JP2001332954A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave(SAW) filter, capable of fully securing an attenuation quantity close to a pass frequency band. SOLUTION: A first comb-line electrode 11 and second and third comb-line electrodes 12 and 13 on both the sides of a SAW propagating direction thereof are located on a piezoelectric substrate 10, first and second reflector electrodes 14 and 15 are provided on both the sides of these electrodes, and the reflector electrode pitch of the first and second reflector electrodes 14 and 15 is changed to gradually turn small, going away from the adjacent second and third comb- line electrodes 12 and 13.

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 used for a high-frequency circuit or the like in a wireless communication device.

[0002]

2. Description of the Related Art Conventionally, as a surface acoustic wave filter suitable for an RF stage, a longitudinal mode coupled resonator type surface acoustic wave filter is well known.
What can selectively secure a high attenuation is demanded.

Hereinafter, a surface acoustic wave filter using a conventional longitudinal mode coupling type design will be described.

FIG. 12 is a top view of a conventional longitudinal mode coupling type surface acoustic wave filter.

[0005] On a piezoelectric substrate 80, three-electrode-type comb electrodes 81 and 82 surrounded by a chain line are connected in cascade. Three-electrode comb electrode 8
Reference numerals 1 and 82 denote first comb-shaped electrodes 81 each surrounded by a dotted line.
a, 82a, the second comb electrodes 81b, 82b, the third comb electrodes 81c, 82c, and the reflector electrodes 8 on both sides thereof.
1d and 82d are arranged in the surface wave propagation direction.

The first comb electrode 81 of the three-electrode comb electrode 81
In a, one of both opposing electrode fingers is connected to the output terminal 83 and the other is connected to the ground terminal 85. Three-electrode comb electrode 82
In the first comb-shaped electrode 82a, one of both opposing electrode fingers is connected to the output terminal 84 and the other is connected to the ground terminal 86.

By applying a voltage to the first comb electrodes 81a and 82a of the three-electrode comb electrodes 81 and 82, surface waves are excited, and energy is confined by the reflector electrodes 81d and 82d so that filter characteristics are improved. It is formed.

The reflector electrodes 81d and 82d are formed with a constant electrode finger width and electrode finger interval.

[0009]

The reflector electrode characteristic is formed by a pass frequency range with good reflection efficiency and a periodic slope characteristic on both sides thereof. Therefore, in the above configuration, the periodic characteristic of the reflector electrode appears as a waveform in the vicinity of the pass band, and spurious is generated. As a result, there is a problem that it is difficult to secure the attenuation in the vicinity of the pass frequency band.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave filter capable of sufficiently securing an attenuation near a pass frequency band.

[0011]

To achieve this object, a surface acoustic wave filter according to the present invention comprises a piezoelectric substrate, a first comb-shaped electrode provided on the piezoelectric substrate, and a first comb-shaped electrode. A second and third comb-shaped electrodes provided on both sides of the electrode in the surface wave propagation direction, and first and second reflector electrodes provided so as to sandwich the second and third comb-shaped electrodes. The width of at least one electrode finger of the first and second reflector electrodes or the period of the electrode finger interval is irregular, and the low or high frequency side near the pass frequency band of the reflector electrode is provided. By disturbing the periodic slope characteristic, spurious can be suppressed, and the above object can be achieved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention provides a piezoelectric substrate, a first comb-shaped electrode provided on the piezoelectric substrate, and the propagation of the surface wave of the first comb-shaped electrode. Second and third comb-shaped electrodes provided on both sides in the direction, and first and second reflector electrodes provided so as to sandwich the second and third comb-shaped electrodes. This is a surface acoustic wave filter in which the width of at least one electrode finger of the second reflector electrode or the period of the electrode finger interval is irregular, and ensures a sufficient amount of attenuation on the low frequency side or high frequency side near the pass frequency band. Is what you can do.

According to a second aspect of the present invention, there is provided the surface acoustic wave filter according to the first aspect, wherein the electrode finger width or the electrode finger interval is gradually reduced from the adjacent comb electrode side. Without affecting the effect,
It is possible to sufficiently secure the attenuation on the low frequency side near the pass frequency band.

According to a third aspect of the present invention, there is provided the surface acoustic wave filter according to the first aspect of the present invention, wherein the electrode finger width or the electrode finger interval is gradually increased from the adjacent comb electrode side. Without affecting the effect,
A sufficient amount of attenuation on the high frequency side near the pass frequency band can be ensured.

