JPH09181554A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize desired group delay characteristics by constituting input and output electrodes of inclined electrodes. SOLUTION: On a piezoelectric substrate 20, comb-shaped input electrode 30 and output electrode 40 are arranged side by side in the propagation direction of a surface acoustic wave. The both of the electrodes 30 and 40 are constituted of inclined electrodes and each center line L1 and L2 in the propagation direction of the surface acoustic waves at the both of the electrodes 30 and 40 are prevented from being in parallel to each other. Since the time when the surface acoustic wave converted from an electric signal at the input electrode 30 attains the output electrode 40 is different according to the locations along the center lines L1 and L2 and the frequency of the signal which is converted into a surface acoustic wave at the input electrode 30 and is reconverted into the electric signal at the output electrode 40 is different according to the locations along the center lines L1 and L2, the group delay time for the change of the frequency of the signal can be changed to an arbitrary characteristic by properly setting the inclinations of the center lines L1 and L2.

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 device suitable for use as a filter, and in particular, an elastic device in which comb-teeth-shaped input electrodes and output electrodes provided on a piezoelectric substrate are composed of inclined electrodes. The present invention relates to a surface wave device.

[0002]

2. Description of the Related Art Conventionally, this type of device is shown in FIG.
As shown in (B), a piezoelectric substrate 10 formed in a thin rectangular parallelepiped shape has comb-teeth-shaped input electrodes 11 and output electrodes 12 arranged in parallel in a direction in which a surface acoustic wave propagates. The plurality of electrode fingers of both electrodes 11 and 12 are respectively inclined with a predetermined curvature coefficient P (also referred to as power factor P). Then, both electrodes 11 and 12 are arranged such that lines (center lines L1 and L2) connecting center positions between both ends of the surface acoustic wave propagation direction of the electrodes 11 and 12 along the extending direction of the electrode fingers are parallel to each other. , 12 are arranged, and both electrodes 11, 12 are configured to be symmetrical with respect to the center lines L1, L2.

[0003]

However, in the above-described conventional surface acoustic wave device, the surface acoustic wave diffraction phenomenon, the beam deviation (beam steering), etc. cause the influence of FIG.
As shown in, the group delay time in the group delay characteristic becomes longer as the frequency becomes higher, and there is a problem that it is difficult to manufacture a surface acoustic wave device having a desired group delay characteristic. Usually, it is desirable that the group delay characteristic has a flat group delay time with respect to a change in frequency.

The present invention has been made to solve the above problems, and an object thereof is to provide a surface acoustic wave device capable of obtaining a desired group delay characteristic.

[0005]

In order to achieve the above-mentioned object, a structural feature of the present invention is that the input and output electrodes are composed of inclined electrodes, and each electrode has a surface acoustic wave propagating direction between both ends. Both electrodes are arranged so that the lines connecting the central positions along the extending direction of the electrode fingers are not parallel to each other.

In this case, for example, each line connecting the central positions between both ends in the propagation direction of the surface acoustic wave in each electrode along the extending direction of the electrode fingers is a straight line, and one end side between the respective lines is connected. It is preferable to configure both electrodes so that the distance is shorter than the distance on the other end side, or to configure both electrodes so that each line is a curve.

[0007]

In the surface acoustic wave device configured as described above, the respective lines connecting the respective central positions between both ends of the surface acoustic wave in the respective electrodes in the propagation direction of the electrodes are connected to each other along the extending direction of the electrode fingers. Since they are not parallel, the time until the surface acoustic wave converted from the electric signal at the input electrode reaches the output electrode differs depending on the position along each line connecting the central positions. On the other hand, in the inclined electrode, the frequency of the signal generally converted into the surface acoustic wave at the input electrode and reconverted into the electric signal at the output electrode depends on the position along each line connecting the central positions. Since it is determined, the difference in arrival times will change depending on the frequency of the propagated signal. Therefore, by appropriately setting the angle (excluding 0 degrees) formed by the line connecting the central positions of the input electrodes and the line connecting the central positions of the output electrodes, the group delay time can be changed to the frequency of the signal. On the other hand, it is possible to realize a surface acoustic wave device having a group delay characteristic that becomes flat, or a surface acoustic wave device in which the group delay time arbitrarily changes in response to a change in signal frequency. As a result, according to the present invention, a surface acoustic wave device having a desired group delay characteristic can be easily manufactured.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 (A) schematically shows a surface acoustic wave device according to the embodiment in a plan view.

