Surface acoustic wave filter

Abstract

A surface acoustic wave (SAW) filter has a piezoelectric substrate and a conductive transducer formed over the substrate. The transducer has first and second bus bars arranged in parallel at a prescribed interval from each other, a plurality of pairs of first electrode fingers having the same lengths, and a plurality of pairs of second electrode fingers having the same lengths. The tips of the second electrode fingers are positioned opposite those of the first electrode fingers. The transducer also has first and second weighted electrode pairs positioned between two adjacent pairs of the first electrode fingers and two adjacent pairs of the second electrode fingers, respectively. Each pair of first weighted electrodes has a pair of first electrode sections whose lengths of overlap with the paired second electrode fingers are determined by the negative tap coefficients of an FIR filter having a desired low pass characteristic and a pair of second electrode sections positioned on the elongations of these first electrode sections, one end of each such second electrode section been connected to the first bus bar. The second weighted electrode pairs are similarly formed, but the lengths of overlap are determined by the positive tap coefficients of the FIR filter.