JP2002164763A - Surface acoustic wave filter and communication apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter which is small and has a wide passing band, a steep attenuation characteristic in the vicinity of the passing band and also a flat characteristic in the passing band. SOLUTION: This surface acoustic wave filter is provided with a piezoelectric substrate 101 and at least two filter tracks having at least input interdigital transducer electrodes 104 and 106 and output interdigital transducer electrodes 105 and 107 provided on the piezoelectric substrate 101, the respective input interdigital transducer electrodes 104 and 106 of the at least two filter tracks are connected parallelly, the respective output interdigital transducer electrodes 105 and 107 of the at least two filter tracks are connected parallelly, and the cross widths W1 and W2 of the at least two filter tracks are different, respectively.

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 a communication device using the same.

[0002]

2. Description of the Related Art In recent years, the amount of information transmitted has increased due to the development of the information communication field. Accordingly, a surface acoustic wave filter having a relatively wide band and excellent in phase linearity in a pass band is required. Conventionally, a transversal type surface acoustic wave filter is suitable as such a surface acoustic wave filter. I was On the other hand, as is well known, a transversal type surface acoustic wave filter has a large insertion loss. Therefore, as a technique for reducing insertion loss, a transversal type surface acoustic wave filter using a unidirectional electrode is expected. Is being considered.

[0003] A transversal surface acoustic wave filter using a conventional unidirectional electrode will be described below.

FIG. 10A is a view showing a conventional transversal type surface acoustic wave filter using a unidirectional electrode. Reference numeral 1001 denotes a piezoelectric substrate.
And input and output interdigital transducer electrodes (hereinafter referred to as IDT electrodes) are formed on the
A surface acoustic wave filter is configured by arranging the T electrode 1002 and the output IDT electrode 1003 at a predetermined distance. Input IDT electrode 1002 and output IDT
The electrode 1003 includes IEEE Ultrasonics
symposium, 1989, pp. 77-89 include first and second unidirectional electrodes 1004, 1005 according to the prior art.

FIG. 10B shows a first unidirectional electrode 100.
4 is an enlarged view of FIG. As a basic configuration, the piezoelectric substrate 10
01 of λ / of the wavelength λ of the surface acoustic wave propagating on
A basic unit is constituted by a total of three electrode fingers including one 4-width electrode finger 1004a and two λ / 8-width electrode fingers 1004b. Further, the second unidirectional electrode 1005 has a left-right symmetric configuration with the unidirectional electrode 1004. One type of unidirectional electrode of this type is EWC-SPUDT (El
electron Width Controlled
Single-Phase Unidirection
al Transducer), which has been conventionally used as a technique for reducing insertion loss.

[0006] The surface acoustic wave filter configured as described above has an input IDT electrode 1002 and an output IDT electrode 1002.
The frequency characteristics of the filter are determined by thinning out the three electrode fingers and performing various weighting. In the prior art, in this way, a filter characteristic with a wide band and a flat pass band and a steep attenuation near the pass band are realized in this way.

[0007] Japanese Patent Application Laid-Open No. 2000-77974 discloses a surface acoustic wave filter having first and second channels on a piezoelectric substrate. FIG. 11 shows a schematic configuration diagram of a surface acoustic wave filter having first and second channels according to a conventional technique. The two-channel filter includes input IDT electrodes 1102a and 1103a and output IDT electrodes 1102 provided on a piezoelectric substrate 1101.
First channel 110 having 2b and 1103b respectively
2 and a second channel 1103. Such a surface acoustic wave filter includes a first channel 1
The phase characteristics of the second channel 1103 and the second channel 1103 are in phase in the pass band and opposite in the stop band.

[0008]

In recent years, portable terminals have been reduced in size and weight, and accordingly, there has been a demand for smaller surface acoustic wave filters. However, when trying to obtain a steep attenuation near the pass band with the above-described transversal surface acoustic wave filter as shown in FIG. 10, sufficient weighting is required for the input and output IDT electrodes, and the IDT electrode length becomes long. Therefore, there is a problem that miniaturization is difficult.

In a surface acoustic wave filter having a two-channel filter configuration as shown in FIG. 11, a small surface acoustic wave filter having a sharp band characteristic can be obtained. There was a problem of lack.

Accordingly, it is an object of the present invention to provide a surface acoustic wave filter which is small in size, has a wide pass band, has a steep attenuation characteristic near the pass band, and has a flat characteristic in the pass band.

[0011]

In order to achieve the above object, a first aspect of the present invention (corresponding to claim 1) is to provide a piezoelectric substrate and at least an input interdigital transducer provided on the piezoelectric substrate. At least two having electrodes and output interdigital transducer electrodes
Filter tracks, wherein the input interdigital transducer electrodes of each of the at least two filter tracks are connected in parallel;
The output interdigital transducer electrodes of each of the filter tracks are connected in parallel, and the cross width of the electrode fingers of the input and output interdigital transducer electrodes is at least one of the at least two filter tracks. Different surface acoustic wave filters.

Further, the second invention (corresponding to claim 2)
The filter tracks are two filter tracks, a first filter track and a second filter track, the input interdigital transducer electrodes of the first and second filter tracks are connected in parallel,
The width of the electrode fingers of the input and output interdigital transducer electrodes in the first filter track and the width of the electrode fingers of the input and output interdigital transducer electrodes in the second filter track; 1 is a surface acoustic wave filter according to a first aspect of the present invention, which has different cross widths.

