Patent ID: 7078984

Claim:
A duplexer comprising a transmission filter for passing a transmission signal therethrough and interrupting a reception signal and a reception filter for passing a reception signal therethrough and interrupting a transmission signal, the duplexer being connected to an antenna, wherein: the duplexer further comprises a base; each of the transmission filter and the reception filter includes thin-film piezoelectric resonators each of which has a piezoelectric thin film that exhibits a piezoelectric property and first and second excitation electrodes that are disposed on both surfaces of the piezoelectric thin film and apply an excitation voltage to the piezoelectric thin film; all of the thin-film piezoelectric resonators that the transmission filter and the reception filter include are disposed on the base; the piezoelectric thin films of all of the thin-film piezoelectric resonators are continuous; the transmission filter includes a first series resonator and a first parallel resonator that constitute a ladder-type filter circuit, each of the first series resonator and the first parallel resonator being made up of one of the thin-film piezoelectric resonators; the reception filter includes a second series resonator and a second parallel resonator that constitute a ladder-type filter circuit, each of the second series resonator and the second parallel resonator being made up of one of the thin-film piezoelectric resonators; in the transmission filter, the excitation electrode of the first series resonator and the excitation electrode of the first parallel resonator each disposed on one of the surfaces of the piezoelectric thin film have different thicknesses; in the reception filter, the excitation electrode of the second series resonator and the excitation electrode of the second parallel resonator each disposed on one of the surfaces of the piezoelectric thin film have different thicknesses; and the difference in thickness between the excitation electrode of the first series resonator and the excitation electrode of the first parallel resonator is equal to the difference in thickness between the excitation electrode of the second series resonator and the excitation electrode of the second parallel resonator.