JP4182976B2 - Longitudinal coupled resonator type surface acoustic wave filter - Google Patents

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 three or more IDTs (interdigital transducers).

  Conventionally, a surface acoustic wave filter has been widely used as a band-pass filter of an RF stage of a mobile phone. A band-pass filter is required to have a low loss, a high attenuation, and a wide band, and various proposals have been made for a surface acoustic wave filter to satisfy these requirements.

Patent Document 1 below discloses an example of a method for achieving a wide band in a longitudinally coupled resonator type surface acoustic wave filter. Here, the condition that electrode fingers are periodically arranged between adjacent IDTs, more specifically, the distance between the electrode finger centers of two IDTs adjacent to each other in the surface acoustic wave propagation direction is expressed by the period of the electrode fingers. A method of optimally arranging the resonance mode by shifting from 0.5 times the determined wavelength is employed.
Japanese Patent Application Laid-Open No. 5-267990

However, as in Patent Document 1, when the distance between the centers of adjacent electrode fingers is shifted from 0.5 times the wavelength determined by the period of the electrode fingers between adjacent IDTs, the surface acoustic wave propagation path in that portion The periodic continuity of deteriorates. In particular, when a piezoelectric substrate such as 36 ° Y-cut X-propagating LiTaO ₃ or 64 ° Y-cut X-propagating LiNbO ₃ using leaky surface acoustic waves (leaky waves) is used, loss due to bulk wave radiation increases. It becomes. As a result, there is a problem that the insertion loss is increased even though it is possible to increase the bandwidth.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a longitudinally coupled resonator type surface acoustic wave filter that can solve the above-described problems of Patent Document 1 and can not only achieve a wider band but also reduce the insertion loss in the passband. It is in.

According to a wide aspect of the present invention, there is provided a piezoelectric substrate and at least three IDTs formed along the surface acoustic wave propagation direction on the piezoelectric substrate, each having a plurality of electrode fingers, and at least one IDT is the period of a portion of the electrode finger from the other IDT end portions adjacent to the surface acoustic wave propagation direction, have a remaining portion smaller pitch portion than the period of the electrode fingers of the IDT, the narrow It is the wavelength of surface waves determined by the period of electrode finger pitch portion Ramudaai1, the remaining portion of the wavelength λI2 der of the surface wave determined by the period of electrode fingers Rutotomoni, 0-order mode, second order mode, IDT- At least two stages of longitudinally coupled resonator type surface acoustic wave filters using the IDT resonance mode are connected in cascade, and at least one stage of the longitudinally coupled resonator type surface acoustic wave filters of the plurality of stages of longitudinally coupled resonator type surface acoustic wave filters is coupled. The configuration of the narrow pitch portion in the pendulum type surface acoustic wave filter is different from the configuration of the narrow pitch portion in the longitudinally coupled resonator type surface acoustic wave filter of the other stage, and the multistage longitudinally coupled resonator type The period of the electrode fingers of the narrow pitch portion in the longitudinally coupled resonator type surface acoustic wave filter of at least one stage of the surface acoustic wave filter is the electrode of the narrow pitch part in the longitudinally coupled resonator type surface acoustic wave filter of the other stage. A longitudinally coupled resonator type surface acoustic wave filter characterized by being different from the period of a finger is provided.

  In a more limited aspect of the present invention, the period of the electrode fingers in the narrow pitch portion is 0.82 to 0.99 times the period of the electrode fingers in the remaining portion.

  In another specific aspect of the present invention, both of the pair of adjacent IDTs are configured such that the period of the electrode fingers in the narrow pitch part is different from the period of the electrode fingers in the remaining part, The distance between adjacent electrode finger centers is substantially equal to 0.5λI1.

  In another specific aspect of the present invention, only one of the pair of adjacent IDTs is configured such that the period of the electrode fingers in the narrow pitch portion is different from the period of the electrode fingers in the remaining portion, The distance between the electrode finger centers of IDTs is approximately equal to 0.25λI1 + 0.25λI2.

  In still another specific aspect of the present invention, in the IDT in which the period of the electrode fingers of the narrow pitch portion is different from the period of the electrode fingers of the remaining portion, the electrode fingers of the narrow pitch portion and the electrodes of the remaining portion The distance between the electrode finger centers at locations where the fingers are adjacent is approximately equal to 0.25λI1 + 0.25λI2.

  In yet another specific aspect of the present invention, the polarities of electrode fingers adjacent to an IDT having a narrow pitch portion and an IDT adjacent to the IDT are different.

  In another specific aspect of the present invention, the total number of electrode fingers in a narrow pitch portion is set to 18 or less on both sides of adjacent portions of a pair of adjacent IDTs.

  In still another specific aspect of the present invention, the distance between the centers of electrode fingers of a pair of adjacent IDTs whose periods are not different is set to (0.08 + 0.5n) λI2− (0.24 + 0.5n) λI2. (N = 1, 2, 3,...).

  In still another specific aspect of the present invention, the distance between the centers of electrode fingers of a pair of adjacent IDTs whose periods are not different is set to (0.13 + 0.5n) λI2− (0.23 + 0.5n) λI2. (N = 1, 2, 3,...)

  In still another specific aspect of the present invention, both of a pair of IDTs adjacent in the surface wave propagation direction have the narrow pitch portion, and the number of electrode fingers of the narrow pitch portion in both IDTs is different. Has been.

In the present invention, the piezoelectric material constituting the piezoelectric substrate is not particularly limited, but preferably, the LiTaO ₃ single crystal is rotated in the range of 36 to 44 degrees in the Y axis direction about the X axis. Things are used.

  In another specific aspect of the present invention, the film thickness of the electrode fingers in the narrow pitch portion is configured to be different from the film thickness of the electrode fingers in the remaining portion. In this case, preferably, the film thickness of the electrode fingers in the narrow pitch portion is made smaller than the film thickness of the electrode fingers in the remaining portion.

  In still another specific aspect of the present invention, the electrode fingers of the narrow pitch portion are constituted by split electrodes.

  In a more limited aspect of the present invention, the period of the electrode fingers of the narrow pitch portion is different in each stage of the multistage longitudinally coupled resonator type surface acoustic wave filter.

  In still another specific aspect of the present invention, at least one series resonator and / or parallel resonator is connected to the input side and / or the output side.

  The longitudinally coupled resonator type surface acoustic wave filter according to the present invention may be configured to have a balanced-unbalanced input / output, or may be configured to have a balanced-balanced input / output.

  The communication device according to the present invention includes a longitudinally coupled resonator type surface acoustic wave filter configured according to the present invention as a bandpass filter.

  In the longitudinally coupled resonator type surface acoustic wave filter according to the present invention, at least one IDT of at least three IDTs is a narrow-pitch electrode that is a part from another IDT end adjacent to the surface wave propagation direction. The period of the finger is configured to be different from the period of the electrode fingers in the remaining portion, and the zero-order mode, the second-order mode, and the IDT-IDT resonance mode are used, so that the passband width can be increased. Not only can this be achieved, but insertion loss in the passband can be reduced.

  Therefore, it is possible to provide a longitudinally coupled resonator type surface acoustic wave filter that has a wide band and a small loss in the passband.

  When the period of the electrode fingers in the narrow pitch part is smaller than the period of the electrode fingers in the remaining part, the propagation loss of the surface wave can be reduced, and the insertion loss in the pass band can be further reduced. .

  Further, in a configuration in which a plurality of stages of longitudinally coupled resonator type surface acoustic wave filters are connected in cascade, the period of the electrode fingers of the narrow pitch portion in the longitudinally coupled resonator type surface acoustic wave filter of at least one stage is other than Since it differs from the period of the electrode fingers of the narrow pitch portion in the stage longitudinally coupled resonator type surface acoustic wave filter, it becomes possible to further widen the passband without causing deterioration of VSWR.

  In addition, in each stage of a plurality of stages of longitudinally coupled resonator type surface acoustic wave filters, when the periods of the electrode fingers of the narrow pitch portion are different, the passband width can be more effectively widened.

  In particular, when the period of the electrode fingers in the narrow pitch part is 0.82 to 0.99 times the period of the electrode fingers in the remaining part, the propagation loss of the surface wave can be further reduced.

  When the distance between adjacent electrode finger centers of a pair of IDTs is approximately equal to 0.5λI1, loss radiated as a bulk wave can be reduced, and insertion loss can be further reduced.

