JPH1141056A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce re-excitation of a surface acoustic wave while minimizing changes in a frequency characteristic. SOLUTION: A cross length L1 of each crossing of 1st and 2nd electrode fingers 33, 34 of one comb-shaped electrode 30 of a pair of comb-shaped electrodes placed side by side on a piezoelectric substrate is made different to obtain a desired frequency characteristic, while a line L2 tying centers C1 of each cross lengthwise direction is tilted by a prescribed angle in the extending direction of the 1st and 2nd connection sections 31, 32 so as to reduce re- excitation of a surface acoustic wave. The 1st and 2nd electrode fingers 31, 32 are configured respectively by a pair of split electrode fingers 33a, 33b, and 34a, 34b, while the length of the split electrode fingers 33a, 33b, 34a, 34b in parts is selected differently to change freely the gradient of the line L2 tying the centers C1 without changing each cross difference length L1.

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 device in which a pair of comb-like electrodes are arranged on a piezoelectric substrate in the direction of surface acoustic wave propagation to obtain a predetermined frequency characteristic.

[0002]

2. Description of the Related Art Conventionally, in this type of surface acoustic wave filter device, as shown in FIG. 5A, at least one of a pair of The first and second connecting portions 11 and 12 extend in parallel and in opposition to each other along the propagation direction, and extend from the first and second connecting portions 11 and 12 at right angles to each other and cross each other. A plurality of first and second electrode fingers 13 and 14 are provided, and a desired frequency characteristic is obtained by making the intersection length L1 of each intersection with the plurality of first and second electrode fingers 13 and 14 different. And the line L2 connecting the centers C1 of the intersections in the direction of the intersection length of each intersection is inclined by a predetermined angle with respect to the extending direction of the first and second connecting portions 11 and 12, so that the surface acoustic wave It is known to prevent re-excitation . In addition, it is shown in the lower part of FIG.
(ai) is a weighting coefficient indicating the ratio of each intersection length to the maximum intersection length. In each intersection, the case where the first electrode finger 13 is located on the right side in the drawing is represented by a negative value, and the second electrode finger 14 is located on the right side in the drawing. Is positively represented.

Conventionally, a plurality of first and second electrode fingers 13 and 14 are respectively connected to first and second connecting portions 11 and 12.
A pair of divided electrode fingers 13a divided into two in the extension direction of
It has also been known that the configuration of 13b, 14a, and 14b reduces reflection of surface acoustic waves to reduce the conversion loss of surface acoustic waves. Further, one of the comb-shaped electrodes 10
In addition, on the extension line of each of the divided electrode fingers 14a, 14b constituting the plurality of second electrode fingers 14, respectively, the first electrode 11 extends from the first connecting portion 11 to a position separated by a predetermined distance from the tip of the divided electrode finger 14a, 14b. The plurality of first dummy electrode fingers 15 and the divided electrode fingers 13 a and 13 b constituting the plurality of first electrode fingers 13, respectively, are extended along the second connecting portion 1.
2 and a plurality of second dummy electrode fingers 16 extending from the tips of the divided electrode fingers 13a and 13b by a predetermined distance to make the propagation state of the surface acoustic wave as uniform as possible. It has also been known that the surface acoustic wave waveform is not distorted.

[0004]

In the above-described conventional surface acoustic wave filter device, when the re-excitation of the surface acoustic wave is large as described above, the intersection length of each intersection is determined as shown in FIG. A line L2 connecting the centers C1 of the directions is a comb-shaped electrode 10 parallel to the extending direction of the first and second connecting portions 11 and 12,
First and second connecting portions 11, 1 of a line L2 connecting the same center C1
It was necessary to adjust the angle of inclination of the No. 2 with respect to the extending direction to configure as shown in FIG. Further, as shown in FIG. 4 (C), when the inclination of the line L2 connecting the center C1 with respect to the extending direction of the first and second connecting portions 11 and 12 is too large, it is impossible to geometrically configure the electrode. In this case, it was necessary to form the comb-teeth-shaped electrode 10 as shown in FIGS.

