2.2 A +70dBm IIP3 single-ended electrical-balance duplexer in 0.18um SOI CMOS

The electrical-balance (EB) duplexer concept explored in [1-4] suggests a possible integrated multiband alternative to conventional fixed-frequency surface-acoustic-wave (SAW) duplexers. The basic principle of the EB duplexer is to balance the impedances seen at the ports of a hybrid transformer to suppress signal transfer from the TX to the RX through signal cancellation (Fig. 2.2.1). While the potential payoff is tantalizing, several challenges must still be solved before EB duplexers can become commercially viable. Specifically, the duplexer must provide high isolation and linearity in both the TX and RX bands across wide bandwidth (BW), with low insertion loss (IL), all in the presence of a real antenna whose impedance is constantly varying due to real-world user interaction. In this paper, we present a duplexer that significantly advances the state-of-the-art for two of these critical challenges: linearity and insertion loss.