JP2015109622A - Longitudinal coupling resonator type surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure for improving amplitude balancing and phase balancing in a longitudinal coupling resonator type surface acoustic wave filter having a balanced-unbalanced conversion function.SOLUTION: There is provided a longitudinal coupling resonator type surface acoustic wave filter comprising: a multilayer substrate including a laminated structure of a piezoelectric film/a low sound velocity film/a high sound velocity film/a support substrate; and first to third IDT201 to 203 which re-arranged in order along a propagation direction of surface acoustic wave on the multilayer substrate, in which two stages of the filters are cascade connected, one end of a first IDT201 of a first stage filter is connected to one end of a first IDT201 of a second filter by first signal line, one end of a third IDT203 of the first stage filter is connected to one end of a third IDT203 of the second stage filter by second signal line, and an electric signal propagating the first signal line and an electric signal propagating the second signal line are in opposite phases.

Description

  The present invention relates to a longitudinally coupled resonator type surface acoustic wave filter, and more particularly to a longitudinally coupled resonator type surface acoustic wave filter having a balanced-unbalanced conversion function.

  In recent years, mobile phones have become smaller and lighter. In view of this, in mobile phones, the number of component parts has been reduced, the size of parts has been reduced, and functions have been combined.

  In view of the above situation, various types of surface acoustic wave filters used in the RF stage of a mobile phone have been proposed which have a balanced-unbalanced conversion function, a so-called balun function.

  FIG. 26 is a schematic plan view showing an electrode structure of a surface acoustic wave filter having a conventional balance-unbalance conversion function. Here, the first to third IDTs 101 to 103 are arranged along the surface acoustic wave propagation direction. Reflectors 104 and 105 are arranged on both sides of the surface wave propagation direction in the region where IDTs 101 to 103 are provided. The distance between the centers of the electrode fingers adjacent to IDT 101 and IDT 102 and the distance between the centers of the electrode fingers adjacent to IDT 102 and IDT 103 are both 0.75 λI when the wavelength λI is determined by the electrode finger pitch of IDTs 101 to 103. Has been. By thickening the electrode fingers 109 and 110 at both ends of the IDT 102, a free portion between the IDT and the IDT is reduced, and loss due to bulk wave radiation is reduced. In FIG. 26, terminals 106 and 107 are balanced signal terminals, and a terminal 108 is an unbalanced signal terminal.

  In the surface acoustic wave filter having a balanced-unbalanced conversion function, transmission characteristics in the passbands between the unbalanced signal terminal 108 and the balanced signal terminal 106 and between the unbalanced signal terminal 108 and the balanced terminal 107 are shown. It is required that the amplitude characteristics are equal and the phase is inverted by 180 °. The condition where the amplitude characteristics are equal is called amplitude balance, and the degree of phase inversion by 180 ° is called phase balance.

As for the amplitude balance and the phase balance, a surface acoustic wave filter having a balance-unbalance conversion function is considered as a three-port device. For example, the unbalanced input terminal is port 1 and the balanced output terminal is port 2, port. When it is 3, it is defined as follows.
Amplitude balance = | A |, where A = | 20logS21 | − | 20logS31 |
Phase balance = | B−180 |, where B = | ∠S21−∠S31 |
S21 represents a transmission coefficient from port 1 to port 2, and S31 represents a transmission coefficient from port 1 to port 3.

  Ideally, the amplitude balance should be 0 dB and the phase balance should be 0 degrees within the passband of the filter. However, in the configuration shown in FIG. 26, when trying to obtain a filter having a balanced-unbalanced conversion function, the number of electrode fingers of the IDT 102 is an odd number, so the number of electrode fingers connected to the balanced signal terminal 106 However, there is a problem that the number of electrode fingers connected to the balanced signal terminal 107 is one more, and the degree of balance deteriorates. This problem becomes more prominent as the center frequency of the filter becomes higher, and sufficient balance cannot be obtained with a filter having a center frequency near 1.9 GHz, such as for DCS and PCS.

  An object of the present invention is to provide a longitudinally coupled resonator type surface acoustic wave filter having a balance-unbalance conversion function with improved balance such as amplitude balance and phase balance.

  A longitudinally coupled resonator type surface acoustic wave filter according to the present invention includes a laminated substrate having a laminated structure of piezoelectric film / low acoustic velocity film / high acoustic velocity membrane / support substrate, and a surface acoustic wave propagation direction on the laminated substrate. Two stages of longitudinally coupled resonator type surface acoustic wave filters including first to third IDTs arranged in order along the cascade are connected in cascade, and the first stage longitudinally coupled resonator type surface acoustic wave filter includes One end of the second IDT is connected to the unbalanced signal terminal, and one end and the other end of the second IDT of the second stage longitudinally coupled resonator surface acoustic wave filter are connected to the first and second balanced signal terminals. One end of the first IDT of the first stage longitudinally coupled resonator type surface acoustic wave filter and one end of the first IDT of the second longitudinally coupled resonator type surface acoustic wave filter are connected to each other. With the signal line, the third stage of the first stage longitudinally coupled resonator type surface acoustic wave filter is provided. One end of the DT and one end of the third IDT of the second-stage longitudinally coupled resonator type surface acoustic wave filter are connected by a second signal line, respectively, and a longitudinally coupled resonator having a balance-unbalance conversion function The type surface acoustic wave filter is characterized in that the electrical signal propagating through the first signal line and the electrical signal propagating through the second signal line have opposite phases.

  In a specific aspect of the present invention, the number of electrode fingers of the second IDT is an even number of at least one of the first-stage and second-stage longitudinally coupled resonator-type surface acoustic wave filters.