  When only one of a pair of adjacent IDTs is configured to have a narrow pitch part and the remaining part, the distance between the electrode finger centers of the pair of IDTs is approximately equal to 0.25λI1 + 0.25λI2. In the same manner, the loss radiated as a bulk wave can be reduced, and the insertion loss in the passband can be further reduced.

  When the distance between the electrode fingers in the portion where the electrode fingers of the narrow pitch part and the remaining part of the electrode fingers are adjacent to each other is substantially equal to 0.25λI1 + 0.25λI2, the loss radiated as a bulk wave is similarly reduced. Thus, the insertion loss in the passband can be further reduced.

  When the polarities of the adjacent electrode fingers of the IDT having the narrow pitch portion and the remaining portion and the IDT adjacent to the IDT are different, the surface acoustic wave is also converted into an electric signal between the IDT and the IDT, thereby The conversion efficiency into an electric signal can be increased, insertion loss in the passband can be further improved, and the passband width can be increased.

  When the total number of electrode fingers in a narrow pitch portion is 18 or less on both sides of adjacent portions of a pair of adjacent IDTs, the impedance concentration is increased and the longitudinally coupled resonator type elasticity with a small VSWR is increased. A surface wave filter can be provided.

  In the case where the distance between the centers of the electrodes of the pair of adjacent IDTs whose periods are not different is (0.08 + 0.5n) λI2 to (0.24 + 0.5n) λI2, more preferably (0. When 13 + 0.5n +) λI2 to (0.23 + 0.5n) λI2, the necessary bandwidth can be secured according to various applications such as the EGSM method, the DCS method, the PCS method, and the VSWR is surely reduced. can do.

  When both of a pair of IDTs adjacent in the surface wave propagation direction have a narrow pitch part and the remaining part, and the number of electrode fingers of the narrow pitch part in both IDTs is different, the impedance concentration degree deteriorates, and VSWR However, the pass bandwidth can be further expanded.

When a piezoelectric substrate in which a LiTaO ₃ single crystal is rotated about the X axis in the range of 36 to 44 ° in the Y axis direction has a wide pass band according to the present invention and within the pass band A longitudinally coupled resonator type surface acoustic wave filter with a small insertion loss can be easily obtained.

  When the film thickness of the electrode finger in the narrow pitch portion is different from the film thickness of the electrode finger in the remaining portion, the loss due to bulk wave radiation can be reduced by adjusting the electrode film thickness. In particular, when the film thickness of the electrode fingers in the narrow pitch portion is made thinner than the film thickness of the electrode fingers in the remaining portions, the loss due to the bulk wave radiation in the interval between IDT and IDT where the bulk wave radiation is most generated. Therefore, it is possible to further reduce the insertion loss while maintaining the wide bandwidth.

  If at least one series resonator and / or parallel resonator is connected to the input side and / or the output side, not only can the insertion loss in the passband be reduced according to the present invention, but also outside the passband. The amount of attenuation can be increased.

  The longitudinally coupled resonator type surface acoustic wave filter of the present invention may be configured to have a balanced-unbalanced input / output, or may be configured to have a balanced-balanced input / output.

  That is, it is possible to easily provide longitudinally coupled resonator type surface acoustic wave filters of various input / output types according to the application.

  Further, since the communication device according to the present invention includes the longitudinally coupled resonator type surface acoustic wave filter configured according to the present invention as a band filter, it is possible to configure a communication device having a wide bandwidth and low loss. it can.

  Hereinafter, the present invention will be described in more detail by describing reference examples and specific examples of the present invention.

  FIG. 1 is a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter according to a first reference example. Note that this reference example and the following reference examples are applied to a reception band-pass filter of an EGSM mobile phone. However, the longitudinally coupled resonator type surface acoustic wave filter according to the present invention can also be used as a band-pass filter in other types of cellular phones and other communication devices other than cellular phones.

The longitudinally coupled resonator type surface acoustic wave filter 1 of this reference example is configured by forming an electrode structure shown in a schematic plan view in FIG. 1 on a piezoelectric substrate 2. The piezoelectric substrate 2 is configured using a 36 ° Y-cut X-propagation LiTaO ₃ substrate. However, the piezoelectric substrate 2 may be configured using a LiTaO ₃ substrate having another crystal orientation, or other piezoelectric material other than the LiTaO ₃ substrate, for example, a piezoelectric single crystal such as a LiNbO ₃ substrate or quartz crystal, or a piezoelectric ceramic. You may comprise using. Furthermore, the piezoelectric substrate 2 may be configured by forming a piezoelectric thin film such as a ZnO thin film on an insulating substrate.

  In the longitudinally coupled resonator type surface acoustic wave filter 1 of this reference example, an electrode structure, which will be described in detail below, is formed of Al on a piezoelectric substrate 2. However, a metal or alloy other than Al may be used as the electrode material.

  In this reference example, first and second longitudinally coupled resonator type surface acoustic wave filters 11 and 12 are cascaded. That is, two longitudinally coupled resonator type surface acoustic wave filters 11 and 12 are cascaded in two stages.

  The surface acoustic wave filters 11 and 12 each have three IDTs arranged along the surface wave propagation direction. That is, these surface acoustic wave filters 11 and 12 are 3IDT type longitudinally coupled resonator type surface acoustic wave filters. The electrode designs of the surface acoustic wave filters 11 and 12 are the same.

  The surface acoustic wave filter 11 has IDTs 13 to 15. Grating-type reflectors 16 and 17 are arranged on both sides of the surface wave propagation direction of the portion where the IDTs 13 to 15 are formed. Similarly, the surface acoustic wave filter 12 also includes grating-type reflectors 21 and 22 disposed on both sides of the surface wave propagation direction in the region where the three IDTs 18 to 20 and IDTs 18 to 20 are formed.

  In this reference example, one end of the IDT 14 arranged at the center of the surface acoustic wave filter 11 is an input end, and the IDT 19 arranged at the center of the surface acoustic wave filter 12 is an output end. Further, one ends of the IDTs 13 and 15 are connected to one ends of the IDTs 18 and 20, respectively. As is apparent from FIG. 1, the ends of the IDTs 13 to 15 and 18 to 20 opposite to the input / output ends or the ends connected to the IDT are connected to the ground potential.

  The longitudinally coupled resonator type surface acoustic wave filter 1 of the present reference example is characterized in that, in the surface acoustic wave filters 11 and 12, on both sides between adjacent IDTs, the electrode finger pitch of a part of the IDT is the remaining part of the IDT. That is, the pitch is narrower than the electrode finger pitch of the portion. This will be described more specifically by taking the IDTs 13 and 14 as an example.

  IDT 13 and IDT 14 are adjacent to each other in the surface wave propagation direction. The electrode finger pitch between several electrode fingers 13a, 13b from the end of IDT 13 on the IDT 14 side is narrower than the electrode finger pitch between the remaining electrode fingers 13c, 13d, 13e, 13f, 13g. Similarly, in the IDT 14, the electrode finger pitch between several electrode fingers 14a and 14b at the end on the IDT 13 side is narrower than the electrode finger pitch between the electrode fingers 14c, 14d, 14e, 14f, and 14g. . In the IDT 13, the portion where the electrode finger pitch between the plurality of electrode fingers 13a and 13b is narrowed from the end on the IDT 14 side as described above is defined as a narrow pitch portion, and the remaining electrode fingers 13c to 13g are arranged. The remaining part is the remaining part. Thus, in the surface acoustic wave filter 1 of the present reference example, each IDT has a pitch of a plurality of electrode fingers narrower than a pitch of the remaining electrode fingers from an adjacent IDT side end.

  In the IDT 14 disposed in the center, the narrow pitch portions are disposed on both sides of the surface wave propagation direction. That is, the electrode finger pitch is narrowed not only in the portion where the electrode fingers 14a and 14b described above are provided, but also in the portion where the plurality of electrode fingers 14h and 14i at the end on the IDT 15 side are arranged, Accordingly, the portions where the electrode fingers 14h and 14i are provided are also narrow pitch portions.

  Also in the IDT 15, a narrow pitch portion is formed on the IDT 14 side as in the IDT 13, and a portion other than the narrow pitch portion forms the remaining portion. The IDTs 18 to 20 on the surface acoustic wave filter 12 side are configured in the same manner as the IDTs 13 to 15.