However, when the inclination is changed, it is necessary to correct the intersection length L1 of the first and second electrode fingers 13 and 14 (substantially the same as the weighting coefficient ai). For example, in the comb-shaped electrode of FIG.
The weighting coefficients ai of “7” and “0.6” are changed to “−0.9” and “0.4” as shown in FIG. This means a change in the frequency characteristic, and in the actual design, a compromise between the re-excitation and the problem that the electrode cannot be configured geometrically and the problem that the frequency characteristic changes is adopted. Was.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to address the above-described problem, and has as its object to minimize the change in the frequency characteristic and minimize the line L2 connecting the centers C1 of the intersections in the direction of the intersection length. To provide a surface acoustic wave filter device that can be relatively freely inclined with respect to the extending direction of the first and second connecting portions to reduce re-excitation of surface acoustic waves. .

In order to achieve the above object, the first aspect of the present invention is described.
The feature of the present invention is that a pair of comb-shaped electrodes are arranged side by side in the propagation direction of the surface acoustic wave on the piezoelectric substrate, and at least one of the comb-shaped electrodes is parallel and opposed to each other along the propagation direction of the surface acoustic wave. And a plurality of first and second electrode fingers extending in a direction perpendicular to the first and second connection portions and intersecting with each other. The intersection lengths of the respective intersections with the first and second electrode fingers are made different from each other, and a line connecting the centers of the intersections in the direction of the intersection length is inclined by a predetermined angle with respect to the extending direction of the first and second connection parts. In the surface acoustic wave filter device, the plurality of first and second electrode fingers are each constituted by a pair of divided electrode fingers that are divided into two in the direction in which the first and second connecting portions extend, and each pair of divided electrode fingers is divided into two. That is, the lengths of the electrode fingers are different from each other.

In the first aspect of the present invention, the first
Since each of the first and second electrode fingers is composed of a pair of split electrode fingers, one intersection between the first electrode finger and the second electrode finger is caused by one split electrode finger and the second electrode finger of the adjacent first electrode fingers. This is realized by the intersection of one split electrode finger of the finger. And
The other split electrode finger of the first electrode finger is the second split electrode finger on the opposite side.
It is used to realize the intersection with the electrode finger,
The other split electrode finger of the second electrode finger is also the first electrode finger on the opposite side.
It will be used to realize the intersection with the electrode finger. In the first aspect, the length of each of the pair of divided electrode fingers of the first and second electrode fingers is made different from each other, so that one of the divided electrode fingers of the first electrode finger and the second electrode finger have the same length. Without changing the intersection length of the intersection of one split electrode finger of the electrode fingers, that is, the intersection length between the first electrode finger and the second electrode finger, the position of the intersection is determined by extending the first and second electrode fingers. It can be set relatively freely in the installation direction, that is, the center of each intersection in the direction of the intersection length can be relatively freely moved in the direction of the intersection length. Therefore, according to the first aspect of the present invention, the first electrode finger and the second electrode finger
A line connecting the centers of the intersections in the direction of the intersection length of each intersection can be relatively freely inclined with respect to the extending direction of the first and second connecting portions without changing the intersection length of each intersection with the electrode finger. Since the change in the frequency characteristics of the surface acoustic wave filter device can be minimized, re-excitation of the surface acoustic wave can be satisfactorily prevented.

A second feature of the present invention is that at least one of the comb-shaped electrodes is divided from the first connecting portion on the extension of each of the divided electrode fingers constituting the plurality of second electrode fingers. A plurality of first dummy electrode fingers each extending to a position separated by a predetermined distance from the tip of the electrode finger;
A plurality of second dummy electrode fingers each extending from the second connecting portion to a position separated by a predetermined distance from the tip of the split electrode finger on an extension of each split electrode finger constituting the electrode finger; The tip of a part of the plurality of first and second dummy electrode fingers is cut off to form a floating electrode, and the remaining part of the tip of the part of the dummy electrode finger is cut off from the first and second dummy electrode fingers. This is to prevent the electrode fingers from intersecting.

In the second feature of the present invention, a tip of a part of the plurality of first and second dummy electrode fingers is cut off to form a floating electrode, and a tip of the part of the dummy electrode finger is separated. Since the remaining portion obtained by separating the portion does not intersect the first and second electrode fingers, even if the lengths of the pair of divided electrode fingers constituting the first or second electrode finger are significantly different, the first electrode finger can be used. Alternatively, the second dummy electrode finger can be effectively provided, and the floating electrode can effectively function as the dummy electrode. As a result, the second aspect of the present invention
According to the feature of the first aspect, in addition to the effect of the feature of the first aspect, it is possible to make the propagation state of the surface acoustic wave on the piezoelectric substrate substantially uniform so that the waveform of the surface acoustic wave is not distorted, The signal transmission characteristics of the surface acoustic wave filter device can be improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the surface acoustic wave filter device as viewed from above.

