JPS61120510A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain small-ripple characteristics by thinning out alternate close- interval parts of weighting double electrode fingers obtained by a specific electrode designing method, and providing a dummy electrode finger whose interval is one-third between electrode fingers at the thinned-out part. CONSTITUTION:A normal double electrodes 2 and a weighting double electrode 3 are arranged on a substrate 1 in which a surface acoustic wave is propagated. Electrode fingers a6-a10 among a1-a14 of the weighting double electrode 3 obtained by the specific electrode designing method are narrow in interval T and hardly formed by a photoetching method, so alternate electrode fingers a7 and a9 are thinned out among the electrode fingers a6-a10 and a dummy electrode finger 5 whose width is one-third the interval T is provided between the electrode fingers at the thinned-out part.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a surface acoustic wave filter used in V-F circuits of television receivers and video tape recorders.

2. Description of the Related Art Conventionally, in this type of surface acoustic wave filter, as shown in FIGS. 2 to 4, a comb-shaped regular double electrode 2 and a weighted double electrode 3 are arranged on a substrate 1. The method is to propagate elastic waves between the weighted double electromagnetic images. At this time, the interval T between the electrode fingers is determined by a predetermined electrode design method, as shown in FIG. However, in cases where the spacing is so narrow that electrode fingers cannot be formed using the photoetching method, two electrode fingers protruding from the same direction as shown in Figure 4 may be used.
A pair of electrode fingers is thinned out for each pair.

Problems to be Solved by the Invention However, with the above configuration, by thinning out the electrode fingers for each pair, the desired frequency characteristics designed as shown in FIG. It causes.

The present invention eliminates the above-mentioned conventional drawbacks and provides a surface acoustic wave filter that can obtain the desired designed frequency characteristics and has less ripple.

Means to Solve the Problem In the surface acoustic wave filling according to the present invention, electrode fingers that are close to each other are not thinned out oppositely, but every other electrode finger is thinned out so that a distance between the electrode fingers that can be photoetched is obtained. Dummy electrode fingers having a width of one-third of the spacing are provided between the electrode fingers in the thinned out portion.

Effect By providing the above dummy electrode, the characteristics can be improved.

EXAMPLE An example of the present invention will be described below. The basic structure consists of a substrate 1 on which surface acoustic waves propagate, as shown in Figure 2.
A regular double electrode 2 and a weighted double electrode 3 are placed on top. Regarding the spacing between the electrode fingers of the weighted double electrode 3, the electrode fingers a6 of the electrode fingers 11 to 114 of the weighted double electrode 4 obtained by a predetermined electrode design method are used.
Since the interval T between ~'1LIF+ is narrow and difficult to form using the photoetching method, electrode fingers &6 are used as shown in Figure 1.
-1L10, every other electrode fingers a7 and &9 are thinned out, and dummy electrode fingers 6 having a width of 1/3 of the interval T are provided between the thinned out electrode fingers.

Effects of the Invention The surface acoustic wave filter of the present invention thins out every other part of the weighted Dagurumi bar area obtained by a predetermined electric design method, and further reduces the spacing between electrode fingers in the thinned out part. Since dummy electrode fingers with a width of 1/3 of the spacing are provided at the center, it is possible to achieve a frequency characteristic with less ripple and the same frequency characteristics as the design shown in Figure 5, which is effective in improving performance. be.

[Brief explanation of the drawing]

Fig. 1 is a plan view of essential parts of an embodiment of the surface acoustic wave filter of the present invention, Fig. 2 is an electrode arrangement diagram of the surface acoustic wave filter, and Fig. 3 is a weighted double electrode obtained by the electrode design method. 4 is a plan view of a weighted double electrode by the conventional electrode finger thinning method, FIG. 5 is a frequency characteristic diagram of the surface acoustic wave filter of the present invention, and FIG. 6 is a frequency characteristic diagram of the conventional example. It is. 1...Substrate, 2...Regular double electrode, 3...Weighted double electrode, 4...
Weighted double electrode obtained by electrode design method, 6.
...Dummy electrode finger. Name of agent: Patent attorney Toshio Nakao and one other person wE
Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1+11 wave number (MHz) Figure 6 → Zhou Bao Song (MM Su

Claims (1)

[Claims] When providing a comb-shaped regular double electrode and a weighted double electrode on a substrate that propagates surface acoustic waves, the portion where the electrode fingers of the weighted double electrode approach each other in one direction, which is obtained by a predetermined electrode design method, is The two and one pair of electrode fingers coming out from the other direction and the two and one pair of electrode fingers coming out from the other direction are thinned out every other, and the thinned out part has a width of one-third of the electrode finger spacing. A surface acoustic wave filter characterized by having dummy electrode fingers.