Patent ID: 6717489
Filing Date: 2004-04-06
Classification: H03H

Abstract:
A longitudinally connected resonator type surface acoustic wave filter, comprising:first and second longitudinally connected resonator type surface acoustic wave filters each having a plurality of IDTs which are successively arranged on a piezoelectric substrate along a propagation direction of a surface acoustic wave; wherein said first longitudinally connected resonator type surface acoustic wave filter has a transmission phase that is substantially opposite to a transmission phase of said second longitudinally connected resonator type surface acoustic wave filter; first terminals of said first and second longitudinally connected resonator type surface acoustic wave filters each defining unbalanced terminals by being connected in parallel with each other, and second terminals of said first and second longitudinally connected resonator type surface acoustic wave filters defining balanced terminals by being connected via a ground or connected in series with each other, whereby said longitudinally connected resonator type surface acoustic wave filter has a balanced-unbalanced conversion function; wherein in said first and second longitudinally connected resonator type surface acoustic wave filters, each of said plurality of IDTs includes a narrow-pitch electrode finger portion, and the pitch of one electrode finger portion from the adjacent IDT-side end of said each IDT, is narrower than that of other electrode finger portions of the IDT; and the duty of the electrode fingers in said narrow-pitch electrode finger portion is different between said first and second longitudinally connected resonator type surface acoustic wave filters.