Patent ID: 8193877

Claim:
A duplexer interfacing a receiver and a transmitter with a common antenna, the duplexer comprising: a first acoustic filter connected in series between the antenna and the transmitter, the first acoustic filter having a first passband; a second acoustic filter connected in series between the antenna and the receiver, the second acoustic filter having a second passband; and a phase shifter comprising at least one series capacitor connected in series with the antenna and at least one shunt inductor connected between the at least one capacitor and ground, wherein the phase shifter is connected between the antenna and the first acoustic filter when the first passband is higher than the second passband, and provides a negative phase shift of an output impedance of the first acoustic filter, and wherein the phase shifter is connected between the antenna and the second acoustic filter when the second passband is higher than the first passband, and provides a negative phase shift of an input impedance of the second acoustic filter.