JPH09326669A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a distribution function for a surface acoustic wave filter by grounding the connection terminals of the 1st and 2nd interdigital electrodes or connecting these terminals to each other. SOLUTION: An input interdigital electrode 101 includes the input electrode branches connected to an input terminal 104 and the ground electrode branches connected to a ground terminal which are formed alternately and in parallel to each other. The output interdigital electrodes 102-1 and 102-2 include the output electrode branches connected to the output terminals 106 and 105 and the connection electrode branches connected to the connection electrodes which are formed alternately and in parallel to each other. An electrode pattern is formed symmetrically to the center line of the electrode 101, and the connection terminals of electrodes 102-1 and 102-2 are grounded. In such a constitution, the signals having the prescribed frequency are filtered among those input signals and also can be distributed to the terminals 105 and 106.

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 filter, and more particularly to a surface acoustic wave filter used in a high frequency range.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave elements, particularly surface acoustic wave filters, have been actively developed due to the development of mobile communication and higher frequencies.

Conventionally, several kinds of methods are known for constructing a filter with a surface acoustic wave element in a high frequency band, particularly several hundred MHz. As a typical one, a ladder type is disclosed in which a filter is constructed by using a plurality of surface acoustic wave resonators as shown in JP-A-52-19044, JP-A-3-222512 and JP-A-61-261. 23
There is a so-called longitudinal mode type in which surface acoustic wave resonators such as those disclosed in 0419 and Japanese Patent Application Laid-Open No. 1-231417 are installed adjacent to each other and coupling between resonators is utilized.

All of these filters handle unbalanced signals, and most of the input / output impedances are 50 due to the requirements from the side using the filters.
It is set to ohms. Further, there is no surface acoustic wave filter having a distribution function, and when a distribution function is required, a distributor is used separately.

[0005]

Recently, there has been a movement to reduce the number of parts by giving a large number of functions to parts of a high frequency circuit. This is due to the demand for miniaturization and cost reduction, and this demand is expected to increase in the future. For example, it is convenient if the distributor and the filter are integrated. In addition, there is a movement to balance circuits in order to improve the performance of high frequency circuits. In such a case, the circuit components also need to be compatible with the balanced circuit, and the impedance thereof is not always 50 ohms.

Particularly, in the transition period from the unbalanced circuit to the balanced circuit, a component having an unbalanced terminal at the input and a balanced terminal at the output is required. An example is the balun.

The balun can control the impedance of the balanced terminal and the unbalanced terminal depending on its configuration, but is a component that is not necessary in the conventional case, that is, when an unbalanced circuit is used. Therefore, when a balun is used for balancing a conventional circuit, there are drawbacks such as an increase in component cost and a mounting area.

A first object of the present invention is to provide a surface acoustic wave filter having a distribution function.

A second object of the present invention is to provide an unbalanced input terminal-
It is to provide a balanced output surface acoustic wave filter.

[0010]

That is, a surface acoustic wave filter according to the present invention comprises an input interdigital transducer and an input interdigital transducer between a surface acoustic wave reflector provided on a piezoelectric substrate at a predetermined distance from each other. A first and second output interdigital transducers formed on both sides of the input interdigital transducer, wherein the input interdigital transducers are respectively connected to input terminal branches and ground terminals. Ground electrode branches connected to each other are provided in parallel with each other, and the first and second output interdigital electrodes are respectively connected to output electrode branches connected to output terminals and connection terminals. A surface acoustic wave filter in which the connection electrode branches are provided in parallel with each other, and the connection terminals of the first and second output interdigital transducers are grounded or connected to each other, and the connection terminals are connected via the input terminals. Entered And wherein the splitting and outputting to an output terminal coupled to the first output interdigital output terminal connected to the electrode and the second output interdigital transducer.

In the surface acoustic wave filter, in order to match the input impedance and the output impedance, the number of input electrode branches of the input interdigital electrode and the output electrode of the first output interdigital electrode are set. It is preferable that the number of branches and the number of output electrode branches of the second output interdigital transducer are substantially equal to each other.

