JP5135763B2 - Surface acoustic wave filter device and duplexer - Google Patents

Description

  The present invention relates to a surface acoustic wave filter device used, for example, in a band filter of an RF stage of a mobile phone, and more specifically, has a structure in which a plurality of longitudinally coupled resonator type surface acoustic wave filter sections are connected in cascade. The present invention relates to a coupled resonator type surface acoustic wave filter device and a duplexer using the surface acoustic wave filter device.

  A surface acoustic wave filter device is widely used as a bandpass filter used in the RF stage of a mobile phone. In this type of application, it is required to increase the attenuation in the attenuation region near the passband. In addition, the band-pass filter of the RF stage is connected between the antenna terminal and an amplifier circuit having a balanced input, and thus is required to have a balanced-unbalanced conversion function. Therefore, in the surface acoustic wave filter device used as an RF stage bandpass filter, by connecting a plurality of longitudinally coupled resonator type surface acoustic wave filters or combining surface acoustic wave resonators, It corresponds to the request of.

  The following Patent Document 1 discloses a surface acoustic wave filter device used for this type of application. FIG. 17 is a schematic plan view showing an electrode structure of the surface acoustic wave filter device described in Patent Document 1. As shown in FIG.

  In the surface acoustic wave filter device 1000, the illustrated electrode structure is formed on a piezoelectric substrate. Here, longitudinally coupled resonator type first and second surface acoustic wave filter sections 1001 and 1002 are cascade-connected. The first surface acoustic wave filter unit 1001 includes a first IDT 1011 and second and third IDTs 1012 and 1013 disposed on both sides of the first IDT 1011 in the surface wave propagation direction. In addition, reflectors 1014 and 1015 are arranged on both sides of a region where IDTs 1011 to 1013 are provided.

  Similarly, the second surface acoustic wave filter unit 1002 also includes a first IDT 1021, second and third IDTs 1022 and 1023 disposed on both sides of the first IDT 1021, and reflectors 1024 and 1025.

  One end of the first IDT 1011 of the first surface acoustic wave filter unit 1001 is connected to the unbalanced terminal 1003, and the other end of the first IDT 1011 is connected to the ground potential. In addition, one end of each of the second and third IDTs 1012 and 1013 is commonly connected by a wiring pattern 1016 and connected to the ground potential.

  On the other hand, the other ends of the IDTs 1012 and 1013 are electrically connected to one ends of the second and third IDTs 1022 and 1023 of the second surface acoustic wave filter unit 1002 through signal lines 1006 and 1007, respectively. The other ends of the IDTs 1022 and 1023 are connected in common by the wiring pattern 1026 and connected to the ground potential.

  One end of the IDT 1021 is electrically connected to the first balanced terminal 1004 and the other end is electrically connected to the second balanced terminal 1005.

Here, when a signal is input from the unbalanced terminal 1003, the phase of the signal extracted from the first balanced terminal 1004 is 180 ° different from the phase of the signal extracted from the second balanced terminal 1005. IDTs 1011 to 1013 and IDTs 1021 to 1023 are configured. Therefore, a balanced-unbalanced conversion function is realized. Further, it is possible to increase the attenuation outside the passband by connecting the first and second surface acoustic wave filter sections 1001 and 1002 in cascade.
JP 2002-84164 A

  When a longitudinally coupled resonator type surface acoustic wave filter device is configured by combining a plurality of surface acoustic wave elements, such as the surface acoustic wave filter device 1000 described in Patent Document 1, wiring patterns and signal lines on a piezoelectric substrate are formed. The routing tends to be complicated. For example, in the surface acoustic wave filter device 1000, the unbalanced terminal 1003 is disposed outside the surface acoustic wave filter unit 1001, but the wiring pattern 1016 is routed so as to surround the unbalanced terminal 1003. . In addition, on the outside of the second surface acoustic wave filter unit 1024, a wiring pattern 1026 is routed so as to surround the second balanced terminal 1005. Then, the wiring patterns 1016 and 1026 had to be electrically connected to electrode pads connected to the ground potential. Therefore, the area of the wiring pattern connected to the ground potential has to be increased. For this reason, the grounding capacity is increased, the VSWR is deteriorated, the pass bandwidth is narrowed, and the filter characteristics may be impaired.

  The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and to have a plurality of longitudinally coupled resonator type surface acoustic wave filter sections, which can improve the VSWR and expand the passband width. An object of the present invention is to provide a surface acoustic wave filter device capable of obtaining good filter characteristics.

According to the present invention, a piezoelectric substrate, and longitudinally coupled resonator type first and second surface acoustic wave filter portions formed on the piezoelectric substrate, the first and second surface acoustic wave filter portions are provided. Are connected to the unbalanced terminal, the other end of the first surface acoustic wave filter unit is connected to the first balanced terminal, and the other end of the second surface acoustic wave filter unit is connected to the second balanced terminal. A surface acoustic wave filter device connected to a terminal, wherein the first and second surface acoustic wave filter sections are disposed on both sides of the first IDT and the surface acoustic wave propagation direction of the first IDT, respectively. Second and third IDTs, and first and second reflectors disposed at both ends of the surface acoustic wave propagation direction, and the first and second surface acoustic wave filter sections of the first The IDT includes a first terminal on the hot side through which a signal current flows and a second terminal on the opposite side of the first terminal. In addition, one end of each of the second and third IDTs of the first and second surface acoustic wave filter sections is connected in common and connected to the unbalanced terminal, and the other end is connected to a ground potential. The first IDT first terminal of the first surface acoustic wave filter section is connected to the first balanced terminal, and the first IDT first terminal of the second surface acoustic wave filter section is used. Are connected to the second balanced terminal, and the first to third of the first and second surface acoustic wave filter sections are arranged so that the phases of the signals extracted from the first and second balanced terminals differ by 180 °. The first IDT second terminals of the first and second surface acoustic wave filter sections are connected in common and are not connected to the ground potential, so that the Surface acoustic wave filter device characterized by being floated on the surface Is provided.

