JP2008283425A - Longitudinally coupled multi-mode resonator type surface acoustic wave filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve phase balance by miniaturizing a longitudinally coupled multi-mode resonator type SAW filter having a balance terminal. <P>SOLUTION: The longitudinally coupled multi-mode filter includes a plurality of IDTs arrayed in a propagation direction of a surface acoustic wave, a first signal terminal being a balance or unbalance terminal, and second signal terminals being balance terminals. The plurality of IDTs include a first IDT group, a second IDT group, and a center IDT which is disposed between both IDT groups and acoustically couples them, wherein one or more IDTs in the first IDT group and one or more IDTs in the second IDT group are connected to the first signal terminal, and one or more IDTs in the first IDT group and one or more IDTs in the second IDT group are connected to the second signal terminals, and the center IDT is divided into two, and these divided IDT parts are each connected to one of the second signal terminals and the other. One of a pair of comb-like electrodes constituting each of two IDT parts of the center IDT is connected to the second signal terminals, and the other is a floating electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a longitudinally coupled multimode resonator type surface acoustic wave filter, and more particularly to a technique for improving the phase balance of the surface acoustic wave filter having a balanced signal terminal.

  Surface acoustic wave filters (hereinafter referred to as SAW filters) using surface acoustic waves (SAW) generated by the piezoelectric effect are small, light and excellent in reliability. Therefore, transmission / reception filters and antennas for mobile communication devices are used. Widely used in duplexers today. Such SAW filters generally have a plurality of interdigitated electrodes (Interdigital Transducer / hereinafter referred to as IDT) for exciting surface acoustic waves formed on a piezoelectric substrate, and these IDTs are electrically or acoustically formed. It is comprised by connecting to.

  As the IDT connection structure, for example, a ladder type structure in which a plurality of IDTs are connected in a ladder shape, or a longitudinally coupled resonator type structure in which a plurality of IDTs are arranged in a propagation path of a surface acoustic wave and are acoustically coupled. As is known, the longitudinally coupled resonator type structure has an advantage that it can easily realize a balanced output that is generally excellent in attenuation characteristics in a wide band and excellent in noise resistance as compared with a ladder type structure.

  In order to obtain a balanced output, for example, two longitudinally coupled resonator multimode filters are electrically connected in parallel between the input and output terminals, and these two longitudinally coupled resonator multimode filters are propagated by surface acoustic wave propagation. The structure which arranges in a direction and couple | bonds acoustically is known (for example, refer the following nonpatent literature 1 and patent documents 1-4).

2004 IEEE Ultrasonics Symposium Proceeding, pages 294-297 “DMS Filter with Reduced Resistive Losses” (page 297, Fig. 7) WO2005 / 107065 JP 2004-304513 A JP 2006-186433 A JP 2004-096244 A

  By the way, since the longitudinally coupled resonator multimode filter having a balanced terminal has a configuration in which two filters are arranged, the size of the device has to be increased correspondingly, and thus further downsizing can be achieved. Desired. At the same time, it is required that the phase balance of the output signal is good as a filter characteristic.

  However, in the conventional filter structure, various methods for reducing the device size have been proposed as described in the above document, but at the same time, sufficient proposals have not been made for means for improving the phase balance.

  Specifically, in Non-Patent Document 1 (2004 IEEE Ultrasonics Symposium Proceeding), when two 3-IDT type multimode filters are connected in parallel, one of the reflectors is removed and acoustically coupled. Although it has been shown that the filter can be miniaturized and that balanced output and impedance conversion are possible, no method for improving the filter characteristics is described.

On the other hand, in Patent Document 1 (WO2005 / 107065), in a multi-mode structure in which a plurality of IDTs are arranged, characteristics can be improved by grounding the floating bus bar SS1 with a connection electrode via an electrode finger. . However, although a characteristic comparison is performed using a balanced output multimode filter having three IDTs as a conventional example, the effect of improving the phase balance due to the use of connection electrodes has not been clarified. Further, in an actual device, as shown in FIG. 19, a parasitic component is interposed from the bump 61 to the grounding electrode 62, which is not ideal grounding. It is difficult to obtain a sufficient effect only by connecting to the electrode 63. Furthermore, even if the configuration shown in FIG. 20 is adopted for miniaturization, there are not a few parasitic components. The structure shown in FIG. 20 has a non-piezoelectric material 66 (for example, a non-piezoelectric material for forming a sealing resin, another substrate / film, or a boundary acoustic wave filter) on the surface of the piezoelectric substrate 51 on which the IDT 53 is formed. A material (for example, SiO ₂ or Si) is disposed, and a bump 61 is provided on the upper surface of the non-piezoelectric material, and the bump 61 and the IDT 53 are electrically connected via a via 65 penetrating the non-piezoelectric material 52. It is a thing.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-304513) discloses a structure in which two multimode filters are arranged in parallel, and the filter is reduced in size by taking out a grounding wiring and a grounding pad from one side. Further, when connecting in parallel, a single reflector is provided between them to further reduce the size. However, this document only achieves balancing and miniaturization, and does not enable improvement of characteristics.

  Further, Patent Document 3 (Japanese Patent Laid-Open No. 2006-186433) provides a common reflector when two multi-mode filters are connected in parallel, and reduces the characteristic deterioration by adjusting the number and pitch of the reflectors. It is not related to a filter having a balanced terminal, although it is reduced in size while being suppressed.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-096244) is intended to improve the phase balance, but adds a reactance component to the balanced signal terminal to equalize the reactance generated at each terminal. It is necessary to add a lead line from the balanced terminal separately, and it has not been shown that an improvement effect is obtained by the configuration of the filter itself.