  In another aspect of the present invention, a communication device using the longitudinally coupled resonator type surface acoustic wave filter according to the present invention is provided.

  According to the longitudinally coupled resonator type surface acoustic wave filter according to the present invention, the longitudinally coupled resonator type surface acoustic wave filters having the first to third IDTs are cascade-connected, and the first stage longitudinally coupled One end of the second IDT of the resonator type surface acoustic wave filter is connected to the unbalanced signal terminal, and both ends of the second IDT of the second stage longitudinally coupled resonator type surface acoustic wave filter are connected to the pair of balanced signal terminals. In the connected configuration, one end of the first IDT of the first-stage longitudinally coupled resonator type surface acoustic wave filter is connected to one end of the first IDT of the second longitudinally coupled resonator type surface acoustic wave filter. The first signal line propagating through the first signal line, one end of the third IDT of the first-stage longitudinally coupled resonator-type surface acoustic wave filter, and the second stage longitudinally-coupled resonator-type surface acoustic wave filter. A second signal line connecting one end of the third IDT. Since there is an electric signal to transportable have opposite phases, it can be a second IDT, a first, same polarities of the third IDT adjacent electrode fingers. Therefore, the amplitude balance and the phase balance can be effectively improved.

  In the present invention, in at least one of the first-stage and second-stage longitudinally coupled resonator-type surface acoustic wave filters, when the number of electrode fingers of the second IDT is an even number, amplitude balance is further increased. Degree and phase balance can be improved.

  The longitudinally coupled resonator type surface acoustic wave filter according to the present invention has a balanced-unbalanced conversion function as described above, and the balance between the pair of balanced signal terminals is improved. By configuring the communication device using the longitudinally coupled resonator type surface acoustic wave filter, it is possible to improve the characteristics of the communication device and reduce the size thereof.

FIG. 1 is a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter according to a first embodiment of the present invention. FIG. 2A is a cross-sectional view showing a multilayer substrate having a multilayer structure of a piezoelectric film / low acoustic velocity film / high acoustic velocity membrane / supporting substrate of the longitudinally coupled resonator type surface acoustic wave filter of the first embodiment. . FIG. 2B and FIG. 2C are modified examples thereof. FIG. 2 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter that is a premise of the first embodiment. FIG. 2 is a schematic plan view of a longitudinally coupled resonator type surface acoustic wave filter that is a premise of the first embodiment. The figure which shows the amplitude balance-frequency characteristic of 1st Embodiment and a prior art example. The figure which shows the phase balance-frequency characteristic of 1st Embodiment and a prior art example. FIG. 6 is a schematic plan view showing a longitudinally coupled resonator type surface acoustic wave filter according to a first modification of the first embodiment. FIG. 6 is a schematic plan view showing a longitudinally coupled resonator type surface acoustic wave filter according to a second modification of the first embodiment. FIG. 9 is a schematic plan view showing a longitudinally coupled resonator type surface acoustic wave filter according to a third modification of the first embodiment. FIG. 9 is a schematic plan view showing a longitudinally coupled resonator type surface acoustic wave filter according to a fourth modification of the first embodiment. FIG. 10 is a schematic plan view showing a longitudinally coupled resonator type surface acoustic wave filter according to a fifth modification of the first embodiment. The typical top view for demonstrating the longitudinal coupling resonator type | mold surface acoustic wave filter of 2nd Embodiment. The typical top view which shows the modification of the surface acoustic wave filter of 2nd Embodiment. The figure which shows the amplitude balance-frequency characteristic of 2nd Embodiment and a prior art example. The figure which shows the phase balance degree-frequency characteristic of 2nd Embodiment and a prior art example. The typical top view for demonstrating the prior art example prepared for the comparison of 2nd Embodiment. The typical top view for explaining the modification of a 2nd embodiment. The typical top view for explaining the longitudinal coupling resonator type surface acoustic wave filter of a 3rd embodiment. The figure which shows the amplitude balance-frequency characteristic of 3rd Embodiment and a prior art example. The figure which shows the phase balance-frequency characteristic of 3rd Embodiment and a prior art example. FIG. 9 is a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter according to a fourth embodiment. The figure which shows the amplitude balance-frequency characteristic of 4th Embodiment and a prior art example. The figure which shows the phase balance degree-frequency characteristic of 4th Embodiment and a prior art example. FIG. 10 is a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter according to a fifth embodiment. The schematic block diagram which shows an example of the communication apparatus comprised using the longitudinally coupled resonator type | mold surface acoustic wave filter which concerns on this invention. FIG. 6 is a schematic plan view for explaining a conventional longitudinally coupled resonator type surface acoustic wave filter.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the longitudinally coupled resonator type surface acoustic wave filter of the present invention with reference to the drawings.

  FIG. 1 is a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter used for a PCS reception filter according to a first embodiment of the present invention. In the longitudinally coupled resonator-type surface acoustic wave filter 200, the illustrated electrode structure is configured on the multilayer substrate 200A. As shown in FIG. 2, the laminated substrate 200 </ b> A has a laminated structure of a piezoelectric film 54 / a low acoustic velocity film 53 / a high acoustic velocity film 52 / a support substrate 51. IDTs 201 to 203 and reflectors 204 and 205 are formed on the multilayer substrate 200A.

  First to third IDTs 201 to 203 are formed on the piezoelectric film 54 along the surface wave propagation direction. Reflectors 204 and 205 are disposed on both sides of the surface wave propagation direction of the region where the IDTs 201 to 203 are provided. The IDTs 201 to 203 and the reflectors 204 and 205 are made of Al.