Further, the unbalanced input-balanced output type surface acoustic wave filter according to the present invention has an input interdigital electrode between surface acoustic wave reflectors provided on the piezoelectric substrate at a predetermined distance from each other. And first and second output interdigital transducers formed on both sides of the input interdigital transducer, wherein the input interdigital transducers are respectively connected to input electrode branches and grounded. Ground electrode branches connected to the terminals are provided in parallel to each other, and the first and second output interdigital electrodes are respectively connected to the output electrode branches connected to the output terminals and the connection terminals, respectively. A surface acoustic wave filter in which connected connection electrode branches are provided in parallel with each other, wherein a distance between the output electrode branch of the first output interdigital electrode and the input electrode branch, 2 output interdigital Each other and spacing between the output electrode branches and the input electrode branches, the wavelength of the acoustic waves excited on the surface of the piezoelectric substrate {(2n + 1) / 2} times (where, n =
0, 1, 2, 3 ...), and by connecting the connection terminals of the first and second output interdigital transducers to the ground or to each other, the first output interdigital transducers. From the output terminal connected to the electrode and the output terminal connected to the second output interdigital electrode, approximately 180 ° from each other.
It is characterized by outputting signals having different phases.

Further, in the unbalanced input-balanced output type surface acoustic wave filter, in order to increase the output impedance as compared with the input impedance, the number of the input electrode branches is made larger than the number of the input electrode branches. It is preferable to reduce the number of output electrode branches of the output interdigital transducer and the number of output electrode branches of the second output interdigital transducer.

In the unbalanced input-balanced output type surface acoustic wave filter, the distance between the input interdigital transducer and the first output interdigital transducer, the input interdigital transducer and the second interdigital transducer. The distance from the output blind electrode may be different from each other.

Further, in the unbalanced input-balanced output type surface acoustic wave filter, the distance between the input interdigital transducer and the first output interdigital transducer, the input interdigital transducer and the second interdigital transducer. The interval with the output blind electrode may be the same as each other.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) A surface acoustic wave filter according to a first embodiment of the present invention will be described. The surface acoustic wave filter comprises a comb-shaped electrode 1 for input on a 64 ° Y-cut X-propagation lithium niobate substrate as a piezoelectric substrate.
01, output interdigital electrodes 102-1 and 102-2, and reflectors 103-1 and 103-2 are formed as shown in FIG. In FIG. 1, 104 is an input terminal and 105 and 106 are output terminals.

Here, the input interdigital transducer 101 is composed of input electrode branches connected to the input terminals 104 and ground electrode branches connected to the ground terminals in parallel and alternately. The distance between the electrode branches and the distance between the ground electrode branches are set to the length of one wavelength of the elastic wave excited in the piezoelectric substrate, and the distance between the input electrode branch and the ground electrode branch is ½ of the elastic wave. It is set to the length of the wavelength. Further, as shown in FIG. 1, in the output interdigital electrode 102-1, output electrode branches connected to the output terminals 106 and connection electrode branches connected to the connection terminals are parallel and alternately. The distance between the output electrode branches and the distance between the connection electrode branches are set to the length of one wavelength of the elastic wave excited in the piezoelectric substrate, and the distance between the adjacent input electrode branch and the connection electrode branch is The length is set to 1/2 wavelength of the wave. Also,
The output interdigital transducer 102-2 has the same configuration as the output interdigital transducer 102-1.

In the first embodiment, the electrode pattern is the center line of the input interdigital transducer 101 (parallel to the electrode branch).
It is formed so as to be line-symmetrical with respect to, and the connection terminals of the output interdigital electrodes 102-1 and 102-2 are grounded. In FIG. 1, for simplification, the number of electrode branches of each interdigital electrode and the number of electrode branches forming a reflector are reduced. The characteristics of the surface acoustic wave filter of Embodiment 1 configured as described above were measured. As a result of the measurement, it was confirmed that signals having a predetermined frequency among the input signals were output from the output terminals 105 and 106, respectively. Output terminal 105 and output terminal 1
The signal output from 06 was 3 dB less than that of the conventional filter.

That is, the surface acoustic wave filter according to the first embodiment can filter the input signal and also distribute and output the signal to the output terminals 105 and 106. Such a filter, for example, is used as a filter for output of a local oscillator in a transmission / reception radio circuit of mobile communication, thereby filtering the local oscillation signal and distributing and supplying it to a transmission circuit and a reception circuit. Will be possible.

