Patent ID: 7429905

Claim:
A balanced acoustic wave filter device having an unbalanced terminal and first and second balanced terminals, the device comprising: a piezoelectric substrate; and first and second longitudinally coupled resonator type acoustic wave filter units, the first and second acoustic wave filter units being provided on the piezoelectric substrate; wherein the first acoustic wave filter unit includes a second IDT connected to one of the unbalanced terminal and the first balanced terminal, and also includes first and third IDTs arranged on both sides of the second IDT in an acoustic wave propagation direction and connected to the other one of the first balanced terminal and the unbalanced terminal; the second acoustic wave filter unit includes a fifth IDT connected to one of the unbalanced terminal and the second balanced terminal, and also includes fourth and sixth IDTs arranged on both sides of the fifth IDT in the acoustic wave propagation direction and connected to the other one of the second balanced terminal and the unbalanced terminal; the first to sixth IDTs are configured such that a phase of an electric signal flowing to the first balanced terminal is different by 180 degrees from a phase of an electric signal flowing to the second balanced terminal; and an IDT included in the first acoustic wave filter unit and connected to the first balanced terminal and an IDT included in the second acoustic wave filter unit and connected to the second balanced terminal each include at least first and second sub-IDT portions obtained by dividing the IDT and arranged in a crossing width direction that is substantially perpendicular to the acoustic wave propagation direction, and the at least first and second sub-IDT portions are connected electrically in series; and outermost electrode fingers that are located on outermost sides, in the acoustic wave propagation direction, of IDTs connected to the unbalanced terminal and are adjacent, in the acoustic wave propagation direction, to an IDT connected to the first or second balanced terminal, are connected to ground.