Further, the third invention (corresponding to claim 3)
Is a surface acoustic wave filter according to a second aspect of the present invention, wherein the first filter track and the second filter track have different weighting functions.

A fourth aspect of the present invention (corresponding to claim 4)
Is that the phase relationship between the first and second filter tracks is substantially in phase within the passband and substantially out of phase outside the passband, and the first and second filter tracks The center frequency is substantially the same as the second
Alternatively, it is the surface acoustic wave filter according to the third aspect of the present invention.

Further, a fifth aspect of the present invention (corresponding to claim 5)
Wherein the first filter track has a transfer characteristic having two peaks in a pass band, and the second filter track has a transfer characteristic having one peak in a pass band. The amplitude characteristics of the track and the second filter track are substantially 3d from the value of the maximum attenuation.
The surface acoustic wave filter according to the fourth aspect of the present invention, in which the frequencies at which B becomes lower substantially match.

A sixth aspect of the present invention (corresponding to claim 6)
Where W1 is the intersection width of the first filter track and W2 is the intersection width of the second filter track.
A fifth surface acoustic wave filter according to the present invention that satisfies the relationship of 0.8 ≦ W1 / W2 ≦ 0.95.

The seventh invention (corresponding to claim 7)
Is the surface acoustic wave filter according to any one of the first to sixth aspects of the present invention, wherein at least one of the input interdigital transducer electrode and / or the output interdigital transducer electrode includes a unidirectional electrode.

The eighth invention (corresponding to claim 8)
The one-way electrode comprises a first one-way electrode that strengthens surface acoustic waves in a predetermined direction and a second one-way electrode that strengthens surface acoustic waves in a direction opposite to the predetermined direction. It is a seventh surface acoustic wave filter including two types.

The ninth aspect of the present invention (corresponding to claim 9)
The parallel connection at the input interdigital transducer electrode of the filter track is configured to connect adjacent electrode fingers, and the parallel connection at the output interdigital transducer electrode of the filter track connects the adjacent electrode fingers. The surface acoustic wave filter according to any one of the first to sixth aspects of the present invention, which is configured to be connected.

According to a tenth aspect of the present invention (corresponding to claim 10), at least one filter having a piezoelectric substrate and an input interdigital transducer electrode and an output interdigital transducer electrode provided on the piezoelectric substrate. A track, wherein the input interdigital transducer electrode and / or the output interdigital transducer electrode include a first unidirectional electrode for enhancing a surface acoustic wave in one direction, and a surface acoustic wave in a direction opposite to the one direction. A surface acoustic wave filter including an enhanced second unidirectional electrode.

According to an eleventh aspect of the present invention (corresponding to claim 11), the first and second unidirectional electrodes have four electrode fingers within one wavelength, and The finger has two electrode finger pairs, and the electrode finger pairs have different electrode finger widths. The electrode finger width has a narrow electrode finger width (L1) and a wide electrode finger width (L2). The width ratio (L2 / L1) is a surface acoustic wave filter according to the tenth aspect of the present invention, which is larger than 1.

According to a twelfth aspect of the present invention (corresponding to claim 12), in the electrode finger pair, the distance between the thin electrode finger and the thick electrode finger is γ, the input interdigital transducer electrode and / or Alternatively, the distance between the left end of the area where the output interdigital transducer electrode is divided in half-wavelength units and the thick electrode finger is α, and the input interdigital transducer electrode and / or the output interdigital transducer electrode is divided in half-wavelength units. An eleventh surface acoustic wave filter according to the present invention, wherein γ> α + β and α <β, where β is the distance between the right end of the region and the thin electrode finger.

According to a thirteenth aspect of the present invention (corresponding to claim 13), the electrode width ratio (L2 /
L1) is the surface acoustic wave filter according to the twelfth aspect of the present invention, in which 1.4 ≦ (L2 / L1) ≦ 3.6.

According to a fourteenth aspect of the present invention (corresponding to claim 14), the positions of the thin electrode finger and the thick electrode finger in the first unidirectional electrode and the position of the second unidirectional electrode in the second unidirectional electrode are different. An eleventh surface acoustic wave filter according to the present invention, wherein the positions of the thin electrode finger and the thick electrode finger are opposite to each other.

According to a fifteenth aspect of the present invention (corresponding to claim 15), the piezoelectric substrate according to any one of the first to tenth aspects, wherein the piezoelectric substrate is a 28 ° to 42 ° rotating Y-cut quartz substrate. This is a surface acoustic wave filter.

According to a sixteenth aspect of the present invention (corresponding to claim 16), a transmitting means for transmitting a signal and a receiving means for receiving a signal are provided, wherein the transmitting means and / or the receiving means comprises: A communication device comprising the surface acoustic wave filter according to claim 1.

[0027]

Embodiments of a surface acoustic wave filter according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a surface acoustic wave filter according to a first embodiment of the present invention. In FIG. 1, reference numeral 101 denotes a piezoelectric substrate on which a first filter track 102 and a second filter track 103 are arranged in parallel. First
The filter track 102 is configured by arranging an input IDT electrode 104 and an output IDT electrode 105 at a predetermined distance. Similarly, the second filter track 103 is configured by arranging the input IDT electrode 106 and the output IDT electrode 107 at a predetermined distance.