  That is, the longitudinally coupled resonator type surface acoustic wave filter 200 is a 3IDT type longitudinally coupled resonator type surface acoustic wave filter, like the conventional longitudinally coupled resonator type surface acoustic wave filter 100 shown in FIG.

  In FIG. 1, for the sake of simplicity, the number of electrode fingers is shown smaller than the actual structure. Further, one ends of the IDTs 201 and 203 are connected to the unbalanced signal terminal 212. One end of the IDT 202 is connected to the balanced signal terminal 210 and the other end is connected to the balanced signal terminal 211.

A detailed design of the longitudinally coupled resonator type surface acoustic wave filter 200 of the present embodiment is shown below.
Electrode finger crossing width W = 78.8λI
Number of electrode fingers of IDTs 201 and 203... 24 each of electrode fingers of IDT 202 = 40 IDT wavelength λI = 2.03 μm
Wavelength λR of reflectors 204 and 205 = 2.05 μm
Number of electrode fingers in reflectors 204 and 205 = 100 IDT-IDT interval = 0.77λI, where the IDT-IDT interval refers to the distance between adjacent electrode finger centers of adjacent IDTs.
IDT-reflector interval = 0.55λR, where IDT-reflector interval refers to the distance between adjacent IDTs and the electrode electrode centers of the reflectors.
IDT duty = 0.60
Reflector duty = 0.60
Electrode thickness = 0.08λI
Further, as shown in FIG. 1, the electrode fingers 206 and 207 at both ends of the IDT 202 are made thicker than the other electrode fingers, thereby reducing the free portion of the IDT-IDT interval portion. .

  The feature of this embodiment is that the total electrode index of the IDT 202 arranged in the center is an even number, the electrode finger 201a of the IDT 201 adjacent to the IDT 202 is a signal electrode, and the electrode finger 203a of the IDT 203 adjacent to the IDT 202 is grounded. This is because it is an electrode. The reason why the polarity of the electrode fingers 201a and 203a adjacent to the center second IDT 202 among the electrode fingers of the left and right IDTs 201 and 203 is reversed will be described with reference to FIGS. .

  In the conventional longitudinally coupled resonator type surface acoustic wave filter 100 shown in FIG. 26, if one electrode finger of the center IDT 102 is deleted, as shown in FIG. 3, the number of electrode fingers of the center IDT 102A is an even number. Become. However, the distance A between the IDT 102A and the IDT 103 increases by 0.5λI, and the loss due to the emission of the bulk wave increases.

  Therefore, as shown in FIG. 4, a structure in which the third IDT 103 is shifted by 0.5λI toward the IDT 102A with respect to the IDT 102A can be considered. However, in the structure shown in FIG. 4, IDT 101 and IDT 103 are in opposite phases.

  Therefore, in this embodiment, as shown in FIG. 1, the IDT 201 is inverted with respect to the IDT 203, so that the IDT 201 and the IDT 203 are in phase.

  FIG. 5 shows the degree of amplitude balance with respect to frequency in the longitudinally coupled resonator type surface acoustic wave filter of this embodiment, and FIG. 6 shows the degree of phase balance with respect to frequency. 5 and 6, the solid line indicates the result of the embodiment. For comparison, the characteristics of the conventional example shown in FIG. 26 are also shown by broken lines in FIGS.

  Here, the conventional example is the same except that the number of electrode fingers of the central IDT is one less than the detailed design of the above embodiment. The frequency range of the pass band in the PCS reception filter is 1930 to 1990 MHz. As is apparent from FIG. 5, in this frequency band, the maximum amplitude balance is 3.2 dB in the conventional example, whereas in this embodiment, it is 2.7 dB, and the 0.5 dB amplitude balance is improved. You can see that Further, as is clear from FIG. 6, the maximum phase balance is 21 ° in the conventional example, whereas it is 17 ° in the present embodiment, and the phase balance is improved by 4 °. Recognize.

  As described above, in this embodiment, the total electrode index of the center IDT 202 is an even number, and the polarities of the electrode fingers adjacent to the second IDT 202 in the center of the first and third IDTs 201 and 203 are also the same. Since it is inverted, it can be seen that a longitudinally coupled resonator type surface acoustic wave filter having a balanced-unbalanced conversion function in which both the amplitude balance and the phase balance are improved as compared with the conventional example can be obtained. .

  As described above, the longitudinally coupled resonator type surface acoustic wave filter of the present invention includes a laminated substrate having a laminated structure of piezoelectric film / low acoustic velocity film / high acoustic velocity membrane / support substrate, and an IDT is formed on the substrate. Consists of structure.

  FIG. 2 shows a multilayer substrate 200A of the longitudinally coupled resonator type surface acoustic wave filter 200 according to the first embodiment.

  The laminated substrate 200 </ b> A has a support substrate 51. A high sound velocity film 52 having a relatively high sound velocity is laminated on the support substrate 51. On the high sound velocity film 52, a low sound velocity film 53 having a relatively low sound velocity is laminated. A piezoelectric film 54 is laminated on the low acoustic velocity film 53. IDTs 201 to 203 and reflectors 204 and 205 are laminated on the upper surface of the piezoelectric film 54. The IDTs 201 to 203 and the reflectors 204 and 205 may be laminated on the lower surface of the piezoelectric film 54.

  The laminated substrate 200A can be made of an appropriate material as long as the laminated substrate 200A can support the laminated structure including the high sound velocity film 52, the low sound velocity film 53, the piezoelectric film 54, the IDTs 201 to 203, and the reflectors 204 and 205. Such materials include piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, quartz, alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, etc. Various ceramics, dielectrics such as glass, semiconductors such as silicon and gallium nitride, resin substrates, and the like can be used. In the present embodiment, the support substrate 51 is made of glass.

