JP3298769B2 - Surface acoustic wave multimode filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave multi-mode filter used for a high-frequency circuit in a radio communication device.

[0002]

2. Description of the Related Art Electromechanical functional components using surface acoustic waves have a property that the sound speed of waves is several km / s and the energy of waves is concentrated on the surface of a propagation medium. Attention is being paid to this trend. Electromechanical functional components using surface acoustic waves have been developed through the development of interdigital transducer (hereinafter abbreviated as “IDT”) electrodes and the development of thin film fabrication technology and surface processing technology that have enabled their deformation and development. It has been put to practical use as a delay line for radar, a bandpass filter for television receivers, and the like, and is currently widely used as an RF and IF stage filter in a transmission / reception circuit of a wireless communication device.

[0003] In recent years, with the digitization of mobile communication devices, the development of digital mobile phones, digital cordless phones, and the like has been actively pursued. In the communication system used for these devices, since information is given to the amplitude and phase of the signal, the filter used in the IF stage is required to have flat amplitude characteristics and group delay deviation characteristics. In addition, since excellent characteristics are required for selectivity for distinguishing a signal of an adjacent channel from a desired signal, a filter used in an IF stage is required to have a sharp cutoff characteristic with a narrow transition bandwidth. You.

Conventionally, as a surface acoustic wave filter suitable for the IF stage, two types of surface acoustic wave multimode filters, a transversal type surface acoustic wave filter and a longitudinal mode coupling type and a transverse mode coupling type, are known. Although the transversal surface acoustic wave filter has excellent group delay deviation characteristics, it has a large insertion loss, large element size, and poor blocking characteristics. On the other hand, a surface acoustic wave multi-mode filter has a steep cutoff characteristic and a small insertion loss and a small element size, but is inferior in group delay deviation characteristics as compared with a transversal type surface acoustic wave filter. Further, the longitudinal mode coupling type surface acoustic wave multimode filter is characterized in that a relatively large spurious component exists on the high frequency side near the passband, and the transverse mode coupling type surface acoustic wave multimode filter is very narrow. It is characterized by having bandpass characteristics. Due to the above characteristics, a transverse mode coupling type surface acoustic wave multi-mode filter having a small size and excellent cutoff characteristics has been generally used as an IF filter for mobile communication equipment.

A conventional transverse mode coupled surface acoustic wave multimode filter will be described below. FIG. 14 is a configuration diagram showing a transverse mode coupling type surface acoustic wave multimode filter according to the related art. In FIG. 14, reference numeral 141 denotes a single crystal piezoelectric substrate. By forming an electrode pattern on the piezoelectric substrate 141, surface acoustic waves can be excited. 142a is an IDT electrode formed on the piezoelectric substrate 141, and reflectors 142b, 14
By arranging 2c, an energy trapping type surface acoustic wave resonator is formed. Also, the piezoelectric substrate 14
1 above, an IDT electrode 143a and a reflector 143b, 1
43c form a similar surface acoustic wave resonator. These two resonators are arranged close to each other, and acoustic coupling occurs therebetween to form a first-stage surface acoustic wave multimode filter. Further, on the piezoelectric substrate 141, IDT electrodes 144a,
145a and reflectors 144b, 144c, 145b, 14
5c constitutes a second-stage surface acoustic wave multi-mode filter in the same manner as described above. These first-stage and second-stage surface acoustic wave multi-mode filters are electrically connected in cascade by an electrode pattern 146, thereby forming a multi-stage connected surface acoustic wave multi-mode filter.

In the surface acoustic wave multi-mode filter configured as described above, the mode frequencies of two types of surface acoustic waves excited on the piezoelectric substrate are determined by the dimension of the electrode finger crossing width of the IDT electrode, and the filter passes through the filter. A bandwidth is defined. In this surface acoustic wave multimode filter, the obtained pass characteristic is extremely narrow, and the specific bandwidth (the bandwidth standardized by the center frequency of the filter) is at most 0.1%.
It is about. FIG. 15 shows a typical measurement example of a frequency characteristic representing a pass bandwidth of the surface acoustic wave multimode filter.

[0007]

In order to cope with the above-mentioned digitization, it is required to widen the pass characteristic of the filter and widen the flat band of the group delay deviation characteristic. Conventionally, in order to realize a wide band, a method of inserting an extension coil between the stage of the surface acoustic wave multimode filter and the ground has been adopted.

In recent years, balanced input / output of IC elements before and after an IF filter has been progressing, and a balanced input / output type is also required for an IF filter. However, in the conventional filter having the above-described configuration, the characteristics of the filter are likely to be unstable due to the influence of an external coil such as an extension coil, and the out-of-band attenuation characteristics are also deteriorated. Further, in the conventional filter having the above configuration, there is a problem that the input / output terminal can be connected only as an unbalanced type.

According to the present invention, in order to solve the above-mentioned problems in the prior art, it is possible to broaden the pass characteristic, achieve good out-of-band attenuation characteristics, and obtain a balanced input / output configuration. It is an object of the present invention to provide a surface acoustic wave multi-mode filter which can also realize the following.

[0010]

In order to achieve the above object, a first aspect of a surface acoustic wave multimode filter according to the present invention is described.
Is formed on a piezoelectric substrate, first and third surface acoustic wave resonators provided with reflectors on both sides of an interdigital transducer electrode, in parallel to the propagation direction of the surface acoustic wave. between the third surface acoustic wave resonators, have a electrode finger crossing width substantially the same length of the interdigital transducer electrodes, and the interdigital tiger
Ends of Nsudeyusa electrodes and a plurality of strip line electrodes for chromatic substantially the same electrode widths are arranged in parallel with the first and the same electrode period and the third surface acoustic wave resonators, the plurality of strip line electrodes Forming a second surface acoustic wave resonator composed of an array of periodic structural electrodes in which the portions are connected to each other by bus bar electrodes, wherein the first and third surface acoustic wave resonators and the second surface acoustic wave resonator Are arranged in close proximity to each other and acoustically coupled, the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators being adjacent to the periodic structure electrode row. the line width of a bus bar electrode W _1, the line width of the bus bar electrode connected to both end portions of the periodic structure shaped electrode rows W _2, the bus bar electrode and the first and second of said periodic structure shaped electrode row The width of the electrical isolation zone of said periodic structure shaped electrode row bus bar electrodes on the side adjacent to the interdigital transducer electrodes of the surface acoustic wave resonator as W ₃ of the W _1, W _2, W ₃ The relative dimension of
₁ > W ₂ , and W ₁ > W ₃ .

