JP4936102B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave (hereinafter referred to as SAW) device, and more particularly to a SAW filter in which two double mode SAW (DMS) filters are arranged on the same piezoelectric substrate and are electrically connected in parallel.

  2. Description of the Related Art Conventionally, SAW devices such as resonators, filters, and oscillators using SAW excited by an IDT (interdigital transducer) formed of crossed finger electrodes formed on the surface of a piezoelectric substrate have been widely used in various electronic devices. Particularly in the field of communication equipment, SAW filters are frequently used as band filters for mobile communication devices. In particular, a SAW filter used for a mobile communication system in a digital system is required to have a steep attenuation characteristic outside a pass band and a wide band in addition to stability to temperature.

  As a filter using a SAW resonator, a DMS filter utilizing two resonance modes in which two IDTs are arranged close to each other along the SAW propagation direction on a piezoelectric substrate and excited by acoustic coupling between both IDTs is well known. (For example, see Patent Document 1). Conventionally, various ideas have been made to widen the bandwidth of such SAW filters.

  For example, two sets of two-port SAW resonators each having an input and output IDT and a reflector on the outside thereof and generating three different longitudinal modes are arranged on the same piezoelectric substrate and electrically connected in parallel. SAW filters are known (see, for example, Patent Documents 2 and 3). This SAW filter is constructed so that two resonance points on one high-frequency side and two resonance points on the other low-frequency side coincide with each other at the same time, thereby improving the filter characteristics in the vicinity of the passband and enabling a wider band. ing.

  Similarly, as SAW filters that use three resonance modes to widen the bandwidth, reflectors are arranged on both sides of two input / output IDTs along the SAW propagation direction on the same piezoelectric substrate, and between the two IDTs. A resonant synthesis type SAW filter has been proposed in which two coupled multimode SAW filters having a third reflector called a middle grating are electrically connected in parallel (see, for example, Patent Document 4). In this SAW filter, one comb electrode constituting each IDT is connected to a ground potential terminal, the other comb electrode is electrically connected to an input or output terminal, and the middle grating is grounded.

  Further, there is known an input 2 × output 2 4-port SAW filter provided with two DMS (twin dual mode SAW) filters connected in parallel via a conductive path on the same piezoelectric substrate (for example, Patent Documents). 5). In this SAW filter, the input and output reflectors arranged outside the input IDT and the output IDT are electrically connected to each other by a conductive path between the DMS tracks A and B, and are arranged between the input and output IDTs. Each reflector is connected to one adjacent IDT and electrically connected to each other by a conductive path between the DMS tracks A and B, and can be operated symmetrically (balanced) or asymmetrically (unbalanced) on the input / output side. is there.

Japanese Patent Laid-Open No. 9-36695 Japanese Patent No. 2560991 Japanese Patent No. 3204112 Japanese Patent Laid-Open No. 10-209808 Japanese Patent No. 3419465

  Generally, as described above, when a 4-port SAW filter in which two DMS filters are connected in parallel on the same piezoelectric substrate operates unbalanced on the input side and balanced on the output side, noise is canceled at the output. A steep attenuation characteristic is obtained, thereby improving the sensitivity and obtaining a good filter characteristic. In addition, there is an advantage that current consumption can be reduced.

  However, the SAW filter having the conventional structure as described in Patent Document 5 described above has one input finger path in which one cross finger electrode of each input IDT of the DMS tracks A and B is connected via a reflector on the input side. And the other input finger path is configured by connecting the other interdigitated electrode of each input IDT via a short reflector between the two IDTs. Similarly, on the output side, one cross finger electrode of each output IDT of the DMS tracks A and B is connected to each other via a reflector on the output side to form one output path, and the other cross finger of each output IDT is formed. The other output path is configured by connecting the electrodes via a short reflector between the two IDTs. The reflector on the input / output side has a very large number and area of electrodes as compared with a short reflector between IDTs, and there is a large difference in electric capacity between the two.

  For this reason, the two input paths and the two output paths are not electrically symmetrical with each other, and as a result of greatly different electric capacities, there is a possibility that noise in each transmission line is not sufficiently canceled out in the output. As a result, the amount of attenuation decreases or unnecessary attenuation occurs, and a steep attenuation characteristic outside the pass band and good sensitivity cannot be obtained. In particular, when used as a balance circuit, there arises a problem that good filter characteristics cannot be obtained.