  Accordingly, an object of the present invention is to provide a new filter structure that can simultaneously realize downsizing and improvement in the degree of phase balance in a longitudinally coupled multimode resonator type SAW filter having a balanced terminal.

  In order to solve the above problems and achieve the object, a longitudinally coupled multimode resonator type SAW filter according to the present invention includes a plurality of IDTs (intersecting finger electrodes) arranged in a propagation direction of a surface acoustic wave on a piezoelectric substrate. A longitudinally coupled multimode resonator type SAW filter having a pair of reflectors arranged on both sides of these IDTs, a first signal terminal that is a balanced terminal or an unbalanced terminal, and a second signal terminal that is a balanced terminal. The plurality of IDTs are arranged in order in the propagation direction of the surface acoustic wave, and a first interdigital electrode group (first IDT group) composed of a plurality of IDTs arranged in order in the propagation direction of the surface acoustic wave. A second interdigitated electrode group (second IDT group) comprising a plurality of IDTs and a central interdigitated electrode disposed between the first IDT group and the second IDT group to acoustically couple both IDT groups (Central IDT) One or more IDTs in the first IDT group and one or more IDTs in the second IDT group are connected to the first signal terminal, and one or more IDTs in the first IDT group are connected. Is connected to one terminal of the second signal terminal which is the balanced terminal, one or more IDTs of the second IDT group are connected to the other terminal of the second signal terminal, and the central IDT is Dividing into two substantially symmetrically so that two intersecting finger electrode portions are arranged in the propagation direction of the surface acoustic wave, one of the divided IDT portions is connected to one of the second signal terminals. The other IDT part is connected to the other terminal of the second signal terminal.

  The longitudinally coupled multimode resonator type surface acoustic wave filter according to the present invention has an IDT arrangement and connection structure in order to obtain a filter configuration that can improve the phase balance of the filter without increasing the overall size of the filter. As a result of various examinations, an IDT is provided between the first IDT group and the second IDT group, each of which is arranged in the propagation direction of the surface acoustic wave as described above, and this IDT is provided. Both IDT groups are acoustically coupled by (central IDT). The central IDT is divided into two substantially symmetrically so that two crossed finger electrode portions (IDT portions) are arranged in the propagation direction of the surface acoustic wave, and each of the divided IDT portions is a second signal that is a balanced terminal. The terminal is connected to one terminal and the other terminal. Thereby, the degree of phase balance is improved. The first signal terminal to which one or more IDTs of the first IDT group and the second IDT group are connected can be either a balanced terminal or an unbalanced terminal, and both ends (both sides) of the filter. ) Is provided with a reflector.

  Further, it has been found that in order to obtain a better phase balance improvement effect, it is preferable to add one or more of the following configurations (1) to (6) to the filter configuration. A specific effect of improving the phase balance will be described in the following description of the embodiment.

(1) The two IDT portions included in the central IDT both connect one comb-shaped electrode of the pair of comb-shaped electrodes constituting them to the second signal terminal, and the other comb-shaped electrode is in an electrically open state. To do. Note that the open state means that the other comb-shaped electrode is a floating electrode that is electrically floating.
(2) The two IDT parts included in the central IDT have the same number of electrode pairs and different electrode finger pitches.
(3) The two IDT portions included in the central IDT are different from each other in the number of electrode pairs.
(4) In (3), the electrode finger pitch of the IDT portion with the larger number of electrode pairs is made smaller than the electrode finger pitch of the IDT portion with the smaller number of electrode pairs.
(5) Two interdigitated electrodes in which the total number of electrode pairs of the central interdigitated electrode and the two interdigitated electrodes arranged adjacent to both sides thereof are arranged adjacent to each of the reflectors More than the total number of electrode pairs.
(6) The first IDT group and the second IDT group are each provided with two or more IDTs.

  Furthermore, in the filter of the present invention, a reflector may be provided between the two IDT portions of the central IDT. Further, the first signal terminal is an unbalanced terminal, and the connection point between one or more IDTs in the first IDT group and one or more IDTs in the second IDT group and the first signal terminal, A surface acoustic wave resonator may be further connected in series. Further, the first signal terminal is an unbalanced terminal, and one or more IDTs in the first IDT group and the first signal terminal, and one or more IDTs in the second IDT group and the first signal terminal. A surface acoustic wave resonator may be further connected in series with each other.

  In addition, one or more IDTs in the first IDT group, one or more IDTs in the second IDT group, and a connection point between one of the two IDT portions of the central IDT, and one of the second signal terminals A surface acoustic wave resonator is further connected in series with the terminal, and two IDT portions of one or more IDTs in the first IDT group, one or more IDTs in the second IDT group, and a central IDT A surface acoustic wave resonator may be further connected in series between the connection point with the other of the two and the other terminal of the second signal terminal.

  The filter configuration described above can be applied not only to a surface acoustic wave filter but also to a boundary acoustic wave filter.