In the first configuration of the present invention,
Is W₁And W_TwoIs the relative dimension of W₁/ W _TwoSet to ≧ 4
Is preferred. Further, in the first configuration of the present invention,
In this case, the first and third surface acoustic wave resonators are configured.
The number of electrode fingers of the interdigital transducer electrode is
Preferably between 150 and 300 pairs
No.

Further, in the first configuration of the present invention, the periodic structured electrode array constituting the second surface acoustic wave resonator is connected to the first and third surface acoustic wave resonators via the reflectors. Preferably, it is grounded. In this case, it is preferable that the first surface acoustic wave resonator electrode is connected to the balanced input terminal, and the third surface acoustic wave resonator electrode is connected to the balanced output terminal.

In the first structure of the present invention, it is preferable that a plurality of cascades are connected by first and second inter-stage connection electrode patterns formed on the piezoelectric substrate. In this case, it is preferable that one of the first and second inter-stage connection electrode patterns is directly grounded, and the other is grounded via a reactance element. In this case, the first surface acoustic wave resonator electrode of the preceding surface acoustic wave multimode filter is connected to the balanced input terminal, and the third surface acoustic wave resonator of the subsequent surface acoustic wave multimode filter is further connected. Preferably, the electrodes are connected to balanced output terminals. In this case, the first inter-stage connection electrode pattern is connected to the second surface acoustic wave resonator of the third surface acoustic wave resonator constituting the front surface acoustic wave multimode filter connected in cascade. An adjacent interdigital transducer electrode is connected to an interdigital transducer electrode adjacent to a second surface acoustic wave resonator of a first surface acoustic wave resonator constituting a surface acoustic wave multimode filter of a subsequent stage connected in cascade. The second inter-stage connection electrode pattern includes an interdigital transducer electrode outside the output end of the cascade-connected front surface acoustic wave multimode filter and an input end outside the cascade-connected post-stage surface acoustic wave multimode filter. Preferably, it is connected to an interdigital transducer electrode. In this case, it is preferable that the first inter-stage connection electrode pattern is grounded via a reactance element, and the second inter-stage connection electrode pattern is directly grounded. The first surface acoustic wave resonator electrode of the mode filter is connected to the balanced input terminal, and the third surface acoustic wave resonator electrode of the subsequent surface acoustic wave multimode filter is connected to the balanced output terminal. Is preferred.

The surface acoustic wave multiplex mode according to the present invention
A second configuration of the filter includes an
With a reflector on each side of the
The first, second and third surface acoustic wave resonators are
Acoustic coupling is arranged close to and parallel to the propagation direction.
Interdigital transducer power between surface wave resonators.
Electrical separation between adjacent busbar electrodes at the poles
The interface of the second surface acoustic wave resonator located at the center
Elastic table with all digital transducer electrodes grounded
A surface wave multi-mode filter, wherein a second
Interdigits constituting first and third surface acoustic wave resonators
The second surface acoustic wave resonance of the ground transducer electrode
The line width of the bus bar electrode on the side adjacent to the₁,Previous
The interdigital transformer of the second surface acoustic wave resonator
Set the line width of the bus bar electrode of the transducer electrode to W_Two, Said adjacent
The width of the electrical separator between the busbar electrodes_ThreeAnd before
Note W ₁, W_Two, W_ThreeThe relative dimensions of₁> W_Two, W₁>
W_ThreeIs set.

Further, in the second configuration of the present invention,
Is W₁And W_TwoIs the relative dimension of W₁/ W _TwoSet to ≧ 4
Is preferred. Further, in the second configuration of the present invention,
In this case, the first, second, and third surface acoustic wave resonators are configured.
Electrode finger of interdigital transducer electrode to be formed
The logarithm is set between 150 and 300 pairs
preferable.

In the second configuration of the present invention, the interdigital transducer electrode of the second surface acoustic wave resonator is grounded via the reflectors of the first and third surface acoustic wave resonators. Is preferred. In this case, the interdigital transducer electrode of the first surface acoustic wave resonator is connected to the balanced input terminal, and the interdigital transducer electrode of the third surface acoustic wave resonator is connected to the balanced output terminal. Is preferred.

Further, in the second configuration of the present invention, it is preferable that a plurality of cascades are connected by first and second inter-stage connection electrode patterns formed on the piezoelectric substrate. In this case, it is preferable that one of the first and second inter-stage connection electrode patterns is grounded, and the other is grounded via a reactance element. In this case, the first surface acoustic wave resonator electrode of the preceding surface acoustic wave multimode filter is connected to the balanced input terminal, and the third surface acoustic wave resonator of the subsequent surface acoustic wave multimode filter is further connected. Preferably, the electrodes are connected to balanced output terminals. In this case, the first inter-stage connection electrode pattern is connected to the second surface acoustic wave resonator of the third surface acoustic wave resonator constituting the front surface acoustic wave multimode filter connected in cascade. An adjacent interdigital transducer electrode is connected to an interdigital transducer electrode adjacent to a second surface acoustic wave resonator of a first surface acoustic wave resonator constituting a surface acoustic wave multimode filter of a subsequent stage connected in cascade. The second inter-stage connection electrode pattern includes an interdigital transducer electrode outside the output end of the cascade-connected front surface acoustic wave multimode filter and an input end outside the cascade-connected post-stage surface acoustic wave multimode filter. Preferably, it is connected to an interdigital transducer electrode. In this case,
Preferably, the first inter-stage connection electrode pattern is grounded via a reactance element, and the second inter-stage connection electrode pattern is directly grounded. Preferably, the surface acoustic wave resonator electrode is connected to the balanced input terminal, and the third surface acoustic wave resonator electrode of the subsequent surface acoustic wave multimode filter is connected to the balanced output terminal.

