A SAW-Less Tunable RF Front End for FDD and IBFD Combining an Electrical-Balance Duplexer and a Switched- LC N-Path LNA

This paper proposes a surface-acoustic wave (SAW)-less tunable RF front end (RF-FE) using an electrical-balance duplexer (EBD) integrated with a switched-LC N-path low-noise amplifier (LNA). The EBD cancels the transmitter–receiver (TX–RX) leakage at the RX frequency by dynamically optimizing the balance of a hybrid transformer, which enables in-band full-duplex (IBFD) operation. A transconductor-based LNA in parallel with a switched-LC N-path network creates input and output notches to reject TX leakage for frequency-division duplexing (FDD) operation. The LNA’s signal-handling capability is enhanced via optimum switch biasing. Fabricated in 0.18- $\mu \text{m}$ SOI CMOS, the RF-FE offers >50-dB tunable rejection from the TX port to LNA output at both TX and RX frequencies, for all 3GPP bands from 0.7 to 1 GHz (i.e., FDD case). It is the first tunable RF-FE including an LNA that achieves +70-dBm TX-path IIP3, and +30-dBm in-band TX power while cancelling the self-interference by >50 dB (i.e., IBFD case). The RF-FE consumes 62.5 mW at 1 GHz with 11.7-dB RX cascaded NF, 3.6-dB TX insertion loss, and 9.62 mm2 active area.