  The high sound velocity film 52 functions so that the surface acoustic wave is confined in the portion where the piezoelectric film 54 and the low sound velocity film 53 are laminated, and does not leak into the structure below the high sound velocity film 52. In the present embodiment, the high acoustic velocity film 52 is made of aluminum nitride. However, as long as the elastic wave can be confined, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC film or diamond, a medium mainly composed of the above materials, and a medium mainly composed of a mixture of the above materials. Various high sound speed materials such as can be used. In order to confine the surface acoustic wave in the portion where the piezoelectric film 54 and the low acoustic velocity film 53 are laminated, it is desirable that the film thickness of the high acoustic velocity film 52 is thicker, more than 0.5 times the wavelength λ of the surface acoustic wave, Is preferably 1.5 times or more.

  In the present specification, the high acoustic velocity film refers to a membrane in which the acoustic velocity of the bulk wave in the high acoustic velocity film is higher than that of the surface wave or boundary wave propagating through the piezoelectric film 54. . The low sound velocity film is a film in which the sound velocity of the bulk wave in the low sound velocity film is lower than the bulk wave propagating through the piezoelectric film 54. In addition, elastic waves of various modes with different sound speeds are excited from an IDT on a certain structure. The elastic waves propagating through the piezoelectric film 54 are used to obtain characteristics of a filter and a resonator. The elastic wave of a specific mode is shown. The bulk wave mode that determines the acoustic velocity of the bulk wave is defined according to the use mode of the elastic wave propagating through the piezoelectric film 54. When the high sonic film 52 and the low sonic film 53 are isotropic with respect to the propagation direction of the bulk wave, the following Table 1 is obtained. That is, the high sound velocity and the low sound velocity are determined according to the right-axis bulk wave mode of Table 1 below with respect to the left-axis elastic wave main mode of Table 1 below. The P wave is a longitudinal wave, and the S wave is a transverse wave.

  In Table 1 below, U1 means a P wave as a main component, U2 means an SH wave as a main component, and U3 means an elastic wave whose main component is an SV wave.

As the material constituting the low sound velocity film 53, an appropriate material having a bulk wave sound velocity lower than the bulk wave propagating through the piezoelectric film 54 can be used. As such a material, a medium mainly composed of the above materials such as silicon oxide, glass, silicon oxynitride, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide can be used.

  The low sound velocity film and the high sound velocity film are made of an appropriate dielectric material capable of realizing the high sound velocity and the low sound velocity determined as described above.

The piezoelectric film 54, in this embodiment, in LiTaO ₃ namely Euler angles 38.5 ° Y-cut made (0 °, 128.5 °, 0 °) LiTaO 3 , the film thickness, the electrode cycle of IDT13 When the wavelength of the surface acoustic wave to be determined is λ, it is 0.25λ. However, the piezoelectric film 54 may be formed of LiTaO _{3 having} other cut angles such as 50 ° Y-cut LiTaO ₃ , or may be formed of a piezoelectric single crystal other than LiTaO ₃ .

  In the present invention, since the low acoustic velocity film 53 is disposed between the high acoustic velocity film 52 and the piezoelectric film 54, the acoustic velocity of the elastic wave is lowered. The energy of an elastic wave is concentrated in a medium that is essentially a low sound velocity. Accordingly, the effect of confining the elastic wave energy in the piezoelectric film 54 and the IDT in which the elastic wave is excited can be enhanced. Therefore, compared with the case where the low acoustic velocity film 53 is not provided, according to the present embodiment, loss can be reduced and the Q value can be increased. The high sound velocity film 52 functions so as to confine the elastic wave in the portion where the piezoelectric film 54 and the low sound velocity film 53 are laminated so as not to leak into the structure below the high sound velocity film 52. That is, in the structure of the present application, the energy of the elastic wave of a specific mode used for obtaining the characteristics of the filter and the resonator is distributed throughout the piezoelectric film 54 and the low sonic film 53, and the low sonic film of the high sonic film 52. It is distributed also to a part of the side and not distributed to the laminated substrate 2. The mechanism for confining the elastic wave by the high acoustic velocity film is a non-leakage SH wave.

  In FIG. 2A, a laminated substrate having a laminated structure of the piezoelectric film 54 / the low acoustic velocity film 53 / the high acoustic velocity film 52 / the supporting substrate 51 is shown. However, as shown in FIG. The layer 22 may be laminated between the support substrate 51 and the high acoustic velocity film 52. Other configurations are the same as those of the first embodiment. Therefore, the description of the first embodiment is incorporated. Accordingly, the IDT electrodes 201 to 203, the piezoelectric film 54, the low acoustic velocity film 53, the high acoustic velocity film 52, the medium layer 22, and the support substrate 51 are laminated in this order from the top.

  As the medium layer 22, any material such as a dielectric, a piezoelectric, a semiconductor, or a metal may be used. Even in this case, the same effect as that of the first embodiment can be obtained. However, when the medium layer 22 is made of metal, the specific band can be reduced. Therefore, for applications where the specific bandwidth is small, the medium layer 22 is preferably made of metal.

  Further, as shown in FIG. 2C, the medium layer 22 and the medium layer 24 may be laminated between the support substrate 51 and the high sound velocity film 52. That is, the IDT electrodes 201 to 203, the piezoelectric film 54, the low sound velocity film 53, the high sound velocity film 52, the medium layer 22, the medium layer 24, and the support substrate 51 are laminated in this order from the top. Except for the medium layer 22 and the medium layer 24, the configuration is the same as in the first embodiment.