[0018]

According to the first configuration of the present invention, first and third surface acoustic wave resonators having reflectors on both sides of an interdigital transducer electrode are formed on a piezoelectric substrate by using an elastic material. A plurality of strip line electrodes formed in parallel to the propagation direction of the surface acoustic wave and having a length substantially equal to the electrode finger intersection width of the interdigital transducer electrode between the first and third surface acoustic wave resonators; Are arranged in parallel with the first and third surface acoustic wave resonators at the same electrode period, and a second electrode comprising a periodic structure electrode row in which both ends of the plurality of strip line electrodes are connected to each other by bus bar electrodes. Forming the surface acoustic wave resonator of
And a surface acoustic wave multi-mode filter in which a third surface acoustic wave resonator and the second surface acoustic wave resonator are disposed close to each other and acoustically coupled, wherein the first and third surface acoustic wave resonance The line width of the bus bar electrode on the side adjacent to the periodic structure electrode row of the interdigital transducer electrode constituting the device is W ₁ , and the line width of the bus bar electrode connecting both ends of the periodic structure electrode row is W ₂ Electrical connection between the bus bar electrode of the periodic structure electrode row and a bus bar electrode on the side of the interdigital transducer electrode constituting the first and third surface acoustic wave resonators adjacent to the periodic structure electrode row. The width of the separator is W _3, and W ₁ ,
By setting the relative dimensions of W ₂ and W ₃ to W ₁ > W ₂ and W ₁ > W ₃ , the insertion loss of the filter can be reduced. Hereinafter, the reason will be described. The distance G between the interdigital transducer electrodes of the opposed surface acoustic wave resonators and the periodic structure electrode row governs the degree of coupling between the two surface acoustic wave resonators. This is preferable for widening the band since the degree of increase is increased. However, if the interval G is too small, the line widths W ₁ and W _{2 of the} bus bar electrodes provided in this portion become small, and the electrical resistance loss of the interdigital transducer electrode in this portion gives an insertion loss of the filter. The effects cannot be ignored. Here, since the bus bar electrodes connecting both ends of the periodic structure electrode row are not electrically connected to the input / output terminals, the line width W ₂ of the bus bar electrodes connecting both ends of the periodic structure electrode row is large. It has no effect on the insertion loss of the filter. Therefore, minute to reduce the line width W ₂ of the bus bar electrode connected to both end portions of the periodic structure shaped electrode column on the periodic structure shaped electrode row of interdigital transducer electrodes of the first and third surface acoustic wave resonator Line width W _{1 of the} bus bar electrode on the adjacent side
(Ie, the relative dimension of W ₁ and W ₂ is W
If set to _1> W _2), without changing the spacing G, it is possible to reduce the electrical resistance loss of input and output,
The insertion loss of the filter can be reduced. Further, an electrical separator between the bus bar electrode of the periodic structure electrode row and the bus bar electrode on the side adjacent to the periodic structure electrode row of the interdigital transducer electrode constituting the first and third surface acoustic wave resonators. If the width W ₃ is smaller than the line width W ₁ of the bus bar electrode on the side adjacent to the periodic structure electrode row of the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators (ie, W
₁ by setting the relative sizes of the W ₃ to _{W 1> W 3), W} 3
It is possible only further increase the W ₁ of the decrease, it is possible to further reduce the insertion loss of the filter.

Further, in the first configuration of the present invention,
According to a preferred example in which the relative dimensions of W ₁ and W ₂ are set to W ₁ / W ₂ ≧ 4, the insertion loss of the filter is greatly improved.

In the first configuration of the present invention,
According to a preferred example in which the number of electrode finger pairs of the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators is set between 150 and 300, the insertion loss is only 7 dB or more, 2 in-band ripples
Fits in ~ 3dB. These insertion loss amounts and ripple values are characteristic values appropriate for a filter.

Further, in the first configuration of the present invention,
According to a preferred example in which the row of periodic structural electrodes constituting the second surface acoustic wave resonator is grounded via the reflectors of the first and third surface acoustic wave resonators, it is disposed outside. Since all of the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators can be independently wired, balanced input / output of the surface acoustic wave multimode filter can be realized. As a result, the filter characteristics are not affected by the stray capacitance or the like due to the grounding state of the electrodes, so that the characteristics of the stop band and the transition region are further improved. In addition, since it becomes possible to connect a balanced element such as an IC to the front and rear stages of the filter without using an external circuit such as a balun, noise characteristics of the entire circuit are also improved. Further, in this case, according to a preferred example in which the first surface acoustic wave resonator electrode is connected to the balanced input terminal and the third surface acoustic wave resonator electrode is connected to the balanced output terminal, 2 are electrically connected to each other, and the electrode fingers of the interdigital transducer electrode of the first surface acoustic wave resonator and the interface of the third surface acoustic wave resonator are electrically connected to each other. The electrode fingers of the digital transducer electrodes become electrically independent. Therefore, the potential of the second surface acoustic wave resonator disposed at the center can be freely distributed, and the potential is canceled between the first and third surface acoustic wave resonators disposed outside. Since there is no second-order mode, the characteristics are also strongly excited. As a result, a surface acoustic wave multi-mode filter using three excitation modes effectively is realized. Thus, according to this configuration,
Since the order of the filter increases, a steep cutoff characteristic over a wide band is obtained (that is, a good out-of-band attenuation characteristic is realized).

In the first configuration of the present invention,
According to a preferred example in which a plurality of cascade connections are made by the first and second inter-stage connection electrode patterns formed on the piezoelectric substrate, the insertion loss is slightly increased, but the characteristics of the stop zone and the transition zone are significantly increased. And better filter characteristics can be obtained. Further, in this case, according to a preferred example in which one of the first and second inter-stage connection electrode patterns is directly grounded and the other is grounded via a reactance element, good transmission characteristics can be obtained. . Also,
In this case, the first inter-stage connection electrode pattern is an interdigital signal adjacent to the second surface acoustic wave resonator of the third surface acoustic wave resonator constituting the preceding surface acoustic wave multimode filter connected in cascade. Connecting the transducer electrode and the interdigital transducer electrode adjacent to the second surface acoustic wave resonator of the first surface acoustic wave resonator constituting the surface acoustic wave multi-mode filter of the subsequent stage connected in cascade; The interstage connection electrode pattern is composed of an interdigital transducer electrode outside the output end of the front surface acoustic wave multimode filter connected in cascade and an interdigital transducer electrode outside the input end of the subsequent surface acoustic wave multimode filter connected in cascade. According to a preferred example of connecting the surface acoustic wave with a multi-stage connection having a balanced input / output configuration Heavy mode filter is realized.

