Resonator ladder type surface acoustic wave filter

摘要

A resonator ladder type surface acoustic wave filter, has an input electrical terminal, an output electrical terminal, and a grounding terminal being formed on a piezoelectric substrate, a series arm surface acoustic wave resonator and a parallel arm surface acoustic wave resonator, each constructed from an interdigital transducer for exciting a surface acoustic wave, being formed between said input electrical terminal and said output electrical terminal, and when the center frequency of said resonator ladder type surface acoustic wave filter is denoted by fc, and capacitance determined by the number of electrode finger pairs and electrode finger overlap width in said interdigital transducer of said parallel arm surface acoustic wave resonator is denoted by Cp (fc: center frequency [GHz], Cp: capacitance of the interdigital transducer of the parallel arm surface acoustic wave resonator), capacitance C of multiples of said parallel arm surface acoustic wave resonator, connected to the same node between said input electrical terminal and said output electrical terminal, always satisfies the relation fcxCp<4