonging to the first IDT electrodes (212b, 214b) has a minimum average of the pitches of the electrode fingers among the plurality of IDT electrodes (211b, 212b, 213b, 214b, 215b). [6] The multiplexer (1A) according to any one of claims 1 to 5, wherein a circuit element (350) different from the second filter (12) is connected between the first IDT electrodes (212b, 214b) and the common terminal (15). [7] Multiplexer 1A according to one of claims 1 to 6, wherein: the second filter (12) contains an odd number of three or more IDTs (211, 212, 213, 214, 215) and a number of the first IDT electrodes (212b, 214b) is smaller than a number of the second IDT electrodes (211b, 213b, 215b). [8] A multiplexer (1A) according to any one of claims 1 to 7, wherein the second filter (12) includes five or more IDTs (211, 212, 213, 214, 215). [9] Multiplexer (1A) according to one of claims 1 to 8, wherein the first filter (11) and the second filter (12) are both receive filters. [10] A multiplexer (1A) according to any one of claims 1 to 9, wherein when the first filter (11) is connected to the common terminal (15), the second filter (12) is connected to the common terminal (15). [11] Radio frequency (RF) front-end module (8) comprising the multiplexer (1A) according to one of claims 1 to 10.

Images