  The duplexer of the present invention includes a surface acoustic wave filter device configured according to the present invention as a bandpass filter. Accordingly, it is possible to increase the VSWR and widen the pass bandwidth.

According to the present invention, the first terminal of the first IDT of the first surface acoustic wave filter section is connected to the first balanced terminal, and the first IDT of the second surface acoustic wave filter section is the first terminal of the first IDT. The terminals are connected to the second balanced terminals, respectively, so that the second terminals of the first IDTs of the first and second surface acoustic wave filter sections are connected in common and are not connected to the ground potential. Therefore, the wiring pattern on the second terminal side of the first IDT of the first and second surface acoustic wave filter sections can be simplified, and the grounding capacity can be reduced. Can be reduced. Therefore, it is possible to improve VSWR and widen the bandwidth.

Therefore, according to the present invention, it is possible to simplify the wiring pattern and improve the filter characteristics of the longitudinally coupled resonator type surface acoustic wave filter device.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a schematic plan view of a surface acoustic wave filter device according to a first embodiment of the present invention.

  The surface acoustic wave filter device 1 of this embodiment is a surface acoustic wave filter device used as a reception-side band filter for EGSM having a balanced-unbalanced conversion function. The transmission frequency band in the EGSM system is 880 to 915 MHz, while the reception frequency band is 925 to 960 MHz.

The surface acoustic wave filter device 1 is configured by forming the illustrated electrode structure on a piezoelectric substrate 2. The surface acoustic wave filter device 1 includes an unbalanced terminal 3 and first and second balanced terminals 4 and 5. In the present embodiment, the impedance at the unbalanced terminal 3 is 50Ω, and the impedance at the first and second balanced terminals 4 and 5 is 100Ω. The piezoelectric substrate 2 is not particularly limited, but a 40 ° ± 5 ° Y-cut X propagation LiTaO ₃ substrate is used.

  The illustrated electrode structure is formed on the piezoelectric substrate 2 by patterning Al. That is, longitudinally coupled resonator type first and second surface acoustic wave filter sections 10 and 20 are configured.

  The first surface acoustic wave filter unit 10 includes a first IDT 11 and second and third IDTs 12 and 13 disposed on both sides of the first IDT 11 in the surface wave propagation direction. First and second reflectors 14 and 15 are disposed on both sides of the surface wave propagation direction of the portion where the first to third IDTs 11 to 13 are provided.

  Similarly, the second surface acoustic wave filter unit 20 also includes a first IDT 21 and second and third IDTs 22 and 23 disposed on both sides of the first IDT 21 in the surface wave propagation direction. First and second reflectors 24 and 25 are disposed on both sides of the surface wave propagation direction of the portion where the first to third IDTs 21 to 23 are provided.

  One end of the first IDT 11 of the first surface acoustic wave filter unit 10 is connected to the unbalanced terminal 3. The other end of the IDT 11 is connected to the ground potential.

  The IDTs 12, 13, 22, and 23 each have a first terminal on the hot side that is connected to the signal current and a second terminal that is located on the opposite side of the first terminal.

  In the first IDT 11, one end is connected to the unbalanced terminal 3 and the other end is connected to the ground potential. The first terminal of the second IDT 12 is connected to the first terminal of the second IDT 22 of the second surface acoustic wave filter unit 20 via the first signal line 6.

  The first terminal of the third IDT 13 is connected to the first terminal of the third IDT 23 of the second surface acoustic wave filter unit via the signal line 7.

  On the other hand, the second terminals of the second and third IDTs 12 and 13 are commonly connected by a wiring pattern 16 as a reference potential pattern. The wiring pattern 16 is not connected to the ground potential but is in an electrically floating state.

  The second terminals of the second and third IDTs 22 and 23 in the second surface acoustic wave filter unit 20 are commonly connected by a wiring pattern 26 as a reference potential pattern. The wiring pattern 26 is also not connected to the ground potential and is in a floating state.

  On the other hand, one end of the first IDT 21 of the second surface acoustic wave filter unit 20 is connected to the first balanced terminal 4 and the other end is connected to the second balanced terminal 5.

  In this embodiment, for example, when a signal is input (output) from the unbalanced terminal 3, the phase of the signal output (input) from the first balanced terminal 4 is output (input) from the second balanced terminal 5. IDTs 11 to 13 and 21 to 23 are formed so as to be 180 ° different from the phase of the signal to be generated. Therefore, a balanced-unbalanced conversion function is realized.

  The feature of this embodiment is that the wiring patterns 16 and 26 provided outside the first and second surface acoustic wave filter portions 10 and 20 are not connected to the ground potential but are electrically floated. There is. Here, the outer side is opposite to the side where the counterpart surface acoustic wave filter unit is located among the first surface acoustic wave filter unit 10 and the second surface acoustic wave filter unit 20 that are cascade-connected in two stages. Means side. The wiring pattern 16 is present outside the first surface acoustic wave filter unit 10, and the wiring pattern 16 is not connected to the ground potential. Therefore, the grounding capacity can be reduced.

