Elastic wave filter and multiplexer

Abstract

An elastic wave filter (1) is provided with a first input terminal (120) and a first output terminal (130), and a longitudinal coupling type resonator (M1) connected between the first input terminal (120) and the first output terminal (130), the longitudinal coupling type resonator (M1) having one or more input side resonators (D2 and D4) connected to the first input terminal (120), and one or more output side resonators (D1, D3, and D5) connected to the first output terminal (130), the total electrostatic capacitance of the one or more input side resonators being smaller than the total electrostatic capacitance of the one or more output side resonators.

Description

Technical Field

[0001] This invention relates to elastic wave filters and multiplexers. Background Technology

[0002] In recent years, multiplexers (demultiplexers) have been widely used in communication devices such as portable telephone terminals to address carrier aggregation, separating (demultiplexing) high-frequency signals according to each frequency band. For example, Patent Document 1 discloses an elastic wave filter with a longitudinally coupled resonator, which is connected to other filters through a common terminal to form a multiplexer.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-23074 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the elastic wave filter disclosed in Patent Document 1, the impedance concentration sometimes deteriorates. In this case, when connected together with other filters, the return loss characteristics of the elastic wave filter as viewed from the common terminal deteriorate.

[0008] Therefore, the object of the present invention is to provide an elastic wave filter, etc., that can improve the concentration of impedance.

[0009] means for solving problems

[0010] An elastic wave filter according to one aspect of the present invention includes: a first input terminal and a first output terminal; and a longitudinally coupled resonator connected between the first input terminal and the first output terminal. The longitudinally coupled resonator has one or more input-side resonators connected to the first input terminal and one or more output-side resonators connected to the first output terminal. The total electrostatic capacitance of the one or more input-side resonators is less than the total electrostatic capacitance of the one or more output-side resonators.

[0011] An elastic wave filter according to one aspect of the present invention includes: a first input terminal and a first output terminal; and a longitudinally coupled resonator connected between the first input terminal and the first output terminal. The longitudinally coupled resonator has one or more input-side resonators connected to the first input terminal and one or more output-side resonators connected to the first output terminal. The one or more input-side resonators and the one or more output-side resonators each have an IDT electrode composed of a plurality of electrode fingers. The sum of the product of the logarithm of the plurality of electrode fingers of the IDT electrode of each of the one or more input-side resonators and the cross width is less than the sum of the product of the logarithm of the plurality of electrode fingers of the IDT electrode of each of the one or more output-side resonators.

[0012] One aspect of the multiplexer of the present invention includes: a common terminal; the aforementioned elastic wave filter; and one or more filters, each having an input terminal and an output terminal, wherein the first input terminal and the input or output terminal of each of the one or more filters are connected to the common terminal.

[0013] Invention Effects

[0014] According to the elastic wave filter and the like of the present invention, the impedance concentration can be improved. Attached Figure Description

[0015] Figure 1 This is a structural diagram illustrating an example of a multiplexer implemented in this way.

[0016] Figure 2 This is a circuit diagram illustrating an example of an elastic wave filter implementation.

[0017] Figure 3A The Smith chart shows the impedance characteristics of a longitudinally coupled resonator of a comparative example as viewed from the first input terminal side.

[0018] Figure 3B This is a Smith chart showing the impedance characteristics of a comparative example elastic wave filter as viewed from the first input terminal side.

[0019] Figure 4A This is a Smith chart showing the impedance characteristics of the longitudinally coupled resonator of an embodiment, viewed from the first input terminal side.

[0020] Figure 4B This is a Smith chart showing the impedance characteristics of the elastic wave filter of an embodiment as viewed from the first input terminal side.

[0021] Figure 5A This is a circuit diagram illustrating the longitudinally coupled resonator of an embodiment.

[0022] Figure 5BThis is a Smith chart showing the impedance characteristics of the longitudinally coupled resonator of an embodiment, viewed from the first input terminal side.

[0023] Figure 6A This is a circuit diagram illustrating an embodiment of a longitudinally coupled resonator with a series arm resonator.

[0024] Figure 6B This is a coordinate graph illustrating the impedance characteristics of the series arm resonator in an embodiment.

[0025] Figure 6C This is a Smith chart showing the impedance characteristics of a longitudinally coupled resonator with series arm resonators, as viewed from the first input terminal side, illustrating an embodiment.

[0026] Figure 7A This is a circuit diagram illustrating an embodiment of a longitudinally coupled resonator with series arm resonators and parallel arm resonators connected together.

[0027] Figure 7B This is a coordinate graph illustrating the impedance characteristics of the parallel arm resonator in an embodiment.

[0028] Figure 7C This is a Smith chart showing the impedance characteristics of a longitudinally coupled resonator (i.e., an elastic wave filter) with series and parallel arm resonators connected in an embodiment, as viewed from the first input terminal side.

[0029] Figure 8A This is a Smith chart showing the impedance characteristics of the multiplexer as viewed from the common terminal side, illustrating an embodiment.

[0030] Figure 8B This is a coordinate graph showing the return loss characteristics of the multiplexer as viewed from the common terminal side, illustrating an embodiment. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described in detail using the accompanying drawings. It should be noted that the embodiments described below are merely illustrative or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of constituent elements, and connection methods shown in the following embodiments are examples and do not limit the scope of the present invention. Constituent elements in the following embodiments not described in the independent claims are described as arbitrary constituent elements. Furthermore, the sizes or size ratios of the constituent elements shown in the drawings are not necessarily strict. Additionally, in the figures, substantially identical structures are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified. Furthermore, in the following embodiments, "connection" includes not only direct connections but also electrical connections via other elements.