  Specifically, the boundary acoustic wave filter includes a piezoelectric substrate, a non-piezoelectric material (for example, a non-piezoelectric substrate or a non-piezoelectric film) disposed in contact with the piezoelectric substrate, and a boundary surface between the piezoelectric substrate and the non-piezoelectric material. A plurality of IDTs arranged in the propagation direction of the boundary acoustic wave, a pair of reflectors arranged on both sides of these IDTs, a first signal terminal that is a balanced terminal or an unbalanced terminal, and a second that is a balanced terminal A longitudinally coupled multimode resonator type boundary acoustic wave filter having a signal terminal, wherein the plurality of IDTs are composed of a plurality of IDTs arranged in order in the propagation direction of the boundary acoustic wave; A second IDT group consisting of a plurality of IDTs arranged in order in the propagation direction of the first IDT group, and a central IDT arranged between the first IDT group and the second IDT group to acoustically couple both IDT groups, 1 of the first IDT group The upper IDT and one or more IDTs in the second IDT group are connected to the first signal terminal, and one or more IDTs in the first IDT group are connected to the balanced terminal as a second signal. One of the terminals, one or more IDTs of the second IDT group are connected to the other terminal of the second signal terminal, and the central IDT is connected to two boundary acoustic wave propagation directions. Dividing into two substantially symmetrically so that the interdigitated electrode portions are arranged, one of the divided IDT portions is connected to one terminal of the second signal terminal, and the other IDT portion Is connected to the other terminal of the second signal terminal.

  Further, in this boundary acoustic wave filter, similarly, adding one or more of the components (1) to (6) described for the boundary acoustic wave filter provides a better effect of improving the phase balance. Is preferable. Similarly to the surface acoustic wave filter, boundary acoustic wave resonators may be appropriately connected to the first signal terminal side and the second signal terminal side.

  According to the present invention, it is possible to obtain a new filter structure that can simultaneously achieve downsizing and improvement in the degree of phase balance in a longitudinally coupled multimode resonator type SAW (or boundary acoustic wave) filter having a balanced terminal.

  Other objects, features, and advantages of the present invention will become apparent from the following description of embodiments of the present invention described with reference to the drawings. In addition, in each figure, the same code | symbol shows the same or an equivalent part.

Embodiment 1
FIG. 1 is a schematic diagram showing a longitudinally coupled multimode resonator type SAW (surface acoustic wave) filter according to a first embodiment of the present invention. As shown in the figure, this SAW filter is provided at the center of a longitudinally coupled multimode resonator type SAW filter having six IDTs 21 to 26 arranged in the propagation direction of the surface acoustic wave on the piezoelectric substrate (more specifically, (Between the first IDT group 11 consisting of three IDTs 21, 22, and 23 arranged on the left side and the second IDT group 12 consisting of three IDTs 24, 25, and 26 arranged on the right side) One IDT (center IDT) 27 is inserted.

  The IDTs 22 and 25 located in the center in the first IDT group 11 and the second IDT group 12 are respectively connected to the input terminal 1 which is an unbalanced terminal. On the other hand, the IDTs 21 and 23 at both left and right ends in the first IDT group 11 are connected to one terminal 2a of the output terminal 2 which is a balanced terminal, and the IDTs 24 and 26 at both left and right ends in the second IDT group 12 are balanced output. Each of the terminals 2 is connected to the other terminal 2b.

  Here, for each IDT, the output phases taken out from the IDTs 21 and 23 at the left and right ends of the first IDT group 11 and the output phases taken out from the IDTs 24 and 26 at the left and right ends of the second IDT group 12 are almost 180 ° different. Thus, a balanced output signal is obtained from the output terminal 2. Specifically, the IDT 22 and the IDT 25 are rotationally symmetric in the plane (in the piezoelectric substrate surface) with respect to the center line YY ′ (see FIG. 1) perpendicular to the propagation direction of the surface acoustic wave. The IDTs 21 and 23 and the IDTs 24 and 26 are arranged so as to be mirror-symmetric.

  Each of the IDTs 21 to 26 constituting the first IDT group 11 and the second IDT group 12 includes a pair of comb-shaped electrodes inserted so as to mesh with each other. Of these, both the input terminal 1 and the output terminal 2 Each comb electrode on the unconnected side is connected to the ground potential. A pair of reflectors 10 is provided on both sides of the IDTs 21 to 26 arranged as described above. Note that each comb electrode on the side not connected to either the input terminal 1 or the output terminal 2 is connected to the ground potential by connecting wirings formed on the piezoelectric substrate, connecting bumps, and the base substrate and the base substrate. This is done through internal wiring.

  The central IDT 27 is composed of two electrode portions 27a and 27b obtained by dividing one IDT so as to be arranged in the propagation direction of the surface acoustic wave and electrically connecting them in series. Makes the output phase of the electrode part 27a substantially equal to the output phase of the IDT 21 and IDT 23 included in the first IDT group 11, while making the output phase of the electrode part 27b substantially equal to the IDT 24 and IDT 26 included in the second IDT group. Thus, the output phases of the electrode part 27a and the electrode part 27b are made to differ from each other by approximately 180 °.

  The electrode portions 27a and 27b are composed of a pair of comb-shaped electrodes inserted so as to mesh with each other like the other IDTs 21 to 26, and one of the comb-shaped electrodes 27d and 27e includes the left electrode portion 27a. The (comb electrode 27d) is connected to one terminal 2a of the balanced output terminal 2, and the right electrode portion 27b (comb electrode 27e) is connected to the other terminal 2b of the balanced output terminal 2. The other comb-shaped electrode 27c of each electrode portion not connected to the output terminal 2 is a floating electrode without being grounded.

