Isolation performance of sub-harmonic Gilbert mixers

This paper analyzes the isolation mechanisms between two types of sub-harmonic Gilbert mixers in detail. The proposed double-compensated structure without additional output balun has inherent LO and 2LO cancellations at each port, which can greatly improve 2LO-to-RF leakage for the down or up converters. The experimental results reveal that the proposed double-compensated structure applied in a 2-um GalnP/GaAs HBT sub-harmonic down converter achieves a 2LO-to-RF isolation of 80 dB, and its f_Lo/2f_Lo leakage is insensitivity to LO power when compared with that of a conventional single-stacked cell.