This surface acoustic wave device comprises a piezoelectric substrate 2 formed of a piezoelectric material such as lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), and quartz in a thin rectangular parallelepiped shape.
0 is provided. An input electrode 30 and an output electrode 40 are arranged side by side on the piezoelectric substrate 20, an electric signal is converted into a surface acoustic wave by the input electrode 30, and the converted surface acoustic wave is shown on the piezoelectric substrate 20 by an arrow. The surface acoustic wave propagates in the direction and reaches the output electrode 40, and the surface acoustic wave reaching the output electrode 40 is converted into an electric signal again at the output electrode 40.

The input electrode 30 is formed on the left side of the piezoelectric substrate 20 in the drawing by a connecting portion 3 formed of a pair of strip-shaped conductors extending parallel to and facing each other in the propagation direction of the surface acoustic wave.
1 and 32 are provided. The connecting portion 31 is configured to be shorter than the connecting portion 32. The connecting portion 3 is connected to the connecting portions 31 and 32.
One end of each of a plurality of electrode fingers 33, 34 that are curvedly curved with a predetermined curvature coefficient so that the distance between the electrode fingers becomes longer from 1 toward the connecting portion 32, is connected to each electrode finger 33, 34. Intersect with each other with different lengths of intersection. The center position between the ends of the connecting portions 31, 32 and the electrode fingers 33, 34 in the surface acoustic wave propagation direction is set to the electrode finger 33,
A line connected along the extending direction of 34 (hereinafter, simply referred to as a center line L1 of the input electrode 30) is a straight line L10 (hereinafter simply referred to as a reference line L10) perpendicular to the extending direction of the connecting portions 31 and 32. On the other hand, the central position of the connecting portion 31 approaches the output electrode 40 and the central position of the connecting portion 32 is inclined in a direction away from the output electrode 40. The input electrode 30 is formed asymmetrically with respect to the center line L1 and the reference line L10. In this case, the center line L1 is a straight line.

The output electrode 40 is also composed of connecting portions 41, 42 and electrode fingers 43, 44 similar to the input electrode 30 on the upper surface of the piezoelectric substrate 20 on the right side in the drawing. Connection part 41,
A line connecting the central positions of the electrode 42 and the electrode fingers 43 and 44 in the propagation direction of the surface acoustic wave along the extending direction of the electrode fingers 43 and 44 (hereinafter, simply referred to as the center line L2 of the output electrode 40) is Straight line L20 perpendicular to the extending direction of the connecting portions 41 and 42
With respect to (hereinafter, simply referred to as reference line L20), the connecting portion 41
Is closer to the input electrode 30 and the central position of the connecting portion 42 is inclined in a direction away from the output electrode 30.
The output electrode 40 is formed asymmetrically with respect to the center line L2 and the reference line L20. In this case as well, the center line L2 is a straight line.

In the surface acoustic wave device configured as described above, the surface acoustic wave converted from the electric signal in the input electrode 30 propagates on the piezoelectric substrate 20 and reaches the output electrode 40, and the output electrode 40. Is converted back into an electrical signal at. In the conversion of this signal, the distance between the electrode fingers depends on the connecting portions 31, 4
Since it becomes longer from 1 toward the connecting portions 32, 42, the frequency of the signal converted into the surface acoustic wave at the input electrode 30 and re-converted into the electric signal at the output electrode 40 is equal to the connecting portion 31, It becomes lower from 41 toward the connecting portions 32 and 42. On the other hand, the center lines L1 and L2 of the electrodes 30 and 40 are not parallel to each other, and the distance between the center lines L1 and L2 is shorter on the side of the connecting portions 31 and 41 than on the side of the connecting portions 32 and 42. The time required for the surface acoustic waves converted by the electrode 30 to reach the output electrode 40 is
It becomes longer from 41 toward the connecting portions 32 and 42. As a result, the group delay time in the group delay characteristic of this surface acoustic wave device is corrected to become longer as the signal frequency becomes lower.

Therefore, the center lines L1 and L2 are so arranged that the distance between the center lines L1 and L2 becomes shorter on the connecting portions 31 and 41 side.
Is inclined with respect to the reference lines L10 and L20 by an appropriate angle, that is, the angle (0 between the center line L1 and the center line L2).
By appropriately setting (except the degree), the group delay time corresponding to the low frequency in the group delay characteristic shown in FIG. 9 (C) can be corrected to be long and the group delay time corresponding to the high frequency can be shortened. It is possible to realize a group delay characteristic as shown in FIG. 1B in which the group delay time becomes flat with respect to a change in frequency.