  Therefore, the present invention has been made in view of the above-described conventional problems, and an object thereof is to provide two DMS resonators in which a third reflector is disposed between two IDTs along the SAW propagation direction. In the 4-port SAW device in which the input / output path is configured by connecting the third reflector to the input side or the output side cross finger electrode of each IDT on the same piezoelectric substrate, By improving the electrical symmetry of the input path and making the capacitances equal, the noise in the transmission line is more effectively canceled from the output.

  It is a further object of the present invention to provide a SAW filter that can obtain a steeper attenuation characteristic and that can obtain a better filter characteristic particularly when used as a balance circuit.

According to the present invention, in order to achieve the above object, the first and second IDTs disposed along the SAW propagation direction, and the first and second reflectors disposed on both sides thereof, respectively. And a third reflector disposed between the first and second IDTs, and comprising first and second SAW resonators provided on the same piezoelectric substrate,
The first and second SAW resonators are
And one of the interdigital electrodes of the first IDT of the first SAW resonator, and one of the interdigital electrodes of the first IDT of the second SAW resonator, the first SAW resonator first A first input path comprising either one of the reflector parts or the third reflector part of the second SAW resonator and electrically connecting them ;
And the other interdigital electrode constituting the first IDT of the first SAW resonator, and the other interdigital electrode constituting the first IDT of the second SAW resonator, the first SAW resonator first A second input path composed of and electrically connected to one of the reflector portions or the third reflector portion of the second SAW resonator;
While the alternate finger electrodes constituting the second IDT of the first SAW resonator, and one of the interdigital electrodes of the second IDT of the second SAW resonator, the second SAW resonator first A first output path comprising either one of the two reflector parts or the third reflector part of the first SAW resonator and electrically connecting them ;
And the other interdigital electrode constituting the second IDT of the first SAW resonator, and the other interdigital electrode constituting the second IDT of the second SAW resonator, the second SAW resonator first The second reflector path or the third reflector section of the first SAW resonator and the second output path electrically connecting them. Connected in parallel,
A SAW device is provided in which the capacitance of the first input path is equal to the capacitance of the second input path, and the capacitance of the first output path is equal to the capacitance of the second output path.

  In this way, two SAW resonators having two SAW resonators connected in parallel and two input and output four-port SAW devices each have improved electrical symmetry in each of the input path and the output path. Can effectively cancel out noise.

Accordingly, the SAW filter of the present invention is , for example, a double mode SAW filter in which the first and second SAW resonators each have the first IDT as the input IDT and the second IDT as the output IDT. when used connected in parallel, it can be conventionally obtain a sufficient attenuation and sensitivity. In particular, when used in a balance circuit, it is possible to achieve better filter characteristics than before.
In one embodiment, the first input path includes one cross finger electrode that constitutes the first IDT of the first SAW resonator and one intersection that constitutes the first IDT of the second SAW resonator. A finger electrode and either the first reflector portion of the first and second SAW resonators or the third reflector portion of the second SAW resonator;
The second input path includes the other cross finger electrode constituting the first IDT of the first SAW resonator, the other cross finger electrode constituting the first IDT of the second SAW resonator, and the first And the first reflector part of the second SAW resonator or the third reflector part of the second SAW resonator.
In this case, the first input path or the second input path can further be configured from the third reflector portion of the first SAW resonator.
In another embodiment, the first output path has one crossing finger electrode constituting the second IDT of the first SAW resonator and one intersection constituting the second IDT of the second SAW resonator. A finger electrode and either the second reflector part of the first and second SAW resonators or the third reflector part of the first SAW resonator;
The second output path includes the other cross finger electrode constituting the second IDT of the first SAW resonator, the other cross finger electrode constituting the second IDT of the second SAW resonator, and the first And the second reflector part of the second SAW resonator or the third reflector part of the first SAW resonator.
In this case, the first output path or the second output path can be further configured by a third reflector portion of the second SAW resonator.

In one embodiment, in order to equalize the capacitances of the first and second input paths and equalize the capacitances of the first and second output paths, the capacitances of the reflectors constituting the first input path; Make the electric capacity of the reflector constituting the second input path equal, and make the electric capacity of the reflector constituting the first output path equal to the electric capacity of the reflector constituting the second output path Can do.

In another embodiment , the electrode area of the reflector that constitutes the first input path is equal to the electrode area of the reflector that constitutes the second input path, and the electrode of the reflector that constitutes the first output path. By making the area equal to the electrode area of the reflector constituting the second output path, the capacitances of the first and second input paths and the first and second output paths can be made equal. .

In still another embodiment , the electrode width and the number of reflectors constituting the first input path are made equal to the electrode width and the number of reflectors constituting the second input path, and the first output path is constituted. By making the electrode width and number of the reflectors to be equal to the electrode width and number of the reflectors constituting the second output path , the electric capacitance of the first and second input paths and the first and second output paths Each electric capacity can be made equal.