  Similarly, the wiring pattern 26 exists outside the second surface acoustic wave filter unit 20, but since the wiring pattern 26 is not electrically connected to the ground potential, it is possible to reduce the grounding capacity. It is said that. Thereby, in the surface acoustic wave filter device 1, it is possible to improve the filter characteristics and widen the passband width. This will be described based on a specific experimental example.

  The 1st surface acoustic wave filter part 10 and the 2nd surface acoustic wave filter part 20 were formed with the following specifications.

  Hereinafter, the wavelength λI refers to a wavelength determined by the pitch of the electrode fingers of the IDT.

(First surface acoustic wave filter unit 10)
Intersection width: 38.0λI
Number of electrode fingers of first IDT 11: 38 Number of electrode fingers of second and third IDTs 12 and 13: 30 Number of electrode fingers of first and second reflectors 14 and 15 Metallization Ratio: 0.73
Electrode film thickness: 0.088λI

(Second surface acoustic wave filter unit 20)
Intersection width: 38.0λI
Number of electrode fingers of the first IDT 21: 40 Number of electrode fingers of the second and third IDTs 22 and 23: 30 Number of electrode fingers of the first and second reflectors 24 and 25: 65 Metallization Ratio: 0.73
Electrode film thickness: 0.088λI
The filter characteristics and reflection characteristics of the surface acoustic wave filter device 1 produced as described above were measured. The results are shown by solid lines in FIG. 2 and FIGS. 3 (a) and 3 (b). FIG. 2 shows the filter characteristics, and FIGS. 3A and 3B show the VSWR on the input side and the output side as the reflection characteristics.

  As a comparative example, a surface acoustic wave filter device 1101 shown in FIG. 4 was produced. In the surface acoustic wave filter device 1101, instead of the wiring patterns 16 and 26, the second terminals of the second and third IDTs 12, 13, 22, and 23 are connected to the ground potential by the wiring patterns, respectively. This is the same as the surface acoustic wave filter device 1 of the above embodiment.

  The filter characteristics and reflection characteristics of the surface acoustic wave filter device 1101 of the comparative example manufactured as described above were measured. The results are shown by broken lines in FIG. 2 and FIGS. 3 (a) and 3 (b).

  As is clear from FIG. 2, according to the above embodiment, the pass bandwidth is widened. More specifically, the bandwidth with an insertion loss of 3 dB from the through level is higher than that of the comparative example. It can be seen that the form is approximately 1.0 MHz wider.

  Further, as is clear from FIGS. 3A and 3B, it can be seen that the value of VSWR is larger according to the above embodiment than the comparative example. More specifically, on the input side, it can be seen that the value of VSRW in the passband is improved by about 0.13, thereby improving the reflection characteristics.

  As described above, the reason why the reflection characteristics can be improved and the pass bandwidth can be widened according to the embodiment as compared with the comparative example is considered as follows.

  In the longitudinally coupled resonator type surface acoustic wave filter device, it is necessary to connect the terminal on the opposite side of the IDT on the hot side to the ground potential. This is because, in each IDT, a potential difference is generated between adjacent electrode fingers to convert an electric signal to a surface acoustic wave. Therefore, when two stages of longitudinally coupled resonator type surface acoustic wave filter units are connected in cascade, as described in Patent Document 1, the area of the wiring pattern connected to the ground potential on the piezoelectric substrate is reduced. I had to get bigger. For this reason, there is a problem that the grounding capacity is increased and the reflection characteristics and the transmission characteristics of the filter are deteriorated.

  On the other hand, in the above embodiment, the phase of the signal transmitted through the first signal line 6 is different from the phase of the signal transmitted through the second signal line by 180 °. Accordingly, the phase on the second terminal side, which is the terminal opposite to the side to which the signal line 6 of the IDT 12 is connected, and the end opposite to the side connected to the signal line 7 of the IDT 13. The phase of the electric signal on the second terminal side is inverted. Then, since the second terminal of the IDT 12 and the second terminal of the IDT 13 are electrically connected by the wiring pattern 16, the two second terminals having substantially the same amplitude and substantially inverted phases. The terminals are connected by the wiring pattern 16.

  Therefore, it becomes a virtual neutral potential, that is, a virtual ground potential.

  Therefore, even if the wiring pattern 16 is not connected to the ground potential, a potential difference is generated between the adjacent electrode fingers in the IDTs 12 and 13, respectively, so that it can operate as a filter. Accordingly, the second terminals of the IDTs 22 and 23 are similarly connected to each other on the IDTs 22 and 23 side by the wiring pattern 26. Therefore, a potential difference is generated between the adjacent electrode fingers of the IDTs 22 and 23. It is possible to work.

  Since the wiring patterns 16 and 26 do not need to be connected to the ground potential, it is possible to greatly reduce the routing area of the wiring patterns 16 and 26 on the piezoelectric substrate. Therefore, it is considered that the grounding capacitance at the input / output terminals can be reduced, thereby improving the VSWR and increasing the passband width.