(Second Embodiment) Next, a surface acoustic wave filter according to a second embodiment of the present invention will be described. The surface acoustic wave filter has a 64 ° Y-cut X as a piezoelectric substrate.
On the propagating lithium niobate substrate, the input interdigital electrode 201 and the output interdigital electrode 202-1 and 202-
2 and reflectors 203-1 and 203-2 are formed and configured as shown in FIG. In FIG. 1, reference numeral 204 is an input terminal, and 205 and 206 are output terminals. In the second embodiment, the input interdigital electrode 201 and the output interdigital electrode 202-1 and 202-2 are the input interdigital electrode 101 and the output interdigital electrode 102-1 and 102-2 of the first embodiment, respectively. -2, but in the second embodiment, the number of electrode branches of the input interdigital electrode 201 is set so that the input impedance and the output impedance are substantially the same (here, 50 ohms). The number of electrode branches of the output interdigital transducers 202-1 and 202-2 are set to be substantially equal to each other. However, in the drawing, for simplification, the number of electrode branches of each interdigital electrode and the number of electrode branches of the reflector are reduced. As a result of measuring the characteristics of the surface acoustic wave filter of the second embodiment configured as described above, the signals having a predetermined frequency among the input signals are respectively output terminals 1 as in the first embodiment.
No. 05 and the output terminal 106 were distributed and output, and its input and output impedances could all be 50 ohms. In this case as well, a signal that is 3 dB less than that in the case of the conventional filter could be obtained at the output terminals of 205 and 206.

(Third Embodiment) Next, a surface acoustic wave filter according to a third embodiment of the present invention will be described. The surface acoustic wave filter has a 64 ° Y-cut X as a piezoelectric substrate.
On the propagating lithium niobate substrate, the input interdigital electrode 301 and the output interdigital electrode 302-1 and 302-
2 and reflectors 303-1 and 303-2 are formed and configured as shown in FIG. In FIG. 3, 304 is an input terminal and 305-1 and 305-2 are output terminals.
In the third embodiment, the interdigital transducer electrode 30 for input is used.
1. The output interdigital transducers 302-1 and 302-2 are configured similarly to the input interdigital transducer 201 and the output interdigital transducers 202-1 and 202-2 of the second embodiment, respectively. In the third form, the interdigital transducer electrode 301 for input is used.
And the interval between the output interdigital transducer 302-1 and the interval between the input interdigital electrode 301 and the output interdigital electrode 302-2 are equal to a half wavelength of the elastic wave excited in the piezoelectric substrate. The settings are different. The third embodiment
Also, in FIG. 3, the number of electrode branches of the interdigital transducer is reduced for simplicity in FIG.

That is, according to the third embodiment, by the above-described configuration, the distance between the input electrode branch of the input interdigital electrode 301 and the output electrode branch of the output interdigital electrode 302-1 and the input The distance between the input electrode branch of the interdigital transducer 301 and the output electrode branch of the output interdigital transducer 302-2 is set to differ by an odd multiple of 1/2 wavelength of the elastic wave excited in the piezoelectric substrate. . This allows the phases of the signals output from the output terminals 305-1 and 305-2 to differ from each other by 180 °. Therefore,
The output terminals 305-1 and 305-2 can be used as a pair of output terminals for balanced output. The input / output impedance is the number of pairs of electrode branches of each interdigital electrode (the number of pairs of input electrode branches and ground electrode branches, or the number of pairs of output electrode branches and connection electrode branches) and the intersection of electrode branches. It depends on the product of widths.

As shown in FIG. 4, the surface acoustic wave filter of the third embodiment was connected using a balun 401 and its characteristics were measured. The balun 401 has a function of converting an unbalanced signal of 50 ohms and a balanced signal of 200 ohms to each other, and output terminals 305-1 and 305 of the surface acoustic wave filter.
The balanced signal output from -2 is converted into an unbalanced signal and output. The reason why the balun 401 is used in this way is that an ordinary measuring instrument is configured to measure an unbalanced signal and cannot measure a balanced signal, so that it is necessary to use the balun to perform an unbalanced-balanced signal conversion. Because there is. As a result of the measurement, it was possible to obtain almost the same characteristics as in the case of the conventional unbalanced signal, and in particular, the impedance on the balanced side could be made higher than the impedance on the unbalanced side. Also,
It was confirmed that the signals output from the output terminals 305-1 and 305-2 had a phase difference of about 180 ° with each other.
In the third embodiment, the distance between the input electrode branch of the input interdigital electrode 301 and the output electrode branch of the output interdigital electrode 302-1 or the input electrode branch of the input interdigital electrode 301 and the output interdigital electrode. It is also possible to adjust the phase difference shift between the balanced terminals by finely adjusting the distance between the electrode 302-2 and the output electrode branch.

