Active Quasi-Circulator MMIC Using OTAs

A very compact, active quasi-circulator is proposed and experimentally demonstrated in this work. It consists of an active balun and a current combiner using operational transconductance amplifiers in CMOS. Experimental results show that the insertion loss between the circulation ports is low and all three ports have input reflection coefficients below -10 dB. The chip operates from 1.5 to 2.7 GHz and it outperforms previously known monolithic microwave integrated circuit circulators covering this frequency range in terms of the S₃₁ isolation, standing at -26 dB, as well as physical size: the integrated circuit measures only 0.25 mm² including bonding pads.