  In FIG. 1 and each of the drawings showing the electrode structures of modifications and examples described later, the number of electrode fingers is shown to be smaller than the actual number of electrode fingers for ease of illustration.

  Next, the details of the electrode structure of the surface acoustic wave filter 1 of this reference example will be described more specifically.

  Now, the wavelength of the surface wave determined by the electrode finger pitch of the narrow pitch portion is λI1, and the wavelength of the surface wave determined by the electrode finger pitch of the remaining portion is λI2.

  The electrode finger crossing widths of the IDTs 13 to 18 are all 35.8λI2 and the electrode film thickness is 0.08λI2.

  The number of electrode fingers of IDTs 13 to 15 is as follows.

  IDT13: 29 electrode fingers, provided that the number of electrode fingers in the narrow pitch portion is 4, and the number of electrode fingers in the remaining portion is 25.

  IDT14... The number of electrode fingers is 33, but the number of electrode fingers in each of the narrow pitch portions on both sides is 4, and the number of electrode fingers in the remaining central portion is 33−8 = 25.

  IDT15: The number of electrode fingers is 29, the number of electrode fingers in the narrow pitch portion is 4, and the number of electrode fingers in the remaining portion is 25.

  The λI1 indicating the wavelength of the IDT is 3.90 μm, and λI2 is 4.19 μm.

  The number of electrode fingers of the reflectors 16 and 17 is 100, and the wavelength λR is 4.29 μm.

  Further, taking the IDT 13 in FIG. 1 as an example, the interval between the narrow pitch portion and the remaining portion is the interval between the center of the electrode finger 13c and the center of the electrode finger 13b, and this interval is 0.25λI1 + 0. 25λI2. The distance between the narrow pitch portion and the remaining portion in the other IDTs is also the same size. Further, an interval between adjacent IDTs, for example, a center-to-center distance between adjacent electrode fingers 14i and 15a of IDT14 and IDT15 is set to 0.50λI1.

  Further, the distance between the IDTs 13 and 15 and the reflectors 16 and 17, that is, the distance between the electrode finger centers between the outer end of the IDT and the inner end of the reflector is 0.50λR.

  Moreover, the duty of each IDT 13-15 is 0.73, and the duty of a reflector is 0.55. Here, the duty indicates the ratio of the width of the electrode finger to (the width of the electrode finger + the interval between the electrode fingers).

  The IDTs 18 to 20 and the reflectors 21 and 22 of the surface wave filter 12 are configured in exactly the same manner as the IDTs 13 to 15 and the reflectors 16 and 17.

  This reference example is characterized in that the interval between the narrow pitch portion and the remaining portion and the interval between adjacent IDTs are designed as described above. As will be described in more detail later, these intervals are 0.50 times the wavelength of the surrounding IDT, and if the wavelengths are different on both sides of the interval, add 0.25 times these wavelengths. It is preferable to keep the intervals at an interval in order to maintain the continuity of IDT.

  For comparison, a conventional longitudinally coupled resonator type surface acoustic wave filter was prepared. The electrode structure of this conventional longitudinally coupled resonator type surface acoustic wave filter is shown in FIG. As is clear from FIG. 2, the longitudinally coupled resonator type surface acoustic wave filter 201 is not provided with two types of intervals as in the longitudinally coupled resonator type surface acoustic wave filter 1, and is provided between all electrode fingers. The configuration is the same except that the intervals are equal. Accordingly, the same parts are given the same reference numerals indicating the respective parts of the longitudinally coupled resonator type surface acoustic wave filter of the above reference example, and a detailed description thereof will be omitted. In the surface acoustic wave filter 201 prepared for this comparison, the details of the electrode structure are as follows.

  That is, the crossing width W of IDTs 213 to 215 and 218 to 220 is 43.2λI. The number of electrode fingers of the IDT was as follows.

  IDT213, 215, 218, 220 ... 25. IDT 214, 219 ... 31 pieces.

  The wavelength λI of the IDT is 4.17 μm, and the wavelength λR of the reflector is 4.29 μm. The number of electrode fingers of the reflector was 100.

  The distance between the electrode finger centers between adjacent IDTs and IDTs was 0.32λI, and the distance between the electrode finger centers between the reflector and the IDT adjacent to the reflector was 0.50λR. Further, the duty of the IDT and the duty of the reflector were the same as in the reference example, and the electrode film thickness was 0.08λI.

  The amplitude characteristics of the longitudinally coupled resonator type surface acoustic wave filters of the reference example and the conventional example prepared as described above were measured. The results are shown in FIG. The solid line in FIG. 3 shows the result of the reference example, and the broken line shows the result of the conventional example. Moreover, the characteristic which expanded the principal part of each amplitude characteristic shown with a broken line and a continuous line with the scale of the right side of a vertical axis | shaft is shown collectively.

  As can be seen from FIG. 3, in the longitudinally coupled resonator type surface acoustic wave filter 1 of this reference example, the insertion loss in the passband can be significantly improved compared to the conventional example. For example, it can be seen that the minimum insertion loss in the passband is about 2.3 dB in the conventional example, and is about 1.7 dB in the present reference example, which is an improvement of about 0.6 dB.

  Further, in the conventional example, the bandwidth of the attenuation amount of 4.5 dB from the through level was about 44 MHz, whereas in the reference example, the same bandwidth was obtained with the attenuation amount of 3.9 dB from the through level. . That is, when compared with the entire passband, according to the reference example, the insertion loss is improved by about 0.6 dB compared to the conventional example.

  In this reference example, the reason why the insertion loss can be improved as described above is as follows.

  In the design of the conventional 3IDT type longitudinally coupled resonator type surface acoustic wave filter, the distance between electrode finger centers between adjacent IDTs is set to about 0.25λI. This is achieved by utilizing three resonance modes having peaks indicated by arrows A to C in the frequency characteristics of the conventional surface acoustic wave filter of FIG. 4 which is clarified by changing the impedance from 50Ω to 500Ω. This is to form a passband. That is, in the electrode structure shown in FIG. 5, in addition to the zero-order mode (arrow B in FIG. 4) and the secondary mode (arrow A in FIG. 4) schematically shown below, A pass band was formed by utilizing a resonance mode (arrow C in FIG. 4) having a peak of the intensity distribution of the surface acoustic wave.

  However, since the interval between IDT and IDT is 0.25λI, a discontinuous portion is generated in the surface wave propagation path. In the discontinuous portion, a component radiated as a bulk wave increases, which causes a problem that propagation loss increases.

  Therefore, in order to reduce the propagation loss, it is considered that the interval between IDT and IDT should be set to 0.50λI and the discontinuous portion should be eliminated. However, when the interval between IDT and IDT is 0.50λI, the above three modes cannot be used, and there is a problem that it is not possible to achieve a wide band.

  In this reference example, in order to solve the above two problems, between the adjacent IDTs, the narrow pitch part and the remaining part are provided, that is, the electrode finger pitch is partially changed within the IDT, Loss radiated as a bulk wave is reduced by forming a pass band using the resonance mode and setting the interval between IDT and IDT to about 0.50 times the wavelength of IDT on both sides of the interval. It has the characteristics.

  In general, when the period of the electrode finger is small with respect to the wavelength of the surface wave propagating in the propagation path, the propagation loss of the surface acoustic wave itself is small. Therefore, as described above, since the electrode finger pitch is smaller in the narrow pitch portion than in the remaining portion, the propagation loss of the surface acoustic wave is also reduced.

  Therefore, as shown in FIG. 3, the insertion loss in the passband can be remarkably reduced as compared with the conventional example, despite having the same passband width as that of the conventional example in which the bandwidth is increased.

  The inventor of the present application studied how much the electrode finger pitch in the narrow pitch portion can be reduced with respect to the remaining portion to obtain better results.

  In other words, the electrode finger pitch in the narrow pitch portion of the longitudinally coupled resonator type surface acoustic wave filter of the reference example shown in FIG. 1 was varied, and how the propagation loss changed due to this was investigated. The results are shown in FIG.

  The horizontal axis of FIG. 6 indicates the ratio of the electrode finger pitch of the narrow pitch portion to the electrode finger pitch of the remaining portion (this is referred to as the pitch ratio of the narrow pitch electrode finger), and the vertical axis indicates the propagation loss. Note that the propagation loss in FIG. 6 is a value obtained by subtracting the loss due to impedance mismatch and the ohmic loss due to the resistance of the electrode finger from the insertion loss in the passband.