[0032] (Implementation Method)

[0033] [1. Structure of a multiplexer]

[0034] Figure 1 This is a structural diagram illustrating an example of a multiplexer 100 according to an embodiment. Figure 1 The diagram also shows an antenna element ANT connected to a common terminal 110 of the multiplexer 100. The antenna element ANT is, for example, a multi-band antenna conforming to communication standards such as LTE (Long Term Evolution).

[0035] Multiplexer 100 is a demultiplexing / multiplexing circuit using an elastic wave filter; here, a quadruple multiplexer is shown as an example. Multiplexer 100 includes a common terminal 110, an elastic wave filter, one or more filters, and a matching circuit 50. The elastic wave filter and the one or more filters have input and output terminals. For example, filter 1 is an example of an elastic wave filter, and filters 10, 20, and 30 are examples of one or more filters. The input or output terminals of filters 1, 10, 20, and 30 are connected to the common terminal 110 via the matching circuit 50.

[0036] The common terminal 110 is configured to be shared by four filters 1, 10, 20, and 30, and is connected to filters 1, 10, 20, and 30 inside the multiplexer 100. Additionally, the common terminal 110 is connected to the antenna element ANT outside the multiplexer 100. That is, the common terminal 110 is also the antenna terminal of the multiplexer 100.

[0037] For example, filters 1, 10, 20 and 30 are connected to the RF signal processing circuit (RFIC: Radio Frequency Integrated Circuit) outside the multiplexer 100 via amplifier circuits, etc.

[0038] For example, the passbands of filters 1, 10, 20 and 30 are each contained in the range of 1.4-2.7 GHz.

[0039] Filter 1 is an elastic wave filter. For example, filter 1 is a receive filter with a passband of LTE Band32Rx (1.452-1.496 GHz). The detailed structure of filter 1 will be described later.

[0040] Filter 10 is the first filter connected together with filter 1, and can be an elastic wave filter or an LC filter. For example, filter 10 is a receive filter with a passband of LTE Band 3Rx (1.805-1.880GHz).

[0041] Filter 20 is a second filter connected together with filter 1. It can be an elastic wave filter or an LC filter. For example, filter 20 is a receive filter with a passband of LTE Band 1Rx (2.110-2.170GHz).

[0042] Filter 30 is a third filter connected together with filter 1. It can be an elastic wave filter or an LC filter. For example, filter 30 is a receive filter with a passband of LTE Band 7Rx (2.620-2.690GHz).

[0043] Thus, the passbands of each filter are, for example, different frequency bands, and through a multiplexer 100, they can correspond to multiple frequency bands, that is, they can correspond to carrier aggregation.

[0044] It should be noted that the passbands of the four filters 1, 10, 20, and 30 are not limited to combinations of Band32Rx, Band3Rx, Band1Rx, and Band7Rx. Furthermore, the number of filters connected to the common terminal 110 can be two or more. Additionally, the multiplexer 100 can be composed of only multiple transmitting filters, or it can be configured to include both receiving and transmitting filters.

[0045] Matching circuit 50 is a circuit with multiple matching elements used to achieve impedance matching between antenna element ANT and filters 1, 10, 20, and 30. Matching elements include, for example, inductors or capacitors. Typically, the impedance of filters is mostly matched to 50Ω, but when connected with other filters to form a multiplexer, it deviates from 50Ω due to the influence of those other filters. Matching circuit 50 can match the impedance of each filter to 50Ω when they are connected together. However, to match the impedance of each filter to 50Ω, the number of matching elements constituting matching circuit 50 may increase. From the viewpoint of component mounting area limitations and performance degradation, it is desirable to perform impedance matching of each filter with a smaller number of elements. In this invention, impedance matching of each filter can be performed using filter 1 with a smaller number of elements.

[0046] [2. Filter Structure]

[0047] Next, the structure of filter 1 in the embodiment will be described.

[0048] Figure 2 This is a circuit diagram illustrating an example of filter 1 according to an embodiment.

[0049] Filter 1 includes a first input terminal 120, a first output terminal 130, and a longitudinally coupled resonator M1. The first input terminal 120 is connected to a common terminal 110. In addition, filter 1 also includes a series arm resonator S1 and a parallel arm resonator P1.

[0050] A longitudinally coupled resonator M1 is connected between the first input terminal 120 and the first output terminal 130. The longitudinally coupled resonator M1 has one or more input-side resonators connected to the first input terminal 120 via a series arm resonator S1, and one or more output-side resonators connected to the first output terminal 130. Each of the input-side and output-side resonators has an IDT (Interdigital Transducer) electrode composed of multiple finger electrodes. It should be noted that the output-side resonators can also be connected to the first output terminal 130 via other resonators. For example, the longitudinally coupled resonator M1 is a five-electrode longitudinally coupled resonator, with one or more input-side resonators being resonators D2 and D4, and one or more output-side resonators being resonators D1, D3, and D5. It should be noted that the number of input-side and output-side resonators is not limited to this, as long as there is one or more of each; there is no particular limitation.

[0051] The series arm resonator S1 is configured on the path connecting the first input terminal 120 and the longitudinally coupled resonator M1, and the parallel arm resonator P1 is connected between node N and ground. Node N is a node on the path connecting the first input terminal 120 and the longitudinally coupled resonator M1.

[0052] The longitudinally coupled resonator M1, the series arm resonator S1, and the parallel arm resonator P1 constitute the passband of filter 1. The resonant frequency of the series arm resonator S1 and the anti-resonant frequency of the parallel arm resonator P1 are designed to be located within the passband of filter 1. Furthermore, the anti-resonant frequency of the series arm resonator S1 is designed to be located near the high-frequency side of the passband of filter 1, while the resonant frequency of the parallel arm resonator P1 is designed to be located near the low-frequency side of the passband of filter 1.