In the input IDT electrode 104, one opposing electrode finger is connected to the bus bar electrode 104a, and the other electrode finger is connected to the bus bar electrode 104b. Further, in the output IDT electrode 105, one opposing electrode finger is commonly connected to the bus bar electrode 105a, and the other electrode finger is commonly connected to the bus bar electrode 105b.

Similarly, in the input IDT electrode 106,
One opposing electrode finger is commonly connected to the bus bar electrode 106a, and the other electrode finger is commonly connected to the bus bar electrode 106b. Further, in the output IDT electrode 107, one of the opposing electrode fingers is a bus bar electrode 107a.
The other electrode finger is a bus bar electrode 107b, which is commonly connected.

The bus bar electrodes 104a and 106a are connected by a common input line 108a.
b and 106b are connected by a common input line 108b.

On the other hand, the bus bar electrodes 105a and 107a are connected by a common output line 109a,
b and 107b are connected by a common output line 109b.

The input and output IDT electrodes 104, 1
Numerals 05, 106, and 107 include a unidirectional electrode. That is, the input and output IDT electrodes 104, 10
When 5, 106, and 107 are divided by the wavelength λ of the surface acoustic wave, they are composed of a total of three electrode fingers, one λ / 4 width electrode finger and two λ / 8 width electrode fingers. An area is provided. Here, the input IDT electrodes 104 and 106 have a rightward direction, and the output IDT electrodes 105 and 107 have a leftward directionality.

Further, the first and second filter tracks 102 and 103 are given different weights by thinning out the electrode fingers of the input IDT electrodes 104 and 106 and the output IDT electrodes 105 and 107.

The first and second filter tracks 1
The center frequencies of 02 and 103 are substantially the same. Further, the input IDT electrode 104 of the first filter track 102 and the input IDT electrode 106 of the second filter track are connected in parallel. Similarly, the output IDT electrode 105 of the second filter track 103 and the output IDT electrode 107 of the second filter track 103 are connected in parallel. Further, the intersection width W1 of the first filter track 102 and the intersection width W2 of the second filter track 103 are different from each other. Here, the intersection width is I
In the DT electrode, it indicates the length of the intersecting electrode fingers that excite the surface acoustic wave.

The operation of the surface acoustic wave filter configured as described above will be described below.

FIG. 2A shows an amplitude characteristic 201 of the first filter track 102 and an amplitude characteristic 202 of the second filter track 103 in FIG. 1, and FIG.
Phase characteristic 20 of the first filter track 102 at
3 shows a phase characteristic 204 of the third filter track 103.

In this embodiment, the center frequencies of the first and second filter tracks 102 and 103 are substantially the same. Further, regarding the pass band, FIG.
As shown in (1), the amplitude characteristic 201 of the first filter track 102 has two peaks and a wide passband characteristic, but has a large insertion loss near the center frequency.

On the other hand, the amplitude characteristic 202 of the second filter track 103 has a peak near the center frequency and a low insertion loss, but has a narrow pass band. Further, as shown in FIG. 2B, the phase difference in the pass band between the first filter track 102 and the second filter track 103 is almost 0 °,
That is, the phases are substantially the same. The term “substantially the same phase” here means that the phase difference is −50 ° to + 50 °, preferably −2 °.
Within the range of 0 ° to + 20 °.

On the other hand, with respect to out of the pass band, FIG.
As shown in FIG. 3, the amplitude characteristic 201 of the first filter track 102 and the amplitude characteristic 2 of the second filter track 103
In the case of 02, spurs are not suppressed outside the pass band, but each spurious is substantially at the same level.

As shown in FIG. 2B, the phase difference between the phase characteristic 203 of the first filter track 102 and the phase characteristic 204 of the second filter track 103 is substantially one.
80 °, ie, out of phase. Here, substantially 180 °
Means a range of 130 ° to 230 °, and preferably a phase difference of 160 ° to 200 °.

Therefore, in the present embodiment, the first filter track 102 and the second filter track 10
3 has substantially the same spurious level outside the pass band and has substantially the opposite phase, so that the spurious components of the first filter track 102 and the second filter track 103 cancel each other out, and as a result, a large amount of attenuation occurs. can get.

Further, in the present embodiment, the intersection width W1 of the first filter track 102 and the intersection width W2 of the second filter track 103 are set to different lengths, so that the first width and the second width within the pass band are different. Since the amplitude characteristics of the two filter tracks can be adjusted so that the frequencies at which the values of the maximum attenuation of each filter track are 3 dB lower are almost the same, a flat and wide pass band can be realized. Things.

As described above, the surface acoustic wave filter of the present embodiment has a wide pass band, secures a steep attenuation outside the pass band, and can realize flatness in the pass band. Things.

Further, in the surface acoustic wave filter of the present embodiment, since the first and second filter tracks are connected in parallel, the input / output impedance can be made lower than that of the conventional surface acoustic wave filter. The impedance matching with the device connected to the former stage and the latter stage of the surface acoustic wave filter is facilitated, and the surface acoustic wave filter of the present invention is
By using the transmitting device and / or the receiving device of the communication device, a higher-performance communication device can be realized.

(Second Embodiment) FIG. 3 shows a surface acoustic wave filter according to a second embodiment of the present invention. In FIG. 3, reference numeral 301 denotes a piezoelectric substrate, on which a first filter track 302 and a second filter track 303 are configured in parallel. First
The filter track 302 is configured by arranging an input IDT electrode 304 and an output IDT electrode 305 at a predetermined distance. Similarly, the second filter track 303 is configured by arranging the input IDT electrode 306 and the output IDT electrode 307 at a predetermined distance. Note that the configuration of the bus bar electrode is the same as that of the first embodiment, and a description thereof will be omitted.