  In obtaining the results of FIG. 6, the results are shown when the number of electrode fingers having a narrow electrode finger pitch is different from 8, 12, and 18. Here, the number of electrode fingers having a narrow electrode finger pitch is, for example, IDTs 13 to 15, the number of electrode fingers in a narrow pitch portion of IDT 13 (two are shown in FIG. 1), and the number of electrode fingers of IDT 14. The total number of narrow-pitch electrode fingers (two in FIG. 1) in the narrow-pitch portion on the IDT 13 side is assumed. In this case, four are shown in FIG. 1, but as described above, eight, 12 Or 18 books.

  Similarly, in the portion where the IDT 15 and the IDT 14 are adjacent to each other, the total number of electrode fingers having a narrow electrode finger pitch is shown as 4 in FIG. The number was 12 and 18. That is, FIG. 1 shows a design in which the number of electrode fingers with the narrow electrode finger pitch is four. In the following description, “the number of narrow pitch electrode fingers” means a value defined as described above.

  As is apparent from FIG. 6, it can be seen that the propagation loss is the smallest for any number of narrow pitch electrode fingers when the pitch ratio of the narrow pitch electrode fingers is around 0.95. The improvement in the propagation loss is considered to be the sum of the reduction in the loss radiated as a bulk wave and the reduction in the propagation loss of the surface acoustic wave caused by reducing the electrode finger pitch.

  That is, in order to reduce the in-band insertion loss, it is preferable that the pitch ratio of the narrow pitch electrode fingers is set to this value.

  Next, the range in which the propagation loss is reduced compared to the conventional example was confirmed. In the conventional design, the propagation loss was about 1.9 dB. In contrast, as will be described later, in the present reference example, the number of narrow pitch electrode fingers is preferably 18 or less.

  As can be seen from FIG. 6, the range in which the effect of reducing the propagation loss is seen is that the pitch ratio of the narrow pitch electrode fingers is in the range of 0.83 to 0.99. However, even if the pitch ratio of the narrow-pitch electrode fingers is less than 0.83, the propagation loss is small depending on the conditions, but considering that there are restrictions on the processing accuracy of the electrodes, the vicinity of 0.83-0.99 is It turns out that it is preferable.

  Next, the preferable range of the number of narrow pitch electrode fingers was confirmed. FIG. 7 shows the reflection characteristics when each design parameter is adjusted so as to achieve impedance matching within the passband when the number of narrow pitch electrode fingers is 8 and 12. FIG. 7A shows a case where the number of narrow pitch electrode fingers is eight, and FIG. 7B shows a case where the number of narrow pitch electrode fingers is twelve.

  When the number of narrow pitch electrode fingers is increased, the degree of concentration of impedance tends to deteriorate, that is, VSWR and in-band deviation tend to deteriorate. Further, the passband width tends to be narrowed due to the deterioration of the in-band deviation. Therefore, based on the design of the above reference example, changes in the VSWR and the pass bandwidth when the number of narrow pitch electrode fingers was changed were measured. The results are shown in FIGS.

  It should be noted that the value of VSWR in FIG. 8 and the value of the pass bandwidth in FIG. 32 are the cross width and the pitch in the narrow pitch electrode fingers so as to achieve impedance matching in the pass band for each number of narrow pitch electrode fingers. It is a value when changing. In general, the value of VSWR is desirably 2.5 or less, and the passband width is desirably 42 MHz or more in the EGSM system in consideration of changes in characteristics due to temperature, characteristic variations, and the like.

  In FIG. 8, in the range where VSWR is 2.5 or less, the number of narrow pitch electrode fingers is 18 or less. As is clear from FIG. 32, the number of narrow pitch electrode fingers having a passband width of 42 MHz or more is 18 or less. That is, it is preferable that the number of narrow-pitch electrode fingers is 18 or less, thereby increasing the concentration of impedance, reducing the VSWR and in-band deviation, and having a sufficient pass bandwidth. It can be seen that a surface wave filter is obtained.

  Next, the change in propagation loss when the interval between adjacent IDTs was changed from the reference example was investigated. The result is shown in FIG. In FIG. 33, the interval between adjacent IDTs, for example, the center-to-center distance between adjacent electrode fingers 14i and 15a of IDT 14 and IDT 15 in FIG. 1 is 0.50λI1 in the reference example, but this 0.50λI1 is As 0, the change of the propagation loss with respect to the change of the distance between the centers is plotted. In FIG. 33, when the center-to-center distance between adjacent IDTs is changed, the propagation loss is deteriorated. That is, in order to obtain a low-loss filter, the center-to-center distance between adjacent IDTs is preferably 0.50λI1. Similarly, in order to obtain a low-loss filter, it is desirable that the interval between the narrow pitch portions having different pitches and the remaining portions is 0.25λI1 + 0.25λI2 as in the reference example.

  Next, the distance between the centers of the electrode fingers whose pitch is not reduced, that is, the distance between the centers of the electrode fingers 13c and 14c, for example, was investigated as shown in FIG. The result is shown in FIG. FIG. 34 shows an electrode finger in which the pitch is not reduced in the configuration of the present invention when the filter is designed to have optimum characteristics not only for the EGSM method but also for various applications such as the DCS method and the PCS method. It is the result of investigating the distance between the centers. All of these designs are designed so as to have the necessary bandwidth in each system and to have a VSWR of 2.5 or less. The horizontal axis shows the distance between the centers of electrode fingers whose pitch is not reduced by the wavelength ratio of electrode fingers whose pitch is not reduced. This value is calculated from the distance between the centers in each case. , 0.5n (n = 1, 2, 3...), All values are 0.0. The value is set to be in a range of ˜0.5. For example, if the wavelength ratio is 4.73, it is plotted as 0.23 in FIG.

  In FIG. 34, the center-to-center distances between the electrode fingers whose pitches are not reduced are concentrated to about 0.13 to 0.23, and in all cases, fall within the range of 0.08 to 0.24. ing. In the prior art as shown in FIG. 2, this center-to-center distance is desirably about 0.25 to 0.30, but in the present invention, 0.08 to 0.24, preferably 0.13. It can be seen that the range of ~ 0.23 is good.

In this reference example, a 36 ° Y-cut X-propagation LiTaO ₃ substrate is used. However, a LiTaO ₃ substrate or a LiNbO ₃ substrate having another crystal orientation may be used, for example, 36 to 44 ° Y-cut X-propagation. A particularly large effect can be obtained in piezoelectric substrates using leaky waves, such as a LiTaO ₃ substrate, a 64-72 ° Y-cut X-propagating LiNbO ₃ substrate, and a 41 ° Y-cut X-propagating LiNbO ₃ substrate.

  In this reference example, the 3IDT type longitudinally coupled resonator type surface acoustic wave filter is cascaded in two stages. However, as shown in FIG. The effects of the present invention can be obtained by configuring in the same manner as in this reference example. Furthermore, the present invention is not limited to one having three IDTs, and the present invention is also applied to one having five IDTs 33 to 37 such as a longitudinally coupled resonator type surface acoustic wave filter 32 shown in FIG. Thus, the effects of the present invention can be obtained.

  That is, in the present invention, the number of IDTs in the longitudinally coupled resonator type surface acoustic wave filter is not limited to three, and may be 5 or more, and a plurality of longitudinally coupled resonator type surface acoustic wave filters. It is not limited to what has a stage structure.

(Second reference example)
FIG. 11 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a second reference example of the present invention.

  The longitudinally coupled resonator type surface acoustic wave filter 41 of the second reference example has the longitudinally coupled resonance of the first reference example except that the IDTs 14 and 19 arranged in the center of the surface wave propagation direction are inverted. The configuration is exactly the same as that of the child-type surface acoustic wave filter 1.

  That is, in the first reference example, adjacent electrode fingers of adjacent IDTs are connected to the ground potential, whereas in the second reference example, the outermost electrode fingers of IDTs 14 and 19 are not at the ground potential. Connected to the input / output terminal. Therefore, between the adjacent IDTs, the electrode fingers that are signal electrodes and the electrode fingers connected to the ground potential of the outer IDT are adjacent to each other.