  In the present embodiment, as described above, the IDT 22 and IDT 25 are rotationally symmetric in the plane and the IDTs 21, 23 and IDTs 24 and 26 are mirror symmetric with respect to the center line YY ′. Conversely, IDT 22 and IDT 25 may be arranged to be mirror-symmetric, and IDTs 21 and 23 and IDT 24 and 26 may be arranged to be rotationally symmetric, or a balanced signal may be extracted from output terminal 2 by other arrangements. good. Also in this case, the output phase of the electrode portion 27a of the central IDT and the output phases of the IDTs 21 and 23 are made substantially equal, and the output phase of the 27b and the output phases of the IDTs 24 and 26 are made substantially the same.

  Each of the IDTs 21 to 27 and the reflector 10 has a base film made of TiN having a thickness of, for example, 4 nm on the surface of a 46 ° Y-cut X-propagating LiTaO 3 substrate, and an Al single crystal film is formed thereon, for example. Each electrode pattern is formed by forming a film with a thickness of 170 nm. A large number of these electrode patterns are simultaneously formed on the piezoelectric substrate and divided by dicing to form individual filter chips. The filter formed into a chip is mounted on a ceramic base substrate by flip chip bonding, and this is sealed with a resin. The system of the present embodiment assumes a PCS reception filter, and the passband is from 1930 MHz to 1990 MHz.

  The specification of each part of the filter according to the present embodiment can be as follows, for example. Of the numerical values below, the underlined ones relate to the central IDT (the left electrode part 27a and the right electrode part 27b). In this embodiment, the left electrode part 27a and the right electrode part of the central IDT used as a floating electrode are used. The electrode part 27b has the same number of electrode pairs, but the electrode period is different. Further, as shown in FIG. 16A, the IDT is composed of a pair of comb electrodes 8a and 8b facing each other. In this specification, the electrode finger pitch of the IDT is the intersection of the comb electrodes 8a and 8b. This is the distance p1 between the centers of the electrode fingers in contact with each other, and twice this electrode finger pitch p1 is the electrode period λ1 of the IDT. On the other hand, as shown in FIG. 16B, the electrode finger pitch of the reflector means a distance p2 between adjacent electrode centers of the reflector 10, and twice this electrode finger pitch p2 is the electrode period of the reflector. λ2.

IDT electrode pairs: (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (17.5 pair, 41.0 pair, 14.5 pair, 3 pair , 3 Pair , 14.5 pair, 41.0 pair, 17.5 pair)
IDT electrode period (twice the electrode finger pitch): (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (2.012 μm, 2.036 μm, 2.012 μm) , 2.017 μm , 2.007 μm , 2.012 μm , 2.036 μm, 2.012 μm)
・ Number of reflector electrodes: 55 ・ Reflector electrode period (twice the electrode finger pitch): 2.013 μm
・ Distance between IDT and reflector: 0.5 × (2.012 + 2.013) / 2 μm
・ Distance between IDT23 and left electrode part 27a: 0.5 × (2.012 + 2.017) / 2 μm
-Distance between right electrode part 27b and IDT 24: 0.5 × (2.007 + 2.012) / 2 μm
Electrode finger duty factor (ratio of electrode line width to electrode finger pitch): 0.60

  17 and 18 show an example of a conventional longitudinally coupled multimode resonator type SAW filter (hereinafter referred to as a first conventional example) and another example (hereinafter referred to as a second conventional example) as a comparison with the present embodiment. Is shown. As shown in FIG. 17, the filter of the first conventional example is a 6-IDT type longitudinally coupled multiple mode having six IDTs 51 to 56 arranged in a propagation direction of a surface acoustic wave between a pair of reflectors 10. In the type SAW filter, two IDTs 53 and 54 located in the center are floating electrodes without being grounded. Further, the filter of the second conventional example is a 6-IDT type longitudinally coupled multimode type SAW filter in which six IDTs 51 to 56 are similarly arranged as shown in FIG. 18, but two IDTs 53 and 54 located at the center are used. Is grounded.

  FIG. 2 is a diagram showing the results of measuring the phase balance of each filter according to the first and second conventional examples and the present embodiment. In the figure, the first conventional example is indicated by a one-dot chain line, the second conventional example is indicated by a broken line, and the present embodiment is indicated by a solid line. When the phase difference between the balanced output terminals 2a and 2b differs by 180 °, Is represented as 0 ° (the following diagram: the same applies to FIGS. 3 to 9). As is clear from this result, in the first conventional example (configuration shown in FIG. 17), the maximum value of the phase balance within the pass band (1930 to 1990 MHz) is 4.8 °, the minimum value is −1.7 °, and the variation is The amount (the difference between the maximum value and the minimum value of the phase balance within the passband) is 6.5 °, and in the second conventional example (configuration of FIG. 18), the maximum value of the phase balance within the passband is In contrast to the 2.9 °, the minimum value of −0.6 °, and the fluctuation amount of 3.5 °, in this embodiment, the maximum value of the phase balance within the passband is 2.9 ° and the minimum value is 0. It can be seen that the phase balance can be improved as compared with the first conventional example according to the filter of this embodiment. Compared with the second conventional example, the maximum value of the phase balance is not changed, but the fluctuation amount in the passband is small, and an improvement effect is obtained.

  FIG. 3 shows the attenuation characteristics. As can be seen from FIG. 3, even when the filter structure of the present embodiment is adopted, the characteristics of the insertion loss and the out-of-band characteristics are degraded as compared with the conventional filter. There is no cause.

