Patent ID: 7330089

Claim:
A balanced acoustic wave filter device comprising: a piezoelectric substrate; and first and second longitudinally coupled resonator-type acoustic wave filter sections provided on the piezoelectric substrate; wherein each of the first and second acoustic wave filter sections includes a plurality of IDTs disposed in a direction in which surface acoustic waves propagate; one of an input and an output of each of the first and second acoustic wave filter sections is connected to an unbalanced terminal; the other of the input and the output of the first acoustic wave filter section is connected to a first balanced terminal, the other of the input and the output of the second acoustic wave filter section is connected to a second balanced terminal, and the phase of a signal of the other of the input and the output of the first acoustic wave filter section is different from the phase of a signal of the other of the input and the output of the second acoustic wave filter section by 180 degrees; in the first acoustic wave filter section, the polarities of electrode fingers that are adjacent to each other in an area in which the IDTs are adjacent to each other in a direction in which acoustic waves propagate are equal to each other; in the second acoustic wave filter section, the polarities of electrode fingers that are adjacent to each other in an area in which the IDTs are adjacent to each other are opposite to each other; and the total number of pairs of electrode fingers of the plurality of IDTs in the second acoustic wave filter section is greater than the total number of pairs of electrode fingers of the plurality of IDTs in the first acoustic wave filter section.