GaAs monolithic implementation of active circulators

A GaAs monolithic three-transistor signal circulator for 0.2- to 2-GHz applications was developed and tested. The circuit consists of three FETs with gates of 150- mu m width and 0.5- mu m length, three capacitors, and seven GaAs resistors. The resulting chip size is 1.1 mm*1.0 mm on a substrate of thickness 0.15 mm. The ability afforded by monolithic construction techniques to locate the active devices in close proximity to each other and avoid interconnecting circuitry stray capacitance is critical to the high-frequency operation of the device. The three-terminal device demonstrated a 6-dB insertion loss and an 18-dB directivity over the above frequency range.<>