As described above, the surface acoustic wave filter according to the third embodiment can filter an input unbalanced input signal and output it as a balanced output signal.

In the above third embodiment, the input electrode branch of the input interdigital electrode 301 and the output interdigital electrode 302-1.
Of the elastic wave excited by the piezoelectric substrate, and the distance between the input electrode branch of the input interdigital electrode 301 and the output electrode branch of the output interdigital electrode 302-2. Although the difference is set to be an odd multiple of, the difference in the interval may be set to another value. In this case, signals having a phase difference corresponding to the difference in the intervals are output terminals 305-1 and 3-3.
It is obtained from 05-2.

In the third embodiment described above, the connection terminals of the output interdigital electrodes 302-1 and 302-2 are grounded, but the present invention is not limited to this, and they are connected to each other as shown in FIG. Good. Even with the above-described configuration, the same operation as in the third embodiment is performed and the same effect is obtained. In the surface acoustic wave filter of FIG. 7, 701 is an interdigital electrode for input, 702-1 and 702-2 are interdigital electrodes for output, and 703-1 and 703-2 are reflectors.

(Fourth Embodiment) Next, a surface acoustic wave filter according to a third embodiment of the present invention will be described. The surface acoustic wave filter has a 64 ° Y-cut X as a piezoelectric substrate.
Input interdigital transducer 501 and output interdigital transducers 502-1 and 502-on a propagating lithium niobate substrate.
2 and reflectors 503-1 and 503-2 are formed and configured as shown in FIG. In FIG. 5, 504 is an input terminal and 505-1 and 505-2 are output terminals.

In the fourth embodiment, the interdigital transducer 501 for input and the interdigital transducers 502-1 and 502 for output are used.
-2 is the input interdigital transducer 20 of the second embodiment, respectively.
1. The same as the output interdigital transducers 202-1 and 202-2. In the fourth embodiment, the interval between the input interdigital electrode 501 and the output interdigital electrode 502-1 and the interval between the input interdigital electrode 501 and the output interdigital electrode 502-2 are set to be equal. In the output interdigital electrode 502-1, the connection electrode branch is formed at the outermost side, and in the output interdigital electrode 502-2, the output electrode branch is formed at the outermost side. Thereby, the distance between the input electrode branch of the input interdigital electrode 501 and the output electrode branch of the output interdigital electrode 502-1, and the output of the input electrode branch of the input interdigital electrode 501 and the output interdigital electrode 502-2. The distance from the electrode branch is set to differ by an odd multiple of 1/2 wavelength of the elastic wave excited in the piezoelectric substrate. Thereby, the output terminals 505-1, 5
The phases of the signals output from 05-2 can be different from each other by 180 °. Therefore, the output terminal 505-
1, 505-2 can be used as a pair of output terminals for balanced output.

This filter is balun 601 as shown in FIG.
Was connected and the characteristics were measured. Balun 601
Has the same function as the balun 401 described in the third embodiment. As a result of the measurement, the same result as that of the third embodiment is obtained, and the impedance of the input terminal 504, which is an unbalanced terminal, is used to determine the output terminals 505-1 and 505, which are balanced terminals.
The impedance of 2 could be increased.

When the impedance of the input terminal 504, which is an unbalanced terminal, is set to 50 ohms, the number of pairs of output electrode branches and connection electrode branches of the output interdigital transducers 502-1 and 502-2 on the side of the balanced terminal is input to the interleaved electrode. The output impedance of the balanced terminal is about 200 ohms when the number of pairs of the input electrode branch and the ground electrode branch is about half, and about 100 ohms when the number of pairs is almost the same, and about 50 ohms when the number of pairs is almost doubled. Impedance can be obtained.