In the above embodiment, both electrodes 3
The distance between the center lines L1 and L2 of 0 and 40 is the connecting portion 31 and 4
Set both center lines L1 and L2 to the reference line L1 so that
Although it is arranged to incline in directions different from each other with respect to 0 and L20, as shown in FIG. 2A, the center line L2 of the output electrode 40 is not inclined with respect to the reference line L20, and the center of the input electrode 30 is Only the line L1 is connected to the reference line L10 by the connecting portion 31.
Tilt toward the side closer to the center line L2 of the output electrode 40,
The distance between the center lines L1 and L2 may be shortened on the connecting portions 31 and 41 side. On the contrary, the center line L1 of the input electrode 30 is not inclined with respect to the reference line L10, and only the center line L2 of the output electrode 40 is connected to the center line L1 of the input electrode 30 at the connecting portion 41 side with respect to the reference line L20. The distance between the center lines L1 and L2 may be shortened on the side of the connecting portions 31 and 41 by inclining toward the approaching side.

Further, as shown in FIG. 2B, both center lines L1 and L2 of both electrodes 30 and 40 are tilted in the same direction with respect to both reference lines L10 and L20, and one center line L1 or L2. May be increased so that the distance between the center lines L1 and L2 becomes shorter on the connecting portions 31 and 41 side.
2A and 2B, the connecting portions 31, 32, 41, 42 extend in parallel with the surface acoustic wave propagation direction.

Even if the above embodiment is modified as described above, the angle (other than 0 degree) formed by the center line L1 and the center line L2 is appropriately set to obtain the group delay characteristic shown in FIG. 9C. As shown in FIG. 1B, the group delay time corresponding to the low frequency can be corrected to be long and the group delay time corresponding to the high frequency can be corrected to be short, and the group delay time becomes flat with respect to the frequency change. Group delay characteristics can be realized.

Next, another modified example of the above embodiment will be described. FIG. 3A schematically shows a surface acoustic wave device according to the modified example in a plan view. Also in this case, the distance between the center lines L1 and L2 of both electrodes 30 and 40 is determined by the connecting portion 3
The center lines L1 and L2 are inclined in directions different from each other with respect to the reference lines L10 and L20 so that the center lines L1 and L2 are shortened on the 1st and 41th sides. Larger than the case. Therefore, in this case, the group delay time for a low frequency becomes longer and the group delay time for a higher frequency becomes shorter, so that the group delay characteristic of this surface acoustic wave device is as shown in FIG. Become. Also in this case, FIG. 2A of the above embodiment is also used.
In the same manner as in the modified example shown in (B), both electrodes 30, 40
One of the center lines L1 and L2 may be tilted, or both may be tilted in the same direction.

In another modification, as shown in FIG. 4 (A), the distance between the center lines L1 and L2 of both electrodes 30 and 40 is shortened on the connecting portions 32 and 42 side. Center line L1,
L2 is tilted in directions different from each other with respect to the reference lines L10 and L20. According to this, contrary to the above case, the group delay time for low frequencies becomes short and the group delay time for high frequencies becomes long, so the group delay characteristic of this surface acoustic wave device is as shown in FIG. 4 (B). become. Also in this case, similarly to the modification of the above-described embodiment as shown in FIGS. 2A and 2B, only one of the center lines L1 and L2 of both electrodes 30 and 40 may be inclined, or both of them may be inclined. You may make it incline in the same direction.

Although the center lines L1 and L2 are straight lines in each of the above-mentioned examples, a modification in which the center lines L1 and L2 are curved will be described below. This kind of modification is shown in FIG.
As shown in (A), both center lines L of both electrodes 30 and 40
Both electrodes 30, 40 are constructed so that 1 and L2 are curved. The distance between the center lines L1 and L2 is the connecting portion 31,
41 side and connecting parts 32, 42 side is shortened,
The center lines L1 and L2 are set so as to be long at the central positions of the connecting portions 31 and 41 and the connecting portions 32 and 42, respectively.
Bent in different directions with respect to 20. According to this, the group delay time for the low frequency band and the high frequency band becomes short, and the group delay time for the middle frequency band becomes long. Therefore, the group delay characteristic of this surface acoustic wave device is shown in FIG. As shown.

Further, in another modification, as shown in FIG. 6 (A), both electrodes 30, 40 are constructed such that both center lines L1, L2 of both electrodes 30, 40 are curved. The distance between the center lines L1 and L2 becomes longer on the side of the connecting portions 31 and 41 and on the side of the connecting portions 32 and 42, and the connecting portions 31 and 41 are
The center lines L1 and L2 are bent in directions different from each other with respect to the reference lines L10 and L20 so that the center lines L1 and L2 are shortened at the central positions of the connecting portions 32 and 42. According to this, the group delay time for the low frequency band and the high frequency band becomes long, and the group delay time for the middle frequency band becomes short. Therefore, the group delay characteristic of this surface acoustic wave device is shown in FIG. 6 (B). As shown.

