14.3 A 26GHz Full-Duplex Circulator Receiver with 53UB/400MHz(40UB/800MHz) Self-Interference Cancellation for mm-Wave Repeaters

Reduction in base-station deployment costs while increasing coverage has motivated Integrated Access and Backhaul (IAB) nodes in mm-wave 5G NR (Fig. 14.3.1). Similarly, high path loss due to shadowing and limited outdoor-to-indoor penetration at mm-wave has led to an interest in repeater/relays to extend 5G NR coverage [1]. Currently, halfduplexlinks based on TDD (preferred for lAB), FDD, spatial, and polarization-duplexare explored, targeting mm-wave TWRX isolation at the cost of channel capacity. While mmwave in-band full-duplex (IBFD) with shared antenna (ANT) interface can enable spectrum reuse in IAB and repeaters/relays, >100dB total self-interference cancellation (SIC) is required with up to 50dB of SIC in the mm-wave front-end [2]. Such SIC has been shown for IBFD at RF [3– 5], however mm-wave IBFD SIC with a shared antenna interface has been limited to 20dBat28GHz and 40dB(22dB at +10dBm TX SI power) at 60GHz [6, 7]. Achieving mm-wave IBFD SIC with a shared ANT interface is particularly challenging given (i) the high frequency of operation, (ii) wide 400MHz/800MHz bandwidths targeted in 5G NR, and (iii) variations in beamformer ANT impedance that changes the SI channel. This paper presents a fully integrated mm-wave circulator RX that addresses these challenges using (i) a hybrid-coupler and non-reciprocal N-path filter-based shared ANT interface that provides wideband SIC while creating an SI replica, enabling (ii) subsequent active cancellation with variable gain/phase shift to accommodate SI channel variations. The circulator RX implementation in 45nm SOI CMOS achieves 52. 8dB cancellation across 400MHz at 26. 4GHz(>100 $\times$ improvement over state of the art at high power levels) with 3.1dB TX-to-ANT insertion loss (IL) and +11.5dBm TX power-handling. System-level feasibility for mm-wave wideband IBFD is shown with the integrated RX supporting 600MS/s128-OAM wireless reception (4.2Gb/s) with 3.3% RX EVM in the presence of an in-band 128-OAM 300MS/s (limited by instrument) TX SI signal, and SIC is demonstrated across SI channel changes using a global optimization approach.