  The medium layers 22 and 24 may use any material such as a dielectric, a piezoelectric, a semiconductor, or a metal. Even in that case, the same effect as the surface acoustic wave device of the first embodiment can be obtained.

  In the present embodiment (modified example), after a laminated structure composed of the piezoelectric film 54, the low acoustic velocity film 53, the high acoustic velocity film 52 and the medium layer 22 and a laminated structure composed of the medium layer 24 and the support substrate 51 are separately manufactured, Both laminated structures are joined. Thereafter, IDT electrodes 201 to 203 are formed on the piezoelectric film 54. Accordingly, the surface acoustic wave device according to the present embodiment can be obtained without depending on the manufacturing constraints when manufacturing each laminated structure. Therefore, the freedom degree of selection of the material which comprises each layer can be raised.

  Note that any joining method can be used for joining the two laminated structures. As such a bonding structure, various methods such as hydrophilic bonding, activation bonding, atomic diffusion bonding, metal diffusion bonding, anodic bonding, bonding with resin or SOG can be used.

  In the first embodiment, the balanced signal is extracted from the center second IDT. However, as shown in FIG. 7, the balanced signal may be extracted from the first and third IDTs 201 and 203 on both sides. Good. In FIG. 7, terminals 213 and 214 are balanced signal terminals, which are connected to the first and third IDTs 201 and 203, and the terminal 215 is an unbalanced signal terminal connected to the second IDT 202 at the center. It is.

  Further, FIG. 8 is a schematic plan view showing an electrode structure of another modification of the first embodiment. As shown in FIG. 8, a surface acoustic wave resonator 216 may be connected between the first and third IDTs 201 and 203 and the terminal 212.

  FIG. 9 is a plan view schematically showing an electrode structure of still another modified example of the longitudinally coupled resonator type surface acoustic wave filter of the first embodiment. In the longitudinally coupled resonator type surface acoustic wave filter 217 shown in FIG. 9, the longitudinally coupled resonator type surface acoustic wave filter 200 of the first embodiment is cascade-connected in two stages.

  FIG. 10 is a schematic plan view of a longitudinally coupled resonator type surface acoustic wave filter according to still another modification of the first embodiment. Here, the longitudinally coupled resonator type surface acoustic wave filter 200 of the first embodiment is connected to a longitudinally coupled resonator type surface acoustic wave filter 219 of the 3IDT type and having an odd number of electrode fingers in the center IDT 218. It is connected. That is, in the longitudinally coupled resonator type surface acoustic wave filter having a plurality of stages, the first embodiment is applied even when at least one stage is constituted by the longitudinally coupled resonator type surface acoustic wave filter 200 of the first embodiment. In the same manner as above, characteristics with improved balance can be obtained.

  FIG. 11 is a schematic plan view showing an electrode structure of still another modified example of the longitudinally coupled resonator type surface acoustic wave filter according to the first embodiment. In the longitudinally coupled resonator type surface acoustic wave filter 220 shown in FIG. 11, narrow pitch electrode finger portions N1 to N4 are provided in the first to third IDTs 221 to 223. That is, the IDT 221 includes a narrow-pitch electrode finger portion N1 in which the pitch of some electrode fingers from the end portion on the IDT 222 side is narrower than the pitch of the remaining electrode finger portions of the IDT 221. Similarly, in the IDT 222, narrow pitch electrode finger portions N2 and N3 are formed at both ends. In the IDT 223, a narrow pitch electrode finger portion N4 is formed on the IDT 222 side. As described above, even when the narrow pitch electrode finger portion having a relatively narrow electrode finger pitch is used in the portion where the IDTs are adjacent to each other, the balance degree is also reduced by making the other configurations the same as those in the first embodiment. Improved properties can be obtained.

  FIG. 12 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to the second embodiment of the present invention. The second embodiment is an embodiment of an AMPS reception filter.

In the second embodiment, the longitudinally coupled resonator type surface acoustic wave filter 300 of the second embodiment is configured by forming the electrode structure shown in FIG. 12 on a 50 ° Y-cut LiTaO ₃ substrate. Yes.

  In the longitudinally coupled resonator type surface acoustic wave filter 300, a longitudinally coupled resonator type surface acoustic wave filter unit 301 and a longitudinally coupled resonator type surface acoustic wave filter unit 302 are cascade-connected in two stages. The longitudinally coupled resonator type surface acoustic wave filter sections 301 and 302 are similarly configured.

  As in the first embodiment, the longitudinally coupled resonator type surface acoustic wave filter sections 301 and 302 are provided with first to third IDTs 303 to 305 and 308 to 310 arranged in the surface wave propagation direction, and an IDT. And reflectors 306, 307, 311 and 312 provided on both sides in the surface wave propagation direction of the region. Also, each one end of the first and third IDTs 303 and 305 of the first stage longitudinally coupled resonator type surface acoustic wave filter unit 301 and the first stage of the second stage longitudinally coupled resonator type surface acoustic wave filter unit 302. , Third ends of the third IDTs 308 and 310 are connected via first and second signal lines 316 and 317, respectively. On the other hand, one end of the IDT 304 is connected to the terminal 313, one end of the IDT 309 is connected to the terminal 314, and the other end is connected to the terminal 315. The remaining ends of the IDTs 303 to 305 and 308 to 310 are all connected to the ground potential.