The surface acoustic wave device shown in each of FIGS. 4 to 6A does not have a flat group delay time with respect to a change in frequency, as shown in the above embodiment, It is used for filters that require unique frequency characteristics. By thus making the center lines L1 and L2 straight and changing their inclinations, or making them curved and changing their curvatures, a surface acoustic wave device having an arbitrary group delay characteristic can be manufactured. .

Further, in the above-described embodiment and various modifications, the surface acoustic wave device in which the electrode fingers 33, 34, 43 and 44 are curved and weighted so that both electrodes 30 and 40 are inclined electrodes has been described. However, the present invention is shown in FIG.
As shown in FIG. 7A, the electrode fingers 33, 34, 43, 44 may be configured to be linear and weighted, or as shown in FIG.
(B) As shown in (C), electrode fingers 33, 34, 43, 4
4 is curved and is not weighted, or as shown in FIG. 7D, the electrode fingers 33, 34, 43,
The present invention can also be applied to a surface acoustic wave device having both electrodes 30 and 40 in which 44 is linear and is not weighted. Further, as shown in FIG. 8, electrode fingers 33, 34, 4
It can also be applied to a surface acoustic wave device having both electrodes 30, 40 in which 3, 44 are doubled.

[Brief description of the drawings]

FIG. 1A is a schematic plan view of a surface acoustic wave device showing an embodiment of the present invention, and FIG. 1B is a graph showing a group delay characteristic of the surface acoustic wave device.

FIG. 2A is a schematic plan view of a surface acoustic wave device showing a modified example of the above embodiment, and FIG. 2B is a schematic plan view of a surface acoustic wave device showing another modified example of the same embodiment. is there.

FIG. 3A is a schematic plan view of a surface acoustic wave device showing another modification of the embodiment of the present invention, and FIG. 3B is a group delay of the surface acoustic wave device according to the other modification. It is a graph which shows a characteristic.

FIG. 4A is a schematic plan view of a surface acoustic wave device showing another modification of the embodiment of the present invention, and FIG. 4B is a group delay of the surface acoustic wave device according to the other modification. It is a graph which shows a characteristic.

FIG. 5A is a schematic plan view of a surface acoustic wave device showing another modification of the above-described embodiment of the present invention, and FIG. 5B is a group delay of the surface acoustic wave device according to the other modification. It is a graph which shows a characteristic.

FIG. 6A is a schematic plan view of a surface acoustic wave device showing another modification of the above-described embodiment of the present invention, and FIG. 6B is a group delay of the surface acoustic wave device according to the other modification. It is a graph which shows a characteristic.

7A to 7D are schematic plan views of a surface acoustic wave device according to another application example of the present invention.

FIG. 8 is a schematic plan view of a surface acoustic wave device according to another application example of the present invention.

9A and 9B are schematic plan views of a conventional surface acoustic wave device, and FIG. 9C is a graph showing group delay characteristics of the surface acoustic wave device.

[Explanation of symbols]

20 ... Piezoelectric substrate, 30 ... Input electrodes, 31, 32 ... Connection parts, 33, 34 ... Electrode fingers, 40 ... Output electrodes, 41, 42
... Connection parts, 43, 44 ... Electrode fingers, L1, L2 ... Center line, L1
0, L20 ... Reference line.

Claims (3)

[Claims] 1. A surface acoustic wave device in which comb-teeth-shaped input electrodes and output electrodes are arranged in parallel on a piezoelectric substrate in a propagation direction of surface acoustic waves, and both electrodes are inclined electrodes. In the surface acoustic wave device, the electrodes are arranged so that the lines connecting the central positions between both ends of the surface acoustic wave in the propagation direction along the extending direction of the electrode fingers are not parallel to each other. 2. The lines connecting the respective central positions between both ends of the surface acoustic wave propagation direction of the respective electrodes along the extending direction of the electrode fingers are straight lines, and the distance between the respective lines on one end side is The surface acoustic wave device according to claim 1, wherein the both electrodes are configured to be shorter than the distance on the multi-end side. 3. The electrodes are configured such that each line connecting the central positions between both ends of the surface acoustic wave propagating direction in each electrode along the extending direction of the electrode fingers is a curve. The surface acoustic wave device according to claim 1.