  In one embodiment, the first and second input terminals for connecting the first and second input paths to the outside, and the first and second for connecting the first and second output paths to the outside. An output terminal is disposed between the first SAW resonator and the second SAW resonator along the SAW propagation direction, or on one side of the piezoelectric substrate along the SAW propagation direction. By arranging them along, the width of the piezoelectric substrate, that is, the dimension of the IDT in the crossing length direction can be shortened, and the entire device can be downsized. In particular, when the first and second input terminals and the first and second output terminals are arranged between the first and second SAW resonators, wire bonding becomes easy, and a sufficient space can be secured. This is advantageous because downsizing can be achieved.

  Hereinafter, the present invention will be described in detail using preferred embodiments with reference to the accompanying drawings.

  FIG. 1 schematically shows the configuration of a first embodiment of a SAW filter to which the present invention is applied. The SAW filter 1 of the present embodiment includes first and second DMS filters 3 and 4 arranged in parallel to the main surface of the piezoelectric substrate 2 made of quartz, lithium tantalate, lithium niobate, or the like. The SAW filter 1 is a 4-port type in which first and second DMS filters 3 and 4 are electrically connected in parallel as will be described later.

  The first DMS filter 3 includes an input side IDT5 composed of a pair of opposed input side cross finger electrodes 5a and 5b and an output side IDT6 composed of a pair of opposed output side cross finger electrodes 6a and 6b. It is arranged along the propagation direction of the SAW excited by the input side IDT. Along the SAW propagation direction, lattice-shaped first and second reflectors 7 and 8 are arranged outside both IDTs 5 and 6, and a lattice-shaped third reflector is disposed between both IDTs 5 and 6. 9 is arranged. The first and second reflectors 7 and 8 of this embodiment are electrically connected to the electrically independent reflector portions 7a and 8a and one input-side cross finger electrodes 5a and 6a of the adjacent IDT. Reflector portions 7b and 8b. The third reflector 9 is electrically connected to the other input side cross finger electrode 6b of the output side IDT6.

  Similarly, the second DMS filter 4 includes an input side IDT 10 composed of a pair of opposed input side cross finger electrodes 10a and 10b, and an output side IDT 11 composed of a pair of opposed output side cross finger electrodes 11a and 11b. Are arranged along the propagation direction of the SAW excited by the input side IDT. Along the SAW propagation direction, lattice-shaped first and second reflectors 12 and 13 are disposed outside both IDTs 10 and 11, and a lattice-shaped third reflector is disposed between both IDTs 10 and 11. 14 is arranged. The first and second reflectors 12 and 13 are electrically connected reflector portions 12a and 13a and one input-side cross finger electrodes 10a and 11a of the adjacent IDT. It is comprised from the parts 12b and 13b, respectively. Conversely, the third reflector 14 is electrically connected to the other input-side cross finger electrode 10 b of the input-side IDT 10.

  Both DMS filters 3 and 4 have reflector portions 7b and 12b of the first reflectors 7 and 12 electrically connected by wiring 15a, so that the input side IDTs 5 and 10 are connected to the one input side thereof. The cross finger electrodes 5a and 10a are electrically connected to each other. The other input side cross finger electrodes 5b and 10b of the input side IDTs 5 and 10 are electrically connected to each other by a wiring 15b. Further, the two DMS filters 3 and 4 are respectively connected to the reflector portions 8b and 13b of the second reflectors 8 and 13 by the wiring 16a, so that the output side IDTs 6 and 11 receive the one input thereof. The side crossing finger electrodes 6a and 11a are electrically connected to each other. The other input side cross finger electrodes 6b and 11b of the output side IDTs 6 and 11 are electrically connected to each other by a wiring 16b.

  The first and second input terminals 17 and 18 are formed by being directly connected to the bus bar of the one input side cross finger electrode 10a of the second DMS filter 4 and the bus bar of the third reflector 14, respectively. It is arranged near the long side of the piezoelectric substrate 2. The first and second output terminals 19 and 20 are formed by directly connecting to the bus bar of the one output-side cross finger electrode 6a of the first DMS filter 3 and the bus bar of the third reflector 9, respectively. It is arranged near the long side of the adjacent piezoelectric substrate 2. In this way, the SAW filter 1 in which the two DMS filters 3 and 4 are electrically connected in parallel is configured.