[0053] In this invention, the correlation between the total electrostatic capacitance of one or more input-side resonators and the total electrostatic capacitance of one or more output-side resonators in the longitudinally coupled resonator M1 is characterized. Specifically, the total electrostatic capacitance of one or more input-side resonators is less than the total electrostatic capacitance of one or more output-side resonators. Hereinafter, an example where the total electrostatic capacitance of one or more input-side resonators (resonators D2 and D4) is less than the total electrostatic capacitance of one or more output-side resonators (resonators D1, D3, and D5) will be described as an embodiment, and an example where the total electrostatic capacitance of one or more input-side resonators (resonators D2 and D4) is greater than or equal to the total electrostatic capacitance of one or more output-side resonators (resonators D1, D3, and D5) will be described as a comparative example. It should be noted that the electrostatic capacitance of the resonator can be adjusted by adjusting the product of the logarithm of the multiple electrode fingers of the IDT electrodes in the resonator and the cross width. This is because the electrostatic capacitance of the resonator is approximately proportional to the product of the logarithm of the multiple electrode fingers of the IDT electrodes in the resonator and the cross width. Therefore, the following example will be described as follows: An example in which the sum of the product of the logarithms and crosswidths of the IDT electrodes of one or more input-side resonators (resonators D2 and D4) is less than the sum of the product of the logarithms and crosswidths of the IDT electrodes of one or more output-side resonators (resonators D1, D3, and D5). Conversely, a comparative example will be described as where the sum of the product of the logarithms and crosswidths of the IDT electrodes of one or more input-side resonators (resonators D2 and D4) is greater than or equal to the sum of the product of the logarithms and crosswidths of the IDT electrodes of one or more output-side resonators (resonators D1, D3, and D5).

[0054] [3. Comparative Example]

[0055] Next, a comparative example will be described where the total electrostatic capacitance of resonators D2 and D4 is equal to or greater than the total electrostatic capacitance of resonators D1, D3, and D5. It should be noted that the circuit structure of the comparative example filter is the same as that of filter 1 in the embodiment. The comparative example filter includes a longitudinally coupled resonator M1, a series arm resonator S1, and a parallel arm resonator P1. Furthermore, the passband of the comparative example filter is the same as that of filter 1 in the embodiment. However, the electrostatic capacitances of resonators D1, D2, D3, D4, and D5 in the longitudinally coupled resonator M1 of the comparative example are different from those in the longitudinally coupled resonator M1 of the embodiment.

[0056] For example, in the comparative example, the cross width of the multiple electrode fingers of the IDT electrodes of each of the resonators D1, D2, D3, D4 and D5 is fixed, as shown in Table 1.

[0057] [Table 1]

[0058] resonator D1 D2 D3 D4 D5 Logarithm (pair) 12.5 43 19 43 12.5

[0059] Here, when the number of pairs of electrode fingers in an IDT electrode is set to n, the total number of electrode fingers is represented by 2n+1. Therefore, for example, an IDT electrode with 12.5 pairs of electrode fingers refers to an IDT electrode with 25 electrode fingers. Furthermore, for example, the number of pairs of electrode fingers in the IDT electrodes of resonators D2 and D4 is greater than the number of pairs of electrode fingers in the IDT electrodes of any resonator D1, D3, and D5. In other words, since the cross-width of the electrode fingers in the IDT electrodes of resonators D1, D2, D3, D4, and D5 is fixed, the product of the number of pairs of electrode fingers and the cross-width in the IDT electrodes of resonators D2 and D4 is greater than the product of the number of pairs of electrode fingers and the cross-width in the IDT electrodes of any resonator D1, D3, and D5. Therefore, the electrostatic capacitance of resonators D2 and D4 is larger than that of any one of the resonators D1, D3, and D5.

[0060] Figure 3A This is a Smith chart showing the impedance characteristics of the longitudinally coupled resonator M1 of the comparative example, as viewed from the first input terminal 120. That is, Figure 3A Showing from Figure 2 The impedance characteristics of the longitudinally coupled resonator M1 are observed at node N.

[0061] Figure 3B This is a Smith chart showing the impedance characteristics of the filter of the comparative example as viewed from the first input terminal 120 side. That is, Figure 3B Showing from Figure 2 The impedance characteristics of a filter in a comparative example, including a series arm resonator S1, a parallel arm resonator P1, and a longitudinally coupled resonator M1, are observed at the first input terminal 120.

[0062] It should be noted that this also includes the Smith chart shown later, with the center of the Smith chart set to 50Ω.

[0063] like Figure 3A As shown, the impedance in the passband of the comparative example filter, as viewed from the first input terminal 120 side, of the longitudinally coupled resonator M1 in the comparative example is approximately 50Ω. Furthermore, as... Figure 3B As shown, the impedance in the passband of the comparative example filter, viewed from the first input terminal 120 side, is approximately 50Ω. Furthermore, regarding... Figure 3A and Figure 3BThe impedance characteristics shown in the figures indicate a decrease in impedance concentration. Impedance concentration represents the degree of concentration at three points in the passband: the low-frequency end, the center, and the high-frequency end. Generally speaking, the more concentrated these three points are, the lower the concentration and the better the concentration. Figure 3A The impedance concentration in the sample becomes 1.69. Figure 3B The impedance concentration in the sample becomes 2.71.

[0064] [4. Example]

[0065] Next, an embodiment in which the total electrostatic capacitance of resonators D2 and D4 is less than the total electrostatic capacitance of resonators D1, D3 and D5 will be described.

