JPH03139008A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To reduce ripples by designating a center electrode interval of electrode pairs of a comb-shaped electrode. CONSTITUTION:Comb-shaped electrodes 12 opposite to each other are provided on a piezoelectric substrate 11 to form a surface acoustic wave filter. Then the electrode interval in the center of the electrode pairs of the electrodes 12 whose width is lambda/4 is selected to be d0 in the middle, selected differently, smaller than the electrode interval (d) of other parts, then equi-pitch is evaded so as to reduce generation of the ripple due to confined surface acoustic wave due to equi-pitch.

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.

2. Description of the Related Art A conventional surface wave filter has a piezoelectric substrate 1 as shown in FIG.
Two sets of comb-shaped electrodes 2 were provided on the top.

Normally, one of the electrodes 2 is called a normal type electrode and has a constant crossing length, and the other is called a weighted electrode and has a different crossing length depending on the comb-shaped electrode fingers. Letting the propagation speed of the surface acoustic wave on the piezoelectric substrate be υ and the wavelength of the surface acoustic wave as λ, the relationship with the center frequency f is expressed as υ−chi·λ,
Usually, the line width of the comb-shaped electrode fingers is λ/4 or λ/8, and even if the weighting is applied to the electrodes, the line width and the electrode spacing are the same near the center.

Problems to be Solved by the Invention In recent years, as the performance of equipment has improved, demands for surface wave filters such as broadband, low ripple, and high selectivity have also increased. While the number of pairs of comb-shaped electrode fingers is increasing due to broadbandization, high selectivity, etc., as the number of pairs increases, surface acoustic waves are reflected and confined within the comb-shaped electrode, increasing ripples. This phenomenon is becoming more common.

The present invention is intended to solve these problems, and aims to provide a surface acoustic wave filter with a wide band, high selectivity, and less ripple.

Means for Solving the Problem In order to solve this problem, the present invention takes a measure in which the electrode finger spacing at the center of the electrode finger pair is made to be different from the electrode finger spacing near the center.

Effect: With this configuration, it is possible to provide a surface acoustic wave filter with less ripple.

EXAMPLES Specific examples of the present invention will be described below with reference to the drawings. FIG. 1 is a pattern diagram of the center portion of a comb-shaped electrode of a surface acoustic wave filter according to an embodiment of the present invention.

In FIG. 1, 11 is a piezoelectric substrate, and a comb-shaped electrode 12
The line width is λ/4, and the electrode finger spacing d near the center is also λ/4.
It becomes 4. If the central electrode finger spacing Coo is different from d, there is an effect of reducing ripples, but it is usually easier to design if do<d.

FIG. 2 is a pattern diagram of a central portion of a comb-shaped electrode of a surface acoustic wave filter according to another embodiment of the present invention. In Figure 2, comb-shaped electrode 1
The line width of No. 2 is λ/8, the electrode finger spacing d near the center is also λ/8, and only the line width of the electrode fingers on both sides of the center is λ/4. If all of these are taken with a line width of λ/8 and do < d, there are cases where do becomes too small and does not adversely affect yield, etc. In that case, two combs with a line width of λ/8 By grouping the electrode fingers into one comb-shaped electrode finger of λ/4, the do can be made larger than when the line width of all the electrode fingers is set to λ/8 with the same design, and the ripple is reduced. The reduction effect can still be expected.

Effects of the Invention As described above, according to the present invention, ripples occur when the electrode fingers are equal to each other.
Surface acoustic waves are trapped and generated by arranging them at a pitch, but by making the electrode finger spacing at the center of the electrode finger pair different from the electrode finger spacing near the center, the electrode fingers near the center can be Even if they are lined up at equal pitches, the overall pitch is not equal, so ripples are less likely to occur.

Therefore, the present invention has a sufficient ripple reduction effect for designs in which the number of electrode finger pairs tends to increase due to broadbandization, high selectivity characteristics, etc., and its practical fliM is great.

[Brief explanation of the drawing]

FIG. 1 is a pattern diagram of the central part of the comb-shaped electrode of a surface acoustic wave filter showing one embodiment of the present invention, FIG. 2 is a pattern diagram of the central part of the comb-shaped electrode of a surface acoustic wave filter of another embodiment, and FIG.
The figure is a perspective view of a conventional example. 11... Piezoelectric substrate, 12... Comb-shaped electrode.

Claims (3)

[Claims] (1) A surface acoustic wave filter having comb-shaped electrodes provided on a piezoelectric substrate, characterized in that the distance between the electrode fingers at the center of at least one pair of electrode fingers is different from the distance between the electrode fingers near the center. filter. (2) Claim 1, characterized in that the electrode finger spacing at the center of the electrode finger pair is smaller than the electrode finger spacing near the center.
The surface acoustic wave filter described in . (3) A patent characterized in that, where the wavelength of the surface acoustic wave is λ, the line width of the electrode fingers on both sides of the center of the electrode finger pair is λ/4, and the line width of the other electrode fingers is λ/8. A surface acoustic wave filter according to claim 1.