A 0.55-to-0.9GHz 2.7dB NF full-duplex hybrid-coupler circulator with 56MHz 40dB TX SI suppression

Simultaneous transmit-and-receive (STAR) radios enable higher spectrum efficiency and dynamic spectrum access. The integration of a shared antenna interface is attractive for small system form factor and MIMO channel estimation and has led to demonstrations of compact reciprocal (electrical balance duplexers (EBD)) and non-reciprocal (circulator) interfaces with self-interference cancellation (SIC) [1-5]. In this paper, we address the challenge of low-noise wideband SIC by demonstrating a wideband hybrid-coupler-circulator antenna interface using N-path mixers that achieves low NF while preserving the linearity of passive-mixer-first RX. The 0.55-to-0.9GHz hybrid-coupler-based circulator-RX achieves 2.7dB NF at 750MHz with +14dBm OOB IIP3 as part of an antenna interface that achieves 2.6-to-4.1dB TX→ANT insertion loss (IL) from 550 to 900MHz. The wideband coupler approach provides >40dB TX-to-RX baseband (BB) isolation across a 32MHz BW (56MHz BW for averaged 40dB isolation) and >30dB isolation across a 190MHz bandwidth without an on-chip balancing network, representing a >3dB improvement in NF and >2.7x increase in cancellation bandwidth compared to previously published circulator-RX.