  For reference, FIG. 5 schematically shows a layout of electrode portions on the piezoelectric substrate 2 of the surface acoustic wave filter device 1 of the first embodiment with hatching. Here, although not a cross section, the signal lines 6 and 7, the electrodes 40 a to 40 c connected to the signal potential, and the electrode 41 connected to the ground potential are indicated by hatching, respectively. The insulating films 42a to 42d are insulating films for preventing a short circuit between the electrodes.

  For comparison, FIG. 6 schematically shows a layout of electrodes on the piezoelectric substrate in the surface acoustic wave filter device 1101 of the comparative example shown in FIG. Here, the signal lines 6 and 7 and the electrodes 1104a to 1104c and 1105a to 1105f connected to the signal potential and the ground potential are indicated by hatching. The insulating films 1106a to 1106d mean insulating films for preventing a short circuit between the electrodes.

  As apparent from comparison between FIGS. 5 and 6, according to the above embodiment, the electrode routing area for connecting to the ground potential on the piezoelectric substrate is overwhelmingly smaller than in the comparative example. I understand. Thereby, not only the grounding capacity can be reduced, but also the wiring area on the piezoelectric substrate is reduced, and the entire surface acoustic wave filter device 1 can be reduced in size.

  In the above embodiment, the second and third IDTs 12 and 13 of the first surface acoustic wave filter unit are electrically connected by the wiring pattern 16 and floated, and further the second surface acoustic wave. Although the second terminals of the second and third IDTs 22 and 23 of the wave filter unit 20 are also electrically connected and floated by the wiring pattern 26, only one of the wiring patterns 16 and 26 is used. May be.

  For example, only the first wiring pattern 16 may be used, and the second terminals of the second and third IDTs 22 and 23 may be connected to the ground potential instead of the second wiring pattern 26. Even in such a case, since the grounding capacitance can be reduced on the side where the wiring pattern 16 is provided, the improvement in electrical characteristics is lower than in the case of the first embodiment, but the conventional elasticity is reduced. Compared with the surface acoustic wave filter device, the grounding capacity can be reduced, so that the VSWR can be improved and the passband width can be increased in the same manner.

  In the first embodiment, the surface acoustic wave filter device 1 having the balance-unbalance conversion function is shown, but the present invention is not limited to the surface acoustic wave filter device having the balance-unbalance conversion function. .

  In the surface acoustic wave filter device 101 according to the second embodiment shown in FIG. 7, the illustrated electrode structure is formed on the piezoelectric substrate 102. Here, between the unbalanced signal input terminal 103 and the unbalanced signal output terminal 104, longitudinally coupled resonator type first and second surface acoustic wave filter units 110 and 120 are cascade-connected. That is, one end of the first IDT 111 of the first surface acoustic wave filter unit 110 is connected to the unbalanced signal input terminal 103, and the other end is connected to the ground potential. In addition, one end of the first IDT 121 of the second longitudinally coupled resonator-type surface acoustic wave filter unit 120 is connected to the ground potential, and the other end is connected to the unbalanced signal output terminal 104. Since the other points are the same as those of the surface acoustic wave filter device 1 of the first embodiment, the same portions are denoted by the same reference numerals, and the description thereof is omitted.

  Thus, the surface acoustic wave filter device of the present invention may be a surface acoustic wave filter device having an unbalanced signal input or output and an unbalanced signal output or input.

  Also in the second embodiment, the second end, which is the end opposite to the side connected to the first and second signal lines 6, 7 of the second and third IDTs 12, 13, 22, 23. Are connected to each other by the wiring pattern 16 and are in an electrically floating state, and the phases of the signals transmitted through the first and second signal lines 6 and 7 are 180 ° different from each other. As in the first embodiment, the VSWR can be improved and the pass bandwidth can be increased.

  In the surface acoustic wave filter device 201 of the third embodiment shown in FIG. 8, the illustrated electrode structure is formed on a piezoelectric substrate 202. That is, between the first and second balanced signal input terminals 203a and 203b and the first and second balanced signal output terminals 204a and 204b, longitudinally coupled resonator type first and second surface acoustic waves are provided. Filter units 210 and 220 are connected in cascade.

  The surface acoustic wave filter units 210 and 220 are configured in the same manner as the surface acoustic wave filter units 10 and 20 of the first embodiment. However, one end of the first IDT 11 is connected to the first balanced signal input terminal 203a, and the other end is connected to the second balanced signal input terminal 203b. In the second surface acoustic wave filter unit 220, one end of the central IDT 21 is connected to the first balanced signal output terminal 204a, and the other end is connected to the second balanced signal output terminal 204b. Other configurations are the same as those of the surface acoustic wave filter device 1 of the first embodiment. Therefore, also in the present embodiment, as in the case of the first embodiment, it is possible to improve the VSWR and increase the pass bandwidth.

  FIG. 9 is a schematic plan view showing an electrode structure of a surface acoustic wave filter device according to the fourth embodiment of the present invention. In the surface acoustic wave filter device 301 of the fourth embodiment, two first surface acoustic wave filter parts 10, 10 A of 3IDT type longitudinally coupled resonator type are connected to the unbalanced terminal 3. A longitudinally coupled resonator type second surface acoustic wave filter unit 20 is connected to the subsequent stage of the first surface acoustic wave filter unit 10. One end of the first IDT 21 of the second surface acoustic wave filter unit 20 is electrically connected to the ground potential, and the other end is electrically connected to the first balanced terminal 4.

