JP3166235B2 - Surface acoustic wave device - Google Patents

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 improved characteristics 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 has an input side bus bar 21A and a ground side bus bar 21A.
At least two transducers are provided on the surface of the piezoelectric substrate, that is, a transducer composed of B and a transducer composed of an output-side bus bar 24A and a ground-side bus bar 24B. In addition, each bus bar 21A, 21B
Are the positive electrode fingers 22A to 22C and the ground electrode fingers 23A to 2
3C are opposed to each other with a predetermined interval. Further, the lengths of the opposing portions of the electrode pattern are all the same in L20. The output electrode fingers 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, and the length L20 is constant in the propagation direction. FIG. 5 shows the transmission characteristics of this surface acoustic wave device. That is, fo, for example, has a pass band of about ± 0.1 MHz centered at 45 MHz, but as shown in FIG. 5, the transverse mode spurious 27 sometimes appeared.

[0003]

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

[0004]

A surface acoustic wave device according to the present invention comprises a comb-shaped ground electrode and a comb-shaped ground electrode on each of a + bus bar and a ground bus on the surface of a piezoelectric substrate.
In a surface acoustic wave device provided with at least two or more transducers in which fingers are arranged to face each other at a predetermined interval, the positive electrode finger and the ground electrode finger face each other.
The opposing length is kept constant, and the tip of the
In the gap between the tip and the ground-side bus bar
The length in the direction perpendicular to the propagation direction of the surface acoustic wave;
The + side where the tip of the ground-side electrode finger faces the tip
Propagation direction of surface acoustic wave in gap between bus bar
The length in the direction perpendicular to the direction in which the surface acoustic wave propagates
In a tapered shape as the distance in the direction changes.
You. In addition, the surface acoustic wave device of the present invention is applied to the surface of the piezoelectric substrate.
Comb tooth-shaped + for each of the + busbar and the ground bus
The side electrode finger and the comb-shaped ground electrode finger
Input transducer and output placed opposite each other at a distance
In the surface acoustic wave device provided with the side transducer,
The ground side where the tip of the + side electrode finger and the tip face each other
Propagation direction of surface acoustic wave in gap between bus bar
And the length in the vertical direction with respect to the tip of the ground-side electrode finger.
In the gap between the above-mentioned + busbar and the opposite end,
Length in the direction perpendicular to the surface acoustic wave propagation direction
In the input transducer, an elastic surface
Taper shape with change in distance in the direction of wave propagation
And the output transducer has an elastic
Due to the change in distance in the direction in which
It is enlarged like a pa.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing an electrode pattern according to a first embodiment of the present invention. In the embodiment shown in FIG. 1, a positive side bus bar 1A and a ground side bus bar 1B are provided on the surface of the piezoelectric substrate as input-side transducers, and a positive side bus bar 4A and a ground side bus bar 4B are provided as output transducers. The bus bars 1A and 1B are connected to the + side electrode fingers 2A, 2B and 2C.
(Six in the figure) and the ground-side electrode fingers 3A, 3B, 3C oppose each other with a predetermined interval. 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 finger 2B and the electrode finger 2C. Also, the ground-side electrode fingers 3A, 3
B also has the length of the opposing portions on both sides of the electrode finger L, respectively.
Only 2 and L4 are changed. 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, the reflected wave is easily scattered at the bus bar portion of the surface acoustic wave, so that the occurrence of the transverse mode can be prevented, and the spurious due to the transverse mode coupling between the transducers can be suppressed. 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 using the conventional electrode pattern is suppressed and eliminated when using the electrode pattern of the present invention.

Next, a second embodiment of the present invention will be described with reference to 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. This will be described below. In FIG. 2, the input-side transducer includes a positive-side bus bar 7A and a ground-side bus bar 7B, and the output-side transducer includes a positive-side bus bar 10A and a ground-side bus bar 10B. Here, the lengths of the opposing surfaces of the positive electrode fingers 8A and 8B are different, and the interval between the two electrode fingers is changed in a tapered manner. The installation-side electrode fingers 9A and 9B also have different lengths of opposing surfaces, and the distance between the electrode fingers is changed in a tapered manner. That is, FIG.
As shown in the figure, the lengths L7 and L8 are tapered from the inside of the positive electrode finger 8A toward the opposite side of the ground electrode finger 9A so that L7> L8, as described in the first embodiment. The reflected waves are easily scattered at L7, L8 of each of the bus bar portions and at each subsequent position to prevent the occurrence of the 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 bus bar and the ground side bus bar changes with the change in the propagation direction of the surface acoustic wave. The effect of the change is that an adverse effect on the surface acoustic wave device due to the transverse mode spurious can be prevented.

[Brief description of the 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 finger 3A-3C, 6A-6C, 9A-9C, 12A-12C
Ground electrode finger

Continuation of front page (56) References JP-A-52-72137 (JP, A) JP-A-2-170610 (JP, A) JP-A-3-125511 (JP, A) JP-A-59-200519 (JP, A) , A) Japanese Utility Model Showa 58-177871 (JP, U) Japanese Utility Model Showa 59-169128 (JP, U) Japanese Utility Model Utility Model No. 4-114225 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB (Name) H03H 9/145

Claims (2)

(57) [Claims] 1. A positive side bus bar and a ground side on a surface of a piezoelectric substrate.
Each of the buses has a comb-shaped + side electrode finger and a comb tooth
Surface acoustic wave device provided with at least two or more transducers in which at least two transducers are arranged so as to face each other at a predetermined interval with respect to each other, the opposing length in which the + electrode finger and the ground electrode finger face each other.
And the ground side where the tip of the + electrode finger and the tip face each other.
Propagation direction of surface acoustic wave in gap between bus bar
And the length in the vertical direction with respect to the tip of the ground-side electrode finger.
In the gap between the above-mentioned + busbar and the opposite end,
Length in the direction perpendicular to the surface acoustic wave propagation direction
The surface acoustic wave device, characterized in that it is changed with the tapering change in distance in the direction in which the surface acoustic wave propagates. 2. A positive side bus bar and a ground side on a surface of a piezoelectric substrate.
Each of the buses has a comb-shaped + side electrode finger and a comb tooth
And ground electrode fingers facing each other at a predetermined interval.
Input and output transducers
In the surface acoustic wave device provided, the tip of the positive electrode finger and the ground side where the tip faces each other.
Propagation direction of surface acoustic wave in gap between bus bar
And the length in the vertical direction with respect to the tip of the ground-side electrode finger.
In the gap between the above-mentioned + busbar and the opposite end,
Length in the direction perpendicular to the surface acoustic wave propagation direction
In the input transducer, an elastic surface
Taper shape with change in distance in the direction of wave propagation
And the output transducer has an elastic
Due to the change in distance in the direction in which
A surface acoustic wave device characterized in that the surface acoustic wave device is enlarged in a pa shape .