18.1 A 1.7-to-2.2GHz full-duplex transceiver system with >50dB self-interference cancellation over 42MHz bandwidth

Full-duplex (FD) radio communication potentially doubles the spectral efficiency in the densely occupied RF spectrum (100MHz to 5GHz). However, significant challenges remain, particularly the presence of a strong transmitter (TX) self-interference (SI) coupling to the receiver (RX). Numerous recent efforts on mitigating SI have focused on using active cancellation techniques [1-5]. However, these methods are challenged by either a degradation in noise performance [2], high power consumption [1,4], large silicon area [5], the inability to adequately cancel a high-output-power TX signal [3-4], or achieve a relatively narrow cancellation bandwidth [3,5]. Moreover, other sources of SI are presented to the RX, including the effects of (1) in-band TX thermal noise, which can exceed the RX noise floor, (2) the RX LO phase noise (PN), which reciprocally mixes with SI, further degrading the C/I ratio. This paper presents several circuit-level techniques, which contribute toward reducing the interaction between the TX and RX in FD radios.