Here, the input and output IDT electrodes 304,
305, 306, and 307 are formed with an electrode configuration called R-SPUDT. This electrode configuration also has input and output IDT electrodes 304, 305, and 3 similarly to the first embodiment.
When 06 and 307 are separated by the surface acoustic wave wavelength λ,
There is provided a region composed of a total of three electrode fingers, one λ / 4 width electrode finger and two λ / 8 width electrode fingers.

FIG. 4 shows one area of the unidirectional electrode constituting input IDT electrode 304 in the present embodiment. First
Region 401 is composed of the λ / 4 width electrode finger 401a and the λ / 8 width electrode finger 4 provided on the same side as the λ / 4 width electrode finger 401a.
01b and a λ / 8 width electrode finger 401c provided on the side opposite to the λ / 4 width electrode finger 401a.

The second region 402 includes a λ / 4 width electrode finger 402a, a λ / 8 width electrode finger 402b and a λ / 4 width electrode finger 40 provided on the same side as the λ / 4 width electrode finger 402a.
Λ / 8 width electrode finger 402c provided on the side facing 2a
It is composed of

The third region 403 includes the λ / 4 width electrode finger 403a, the λ / 8 width electrode finger 403b and the λ / 4 width electrode finger 40 provided on the same side as the λ / 4 width electrode finger 403a.
Λ / 8 width electrode finger 403c provided on the side facing 3a
It is composed of

In FIG. 4, the arrow indicates the first region 4.
01, the direction of each of the second region 402 and the third region 403, and the direction of the entire IDT electrode are shown. The first and third regions 401 and 403 have unidirectionality in the right direction, while the second region 402 has unidirectionality in the opposite direction, that is, the left direction. This is area 40
1 and the region 403, the arrangement of the λ / 4 width electrode fingers and the arrangement of the λ / 8 width electrode fingers are the same.
The arrangement of the λ / 4 width electrode finger 402a and the λ / 8 width electrode finger 402b in 02 is the same as the arrangement of the λ / 4 width electrode fingers 401a and 403a and the λ / 8 width electrode fingers 401b and 403b in the regions 401 and 403. This is because it is reversed.

Further, the input IDT electrode 304 as a whole has a rightward directivity. R-SPUD
At T, ID is given by giving a direction in a part of one IDT electrode in a direction opposite to that of another region.
The structure is such that a resonance cavity is formed in the T electrode.

Other input and output IDT electrodes 305, 30
6 and 307, the input IDT electrode 304 described above.
Has the same configuration as that of the first embodiment, and has one-way characteristics.
The DT electrode 304 and the output IDT electrode 305, and the input IDT electrode 306 and the output IDT electrode 307 are configured to face each other. The amplitude characteristics, phase characteristics, and center frequency relationship of the first and second filter tracks 302 and 303 are the same as in the first embodiment.

Further, in the present embodiment, the first and second filter tracks 302 have a different width between the cross width W1 of the first filter track 302 and the cross width W2 of the second filter track 303, so that the first and second filters within the pass band are different. By adjusting the amplitude characteristics of the two filter tracks so that the frequencies at which the value of the maximum attenuation of each filter track is 3 dB lower are almost the same, a flat and wide pass band can be realized. is there.

As described above, according to the configuration of the surface acoustic wave filter of the present embodiment, the length of the IDT electrode can be further reduced as compared with the first embodiment, and The size of the wave filter can be further reduced. Further, the surface acoustic wave filter according to the present embodiment has a wide pass band, secures a steep attenuation outside the pass band, and can realize flatness in the pass band.

In the surface acoustic wave filter according to the present embodiment, since the first and second filter tracks are connected in parallel, the input / output impedance can be made lower than that of the conventional surface acoustic wave filter. , Impedance matching with devices connected before and after the surface acoustic wave filter can be easily attained. The surface acoustic wave filter of the present invention can be replaced with the surface acoustic wave filter of the present invention, and transmission means and / or reception means of a communication device. , A higher-performance communication device can be realized.

(Third Embodiment) FIG. 5 shows a surface acoustic wave filter according to a third embodiment of the present invention. The difference between the present embodiment and the second embodiment is that, as shown in FIG. 5, the input and output IDTs of the first and second filter tracks 502 and 503 providing the directionality.
The point is that the electrode 504, 505, 506, 507 is configured with four electrode fingers per one wavelength. On the other hand, in the second embodiment, as shown in FIG. 4, directionality is given by three electrode fingers per wavelength.

In the input IDT electrode 504, one opposing electrode finger is commonly connected to a bus bar electrode 504a, and the other electrode finger is commonly connected to a bus bar electrode 504b. Further, in the output IDT electrode 505, one of the opposing electrode fingers is a bus bar electrode 505a.
The other electrode finger is a bus bar electrode 505b, which is commonly connected.

Similarly, in the input IDT electrode 506,
One opposing electrode finger is commonly connected to a bus bar electrode 506a, and the other electrode finger is commonly connected to a bus bar electrode 506b. Further, in the output IDT electrode 507, one of the opposing electrode fingers is a bus bar electrode 507a.
The other electrode finger is a bus bar electrode 507b, which is commonly connected.