Terminals 314 and 315 are balanced signal terminals, and terminal 313 is an unbalanced signal terminal. Detailed design is shown below.
Electrode finger crossing width W = 49.0λI
Number of electrode fingers of first IDTs 303 and 308 = 24 Number of electrode fingers of second IDTs 304 and 309 = 34 Number of electrode fingers of third IDTs 305 and 310 = 25 IDT wavelength λI = 4.49 μm
Wavelength of reflector λR = 4.64 μm
Number of electrode fingers of reflector = 120 adjacent IDT-IDT intervals = 0.79λI
Distance between IDT and reflector = 0.47λR
IDT duty = 0.73
Reflector duty = 0.55
Electrode thickness = 0.08λI
In this embodiment, the electrode fingers 304a, 304b, 309a, 309b at both ends of the center second IDTs 304, 309 are thickened, and the free part between adjacent IDT-IDTs is made small.

  The feature of this embodiment is that the number of electrode fingers of the IDTs 304 and 309 is an even number as in the first embodiment, and the electrode fingers 303a of the IDTs 303, 305, 308, and 310 adjacent to the IDTs 304 and 309. , 305a, 308a, 310a are ground electrodes.

  In the longitudinally coupled resonator type surface acoustic wave filter unit 301, the IDTs 303 and 305 are in antiphase with respect to the IDT 304. Accordingly, the IDTs 303 and 305 are connected in parallel, and the filter characteristics cannot be obtained with only one stage. However, at the same time, since IDTs 308 and 310 are also opposite in phase to IDT 309 of longitudinally coupled resonator-type surface acoustic wave filter unit 302, the surface waves propagating from IDT 308 and 310 to IDT 309 have the same phase, and accordingly It is possible to obtain filter characteristics by connecting the coupled resonator type surface acoustic wave filter sections 301 and 302. That is, the electrical signals propagating through the first signal line 316 and the second signal line 317 are in opposite phases.

  FIG. 14 shows the amplitude balance with respect to the frequency in the second embodiment, and FIG. 15 shows the phase balance with respect to the frequency. In FIGS. 14 and 15, the result of the second embodiment is shown by a solid line, and the result of the conventional example shown in FIG. 16 prepared for comparison is shown by a broken line.

  Note that in the conventional longitudinally coupled resonator type surface acoustic wave filter 401 shown in FIG. 16, the number of electrode fingers of the first to third IDTs 402 to 404 is the number of electrode fingers of the first IDT = 24, The second embodiment is the same as the second embodiment except that the number of electrode fingers in the second IDT = 35 and the number of electrode fingers in the third IDT = 24.

  The frequency range of the pass band in the AMPS reception filter is 860 to 894 MHz. In the above frequency range, the maximum amplitude balance is 1.9 dB in the conventional example, whereas it is 0.9 dB in the second embodiment, and the amplitude balance is improved by 1.0 dB. Recognize.

  Further, the maximum phase balance is 17 ° in the conventional example, whereas it is 8 ° in the second embodiment, and the phase balance is improved by 9 °. As described above, the degree of balance is improved because the number of electrode fingers of the second IDT is an even number, and the electric signals propagating through the first and second signal lines 316 and 317. So that the electrode fingers of the first and third IDTs adjacent to the center second IDT can be ground electrodes, and the electrode fingers connected to the terminal 315 309a and the signal electrode finger 308b of the IDT 308 (see FIG. 12), and the distance C between the electrode finger 309b connected to the terminal 314 and the signal electrode finger 310b of the IDT 310 (see FIG. 12). This is because they are equal. On the other hand, in the conventional example shown in FIG. 16, the distances D and E between the electrode fingers shown in FIG. 16 between adjacent IDTs in the second longitudinally coupled resonator type surface acoustic wave filter are different by 0.5λI. ing.

  In the second embodiment, the left and right electrode fingers of the first and third IDTs adjacent to the second IDT are the ground electrodes, but the same can be achieved by using these electrode fingers as signal electrodes. The effect of can be obtained.

  As described above, in the second embodiment, the longitudinally coupled resonator type surface acoustic wave filters 301 and 302 in which the number of electrode fingers of the second IDT is an even number are cascade-connected in two stages. By making the electrical signals propagating through the first and second signal lines 316 and 317 have opposite phases, the polarities of the electrode fingers adjacent to the central second IDT and the first and third IDTs are made the same. It can be seen that both amplitude balance and phase balance can be improved.

  Further, in the configuration shown in FIG. 12 for the second embodiment, as shown in FIG. 11, when a narrow pitch electrode finger is used in a portion where two IDTs are adjacent to each other, the degree of balance is still high. Improved properties can be obtained.

  FIG. 13 is a schematic plan view showing a modification of the second embodiment. The difference from the second embodiment is that the surface acoustic wave filter 302 is symmetrical with respect to the Z axis in FIG. 13 with respect to the surface acoustic wave filter 301 in the configuration shown in FIG. In the modification shown, it is point-symmetric with respect to the Y point in FIG. 13, that is, the center of the entire electrode structure of the surface acoustic wave filters 301 and 302.

  FIG. 17 is a schematic plan view showing another modification of the second embodiment. In this modification, longitudinally coupled resonator type surface acoustic wave filter sections 301 and 321 are cascade-connected. The difference from the second embodiment is that the second IDT 322 in the center is divided into two in the second-stage longitudinally coupled resonator type surface acoustic wave filter unit 321. Since the other points are the same as those of the second embodiment, the same parts are denoted by the same reference numerals, and the description thereof is omitted.

