Patent ID: 6114927
Filing Date: 2000-09-05
Classification: H03H

Abstract:
A surface acoustic wave filter comprising:a piezoelectric substrate, at least one input IDT and at least one output IDT formed on the piezoelectric substrate, andfirst and second direction changing electrodes,wherein at least one of the input and output IDTs comprises a weighted interdigital transducer, the input and output IDTs being arranged in a direction perpendicular to a propagation direction of a surface acoustic wave oscillated by the input IDT;the first direction changing electrode comprises an electrode disposed at left sides of the input and output IDTs for changing the propagation direction of the surface acoustic wave, which has propagated in a left direction from the input IDT, into a direction towards the output IDT;the second direction changing electrode comprises an electrode disposed at right sides of the input and output IDTs for changing the propagation direction of the surface acoustic wave, which has propagated in a right direction from the input IDT, into a direction towards the output IDT;the weighted interdigital transducer includes a portion of an electrode having a weighting means required for realizing desired frequency characteristics as a surface acoustic wave filter, the portion of the weighted interdigital transducer including a central portion which has the largest weighting means and comprising A% or more of the weighting means wherein 50.ltoreq.A.ltoreq.100; andan interval between the input and output IDTs and the first and second direction changing electrodes is set for time-delaying the surface acoustic wave so that a surface acoustic wave to be generated by the electrode of the weighting means which has not been included in the weighted interdigital transducer is reproduced, and for obtaining at the output IDT the surface acoustic wave having the desired frequency characteristics.