1.2–3.8 GHz active quasi-circulator with >30 dB transmit-receive isolation

An active quasi-circulator (AQC) operating at a frequency band ranging from 1.2–3.8 GHz is designed in a 0.18-μm CMOS process. To improve the isolation between AQC's ports common-gate (CG), common-source (CS) and common-drain (CD) configurations have been employed. To particularly improve the transmitter-to-receiver port isolation, out-of-phase cancellation is employed by making the transmit signal traverse from two different out-of-phase paths. A figure-of-merit (FOM) has also been proposed to enable a fair comparison of different published works. For the proposed design, simulation results indicate >11 dB return losses (RL) for all three AQC ports. The AQC has maximum insertion losses (IL) of −10 dB and −7.8 dB between transmitter-to-antenna and antenna-to-receiver ports respectively. With a power dissipation of 40 mW, the proposed AQC displays a transmit-receive isolation of >30 dB and a high FOM of 1.948 GHz × mW.