Surface acoustic wave filter
AssigneeSony Corporation
InventorsYasutoshi Komatsu, Yuzuru Yanagisawa
Life of this patent
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Abstract
A surface acoustic wave filter having a piezo-electric substrate with a major surface and input and output transducers, each haing a plurality of finger electrodes formed on the major surface to define a propagation path for surface acoustic waves. Finger electrodes of one of the transducers have a step-like configuration to divide the surface wave propagation path into a plurality of surface wave propagation channels. The phase differences of the channels and the length of the steps of the finger electrodes are selected to minimize the multiple reflection echo between the input and output transducers to reduce ripples in the pass band.
Claims6
A surface acoustic wave filter comprising:
- a. a piezo-electric substrate having a major surface;
- b. input and output transducers formed on the major surface of said substrate, each of said transducer consisting of a plurality of transducer elements;
- and
- c. a plurality of surface acoustic wave propagation channels formed on said substrate between said input and output transducer;
- in which, when the width of a channel k is taken as W.sub.k, and the phase difference between the length of the channel k and n times the wave length at the center frequency is taken as .theta..sub.k (n being a positive integer), the values of .theta..sub.k and W.sub.k are selected to satisfy the following condition:
- ##EQU5## where R and R' are, respectively, mechanical reflection coefficients of said input and output transducers, Q and Q' are, respectively, electrical reflection coefficients of said input and output transducers, and .SIGMA..sub.k W.sub.k is normallized as .SIGMA..sub.k W.sub.k = 1, the transducer elements of said input transducer being located close together and electrically connected, and said plurality of surface acoustic wave propagation channels being formed without an overlapping area.
Dependencies are inferred from the claim text.