According to the second configuration of the present invention,
On a piezoelectric substrate, first, second and third surface acoustic wave resonators provided with reflectors on both sides of an interdigital transducer electrode are arranged close to and parallel to the direction of surface acoustic wave propagation and acoustically coupled, A surface acoustic surface in which adjacent busbar electrodes of an interdigital transducer electrode portion between the surface acoustic wave resonators are electrically separated, and all interdigital transducer electrodes of a second surface acoustic wave resonator disposed at the center are grounded. A wave multimode filter, comprising: a busbar electrode on a side adjacent to the second surface acoustic wave resonator of an interdigital transducer electrode constituting first and third surface acoustic wave resonators disposed outside; the line width W _1, the line width of the bus bar electrode of the second SAW resonator interdigital transducer electrode W _2, Serial width of electrical isolation zones between adjacent bus bar electrodes and W _3, by the relative dimensions of the _{W 1, W 2, W 3} , is set to _{W 1> W 2, W 1} > W 3,
The following effects can be obtained. That is, as compared with the first configuration of the present invention, the electrode structure of the second surface acoustic wave resonator disposed at the center is changed from the periodic structure electrode row to the interdigital transducer electrode. Propagates in exactly the same way,
The basic operation is the same as in the case of the first configuration of the present invention. Therefore, as in the case of the first configuration of the present invention,
It is possible to reduce the insertion loss of the filter and obtain a wide band and steep cutoff characteristics. Further, adjacent bus bar electrodes of the interdigital transducer electrode portion between the surface acoustic wave resonators are electrically separated, and all the interdigital transducer electrodes of the second surface acoustic wave resonator disposed at the center are grounded. Thus, all the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators disposed outside can be independently wired, thereby realizing balanced input / output of the surface acoustic wave multimode filter. can do.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. <First Embodiment> FIG. 1 is a block diagram showing a first embodiment of a surface acoustic wave multimode filter according to the present invention. FIG.
In the figure, reference numeral 11 denotes a single-crystal piezoelectric substrate, and a surface acoustic wave can be excited by forming an electrode pattern having a periodic strip line shape on the piezoelectric substrate 11. On the piezoelectric substrate 11, an energy trap type first surface acoustic wave resonator constituted by an IDT electrode 12a and reflectors 12b and 12c is formed. Further, on the piezoelectric substrate 11, a third surface acoustic wave resonator including the IDT electrode 14a and the reflectors 14b and 14c is formed. It should be noted here that the reflectors 13b and 13c are provided, and the first surface acoustic wave resonator and the third
The electrode portion of the second surface acoustic wave resonator formed between the first surface acoustic wave resonator and the first surface acoustic wave resonator has the same structure as the reflector,
And IDT electrode 12 in third surface acoustic wave resonator
The point is that it is constituted by a strip electrode line 13a having a periodic structure having a length substantially equal to the electrode finger intersection width of a and 14a. Thus, even if the structure of the electrode portion of the second surface acoustic wave resonator changes from the IDT electrode to the periodic structure strip line electrode array 13a, the surface acoustic wave propagates in exactly the same manner as long as the electrode period is the same. Therefore, the acoustic behavior of the second surface acoustic wave resonator disposed at the center is the same as that of the IDT electrode structure.

The three surface acoustic wave resonators are arranged close to each other, and the bus bar electrodes in mutually adjacent portions are electrically independent. IDT in first surface acoustic wave resonator
The electrode finger of the electrode 12a is connected to the balanced input terminal IN,
The electrode finger of the IDT electrode 14a in the third surface acoustic wave resonator is connected to the balanced output terminal OUT. Also,
The periodic structure strip line electrode array 13a in the second surface acoustic wave resonator is grounded via a reflector pattern.

The operation of the surface acoustic wave multimode filter configured as described above will be described below. FIG. 2 is an excitation mode distribution diagram of the surface acoustic wave multi-mode filter in the present embodiment, and portions corresponding to FIG. 1 are denoted by the same reference numerals. 2A is an electrode configuration diagram of the surface acoustic wave multimode filter shown in FIG. By arranging the first to third surface acoustic wave resonators close to each other, acoustic coupling occurs therebetween, and FIG.
1st, 2nd, 3rd with potential distribution as shown in
The next mode is excited. Here, the secondary mode corresponds to the portion of the periodic structure stripline electrode array 13a of the second surface acoustic wave resonator in which the node position of the mode distribution is arranged at the center, and the mode polarity is switched above and below. Therefore, the excitation intensity is lower than in the first and third modes. At this time, the characteristic of the pass band of the filter directly connected to 50Ω is as follows.
As shown in FIG. 3 (a), the center of the pass band is sunk. For this reason, in the case of a wideband design in which the difference between the frequency of the first-order mode and the frequency of the third-order mode normalized by the center frequency of the passband exceeds 0.1%, even if a matching circuit is added, the inside of the band is not flat. , Good filter characteristics cannot be obtained. Therefore,
In order to obtain good filter characteristics in the electrode configuration as shown in FIG. 1, it is necessary to strongly excite the secondary mode and use it for the pass characteristics. For this purpose, (1) the potential of the second surface acoustic wave resonator arranged at the center can be freely distributed, and (2) the first surface acoustic wave resonator and the third surface acoustic wave resonator arranged outside. It is necessary that the potential does not cancel with the surface acoustic wave resonator. In order to satisfy these conditions (1) and (2), all the portions corresponding to the IDT electrodes of the second surface acoustic wave resonator are electrically connected, and the IDT electrode fingers of the first surface acoustic wave resonator are connected. 21st and 3rd
The IDT electrode fingers 22 for the surface acoustic wave may be electrically independent. In the present embodiment, a periodic structure strip line electrode array 13a is used for the central second surface acoustic wave resonator, which is grounded via a reflector pattern, and each of the IDT electrode fingers 21 and 22 has a balanced input. Since the terminal is used for the terminal and the output terminal, the above conditions (1) and (2) are satisfied. Therefore, the characteristic of the pass band directly connected to 50Ω in the present embodiment is a characteristic that is strongly excited also in the second mode as shown in FIG. As a result, a surface acoustic wave multi-mode filter using three excitation modes effectively is realized. As described above, according to the configuration of the present embodiment, the order of the filter is increased as compared with a conventional filter using two excitation modes, so that a wide band and a steep cutoff characteristic can be obtained (that is, a favorable cutoff characteristic). Out-of-band attenuation characteristics are realized). FIG. 4 shows a typical actual measurement example of transmission characteristics when the surface acoustic wave multimode filter of this embodiment is matched in a two-stage configuration. In FIG. 4, in addition to the characteristic curve 41 of the present embodiment, the characteristic curve of the conventional example of FIG. As is clear from FIG. 4, a wider band of the pass characteristic and a steep cutoff characteristic are recognized.

