Patent ID: 7733197

Claim:
A duplexer comprising: a piezoelectric substrate; a transmitting filter on the piezoelectric substrate, including a ladder filter having a first resonator group, the first resonator group comprising: one or more resonators disposed in one or more series arms; and one or more resonators disposed in one or more parallel arms; a receiving filter on the piezoelectric substrate, having a passband higher than that of the transmitting filter, and including a second resonator group, the second resonator group comprising: one or more resonators disposed in one or more series arms; and one or more resonators disposed in one or more parallel arms; a node connecting both a transmit-side end portion of the transmitting filter and a receive-side first portion of the receiving filter, wherein the receive-side closest resonator which is in the second resonator group and is closest to the node in the parallel arm is closer to the node than a resonator which is in the second resonator group and is closest to the node in the series arm, and a resonance frequency of the receive-side closest resonator is lower than the passband of the transmitting filter.