  The second IDT 322 includes a comb electrode 322a and two comb electrodes 322b and 322c arranged such that the comb electrode 322a and the electrode fingers are interleaved with each other. That is, one comb electrode of the pair of comb electrodes constituting the IDT is divided into two comb electrodes 322b and 322c, and balanced signal terminals 314 and 315 are provided on the comb electrodes 322b and 322c. It is connected. Here, in the first longitudinally coupled resonator type surface acoustic wave filter unit 301, IDT 303 and IDT 305 are in opposite phases, and the first and first longitudinally coupled resonator type surface acoustic wave filter units 321 have first and second phases. The IDTs 308 and 310 of No. 3 have the opposite phase, so that the electric signals propagating through the signal lines 316 and 317 have the opposite phase, and the polarities of the electrode fingers of the IDTs 308 and 310 adjacent to the IDT 322 are the same. Thus, the balance is improved as in the second embodiment.

  FIG. 18 is a plan view schematically showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to the third embodiment of the present invention. The longitudinally coupled resonator type surface acoustic wave filter 501 of the third embodiment is an AMPS reception filter, similarly to the longitudinally coupled resonator type surface acoustic wave filter of the second embodiment. The third embodiment is the same as the second embodiment except that the following points are different from the second embodiment. That is, one ends of the IDTs 303 and 308 are commonly connected, and the IDTs 303 and 308 are not grounded. Similarly, one ends of the IDTs 305 and 310 are commonly connected, and the IDTs 305 and 310 are not grounded. That is, the IDTs 303 and 305 and the IDTs 305 and 310 are float-connected.

  The amplitude balance-frequency characteristics, phase balance degrees, and frequency characteristics of the longitudinally coupled resonator type surface acoustic wave filter of the third embodiment are shown by solid lines in FIGS. 19 and 20, respectively. For comparison, the result of the conventional example shown in FIG.

  As apparent from FIG. 19 and FIG. 20, in the passband of the AMPS reception filter, the maximum amplitude balance is 1.9 dB in the conventional example, whereas it is 1.2 dB in the third embodiment. It can be seen that the amplitude balance is improved by 0.7 dB. In the conventional example, the maximum phase balance is 17 °, whereas in the third embodiment, it is 9 °, and the phase balance is improved by 8 °.

  Therefore, as in the third embodiment, in addition to the configuration of the second embodiment, the first IDT of the first stage and the first IDT of the second stage are float-connected, and the first stage It can be seen that the balance can be effectively improved by float-connecting the third IDT and the third IDT in the second stage.

  FIG. 21 is a plan view schematically showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to the fourth embodiment. The longitudinally coupled resonator type surface acoustic wave filter 600 of the fourth embodiment is configured in the same manner as in the second embodiment except for the following points.

  Here, in the first-stage longitudinally coupled resonator type surface acoustic wave filters 601 and 602, the number of electrode fingers of the first to third IDTs is the number of electrode fingers of the first IDTs 603 and 608, respectively = 24, the number of electrode fingers of the second IDTs 604 and 609 = 35, and the third IDTs 605 and 610 = 24.

  The feature of the fourth embodiment is that the polarities of the electrode fingers 603a and 605a of the first and third IDTs 603 and 605 adjacent to the IDT 604 and the electrode fingers 608a and 610a of the IDTs 608 and 610 adjacent to the IDT 609 are reversed. There is to be.

  Considering the longitudinally coupled resonator-type surface acoustic wave filter unit 601 alone, the IDTs 603 and 605 are out of phase with respect to the IDT 604, so that the filter characteristics cannot be obtained with only one stage by connecting the IDTs 603 and 605 in parallel. . However, at the same time, since IDTs 608 and 610 are opposite in phase to IDT 609 of longitudinally coupled resonator type surface acoustic wave filter unit 602, the surface acoustic waves propagating from IDT 608 and 610 to IDT 609 are in phase and are connected in two stages in cascade. By doing so, filter characteristics can be obtained.

  Note that the terminal 615 is an unbalanced signal terminal, and the terminals 616 and 617 are balanced signal terminals. FIG. 22 shows the amplitude balance-frequency characteristic of the longitudinally coupled resonator type surface acoustic wave filter of the fourth embodiment, and FIG. 22 shows the phase balance-frequency characteristic by a solid line. For comparison, the result of the conventional example shown in FIG. 16 is indicated by a broken line.

  As is clear from FIG. 21, the maximum amplitude balance in the passband in the AMPS reception filter is 1.9 dB in the conventional example, whereas it is 1.2 dB in the fourth embodiment. Is improved by 0.7 dB. As is clear from FIG. 22, the maximum phase balance is 17 ° in the conventional example, whereas it is 11 ° in the fourth embodiment, and the phase balance is improved by 6 °.

  That is, in the fourth embodiment, longitudinally coupled resonator type surface acoustic wave filter sections having three IDTs are cascaded in two stages, and the electrode fingers of the first and third IDTs adjacent to the center second IDT are connected. It can be seen that the amplitude balance and the phase balance can be effectively improved by reversing the polarity of.

  FIG. 24 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to the fifth embodiment. In the fifth embodiment, 3IDT type longitudinally coupled resonator type surface acoustic wave filter units 901 to 904 having first to third IDTs are used. In each of the longitudinally coupled resonator type surface acoustic wave filter units 901 to 904, the number of electrode fingers of the center second IDT is an even number, and the left and right IDT electrode fingers adjacent to the center second IDT Are of the same polarity. For example, taking the longitudinally coupled resonator type surface acoustic wave filter 901 as an example, the electrode fingers 907a and 909a of the first and third IDTs 907 and 909 adjacent to the second IDT 908 have the same polarity.

