A tunable integrated duplexer with 50dB isolation in 40nm CMOS

Modern RF duplexers rely on frequency-selective filters for isolation. The stringent isolation requirements prohibit the integration of RF duplexers on silicon and particularly in CMOS technology. However, CMOS technology offers superior tuning and calibration capabilities supported by the integrated digital baseband. This work presents the first integrated duplexer in CMOS technology with an adequate performance for full-duplex cellular applications such as WCDMA and HSPA. The proposed implementation is based on electrical balance of a hybrid transformer rather than frequency selectivity which unfavorably requires high-Q elements.