JPH0595250A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To suppress the lateral mode spurious radiation giving adverse effect onto the characteristic of the surface acoustic wave device. CONSTITUTION:The distance between bus bars 1A, 1B and 4A, 4B opposite to each other in a transducer formed on the surface of a piezoelectric substance is changed as lengths L1, L3 as to positive electrode fingers 2A, 2B, 2C attended with a change in the distance of a surface acoustic wave in the propagation direction and as lengths L2, L4 as to ground side electrode fingers 3A, 3B, 3C.

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,
In particular, the present invention relates to a surface acoustic wave device having characteristics improved by changing the structure of an electrode pattern.

[0002]

2. Description of the Related Art As shown in FIG. 6, a conventional surface acoustic wave device includes an input side + side bus bar 21A and a ground side bus bar 21.
At least two transducers, that is, a transducer made of B and a transducer made of + side bus bar 24A on the output side and a transducer made of ground side bus bar 24B, are provided on the surface of the piezoelectric substrate. In addition, each bus bar 21A, 21B
Are + side electrode fingers 22A to 22C and ground side electrode fingers 23A to 2C.
3C are opposed to each other with a predetermined gap. Further, the lengths of the facing portions of this electrode pattern are all the same for L20. The electrode fingers on the output side have the same structure. Now, the surface acoustic wave propagates from the electrode fingers 22A to 22C and from the electrode fingers 25A to 25C, but the length L20 is constant with respect to the propagation direction. FIG. 5 shows the transmission characteristics of this surface acoustic wave device. That is, fo has a pass band of about ± 0.1 MHz around 45 MHz, for example, but as shown in FIG. 5, the transverse mode spurious 27 may appear.

[0003]

The surface acoustic wave device having the conventional electrode pattern structure has a drawback in that spurious due to transverse mode coupling between the transducers is likely to occur and adversely affects the characteristics of the surface acoustic wave device. ..

[0004]

In the surface acoustic wave device of the present invention, at least two or more transducers are provided on the surface of a piezoelectric substrate, in which electrode fingers facing each other in a comb tooth shape are arranged at predetermined intervals on each of the + side bus bars. In the surface acoustic wave device, the pair of the positive side electrode finger and the ground side electrode finger facing each other have a length in the direction perpendicular to the propagation direction of the surface acoustic wave in the propagation direction of the surface acoustic wave. It changes as the distance changes.

[0005]

The present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing an electrode pattern according to the first embodiment of the present invention. The embodiment of FIG. 1 has a + side bus bar 1A and a ground side bus bar 1B as a transducer on the input side and a + side bus bar 4A and a ground side bus bar 4B as an output transducer on the surface of the piezoelectric substrate. In addition, the bus bars 1A, 1B have positive electrode fingers 2A, 2B, 2C.
(Six in the figure) and the ground-side electrode fingers 3A, 3B, 3C are opposed to each other with a predetermined space therebetween. The same applies to the electrode fingers of the output side bus bars 4A and 4B. Here, the length L5 of the facing portion is changed by L1 when comparing the electrode fingers 2A and 2B, and is changed by L3 when comparing the electrode fingers 2B and 2C. Also, the ground side electrode fingers 3A, 3
In B, the length of the facing portions on both sides of the electrode finger is L, respectively.
Only 2 and L4 are changed. In this way, the distance between the opposing electrode fingers is changed in accordance with the change in the distance in the propagation direction of the surface acoustic wave. Therefore, since the reflected wave is easily scattered by the bus bar portion of the surface acoustic wave, it is possible to prevent the generation of the transverse mode and suppress the spurious due to the transverse mode coupling between the transducers. FIG. 4 is a characteristic diagram showing transmission characteristics when the electrode pattern of FIG. 1 is used. As can be seen by comparing FIGS. 4 and 5, the transverse mode spurious generated when the conventional electrode pattern is used is suppressed and erased when the electrode pattern of the present invention is used.

A second embodiment of the present invention is a plan view of the electrode pattern of FIG. 2, a plan view of the electrode pattern of FIG. 2 shown in FIG. 3 and a partially enlarged view of the electrode pattern of FIG. 2 shown in FIG. Will be explained. In FIG. 2, the input side transducer is composed of the + side bus bar 7A and the ground side bus bar 7B, and the output side transducer is composed of the + side bus bar 10A and the ground side bus bar 10B. Here, the + side electrode fingers 8A and 8B have different lengths of the facing surfaces, and the distance between the two electrode fingers is changed in a tapered shape. The electrode fingers 9A and 9B on the installation side also have different lengths of the facing surfaces, and the distance between the two electrode fingers is changed in a tapered manner. That is, FIG.
As shown in, the lengths L7 and L8 are tapered from the inside of the + side electrode finger 8A toward the opposite side of the ground side electrode finger 9A such that L7> L8, and as described in the first embodiment. The reflected waves are easily scattered at L7 and L8 of both bus bar portions and each subsequent position to prevent generation of a transverse mode.

[0007]

As described above, according to the present invention, the length in the direction perpendicular to the propagation direction of the opposing surfaces of the pair of bus bars composed of the + side and the ground side bus bars changes in the propagation direction of the surface acoustic wave. By changing it, there is an effect that the adverse effect on the surface acoustic wave device due to the transverse mode spurious can be prevented.

[Brief description of drawings]

FIG. 1 is a plan view of a first embodiment of the present invention.

FIG. 2 is a plan view of a second embodiment of the present invention.

FIG. 3 is a partially enlarged view of the second embodiment.

FIG. 4 is a characteristic diagram of the first embodiment.

FIG. 5 is a characteristic diagram of a conventional example.

FIG. 6 is a plan view of a conventional surface acoustic wave device.

[Explanation of symbols]

1A, 1B, 4A, 4B, 7A, 7B, 10A, 10B
Bus bar 2A-2C, 5A-5C, 8A-8C, 11A-11C
+ Side electrode fingers 3A to 3C, 6A to 6C, 9A to 9C, 12A to 12C
Ground electrode finger

Claims (2)

[Claims] 1. A surface acoustic wave device provided with at least two or more transducers on a surface of a piezoelectric substrate, wherein electrode fingers facing each other in a comb tooth shape are arranged at a predetermined interval on each of the + side bus bars. It is characterized in that a pair of facing electrode fingers and ground-side electrode fingers change the length in the direction perpendicular to the propagation direction of the surface acoustic wave as the distance in the surface acoustic wave propagation direction changes. And surface acoustic wave device. 2. In the gap between the + side electrode finger and the ground side electrode finger facing the + side electrode finger, the length in the direction perpendicular to the carrying direction of the surface acoustic wave is the direction in which the surface acoustic wave propagates. The surface acoustic wave device according to claim 1, wherein the length is reduced in a taper shape with a change in distance.