Patent ID: 7573354

Claim:
A duplexer comprising: an antenna terminal; a first filter connected to the antenna terminal; and a second filter connected to the antenna terminal, wherein at least one of the first filter and the second filter is a ladder type filter in which multiple parallel resonators and multiple series resonators are included, one or more first inductors are respectively connected in parallel with one or more series resonators out of the multiple series resonators, one or more first inductors are not connected in parallel with the other of the multiple series resonators, and one of the one or more first inductors is connected in parallel with one of the multiple series resonators that is arranged closest to the antenna terminal, wherein 0.3<C 1 /C 2 <1 is satisfied, where the ladder type filter is represented by an equivalent circuit of the ladder type filter, C 1 denotes a capacitance value of the series resonator arranged closest to the antenna terminal, and C 2 denotes an average value of capacitance values of other series resonators in the ladder type filter.