Wideband Switched-Capacitor and Switched-Transmission-line Circulators in 40nm GaN Technology: Design and Device Modeling

This paper presents broadband circulators based on switched capacitor and switched transmission-line architectures implemented in a 40nm Gallium Nitride (GaN) process. Using GaN HEMT as a switch enhances the power handling of these architectures achieving an IP1dB of 9/12dBm, representing an 8/11dB increase over wideband CMOS circulators demonstrated in the past. The switched-transmission-line architecture enhances bandwidth by eliminating the charge/discharge of capacitors. The operating frequency range is DC-1.1GHz for this architecture for a 100MHz clock frequency. The DC insertion loss is 2.2dB/3dB for the switched T-line and switched capacitor architecture and matching and isolation are better than <-15dB, and >18dB for both the architectures within the respective operating frequency ranges. One primary design challenge is the lack of all-region models for GaN transistors, particularly for switch configuration. This paper develops a virtual-source model for the 40nm GaN HEMTs and shows the agreement between measurements and simulations.