Active quasi-circulator with high port-to-port isolation and small area

An active quasi-circulator integrated circuit relying on a differential central core is presented. Measurements on the quasi-circulator reveal that the forward transmission coefficients, S₂₁ and S₃₂, are both close to -4 dB in the range of 2.5 to 6 GHz. The isolation between the ports is greater than 20 dB and can reach up to 59-dB in the case of S₁₃. The chip was fabricated on a standard 130 nm CMOS process and the core circuit area measures 0.105 mm², making it the smallest active quasi-circulator known to date.