Patent ID: 8198959

Claim:
A longitudinally-coupled resonator type acoustic wave filter device comprising: an unbalanced terminal; first and second balanced terminals arranged to provide a balanced-unbalanced conversion function; a piezoelectric substrate; a longitudinally-coupled resonator type acoustic wave filter unit which is disposed on the piezoelectric substrate and which includes an unbalanced end connected to the unbalanced terminal and first and second balanced ends arranged to output respective signals having phases different from each other by 180 degrees; an acoustic wave resonator which is disposed on the piezoelectric substrate and which includes an IDT electrode including first and second bus bars which oppose each other and a pair of reflectors arranged so that the IDT electrode is sandwiched between the reflectors in an acoustic wave propagation direction; and first and second signal lines including first ends connected to the first and second balanced ends of the acoustic wave filter unit, respectively, and second terminals connected to the first and second balanced terminals, respectively; wherein the acoustic wave resonator includes first and second divided electrode sections obtained by dividing the first bus bar of the IDT electrode of the acoustic wave resonator into two, and the first and second divided electrode sections are connected to each other in series in the acoustic wave propagation direction by the second bus bar; one terminal of the first divided electrode section which is arranged opposite to the second bus bar is connected to the first signal line; one terminal of the second divided electrode section which is arranged opposite to the second bus bar is connected to the second signal line; a length of a line which connects the first divided electrode section to the first balanced end is equal or substantially equal to a length of a line which connects the second divided electrode section to the second balanced end, and the first divided electrode section is different from the second divided electrode section; and a number of electrode fingers included in the first divided electrode section is different from a number of electrode fingers included in the second divided electrode section.