Patent ID: 7459997

Claim:
An elastic wave filter device comprising: a piezoelectric substrate; first to third longitudinally coupled resonator elastic wave filters including: first to third IDTs disposed along an elastic wave propagating direction on said piezoelectric substrate; and reflectors disposed at both sides in the elastic wave propagating direction of a region where said first to third IDTs are provided; an unbalanced signal terminal to which each second IDT of said first to third longitudinally coupled resonator elastic wave filters is connected; and first and second balanced signal terminals defining output terminals; wherein a phase of an output signal to an input signal of said first longitudinally coupled resonator elastic wave filter differs by about 180 degrees from a phase of an output signal to an input signal of said third longitudinally coupled resonator elastic wave filter; said second longitudinally coupled resonator elastic wave filter includes first and second output terminals; a phase of a signal to be transmitted to said first output terminal from an input terminal of said second longitudinally coupled resonator elastic wave filter differs by about 180 degrees from a phase of a signal to be transmitted to said second output terminal from the input terminal of said second longitudinally coupled resonator elastic wave filter; a phase of the output signal corresponding to the input signal of said first longitudinally coupled resonator elastic wave filter is the same as a phase of the signal transmitted to said first output terminal from the input terminal of said second longitudinally coupled resonator elastic wave filter; a phase of the output signal corresponding to the input signal of said third longitudinally coupled resonator elastic wave filter is the same as a phase of the signal transmitted to said second output terminal from the input terminal of said second longitudinally coupled resonator elastic wave filter; one of the first and third IDTs of said second longitudinally coupled resonator elastic wave filter is connected to said first output terminal, and the other is connected to said second output terminal; and the first and third IDTs of said first longitudinally coupled resonator elastic wave filter, and said first output terminal of said second longitudinally coupled resonator elastic wave filter are connected to said first balanced signal terminal, and the first and third IDTs of said third longitudinally coupled resonator elastic wave filter, and said second output terminal of said second longitudinally coupled resonator elastic wave filter are connected to said second balanced signal terminal.