The bus bar electrodes 504a and 506a are connected by a common input line 508a.
b and 506b are connected by a common input line 508b.

On the other hand, the bus bar electrodes 505a and 507a are connected by a common output line 509a,
b and 507b are connected by a common output line 509b.

FIG. 6 shows one region of the unidirectional electrode constituting input IDT electrode 504 in the present embodiment. FIG.
, Black arrows indicate the first region 601 and the second region 60
The direction of each of the second and third regions 603 is shown, and the white arrow shows the direction of the entire IDT electrode 504.

In FIG. 6, a first region 601 has two electrode finger pairs, a first electrode finger pair 604 and a second electrode finger pair 605 within 1λ. Are composed of thin electrode fingers 604a and thick electrode fingers 604b. The second electrode finger pair 605 is a thin electrode finger 60.
5a and a thick electrode finger 605b.

The first electrode finger pair 604 is connected to the upper bus bar electrode 606, the second electrode finger pair 605 is connected to the lower bus bar electrode 607, and the first electrode finger pair 604 and the second electrode The finger pair 605 has an intersecting structure, and in the first region 601, the surface acoustic wave has a direction from the thin electrode finger to the thick electrode finger, that is, the right direction.

Further, the second region 602 has two electrode finger pairs of a first electrode finger pair 610 and a second electrode finger pair 611 within 1λ, and the first electrode finger pair 610 is thin. It is composed of an electrode finger 610a and a thick electrode finger 610b.
The second electrode finger pair 611 includes a thin electrode finger 611a and a thick electrode finger 611b.

The first electrode finger pair 610 is connected to the upper bus bar electrode 606, the second electrode finger pair 611 is connected to the lower bus bar electrode 607, and the first electrode finger pair 604 and the second electrode The finger pair 605 has a crossed structure.

That is, the second region 602 is different from the first region 601 in the first and second electrode finger pairs 604 and 60.
5, the positions of the thin electrode and the thick electrode are opposite to each other, and in the second region 602, the surface acoustic wave has a direction from the thin electrode finger toward the thick electrode finger, that is, the left direction.

The third region 603 is the first region 60
This is the same configuration as in FIG.

The first and third regions 601 and 603 are unidirectional in the right direction, while the second region 602 is unidirectional in the opposite direction, that is, left. This means that in region 601 and region 603,
Although the arrangement of the first and second electrode finger pairs is the same, in the first and second electrode finger pairs in the region 402, the positions of the thin and thick electrodes are different from those of the region 601 and the region 603. Is reversed.

Furthermore, the input IDT electrode 604 as a whole has a rightward directivity. R-SPUD
At T, ID is given by giving a direction in a part of one IDT electrode in a direction opposite to that of another region.
The structure is such that a resonance cavity is formed in the T electrode.

Other input and output IDT electrodes 505, 50
6, 507, the input IDT electrode 504 described above.
Has the same configuration as that of the first embodiment, and has one-way characteristics.
The directions of the DT electrode 504 and the output IDT electrode 505 and the direction of the input IDT electrode 506 and the output IDT electrode 507 are configured to face each other.

Further, in FIG.
a, the electrode finger width of 605a is L1, the thick electrode finger 604b,
Assuming that the electrode finger width of 605b is L2, the characteristics of the unidirectional electrode depend on the electrode width ratio L2 / L1, which is the ratio of the width of the thin electrode finger to the width of the thick electrode finger. In the present embodiment, by changing the electrode width ratio, it is possible to control the directionality of the IDT electrode and the excitation efficiency of the surface acoustic wave. At this time, L2 / L1 is larger than 1, preferably in the range of 1.4 to 3.6. Thus, L2 /
By optimizing L1, it is possible to control the directionality and excitation efficiency of the surface acoustic wave and improve the insertion loss of the surface acoustic wave filter.

Further, the distance between the thin electrode finger 604a and the thick electrode finger 604b and the narrow electrode finger 605a and the thick electrode finger 6
Considering a λ / 2 region obtained by dividing the first region 601 into two in the propagation direction of the surface acoustic wave, the λ / 2 region 6 including the thin electrode finger 604 a and the first electrode finger pair 604 is assumed to be γ.
08, the distance between the left end of the λ / 2 cell 609 including the thin electrode finger 605a and the second electrode finger pair 605 is α, and the distance λ including the thick electrode finger 604b and the first electrode finger pair 604. / 2 cell 608 and right electrode 6
/ 2 cell 609 including the first electrode finger pair 605 and the first electrode finger pair 605
Is larger than α + β, and satisfies the relationship α <β. By setting α <β, the symmetry is excellent, the deviation in the pass band is small,
The amount of attenuation outside the pass band can be increased.

The optimum values of α and β are determined by the electrode width ratio (L
2 / L1) and the film thickness ratio (h / λ), but γ is larger than α + β, and for the relationship α <β, the electrode width ratio (L2 / L1) and the film thickness ratio (h / λ) The same applies regardless of λ).

Furthermore, in the present embodiment, the first and second filter tracks 602 have different intersection widths W1 and 603, so that the first and second filter tracks 603 have different lengths. By adjusting the amplitude characteristics of the two filter tracks so that the frequencies at which the value of the maximum attenuation of each filter track is 3 dB lower are almost the same, a flat and wide pass band can be realized. is there.