FIG. 5 is an enlarged view of a portion of the surface acoustic wave multimode filter shown in FIG. 1 where the IDT electrode and the periodic structure strip line electrode row are arranged close to each other.
The distance G between the IDT electrode 12a of the opposed surface acoustic wave resonator and the periodic structure strip line electrode row 13a governs the degree of coupling between the two surface acoustic wave resonators. This is preferable for widening the band because the degree of coupling increases. However, if the gap G is too small, the widths W ₁ , W 2 of the bus bar electrodes 51, 52 provided in this portion are too small.
_{2, the} effect of the electrical resistance loss of the IDT electrode at this portion on the insertion loss of the filter cannot be ignored. Here, the bus bar electrode 51 is directly connected to one of the balanced input terminals IN (see FIG. 1), but the bus bar electrode 52 is a periodic strip forming the second surface acoustic wave resonator at the center. Line electrode row 1
3a for grounding, the balanced input terminal I
N is not electrically connected. That is, the size of the width W ₂ of the bus bar electrode 52 exerts no influence on the insertion loss of the filter. Therefore, the width W of the bus bar electrode 52
If the width W ₁ of the bus bar electrode 51 is increased by decreasing the value of ₂ , the electric resistance loss to the balanced input terminal IN can be reduced without changing the interval G, so that the insertion loss of the filter can be reduced. Can be. In this embodiment, the second surface acoustic wave resonator at the center uses the periodic structure strip line electrode array 13a instead of the IDT electrode, so that the IDT electrode finger and the ground busbar are used as in the case of the IDT electrode. There is no need to provide a gap between the electrode and the bus bar electrode 52.
a. Therefore, it is possible to increase the width W ₁ of the correspondingly bus bar electrode 51. If the width W ₃ of the electrical separation band 53 between the bus bar electrode 51 and the bus bar electrode 52 is made smaller than the width W ₁ of the bus bar electrode 51, the bus bar electrode is further reduced by the reduced width W ₃ of the electrical separation band 53. it is possible to increase the width W ₁ of 51, it is possible to further reduce the insertion loss of the filter. The above configuration is effective for reducing insertion loss. In addition, by providing the electrical separation band 53, discontinuous portions of the electrode pattern between the input and output terminals increase,
The direct wave component of the signal is greatly suppressed, and the isolation characteristic of the filter, that is, the out-of-band attenuation characteristic is significantly improved.

The same effect can be obtained by the same configuration as described above for the output side, that is, the portion where the IDT electrode 14a and the periodic structure strip line electrode array 13a are arranged close to each other. FIG. 6 shows the effect of the bus bar electrode width dimension. FIG. 6 shows measured values of the insertion loss of the filter with respect to the bus bar electrode width ratio W ₁ / W ₂ in the surface acoustic wave multimode filter having the configuration of FIG. FIG. 6 shows a case where the IDT electrode finger intersection width is 6.5 wavelengths and the interval (coupling gap length) G is 1 wavelength, and W ₁ / W ₂ = as compared with the case where W ₁ / W ₂ = _1. In the case of No. 6, it can be seen that the insertion loss is reduced by about 1.5 dB and the characteristics are greatly improved. Also, FIG.
Even by increasing the bus bar electrode width ratio W ₁ / W ₂ to 6 above,
It also shows that the insertion loss is not significantly improved. In fact, by the W ₁ / W ₂ ≧ 4, since the insertion loss is 1dB improvement, W ₁ so as to satisfy this condition,
It is preferable to determine the value of W _2.

In the surface acoustic wave multi-mode filter of this embodiment shown in FIG. 1, the bandwidth of the transmission characteristic of the filter can be changed by changing the width of the IDT electrode fingers. FIG. 7 shows the measured value of the fractional bandwidth with respect to the IDT electrode finger intersection width normalized by the wavelength λ. FIG. 7 shows the IDT
It shows that decreasing the electrode finger cross width increases the fractional bandwidth.

In the surface acoustic wave multi-mode filter of this embodiment shown in FIG. 1, the insertion loss and the ripple in the pass band can be changed by changing the number of IDT electrode pairs. FIG. 8 shows that the sum of the number of IDT electrode pairs and the number of reflectors is constant (logarithmic conversion (the number of reflectors is two and one pair).
FIG. 9 shows measured values of the insertion loss with respect to the number of IDT electrode pairs when the number of IDT electrodes is 50 pairs.
The measured value of the in-band ripple with respect to the number of T electrode pairs is shown. FIG.
Indicates that increasing the number of IDT electrode pairs effectively reduces ripple. On the other hand, FIG. 8 shows that when the number of IDT electrode pairs exceeds a certain number, the number of reflectors relatively decreases, so that resonance characteristics with a sufficiently high Q cannot be obtained, resulting in a sharp increase in insertion loss. From the experimental results of FIGS. 8 and 9, IDs fall within a range of about 150 to 300 pairs.
If the number of pairs of T electrodes is selected, it can be seen that the insertion loss remains at just over 7 dB, and the in-band ripple is also within just over 2 to 3 dB. These insertion loss amounts and ripple values are characteristic values appropriate for a filter.

As described above, according to the present embodiment, three surface acoustic wave resonators are arranged close to each other, and the central electrode of the second surface acoustic wave resonator has the same structure as the reflector. And a periodic structure strip line electrode array 13a having a length approximately equal to the width of the IDT electrode fingers of the first and third surface acoustic wave resonators, and a second surface acoustic wave resonator By grounding all of the electrode portions, it is possible to widen the bandpass characteristics of the surface acoustic wave multimode filter and to realize steep cutoff characteristics. Further, since the bus bar electrode at the center of the IDT electrode is electrically independent, the IDT of the first surface acoustic wave resonator
Electrode 12a and IDT electrode 1 of third surface acoustic wave resonator
Since all the wires 4a can be independently wired, balanced input / output of the surface acoustic wave multimode filter can be realized.

As described above, according to the present embodiment, the balanced input / output of the surface acoustic wave multimode filter can be realized, so that the filter characteristics are not affected by the stray capacitance due to the grounding state of the electrodes. , The characteristics of the stop and transition zones are further improved. In addition, I / Os can be provided before and after the filter without using an external circuit such as a balun.
Since a balanced element such as C can be connected, the noise characteristics of the entire circuit are also improved.

