Patent ID: 7224245

Claim:
A duplexer comprising: a substrate; a transmitter filter integrated on the substrate to pass signals only in a frequency band for transmission; a receiver filter integrated on the substrate to pass signals only in a frequency band for reception; and an isolation part integrally formed with the transmitter filter or integrally formed with the receiver filter to isolate the signals passed through the transmitter filter from the signals passed through the receiver filter, wherein at least one of the transmitter filter and the receiver filter comprises at least one film bulk acoustic resonator (FBAR), said FBAR comprising a cavity part formed on a predetermined area of the substrate, a membrane deposited on the substrate and covering the cavity part, and a stacked resonance part formed on a cavity-covering part of the membrane, the stacked resonance part comprising a lower electrode, a piezoelectric layer and an upper electrode stacked in order, wherein the isolation part comprises at least one capacitor using the membrane as a dielectric layer and having an electrostatic capacitance proportional to a permittivity of the membrane, and at least one inductor formed in a coil type on a surface of the membrane, to isolate the signals passing through the transmitter filter and the signals passing through the receiver filter by making a frequency phase difference of the signals passing through the transmitter filter and the signals passing through the receiver filter to be substantially 90°.