The surface acoustic wave filter device includes a piezoelectric substrate 20 formed of a piezoelectric material such as lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), quartz, or the like into a thin rectangular parallelepiped shape. On the piezoelectric substrate 20, a comb-shaped electrode 30 formed in an apodized shape in the propagation direction of the surface acoustic wave.
And a comb-shaped electrode 40 configured in a normalized form. A well-known comb-shaped electrode 40 can be used as the normalized electrode 40 and is not directly related to the present invention.

As shown in FIGS. 2 and 3, the comb-teeth-shaped electrode 30 has first and second connecting portions 3 formed by a conductor band.
1, 32 and a plurality of first and second electrode fingers 33, 34
It has. The first and second connecting portions 31 and 32 are parallel and opposed to each other at a predetermined distance and extend in the propagation direction of the surface acoustic wave (the direction of the arrow in the drawing). The plurality of first and second electrode fingers 33 and 34 are connected to the first and second connection portions 3.
1 and 32 extend perpendicularly to each other and intersect each other. Each first electrode finger 33 is divided into two in the extending direction of the first and second connecting portions 31 and 32 in order to reduce the reflection of the surface acoustic wave and reduce the conversion loss of the surface acoustic wave. Each of the pair of divided electrode fingers 33a and 33b has a different length. Each of the second electrode fingers 34 is also constituted by a pair of divided electrode fingers 34a and 34b divided into two in the extending direction of the first and second connecting portions 31 and 32 for the same reason as described above. And the divided electrode fingers 34a, 34
b is also set to different lengths.

In this case, the first electrode finger 33 and the second electrode finger 3
4, ie, the first electrode finger 33
Divided electrode finger 33a and divided electrode finger 34 of second electrode finger 34
A predetermined frequency characteristic is obtained by the intersection length L1 of each intersection with the b and the intersection length L1 of each intersection between the divisional electrode finger 33b of the first electrode finger 33 and the divisional electrode finger 34a of the second electrode finger 34. They are different for each. A line L2 connecting the centers C1 of the respective intersections in the direction of the intersection length is formed at a predetermined angle with respect to the extending direction of the first and second connecting portions 31, 32 in order to prevent re-excitation of surface acoustic waves. Just leaning. (Ai) shown in the lower part of FIGS. 2 and 3 is a weighting coefficient indicating the ratio of each intersection length to the maximum intersection length, and in the case where the first electrode finger 33 is located on the right side in each intersection (the divided electrode finger). 33a and 34b intersect) with a negative value,
The case where the second electrode finger 34 is located on the right side in the drawing (the case where the divided electrode fingers 33b and 34a intersect) is represented by a positive value.

In order to make the propagation state of the surface acoustic wave as uniform as possible, the comb-shaped electrode 30 is composed of first and second conductive strips extending from the first and second connecting portions 31 and 32, respectively. Second dummy electrode fingers 35 and 36 are provided. Each of the first dummy electrode fingers 35 is connected to each of the divided electrode fingers 34a and 34b.
Of the divided electrode finger 34 from the first connecting portion 31
a, 34b are extended to a position separated by a predetermined distance from the distal end. Each second dummy electrode finger 36 extends from the second connecting portion 32 to a position separated by a predetermined distance from the tip of the divided electrode finger 33a, 33b on an extension of each of the divided electrode fingers 33a, 33b.

A plurality of first and second dummy electrode fingers 35, 3
6, the distal ends of the dummy electrode fingers are cut off and configured as floating electrodes 35a and 36a as shown in FIG.
The remaining portions of the dummy electrode fingers 35, 36 from which the floating electrodes 35a, 36a are separated are first and second electrode fingers 33, 36.
It does not cross the 34 divided electrode fingers 33a, 33b, 34a, 34b. The floating electrodes 35a, 35
6a is the divided electrode fingers 33a, 33 of the electrode fingers 33, 34.
b, 34a, 34b and the dummy electrode fingers 35, 36.