(Modification) In addition, the above-mentioned first embodiment
In 2 and 3, a 64 ° Y-cut X-propagation lithium niobate substrate was used as the piezoelectric substrate forming the surface acoustic wave filter, but the present invention is not limited to this, and other examples such as lithium tantalate or a quartz substrate may be used. It goes without saying that the same effect can be obtained even if the piezoelectric substrate is used.
Further, in Embodiments 3 and 4, one of the output interdigital electrodes is connected to each other, but the same effect can be obtained by grounding this terminal. In addition, in these embodiments, an example in which the electrode is divided into three is shown. However, in the case where the electrode is divided into five, the first, third, and fifth interdigital electrodes counting from the end are used in the above-described embodiment. The output interdigital transducer, the second interdigital transducer, and the fourth interdigital transducer may be used as the input interdigital transducer, or vice versa.

In each of the above-described first, second, and third embodiments, the input electrode branch of the input interdigital transducer and the ground electrode branch are alternately formed, and the output electrode branch of the output interdigital transducer and the connection electrode branch. And were formed alternately. However, the present invention is not limited to this, and for example, a plurality of output electrode branches or connection electrode branches may be formed on the outermost side of the output interdigital transducer (for example, output electrode branch-output electrode branch-connection). Electrode branch-output electrode branch-connection electrode branch -..., or connection electrode branch-connection electrode branch-output electrode branch-connection electrode branch-output electrode branch -...), most of the input interdigital transducer On the outside,
A plurality of input electrode branches or ground electrode branches may be formed (for example, input electrode branch-input electrode branch-ground electrode branch-
Input electrode branch-ground electrode branch -..., or ground electrode branch-ground electrode branch-input electrode branch-ground electrode branch-input electrode branch-
...). Further, for example, in the output interdigital electrode, a plurality of output electrode branches and a plurality of connection electrode branches may be alternately formed (for example, output electrode branch-output electrode branch-connection electrode branch-connection electrode). Branch-output electrode branch-output electrode branch ... Or connection electrode branch-connection electrode branch-output electrode branch-output electrode branch-connection electrode branch-connection electrode branch ...
.), In the input interdigital transducer, a plurality of input electrode branches and a plurality of ground electrode branches may be alternately formed (for example, input electrode branch-input electrode branch-ground electrode branch-ground electrode branch- Input electrode branch-input electrode branch ... Or, ground electrode branch-ground electrode branch-input electrode branch-input electrode branch-ground electrode branch-ground electrode branch ... That is, the present invention can be applied to an electrode structure normally used as a comb-shaped electrode, and is not limited to the electrode structure shown in the embodiment.

[0034]

As described above, in the surface acoustic wave filter of the present invention, the input interdigital electrodes have the input electrode branches respectively connected to the input terminals and the ground electrode branches respectively connected to the ground terminals. Are provided in parallel with each other,
Each of the first and second output interdigital electrodes is provided with an output electrode branch connected to an output terminal and a connection electrode branch connected to a connection terminal in parallel with each other, and Since the connection terminals of the first and second interdigital transducers for output are grounded or connected to each other, the signal input through the input terminal is output to the first interdigital transducer for output. The output can be distributed to the terminals and the output terminals connected to the second output-shaped interdigital electrodes. That is, according to the present invention, it is possible to provide a surface acoustic wave filter having a distribution function.

Further, in the unbalanced input-balanced output type surface acoustic wave filter according to the present invention, the input interdigital electrodes are connected to a plurality of input electrode branches respectively connected to the input terminals and the ground terminal. Ground electrode branches are provided in parallel with each other, and the first and second output interdigital electrodes are respectively connected to output terminals, and connection electrodes connected to the connection terminals, respectively. A branch is provided in parallel with each other, and a distance between the output electrode branch of the first output interdigital electrode and the input electrode branch,
The interval between the output electrode branch of the second output interdigital transducer and the input electrode branch is {(2n + 1) / 2} times the wavelength of the elastic wave excited on the surface of the piezoelectric substrate. However, since n = 0, 1, 2, 3, ...) are set differently, and the connection terminals of the first and second output interdigital electrodes are grounded or connected to each other, the first From the output terminal connected to the output interdigital transducer and the output terminal connected to the second output interdigital transducer, it is possible to output signals having a phase difference of approximately 180 °.
That is, according to the present invention, it is possible to provide an unbalanced input terminal-balanced output type surface acoustic wave filter.

[Brief description of drawings]

FIG. 1 is a plan view showing an electrode configuration of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 is a plan view showing an electrode configuration of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 3 is a plan view showing an electrode configuration of a surface acoustic wave filter according to a third embodiment of the present invention.

