US 6,707,229 B1 · Surface acoustic wave filter

Abstract

The invention aims at modifying SPUDT-type surface acoustic wave filters in such a way that the wideband filter can be produced with lower insertion loss and a small form factor without substantially enlarging layout. According to the invention, this is achieved by combining the following characteristics: a) the totality of fingers (231-233; 331-333) of each transducer (2; 3) forms a tapering structure and b) the widths and the positions of the fingers are chosen in such a way that the waves reflected on the fingers (231-233; 331-333) together with the waves regenerated by the corresponding source and load resistance (8; 9) result in an lengthening of the impulse response of the filter, which reduces form factor and/or bandwidth. The invention can be used in surface acoustic wave-based components such as wideband bandpass filters and delay lines.

Claims22

Dependent claims

A surface acoustic wave filter on the basis of interdigital single-phase unidirectional transducers (SPUDT-type), in connection with which two of such transducers are arranged on a piezoelectrical substrate with distributed acoustic reflection, such transducers being composed of groups of fingers and collector electrodes, wherein:

(a) The electrodes of each transducer form a structure tapering in the direction of the fingers;
and
(b) The structure is tapered in the direction of the fingers so that not only the width of equivalent fingers and gaps, but also the intermediate space between the two transducers only vary by one and the same factor along the parallel straight lines, wherein said lines of all fingers of both transducers intersect one another in such a manner that in each transducer, the spacings of the center lines of equivalent fingers are the same in all groups of fingers.

Dependencies are inferred from the claim text.

Surface acoustic wave filter

Life of this patent

Surface acoustic wave filter

Life of this patent

Abstract

Claims22