  More specifically, in FIG. 11, the electrode fingers 13a and 15a at the IDT 14 side ends of the IDTs 13 and 15 are connected to the ground potential, whereas the electrode fingers of the IDT 14 adjacent to the electrode fingers 13a and 15a are connected. 14a and 14i are connected to the input terminals. That is, the polarity of adjacent electrode fingers is inverted between adjacent IDTs. The surface acoustic wave filter 12 is similarly configured.

  Therefore, in the longitudinally coupled resonator type surface acoustic wave filter of the second reference example, longitudinally coupled resonator type surface acoustic wave filters in which the polarities of adjacent electrode fingers between adjacent IDTs are inverted are cascaded in two stages. It has a configuration.

  FIG. 12 shows the difference in resonance mode between the surface acoustic wave filter 41 of the second reference example and the surface acoustic wave filter 1 of the first reference example. Here, the result of confirming the resonance mode by changing the input / output impedance from 50Ω to 500Ω is shown.

  In FIG. 12, the solid line indicates the result of the second reference example, and the broken line indicates the result of the first reference example.

  12D shows a standing wave resonance mode having a peak of the intensity distribution of the surface acoustic wave in the IDT-IDT interval, E is the 0th-order mode, G is the second-order mode, and F is the two-stage cascade connection. Is a mode generated by

  The major difference between the first reference example and the second reference example is that the level of the resonance mode indicated by the arrow D is increased in the second reference example.

  In the first reference example, since adjacent electrode fingers of adjacent IDTs are connected to the ground potential, the surface acoustic wave between IDT and IDT cannot be converted into an electric signal. As a result, the conversion efficiency into the electrical signal of the resonance mode D having an intensity peak in the IDT-IDT interval portion is lowered.

  On the other hand, in the second reference example, since the polarities of the adjacent electrode fingers of the adjacent IDTs are inverted, the surface acoustic wave is converted into an electric signal even at the IDT-IDT interval portion. Therefore, the conversion efficiency into the electrical signal of the resonance mode D is increased.

  FIG. 13 shows amplitude characteristics of the longitudinally coupled resonator type surface acoustic wave filters of the second reference example and the first reference example, and respective amplitude characteristics obtained by enlarging the insertion loss on the vertical axis on the right scale. Note that the amplitude characteristics of the second reference example (solid line) in FIG. 13 are calculated based on the design conditions in the first reference example in order to correct the impedance deviation due to the change in the mode frequency and level. Is obtained by changing the wavelength of the narrow pitch electrode finger to 3.88 μm.

  As is apparent from FIG. 13, according to the second reference example, the insertion loss in the passband can be further improved and the passband width can be widened as compared with the first reference example (broken line). I understand that. Therefore, it is preferable to invert the polarity of adjacent electrode fingers between adjacent IDTs, thereby providing a longitudinally coupled resonator type surface acoustic wave filter with even smaller insertion loss and a wider pass bandwidth. .

  The effect of the second reference example is that the polarity of the electrode fingers adjacent between the IDTs is inverted as described above only in one of the longitudinally coupled resonator type surface acoustic wave filters 11 and 12 cascaded in two stages. It can also be obtained in some cases.

(Third reference example)
FIG. 14 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a third reference example of the present invention.

  In the surface acoustic wave filter 51 of the third reference example, the number of narrow pitch electrode fingers is not different from that of the first reference example, but the number of narrow pitch electrode fingers in the narrow pitch portion of the IDT 13 and the IDT 13 side of the IDT 14 are The number of narrow pitch electrode fingers in the narrow pitch portion is different, and the number of narrow pitch electrode fingers in the narrow pitch portion of the IDT 15 and the number of narrow pitch electrode fingers in the narrow pitch portion on the IDT 15 side of the IDT 14 are Configured differently. Since it is configured in the same manner as the first reference example with respect to other points, the description of the first reference example is incorporated by giving the same reference numerals to the same parts. Differences from the first reference example will be described more specifically. In this reference example, the number of electrode fingers of the IDTs 13 to 15 of the surface acoustic wave filter 12 is as follows.

  IDT13... 30, but the number of electrode fingers in the narrow pitch part is 5, and the number of electrode fingers in the remaining part is 25.

  IDT 14... 33 electrode fingers, provided that the narrow pitch portions on both sides each have three narrow pitch electrode fingers, and the remaining central portion has 27 electrode fingers.

  IDT15 ... 30, but the number of electrode fingers in the narrow pitch portion is 5, and the number of electrode fingers in the remaining portion is 25.

  Also in this reference example, the surface acoustic wave filters 11 and 12 are similarly configured. In FIG. 14, the number of electrode fingers is reduced in order to simplify the illustration. That is, in FIG. 14, in the IDT 14, one narrow pitch electrode finger is provided on each of the left and right sides, and in the narrow pitch portion of the IDTs 13 and 15, the number of narrow pitch electrode fingers is illustrated as three. Has been.

  FIG. 15B shows the reflection characteristics of the longitudinally coupled resonator type surface acoustic wave filter 51 of this reference example. For comparison, FIG. 15C shows the reflection characteristics of the surface acoustic wave filter of the first reference example.

  In the third reference example, the number of narrow-pitch electrode fingers in the narrow-pitch portions on both sides between adjacent IDTs is different, and in order to match the impedance to 50Ω, the electrode-finger cross width is 47. 7λI2.

  As can be seen from FIG. 15, the third reference example shows that the degree of impedance concentration is worse than that of the first reference example.

  On the other hand, FIG. 15A shows reflection characteristics when the number of narrow pitch electrode fingers of the IDT 14 is increased. The change in this case is that, in the third reference example, the total number of electrode fingers of IDTs 13, 15, 18, and 20 is 28, the number of electrode fingers in the narrow pitch portion is 3, and the remaining number of electrode fingers is The number of electrode fingers of the IDTs 14 and 19 arranged in the center is 25, the total number of electrode fingers of the narrow pitch portion on both sides is 5 and the number of electrode fingers of the remaining portion in the center is 25 Is 27, and the crossing width is 28.6λI2. As is clear from FIG. 15A, in this case, the impedance concentration degree is higher than that in the first reference example, but it can be seen that the impedance becomes capacitive as a whole.

  The third reference example and the modification having the reflection characteristics shown in FIG. 15B are not necessarily suitable for the band filter of the reception stage of the EGSM system, but the third reference example is used in other applications. And variations may be effective. For example, as shown in FIG. 15B, when the degree of impedance concentration deteriorates, the VSWR tends to deteriorate, but the pass bandwidth tends to widen.

  That is, the solid lines in FIGS. 16A and 16B are diagrams showing the amplitude characteristics and the VSWR characteristics of the longitudinally coupled resonator type surface acoustic wave filter according to the third reference example. For comparison, FIGS. 16A and 16B show the amplitude characteristics and the VSWR characteristics of the longitudinally coupled resonator type surface acoustic wave filter 11 of the first reference example by broken lines.

  As is apparent from FIG. 16, according to the third reference example, VSWR is deteriorated by about 0.2 compared to the case of the first reference example, but the pass bandwidth at 4 dB from the through level is about It can be seen that the frequency is 1.5 MHz. In this case, it can be seen that the insertion loss level in the pass band is hardly changed, and therefore, the band can be widened while maintaining the low loss.

  That is, according to the third reference example, there is provided a longitudinally coupled resonator type surface acoustic wave filter suitable for applications that require a reduction in loss in the passband and an increase in passband even if the VSWR is somewhat deteriorated. It can be seen that it can be provided.

  Next, as shown in FIG. 15A, an example will be described in which the impedance concentration is good but the impedance is capacitive.

  FIGS. 17A and 17B show the amplitude characteristics and VSWR characteristics of the longitudinally coupled resonator type surface acoustic wave filter of the above-described modified example by solid lines. For comparison, the amplitude characteristics and VSWR characteristics of the longitudinally coupled resonator type surface acoustic wave filter of the first reference example are shown by broken lines. 17, the electrode finger crossing width is 31.0λI2, the total number of electrode fingers of IDTs 13, 15, 18, and 20 is 28, and the number of electrode fingers in the narrow pitch portion is 3. The number of electrode fingers in the remaining and remaining portions is 25, the total number of electrode fingers of the central IDTs 14 and 19 is 47, and the number of electrode fingers in the narrow pitch portions on both sides of the IDTs 14 and 19 is 5 each. The number of electrode fingers in the remaining portion at the center was 37. The wavelength λI1 of the IDT is 3.88 μm. The other points were the same as in the first reference example.