According to a fourth aspect of the present invention, at least one of the first and second reflector electrodes is constituted by at least two types of reflector electrode groups having different electrode finger widths or electrode finger intervals. Surface acoustic wave filter, which controls the reflector characteristics on the low frequency side or high frequency side near the pass frequency band, and ensures sufficient attenuation on the low frequency side or high frequency side near the pass frequency band. Things.

According to a fifth aspect of the present invention, there is provided the surface acoustic wave filter according to the fourth aspect, wherein the width of the electrode fingers or the interval between the electrode fingers of the reflector electrode group is reduced from the direction closer to the comb-shaped electrode. It is possible to suppress an adverse effect on the energy trapping effect of the reflector electrode and to secure an attenuation amount on the low frequency side near the pass frequency band.

According to a sixth aspect of the present invention, there is provided the surface acoustic wave filter according to the fourth aspect, wherein the electrode finger width or the period of the electrode finger interval of the reflector electrode group is increased from the side closer to the comb electrode. It is possible to suppress the adverse effect of the reflector electrode on the energy confinement effect, and to secure the attenuation on the high frequency side near the pass frequency band.

According to a seventh aspect of the present invention, there is provided the surface acoustic wave filter according to the fourth aspect, wherein the reflector electrode group adjacent to the comb-shaped electrode is constituted by 10 to 30 electrode fingers, and the pass band is efficiently provided. The spurious in the vicinity can be suppressed, and the attenuation on the low frequency side or the high frequency side near the pass frequency band can be secured.

According to the present invention, the difference between the electrode finger widths or the electrode finger interval widths of the adjacent reflector electrode groups is 0.05% of the reflector electrode pitch (electrode finger width + electrode finger interval width). The surface acoustic wave filter according to claim 4, wherein
The spurious in the vicinity of the pass band can be efficiently suppressed, and the attenuation on the low frequency side or the high frequency side in the vicinity of the pass frequency band can be secured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention.

On a piezoelectric substrate 10, a first comb-shaped electrode 11 and second and third comb-shaped electrodes 1 on both sides in the direction of propagation of the surface wave.
2 and 13 with the first reflector electrode 1 on each side of them.
4 and a second reflector electrode 15. First and second
The reflector electrode pitch of the reflector electrodes 14 and 15 is gradually reduced as the distance from the adjacent second and third comb-shaped electrodes 12 and 13 increases.

With this configuration, the characteristics of the first and second reflector electrodes 14 and 15 are as shown in FIG. 2, and the reflection efficiency on the low frequency side near the pass band can be reduced as compared with the conventional case.

Also, the first and second reflector electrodes 14, 1
When the reflector electrode pitch of No. 5 is greatly changed as the distance from the adjacent second and third comb-shaped electrodes 12 and 13 increases, the reflection efficiency on the high frequency side near the pass band decreases as shown in FIG. be able to.

That is, the first and second reflector electrodes 14 and 1
The reflector characteristics are disturbed by changing the electrode pitch of the reflector 5 in a non-constant manner, and by suppressing the generation of spurious components, a sufficient amount of out-of-band attenuation on the low frequency side or high frequency side near the pass band is ensured. be able to.

(Embodiment 2) FIG. 4 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention.

On the piezoelectric substrate 30, a first comb-shaped electrode 31 and second and third comb-shaped electrodes 3 on both sides in the direction of propagation of the surface wave.
2 and 33, and a first reflector electrode 3 on both sides thereof.
4 and a second reflector electrode 35. First,
The second reflector electrodes 34 and 35 have different reflector electrode pitches. It is composed of two reflector electrode groups 34a, 34b, 35a and 35b (surrounded by dotted lines in FIG. 4). The reflector electrode pitch of the reflector electrode groups 34a and 35a is larger than the reflector electrode pitch of the reflector electrode groups 34b and 35b.

FIG. 5 is a characteristic diagram of the first and second reflector electrodes 34 and 35 shown in FIG.
35 to two reflector electrode groups 34a, 34b, 35a, 3
By dividing into 5b, the reflection efficiency on the low frequency side near the pass band can be reduced.

When the reflector electrode pitch of the reflector electrode groups 34a and 35a is made smaller than the reflector electrode pitch of the reflector electrode groups 34b and 35b, as shown in FIG. Efficiency can be reduced.

That is, the first and second reflector electrodes 34,
By dividing 35 into two or more reflector electrode groups and changing the respective reflector electrode pitches so that the respective periods are different, the peaks and valleys of the reflection characteristics overlap, and the reflector characteristics of this portion are reduced. Flattened, suppresses spurs,
It is possible to sufficiently secure the out-of-band attenuation on the low frequency side or the high frequency side near the pass band.

(Embodiment 3) FIG. 7 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.