Next, the operation of the embodiment configured as described above will be described. Generally, in this type of surface acoustic wave filter device, when re-excitation of surface acoustic waves is large,
As shown in FIG. 4A, the center C1 of each intersection in the intersection length direction.
A line L2 connecting the center C1 to a comb-shaped electrode 30 parallel to the extending direction of the first and second connecting portions 31 and 32
It is necessary to adjust the inclination angle of the first and second connecting portions 31 and 32 with respect to the extending direction of the first and second connecting portions 31 and 32 so as to be configured as shown in FIG. Further, as shown in FIG. 4 (C), when the inclination of the line L2 connecting the center C1 with respect to the extending direction of the first and second connecting portions 31 and 32 is too large, it is impossible to geometrically configure an electrode. In this case, it is necessary to form the comb-shaped electrode 30 as shown in FIGS.

First, a case where the inclination does not need to be largely changed will be described with reference to FIG. Each intersection of the first and second electrode fingers 33, 34
This is realized by the intersection between the electrodes 4b and 33a and the intersection between the divided electrode fingers 33b and 34a. Therefore, the split electrode finger 3
Even if the intersection length between 4b and 33a is set to a predetermined value (for example, the weighting coefficient ai is set to "-0.7") and the intersection position is set to a predetermined position, the length of the split electrode finger 33b is changed to the same electrode finger. The length of the split electrode finger 33a that is paired with the split electrode finger 33a is different from the length of the split electrode finger 34a adjacent to the same electrode finger 33b.
By appropriately determining the length of the divided electrode fingers 33b,
It is possible to change the intersection position while maintaining the intersection length between 34a at a predetermined value (for example, the weighting coefficient ai is “0.6”). Conversely, after appropriately setting the intersection length and the intersection position between the divided electrode fingers 33b and 34a,
The same applies when the lengths of b and 33a are both changed. Thus, while maintaining each intersection length L1 (each weighting coefficient ai) at a predetermined value, each intersection position (the center C1 of each intersection) can be relatively freely set in the extending direction of the first and second electrode fingers 33, 34. Can be moved.

That is, according to the above-described embodiment, a pair of divided electrode fingers 33a, 33a, of the first and second electrode fingers 33, 34, respectively.
Since the lengths of 33b and 34a, 34b are made different from each other, the line L2 connecting the centers C1 of the respective intersections can be changed without changing the intersection length L1 of the first and second electrode fingers 33, 34. The first and second connecting portions 31 and 32 can be relatively freely inclined with respect to the extending direction. As a result, the change in the frequency characteristics of the surface acoustic wave filter device can be minimized, and the re-excitation of the surface acoustic wave can be favorably prevented.

Next, a case where the inclination of the line L2 connecting the centers C1 of the respective intersections needs to be largely changed will be described with reference to FIG. Also in this case, the length of each of the pair of divided electrode fingers 33a, 33b and 34a, 34b of the first and second electrode fingers 33, 34 is maintained in a state where each intersection length L1 (each weighting coefficient ai) is kept at a predetermined value. Are different from each other,
The point of changing each intersection position (the center C1 of each intersection) is the same. However, in this case, the divided electrode fingers 33a, 3
In relation to greatly changing the length of 3b, 34a, 34b,
Divided electrode finger whose length has been changed (eg, divided electrode finger 33b)
May intersect with a dummy electrode finger (for example, the second dummy electrode finger 36) on the extension of the split electrode finger (for example, the split electrode finger 33a) paired with the same split electrode finger. In this case, according to the above embodiment, the dummy electrode finger (for example, the second
Since the tip of the dummy electrode finger 36 is cut off to form a floating electrode (for example, the floating electrode 36a), the remaining dummy electrode finger (for example, the second dummy electrode finger 36) from which the floating electrode is separated is divided electrode finger. (Eg, split electrode finger 33b)
Can be avoided.