FIG. 7A is a diagram showing characteristics of the surface acoustic wave filter according to the third embodiment shown in FIG. The vertical axis is normalized by the minimum insertion loss. Here, 3
A 7 ° rotated Y-cut quartz substrate is used. Further, when the film thickness of the electrode is h, the film thickness ratio is h / λ = 1.8%, and the electrode width ratio is an optimum range of L2 / L1 = 1.7.
5 is assumed. Α to 0.757 × (λ / 16), β
= 0.873 × (λ / 16), γ is larger than α + β, and the relationship satisfies α <β. Further, regarding the intersection width, the intersection width of the first filter track 502 is W1 = 18λ, and the intersection width of the second filter track 503 is W2 = 20λ.

For comparison, FIG. 7B shows the characteristics of a surface acoustic wave filter in which the first and second filter tracks have the same intersection width (W1 = W2 = 19λ). By making the cross width of the first filter track and the second filter track different from each other, the flatness in the band is reduced to 0.4.
It can be seen that it has improved from dB to 0.25 dB.
Further, it can be seen that the surface acoustic wave filter of the present embodiment has a wide pass band and has excellent attenuation characteristics near the pass band.

FIG. 7C shows the filter characteristics when the cross width of the first filter track 502 is W1 = 16λ and the cross width of the second filter track 503 is W2 = 22λ. . Also in this case, the flatness is 0.3
Although improved to 5 dB, the bandwidth of the filter is reduced. Conversely, as shown in FIG. 7D, when the cross width of the first filter track 502 is W1 = 20λ and the cross width of the second filter track 503 is W2 = 18λ, the flatness is 0. .5 dB.

FIG. 8 is a diagram showing the relationship between the intersection width of the first and second tracks and the flatness. The horizontal axis represents the ratio of W1 / W2. 7 and 8, it is effective to improve the flatness when 0.8 ≦ W1 / W2 ≦ 0.95 in consideration of the improvement of the flatness and the reduction of the bandwidth.

In the above embodiment, the first filter track 502 and the second filter track 50
3 on the input side via the busbar electrodes 504b and 506a, and on the output side the busbar electrode 50b and 506a.
5b and 507a are connected in parallel,
As shown in FIG. 9, on the piezoelectric substrate 901, the input IDT electrode 904 of the first filter track 902 and the second
An input IDT electrode 906 of the filter track 903,
Further, in the output IDT electrode 905 of the first filter track 902 and the output IDT electrode 907 of the second filter track 903, the bus bar electrode at the portion facing the first filter track 902 and the second filter track 903 is omitted. However, the same effect can be obtained by connecting the electrode fingers of each IDT electrode.

Furthermore, the length in the cross width direction can be shortened, and a more compact surface acoustic wave filter can be realized.

Further, in the configuration example of FIG. 9, the bus bar electrodes 504b, 506a, 505b, 507 as shown in FIG.
The resistance loss due to a is reduced, and a surface acoustic wave filter with lower insertion loss can be realized. Also in this case, it is the same as FIG. 5 in that the intersection width W1 of the first filter track 902 and the intersection width W2 of the second filter track 903 are different lengths, and the magnitude of the amplitude characteristic is adjusted. And flatness in the pass band can be realized.

When the characteristics of the first filter track and the second filter track are opposite, the aforementioned W1 / W
The relationship of 2 is similarly reversed.

As described above, according to the configuration of the surface acoustic wave filter of the present embodiment, the length of the IDT electrode can be further reduced as compared with the first embodiment, and The size of the wave filter can be further reduced. Further, the surface acoustic wave filter according to the present embodiment has a wide pass band, secures a steep attenuation outside the pass band, and can realize flatness in the pass band.

The surface acoustic wave filter according to the present embodiment is the same as the EWC-SPU shown in the first and second embodiments.
The input / output impedance can be made lower than that of the surface acoustic wave filter using DT, and the impedance matching with the devices connected before and after the surface acoustic wave filter is further facilitated. By using the wave filter as a transmission unit and / or a reception unit of a communication device, a communication device with higher performance can be realized.

Although the present embodiment has been described as a design in which the cross width of the first filter track is shorter than the cross width of the second filter track, this varies depending on the pass characteristics of the entire filter. . That is, the size of the crossing width of each track is determined by the transfer characteristics of each track, and is not limited to the size shown in the present embodiment, but may be the first and second in the pass band. By adjusting the amplitude characteristics of the filter tracks so that the frequencies at which the value of the maximum attenuation of each filter track becomes 3 dB lower than those of the filter tracks are almost the same, the effect of realizing a flat and wide pass band is the same. It is.

In the present embodiment, the relationship between α and β is such that h / λ is approximately 1.8% and L2 / L1 =
Although described as 1.75, h / λ may be other film thickness ratios, and L2 / L1 may be other than 1.75, preferably L2 / L1 is 1.4 to 3. Within the range of 6, if α <β is satisfied, the same effect as the present invention can be obtained.

Further, in the present invention, the connection between the first and second filter tracks is not limited to this, and the connection between the first and second filter tracks is parallel, and the intersection width of each filter track is provided. Is different, the magnitude of the amplitude characteristics of the first and second filter tracks in the pass band is adjusted, and the same effect as that of the present invention that flatness in the pass band can be realized is obtained.

In the first to third embodiments, the unidirectional electrodes in the regions 401, 403, 601, 603 correspond to the first unidirectional electrode of the present invention, and
02, 602 unidirectional electrode corresponds to the second unidirectional electrode of the present invention. However, the first unidirectional electrode of the present invention may be realized as a unidirectional electrode of the regions 402 and 602. At this time, the second unidirectional electrode of the present invention is realized as a unidirectional electrode in the regions 401, 403, 601, 603.