  The input side of the SAW filter 1 includes one input side cross finger electrode 5a of the input side IDT 5 of the first DMS filter 3, one input side cross finger electrode 10a of the input side IDT 10 of the second DMS filter 4, A first input path is constituted by the reflector portions 7 b and 12 b of the first reflectors 7 and 12 connected via the wiring 15 a and is connected to the outside via the first input terminal 17. Further, the other input side cross finger electrode 5b of the input side IDT 5 of the first DMS filter 3 and the other input side cross finger electrode of the input side IDT 10 of the second DMS filter 4 connected thereto via the wiring 15b. 10b and the third reflector 14 constitute a second input path, which is connected to the outside via the second input terminal 18.

  According to the present invention, the line width, the pitch, and the total number of the grid-like electrodes forming the reflector portions 7b and 12b of the first input path, and the grid-like electrodes forming the third reflector 14 of the second input path The line width, the pitch, and the number of lines are set so as to match or substantially match. In the first and second DMS filters 3 and 4, the cross finger electrodes 5a and 5b of the input side IDT 5 have the same line width, pitch and number, and the cross finger electrodes 10a and 10b of the input side IDT 10 have the same line. It has width, pitch and number. Therefore, the first input path and the second input path can be made substantially equal in capacitance of the electrodes and wirings forming them. Further, by making the electrode areas of the reflector portions 7b and 12b equal to the electrode area of the third reflector 9, the electric capacities of the first input path and the second input path can be made substantially equal. .

The output side of the SAW filter 1 includes one output side cross finger electrode 6a of the output side IDT 6 of the first DMS filter 3, one output side cross finger electrode 11a of the output side IDT 11 of the second DMS filter 4, A first output path is constituted by the reflector portions 8 b and 13 b of the second reflectors 8 and 13 connected via the wiring 16 a and is connected to the outside via the first output terminal 19. Further, the output side of the SAW filter 1 is connected to the other output side cross finger electrode 6b of the output side IDT 6 of the first DMS filter 3 and the output side IDT 11 of the second DMS filter 4 connected thereto via the wiring 16b. The other output-side cross finger electrode 11 b and the third reflector 9 constitute a second output path and is connected to the outside via the second output terminal 20.

  Similarly, the line width, pitch and total number of the grid electrodes forming the reflector portions 8b and 13b of the first output path, and the line width of the grid electrodes forming the third reflector 9 of the second output path , The pitch and the number are set so as to match or substantially match. In the first and second DMS filters 3 and 4, the cross finger electrodes 6a and 6b of the output side IDT 6 have the same line width, pitch and number, and the cross finger electrodes 11a and 11b of the input side IDT 11 have the same line. It has width, pitch and number. Therefore, the first output path and the second output path can have substantially the same capacitance of the electrodes and wirings forming them. Further, by making the electrode areas of the reflector portions 8b and 13b and the electrode area of the third reflector 14 equal, the electric capacities of the first output path and the second output path can be made substantially equal. .

  In actual filter design, the line width, pitch, and number of electrodes of the first to third reflectors 7 to 9 and 12 to 14 are determined so that desired filter characteristics can be obtained. Next, the first and second input paths have the same electric capacity, and the first output path and the second output path have the same electric capacity. The number of electrodes of the reflector portions 7a, 8a, 12a and 13a and the reflector portions 7b, 8b, 12b and 13b constituting the second reflector is determined. In this embodiment, when the number of electrodes of the third reflectors 9 and 14 is four as shown in FIG. 1, the number of the electrodes of the reflector portions 7b, 8b, 12b and 13b can be reduced to two. .

  In this way, the SAW filter 1 of the present invention equalizes the electric capacitances in the first input path and the second input path, and in the first output path and the second output path, so that the output is noise in the transmission line. Can be offset more effectively. Thereby, sufficient attenuation and sensitivity can be obtained compared to the conventional case. Therefore, even when used in a balance circuit, better filter characteristics than before can be obtained.

  FIG. 2 schematically shows the configuration of a second embodiment of the SAW filter according to the present invention. In the SAW filter 1 of the second embodiment, the first and second input terminals 17 and 18 and the first and second output terminals 19 and 20 are not near the long side of the piezoelectric substrate 2 but on the center line of the piezoelectric substrate. The second embodiment differs from the first embodiment in that it is disposed in an intermediate region between the first DMS filter 3 and the second DMS filter 4 along the line.