In this embodiment, a surface acoustic wave multi-mode filter having a one-stage configuration is described as an example. However, as shown in FIG. If the wave multi-mode filters 101 and 102 are connected in cascade to form a multistage connected surface acoustic wave multi-mode filter, the insertion loss is slightly increased, but the characteristics of the stop band and the transition region are greatly improved, and further improved. Filter characteristics are obtained.

By simply connecting the surface acoustic wave multimode filters in cascade, good transmission characteristics may not be obtained due to a mismatch between input and output impedances at each stage. In this case, a reactance element such as an inductor may be connected as a matching element to the connection electrode patterns 107 and 108 between the stages. In this case, providing electrode pads 109 and 110 for bonding wiring wires to the electrode patterns 107 and 108 facilitates connection with an external element such as an inductor and connection with an external circuit. In addition, if a reactance element such as a spiral inductor is formed on the same piezoelectric substrate 100 or another dielectric substrate and connected to the electrode patterns 107 and 108, an external circuit is not required, so that the filter circuit can be reduced in size. Is achieved.

The connection method of the matching inductor in the above-described multistage connection surface acoustic wave multimode filter slightly affects the transmission characteristics of the filter, and controls the characteristics of the transition region and the stop band. FIG. 11 shows a change in the transmission characteristics of the multistage connected surface acoustic wave multimode filter due to the difference in the connection method of the matching inductor. A characteristic curve 111 drawn by a solid line in FIG. 11 indicates an ID facing the central surface acoustic wave resonator of the first surface acoustic wave multimode filter 101.
An electrode pad 109 provided on an inter-stage connection electrode pattern 107 connecting the bus bar electrode 103 of the T electrode and the bus bar electrode 104 of the IDT electrode facing the center surface acoustic wave resonator of the second surface acoustic wave multimode filter 102; The filter characteristic when a matching inductor is connected to the ground is shown, and the characteristic curve 112 drawn by a broken line is the IDT electrode 10 outside the output end of the first surface acoustic wave multimode filter 101.
5 shows a filter characteristic when a matching inductor is connected between an electrode pad 110 provided on an interstage connection electrode pattern 108 connecting the IDT electrode 106 outside the input end of the second surface acoustic wave multimode filter 102 and the ground. Show. still,
The electrode pads on the side to which no matching inductor is connected are directly grounded. There is a clear difference between the characteristic curve 111 and the characteristic curve 112, and the characteristic curve 111 when the matching inductor is connected to the electrode pad 109 is superior from the viewpoint of the symmetry of the transmission characteristic. The bus bar electrode 103 of the IDT electrode facing the center surface acoustic wave resonator of the first surface acoustic wave multimode filter 101 and the second surface acoustic wave multimode filter 102
It can be said that it is preferable to be connected to the electrode pad 109 provided on the inter-stage connection electrode pattern 107 connecting the bus bar electrode 104 of the IDT electrode facing the center surface acoustic wave resonator.

<Second Embodiment> FIG. 12 is a block diagram showing a second embodiment of the surface acoustic wave multimode filter according to the present invention. In FIG. 12, reference numeral 121 denotes a single-crystal piezoelectric substrate. By forming an electrode pattern of a periodic structure strip line on the piezoelectric substrate 121,
Surface acoustic waves can be excited in the same manner as in the embodiment. On the piezoelectric substrate 121, an energy trap type first surface acoustic wave resonator constituted by an IDT electrode 122a and reflectors 122b and 122c is formed. On the piezoelectric substrate 121, an IDT electrode 123 is provided.
a and the reflectors 123b and 123c
Surface acoustic wave resonator, IDT electrode 124a and reflector 1
A third surface acoustic wave resonator constituted by 24b and 124c is formed. The three surface acoustic wave resonators are arranged close to each other, and the I
The DT electrodes are electrically independent and the reflectors are connected by a common bus bar. The electrode finger of the IDT electrode 122a is connected to the balanced input terminal IN, and the IDT electrode 122a
The electrode finger 4a is connected to the balanced output terminal OUT. The electrode finger of the IDT electrode 123a is grounded via reflectors 123b and 123c on both sides.

As described above, in the surface acoustic wave multi-mode filter according to the present embodiment, the electrode structure of the second surface acoustic wave resonator at the center is the same as that of the periodic structure strip line electrode array.
Although the DT electrode 123a is used, the propagation of the surface acoustic wave is performed in exactly the same manner, and the basic operation is the same as that of the first embodiment shown in FIG.

FIG. 13 shows the surface acoustic wave multiplex shown in FIG.
The IDT electrode of the mode filter is arranged close to
FIG. As in the first embodiment, the distance
As G is smaller, the degree of coupling between the resonators increases, so that the bandwidth becomes wider.
Is preferable, but if the interval G is too small,
Of the busbar electrodes 131 and 132 provided in
W ₁, W_TwoAnd the IDT electrode in this part
The effect of electrical resistance loss on filter insertion loss
You will not be able to see it. Here, the bus bar electrode 13
1 is directly connected to one of the balanced input terminals IN,
(See FIG. 12), the bus bar electrode 132 is located at the center of the second bullet.
The IDT electrode 123a constituting the surface acoustic wave resonator is connected.
The balanced input terminal IN is
It is not connected pneumatically (see FIG. 12). That is,
The width W of the sub electrode 132_TwoIs the filter insertion loss
It has no effect on loss. Therefore, the bus bar electrode 1
32 width W_TwoIs reduced by the width of the bus bar electrode 131.
W₁If the value of
Reduce the electric resistance loss to the input terminal IN and insert the filter.
The input loss can be reduced. Output side, ie ID
T electrode 124a and IDT electrode 123a are arranged close to each other
The same configuration as above
Thereby, a similar effect can be obtained.

As described above, according to the present embodiment, three surface acoustic wave resonators are arranged close to each other, and all of the IDT electrodes 123a constituting the central second surface acoustic wave resonator are grounded. Accordingly, it is possible to widen the bandpass characteristics of the surface acoustic wave multimode filter, and to realize steep cutoff characteristics. Further, since the bus bar electrode at the center of the IDT electrode is electrically independent, the IDT electrode 122a of the first surface acoustic wave resonator and the IDT electrode 124a of the third surface acoustic wave resonator are all independently wired. Therefore, balanced input / output of the surface acoustic wave multimode filter can be realized.

