Integrated Non-Magnetic Non-Reciprocal Components Based on Switch-Based Conductivity Modulation

A passive, linear, and time-invariant medium with symmetric permittivity and permeability tensors is reciprocal and has identical transmission properties in forward and reverse directions. However, non-reciprocal components such as isolators and circulators have a wide range of applications at radio frequencies, in wireless communications and radar systems to name a few. Traditionally, non-reciprocal components have been implemented using ferrite materials biased by a permanent magnet, but there has been exciting recent resarch on non-reciprocity induced by periodic time modulation in RF circuits. In this paper, we review our recent research on non-magnetic CMOS-compatible non-reciprocal RF components using switch-based conductivity modulation. We demonstrate that by modulating the conductivity around a delay medium, non-magnetic, low-loss, compact and broadband non-reciprocity can be achieved. We present measured results from CMOS circulators at 750 MHz and 28 GHz to validate our results. We also briefly describe the co-design opportunities that arise once the circulator is integrated on the same CMOS chip as the rest of the transceiver.