  FIG. 4 shows a modification of the SAW filter according to the present embodiment. As shown in this figure, in the filter of the present embodiment, in contrast to the connection example shown in FIG. 1, IDTs 21 and 23 and IDTs 24 and 26 located at both left and right ends in the first IDT group and the second IDT group, respectively. Are connected to the input terminal 1 which is an unbalanced terminal, while the IDTs 22 and 25 located in the center in the first IDT group and the second IDT group are respectively connected to the output terminals 2a and 2b which are balanced terminals. good. One electrode part 27a of the central IDT is connected to one terminal 2a of the output terminal, and the other electrode part 27b of the central IDT is connected to the other terminal 2b of the output terminal.

[Embodiment 2]
The longitudinally coupled multimode resonator type SAW filter according to the second embodiment of the present invention has a pair of reflectors 10 along the propagation direction of the surface acoustic wave, like the filter of the first embodiment (FIG. 1). Seven IDTs 21 to 27 including the central IDT 27 are arranged between them, and the central IDT 27 is divided into two electrode parts 27a and 27b. However, the specifications of each part of the filter are different from those of the first embodiment. Specifically, as described below, the number of pairs of the left electrode portion 27a of the central IDT 27 is 2 pairs, and the number of pairs of the right electrode portion 27b is 4 pairs. The electrode period of both electrode portions 27a and 27b is the same as that in the first embodiment.

IDT electrode pairs: (IDT21, IDT22, IDT23, left electrode portion 27a, right electrode portion 27b, IDT24, IDT25, IDT26) = (17.5 pairs, 41.0 pairs, 14.5 pairs, 2 pairs , 4 Pair , 14.5 pair, 41.0 pair, 17.5 pair)
Electrode period (twice the electrode finger pitch): (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (2.012 μm, 2.036 μm, 2.012 μm, 2 .17 μm , 2.007 μm , 2.012 μm , 2.036 μm, 2.012 μm)
・ Number of reflector electrodes: 55 ・ Reflector electrode period (twice the electrode finger pitch): 2.013 μm
・ Distance between IDT and reflector: 0.5 × (2.012 + 2.013) / 2 μm
・ Distance between IDT23 and left electrode part 27a: 0.5 × (2.017 + 2.012) / 2 μm
-Distance between right electrode part 27b and IDT 24: 0.5 × (2.007 + 2.012) / 2 μm
・ Electrode finger duty factor: 0.60

  FIG. 5 shows the results of measuring the phase balance of each filter of the first conventional example, the second conventional example, and this embodiment, as in FIG. As is clear from this result, in the filter of the present embodiment, the maximum value of the phase balance within the pass band (1930 to 1990 MHz) is 2.9 °, the minimum value is 0.7 °, and the variation is 2.2 °. Also in this embodiment, the degree of phase balance in the passband can be improved as compared with the conventional example as in the above embodiment.

[Embodiment 3]
The longitudinally coupled multimode resonator type SAW filter according to the third embodiment of the present invention includes six IDTs and a central IDT as in the above-described embodiment (FIG. 1). The distance between the left electrode portion 27a and the IDT 23 adjacent to the left electrode portion 27a is different from that in each of the embodiments. Specifically, it is as follows.

IDT electrode pairs: (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (17.5 pair, 41.0 pair, 14.5 pair, 3 pair , 3 Pair , 14.5 pair, 41.0 pair, 17.5 pair)
Electrode period (twice the electrode finger pitch): (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (2.012 μm, 2.036 μm, 2.012 μm, 2 .012 μm , 2.012 μm , 2.012 μm , 2.036 μm, 2.012 μm)
・ Number of reflector electrodes: 55 ・ Reflector electrode period (twice the electrode finger pitch): 2.013 μm
・ Distance between IDT and reflector: 0.5 × (2.013 + 2.012) / 2 μm
・ Distance between IDT23 and left electrode part 27a: 0.508 × (2.012 + 2.012) / 2 μm
-Distance between right electrode part 27b and IDT 24: 0.5 × (2.012 + 2.012) / 2 μm
・ Electrode finger duty factor: 0.60

  FIG. 6 shows the results of measuring the phase balance of each filter of the first conventional example, the second conventional example, and this embodiment. As is clear from this figure, in the filter of the present embodiment, the maximum value of the phase balance within the passband (1930 to 1990 MHz) is 2.9 °, the minimum value is 0.4 °, and the variation is 2.5 °. Also in this embodiment, the degree of phase balance in the passband can be improved as compared with the conventional example as in the above embodiment.

[Embodiment 4]
The longitudinally coupled multimode resonator type SAW filter according to the fourth embodiment of the present invention includes six IDTs and a central IDT as in the above-described embodiment (FIG. 1). The electrode finger pitch was varied between the left electrode part 27a and the right electrode part 27b. Further, in the first to third embodiments, the total number of electrode pairs of IDT 21 and IDT 26 and the total number of electrode pairs of IDT 23, IDT 24, and IDT 27 are matched (log total: 35 pairs). Then, the latter (total logarithm of IDT23, IDT24, and IDT27) is made larger. Specifically, it is as follows.