As described above, according to this embodiment, since the balanced input / output of the surface acoustic wave multimode filter can be realized, the filter characteristics are not affected by the stray capacitance due to the grounding state of the electrodes. Therefore, the characteristics of the stop band and the transition region are improved. In addition, since it becomes possible to connect a balanced element such as an IC to the front and rear stages of the filter without using an external circuit such as a balun, noise characteristics of the entire circuit are also improved.

Further, also in this embodiment, if a plurality of surface acoustic wave multi-mode filters are connected in cascade to form a multi-stage connected surface acoustic wave multi-mode filter, the characteristics of the transition region and the stop band are greatly improved. Is done. The effect of the cascade connection method and the connection of the reactance element (matching element) between the stages on the filter characteristics in this case is exactly the same as in the case of the first embodiment shown in FIGS.

In the first embodiment, as shown in FIG. 1, the IDT electrode 12a and the IDT electrode 14a are arranged in an opposite phase to each other, but are not necessarily limited to this configuration. is not. IDT electrode 12a and ID
Even if the T electrodes 14a are arranged in the same phase as each other, only the appearance of the out-of-band spurious signal is slightly different, and the operation and effect are not changed. This is the same for the second embodiment. In the first and second embodiments, the input / output terminals are of a balanced type. However, it is also possible to ground one side of each of the input / output terminals so as to be of an unbalanced type.

Further, as the piezoelectric substrate in the present invention,
It is preferable to use ST-cut quartz having excellent temperature characteristics, but a substrate of LiTaO ₃ , LiNbO ₃ , Li ₂ B ₄ O ₇ or the like can also be used. Further, as the electrode material, it is preferable to use aluminum having a relatively low density because the thickness of the electrode can be easily controlled, but it is also possible to use a gold electrode. Furthermore, the present invention can be applied to a resonator using not only a surface acoustic wave but also a slip wave (SSBW), a pseudo surface acoustic wave (Leaky SAW), and the like.

[0044]

As described above, according to the present invention,
Since the insertion loss of the filter can be reduced and a surface acoustic wave multi-mode filter that effectively utilizes three excitation modes is realized, a wide band and steep cutoff characteristics can be obtained. Further, a compact surface acoustic wave multi-mode filter having a balanced input / output configuration is realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a surface acoustic wave multimode filter according to the present invention.

FIG. 2 is an excitation mode distribution diagram illustrating an operation of the surface acoustic wave multi-mode filter in the first embodiment.

FIG. 3 is a diagram illustrating pass band characteristics of the surface acoustic wave multimode filter according to the first embodiment.

FIG. 4 is a representative measurement diagram of transmission characteristics of a surface acoustic wave multi-mode filter according to the first embodiment.

FIG. 5 is an enlarged view of a portion of the surface acoustic wave multimode filter according to the first embodiment in which an IDT electrode and a periodic structure stripline electrode row are arranged close to each other.

FIG. 6 is an actual measurement diagram of insertion loss with respect to a bus bar electrode width ratio of the surface acoustic wave multimode filter in the first embodiment.

FIG. 7 is an actual measurement diagram of the relative bandwidth with respect to the IDT electrode finger intersection width of the surface acoustic wave multimode filter in the first embodiment.

FIG. 8 is an actual measurement diagram of insertion loss with respect to the number of IDT electrode pairs of the surface acoustic wave multimode filter according to the first embodiment.

FIG. 9 is an actual measurement diagram of in-band ripple with respect to the number of IDT electrode pairs of the surface acoustic wave multimode filter in the first embodiment.

FIG. 10 is a configuration diagram illustrating a multi-stage connected surface acoustic wave multimode filter according to the first embodiment.

FIG. 11 is an actual measurement diagram of transmission characteristics of a multistage connected surface acoustic wave multimode filter in the first embodiment.

FIG. 12 is a configuration diagram showing a second embodiment of the surface acoustic wave multimode filter according to the present invention.

FIG. 13 is an enlarged view of a portion of the surface acoustic wave multi-mode filter according to the second embodiment where the IDT electrodes are arranged close to each other.

FIG. 14 is a configuration diagram showing a surface acoustic wave multi-mode filter according to the related art.

FIG. 15 is a representative measurement diagram of transmission characteristics of a surface acoustic wave multi-mode filter according to the related art.

[Explanation of symbols]

11, 100, 121 Single crystal piezoelectric substrate 12a, 14a, 122a, 123a, 124a ID
T electrode 12b, 12c, 13b, 13c, 14b, 14c, 1
22b, 122c, 123b, 123c, 124b, 1
24c Reflector 13a Periodic Structure Stripline Electrode Array 51, 52, 103, 104, 131, 132 Busbar Electrode 53, 133 Electrical Separation Band 101 Front Surface Acoustic Wave Multimode Filter 102 Poststage Surface Acoustic Wave Multimode Filter 105 Output Outer end IDT electrode 106 Input end outer IDT electrode 107, 108 Interstage connection electrode pattern 109, 110 Electrode pad

Continuation of the front page (56) References JP-A-2-81511 (JP, A) JP-A-4-373304 (JP, A) JP-A-2-305015 (JP, A) JP-A-59-36415 (JP) , A) JP-A-59-21114 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/64 H03H 9/145 H03H 9/25

Claims (20)