  The first input terminal 17 is directly formed on the wiring 15 a that connects the reflector portions 7 b and 12 b of the first reflectors 7 and 12. The second input terminal 18 is directly formed on the wiring 15b connecting the input-side intersecting finger electrodes 5b and 10b of both the input-side IDTs 5 and 10. The first output terminal 19 is directly formed on the wiring 16 a that connects the reflector portions 8 b and 13 b of the second reflectors 8 and 13. The second output terminal 20 is directly formed on the wiring 16b that connects the output-side intersecting finger electrodes 6b and 11b of both the output-side IDTs 6 and 11. By arranging all the input and output terminals in the middle region between the DMS filters 3 and 4 of the piezoelectric substrate 2 in this way, the width of the piezoelectric substrate 2, that is, the length of the IDT in the crossing length direction is set in the first embodiment. The SAW filter 1 can be reduced in size.

  Further, such a SAW filter is generally connected to an external circuit by wire bonding. In this embodiment, a sufficient space necessary for wire bonding wiring and connection can be secured around each input terminal and each output terminal. Therefore, workability at the time of mounting is improved, and the entire device can be further downsized.

Also in this embodiment, on the input side, the first input path consisting of the input side crossed finger electrodes 5a and 10a of the input side IDTs 5 and 10, the reflector portions 7b and 12b of the first reflectors 7 and 12, and the wiring 15a. The two capacitances are set so that the capacitance is equal to the capacitance of the second input path composed of the other input side crossed finger electrodes 5b, 10b of the input side IDTs 5, 10 and the third reflector 14 and the wiring 15b. The first reflector and the third reflector 14 are configured in the same manner as in the first embodiment. Similarly, on the output side, the capacitance of the first output path composed of the output-side crossed finger electrodes 6a and 11a of the output-side IDTs 6 and 11, the reflector portions 8b and 13b of the second reflectors 8 and 13, and the wiring 16a The second reflection paths are formed so that the second output path consisting of the other output-side crossed finger electrodes 6b and 11b of the output-side IDTs 6 and 11 and the third reflector 9 and the wiring 16b have the same capacitance. The third reflector 14 and the third reflector 14 are configured in the same manner as in the first embodiment.

  The SAW filter 1 of the present embodiment also has the same output by making the capacitances equal in the first input path and the second input path and in the first output path and the second output path, respectively. The noise in the transmission line can be canceled more effectively. Accordingly, sufficient attenuation and sensitivity can be obtained compared to the conventional case, and filter characteristics better than the conventional one can be obtained especially when used in a balance circuit.

  In another embodiment, the reflector portions 7b, 12b of the first reflector are connected to the other input cross finger electrode 5b, 10b, and the third reflector 14 is connected to the one input cross finger electrode. 5a and 10a, the reflector portions 8b and 13b of the second reflector are connected to the other output-side cross finger electrodes 6b and 11b, and the third reflector 9 is connected to the one output-side intersection. It can be connected to the finger electrodes 6a and 11a. In this case as well, an effect of more effectively canceling out noise in the transmission line can be obtained by equalizing the electric capacities in the first and second input paths and the first and second output paths.

  FIG. 3 schematically shows the configuration of a third embodiment of the SAW filter according to the present invention. The SAW filter 1 of the third embodiment is different from the first embodiment in the following points. That is, the third reflectors 9 and 14 are divided into two reflector portions 9a, 9b, 14a and 14b. The reflector portions 9a, 9b, 14a, and 14b have, for example, the same number of electrodes or the same area so as to have the same electric capacity. The reflector portions 9a and 9b of the third reflector 9 are electrically connected to the other input side and output side interdigitated electrodes 5b and 6b, respectively, which are adjacent to each other. Similarly, the reflector portions 14a and 14b of the third reflector 14 are electrically connected to the other input side and output side cross finger electrodes 10b and 11b adjacent to each other.

  The first and second input terminals 17 and 18 and the first and second output terminals 19 and 20 are arranged along one long side of the piezoelectric substrate 2. The first and second input terminals 17 and 18 are directly connected to the bus bar of the one input side cross finger electrode 5a of the first DMS filter 3 and the bus bar of the reflector portion 9a of the third reflector 9, respectively. Is formed. The first and second output terminals 19 and 20 are directly connected to the bus bar of the reflector portion 9 b of the third reflector 9 and the bus bar of the one output-side cross finger electrode 6 a of the first DMS filter 3. Is formed. By arranging all the input and output terminals along one long side of the piezoelectric substrate 2 in this way, the width of the piezoelectric substrate 2, that is, the length in the crossing length direction of the IDT is shortened compared to the first embodiment. In addition, the SAW filter 1 can be reduced in size.