[0066] For example, in the embodiment, the cross width of the multiple electrode fingers of the IDT electrodes of each of the resonators D1, D2, D3, D4 and D5 is fixed, as shown in Table 2.

[0067] [Table 2]

[0068] resonator D1 D2 D3 D4 D5 Logarithm (pair) 47.5 14 53 14 45.5

[0069] For example, the number of pairs of electrodes on the IDT electrodes of resonators D2 and D4 is less than the number of pairs of electrodes on the IDT electrodes of any resonator D1, D3, and D5. In other words, since the cross-width of the electrodes on the IDT electrodes of resonators D1, D2, D3, D4, and D5 is fixed, the product of the number of pairs of electrodes on the IDT electrodes of resonators D2 and D4 and the cross-width is smaller than the product of the number of pairs of electrodes on the IDT electrodes of any resonator D1, D3, and D5. Therefore, the electrostatic capacitance of resonators D2 and D4 is smaller than the electrostatic capacitance of any resonator D1, D3, and D5.

[0070] Figure 4A This is a Smith chart showing the impedance characteristics of the longitudinally coupled resonator M1 as viewed from the first input terminal 120 side, illustrating an embodiment. That is, Figure 4A Showing from Figure 2 The impedance characteristics of the longitudinally coupled resonator M1 are observed at node N.

[0071] Figure 4B This is a Smith chart showing the impedance characteristics of filter 1 according to embodiment 1, as viewed from the first input terminal 120 side. That is, Figure 4B Showing from Figure 2 The impedance characteristics of filter 1, which includes a series arm resonator S1, a parallel arm resonator P1, and a longitudinally coupled resonator M1, are observed at the first input terminal 120.

[0072] like Figure 4AAs shown, the impedance in the passband of the filter 1 of the embodiment, as viewed from the first input terminal 120 side, of the longitudinally coupled resonator M1 of the embodiment is greater than 50Ω. Additionally, as... Figure 4B As shown, the impedance in the passband of filter 1 of embodiment 1, as viewed from the first input terminal 120 side, is greater than 50Ω. Furthermore, regarding... Figure 4A and Figure 4B The impedance characteristics shown in the figures indicate that the impedance concentration is improved compared to the comparative example. Figure 4A The impedance concentration in the sample becomes 1.49. Figure 4B The impedance concentration in the sample is 1.50.

[0073] In this embodiment, the impedance of the longitudinally coupled resonator M1 at the high-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, is located in the first quadrant of the Smith chart, and the impedance of the longitudinally coupled resonator M1 at the low-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, is located in the fourth quadrant of the Smith chart. By making the total electrostatic capacitance of resonators D2 and D4 smaller than the total electrostatic capacitance of resonators D1, D3, and D5, the impedance at the high-frequency end of the passband of filter 1 can be located in the first quadrant, and the impedance at the low-frequency end can be located in the fourth quadrant. Figure 4A As shown, the high-frequency end of the passband of filter 1 ( Figure 4A The impedance of part A in the filter is located in the first quadrant, and the low-frequency end of the passband of filter 1 ( Figure 4A The impedance of part B) is located in the fourth quadrant.

[0074] On the other hand, in the comparative example, the impedance of the longitudinally coupled resonator M1 at the high-frequency end of the passband of the filter of the comparative example, as viewed from the first input terminal 120 side, is located near the boundary between the first and fourth quadrants on the Smith chart. The impedance of the longitudinally coupled resonator M1 at the low-frequency end of the passband of the filter of the comparative example, as viewed from the first input terminal 120 side, is located in the second quadrant on the Smith chart. For example... Figure 3A As shown, the high-frequency end of the passband of the comparative example filter ( Figure 3A The impedance of part A in the comparative example is located near the boundary between the first and fourth quadrants. The low-frequency end of the passband of the filter in the comparative example ( Figure 3A The impedance of part B) is located in the second quadrant.

[0075] It should be noted that, when the line representing pure resistance is designated as the first line, and the line connecting the point at which the phase of the point on the outer perimeter of the Smith chart is 90° with the point of reference impedance is designated as the second line, the first, second, third, and fourth quadrants on the Smith chart refer to the four quadrants divided by the first and second lines. The upper right quadrant is the first quadrant. Starting from the first quadrant and rotating counterclockwise, the upper left quadrant becomes the second quadrant, the lower left quadrant becomes the third quadrant, and the lower right quadrant becomes the fourth quadrant.

[0076] As in the embodiment, the impedance of the longitudinally coupled resonator M1 at the high-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, is located in the first quadrant of the Smith chart, and the impedance of the longitudinally coupled resonator M1 at the low-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, is located in the fourth quadrant of the Smith chart. Therefore, while maintaining impedance concentration, the impedance of filter 1 in the passbands (also called the crossbands) of the commonly connected filters 10, 20, and 30, as viewed from the first input terminal 120 side, can be shifted towards an open circuit (infinity). Specifically, by connecting the series arm resonator S1 and the parallel arm resonator P1 to the longitudinally coupled resonator M1 with this impedance characteristic, the impedance of filter 1 in the crossband, as viewed from the first input terminal 120 side, can be shifted towards infinity while maintaining impedance concentration. Figures 5A to 7C This needs to be explained.

[0077] Figure 5A This is a circuit diagram illustrating the longitudinally coupled resonator M1 of an embodiment.

[0078] Figure 5B This is a Smith chart showing the impedance characteristics of the longitudinally coupled resonator M1 as viewed from the first input terminal 120 side, illustrating an embodiment.