IDT electrode pairs: (IDT21, IDT22, IDT23, left electrode portion 27a, right electrode portion 27b, IDT24, IDT25, IDT26) = (17.5 pairs, 41.0 pairs, 17.5 pairs, 2 pairs , 2 Pair , 17.5 pair, 41.0 pair, 17.5 pair)
Electrode period (twice the electrode finger pitch): (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (2.012 μm, 2.036 μm, 2.012 μm, 2 .042 μm , 2.032 μm , 2.012 μm , 2.036 μm, 2.012 μm)
・ Number of reflector electrodes: 55 ・ Reflector electrode period (twice the electrode finger pitch): 2.013 μm
・ Distance between IDT and reflector: 0.5 × (2.012 + 2.013) / 2 μm
-Distance between IDT 23 and left electrode portion 27a: 0.5 × (2.012 + 2.042) / 2 μm
-Distance between right electrode part 27b and IDT 24: 0.5 × (2.032 + 2.012) / 2 μm
・ Electrode finger duty factor: 0.60

  FIG. 7 shows the result of measuring the phase balance of each filter of the first conventional example, the second conventional example, and this embodiment, and FIG. 8 shows the attenuation characteristics. As is clear from these figures, in the filter of the present embodiment, the maximum value of the phase balance within the pass band (1930 to 1990 MHz) is 2.7 °, the minimum value is −0.2 °, and the variation is 2.9. In this embodiment, the degree of phase balance can be improved without affecting the characteristics in the passband.

[Embodiment 5]
The longitudinally coupled multimode resonator type SAW filter according to the fifth embodiment of the present invention includes six IDTs and a central IDT as in the above embodiment (FIG. 1). The distance between the right electrode portion 27b and the IDT 24 adjacent to the right electrode portion 27b and the distance between the electrode portions 27a and 27b of the central IDT 27 were varied. Similarly to the fourth embodiment, the number of electrode pairs of IDT at both ends of each IDT group 11 and 12 is made equal, and the total number of electrode pairs of IDT23, IDT24 and IDT27 is greater than the total number of electrode pairs of IDT21 and IDT26. Was made larger. Specifically, it is as follows.

IDT electrode pairs: (IDT21, IDT22, IDT23, left electrode portion 27a, right electrode portion 27b, IDT24, IDT25, IDT26) = (17.5 pairs, 41.0 pairs, 17.5 pairs, 2 pairs , 2 Pair , 17.5 pair, 41.0 pair, 17.5 pair)
IDT electrode period (twice the electrode pitch): (IDT21, IDT22, IDT23, left electrode part 27a, right electrode part 27b, IDT24, IDT25, IDT26) = (2.012 μm, 2.036 μm, 2.012 μm, (2.012 μm , 2.012 μm , 2.012 μm , 2.036 μm, 2.012 μm)
・ Number of reflector electrodes: 55 ・ Reflector electrode period (twice the electrode pitch): 2.013 μm
・ Distance between IDT and reflector: 0.5 × (2.012 + 2.013) / 2 μm
・ Distance between IDT23 and left electrode part 27a: 0.5 × (2.012 + 2.012) / 2 μm
-Distance between right electrode portion 27b and IDT 24: 0.488 × (2.012 + 2.012) / 2 μm
-Distance between left electrode portion 27a and right electrode portion 27b: 0.55 × (2.012 + 2.012) / 2 μm
・ Electrode finger duty factor: 0.60

  FIG. 9 shows the results of measuring the phase balance of each filter of the first conventional example, the second conventional example, and this embodiment, and FIG. 10 shows the attenuation characteristics. As is clear from these figures, in the filter of the present embodiment, the maximum value of the phase balance within the passband (1930 to 1990 MHz) is 2.8 °, the minimum value is 0.4 °, and the fluctuation amount is 2.4 °. Thus, this embodiment can also improve the degree of phase balance without affecting the characteristics in the passband.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these, It is clear to those skilled in the art that a various change can be made within the range as described in a claim. .

  For example, in the above embodiment, the other comb electrode of the left and right electrode portions of the central IDT is a floating electrode, but it may be grounded (connected to the ground potential). The number of IDTs is 6 in total, excluding the central IDT, but may be other numbers, for example, 7 or more. Further, the pass band of the filter is only an example in the embodiment, and filters having various band frequencies other than this can be configured based on the present invention. Furthermore, in the above-described embodiment, the input side is an unbalanced terminal and the output side is a balanced terminal. Conversely, the input side can be a balanced terminal and the output side can be an unbalanced terminal. It can also be a balanced terminal. Further, as shown in FIG. 11, a reflector 27r may be provided between the left electrode portion 27a and the right electrode portion 27b of the central IDT 27. In this case, it is desirable that the reflector 27r has a number of electrodes that does not hinder the acoustic coupling of the left and right IDT electrode portions 27a and 27b.

  In the longitudinally coupled resonator multimode type SAW filter according to the present invention or the embodiment, one or more SAW resonators may be further connected. For example, as shown in FIG. 12, in the filter of the embodiment (FIG. 1), the connection point 3 between the IDT 22 in the first IDT group 11 and the IDT 25 in the second IDT group 12 and the unbalanced input terminal 1 A SAW resonator 101 can be inserted (connected in series) between them. This SAW resonator 101 includes reflectors 102 on both sides of an IDT 103. Further, as shown in FIG. 13, SAW resonance occurs between the IDT 22 in the first IDT group 11 and the unbalanced input terminal 1 and between the IDT 25 in the second IDT group 12 and the unbalanced input terminal 1. The children 110 and 111 may be inserted.

  Further, as shown in FIG. 14, the SAW resonator 201 is connected between the connection point 4a of the IDTs 21 and 23 on the left and right sides of the first IDT group and the left electrode portion 27a of the central IDT and one terminal 2a of the balanced output terminal. And the SAW resonator 301 is inserted between the connection point 4b of the IDTs 24 and 26 on the left and right sides of the second IDT group and the right electrode portion 27b of the central IDT and the other terminal 2b of the balanced output terminal. May be.

