Hybrid transformer-based tunable integrated duplexer with antenna impedance tracking loop

Electrical balance between the antenna and the balance network impedances is crucial for achieving high isolation in a hybrid transformer duplexer. In this paper an auto calibration loop for tuning a novel integrated balance network to track the antenna impedance variations is introduced. It achieves an isolation of more than 50 dB in the transmit and receive bands with an antenna VSWR within 2:1 and between 1.7 and 2.2 GHz. 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 34 mA. 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.