[0079] exist Figure 5A The image shows a longitudinally coupled resonator M1 without the series arm resonator S1 and the parallel arm resonator P1 connected. Figure 5B In the diagram, the impedance within the passband of filter 1 is shown by a thick solid line, and the impedance outside the passband is shown by a solid line. The upper semicircle on the Smith chart represents the inductive (L-type) region, and the lower semicircle represents the capacitive (C-type) region. The high-frequency end of the passband of filter 1 (…) Figure 5B The impedance of the longitudinally coupled resonator M1, viewed from the first input terminal 120 side (part A) of the filter 1, is located in the first quadrant on the Smith chart, indicating inductive behavior. The low-frequency end of the passband of filter 1... Figure 5BIn part B), the impedance of the longitudinally coupled resonator M1, viewed from the first input terminal 120 side, is located in the fourth quadrant on the Smith chart, and is capacitive. Furthermore, the impedance concentration in the passband of the filter 1, viewed from the first input terminal 120 side, of the longitudinally coupled resonator M1 in this embodiment is 1.49.

[0080] In the multiplexer 100, when filter 1 is connected together with other filters (e.g., filters 10, 20, and 30), for signals in the other frequency band, in order to suppress the degradation of the pass-through characteristics of other filters by reflecting them in filter 1, it is desirable to make the impedance of filter 1 in the other frequency band approach infinity. In other words, in Figure 5B In the diagram, the portion enclosed by the dashed box represents the impedance in the other party's frequency band, which is intended to be moved counterclockwise. Therefore, to make the impedance of filter 1 in the other party's frequency band approach infinity, the series arm resonator S1 is connected to the longitudinally coupled resonator M1.

[0081] Figure 6A This is a circuit diagram illustrating the longitudinally coupled resonator M1 connected to a series arm resonator S1 according to an embodiment.

[0082] Figure 6B This is a coordinate graph illustrating the impedance characteristics of the series arm resonator S1 in an embodiment.

[0083] Figure 6C This is a Smith chart showing the impedance characteristics of a longitudinally coupled resonator M1 with a series arm resonator S1 connected to an embodiment, as viewed from the first input terminal 120 side.

[0084] exist Figure 6A The image shows a longitudinally coupled resonator M1 with a series arm resonator S1 connected but no parallel arm resonator P1 connected. Figure 6B The impedance characteristics of the series arm resonator S1 are shown in the diagram. An elastic wave resonator is inductive in the frequency band between its resonant and anti-resonant frequencies, and capacitive in the frequency bands lower than the resonant frequency and higher than the anti-resonant frequency. The resonant frequency of the series arm resonator S1 is located near the center frequency of the passband of filter 1, and at the high-frequency end of the passband of filter 1 (…). Figure 6B In the frequency band between part A) and the resonant frequency, the series arm resonator S1 becomes inductive at the low-frequency end of the passband of filter 1. Figure 6B In the frequency band between part B) and the resonant frequency, the series arm resonator S1 becomes capacitive. Additionally, in the opposite frequency band, the series arm resonator S1 becomes capacitive.

[0085] exist Figure 6CIn the diagram, the portion enclosed by the dashed box shows the impedance of the opposite frequency band before the series arm resonator S1 is connected, and the portion enclosed by the solid box shows the impedance of the opposite frequency band when the series arm resonator S1 is connected. Figure 6C As shown, by connecting the series arm resonator S1 to the longitudinally coupled resonator M1, the impedance in the opposite frequency band rotates counterclockwise and approaches infinity. This is because, in the opposite frequency band, the series arm resonator S1 becomes capacitive.

[0086] On the other hand, it can be seen that the impedance concentration was 1.49 before connecting the series arm resonator S1, but deteriorated to 1.66 after connecting the series arm resonator S1. This is because, at the high-frequency end of the passband of filter 1, the longitudinally coupled resonator M1 is inductive, and the series arm resonator S1 connected to it is also inductive. Therefore, the impedance at the high-frequency end of the passband of filter 1 with the longitudinally coupled resonator M1 connected to the series arm resonator S1 further shifts towards the inductive region on the Smith chart. Additionally, at the low-frequency end of the passband of filter 1, the longitudinally coupled resonator M1 is capacitive, and the series arm resonator S1 connected to it is also capacitive. Therefore, the impedance at the low-frequency end of the passband of filter 1 with the longitudinally coupled resonator M1 connected to the series arm resonator S1 further shifts towards the capacitive region on the Smith chart. Therefore, to improve the impedance concentration, a parallel arm resonator P1 is also connected.

[0087] Figure 7A This is a circuit diagram illustrating an embodiment of a longitudinally coupled resonator M1 connected with a series arm resonator S1 and a parallel arm resonator P1.

[0088] Figure 7B This is a coordinate graph illustrating the impedance characteristics of the parallel arm resonator P1 in an embodiment.

[0089] Figure 7C The Smith chart shows the impedance characteristics of a longitudinally coupled resonator M1 (i.e., filter 1) connected to a series arm resonator S1 and a parallel arm resonator P1, as observed from the first input terminal 120 side.

[0090] exist Figure 7A The diagram shows a longitudinally coupled resonator M1 with both a series arm resonator S1 and a parallel arm resonator P1 connected. That is, in... Figure 7A In the diagram, filter 1 is shown. Figure 7B The impedance characteristics of the parallel arm resonator P1 are shown in the figure. The resonant frequency of the parallel arm resonator P1 is located near the center frequency of the passband of filter 1, at the high-frequency end of the passband of filter 1. Figure 7BIn the frequency band between the part A) and the anti-resonant frequency, the parallel arm resonator P1 becomes capacitive, at the low-frequency end of the passband of filter 1 ( Figure 7B In the frequency band between the B) and the anti-resonance frequency, the parallel arm resonator P1 becomes inductive.