  On the other hand, a 3IDT type longitudinally coupled resonator type second surface acoustic wave filter unit 20A is also connected to the subsequent stage of the first surface acoustic wave filter unit 10A. One end of the first IDT 21 </ b> A of the second surface acoustic wave filter unit 20 </ b> A is connected to the ground potential, and the other end is connected to the second balanced terminal 5.

  In the present embodiment, the phases of the signals transmitted through the first and second signal lines 6 and 7 are 180 degrees different from each other, and the phases of the signals transmitted through the first and second signal lines 6A and 7A are also 180 degrees. The IDTs 11 to 13, 11A to 13A, 21 to 23, and 21A to 23A are configured so that the phases of the signals extracted from the first and second balanced terminals 4 and 5 are 180 degrees different from each other.

  In the present embodiment, the second terminal which is the end opposite to the side where the signal lines 6 and 7 of the second and third IDTs 12 and 13 are connected is connected by the wiring pattern 16. The second terminal, which is the end of the second and third IDTs 12 and 13 opposite to the side where the signal lines 6 and 7 are connected, is electrically connected by the wiring pattern 26. Similarly, the end of the IDT 12A, 13A opposite to the side where the signal lines 6A, 7A are connected is electrically connected by the wiring pattern 16A, and is connected to the signal lines 6A, 7A of the IDTs 22A, 23A. The end on the side opposite to the electrically connected side is electrically connected by the wiring pattern 26A.

  The wiring patterns 16, 26, 16A, and 26A are not connected to the ground potential but are in an electrically floating state. Therefore, also in this embodiment, it is possible to improve the VSWR and increase the pass bandwidth.

  FIG. 10 is a schematic plan view showing a surface acoustic wave filter device 351 according to the fifth embodiment. The surface acoustic wave filter device 351 according to the fifth embodiment is a modification of the surface acoustic wave filter device 301 according to the fourth embodiment, except that the wiring pattern is replaced with the wiring patterns 16, 26, 16A, and 26A. 352 and 353 are formed. That is, the wiring pattern 352 has a second terminal which is the end opposite to the side electrically connected to the signal line 7 of the IDT 13 and a side where the signal line 6A of the IDT 11A is electrically connected. The second terminal, which is the end on the opposite side, is commonly connected, is not connected to the ground potential, and is in an electrically floating state. Further, the wiring pattern 353 has a second terminal which is an end opposite to the side electrically connected to the signal line 7 of the IDT 23 and a side opposite to the side where the signal line 6A of the IDT 21A is connected. Are connected in common to the second terminal, which is not connected to the ground potential, and are in an electrically floating state.

  The ends of the IDTs 12, 22, 13A, 23A opposite to the side electrically connected to the signal line 6 or the signal line 7A are connected to the ground potential. In this way, instead of using the wiring patterns 16, 26, 16A, and 26A, the wiring patterns 352 and 353 may be formed. In this case, one end of the IDTs 12, 22, 13A, and 23A is at the ground potential. Although connected, the grounding capacitance can be reduced by forming the wiring patterns 352 and 353. Therefore, the VSWR can be improved and the pass bandwidth can be increased.

  As described above, the present invention is limited to the surface acoustic wave filter device having the float-type balanced-unbalanced conversion function shown in FIG. 1, and the surface acoustic wave filter devices 301 and 351 of the fourth and fifth embodiments. As described above, a surface acoustic wave filter device having a so-called neutral point type balance-unbalance conversion function may be used.

  11 and 12, a surface acoustic wave filter device using a 5IDT type longitudinally coupled resonator type surface acoustic wave filter may be used.

  In the surface acoustic wave filter device 401 of the sixth embodiment shown in FIG. 11, the illustrated electrode structure is formed on a piezoelectric substrate 402. Here, between the unbalanced terminal 3 and the first and second balanced terminals 4 and 5, 5IDT type longitudinally coupled resonator type first and second surface acoustic wave filter units 410 and 420 are cascade-connected. Has been.

  The surface acoustic wave filter unit 410 includes a first IDT 411, second and third IDTs 412 and 413 disposed on both sides of the surface wave propagation of the first IDT 411, and first to third IDTs 411 to 413. The fourth IDT 414 and the fifth IDT 415 are arranged on both sides of the surface wave propagation of the portion. First and second reflectors 416 and 417 are disposed outside the fourth and fifth IDTs 414 and 415 in the surface wave propagation direction, respectively.

  The second surface acoustic wave filter unit 420 also includes first to fifth IDTs 421 to 425 configured similarly, and first and second reflectors 426 and 427.

  Here, the first IDTs 411 and 421 at the center have first and second divided IDT portions 411a, 411b, 421a, and 421b provided by dividing one comb electrode in the surface wave propagation direction. .

  The first terminals of the second and third IDTs 412 and 413 are commonly connected to the unbalanced terminal 3. The second terminals of the IDTs 412 and 413 are connected to the ground potential. The first terminal of the fourth IDT 414 is connected to the first terminal of the fourth IDT 424 of the second surface acoustic wave filter unit 420 by the first signal line 6a.

  The second terminal, which is the end of the fourth IDT 414 opposite to the side electrically connected to the signal line 6 a, is electrically connected to the wiring pattern 418. Similarly, the second terminal which is the end of the IDT 424 opposite to the side electrically connected to the signal line 6 a is electrically connected to the wiring pattern 428.

  The first terminal of the first divided IDT unit 411a is connected to the first terminal of the first divided IDT unit 421a by the second signal line 7a.

  The first terminal of the second divided IDT unit 411b and the first terminal of the second divided IDT unit 421b are electrically connected by the third signal line 6b.

