Non-Magnetic CMOS Switched-Transmission-Line Circulators With High Power Handling and Antenna Balancing: Theory and Implementation

Recently, CMOS non-magnetic circulators have been demonstrated based on switch-based spatio-temporal conductivity modulation, but these initial demonstrations remain limited in transmitter power handling, linearity, and ability to combat antenna variations. This paper describes a non-magnetic circulator architecture that uses no external components, and employs a variety of linearity enhancement techniques, such as device stacking, optimal switch biasing, and localized electrostatic discharge (ESD) design to achieve watt-class power handling and high IIP3. A new antenna balancing approach is described that uses no inductors or lossy resistors and yet allows high isolation in the face of strong antenna reflections. The concepts are validated through a 1-GHz 180-nm SOI CMOS prototype that achieves 1-W TX-ANT P
₁
dB, +50-dBm TX-ANT IIP3, and high isolation for as high as 1.85 ANT VSWR and beyond. The circulator also exhibits low insertion losses of 2.1/2.9 dB in the TX-ANT and ANT-RX paths, and ANT-RX noise figure (NF) of 3.1 dB. These results represent a 10-100× enhancement in linearity/power handling over prior non-magnetic circulators and are shown to lower the power consumption of a communication link when compared with the state-of-the-art electrical balance duplexers in scenarios, where dynamic range is limited by P
₁
dB and NF.