On the piezoelectric substrate 50, a first comb-shaped electrode 51 and second and third comb-shaped electrodes 5 on both sides in the direction of propagation of the surface wave.
2 and 53, and a first reflector electrode 5 on both sides thereof.
A three-electrode longitudinal mode-coupled comb electrode 56 including the fourth and second reflector electrodes 55 is formed. Further, the first reflector electrode 54 and the second reflector electrode 55 include three reflector electrode groups 54a, 54b, 54c, with different reflector electrode pitches.
It comprises 55a, 55b and 55c. The reflector electrode pitch is the largest for the reflector electrode groups 54a and 55a, the largest for the reflector electrode groups 54b and 55b, and the smallest for the reflector electrode groups 54c and 55c.

Further, a three-electrode longitudinal mode coupling type comb electrode 56
A three-electrode longitudinal mode-coupled comb electrode 57 having the same configuration is connected in cascade.

In the surface acoustic wave filter having such a configuration, the reflector electrode groups 54a, 54b, 54c, 55a,
FIG. 8 shows the characteristics of the first and second reflector electrodes 54 and 55 when the configurations of 55b and 55c are configured as shown in (Table 1). FIG. 9 is an enlarged view of a main part of FIG.

[0035]

[Table 1]

As can be seen from FIG. 9, the reflector electrode group 5
The reflection efficiency of the first and second reflector electrodes 5a and 55a
To the extent that it does not dominate the reflection efficiency of 4,55,
By changing the reflector electrode characteristics, spurious components on the low frequency side near the pass band can be suppressed, and the attenuation can be secured.

That is, it is desirable that the number of electrode fingers of the reflector electrode groups 54a and 55a be 10 to 30. Considering that the reflector electrode groups 54a and 55a closest to the second and third comb-shaped electrodes 52 and 53 largely contribute to the reflection efficiency of the first and second reflector electrodes 54 and 55, Even if the number of electrode fingers constituting the first and second reflector electrodes 54 and 55 changes, the reflector electrode group 54
It is desirable that the number of electrode fingers a and 55a is 10 to 30.

When the number of electrode fingers of the reflector electrode groups 54a and 55a exceeds 30 (FIG. 9D), the reflection efficiency of the reflector electrode groups 54a and 55a becomes dominant,
It becomes difficult to change the characteristics of the first and second reflector electrodes 54 and 55 to suppress spurious near the pass band. Conversely, if the number of electrode fingers of the reflector electrode groups 54a and 55a is nine or less, the reflection efficiency becomes insufficient and it is difficult to secure desired characteristics.

Next, the reflector electrode pitch of the reflector electrode groups 54a and 55a is λa, the reflector electrode pitch of the reflector electrode groups 54b and 55b is λb, and the reflector pitch of the reflector electrode groups 54c and 55c is λc. FIG. 10 shows the characteristics of the first and second reflector electrodes 54 and 55 in the configuration shown in (Table 2), and FIG.

[0040]

[Table 2]

As can be seen from FIG. 10, in order to secure the attenuation on the low frequency side near the pass band, the reflector electrode pitch is larger as it is closer to the second and third comb-shaped electrodes 52 and 53. The reflector pitch between anti-adjacent reflector electrode groups is 0.0
The difference should be 5% or more, preferably 0.1% or more, and the reflector electrode pitch should be smaller as the distance between the second and third comb-shaped electrodes 52 and 53 is longer.

In the third embodiment, the first and second reflector electrodes 54 and 55 are divided into a plurality of reflector electrode groups, respectively. The longer the distance of the reflector electrode group is, the smaller the reflector electrode pitch is, and the spurious on the low frequency side near the pass band is suppressed, and the attenuation is secured. When it is desired to secure the attenuation on the high frequency side, the reflector electrode pitch may be increased as the distance from the second and third comb-shaped electrodes 52 and 53 increases.

Although only the three-electrode longitudinal mode-coupled comb electrode 56 has been described, the same can be said for the three-electrode longitudinal-mode coupled comb electrode 57 having the same configuration.

Further, in the third embodiment, a surface acoustic wave filter in which a plurality of two three-electrode longitudinal mode coupling type comb electrodes 56 and 57 are connected in cascade has been described. However, as shown in FIGS. Also for the surface acoustic wave filter composed of one or more three-electrode longitudinal mode-coupled comb electrodes, the first and second reflector electrodes of each three-electrode longitudinal mode-coupled comb electrode are the same as those of the third embodiment. With such a configuration, a similar effect can be obtained.

Further, in each of the above embodiments, the first
And second reflector electrodes 14, 15, 34, 35, 54,
Although only the case where 55 has the same configuration has been described, the first reflector electrode 14, 34, 54 and the second reflector electrode 15,
The configuration may be different from 35 and 55.

