Patent ID: 7902716
Filing Date: 2011-03-08
Classification: H03H

Abstract:
1. A surface acoustic wave device, which has an unbalance/balance conversion function, comprising: a surface acoustic wave resonator to which an unbalanced input/output terminal is connected; and first and second surface acoustic wave elements parallel-connected to each other through said surface acoustic wave resonator, which are formed on a piezoelectric substrate, said first and second surface acoustic wave elements, each being provided with three or more odd-numbered IDTs placed along a propagation direction of a surface acoustic wave propagated over said piezoelectric substrate and provided with a plurality of electrode fingers the longitudinal direction of which is made orthogonal to the propagation direction, and first reflectors, placed on the two ends of an IDT row composed of said odd-numbered IDTs, each having a plurality of electrode fingers the longitudinal direction of which is made orthogonal to said propagation direction, with each of said first and second surface acoustic wave elements being provided with a balanced input/output terminal connected to the IDT in the center among said odd-numbered IDTs, wherein among electrode fingers possessed by said odd-numbered IDTs and said first reflector, the electrode fingers to which different one of said IDTs or said first reflectors is adjacent have polarities that are arranged symmetrically centered on said IDT in the center of said first or said second surface acoustic wave element, a second reflector composed of a plurality of electrode fingers the longitudinal direction of which is made orthogonal to said propagation direction are further placed between adjacent IDTs in said propagation direction among said odd-numbered IDTs, each of said first and second surface acoustic wave elements has a first portion in which electrode finger pitches vary along said propagation direction and a second portion in which said electrode finger pitches are constant, said first and second portions being arranged so that the average value of electrode finger pitches in said first portion is made shorter than that of the electrode finger pitches in said second portion, with the electrode finger pitch of said first portion being made shorter toward the border of the adjoining two IDTs, and the electrode finger pitch of said second reflector is made shorter than the electrode finger pitch of said second portion, and in said first and second surface acoustic wave elements, the electrode finger pitches in IDTs other than said IDT in the center among said odd-numbered IDTs have a maximum value so that a portion having a greater electrode finger pitch than the electrode finger pitch of said second portion is placed in said first portion.