  As is clear from FIG. 17, in the above modification, the passband width from the through level at 4 dB is about 3.5 MHz narrower than the surface acoustic wave filter 11 of the first reference example, but the VSWR is about It is improved by 0.7. In this case, the insertion loss level in the passband has hardly changed, and thus the VSWR is improved while maintaining a low loss. That is, it can be seen that a longitudinally coupled resonator type surface acoustic wave filter can be provided that is effective for applications that require a reduction in loss in the passband and a reduction in VSWR even when the passband width is narrow.

  As described above, as in the third reference example, by changing the balance of the number of electrode fingers in a narrow pitch portion, that is, the number of narrow pitch electrode fingers, various reductions can be made while reducing the insertion loss in the passband. It can be seen that a band-pass filter according to the application can be easily provided.

(Fourth reference example)
18A and 18B are a schematic plan view for explaining a longitudinally coupled resonator type surface acoustic wave filter according to a fourth reference example, and a schematic cross-sectional view along a direction intersecting the electrode fingers. is there. FIG. 18B is a schematic cross-sectional view taken along the alternate long and short dash line X, X in FIG. The electrode structure shown in FIG. 18A is exactly the same as the first reference example shown in FIG.

  Accordingly, the same reference numerals are assigned to the same parts. The features of this reference example are clearly shown in FIG. That is, as representatively showing the portion where the IDTs 19 and 20 and the reflector 22 are provided, the film thickness of the narrow-pitch electrode fingers is made thinner than the film thickness of the other electrode fingers or reflector electrodes. . That is, as shown in FIG. 18B, the film thicknesses of the electrode fingers 19f and 19g in the narrow pitch portion on the IDT 20 side of the IDT 19 and the electrode fingers 20a and 20b in the narrow pitch portion on the IDT 19 side of the IDT 20 are the remaining electrode fingers. And the thickness of the electrode finger of the reflector 22 is made thinner. Similarly, in the portion between adjacent IDTs shown in FIG. 18A, the film thickness of the narrow pitch electrode fingers on both sides is made thinner than the film thickness of the remaining electrode fingers. More specifically, in this reference example, the film thickness of the electrode of the narrow pitch electrode finger is 0.06λI2, and the film thickness of the remaining electrode fingers is 0.08λI2.

  Further, in this reference example, since the film thickness of the narrow pitch electrode fingers is reduced, the design is changed so that the electrode finger crossing widths are 38.2λI2 and λI1 = 3.93 μm. Other points are the same as in the first reference example.

  The amplitude characteristics of the longitudinally coupled resonator type surface acoustic wave filter of the fourth reference example are shown by a solid line in FIG. For comparison, the amplitude characteristic of the longitudinally coupled resonator-type surface acoustic wave filter 11 of the first reference example is indicated by a broken line.

  As is apparent from FIG. 19, the insertion loss in the passband is further improved according to the fourth reference example as compared with the first reference example. In general, in a surface acoustic wave filter using a leaky wave, loss due to bulk wave radiation tends to be reduced by reducing the film thickness of an electrode made of Al. However, when the thickness of the electrode is reduced, the electromechanical coupling coefficient is reduced, and the stop band width of the reflector is reduced, so that there is a problem that it is not possible to widen the band.

  In the fourth reference example, in order to solve this problem, the film thickness of the electrode fingers is reduced between IDT and IDT where the emission of bulk waves is most likely to occur, that is, in the portion where the narrow pitch electrode fingers are provided. . As a result, loss due to bulk wave radiation can be reduced while maintaining a wide bandwidth, and good characteristics can be obtained.

(Fifth reference example)
FIG. 20 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a fifth reference example.

A feature of this reference example is that the narrow pitch electrode fingers are constituted by split electrodes represented by the divided electrode fingers 13f ₁ and 13f ₂ . The other points are almost the same as in the first reference example. Only the changes are described below.

  That is, in the fifth reference example, the electrode finger crossing width is 35.7λI2, the IDT wavelength λI2 is 4.20 μm, and λI1 is 4.04 μm.

  In FIG. 21, the amplitude characteristic of the longitudinally coupled resonator type surface acoustic wave filter according to the fifth reference example is indicated by a solid line. A broken line shows the amplitude characteristic of the conventional longitudinally coupled resonator type surface acoustic wave filter shown in the first reference example.

  As is apparent from FIG. 21, it can be seen that also in the fifth reference example, the insertion loss in the passband can be improved as compared with the conventional longitudinally coupled resonator type surface acoustic wave filter.

  Therefore, in the present invention, it can be seen that the narrow pitch electrode fingers may be constituted by using a split electrode composed of a plurality of, usually two, split electrode fingers.

(Example)
This embodiment has the same circuit configuration as that of the first reference example. Therefore, the detailed description is abbreviate | omitted by using description demonstrated about the 1st reference example.

  The difference between this embodiment and the first reference example is that the wavelength of the electrode fingers of the narrow pitch portion in the IDTs 18 to 20 of the surface acoustic wave filter 12, that is, the wavelength of the narrow pitch electrode fingers is 3.88 μm. Other points are the same as in the first reference example.

  That is, in the present embodiment, the wavelengths of the narrow-pitch electrode fingers are different in the longitudinally coupled resonator type surface acoustic wave filters 11 and 12 shown in FIG.

  FIG. 22 shows the amplitude characteristics of the longitudinally coupled resonator type surface acoustic wave filter according to the present embodiment with a solid line, and shows the amplitude characteristics of the longitudinally coupled resonator type surface acoustic wave filter of the first reference example with a broken line.

  As is apparent from FIG. 22, according to the present embodiment, it can be seen that the pass bandwidth can be expanded as compared with the first reference example. In this case, the value of VSWR was about 2.0 in both the present example and the first reference example. Therefore, according to the present embodiment, the pass bandwidth can be expanded without deteriorating the VSWR.

  As described above, when a plurality of surface acoustic wave filters are connected in cascade, the configuration of the narrow pitch electrode fingers of the surface acoustic wave filters at each stage is changed, that is, the narrow pitch electrodes of the surface acoustic wave filter at least one stage. It can be seen that the passband width can be increased by making the finger configuration different from that of the narrow pitch electrode fingers of the remaining surface acoustic wave filters.

(Sixth reference example)
FIG. 23 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter 61 according to a sixth reference example. This reference example corresponds to a modification of the longitudinally coupled resonator type surface acoustic wave filter 31 shown in FIG. That is, the surface acoustic wave resonator 62 as a series resonator is connected in series between the IDT 14 at the center of the one-stage longitudinally coupled resonator type surface acoustic wave filter 31 and the input end.

  As in this reference example, in the present invention, a surface acoustic wave resonator may be connected in series to a longitudinally coupled resonator type surface acoustic wave filter.

  Conventionally, it is known that the attenuation amount outside the passband can be increased by connecting a surface acoustic wave resonator in series to a longitudinally coupled resonator type surface acoustic wave filter. However, although the attenuation outside the passband increases, there is a problem that the insertion loss in the passband increases.

  On the other hand, in the present reference example, since the longitudinally coupled resonator type surface acoustic wave filter configured according to the present invention is used, the deterioration of the insertion loss is reduced. That is, by connecting the surface acoustic wave resonator 62 in series to the longitudinally coupled resonator type surface acoustic wave filter 31, the amount of attenuation outside the pass band can be increased while reducing the insertion loss in the pass band. Good filter characteristics can be obtained.

  Similarly, in the longitudinally coupled resonator type surface acoustic wave filter according to the present invention, the insertion loss in the passband can be reduced. Therefore, the surface acoustic wave in parallel with the longitudinally coupled resonator type surface acoustic wave filter configured according to the present invention is used. A resonator may be connected. In this case, the attenuation outside the passband can be increased while reducing the insertion loss in the passband.

  Moreover, you may have both the surface acoustic wave resonator connected in series, and the surface acoustic wave resonator connected in parallel.

(Seventh reference example)
FIG. 24 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a seventh reference example. The longitudinally coupled resonator type surface acoustic wave filter 71 according to the seventh reference example has the same electrode structure as the longitudinally coupled resonator type surface acoustic wave filter shown in FIG. The difference is that the surface acoustic wave filter shown in FIG. 9 has an unbalanced input-unbalanced output, whereas in this reference example, only one end of the center IDT is connected to the input end. The terminal 72 is provided so that a signal can be taken out from the other end.