  The longitudinally coupled resonator type surface acoustic wave filter units 901 to 903 have the same configuration, but the second IDT 910 is inverted only in the longitudinally coupled resonator type surface acoustic wave filter unit 902.

  In addition, 911 is an unbalanced signal terminal, and 912 and 913 are balanced signal terminals. In the first to fourth longitudinally coupled resonator-type surface acoustic wave filter units 901 to 904, the first and third IDTs have opposite phases. For example, taking the longitudinally coupled resonator type surface acoustic wave filter 901 as an example, the first IDT 907 and the third IDT 909 are in anti-phase.

  In the fifth embodiment, similarly to the second to fourth embodiments, the amplitude balance and the phase balance can be improved, and in the fifth embodiment, the output impedance is made about four times different. Will be.

  FIG. 25 is a schematic block diagram for explaining the communication device 60 using the longitudinally coupled resonator type surface acoustic wave filter according to the present invention. In FIG. 25, a diplexer 62 is connected to the antenna 61. A surface acoustic wave filter 64 and an amplifier 65 are connected between the diplexer 62 and the receiving-side mixer 63. An amplifier 67 and a surface acoustic wave filter 68 are connected between the diplexer 62 and the mixer 66 on the transmission side. Thus, when the amplifier 65 is compatible with a balanced signal, a longitudinally coupled resonator type surface acoustic wave filter configured in accordance with the present invention can be suitably used as the surface acoustic wave filter 64.

60 ... communication devices 101-103 ... first to third IDTs
102A ... IDT
104, 105 ... reflectors 106, 107 ... balanced signal terminal 108 ... unbalanced signal terminals 109, 110 ... electrode finger 200 ... longitudinally coupled resonator type surface acoustic wave filter 200A ... laminated substrate (piezoelectric film / low sound speed film / high sound speed) (With membrane / support substrate)
DESCRIPTION OF SYMBOLS 51 ... Support substrate 52 ... High sonic film 53 ... Low sonic film 54 ... Piezoelectric film 22, 24 ... Medium layer 201 ... 1st IDT
201a, 203a ... electrode finger 202 ... second IDT
203 ... Third IDT
204, 205 ... reflectors 206, 207 ... electrode fingers 210, 211 ... balanced signal terminal 212 ... unbalanced signal terminals 213, 214 ... balanced signal terminal 215 ... unbalanced signal terminal 216 ... surface acoustic wave resonator 217 ... longitudinally coupled resonance Sub-surface acoustic wave filter 218 ... second IDT
219: Longitudinal coupled resonator type surface acoustic wave filter 220: Surface acoustic wave filters 221 to 223 ... First to third IDTs
300 ... longitudinally coupled resonator type surface acoustic wave filters 301, 302 ... longitudinally coupled resonator type surface acoustic wave filters 303 to 305 ... first to third IDTs
303a, 305a ... electrode fingers 304a, 304b ... electrode fingers 306, 307 ... reflectors 308-310 ... first to third IDTs
308a, 310a ... electrode fingers 309a, 309b ... electrode fingers 311, 312 ... reflector 313 ... unbalanced signal terminals 314, 315 ... balanced signal terminal 321 ... longitudinally coupled resonator type surface acoustic wave filter 322 ... IDT
322a ... comb electrodes 322b, 322c ... comb electrodes 401 ... longitudinally coupled resonator type surface acoustic wave filters 402-403 ... first to third IDTs
501 ... Longitudinal coupled resonator type surface acoustic wave filter 600 ... Longitudinal coupled resonator type surface acoustic wave filters 601 and 602 ... Longitudinal coupled resonator type surface acoustic wave filters 603 to 605 ... First to third IDTs
608 to 610 ... 1st to 3rd IDT
615: Unbalanced signal terminals 616, 617 ... Balanced signal terminals 901-904 ... Longitudinal coupled resonator type surface acoustic wave filters 907-909 ... First to third IDTs
907a, 909a ... Electrode finger 910 ... IDT
911... Unbalanced signal terminals 912 and 913... Balanced signal terminals N1 to N4.

Claims (3)

A laminated substrate having a laminated structure of piezoelectric film / low sound velocity film / high sound velocity film / support substrate;
Two stages of longitudinally coupled resonator type surface acoustic wave filters including first to third IDTs arranged in order along the propagation direction of the surface acoustic wave on the multilayer substrate are cascade-connected,
One end of the second IDT of the first stage longitudinally coupled resonator type surface acoustic wave filter is connected to the unbalanced signal terminal,
One end and the other end of the second IDT of the second-stage longitudinally coupled resonator type surface acoustic wave filter are connected to the first and second balanced signal terminals,
One end of the first IDT of the first-stage longitudinally coupled resonator type surface acoustic wave filter and one end of the first IDT of the second longitudinally coupled resonator type surface acoustic wave filter are connected by the first signal line. One end of the third IDT of the first-stage longitudinally coupled resonator type surface acoustic wave filter and one end of the third IDT of the second-stage longitudinally coupled resonator type surface acoustic wave filter are connected by the second signal line, respectively. Has been
In a longitudinally coupled resonator type surface acoustic wave filter having a balance-unbalance conversion function,
A longitudinally coupled resonator type surface acoustic wave filter, wherein an electrical signal propagating through the first signal line and an electric signal propagating through the second signal line are in opposite phases.   2. The longitudinal axis according to claim 1, wherein the number of electrode fingers of the second IDT is an even number of at least one of the first-stage and second-stage longitudinally coupled resonator-type surface acoustic wave filters. Coupled resonator type surface acoustic wave filter.   A communication device using the longitudinally coupled resonator type surface acoustic wave filter according to claim 1.