[0046]

As described above, according to the present invention, it is possible to provide a surface acoustic wave filter that suppresses spurious components on the low frequency side or high frequency side near the pass frequency band and has a sufficient amount of out-of-band attenuation. Therefore, it is possible to improve the performance and simplify the circuit of a wireless device such as a mobile phone using the surface acoustic wave filter.

[Brief description of the drawings]

FIG. 1 is a top view of a surface acoustic wave filter according to Embodiment 1 of the present invention.

FIG. 2 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 3 is a frequency characteristic curve diagram of the surface acoustic wave filter according to Embodiment 1 of the present invention.

FIG. 4 is a top view of a surface acoustic wave filter according to Embodiment 2 of the present invention.

5 is a frequency characteristic curve diagram of the surface acoustic wave filter shown in FIG.

FIG. 6 is a frequency characteristic curve diagram of the surface acoustic wave filter according to Embodiment 2 of the present invention.

FIG. 7 is a top view of a surface acoustic wave filter according to Embodiment 3 of the present invention.

FIG. 8 is a frequency characteristic curve diagram of the surface acoustic wave filter according to Embodiment 3 of the present invention.

FIG. 9 is an enlarged view of a main part of FIG. 8;

FIG. 10 is a frequency characteristic curve diagram of the surface acoustic wave filter according to Embodiment 3 of the present invention.

FIG. 11 is an enlarged view of a main part of FIG. 10;

FIG. 12 is a top view of a conventional surface acoustic wave filter.

[Explanation of symbols]

 Reference Signs List 10 piezoelectric substrate 11 first comb-shaped electrode 12 second comb-shaped electrode 13 third comb-shaped electrode 14 first reflector electrode 15 second reflector electrode 30 piezoelectric substrate 31 first comb-shaped electrode 32 first 2nd comb electrode 33 third comb electrode 34 first reflector electrode 34a reflector electrode group 34b reflector electrode group 35 second reflector electrode 35a reflector electrode group 35b reflector electrode group 50 piezoelectric substrate 51 First comb-shaped electrode 52 Second comb-shaped electrode 53 Third comb-shaped electrode 54 First reflector electrode 54a Reflector electrode group 54b Reflector electrode group 54c Reflector electrode group 55 Second reflector electrode 55a Reflector electrode group 55b Reflector electrode group 55c Reflector electrode group 56 Three-electrode longitudinal mode coupling type comb electrode 57 Three-electrode vertical mode coupling type comb electrode

 ──────────────────────────────────────────────────の Continuing on the front page (72) Kazuo Ikeda 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Shunichi Seki 1006 Kadoma Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. F term (reference) 5J097 AA14 AA16 BB11 DD14 DD16 KK03

Claims (8)

[Claims] 1. A piezoelectric substrate, a first comb-shaped electrode provided on the piezoelectric substrate, and second and third comb-shaped electrodes provided on both sides of the first comb-shaped electrode in the surface wave propagation direction. Electrodes and this second
And first and second reflector electrodes provided so as to sandwich the third comb-shaped electrode. The width of at least one of the first and second reflector electrodes or the period of the electrode finger interval is An irregular surface acoustic wave filter. 2. The surface acoustic wave filter according to claim 1, wherein an electrode finger width or an electrode finger interval is gradually reduced from an adjacent comb-shaped electrode side. 3. The surface acoustic wave filter according to claim 1, wherein an electrode finger width or an electrode finger interval is gradually increased from an adjacent comb-shaped electrode side. 4. The surface acoustic wave filter according to claim 1, wherein at least one of the first and second reflector electrodes comprises at least two types of reflector electrode groups having different electrode finger widths or electrode finger intervals. 5. The surface acoustic wave filter according to claim 4, wherein the width of the electrode finger or the period of the electrode finger interval of the reflector electrode group is reduced from the side closer to the comb-shaped electrode. 6. The surface acoustic wave filter according to claim 4, wherein the width of the electrode finger or the period of the electrode finger interval of the reflector electrode group is increased from the side closer to the comb-shaped electrode. 7. The reflector electrode group adjacent to the comb-shaped electrode is 10
5. The surface acoustic wave filter according to claim 4, wherein the surface acoustic wave filter is configured by 30 to 30 electrode fingers. 8. The difference between the electrode finger widths or electrode finger interval widths of adjacent reflector electrode groups is determined by the reflector electrode pitch (electrode finger width + electrode finger width).
The surface acoustic wave filter according to claim 4, wherein the surface acoustic wave filter is set to 0.05% or more of an electrode finger interval width).