A transformer-less duplexer with out-of-band filtering for same-channel full-duplex radios

This paper presents a transformer-less duplexer based on 2-port N-path bandpass filters (BPFs). The proposed duplexer consists of two quarter-wavelength transmission lines, and an N-path balun BPF which provides an out-of-band (OOB) blocker support for the receiver. A 0.45-0.65 GHz duplexer is implemented in a CMOS 65 nm technology. The duplexer occupies an active area of ≈ 0.7 mm². In post-layout simulations, the duplexer has > 55 dB of transmitter-to-receiver isolation, <; 6 dB of transmitter-to-antenna insertion loss (IL) and <; 7 dB of antenna-to-receiver IL.