  The ends of the IDTs 411 and 421 having the common bus bar are electrically connected to the wiring patterns 418 and 428, respectively. One end of the fifth IDT 415 is connected to the wiring pattern 418, and the other end is connected to one end of the fifth IDT 425 through the fourth signal line 7b. The other end of the fifth IDT 425 is electrically connected to the wiring pattern 428.

  One end of the second IDT 422 is connected to the ground potential, and the other end is connected to the first balanced terminal 4. Similarly, one end of the third IDT 423 is connected to the ground potential, and the other end is connected to the second balanced terminal 5.

  Here, the phase of the signal flowing through the third signal line 6b and the fourth signal line so that the phase of the signal flowing through the first signal line 6a and the phase of the signal flowing through the second signal line 7a are 180 ° different from each other. IDTs 411 to 415 and IDTs 421 to 425 are configured so that the phase of the signal flowing through 7b is 180 degrees different from that of the signals extracted from the first and second balanced terminals 4 and 5 by 180 degrees. Yes.

  Since the wiring patterns 418 and 428 are provided and the wiring patterns 418 and 428 are not electrically connected to the ground potential but are in an electrically floating state, the routing area of the wiring pattern connected to the ground potential is provided. The grounding capacity can be reduced. Therefore, also in this embodiment, it is possible to improve the VSWR and increase the pass bandwidth.

  The surface acoustic wave filter device 501 shown in FIG. 12 is the same as the surface acoustic wave filter device 401 except that the connection mode between the unbalanced terminal 3 and the first and second balanced terminals 4 and 5 is different. ing. That is, in the surface acoustic wave filter device 501 of the sixth embodiment, the first balanced terminal 4 is connected to one end of the second and third IDTs 422 and 424, and the second balanced terminal 5 is connected to the first balanced terminal 5. The surface acoustic wave filter device 401 is configured in the same manner as the surface acoustic wave filter device 401 except that it is electrically connected to the other ends of the second and fourth IDTs 422 and 424. Thus, also in the surface acoustic wave filter device using the 5IDT type longitudinally coupled resonator type surface acoustic wave filter, the connection form of the first and second balanced terminals for realizing the balanced-unbalanced conversion function is as follows. It may be a float type.

  FIG. 13 is a schematic plan view showing an electrode structure of the surface acoustic wave filter device according to the eighth embodiment of the present invention. In the eighth embodiment, in the surface acoustic wave filter device 701, the illustrated electrode structure is formed on a piezoelectric substrate. That is, the illustrated electrode structure is connected between the unbalanced terminal 3 and the first and second balanced terminals 4 and 5. Here, as shown in the drawing, the first IDT 711 is arranged, and the second and third IDTs 712 and 713 are arranged on both sides of the first IDT 711 in the surface acoustic wave propagation direction. First and second reflectors 714 and 715 are arranged on both sides of the surface wave propagation direction of the region where IDTs 711 to 713 are provided. One end of the IDT 711 is connected to the unbalanced terminal 3, and the other end is connected to the ground potential. The first terminals of the second and third IDTs 712 and 713 are connected to the first and second balanced terminals 4 and 5, respectively. The second terminals that are not on the hot side of the IDTs 712 and 713 are commonly connected, and are electrically floated so as not to be connected to the ground potential.

  The IDTs 711 to 713 are formed such that when a signal is input from the unbalanced terminal 3, the phase of the signal extracted from the balanced terminal 4 and the phase of the signal extracted from the balanced terminal 5 differ by 180 °. Accordingly, the surface acoustic wave filter device 701 has a balance-unbalance conversion function.

  Since the second terminals of the IDTs 712 and 713 are connected in common and are in an electrically floating state, the wiring pattern on the second terminal side of the IDTs 712 and 713, that is, the unbalanced terminal 3 is arranged. It is possible to simplify the existing wiring pattern and to reduce the grounding resistance.

  Therefore, also in the present embodiment, it is possible to improve the VSWR and expand the bandwidth.

  FIG. 14 is a schematic plan view showing an electrode structure of a surface acoustic wave filter device according to the ninth embodiment of the present invention. In the surface acoustic wave filter device 801, the illustrated electrode structure is formed on a piezoelectric substrate. That is, longitudinally coupled resonator type first and second surface acoustic wave filter sections 802 and 803 are formed on the piezoelectric substrate. Each of the first and second surface acoustic wave filter units 802 and 803 includes the first IDTs 811 and 821 and the second and third surface acoustic wave propagation units disposed on both sides of the first IDTs 811 and 821 in the surface acoustic wave propagation direction. IDTs 812, 822, and 823, and first and second reflectors 814, 815, 824, and 825 disposed at both ends of the surface acoustic wave propagation direction.

  One end of the first IDT 811 of the first surface acoustic wave filter unit 802 and the first IDT 821 of the second surface acoustic wave filter unit 813 are connected in common and connected to the unbalanced terminal 3. The other ends of the first IDTs 811 and 821 are connected to the ground potential.

  On the other hand, the first terminal, which is the hot-side terminal of the second and third IDTs 812 and 813 of the first surface acoustic wave filter unit 802, is connected in common and connected to the first balanced terminal 4. Similarly, the first terminals which are the hot-side terminals of the second and third 822 and 823 of the second surface acoustic wave filter unit 803 are connected in common and connected to the second balanced terminal 5. .

