I. Introduction
A DUPLEXER is used in frequency division duplex (FDD) transceivers to isolate the transmitter and receiver while sharing the same antenna. A high isolation between the transmit and receive ports is required to avoid saturating the receiver, and keep its noise and linearity requirements feasible. These duplexers are currently implemented as two highly selective off-chip filters using high- surface acoustic wave (SAW) resonators. The need for high- resonators to implement these filters prohibits duplexer integration in a CMOS process. Moreover, since the center frequency of these SAW filters depends on material properties and the physical dimensions used to build them, the filter center frequency is not programmable and a different duplexer is needed for each band supported. With over 40 bands currently envisioned for cellular applications [1], the system cost and complexity rises significantly. Replacing the bank of off-chip duplexers with a single integrated tunable duplexer would enable a fully integrated and reconfigurable multiband transceiver.