Rethinking the RF Front-End: Integrated Magnetic-Free Non-Reciprocity and Its Application in Emerging Wireless Communication Paradigms

Lorentz reciprocity is a fundamental characteristic of the vast majority of electronic materials, circuits and components which can be broken by violating one of three necessary conditions – time-invariance, linearity or symmetry in permittivity or permeability matrix of the medium. We have demonstrated the world's first CMOS passive magnetic-free non-reciprocal circulator through spatio-temporal conductivity modulation, a form of linear periodically time-varying (LPTV) circuits. One of the emerging applications of non-reciprocity is within the next generation of wireless communication networks. Various emergent wireless technologies are under investigation to enable the “5G” revolution, including massive MIMO and full-duplex wireless. Enabling these technologies requires a re-evaluation and redesign of various layers of the communication system, from the PHY layer all the way up to the application layer. In this talk, I will describe the fundamental physical principles and cover our recent research on using LPTV circuits to break reciprocity to build passive non-reciprocal components such as circulators and isolators. I will also present our efforts on designing full-duplex front-ends, which take advantage of our integrated non-reciprocal components to co-design and co-optimize the system performance as a whole. While research efforts on the topic of integrated magnetic-free non-reciprocity is still in its prime days, I believe there exists many more exciting circuits, systems and applications yet to be discovered.