Patent ID: 7528683

Claim:
A balanced acoustic wave filter device having an unbalanced terminal and first and second balanced terminals and having a balanced-unbalanced conversion function, comprising: a piezoelectric substrate; and first, second and third IDTs disposed on the piezoelectric substrate in a surface wave propagating direction; wherein the second IDT includes first and second divided IDT portions obtained by dividing the second IDT into two in the surface wave propagating direction; one end of the first divided IDT portion is connected to one end of the second divided IDT portion such that the first divided IDT portion is connected to the second divided IDT portion in series; the other end of the first divided IDT portion is connected to the first balanced terminal, and the other end of the second divided IDT portion is connected to the second balanced terminal; the first, second and third IDTs are arranged such that electrical signals flowing from the unbalanced terminal to the first balanced terminal and flowing from the unbalanced terminal to the second balanced terminal have a 180-degree phase difference; each of the first and second divided IDT portions includes at least first and second sub-divided IDT portions obtained by dividing each of the first and second divided IDT portions in a crossing width direction that is substantially perpendicular to the surface wave propagating direction; and at least the first and second sub-divided IDT portions are electrically connected in series.