In the first to third embodiments, the description has been given of the configuration in which the unidirectional electrode is used as the IDT electrode forming the first and second filter tracks.
A similar effect can be obtained with respect to low insertion loss by using a combination of a bidirectional electrode having a λ / 8 electrode width or a bidirectional electrode having a λ / 4 electrode width, which is generally used conventionally.

Further, it has a single filter track,
Similar effects can be obtained with respect to low insertion loss even when the unidirectional electrode of the present invention is used for a surface acoustic wave filter having one input IDT electrode and one output IDT electrode.

Note that such a combination is
The present invention is not limited to this, and is determined by a weighting function for obtaining a desired filter characteristic. Also,
In the present embodiment, the arrangement of the unidirectional electrodes constituting the first and second filter tracks is defined by a weighting function for obtaining a desired filter characteristic, and is not limited to this. .

Although the first to third embodiments have been described using the first and second two filter tracks, this is a surface acoustic wave filter having three or more filter tracks. If the crossing width is different in at least one filter track, the same effect can be obtained. In this case, although the weighting function of each filter track is different, the magnitude of the amplitude characteristic of each filter track in the pass band is adjusted by changing the cross width of each filter track, and the flatness in the pass band is adjusted. The third embodiment is the same as the first to third embodiments in that the characteristics can be realized.

In the embodiment of the present invention, a description has been given using a 37 ° rotated Y-cut quartz substrate as the piezoelectric substrate. However, this may be another cut angle, and the thickness of the electrode, the metallization ratio, The temperature is selected so that optimum temperature characteristics can be obtained in the operating temperature range. Especially 28 °
A ~ 42 degree angle is desirable. LiT is used as a piezoelectric substrate.
Similar effects can be obtained by using other piezoelectric substrates such as aO ₃ and Li ₂ B ₄ O ₇ .

In each of the above embodiments, the input and output IDT electrodes are configured to include the unidirectional electrode. However, this is because either the input or output IDT electrode is a unidirectional electrode. May be included.

In the first and second embodiments, the unidirectional electrode is connected to one λ / 4 electrode finger having a 幅 width of the wavelength.
Although the description has been made assuming that two λ / 8 width 指 / 8 electrode fingers are used, λ / 4
The electrode finger is not limited to this value and may have another width.

Further, a communication device using the surface acoustic wave filter of the present invention as transmitting means for transmitting a signal and / or receiving means for receiving a signal also belongs to the present invention.

[0098]

As is apparent from the above description,
According to the present invention, it is possible to provide a surface acoustic wave filter having a small size, a wide pass band, a steep attenuation characteristic near the pass band, and a flat characteristic in the pass band.

[Brief description of the drawings]

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

2A is a diagram showing amplitude characteristics of first and second filter tracks 102 in FIG. 1; and FIG. 2B is a diagram showing phase characteristics of first and second filter tracks 102 in FIG.

FIG. 3 is a configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 4 is a diagram showing one region of a unidirectional electrode constituting an input IDT electrode in FIG. 3;

FIG. 5 is a configuration diagram of a surface acoustic wave filter according to a third embodiment of the present invention.

FIG. 6 is a diagram showing one region of a unidirectional electrode constituting an input IDT electrode in FIG. 5;

7A is a diagram showing a pass characteristic of the surface acoustic wave filter in FIG. 5; FIG. 7B is a diagram showing a pass characteristic of a comparative example of the surface acoustic wave filter in FIG. 5; Characteristic diagram (d) Pass characteristic diagram of a comparative example of the surface acoustic wave filter in FIG.

FIG. 8 is a diagram showing a relationship between W1 / W2 and flatness.

FIG. 9 is a configuration diagram of a surface acoustic wave filter according to another embodiment of the present invention.

10A is a configuration diagram of a conventional surface acoustic wave filter. FIG. 10B is an enlarged view of a first unidirectional electrode 1004.

FIG. 11 is a schematic configuration diagram of a conventional surface acoustic wave filter having a two-channel filter.

[Explanation of symbols]

101, 301, 501, 901, 1001 Piezoelectric substrate 102, 302, 502, 902 First filter track 103, 303, 503, 903 Second filter track 104, 304, 504, 904 Input IDT of first filter track Electrodes 105, 305, 505, 905 Output IDT electrodes of the first filter track 106, 306, 506, 906 Input IDT electrodes 107, 307, 507, 907 of the second filter track Output IDT electrodes of the second filter track 201 Amplitude characteristic of first filter track 202 Amplitude characteristic of second filter track 203 Phase characteristic of first filter track 204 Phase characteristic of second filter track 401, 601 First region 402, 602 Second region 403 , 603 Third area 604 First electrode finger pair 604a Thin electrode finger of first electrode finger pair 604 604b Thick electrode finger of first electrode finger pair 604 605 Second electrode finger pair 605a Thin electrode finger of second electrode finger pair 605 605b Thick electrode finger of second electrode finger pair 605 606 Upper bus bar electrode 607 Lower bus bar electrode 608 λ / 2 cell including first electrode finger pair 604 609 λ / 2 including first electrode finger pair 605 Cell 401a, 402a, 403a λ / 4 width electrode finger 401b, 401c, 402b, 402c, 403b,
403c λ / 8 width electrode finger 1002 Input IDT electrode 1003 Output IDT electrode 1004 First unidirectional electrode 1005 Second unidirectional electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Tsuzuki 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuki Nishimura 1006 Okadoma Kadoma Kadoma City, Osaka Matsushita Electric Industrial F Term (reference) 5J097 AA14 AA16 CC04 CC15 DD04 DD05 GG02 KK04

