Patent ID: 7876176

Claim:
An acoustic wave filter device, comprising: a piezoelectric substrate; first to fourth longitudinally coupled resonator type acoustic wave filters, each of which includes first to third IDTs arranged on the piezoelectric substrate in an acoustic wave propagation direction; an unbalanced signal terminal connected to input terminals of the first to fourth longitudinally coupled resonator type acoustic wave filters; a first balanced signal terminal connected to output terminals of the first and second longitudinally coupled resonator type acoustic wave filters; and a second balanced signal terminal connected to output terminals of the third and fourth longitudinally coupled resonator type acoustic wave filters; wherein a phase of an output signal of the first longitudinally coupled resonator type acoustic wave filter relative to an input signal is substantially the same as a phase of an output signal of the second longitudinally coupled resonator type acoustic wave filter relative to an input signal; a phase of an output signal of the third longitudinally coupled resonator type acoustic wave filter relative to an input signal is substantially the same as a phase of an output signal of the fourth longitudinally coupled resonator type acoustic wave filter relative to an input signal; the phase of the output signal of the first longitudinally coupled resonator type acoustic wave filter relative to the input signal differs by about 180 degrees with respect to the phase of the output signal of the third longitudinally coupled resonator type acoustic wave filter relative to the input signal; and a number of pairs of electrode fingers of at least one of the IDTs of at least one of the first to fourth longitudinally coupled resonator type acoustic wave filters is different from a number of pairs of electrode fingers of the IDTs of the first to fourth longitudinally coupled resonator type acoustic wave filters other than the at least one of the first to fourth longitudinally coupled resonator type acoustic wave filters.