FILTER DEVICE AND DUPLEXER

摘要

Provided is a filter device that enables an attenuation amount to be expanded at a desired out-of-band frequency position across a wider frequency range. This filter device has a transversal acoustic wave filter (11) connected in parallel to a bandpass filter (10) as a delay element. The transversal wave acoustic filter (11) has the characteristic of having the same amplitude characteristics as the bandpass filter (10) and the opposite phase at a desired frequency in the attenuation band of the bandpass filter (10). When the wavelength determined by the electrode finger period of a first interdigital transducer (IDT) (15) and a second IDT (16) of the acoustic wave filter (11) is denoted as lambda, the distance between the IDTs (15, 16) is set at 12lambda or less.