[0091] The impedance concentration is 1.66 before connecting the series arm resonator S1 and the parallel arm resonator P1, but as... Figure 7C As shown, by connecting the parallel arm resonator P1, the impedance concentration before connecting the series arm resonator S1 and the parallel arm resonator P1 can be maintained at 1.50. This is because, at the high-frequency end of the passband of filter 1, the longitudinally coupled resonator M1 is inductive, and the parallel arm resonator P1 connected to it is capacitive. Therefore, the impedance at the high-frequency end of the passband of filter 1, with the longitudinally coupled resonator M1 connected to the series arm resonator S1 and the parallel arm resonator P1, shifts towards the capacitive region on the Smith chart. Furthermore, because at the low-frequency end of the passband of filter 1, the longitudinally coupled resonator M1 is capacitive, and the parallel arm resonator P1 connected to it is inductive, the impedance at the low-frequency end of the passband of filter 1, with the longitudinally coupled resonator M1 connected to the series arm resonator S1 and the parallel arm resonator P1, shifts towards the inductive region on the Smith chart. In this way, by connecting the series arm resonator S1, the concentration of the degraded impedance can be improved.

[0092] exist Figure 7C In the diagram, the portion enclosed by the dashed box shows the impedance of the opposite frequency band before connecting the series arm resonator S1 and the parallel arm resonator P1, while the portion enclosed by the solid box shows the impedance of the opposite frequency band when the series arm resonator S1 and the parallel arm resonator P1 are connected. For example... Figure 7C As shown, by connecting a series arm resonator S1 and a parallel arm resonator P1 to a longitudinally coupled resonator M1, the impedance in the opposite frequency band rotates counterclockwise. It can be seen that the amount of counterclockwise rotation of the impedance in the opposite frequency band when both the series arm resonator S1 and the parallel arm resonator P1 are connected is less than when only the series arm resonator S1 is connected, but compared to when neither the series arm resonator S1 nor the parallel arm resonator P1 is connected, the impedance in the opposite frequency band is close to infinite.

[0093] In this way, in the longitudinally coupled resonator M1, where the impedance observed from the first input terminal 120 side at the high-frequency end of the passband of filter 1 is located in the first quadrant of the Smith chart and the impedance observed from the first input terminal 120 side at the low-frequency end of the passband of filter 1 is located in the fourth quadrant of the Smith chart, by connecting the series arm resonator S1 and the parallel arm resonator P1, it is possible to shift the impedance of filter 1 in the opposite frequency band, as observed from the first input terminal 120 side, toward infinity while maintaining the concentration of impedance.

[0094] [5. Comparison between the Example and the Comparative Example]

[0095] Next, the embodiments and comparative examples are compared to illustrate that the return loss characteristics of the multiplexer 100 with the filter 1 of the embodiments are improved compared with the comparative examples.

[0096] Figure 8A This is a Smith chart showing the impedance characteristics of the multiplexer 100 of an embodiment, viewed from the common terminal 110 side. Figure 8A In the middle, starting from top, is a Smith chart showing the impedance characteristics of the passbands of filter 1, filter 10, filter 20, and filter 30, as viewed from the common terminal 110 side of multiplexer 100. Figure 8A In the diagram, solid lines show the impedance characteristics in the embodiments, and dashed lines show the impedance characteristics in the comparative examples.

[0097] Figure 8B This is a coordinate graph showing the return loss characteristics of the multiplexer 100 of the embodiment, viewed from the common terminal 110 side. Figure 8B In the diagram, the solid line shows the return loss characteristics in the embodiment, and the dashed line shows the return loss characteristics in the comparative example.

[0098] exist Figure 8A and Figure 8B The characteristics of the multiplexer 100 during carrier aggregation are shown in the figure.

[0099] like Figure 8A As shown, in the passband of filter 1, the impedance of the multiplexer 100 in this embodiment is approximately 50Ω compared to the comparative example. Figure 4B As shown, considering the influence when connected with other filters, the impedance in the passband of filter 1 is greater than 50Ω. The impedance of the multiplexer 100 formed by connecting filter 1 with other filters can be around 50Ω in the passband of filter 1.

[0100] In addition, such as Figure 8B As shown, the minimum return loss in the passband (1.452-1.496 GHz) of filter 1 is approximately 6 dB in the comparative example, compared to approximately 10 dB in the embodiment, representing an improvement of about 4 dB. Furthermore, it is also observed that the minimum return loss in the passband (1.805-1.880 GHz) of filter 10 is also improved by approximately 1-2 dB.

[0101] Thus, in this embodiment, the total electrostatic capacitance of the input-side resonator of the longitudinally coupled resonator M1 is smaller than the total electrostatic capacitance of the output-side resonator. Therefore, return loss characteristics can be improved during carrier aggregation without adding matching elements. In other words, the matching performance of the antenna terminals can be improved without adding matching elements.

[0102] [6. Summary]

[0103] As described above, the filter 1 includes a first input terminal 120 and a first output terminal 130, and a longitudinally coupled resonator M1 connected between the first input terminal 120 and the first output terminal 130. The longitudinally coupled resonator M1 has one or more input-side resonators (e.g., resonators D2 and D4) connected to the first input terminal 120, and one or more output-side resonators (e.g., resonators D1, D3, and D5) connected to the first output terminal 130. The total electrostatic capacitance of the one or more input-side resonators is less than the total electrostatic capacitance of the one or more output-side resonators.