FIG. 4 is a measurement circuit diagram of a surface acoustic wave filter according to a third embodiment.

FIG. 5 is a plan view showing an electrode configuration of a surface acoustic wave filter according to a fourth embodiment of the present invention.

FIG. 6 is a measurement circuit diagram of a surface acoustic wave filter according to a fourth embodiment.

FIG. 7 is a plan view showing an electrode configuration of a surface acoustic wave filter according to a modified example of the third embodiment.

[Explanation of symbols]

101, 201, 301, 401, 501 interdigital transducers for input, 102-1, 102-2 202-1, 20
2-2, 301-1, 301-2, 402-1, 402
-2, 502-1, 502-2 output interdigital electrodes,
103-1, 103-2, 203-1, 203-2, 3
03-1, 303-2, 403-1, 403-2, 50
3-1 and 503-2 reflector, 104, 204 and 30
4,404,504 input terminals, 105, 106, 20
5,206,305-1, 305-2,405-1,4
05-2, 505-1, 505-2 Output terminals.

Front page continued (72) Keiji Onishi Keiji Onishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Kazuki Nishimura, 1006, Kadoma, Kadoma, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Inventor, Seidai Mita, 1006, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial

Claims (6)

[Claims] 1. An interdigital transducer for input and first interdigital transducers formed on both sides of the interdigital transducer for input between surface acoustic wave reflectors provided on a piezoelectric substrate at a predetermined distance from each other. A second output interdigital electrode, wherein the input interdigital electrode is provided with an input electrode branch connected to an input terminal and a plurality of ground electrode branches connected to a ground terminal in parallel to each other. The first and second interdigital transducers for output are each provided with an output electrode branch connected to an output terminal and a connection electrode branch connected to a connection terminal in parallel with each other. A surface acoustic wave filter, wherein each of the connection terminals of the first and second interdigital transducers for output is grounded or connected to each other, and a signal input through the input terminal is used for the first output. Output connected to the interdigital transducer Terminal and said second surface acoustic wave filter characterized by splitting and outputting to and an output terminal connected to the output interdigital transducer. 2. The number of input electrode branches of the input interdigital transducer, the number of output electrode branches of the first output interdigital transducer, and the number of output electrode branches of the second output interdigital transducer. The surface acoustic wave filter according to claim 1, wherein and are substantially equal to each other. 3. An interdigital transducer for input and first interdigital transducers formed on both sides of the interdigital transducer for input between surface acoustic wave reflectors provided on a piezoelectric substrate at a predetermined distance from each other. A second output interdigital electrode, wherein each of the input interdigital electrodes includes an input electrode branch connected to an input terminal and a ground electrode branch connected to a ground terminal, respectively, provided in parallel to each other. The surface elasticity of each of the first and second output interdigital electrodes includes output electrode branches connected to the output terminals and connection electrode branches connected to the connection terminals in parallel with each other. A wave filter comprising: a space between the output electrode branch of the first output interdigital transducer and the input electrode branch; and an output electrode branch of the second output interdigital transducer and the input electrode branch. Between the above and each other, Of the wavelength of the acoustic waves excited on the surface of the substrate {(2n + 1) / 2} times (where, n = 0, 1, 2, 3
...) are set differently, and the connection terminals of the first and second output interdigital electrodes are grounded or connected to each other, so that the output terminals connected to the first output interdigital electrode are connected. And an unbalanced input-balanced output type surface acoustic wave filter, which outputs signals having a phase difference of approximately 180 ° from each other from an output terminal connected to the second output interdigital transducer. 4. The number of output electrode branches of the first output interdigital transducer and the second number of output electrode branches compared to the number of input electrode branches.
4. The unbalanced input-balanced output type surface acoustic wave filter according to claim 3, wherein the number of output electrode branches of the output interdigital transducer is reduced. 5. A gap between the input interdigital transducer and the first output interdigital transducer and a gap between the input interdigital transducer and the second output interdigital transducer are different from each other. Item 3. An unbalanced input-balanced output type surface acoustic wave filter according to item 3 or 4. 6. The interval between the input interdigital transducer and the first output interdigital electrode and the interval between the input interdigital electrode and the second output interdigital electrode are the same. Item 3. An unbalanced input-balanced output type surface acoustic wave filter according to item 3 or 4.