CMOS Active Quasi-Circulator With Dual Transmission Gains Incorporating Feedforward Technique at $K$-Band

This paper presents an innovative architecture for the active quasi-circulator to break the structural limitation on the leakage suppression. A practical prototype is implemented at
K
-band and fabricated by using standard 0.18- μm 1P6M CMOS technology. The comparisons between simulations and on-wafer measurements are reported in detail to confirm the feasibility and capability of the proposed active quasi-circulator. At 24 GHz, the prototype has dual transmission gains of 22.4 and 12.3 dB in the transmitting and receiving paths, respectively. The measured isolation, which is defined by the ratio of the forward transmission to reverse transmission coefficient in the same path, is higher than 50.0 dB at 24.0 GHz. By comparing the leakage phenomena between the prototype with and without feedforward cancellations, the leakage suppression can be improved with a maximum value of 44.7 dB at 23.63 GHz.