  In the present embodiment, on the input side, the first input path consisting of the input side cross finger electrodes 5a and 10a of the input side IDTs 5 and 10, the reflector portions 7b and 12b of the first reflectors 7 and 12, and the wiring 15a. The electric capacity and the electric capacity of the second input path composed of the other input side cross finger electrodes 5b and 10b of the input side IDTs 5 and 10, the reflector portions 9a and 14a of the third reflectors 9 and 14, and the wiring 15b Are equal. Since the input side cross finger electrodes 5a and 10a and the input side cross finger electrodes 5b and 10b have the same capacitance, the reflector portions 7b and 12b of the first reflector and the reflector portions 9a and 14a of the third reflector are used. For example, the total number or the total area of these electrodes is made the same so that the electric capacities of the electrodes are equal.

  On the output side, the output side cross finger electrodes 6a and 11a of the output side IDTs 6 and 11, the reflector portions 8b and 13b of the second reflectors 8 and 13, and the electric capacity of the first output path composed of the wiring 16a, and the output The electric capacity of the second output path composed of the other output side crossing finger electrodes 6b, 11b of the side IDTs 6, 11 and the reflector portions 9b, 14b of the third reflectors 9, 14, and the wiring 16b is made equal. Since the output side cross finger electrodes 6a and 11a and the output side cross finger electrodes 6b and 11b have the same capacitance, the reflector portions 8b and 13b of the second reflector and the reflector portions 9b and 14b of the third reflector are used. For example, the total number or the total area of these electrodes is made the same so that the electric capacities of the electrodes are equal.

  The SAW filter 1 of the present embodiment also has the same output in the first input path and the second input path as well as in the first output path and the second output path in this way. Noise in the transmission line can be canceled more effectively. Accordingly, sufficient attenuation and sensitivity can be obtained compared to the conventional case, and filter characteristics better than the conventional one can be obtained especially when used in a balance circuit.

  In another embodiment, the reflector portions 7b, 12b of the first reflector are connected to the other input side interdigitated electrodes 5b, 10b, and the reflector portions 14a, 14b of the third reflector 14 are respectively connected. The one input side cross finger electrode 10a and the one output side cross finger electrode 11a that are adjacent to each other are connected, and the reflector portions 8b and 13b of the second reflector are connected to the other output side cross finger electrodes 6b and 11b. And the reflector portions 9a and 9b of the third reflector 9 can be connected to the one input side cross finger electrode 5a and the one output side cross finger electrode 6a, respectively. In this case as well, an effect of more effectively canceling out noise in the transmission line can be obtained by equalizing the electric capacities in the first and second input paths and the first and second output paths.

FIG. 4 schematically shows the configuration of a fourth embodiment of the SAW filter according to the present invention. The SAW filter 1 of the fourth embodiment is different from the second embodiment in the following points. That is, in the first DMS filter 3, the first reflector 7 is electrically connected to the electrically independent reflector portion 7a and one input side cross finger electrode 5a of the adjacent input side IDT5. The second reflector 8 as a whole is electrically independent while being divided into the reflector portion 7b. The reflector portion 7b is further connected to the input side cross finger electrode 10b of the second DMS filter 4 via the wiring 15a. The second DMS filter 4 includes a reflector portion 13b in which a second reflector 13 is electrically connected to an electrically independent reflector portion 13a and an output-side cross finger electrode 11b of an adjacent output-side IDT 11. In contrast, the entire first reflector 12 is electrically independent. The reflector portion 13b is further connected to the output- side cross finger electrode 6b of the first DMS filter 3 via the wiring 16b.

  The third reflector 9 of the first DMS filter 3 includes an output side cross finger electrode 6a of the adjacent output side IDT 6 and an output side cross finger electrode 11b of the output side IDT 11 of the second DMS filter 4 by the wiring 16b. It is connected to the. The third reflector 14 of the second DMS filter 4 includes an input side cross finger electrode 10a of the adjacent input side IDT 10 and an input side cross finger electrode 5b of the input side IDT 5 of the first DMS filter 3 by the wiring 15b. It is connected to the.

  As in the second embodiment, the first and second input terminals 17 and 18 and the first and second output terminals 19 and 20 are directly formed on the wirings 15a, 15b, 16a, and 16b, respectively. By arranging all the input and output terminals in the middle region between the DMS filters 3 and 4 of the piezoelectric substrate 2 in this way, the width of the piezoelectric substrate 2, that is, the length of the IDT in the crossing length direction is set in the first embodiment. The SAW filter 1 can be reduced in size. Furthermore, when connecting to an external circuit by wire bonding, sufficient space necessary for wiring and connection can be secured around each input and output terminal, so that workability during mounting is improved and the entire device is Can be further reduced in size.

