Analysis and Design of Commutation-Based Circulator-Receivers for Integrated Full-Duplex Wireless

Previously, we presented a non-magnetic, non-reciprocal N-path-filter-based circulator-receiver (circ.-RX) architecture for single-frequency full-duplex (SF-FD) wireless, which merges a commutation-based linear periodically time-varying (LPTV) non-magnetic circulator with a down-converting mixer and directly provides the baseband (BB) RX signals at its output, while suppressing the noise contribution of one set of the commutating switches. The architecture also incorporates an on-chip balance network to enhance the transmitter (TX)-RX isolation. In this paper, we present a detailed analysis of the architecture, including a noise analysis and an analysis of the effect of the balance network. The analyses are verified by the simulation and measurement results of a 65-nm CMOS 750-MHz circ.-RX prototype. The circ.-RX can handle up to +8 dBm of TX power with 8-dB noise figure (NF) and 40-dB average isolation over 20-MHz radio frequency (RF) bandwidth (BW). In conjunction with digital self-interference (SI) and its third-order intermodulation (IM3) cancellation, the SF-FD circ.-RX demonstrates 80-dB overall SI suppression for up to +8-dBm TX average output power. The claims are also verified through an SF-FD demonstration where a -50-dBm weak desired received signal is recovered while transmitting a 0-dBm average power orthogonal frequency-division multiplexing (OFDM)-like TX signal.