  On the other hand, the second terminals of the second and third IDTs 812 and 813 of the first surface acoustic wave filter unit 803 and the second terminals of the second and third IDTs 822 and 823 of the second surface acoustic wave filter unit 803 are used. These terminals are all connected in common and are electrically floated so as not to be connected to the ground potential.

  Also in this embodiment, when a signal is input from the unbalanced terminal 3, the surface acoustic wave filter units 802 and 803 are extracted so that signals having a phase difference of 180 ° are extracted from the first and second balanced terminals 4 and 5. The first to third IDTs 811 to 813 and 821 to 823 are formed. In order to increase the degree of balance, serial weighting is performed in the IDT 821. Series weighting has a structure in which crank-shaped floating electrode fingers 821a and 821b are provided so as to extend over a plurality of electrode fingers including electrode fingers at both ends of the IDT 821 in the surface acoustic wave propagation direction. Has been enhanced.

  Also in this embodiment, the second terminals of the second and third IDTs 812, 813, 822, and 823 of the first and second surface acoustic wave filter units 802 and 803 are all connected in common and are electrically floated. Therefore, the wiring pattern on the second terminal side of the IDTs 812, 813, 822, and 823 can be simplified and the grounding capacity can be reduced. Therefore, VSWR can be improved and the bandwidth can be increased.

  FIG. 15 is a schematic plan view showing an electrode structure of a surface acoustic wave filter device according to the tenth embodiment of the present invention.

  In the surface acoustic wave filter device 901 of the present embodiment, the first and second longitudinally coupled resonator type surface acoustic wave filter sections 902 and 903 are connected to the unbalanced terminal 3 as in the ninth embodiment. Yes. The first and second surface acoustic wave filter units 902 and 903 both have a first IDT 911 and 921, and second and third IDTs 912 and 913 arranged on both sides of the first IDT 911 and 921. , 922, 923 and first and second reflectors 914, 915, 924, 925 arranged at both ends of the surface acoustic wave propagation direction, are 3IDT type longitudinally coupled resonator type surface acoustic wave filter sections. .

  Here, unlike the ninth embodiment, one end of the second and third IDTs 912 and 913 of the first surface acoustic wave filter unit 902 and the second and third IDTs 922 of the second surface acoustic wave filter unit 903 are different. , 923 are all connected in common and connected to the unbalanced terminal 3, and the other ends are connected to the ground potential. The first terminals which are the hot-side terminals of the first IDTs 911 and 921 of the first and second surface acoustic wave filter units 902 and 903 are respectively the first and second balanced terminals 4 and 5. The second terminals, which are the opposite terminals, are connected in common and are electrically floated so as not to be connected to the ground potential.

  Also in the present embodiment, the first to third IDTs 911 to 913 and 921 to 923 are formed so that the balanced-unbalanced conversion function can be realized, and serial weighting is performed in the first IDT 921. Therefore, the balance is improved.

  In addition, also in this embodiment, the second terminal opposite to the first terminal connected to the first and second balanced terminals is connected in common so that it is not electrically connected to the ground potential. Since it is in a floating state, the wiring pattern on the second terminal side of the IDTs 911 and 921 can be simplified and the grounding resistance can be reduced. Therefore, it is possible to improve the VSWR and widen the bandwidth, and it is possible to provide a surface acoustic wave filter device with good filter characteristics.

  The surface acoustic wave filter device according to the present invention is suitably used as an RF stage band-pass filter of a mobile phone, but is particularly suitably used to configure the duplexer 601 shown in FIG. In the duplexer 601, the surface acoustic wave filter device 1 of the first embodiment is connected to an unbalanced terminal 603 connected to an antenna via a surface acoustic wave resonator 604. As a result, a reception-side band filter having the first and second balanced terminals 4 and 5 as reception terminals is configured. On the other hand, a transmission side band filter 605 is also connected to the unbalanced terminal 603 connected to the antenna terminal. In this embodiment, the transmission-side band filter 605 has a ladder-type circuit configuration having a plurality of series arm resonators 605a to 605c and a plurality of parallel arm resonators 605d and 605e. A plurality of series arm resonators 605 a to 605 c are connected between the transmission terminal 606 and the unbalanced terminal 603.

In the first embodiment, the piezoelectric substrate is composed of a 40 ° ± 5 ° Y-cut X-propagation LiTaO ₃ substrate. However, in the present invention, the piezoelectric substrate is a 64 ° to 72 ° Y-cut X-propagation. Other cut angles such as a LiNbO ₃ substrate, a 41 ° Y-cut X-propagation LiNbO ₃ substrate, or a piezoelectric substrate made of another piezoelectric material may be used.