  In recent years, longitudinally coupled resonator type surface acoustic wave filters are required to have a balanced-unbalanced conversion function. In the seventh reference example shown in FIG. 24, an unbalanced input-balanced output type filter can be configured by using the terminal 74 as an input terminal and the terminals 72 and 73 as output terminals. On the contrary, if the terminals 72 and 73 are input terminals and the terminal 74 is an output terminal, a balanced input-unbalanced output type filter can be configured. Therefore, it is possible to provide a surface acoustic wave filter having a balanced-unbalanced conversion function with a small insertion loss in the passband. Modification examples of the surface acoustic wave filter having such a balance-unbalance conversion function are shown in FIGS.

  In the longitudinally coupled resonator type surface acoustic wave filter 81 shown in FIG. 25, the outer IDTs 13 and 15 are configured to be able to take out balanced input / output, and the center IDT 14 is connected to the unbalanced input / output terminal 82. .

  In the longitudinally coupled resonator type surface acoustic wave filter 85 shown in FIG. 26, the phases of the IDTs 13 and 15 with respect to the IDT 14 are reversed to realize a balanced-unbalanced conversion function.

  Further, in the longitudinally coupled resonator type surface acoustic wave filter 86 shown in FIG. 27, the phases of the IDTs 18 and 20 are inverted in the surface acoustic wave filters 11 and 12 cascaded in two stages, and a balance signal is output from the IDT 19. Terminals 87 and 88 are connected to the IDT 19 so that they can be taken out.

  In the longitudinally coupled resonator type surface acoustic wave filter 91 shown in FIG. 28, in the two-stage longitudinally coupled resonator type surface acoustic wave filters 11 and 12, the surface acoustic wave filter 12 on the side from which the balance terminal is taken out has an elastic crossing width. The surface acoustic wave filter 11 is divided into two surface acoustic wave filters 92 and 93, which are half of the surface acoustic wave filter 11, and the phases of the surface acoustic wave filters 92 and 93 are inverted.

  Further, as shown in FIG. 29, in the configuration having the two-stage longitudinally coupled resonator type surface acoustic wave filters 11 and 12, the second surface acoustic wave filter 12 is replaced with the longitudinally coupled resonator type surface acoustic wave filters 96 and 97. By dividing the phase of the IDTs 13 and 15 with respect to the IDT 14 of the first surface acoustic wave filter 11, the balance-unbalance conversion function is provided.

  In the longitudinally coupled resonator type surface acoustic wave filter 101 shown in FIG. 30, each of the two stages of longitudinally coupled resonator type surface acoustic wave filters is divided in half with a crossing width and connected in parallel. That is, the longitudinally coupled resonator type surface acoustic wave filter 11 is divided into two longitudinally coupled resonator type surface acoustic wave filters 11A and 11B, and the longitudinally coupled resonator type surface acoustic wave filter 12 is divided into longitudinally coupled resonators. It is divided into type surface acoustic wave filters 12A and 12B.

  Among these, the balance-unbalance conversion function is provided by inverting the phase of a set of surface acoustic wave filters.

  That is, as shown in FIGS. 25 to 30, to provide a surface acoustic wave filter having a balanced-unbalanced conversion function while reducing insertion loss by various structures as in the seventh reference example. Can do.

(Eighth reference example)
FIG. 31 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to an eighth reference example of the present invention. The longitudinally coupled resonator type surface acoustic wave filter 111 of this reference example has the same electrode structure as the longitudinally coupled resonator type surface acoustic wave filter shown in FIG. The difference is that terminals 112 to 115 are provided so that signals can be taken out from the ends of all IDTs 13 to 15.

  Here, since a balance signal can be obtained from each of the terminals 112 and 115 and the terminals 113 and 114, a balanced input-balanced output surface acoustic wave filter can be obtained. Also in this reference example, since the longitudinally coupled resonator type surface acoustic wave filter is configured according to the present invention, it is possible to provide a balanced input / output type surface acoustic wave filter with a small insertion loss in the passband.

  FIG. 35 is a schematic block diagram for explaining the communication device 160 using the surface acoustic wave device according to the present invention.

  In FIG. 35, a duplexer 162 is connected to the antenna 161. A surface acoustic wave filter 164 and an amplifier 165 that constitute an RF stage are connected between the duplexer 162 and the reception-side mixer 163. Further, an IF-stage surface acoustic wave filter 169 is connected to the mixer 163. Further, an amplifier 167 and a surface acoustic wave filter 168 constituting an RF stage are connected between the duplexer 162 and the mixer 166 on the transmission side.

  Longitudinal coupled resonator type surface acoustic wave filters configured in accordance with the present invention can be suitably used as the RF stage surface acoustic wave filters 164, 168, and 169 in the communication device 160.

1 is a schematic plan view of a longitudinally coupled resonator type surface acoustic wave filter according to a first reference example of the present invention. FIG. 5 is a schematic plan view showing an electrode structure of a conventional longitudinally coupled resonator type surface acoustic wave filter. The figure which shows the amplitude characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter of a 1st reference example and a prior art example. The figure which shows the amplitude characteristic of the conventional longitudinal coupling resonator type | mold surface acoustic wave filter. The schematic diagram for demonstrating the relationship between the electrode structure and resonance mode of the conventional 3IDT type longitudinal coupling resonator type | mold surface acoustic wave filter. The figure which shows the ratio of the ratio with respect to the electrode finger pitch of the remaining part of the electrode finger pitch in the narrow pitch part of the longitudinally coupled resonator type surface acoustic wave filter of the first reference example, and the propagation loss. (A) And (b) is a figure which shows each reflection characteristic in the case where the number of the narrow pitch electrode fingers in the longitudinally coupled resonator type surface acoustic wave filter of the first reference example is eight and twelve. The figure which shows the change of VSWR when the number of narrow pitch electrode fingers is changed in the first reference example. The typical top view which shows the electrode structure of the 1 step | paragraph longitudinally coupled resonator type | mold surface acoustic wave filter which concerns on the modification of a 1st reference example. The typical top view which shows the electrode structure of the other modification of the longitudinal coupling resonator type | mold surface acoustic wave filter of a 1st reference example. FIG. 9 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a second reference example. The figure for demonstrating the difference between the resonance mode of the longitudinally coupled resonator type surface acoustic wave filter of the second reference example and the resonance mode of the longitudinally coupled resonator type surface acoustic wave filter of the first reference example. The figure which shows the amplitude characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter of a 2nd reference example and a 1st reference example. FIG. 10 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a third reference example. (A) to (c) are the longitudinally coupled resonator type surface acoustic wave filter of the first reference example, the longitudinally coupled resonator type surface acoustic wave filter of the third reference example, and the longitudinal direction of the third reference example, respectively. The figure which shows the reflective characteristic of the structure which changed the balance of the number of the narrow pitch electrode fingers in a coupled resonator type surface acoustic wave filter. (A) And (b) is a figure which shows the amplitude characteristic and VSWR characteristic of the longitudinally coupled resonator type surface acoustic wave filter according to the third reference example and the longitudinally coupled resonator type surface acoustic wave filter of the first reference example. . (A) And (b) is a figure which shows the amplitude characteristic and VSWR characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter of the modification shown in FIG.15 (c). (A) And (b) is a typical top view which shows the electrode structure of the longitudinal coupling resonator type | mold surface acoustic wave filter which concerns on a 4th reference example, and principal part sectional drawing along the direction which cross | intersects an electrode finger. The figure which shows the amplitude characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter of a 4th reference example and a 1st reference example. FIG. 9 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a fifth reference example. The figure which shows the amplitude characteristic of the longitudinally coupled resonator type | mold surface acoustic wave filter which concerns on a 5th reference example, and the conventional longitudinally coupled resonator type | mold surface acoustic wave filter. The figure which shows the amplitude characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter which concerns on a present Example, and the amplitude characteristic of the longitudinal coupling resonator type | mold surface acoustic wave filter of a 1st reference example. FIG. 10 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a sixth reference example. FIG. 10 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to a seventh reference example. The typical top view which shows the modification of the longitudinally coupled resonator type | mold surface acoustic wave filter of a 7th reference example. FIG. 15 is a schematic plan view for explaining another modification of the longitudinally coupled resonator type surface acoustic wave filter according to the seventh reference example. FIG. 15 is a schematic plan view showing still another modification of the longitudinally coupled resonator type surface acoustic wave filter according to the seventh reference example. FIG. 15 is a schematic plan view for explaining another modification of the longitudinally coupled resonator type surface acoustic wave filter according to the seventh reference example. FIG. 10 is a schematic plan view for explaining still another modification of the longitudinally coupled resonator type surface acoustic wave filter of the seventh reference example. FIG. 10 is a schematic plan view for explaining still another modification of the longitudinally coupled resonator type surface acoustic wave filter of the seventh reference example. FIG. 20 is a schematic plan view showing an electrode structure of a longitudinally coupled resonator type surface acoustic wave filter according to an eighth reference example. The figure which shows the relationship between the number of narrow pitch electrode fingers, and a pass bandwidth. The figure which shows the relationship between the distance change between center of IDT, and a propagation loss. It is a figure for demonstrating the preferable range of the electrode finger distance which does not make pitch small, and shows the relationship between the electrode finger distance which does not make pitch small, and the number of narrow pitch electrode fingers which can obtain a favorable filter characteristic. FIG. The block diagram for demonstrating the communication apparatus provided with the longitudinal coupling resonator type | mold surface acoustic wave filter which concerns on this invention as a band pass filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Longitudinal coupling resonator type | mold surface acoustic wave filter 2 ... Piezoelectric substrate 11, 12, 11A, 11B, 12A, 12B ... Longitudinal coupling resonator type | mold surface acoustic wave filter 13-15 ... IDT
13 a to 13 h ... electrode finger 13f _1, 13f ₂ ... split electrode fingers 14 a to 14 i ... electrode finger 15a ... electrode fingers 16, 17 ... reflectors 18-20 ... IDT
19f, 19g ... electrode fingers 20a-20h ... electrode fingers 21, 22 ... reflector 31 ... longitudinally coupled resonator type surface acoustic wave filter 32 ... longitudinally coupled resonator type surface acoustic wave filter 33-37 ... IDT
DESCRIPTION OF SYMBOLS 41 ... Longitudinal coupled resonator type surface acoustic wave filter 51 ... Longitudinal coupled resonator type surface acoustic wave filter 61 ... Longitudinal coupled resonator type surface acoustic wave filter 62 ... Surface acoustic wave resonator 71 ... Longitudinal coupled resonator type surface acoustic wave Filters 72 to 74 ... terminals 81, 85, 86, 91 ... longitudinally coupled resonator type surface acoustic wave filters 87, 88 ... terminals 92, 93, 96, 97 ... longitudinally coupled resonator type surface acoustic wave filters 101 ... longitudinally coupled resonance Child type surface acoustic wave filter 111... Longitudinally coupled resonator type surface acoustic wave filter 112 to 115... Terminal 160 .. communication device 161... Antenna 162 ... duplexer 163 and 166 ... mixer 164 ... surface acoustic wave filter 165 ... amplifier 167 ... amplifier 168 ... Surface acoustic wave filter 169 ... Surface acoustic wave filter