  In the present embodiment, on the input side, the capacitance of the first input path consisting of the input-side crossed finger electrodes 5a and 10b of the input-side IDTs 5 and 10, the reflector portion 7b of the first reflector 7 and the wiring 15a; The electric capacity of the second input path made up of the input side crossing finger electrodes 5b, 10a, the third reflector 14, and the wiring 15b of the input side IDTs 5, 10 is made equal. Since the input side cross finger electrodes 5a and 10b and the input side cross finger electrodes 5b and 10a have the same electric capacity, for example, the electric capacity of the reflector part 7b and the third reflector 14 is made equal. Make the number or area the same.

  On the output side, the capacitance of the first output path composed of the output-side crossed finger electrodes 6a and 11b of the output-side IDTs 6 and 11, the third reflector 9 and the wiring 16a and the output-side crossed fingers of the output-side IDTs 6 and 11 The electric capacity of the second output path composed of the electrodes 6b and 11a, the reflector portion 13b of the second reflector 13 and the wiring 16b is made equal. Since the output side crossing finger electrodes 6a and 11b and the output side crossing finger electrodes 6b and 11a have the same electric capacity, for example, the electric capacity of the third reflector 9 and the reflector portion 13b is made equal. Make the number or area the same.

  In particular, in this embodiment, the bus bar and wiring 15a of the reflector portion 7b connected to the input side cross finger electrode 5a and the bus bar and wiring 15b of the third reflector 14 connected to the input side cross finger electrode 10a are provided. In addition, the symmetry between the first input path and the second input path is good. Similarly, including the bus bar and wiring 16a of the third reflector 9 connected to the output side cross finger electrode 6a, and the bus bar and wiring 16b of the reflector portion 13b connected to the output side cross finger electrode 11a, The symmetry between the first output path and the second output path is good.

  Therefore, the SAW filter 1 of the present embodiment can make the electric capacities of the first and second input paths and the electric capacities of the first and second output paths more equal. Thereby, the output can more effectively cancel the noise in the transmission line. Therefore, a sufficient attenuation amount and sensitivity can be obtained as compared with the above-described embodiments, and good filter characteristics more suitable for the balance circuit can be obtained.

In another embodiment, the reflector portion 7b of the first reflector is connected to the input side interdigitated electrodes 5b, 10a of the second input path , and the third reflector 14 is connected to the first input path. Are connected to the input side cross finger electrodes 5a and 10b , the reflector part 13b of the second reflector is connected to the output side cross finger electrodes 6a and 11b of the first output path , and the third reflector 9 is connected. Can be connected to the input-side intersecting finger electrodes 6b and 11a of the second output path . In still another embodiment, the first DMS filter 3 and the second DMS filter 4 may be arranged symmetrically with respect to the center line of the piezoelectric substrate 2.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications and changes can be made within the technical scope thereof. Further, although the SAW filter has been described in the above embodiment, the present invention can be similarly applied to other SAW devices.

The top view which shows 1st Example of the SAW filter to which this invention is applied. The top view which shows 2nd Example of the SAW filter to which this invention is applied. The top view which shows 3rd Example of the SAW filter to which this invention is applied. The top view which shows 4th Example of the SAW filter to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... SAW filter, 2 ... Piezoelectric substrate, 3 ... 1st DMS filter, 4 ... 2nd DMS filter, 5, 10 ... Input side IDT, 5a, 5b, 10a, 10b ... Input side cross finger electrode, 6, DESCRIPTION OF SYMBOLS 11 ... Output side IDT, 6a, 6b, 11a, 11b ... Output side cross finger electrode, 7-9, 12-14 ... 1st-3rd reflector, 7a-9a, 7b-9b, 12a-14a, 12b -14b ... reflector portion, 15a, 15b, 16a, 16b ... wiring, 17 ... first input terminal, 18 ... second input terminal, 19 ... first output terminal, 20 ... second output terminal.