1 is a schematic plan view of a surface acoustic wave filter device according to a first embodiment of the present invention. The figure which shows the filter characteristic of the surface acoustic wave filter apparatus of 1st Embodiment and a comparative example. (A) And (b) is each figure which shows the VSWR characteristic as a reflection characteristic of the surface acoustic wave filter apparatus of the comparative example of 1st Embodiment, (a) is a VSWR characteristic in the input side, (b ) Shows the VSWR characteristic on the output side. FIG. 2 is a schematic plan view of a surface acoustic wave filter device prepared as a comparative example. The typical top view for demonstrating arrangement | positioning of the electrode part on the piezoelectric substrate in the surface acoustic wave filter apparatus of 1st Embodiment. The typical top view for demonstrating arrangement | positioning of the electrode part on the piezoelectric substrate in the surface acoustic wave filter apparatus of a comparative example. FIG. 6 is a schematic plan view of a surface acoustic wave filter device according to a second embodiment. FIG. 6 is a schematic plan view of a surface acoustic wave filter device according to a third embodiment. FIG. 9 is a schematic plan view of a surface acoustic wave filter device according to a fourth embodiment. FIG. 9 is a schematic plan view of a surface acoustic wave filter device according to a fifth embodiment. FIG. 10 is a schematic plan view of a surface acoustic wave filter device according to a sixth embodiment. FIG. 10 is a schematic plan view of a surface acoustic wave filter device according to a seventh embodiment. FIG. 10 is a schematic plan view of a surface acoustic wave filter device according to an eighth embodiment. FIG. 10 is a schematic plan view of a surface acoustic wave filter device according to a ninth embodiment. FIG. 10 is a schematic plan view of a surface acoustic wave filter device according to a tenth embodiment. 1 is a schematic plan view showing a duplexer in which a surface acoustic wave filter device according to a first embodiment of the present invention is provided as a reception-side band filter. The typical top view of the conventional surface acoustic wave filter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave filter apparatus 2 ... Piezoelectric substrate 3 ... Unbalanced terminal 4,5 ... 1st, 2nd balanced terminal 6,7 ... 1st, 2nd signal line 6a, 7a ... 1st, 2nd Signal lines 6b, 7b ... 3rd and 4th signal lines 10, 10A ... 1st surface acoustic wave filter part 11-13, 11A-13A ... 1st-3rd IDT
DESCRIPTION OF SYMBOLS 14, 15 ... Reflector 16 ... Wiring pattern 20, 20A ... 2nd surface acoustic wave filter part 21-23, 21A-23A ... 1st-3rd IDT
24, 25 ... first and second reflectors 26 ... wiring pattern 32 ... IDT
33, 34 ... reflector 101 ... surface acoustic wave filter device 110 ... first surface acoustic wave filter unit 120 ... second surface acoustic wave filter unit 103 ... unbalanced input terminal 104 ... unbalanced output terminal 111, 121 ... first 1 IDT
DESCRIPTION OF SYMBOLS 201 ... Surface acoustic wave filter apparatus 203a, 203b ... Balance signal input terminal 204a, 204b ... Balance signal output terminal 210, 220 ... 1st, 2nd surface acoustic wave filter part 301 ... Surface acoustic wave filter apparatus 351 ... Wiring pattern 352 , 353 ... wiring pattern 401 ... surface acoustic wave filter device 410 ... first surface acoustic wave filter section 411 to 415 ... first to fifth IDTs
411a, 411b ... 1st, 2nd division | segmentation IDT part 416, 417 ... Reflector 420 ... 2nd surface acoustic wave filter part 421-425 ... 1st-5th IDT
421a, 421b ... 1st, 2nd division | segmentation IDT part 426, 427 ... Reflector 451 ... Surface acoustic wave filter apparatus 452,453 ... Wiring pattern 501 ... Surface acoustic wave filter apparatus 601 ... Duplexer 603 ... Antenna terminal 604 ... Elastic surface Wave resonator 605 ... Transmission side band filters 605a to 605c ... Series arm resonators 605c and 605d ... Parallel arm resonators 701 ... Surface acoustic wave filter devices 711 to 713 ... First to third IDTs
714, 715 ... reflector 801 ... surface acoustic wave filter device 802, 803 ... first and second surface acoustic wave filter sections 811-813 ... first to third IDTs
821-823 ... 1st-3rd IDT
814, 815, 824, 825 ... reflector 901 ... surface acoustic wave filter device 902, 903 ... first and second surface acoustic wave filter sections 911-913 ... first to third IDTs
921-923 ... 1st-3rd IDT
914, 915 ... reflector 924, 925 ... reflector

Claims (2)

A piezoelectric substrate;
A longitudinally coupled resonator type first and second surface acoustic wave filter parts formed on a piezoelectric substrate;
One end of each of the first and second surface acoustic wave filter sections is connected to an unbalanced terminal, and the other end of the first surface acoustic wave filter section is connected to a first balanced terminal, A surface acoustic wave filter device in which the other end of the wave filter unit is connected to the second balanced terminal,
The first and second surface acoustic wave filter units respectively include a first IDT, second and third IDTs disposed on both sides of the first IDT in the surface acoustic wave propagation direction, and surface acoustic wave propagation. First and second reflectors disposed at both ends in the direction,
The first IDT of the first and second surface acoustic wave filter units includes a hot-side first terminal through which a signal current flows, and a second terminal opposite to the first terminal,
One ends of the second and third IDTs of the first and second surface acoustic wave filter sections are commonly connected, connected to the unbalanced terminal, and each other end is connected to a ground potential. The first IDT first terminal of the first surface acoustic wave filter section is the first balanced terminal, and the first IDT first terminal of the second surface acoustic wave filter section is the first terminal. 2 balanced terminals,
The first to third IDTs of the first and second surface acoustic wave filter sections are formed so that the phases of the signals extracted from the first and second balanced terminals are 180 ° different from each other.
The second terminals of the first IDTs of the first and second surface acoustic wave filter sections are connected in common and are not electrically connected to the ground potential and are in an electrically floating state. A surface acoustic wave filter device. A duplexer comprising the surface acoustic wave filter device according to claim 1 as a bandpass filter.

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