Filter, duplexer and electronic device

摘要

A ladder type filter includes series resonators S1˜S4 connected in series between an input terminal In and an output terminal Out, parallel resonators P1˜P3 connected in parallel between the input terminal In and the output terminal Out, a resonator RP connected in series with the series resonators S1˜S4 between the input terminal and the output terminal, the resonator RP having a resonance frequency lower than resonance frequencies of the series resonators S1˜S4, and an inductor Lp connected in parallel with the resonator. According to the present ladder filter, signals having frequencies away from the pass band can be suppressed by an attenuation pole formed by the inductor. It is further possible to suppress the insertion loss in the pass band by the resonator.

主权项

1. A duplexer comprising:
a transmission filter connected in series between a node and a transmission terminal and a reception filter connected in series between the node and a reception terminal, at least one of which includes series resonators connected in series between the node and at least one of the transmission terminal and the reception terminal, and parallel resonators connected in parallel between the node and the at least one of the transmission terminal and the reception terminal; a resonator connected in series between the node and a common terminal; and an inductor connected in parallel with the resonator between the node and the common terminal, wherein the resonator has a resonance frequency lower than resonance frequencies of the series resonators when the inductor is not connected to the resonator.