A 3.4–4.6GHz In-Band Full-Duplex Front-End in CMOS Using a Bi-Directional Frequency Converter

Magnetic-free circulators using phase nonreciprocity of spatial-temporal modulated structures have enabled in-band full-duplex systems on CMOS chips. In this paper, we present an alternative and simple integrated circuit scheme based on a bi-directional frequency converter, which not only realizes nonreciprocal signal flow for in-band full-duplex systems but also improves the isolation performance by completely eliminating any chip-level TX-to-RX coupling. These functions are implemented through a direction/frequency-independent single-sideband down-conversion process, which well splits the on-chip TX and RX frequencies. That principle also leads to extension of isolation bandwidth and integrated receiver down-mixing function. Implemented in a 65-nm bulk CMOS technology, a circuit prototype operates from 3.4 to 4.6 GHz (30% fractional bandwidth) and achieves >25.5-dB measured TX-RX isolation. The measured TX-ANT and ANT-RX insertion loss are 3.0 and 3.2 dB, respectively, and the TX-ANT and ANT-RX IIP3 are 29.5 and 27.6 dBm, respectively. This full-duplex front-end component occupies 0.27mm ² area and has 48 mW of power consumption.