Claims (16)

[Claims] 1. A piezoelectric substrate, comprising: a piezoelectric substrate; and at least two filter tracks provided on the piezoelectric substrate and having at least an input interdigital transducer electrode and an output interdigital transducer electrode, each of the at least two filter tracks. The input interdigital transducer electrodes of each of the at least two filter tracks are connected in parallel; and the intersection width of the electrode fingers of the input interdigital transducer electrode and the output interdigital transducer electrode. Is a surface acoustic wave filter that differs in at least one of said at least two filter tracks. 2. The filter track is two filter tracks, a first filter track and a second filter track, and input interdigital transducer electrodes of the first and second filter tracks are connected in parallel; The output interdigital transducer electrodes of the first and second filter tracks are connected in parallel, the intersection width of the electrode fingers of the input interdigital transducer electrode and the output interdigital transducer electrode in the first filter track, and 2. The surface acoustic wave filter according to claim 1, wherein the widths of the electrode fingers of the input interdigital transducer electrode and the output interdigital transducer electrode in the filter track are different from each other. 3. The first filter track and the second filter track.
3. The surface acoustic wave filter according to claim 2, wherein the surface acoustic wave filter has a different weighting function from that of the filter track. 4. The first filter track and the second filter track.
The phase relationship between the first and second filter tracks is substantially the same in the pass band and substantially in the opposite phase outside the pass band, and the center frequencies of the first and second filter tracks substantially coincide with each other. The surface acoustic wave filter according to any one of the preceding claims. 5. The first filter track has a transfer characteristic having two peaks in a pass band, and the second filter track has a transfer characteristic having one peak in a pass band. 5. The surface acoustic wave filter according to claim 4, wherein the amplitude characteristics of the first filter track and the second filter track have substantially the same frequency whose value is substantially 3 dB lower than the value of the maximum attenuation. 6. The relationship of 0.8 ≦ W1 / W2 ≦ 0.95, where W1 is the cross width of the first filter track and W2 is the cross width of the second filter track. Item 6. A surface acoustic wave filter according to item 5. 7. The surface acoustic wave filter according to claim 1, wherein at least one of the input interdigital transducer electrode and / or the output interdigital transducer electrode includes a unidirectional electrode. 8. The unidirectional electrode includes a first unidirectional electrode that enhances a surface acoustic wave in a predetermined direction and a second unidirectional electrode that enhances a surface acoustic wave in a direction opposite to the predetermined direction. The surface acoustic wave filter according to claim 7, including two types of electrodes: an electrode and an electrode. 9. The parallel connection of the input interdigital transducer electrodes of the filter track is configured to connect adjacent electrode fingers, and the parallel connection of the output interdigital transducer electrodes of the filter track includes the adjacent electrodes. The surface acoustic wave filter according to any one of claims 1 to 6, wherein the surface acoustic wave filter is configured to connect fingers. 10. At least one filter track having a piezoelectric substrate, and an input interdigital transducer electrode and an output interdigital transducer electrode provided on the piezoelectric substrate, wherein the input interdigital transducer electrode and / or the The output interdigital transducer electrode includes a first unidirectional electrode for enhancing a surface acoustic wave in one direction and a second unidirectional electrode for enhancing a surface acoustic wave in a direction opposite to the one direction. Surface wave filter. 11. The first and second unidirectional electrodes have four electrode fingers within one wavelength, the four electrode fingers have two electrode finger pairs, and the electrode The finger pairs have different electrode finger widths, and the electrode width ratio (L2 / L1) of the thin electrode finger width (L1) and the thick electrode finger width (L2) is greater than 1. A surface acoustic wave filter according to claim 10. 12. The electrode finger pair, wherein the distance between the thin electrode finger and the thick electrode finger is γ, and the input interdigital transducer electrode and / or the output interdigital transducer electrode are divided in half-wavelength units. Α is the distance between the left end of the region and the thick electrode finger, and β is the distance between the right end of the input interdigital transducer electrode and / or the output interdigital transducer electrode divided in half-wavelength units and the thin electrode finger. 12. The surface acoustic wave filter according to claim 11, wherein the relation of γ> α + β and α <β is satisfied. 13. The surface acoustic wave filter according to claim 12, wherein the electrode width ratio (L2 / L1) in the electrode finger pair is in a range of 1.4 ≦ (L2 / L1) ≦ 3.6. 14. The position of said thin electrode finger and said thick electrode finger in said first unidirectional electrode and the position of said thin electrode finger and said thick electrode finger in said second unidirectional electrode are opposite to each other. The surface acoustic wave filter according to claim 11, wherein: 15. The surface acoustic wave filter according to claim 1, wherein the piezoelectric substrate is a 28 ° to 42 ° rotated Y-cut quartz substrate. 16. A transmitting device for transmitting a signal, and a receiving device for receiving a signal, wherein the transmitting device and / or the receiving device is configured to transmit the signal.
A communication device having the surface acoustic wave filter according to any one of claims 15 to 15.