Claims (11)

Between the first and second IDTs disposed along the propagation direction of the surface acoustic wave, the first and second reflectors disposed on both sides thereof, and the first and second IDTs, respectively. A first reflector and a second surface acoustic wave resonator provided on the same piezoelectric substrate, and a third reflector disposed,
The first and second surface acoustic wave resonators are
While the alternate finger electrodes constituting the first IDT of the first surface acoustic wave resonator, while the interdigital electrodes which constitute the first IDT of the second surface acoustic wave resonator, is composed of a one of the first of the third reflector portion of said surface acoustic wave resonator a first reflector portion or the second surface acoustic wave resonator, and electrically they Connected first input paths,
And the other interdigital electrode constituting the first IDT of the first surface acoustic wave resonator, and the other interdigital electrode constituting the first IDT of the second surface acoustic wave resonator, The first surface acoustic wave resonator is composed of either the first reflector portion or the second surface acoustic wave resonator of the third reflector portion, and is electrically connected to the other. Connected second input path,
While the alternate finger electrodes constituting the second IDT of the first surface acoustic wave resonator, while the interdigital electrodes of which constitute the second IDT of the second surface acoustic wave resonator, the constructed from either the second of the third reflector portion of the second reflector portion or said first surface acoustic wave resonator of the surface acoustic wave resonator, and electrically they Connected first output paths,
And the other interdigital electrode constituting the second IDT of the first surface acoustic wave resonator, and the other interdigital electrode constituting the second IDT of the second surface acoustic wave resonator, The second surface acoustic wave resonator is composed of either the second reflector portion or the first surface acoustic wave resonator of the third reflector portion, and they are electrically connected. Electrically connected in parallel so as to have a second output path connected electrically,
Elasticity characterized in that the electric capacity of the first input path and the electric capacity of the second input path are made equal, and the electric capacity of the first output path and the electric capacity of the second output path are made equal. Surface wave device. The first input path constitutes one cross finger electrode constituting the first IDT of the first surface acoustic wave resonator and the first IDT of the second surface acoustic wave resonator. One of the interdigitated electrodes and the first reflector portion of the first and second surface acoustic wave resonators or the third reflector portion of the second surface acoustic wave resonator It consists of one side and
The second input path forms the first IDT of the second surface acoustic wave resonator and the other cross finger electrode that forms the first IDT of the first surface acoustic wave resonator. Either the other interdigitated electrode and the first reflector portion of the first and second surface acoustic wave resonators or the third reflector portion of the second surface acoustic wave resonator The surface acoustic wave device according to claim 1, comprising the other. The first output path forms one second finger electrode constituting the second IDT of the first surface acoustic wave resonator and the second IDT of the second surface acoustic wave resonator. Either one of the interdigitated electrodes and the second reflector portion of the first and second surface acoustic wave resonators or the third reflector portion of the first surface acoustic wave resonator It consists of one side and
The second output path forms the second IDT of the second surface acoustic wave resonator and the other crossed finger electrode that forms the second IDT of the first surface acoustic wave resonator. Either the other interdigitated electrode and the second reflector portion of the first and second surface acoustic wave resonators or the third reflector portion of the first surface acoustic wave resonator The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device comprises the other. 3. The surface acoustic wave according to claim 2, wherein the first input path or the second input path further includes a portion of the third reflector of the first surface acoustic wave resonator. device. 4. The surface acoustic wave according to claim 3, wherein the first output path or the second output path further includes a portion of the third reflector of the second surface acoustic wave resonator. device. Making the electric capacity of the reflector constituting the first input path equal to the electric capacity of the reflector constituting the second input path; and
The elasticity according to any one of claims 1 to 5 , wherein an electric capacity of the reflector constituting the first output path is equal to an electric capacity of the reflector constituting the second output path. Surface wave device. Making the electrode area of the reflector constituting the first input path equal to the electrode area of the reflector constituting the second input path; and
The surface acoustic wave device according to claim 6 , wherein an electrode area of the reflector constituting the first output path is equal to an electrode area of the reflector constituting the second output path. Making the electrode width and number of the reflectors constituting the first input path equal to the electrode width and number of the reflectors constituting the second input path; and
The elastic surface according to claim 6 , wherein the electrode width and the number of the reflectors constituting the first output path are equal to the electrode width and the number of the reflectors constituting the second output path. Wave device. First and second input terminals for connecting the first and second input paths to the outside, and first and second output terminals for connecting the first and second output paths to the outside, The elasticity according to any one of claims 1 to 8 , wherein the elastic member is disposed between the first surface acoustic wave resonator and the second surface acoustic wave resonator along a propagation direction of the surface acoustic wave. Surface wave device. First and second input terminals for connecting the first and second input paths to the outside, and first and second output terminals for connecting the first and second output paths to the outside, the surface acoustic wave device according to any one of claims 1 to 8, characterized in along the propagation direction of a surface acoustic wave that is arranged along one side of the piezoelectric substrate. The first and second surface acoustic wave resonators are double-mode surface acoustic wave filters in which the first IDT is an input IDT and the second IDT is an output IDT. Item 11. The surface acoustic wave device according to any one of Items 1 to 10 .

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