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

Abstract

Previously, we presented a non-magnetic, nonreciprocal N-path-filter-based circulator-receiver (circ.-RX) architecture for full-duplex (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) receiver 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)receiver (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 simulation and measurement results of a 65 nm CMOS 750 MHz circulator-receiver prototype. The circulator-receiver can handle up to +8 dBm of TX power, with 8 dB noise figure (NF) and 40 dB average isolation over 20 MHz RF bandwidth (BW). In conjunction with digital self-interference (SI) and its third-order intermodulation (IM3) cancellation, the 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 FD demonstration where a -50 dBm weak desired received signal is recovered while transmitting a 0 dBm average-power OFDM-like TX signal.

Isolating Bandpass Filters Using Time-Modulated Resonators

“…Here ω is the diagonal frequency matrix given by (4). Thus, the spectral ABCD matrix of the timevarying resonator is…”

Non-Magnetic Non-Reciprocal Microwave Components — State of the Art and Future Directions

“…The insertion loss of such circulators must be compared with loss of a ferrite circulator summed with that of the antenna tuner. In [84], the authors describe an N-pathfilter-based circulator-receiver,where the N-path switches are repurposed to serve as a down-conversion mixer, thereby realizing the combination of a circulator and a receiver in a single circuit. This concept has been further scaled to array implementations for full-duplex multi-antenna systems, including phased-array circulator-receiver arrays [85] and multi-input multi-output (MIMO) arrays [86].…”

Techniques for Achieving High Isolation in RF Domain for Simultaneous Transmit and Receive

“…These radios employ a single antenna for transmission and reception using a single feed network that divides the transmitter and receiver circuits as depicted in Fig. 2 (left)) [24]- [27]. However, employing TDD or FDD implies double the time and/or frequency resource allocation.…”