The present invention is not limited to a surface acoustic wave filter, and as shown in FIG. 15, a piezoelectric substrate (for example, a substrate made of LiTaO ₃ , LiNbO _3, etc.) 51 and a non-piezoelectric material (for example, a film or substrate made of SiO ₂ , Si, etc.) The present invention can be similarly applied to a boundary acoustic wave filter provided with an IDT 53 between them. Further, the present invention can be applied to the device structure as shown in FIG.

1 is a schematic diagram showing a longitudinally coupled multimode resonator type SAW filter according to a first embodiment of the present invention. It is a diagram which shows the measurement result of a phase balance degree compared with the conventional filter about the SAW filter which concerns on said 1st embodiment. It is a diagram which shows the result of having measured the attenuation characteristic of the SAW filter which concerns on said 1st embodiment compared with the conventional filter. It is a schematic diagram which shows the modification of the SAW filter which concerns on said 1st embodiment. It is a diagram which shows the measurement result of a phase balance degree compared with the conventional filter about the SAW filter which concerns on 2nd embodiment of this invention. It is a diagram which shows the measurement result of a phase balance degree compared with the conventional filter about the SAW filter which concerns on 3rd embodiment of this invention. It is a diagram which shows the measurement result of a phase balance degree compared with the conventional filter about the SAW filter which concerns on 4th embodiment of this invention. It is a diagram which shows the result of having measured the attenuation characteristic of the SAW filter which concerns on the said 4th embodiment compared with the conventional filter. It is a diagram which shows the measurement result of a phase balance degree compared with the conventional filter about the SAW filter which concerns on 5th embodiment of this invention. It is a diagram which shows the result of having measured the attenuation characteristic of the SAW filter which concerns on the said 5th embodiment compared with the conventional filter. It is a schematic diagram which shows another structural example of the longitudinally coupled multimode resonator type SAW filter according to the present invention. It is a schematic diagram which shows another structural example of the longitudinally coupled multimode resonator type SAW filter according to the present invention. It is a schematic diagram which shows another structural example of the longitudinally coupled multimode resonator type SAW filter according to the present invention. It is a schematic diagram which shows another structural example of the longitudinally coupled multimode resonator type SAW filter according to the present invention. It is a figure which shows typically the cross-section of the boundary acoustic wave filter which can apply this invention. It is a figure explaining the pitch of IDT (a) and a reflector (b). It is a schematic diagram which shows an example (1st prior art example) of the conventional longitudinally coupled multimode resonator type SAW filter. It is a schematic diagram which shows another example (2nd prior art example) of the conventional longitudinally coupled multimode resonator type SAW filter. It is a schematic diagram which illustrates the cross-sectional structure of the conventional SAW filter. It is a schematic diagram which shows an example of the cross-section of a SAW filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Output terminal 10, 27r, 102 ... Reflector 11 ... 1st IDT group 12 ... 2nd IDT group 21, 22, 23, 24, 25, 26, 51, 52, 53, 54, 55, 56,103 ... IDT
27 ... Central IDT
27a, 27b ... electrode portion 27c, 27d, 27e ... comb-shaped electrode 51 ... piezoelectric substrate 52 ... non-piezoelectric material (non-piezoelectric film or non-piezoelectric substrate)
53 ... Electrode (IDT electrode finger or reflector electrode)
101, 201, 301 ... surface acoustic wave resonators

Claims (12)

