| 摘要 |
To provide an acoustic wave filter device that includes longitudinally-coupled-resonator acoustic wave filters having a balanced-unbalanced conversion function and that is capable of increasing the amount of attenuation in an attenuation band and capable of improving the isolation characteristics when the acoustic wave filter device is used as a reception filter of a duplexer, an acoustic wave filter device includes an unbalanced terminal (7); first and second balanced terminals (8 and 9); first and second longitudinally-coupled-resonator acoustic wave filters (11 and 12) that are connected between the unbalanced terminal (7) and the first balanced terminal (8) and between the unbalanced terminal (7) and the second balanced terminal (9), respectively; a first parallel resonator (13) connected between the first balanced terminal (8) and a ground potential; and a second parallel resonator (14) connected between the second balanced terminal (9) and the ground potential. The electrostatic capacitance of the first parallel resonator (13) is different from the electrostatic capacitance of the second parallel resonator (14). Among the first parallel resonator (13) and the second parallel resonator (14), the wavelength of the first parallel resonator (13) having a relatively small electrostatic capacitance is made shorter than the wavelength of the second parallel resonator (14) having a relatively large electrostatic capacitance. |