Claims (19)

A piezoelectric substrate;
Formed along the surface acoustic wave propagation direction on the piezoelectric substrate, each including at least three IDTs having a plurality of electrode fingers,
At least one IDT is the period of a portion of the electrode finger from the other IDT end portions adjacent to the surface acoustic wave propagation direction, have a remaining small pitch portion than the period of electrode fingers of portions of the IDT the narrow wavelength of the surface wave determined by the period of electrode fingers of the pitch portion is Ramudaai1, the remaining portion of the wavelength of the surface wave determined by the period of electrode fingers λI2 der Rutotomoni, 0-order mode, second order mode , Longitudinally coupled resonator-type surface acoustic wave filters that use the IDT-IDT resonance mode are cascaded in at least two stages,
The configuration of the narrow pitch portion in the longitudinally coupled resonator type surface acoustic wave filter of at least one stage of the multiple stage longitudinally coupled resonator type surface acoustic wave filter is the same as in the longitudinally coupled resonator type surface acoustic wave filter of the other stage. While different from the configuration of the narrow pitch portion,
The period of the electrode fingers of the narrow pitch portion in the longitudinally coupled resonator type surface acoustic wave filter of at least one stage of the multiple stage longitudinally coupled resonator type surface acoustic wave filter is the longitudinally coupled resonator type surface acoustic wave of the other stage. A longitudinally coupled resonator type surface acoustic wave filter characterized in that it is different from the period of the electrode fingers of the narrow pitch portion in the wave filter.   2. The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein a period of the electrode fingers in the narrow pitch portion is 0.82 to 0.99 times a period of the electrode fingers in the remaining portion.   Both of the pair of adjacent IDTs are configured such that the period of the electrode fingers in the narrow pitch part is different from the period of the electrode fingers in the remaining part, and the distance between the electrode finger centers of the pair of IDTs is 0. The longitudinally coupled resonator type surface acoustic wave filter according to claim 1 or 2, which is substantially coincident with .5λI1.   Only one of the pair of adjacent IDTs is configured such that the period of the electrode fingers in the narrow pitch part is different from the period of the electrode fingers in the remaining part, and the distance between the electrode finger centers of the pair of IDTs is The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the longitudinally coupled resonator type surface acoustic wave filter is substantially matched with 0.25λI1 + 0.25λI2.   In the IDT in which the period of the electrode fingers of the narrow pitch portion is different from the period of the electrode fingers of the remaining portion, the distance between the electrode finger centers at the location where the electrode fingers of the narrow pitch portion and the electrode fingers of the remaining portion are adjacent to each other 5. The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the distance is substantially equal to 0.25λI1 + 0.25λI2.   6. The longitudinally coupled resonator-type surface acoustic wave filter according to claim 1, wherein polarities of adjacent electrode fingers of an IDT having a narrow pitch portion and an IDT adjacent to the IDT are different. .   The longitudinally coupled resonator type elastic surface according to any one of claims 1 to 6, wherein the total number of electrode fingers in a narrow pitch portion is 18 or less on both sides of adjacent portions of a pair of adjacent IDTs. Wave filter.   The distance between the centers of the electrode fingers of the pair of adjacent IDTs whose periods are not different is expressed as (0.08 + 0.5n) λI2− (0.24 + 0.5n) λI2 (n = 1, 2, 3,...) The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is a longitudinally coupled resonator type surface acoustic wave filter.   The distance between the centers of the electrode fingers of the pair of adjacent IDTs whose periods are not different is expressed as (0.13 + 0.5n) λI2− (0.23 + 0.5n) λI2 (n = 1, 2, 3,...) The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is a longitudinally coupled resonator type surface acoustic wave filter.   Either of a pair of IDT adjacent in a surface wave propagation direction has the said narrow pitch part, The number of the electrode fingers of the narrow pitch part in both IDTs differs, The one of Claims 1-9 characterized by the above-mentioned. 2. A longitudinally coupled resonator type surface acoustic wave filter according to 1. 11. The longitudinally coupled resonator-type elasticity according to claim 1, wherein the piezoelectric substrate is obtained by rotating a LiTaO ₃ single crystal in the range of 36 to 44 degrees in the Y axis direction around the X axis. Surface wave filter.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein a film thickness of the electrode fingers in the narrow pitch portion is different from a film thickness of the electrode fingers in the remaining portions.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 12, wherein a film thickness of the electrode fingers in the narrow pitch portion is made thinner than a film thickness of the electrode fingers in the remaining portion.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the electrode fingers of the narrow pitch portion are constituted by split electrodes.   The longitudinally coupled resonator type surface acoustic wave according to any one of claims 1 to 14, wherein each of the stages of the multistage longitudinally coupled resonator type surface acoustic wave filter has different periods of the electrode fingers of the narrow pitch portion. filter.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein at least one series resonator and / or parallel resonator is connected to an input side and / or an output side.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, wherein the longitudinally coupled resonator type surface acoustic wave filter is configured to have a balanced-unbalanced input / output.   The longitudinally coupled resonator type surface acoustic wave filter according to claim 1, which is configured to have a balanced-balanced input / output.   A communication device comprising the longitudinally coupled resonator surface acoustic wave filter according to claim 1 as a bandpass filter.

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