(57) [Claims] 1. A first and a third device having reflectors on both sides of an interdigital transducer electrode on a piezoelectric substrate.
Is formed in parallel with the direction of propagation of the surface acoustic wave, and has a length substantially equal to the electrode finger intersection width of the interdigital transducer electrode between the first and third surface acoustic wave resonators. have a of, and the interdigital
Both ends of the plurality of strip line electrodes placed in parallel at the same electrode period as in the first and third surface acoustic wave resonators, the plurality of strip line electrodes for chromatic transducer electrode approximately the same electrode width Forming a second surface acoustic wave resonator composed of an array of periodic structural electrodes in which the portions are connected to each other by bus bar electrodes, wherein the first and third surface acoustic wave resonators and the second surface acoustic wave resonator Are arranged in close proximity to each other and acoustically coupled, the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators being adjacent to the periodic structure electrode row. When the line width of a certain busbar electrode is W
_1. The line width of a bus bar electrode connecting both ends of the periodic structure electrode row is W ₂ , and the bus bar electrode of the periodic structure electrode row and an interface forming the first and third surface acoustic wave resonators the width of the electrical isolation zone of the bus bar electrode on the side adjacent to the periodic structure shaped electrode rows digital transducer electrode is W _3, the relative dimensions of the _{W 1, W 2, W 3} W 1> W 2, A surface acoustic wave multi-mode filter, wherein W ₁ > W ₃ is set. _2. The relative dimension of W ₁ and W ₂ is W ₁ / W ₂ ≧ 4.
The surface acoustic wave multi-mode filter according to claim 1, wherein 3. The surface acoustic wave according to claim 1, wherein the number of electrode finger pairs of the interdigital transducer electrodes constituting the first and third surface acoustic wave resonators is set between 150 and 300 pairs. Multi-mode filter. 4. The method according to claim 1, wherein the electrode array of the periodic structure constituting the second surface acoustic wave resonator is grounded via the reflectors of the first and third surface acoustic wave resonators. The surface acoustic wave multi-mode filter according to claim 1. 5. The surface acoustic wave according to claim 4, wherein the first surface acoustic wave resonator electrode is connected to a balanced input terminal, and the third surface acoustic wave resonator electrode is connected to a balanced output terminal. Multi-mode filter. 6. The surface acoustic wave multi-mode filter according to claim 1, wherein a plurality of the surface acoustic wave multi-mode filters are connected in cascade by first and second inter-stage connection electrode patterns formed on the piezoelectric substrate. 7. The surface acoustic wave multimode filter according to claim 6, wherein one of the first and second inter-stage connection electrode patterns is directly grounded, and the other is grounded via a reactance element. 8. The first inter-stage connecting electrode pattern is adjacent to the second surface acoustic wave resonator of the third surface acoustic wave resonator constituting the preceding surface acoustic wave multimode filter connected in cascade. Connecting the interdigital transducer electrode and an interdigital transducer electrode adjacent to the second surface acoustic wave resonator of the first surface acoustic wave resonator constituting the surface acoustic wave multimode filter in the cascade connection at the subsequent stage; The second inter-stage connection electrode pattern includes an interdigital transducer electrode outside the output terminal of the front surface acoustic wave multimode filter connected in cascade, and an interdigital transducer electrode outside the input terminal of the post-stage surface acoustic wave multimode filter connected in cascade. The surface acoustic wave multi-mode filter according to claim 6, which is connected to a transducer electrode. 9. The surface acoustic wave multi-mode filter according to claim 8, wherein the first inter-stage connection electrode pattern is grounded via a reactance element, and the second inter-stage connection electrode pattern is directly grounded. 10. A first surface acoustic wave resonator electrode of a front surface acoustic wave multimode filter is connected to a balanced input terminal, and a third surface acoustic wave resonator electrode of a subsequent surface acoustic wave multimode filter. The surface acoustic wave multi-mode filter according to claim 7 or 9, wherein is connected to a balanced output terminal. 11. A first and second reflectors provided on both sides of an interdigital transducer electrode on a piezoelectric substrate.
And the third surface acoustic wave resonator is disposed close to and in parallel with the direction of propagation of the surface acoustic wave, and is acoustically coupled, and an adjacent bus bar electrode of the interdigital transducer electrode between the surface acoustic wave resonators is electrically connected. A surface acoustic wave multi-mode filter in which all interdigital transducer electrodes of a second surface acoustic wave resonator disposed in the center are separated from each other, and wherein first and third externally disposed
The line width of the bus bar electrode on the side adjacent to the second surface acoustic wave resonator of the interdigital transducer electrode constituting the surface acoustic wave resonator is W ₁ , the interdigital transducer of the second surface acoustic wave resonator The line width of the bus bar electrode of the transducer electrode is W ₂ , the width of the electrical separator between the adjacent bus bar electrodes is W ₃ , and the W ₁ , W
_2, the relative dimensions of the _{W 3, W 1> W 2} , W 1> SAW multi-mode filter, characterized in that set to W _3. 12. The relative dimension of W ₁ and W ₂ is W ₁ / W ₂ ≧
The surface acoustic wave multi-mode filter according to claim 11, wherein the filter is set to 4. 13. The interdigital transducer electrode constituting the first, second and third surface acoustic wave resonators, wherein the number of electrode finger pairs is set between 150 and 300 pairs. Surface acoustic wave multimode filter. 14. The interdigital transducer electrode of the second surface acoustic wave resonator is grounded via the reflectors of the first and third surface acoustic wave resonators.
Or a surface acoustic wave multimode filter according to item 13. 15. The interdigital transducer electrode of the first surface acoustic wave resonator is connected to a balanced input terminal, and the interdigital transducer electrode of the third surface acoustic wave resonator is connected to a balanced output terminal. Item 1
5. The surface acoustic wave multimode filter according to 4. 16. A method according to claim 1, wherein the first and second substrates are formed on a piezoelectric substrate.
The surface acoustic wave multi-mode filter according to claim 11, wherein a plurality of the surface acoustic wave multi-mode filters are connected in cascade by the interstage connection electrode pattern. 17. The surface acoustic wave multimode filter according to claim 16, wherein one of the first and second inter-stage connection electrode patterns is grounded, and the other is grounded via a reactance element. 18. The first inter-stage connecting electrode pattern is adjacent to a second surface acoustic wave resonator of a third surface acoustic wave resonator constituting a front surface acoustic wave multimode filter connected in cascade. Interdigital transducer electrodes,
A second interstage connection is made by connecting an interdigital transducer electrode adjacent to a second surface acoustic wave resonator of a first surface acoustic wave resonator constituting a subsequent stage surface acoustic wave multimode filter connected in cascade. The electrode pattern connects the interdigital transducer electrode outside the output end of the front surface acoustic wave multimode filter connected in cascade with the interdigital transducer electrode outside the input end of the downstream surface acoustic wave multimode filter connected in cascade. A surface acoustic wave multi-mode filter according to claim 16. 19. The surface acoustic wave multi-mode filter according to claim 18, wherein the first inter-stage connection electrode pattern is grounded via a reactance element, and the second inter-stage connection electrode pattern is directly grounded. 20. A first surface acoustic wave resonator electrode of a front surface acoustic wave multimode filter is connected to a balanced input terminal, and a third surface acoustic wave resonator electrode of a subsequent surface acoustic wave multimode filter. The surface acoustic wave multimode filter according to claim 17 or 19, wherein is connected to a balanced output terminal.