[0104] In other words, the filter 1 includes a first input terminal 120 and a first output terminal 130, and a longitudinally coupled resonator M1 connected between the first input terminal 120 and the first output terminal 130. The longitudinally coupled resonator M1 has one or more input-side resonators (e.g., resonators D2 and D4) connected to the first input terminal 120, and one or more output-side resonators (e.g., resonators D1, D3, and D5) connected to the first output terminal 130. The one or more input-side resonators and the one or more output-side resonators each have an IDT electrode composed of multiple electrode fingers. The sum of the product of the logarithm of the multiple electrode fingers of the IDT electrode of each of the one or more input-side resonators and the cross width is less than the sum of the product of the logarithm of the multiple electrode fingers of the IDT electrode of each of the one or more output-side resonators.

[0105] By designing the longitudinally coupled resonator M1 such that the total electrostatic capacitance of one or more input-side resonators is less than the total electrostatic capacitance of one or more output-side resonators, the impedance concentration observed from the first input terminal 120 of the filter 1 can be improved. In other words, by designing the longitudinally coupled resonator M1 such that the sum of the product of the logarithm of the multiple electrode fingers of each IDT electrode and the cross width of one or more input-side resonators is less than the sum of the product of the logarithm of the multiple electrode fingers of each IDT electrode and the cross width of one or more output-side resonators, the total electrostatic capacitance of one or more input-side resonators can be less than the total electrostatic capacitance of one or more output-side resonators, thereby improving the impedance concentration observed from the first input terminal 120 of the filter 1. Furthermore, since a smaller input-side electrostatic capacitance of the longitudinally coupled resonator M1 results in a larger input-side impedance, the impedance observed from the first input terminal 120 of the filter 1 can be increased. When filter 1 is connected to other filters (e.g., filters 10, 20, and 30) to form a multiplexer 100, the impedance characteristics of filter 1 are affected by the other filters. However, this effect is taken into account in filter 1, and the impedance of filter 1 before connecting to other filters is increased by reducing the electrostatic capacitance on the input side of the longitudinally coupled resonator M1. Therefore, when filter 1 is connected to other filters to form a multiplexer 100, impedance matching can be achieved using a matching circuit 50 with a small number of components.

[0106] For example, the capacitance of each of the input-side resonators can be less than the capacitance of any single output-side resonator among the more than one output-side resonators. In other words, the product of the logarithm of the multiple electrode fingers of the IDT electrodes of the more than one input-side resonators and the cross width can also be less than the product of the logarithm of the multiple electrode fingers of the IDT electrodes of any single output-side resonator among the more than one output-side resonators and the cross width.

[0107] Therefore, the total electrostatic capacitance of one or more input-side resonators can be further reduced to less than the total electrostatic capacitance of one or more output-side resonators. Consequently, the input impedance of the longitudinally coupled resonator M1 can be further increased.

[0108] For example, the impedance of the longitudinally coupled resonator M1 at the high-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, may be located in the first quadrant of the Smith chart, while the impedance of the longitudinally coupled resonator M1 at the low-frequency end of the passband of filter 1, as viewed from the first input terminal 120 side, may be located in the fourth quadrant of the Smith chart.

[0109] Therefore, while maintaining impedance concentration, the impedance of filter 1, as viewed from the first input terminal 120 side, in the passband of the other commonly connected filters can be shifted towards infinity. That is, the degradation of the pass characteristics of the other filters can be suppressed.

[0110] For example, the filter 1 may also include a series arm resonator S1 disposed on the path connecting the first input terminal 120 and the longitudinally coupled resonator M1, the resonant frequency of the series arm resonator S1 being located in the passband of the filter 1.

[0111] As a result, the impedance of filter 1, as viewed from the first input terminal 120 side, in the passband of other commonly connected filters can be shifted toward infinity.

[0112] For example, filter 1 may also include a parallel arm resonator P1 connected between node N and ground, where node N is a node on the path connecting the first input terminal 120 and the longitudinally coupled resonator M1, and the anti-resonance frequency of the parallel arm resonator P1 is located in the passband of filter 1.

[0113] This allows for an increase in impedance concentration.

[0114] In addition, the multiplexer 100 includes a common terminal 110, a filter 1, and one or more filters, each having an input terminal and an output terminal. The first input terminal 120 and the input or output terminals of the one or more filters are connected to the common terminal 110.

[0115] Therefore, a multiplexer 100 that can improve impedance concentration can be provided. In addition, impedance matching can be performed in the multiplexer 100 using a matching circuit 50 with a small number of components.

[0116] For example, the passband of filter 1 and more filters may also be included in the range of 1.4 GHz to 2.7 GHz. Alternatively, for example, multiplexer 100 may have filters 10, 20 and 30 as more than one filter, with filter 1 having a passband of 1.452 GHz to 1.496 GHz, filter 10 having a passband of 1.805 GHz to 1.880 GHz, filter 20 having a passband of 2.110 GHz to 2.170 GHz, and filter 30 having a passband of 2.620 GHz to 2.690 GHz.

[0117] (Other implementation methods)

[0118] The filter 1 (elastic wave filter) and multiplexer 100 of the embodiments of the present invention have been described above. However, other embodiments implemented by combining any of the constituent elements of the above embodiments, as well as various modifications that can be conceived by those skilled in the art to implement the above embodiments without departing from the spirit of the present invention, are also included in the present invention.

[0119] For example, the filter 1 and multiplexer 100 of the embodiments can be applied to high-frequency front-end circuits, and further to communication devices equipped with high-frequency front-end circuits. Various devices that incorporate high-frequency front-end circuits and communication devices incorporating the filter 1 or multiplexer 100 are also included in this invention.

[0120] For example, in the above embodiment, an example was described in which the electrostatic capacitance of each of the more than one input-side resonator is less than the electrostatic capacitance of any one of the more than one output-side resonators. However, among the more than one input-side resonators, there may also be resonators whose electrostatic capacitance is greater than the electrostatic capacitance of any one of the more than one output-side resonators.