That is, according to the above-described embodiment, a part of the dummy electrode fingers of the first and second dummy electrode fingers 35, 36 is cut off to form floating electrodes 35a, 36a. The remaining portion of the electrode finger from which the distal end is cut off is prevented from intersecting the first and second electrode fingers 33 and 34, so that the first or second dummy electrode fingers 35 and 36 can be provided effectively. In addition, the floating electrodes 35a, 3
6a also acts as a kind of dummy electrode, and the first and second
Like the dummy electrode fingers 35 and 36, the surface acoustic wave propagates on the piezoelectric substrate 20 so as to make the propagation state substantially uniform, so that the waveform of the surface acoustic wave can be prevented from being distorted. The signal transmission characteristics of the filter device can be improved.

In the above embodiment, the first dummy electrode finger 35, the second dummy electrode finger 36 and the floating electrode 35
Since a and 36a make the propagation state of the surface acoustic wave uniform, if the propagation state of the surface acoustic wave is uniform without providing these dummy electrode fingers 35 and 36 and floating electrodes 35a and 36a, It is not necessary to provide the dummy electrode fingers 35 and 36 and the floating electrodes 35a and 36a.

Further, in the above-described embodiment, an example has been described in which the lengths of all the paired divided electrode fingers 33a, 33b and 34a, 34b are different from each other, but the inclination of the line L2 connecting the centers C1 of the respective intersections is described. In some cases, the lengths of the pair of divided electrode fingers 33a, 33b and 34a, 34b may be made different from each other, and therefore, the present invention provides the partial electrode fingers 33a, 33b and 34a, 34b.
The present invention is also applicable to surface acoustic wave filter devices having different lengths. In addition, the floating electrodes 35a, 36a
The present invention is partially related to the floating electrode 35.
a, 36a can also be applied to the surface acoustic wave filter device.

Further, in the above embodiment, only one of the pair of comb-shaped electrodes 30, 40 is formed of the apotized electrode according to the present invention, but a multi-strip coupler is provided. By devising such methods, both the comb-tooth electrodes 30 and 40 may be constituted by the apotized electrode according to the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic view of a surface acoustic wave filter device according to an embodiment of the present invention as viewed from above.

FIG. 2 is a plan view showing an example in which a part of one comb-shaped electrode of FIG. 2 is enlarged.

FIG. 3 is a plan view showing another example in which a part of the comb-shaped electrode is enlarged.

FIGS. 4A to 4C are schematic plan views of the comb-tooth electrode for explaining the state of inclination of the center of the intersection of the comb-tooth electrode.

FIGS. 5A and 5B are plan views showing a conventional comb-shaped electrode.

[Explanation of symbols]

20: piezoelectric substrate, 30, 40: comb-shaped electrode, 31, 32
... Connecting parts, 33, 34 ... Electrode fingers, 33a, 33b, 34
a, 34b ... divided electrode fingers, 35, 36 ... dummy electrode fingers,
35a, 36a: floating electrodes.

Claims (2)

[Claims] A pair of comb-shaped electrodes are arranged on a piezoelectric substrate in the propagation direction of a surface acoustic wave, and at least one of the comb-shaped electrodes is parallel and relatively parallel to the propagation direction of the surface acoustic wave. And a plurality of first and second electrode fingers extending in a direction perpendicular to the first and second connection parts and intersecting with each other. The intersection lengths of the intersections with the plurality of first and second electrode fingers are made different from each other, and a line connecting the centers of the intersections in the direction of the intersection length is formed with respect to the extending direction of the first and second connection parts. In the surface acoustic wave filter device tilted by a predetermined angle, the plurality of first and second electrode fingers are each constituted by a pair of divided electrode fingers that are divided into two in the extending direction of the first and second connecting portions. And the length of each pair of split electrode fingers is different from each other. Surface acoustic wave filter device. 2. The surface acoustic wave filter device according to claim 1, wherein at least one of the comb-like electrodes has:
A plurality of first dummies each extending from the first connection portion to a position separated by a predetermined distance from a tip of the split electrode finger on an extension of each split electrode finger constituting each of the plurality of second electrode fingers. An electrode finger and a plurality of electrodes each extending from the second connection portion to a position separated by a predetermined distance from the tip of the same electrode finger on the extension of each of the electrode fingers constituting the plurality of first electrode fingers. Of the plurality of first and second dummy electrode fingers, and the leading ends of the dummy electrode fingers are cut off to form floating electrodes, and the leading ends of the dummy electrode fingers are The surface acoustic wave filter device is characterized in that the separated remaining portion does not cross the first and second electrode fingers.