A plurality of interdigitated electrodes arranged in a propagation direction of surface acoustic waves on a piezoelectric substrate;
A pair of reflectors on either side of these interdigitated electrodes;
A first signal terminal which is a balanced or unbalanced terminal;
A second signal terminal which is a balanced terminal;
A longitudinally coupled multimode resonator type surface acoustic wave filter comprising:
The plurality of interdigitated electrodes are
A first interdigitated electrode group composed of a plurality of interdigitated electrodes arranged in order in the propagation direction of the surface acoustic wave;
A second interdigitated electrode group consisting of a plurality of interdigitated electrodes arranged in order in the propagation direction of the surface acoustic wave;
A central interdigitated electrode disposed between the first interdigital electrode group and the second interdigital electrode group to acoustically couple both interdigital fingers,
Including
Connecting one or more interdigitated electrodes of the first interdigitated electrode group and one or more interdigitated electrodes of the second interdigitated electrode group to the first signal terminal;
Connecting one or more interdigitated electrodes of the first interdigitated electrode group to one terminal of the second signal terminal which is the balanced terminal;
One or more interdigitated electrodes of the second interdigitated electrode group are connected to the other terminal of the second signal terminal, and the central interdigitated electrode is connected to two surface acoustic wave propagation directions. Dividing into two substantially symmetrically so that the interdigital electrodes are arranged, and connecting one of the divided interdigital electrodes to one terminal of the second signal terminal The other interdigitated electrode portion is connected to the other terminal of the second signal terminal. A longitudinally coupled multimode resonator type surface acoustic wave filter, wherein: A piezoelectric substrate;
A non-piezoelectric material arranged in contact with the piezoelectric substrate;
A plurality of interdigitated electrodes arranged in a boundary acoustic wave propagation direction on a boundary surface between the piezoelectric substrate and the non-piezoelectric material;
A pair of reflectors on either side of these interdigitated electrodes;
A first signal terminal which is a balanced or unbalanced terminal;
A second signal terminal which is a balanced terminal;
A longitudinally coupled multimode resonator type boundary acoustic wave filter having
The plurality of interdigitated electrodes are
A first interdigitated electrode group consisting of a plurality of interdigitated electrodes arranged in order in the propagation direction of the boundary acoustic wave;
A second interdigitated electrode group composed of a plurality of interdigitated electrodes arranged in order in the propagation direction of the boundary acoustic wave;
A central interdigitated electrode disposed between the first interdigital electrode group and the second interdigital electrode group to acoustically couple both interdigital fingers,
Including
Connecting one or more interdigitated electrodes of the first interdigitated electrode group and one or more interdigitated electrodes of the second interdigitated electrode group to the first signal terminal;
Connecting one or more interdigitated electrodes of the first interdigitated electrode group to one terminal of the second signal terminal which is the balanced terminal;
One or more interdigitated electrodes of the second interdigitated electrode group are connected to the other terminal of the second signal terminal, and the central interdigitated electrode is connected to two boundary acoustic wave propagation directions. Dividing into two substantially symmetrically so that the interdigital electrodes are arranged, and connecting one of the divided interdigital electrodes to one terminal of the second signal terminal The other interdigitated electrode portion is connected to the other terminal of the second signal terminal. A longitudinally coupled multimode resonator type boundary acoustic wave filter, wherein: The two interdigitated electrode portions included in the central interdigitated electrode both connect one comb electrode of the pair of comb electrodes constituting them to the second signal terminal and float the other comb electrode. The longitudinally coupled multimode resonator type surface acoustic wave filter according to claim 1 or the longitudinally coupled multimode resonator type boundary acoustic wave filter according to claim 2, wherein the longitudinally coupled multimode resonator type surface acoustic wave filter is an electrode. 4. The longitudinally coupled multimode resonator according to claim 1, wherein the two interdigitated electrode portions included in the central interdigitated electrode have the same number of electrode pairs and different electrode finger pitches. Type surface acoustic wave filter or longitudinally coupled multimode resonator type boundary acoustic wave filter. 4. The longitudinally coupled multimode resonator surface acoustic wave filter or longitudinal coupling according to claim 1, wherein the two intersecting finger electrode parts included in the central intersecting finger electrode have different numbers of electrode pairs. Multimode resonator type boundary acoustic wave filter. The two interdigitated electrode portions included in the central interdigitated electrode are electrode fingers of the interdigitated electrode portion having the larger number of electrode pairs than the electrode finger pitch of the intersecting finger electrode portion having the smaller number of electrode pairs. The longitudinally coupled multimode resonator type surface acoustic wave filter or longitudinally coupled multimode resonator type boundary acoustic wave filter according to claim 5, wherein the pitch is small. The total number of electrode pairs of the central interdigitated electrode and the two interdigitated electrodes arranged adjacent to both sides is the sum of the two interdigitated electrodes arranged adjacent to each of the reflectors. The longitudinally coupled multimode resonator type surface acoustic wave filter or longitudinally coupled multimode resonator type boundary acoustic wave filter according to any one of claims 1 to 6. The longitudinally coupled multimode resonator according to any one of claims 1 to 7, wherein each of the first cross finger electrode group and the second cross finger electrode group includes two or more cross finger electrodes. Type surface acoustic wave filter or longitudinally coupled multimode resonator type boundary acoustic wave filter. The longitudinally coupled multimode resonator type surface acoustic wave filter or longitudinally coupled multiplex filter according to any one of claims 1 to 8, further comprising a reflector between two intersecting finger electrode portions of the central intersecting finger electrode. Modal resonator type boundary acoustic wave filter. The first signal terminal is an unbalanced terminal;
A connection point between one or more interdigitated electrodes of the first interdigitated electrode group and one or more interdigitated electrodes of the second interdigital electrode group, and the first signal terminal 10. A longitudinally coupled resonator multimode surface acoustic wave filter or longitudinally coupled resonator multiplexing according to claim 1, further comprising a surface acoustic wave resonator or a boundary acoustic wave resonator connected in series therebetween. Modal boundary acoustic wave filter. The first signal terminal is an unbalanced terminal;
Between one or more interdigitated electrodes of the first interdigitated electrode group and the first signal terminal, and one or more interdigitated electrodes of the second interdigitated electrode group and the 11. The longitudinally coupled resonator multimode surface acoustic wave filter according to claim 1, wherein a surface acoustic wave resonator or a boundary acoustic wave resonator is further connected in series with each of the first signal terminals. Or a longitudinally coupled resonator multimode boundary acoustic wave filter. Two interdigitated electrodes, one or more interdigitated electrodes of the first interdigitated electrode group, one or more interdigitated electrodes of the second interdigitated electrode group, and the central interdigitated electrode. A surface acoustic wave resonator or a boundary acoustic wave resonator is further connected in series between a connection point with one of the electrode portions and one terminal of the second signal terminal, and
Two interdigitated electrodes, one or more interdigitated electrodes of the first interdigitated electrode group, one or more interdigitated electrodes of the second interdigitated electrode group, and the central interdigitated electrode. The surface acoustic wave resonator or the boundary acoustic wave resonator is further connected in series between a connection point with the other of the electrode portions and the other terminal of the second signal terminal. The longitudinally coupled resonator multimode type surface acoustic wave filter or longitudinally coupled resonator multimode type boundary acoustic wave filter according to claim 1.

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