[0121] For example, in the above embodiment, an example was described where the impedance of the longitudinally coupled resonator M1 at the high-frequency end of the passband of filter 1, viewed from the first input terminal 120 side, is located in the first quadrant on the Smith chart, but it may not be located in the first quadrant. Similarly, an example was described where the impedance of the longitudinally coupled resonator M1 at the low-frequency end of the passband of filter 1, viewed from the first input terminal 120 side, is located in the fourth quadrant on the Smith chart, but it may not be located in the fourth quadrant.

[0122] For example, in the above embodiment, an example of filter 1 having a series arm resonator S1 was described, but it may also not have a series arm resonator S1.

[0123] For example, in the above embodiment, an example of filter 1 having a parallel arm resonator P1 is described, but it may also not have a parallel arm resonator P1.

[0124] Industrial availability

[0125] This invention, as an elastic wave filter and multiplexer applicable to multi-band systems, can be widely used in communication devices such as portable telephones.

[0126] Explanation of reference numerals in the attached figures

[0127] 1, 10, 20, 30 filters;

[0128] 50 matching circuit;

[0129] More than 100 tools;

[0130] 110 common terminal;

[0131] 120 First Input Terminal;

[0132] 130 First Output Terminal;

[0133] ANT antenna elements;

[0134] D1, D2, D3, D4, D5 resonators;

[0135] M1 longitudinally coupled resonator;

[0136] P1 parallel arm resonator;

[0137] S1 series arm resonator.

Claims

1. An elastic wave filter, comprising: The first input terminal and the first output terminal; and A longitudinally coupled resonator is connected between the first input terminal and the first output terminal. The longitudinally coupled resonator has one or more input-side resonators connected to the first input terminal and one or more output-side resonators connected to the first output terminal. The total electrostatic capacitance of the one or more input-side resonators is less than the total electrostatic capacitance of the one or more output-side resonators. The impedance of the longitudinally coupled resonator at the high-frequency end of the passband of the elastic wave filter, as viewed from the first input terminal side, is located in the first quadrant of the Smith chart. The impedance of the longitudinally coupled resonator at the low-frequency end of the passband of the elastic wave filter, as viewed from the first input terminal side, is located in the fourth quadrant on the Smith chart.

2. The elastic wave filter according to claim 1, wherein, The electrostatic capacitance of each of the more than one input-side resonators is less than the electrostatic capacitance of any one of the more than one output-side resonators.

3. The elastic wave filter according to claim 1 or 2, wherein, The elastic wave filter also includes a series arm resonator disposed on the path connecting the first input terminal and the longitudinally coupled resonator. The resonant frequency of the series arm resonator is located in the passband of the elastic wave filter.

4. The elastic wave filter according to claim 1 or 2, wherein, The elastic wave filter also includes a parallel arm resonator connected between the node and ground, the node being a node on the path connecting the first input terminal and the longitudinally coupled resonator. The anti-resonance frequency of the parallel arm resonator is located in the passband of the elastic wave filter.

5. An elastic wave filter, comprising: The first input terminal and the first output terminal; and A longitudinally coupled resonator is connected between the first input terminal and the first output terminal. The longitudinally coupled resonator has one or more input-side resonators connected to the first input terminal and one or more output-side resonators connected to the first output terminal. The one or more input-side resonators and the one or more output-side resonators each have interdigitated transducer (IDT) electrodes composed of multiple electrode fingers. The sum of the product of the logarithms of the multiple electrode fingers of the IDT electrodes of the more than one input-side resonator and the cross width is less than the sum of the product of the logarithms of the multiple electrode fingers of the IDT electrodes of the more than one output-side resonator. The impedance of the longitudinally coupled resonator at the high-frequency end of the passband of the elastic wave filter, as viewed from the first input terminal side, is located in the first quadrant of the Smith chart. The impedance of the longitudinally coupled resonator at the low-frequency end of the passband of the elastic wave filter, as viewed from the first input terminal side, is located in the fourth quadrant on the Smith chart.

6. The elastic wave filter according to claim 5, wherein, The product of the logarithm of the multiple electrode fingers of the IDT electrodes of the more than one input-side resonator and the cross width is less than the product of the logarithm of the multiple electrode fingers of the IDT electrodes of any one of the more than one output-side resonators.

7. The elastic wave filter according to claim 5 or 6, wherein, The elastic wave filter also includes a series arm resonator disposed on the path connecting the first input terminal and the longitudinally coupled resonator. The resonant frequency of the series arm resonator is located in the passband of the elastic wave filter.

8. The elastic wave filter according to claim 5 or 6, wherein, The elastic wave filter also includes a parallel arm resonator connected between the node and ground, the node being a node on the path connecting the first input terminal and the longitudinally coupled resonator. The anti-resonance frequency of the parallel arm resonator is located in the passband of the elastic wave filter.

9. A multiplexer, comprising: Common terminal; The elastic wave filter according to any one of claims 1 to 8; One or more filters, each with input and output terminals. The first input terminal and the respective input or output terminals of the one or more filters are connected to the common terminal.

10. The multiplexer according to claim 9, wherein, The passband of each of the elastic wave filter and the one or more filters is contained in the range of 1.4 GHz to 2.7 GHz.

11. The multiplexer according to claim 10, wherein, The multiplexer includes a first filter, a second filter, and a third filter as one or more filters. The passband of the elastic wave filter is 1.452 GHz to 1.496 GHz. The passband of the first filter is 1.805 GHz to 1.880 GHz. The passband of the second filter is 2.110 GHz to 2.170 GHz. The passband of the third filter is 2.620 GHz to 2.690 GHz.

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