Tunable CMOS Integrated Duplexer With Antenna Impedance Tracking and High Isolation in the Transmit and Receive Bands

A hybrid transformer-based integrated tunable duplexer is demonstrated. High isolation between the transmit and receive ports is achieved through electrical balance between the antenna and balance network impedances. A novel high-power-tolerant balance network, which can be tuned at both the transmit and receive frequencies, allows high isolation in both the transmit and receive bands even under realistic antenna impedance frequency dependence. To maintain high isolation despite antenna impedance variation, a feedback loop is employed to measure the transmitter leakage and correct the impedance of the balance network. An isolation > 50 dB in the transmit and receive bands with an antenna voltage standing-wave ratio within 2:1 was achieved. The duplexer, along with a cascaded direct-conversion receiver, achieves a noise figure of 5.3 dB, a conversion gain of 45 dB, and consumes 51 mW of power. The insertion loss in the transmit path was less than 3.8 dB. Implemented in a 65-nm CMOS process, the chip occupies an active area of 2.2 mm².