JPH03173212A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To reduce a ripple due to a triple transit echo TTE and to attain high performance by dividing a surface acoustic wave propagation path of one of interdigital electrode finger pairs and shifting the path by a dimension corresponding to equivalent to the wire width of the interdigital electrode finger in the direction of propagation. CONSTITUTION:Input electrode fingers 4 set singly are provided on a piezoelectric substrate 1 and output electrode fingers 3 are divided in the middle and shifted in the direction of propagation. In figure, l1 is a line width of the electrode fingers and equal to 1/4 of the wavelength of the surface acoustic wave with respect to the center frequency. The dimension A to be deviated is equivalent to the line width l1. The phase of a reflected wave is inverted by deviating the electrode fingers 3 by a dimension equivalent to the line width in the direction of propagation and the ripple in the usual band is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a surface acoustic wave filter used in video equipment, communication equipment, etc.

Conventional technology A conventional surface acoustic wave filter will be explained below.

FIG. 3 is a plan view of a piezoelectric body of a conventional surface acoustic wave filter. In FIG. 3, 1 is a piezoelectric substrate, and 2 is a pair of comb-shaped electrode fingers.

Problems to be Solved by the Invention However, in the conventional configuration, the surface acoustic waves generated at the input side electrode are reflected at the output side electrode, and the returning surface acoustic waves are further reflected at the input side electrode and enter the output side electrode. Therefore, the so-called triple transitionotoe: 7- (Trip
This has a problem in that ripples are likely to occur within the normal band due to transit echo (hereinafter abbreviated as TTE). This TTE can be reduced by using a double electrode structure with a linewidth of one-eighth of the wavelength, but if a piezoelectric material with a large electromechanical coupling coefficient is used or the number of pairs of interdigitated electrodes is large, the ripple due to TTE can be reduced. is likely to occur.

The present invention solves the above-mentioned problems, and aims to provide a high-performance surface acoustic wave filter in which the ripple within the passband is reduced by reducing TTli:.

Means for Solving the Problems In order to achieve this object, the surface acoustic wave filter of the present invention divides the surface acoustic wave propagation path of one pair of comb-shaped electrode fingers, and divides the surface acoustic wave propagation path of one pair of comb-shaped electrode fingers to correspond to the line width of the comb-shaped electrode fingers. It has a configuration in which the dimensions are shifted in the propagation direction.

Effect With this configuration, the reflection at the comb-shaped electrode fingers is due to the difference in acoustic impedance between the edge portions of the electrode fingers, so when the light is incident from a part not covered with metal to a part covered with metal, and vice versa, Since the phases of the reflected waves are reversed, the phases of half of the simultaneously incident surface acoustic waves are reversed and reflected, and they cancel each other out, reducing the TTE and reducing ripples.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a plan view of a piezoelectric body of a surface acoustic wave filter in a first embodiment of the present invention. 1st
In the figure, input electrode fingers 4 and output electrode fingers 3, which are single set on a piezoelectric substrate 1, are divided at the center and shifted in the direction of propagation of surface waves. I'i will be established. l is the line width of the electrode finger, which is one quarter of the wavelength of the surface acoustic wave corresponding to the center frequency.

The shifting dimension a is set to a length equivalent to the line width e1 of the electrode finger.

FIG. 2 is a plan view of a piezoelectric body of a surface acoustic wave filter showing a second embodiment of the present invention. In the same figure, piezoelectric substrate 1
The input electrode finger 6 and the output electrode finger 6 set double on the
The structure is divided into sections and shifted in the direction of surface wave propagation.
Its position is that the center dimension d2 is 1, the both end dimensions d1 and d
5, so that d2=d, +43. 12 is the line width of the electrode finger, which is one-eighth of the wavelength of the surface acoustic wave corresponding to the center frequency. The dimension opening to be shifted in the propagation direction has a length equivalent to the line width 12 of the electrode finger.

As described above, according to the first and second embodiments, by shifting the electrode fingers in the propagation direction by a dimension equivalent to the line width, the phase of the reflected wave can be inverted, and the ripple within the normal band can be reduced. can do.

Note that the electrode pair to be shifted may be either one or both of the input side and output side.

Effects of the Invention As described above, the present invention can realize an excellent surface acoustic wave filter that can reduce ripples due to TTX even when a material with a large electromechanical coupling coefficient is used or the number of logarithms is large.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a piezoelectric body of a surface acoustic wave filter according to a first embodiment of the present invention, FIG. 2 is a plan view of a piezoelectric body of a surface acoustic wave filter according to a second embodiment of the present invention, and FIG. The figure is a plan view of a piezoelectric body of a conventional surface acoustic wave filter. 1... Piezoelectric substrate, 3, 6... Output electrode finger, 4゜6... Input electrode finger, l, , 12...
Line width of electrode finger, a. Mouth: Dimension to shift the electrode finger.

Claims (3)

[Claims] (1) Two or more pairs of comb-shaped electrode fingers are provided in the same propagation path of surface acoustic waves, the propagation path is divided by at least one pair of comb-shaped electrode fingers, and each electrode finger is connected to the electrode A surface acoustic wave filter that is shifted in the propagation direction by a dimension equivalent to the line width of a finger. (2) The surface acoustic wave filter according to claim 1, wherein the line width of the comb-shaped electrode finger pairs that divide the propagation path is one-fourth of the wavelength of the surface acoustic wave corresponding to the center frequency. (3) The surface acoustic wave filter according to claim 1, wherein the line width of the comb-shaped electrode finger pairs that divide the propagation path is one-eighth of the wavelength of the surface acoustic wave corresponding to the center frequency.