Analysis of leakage in a 77-GHz Quasi Circulator based transceiver with time division IQ switching

A detailed analysis of leakage in a 77-GHz Quasi Circulator (QC) based transceiver is performed. The evaluated system includes an IQ modulator in the LO path for time division IQ switching. A leakage canceler, realized as a varactor based W-band impedance tuner, is employed in the transceiver. The leakage canceler can be controlled based on the DC-offset of the mixer. With an appropriate model of the occurring leakage, the relation between DC-offset and different leakage sources can be explained. Furthermore, the limitations of canceling the DC-offset in the system are derived. A simulator has been developed to demonstrate the effects of the non ideal IQ modulator as well as the nonlinear characteristic of the impedance tuner. This facilitates the understanding of the DC-offset output behavior. The model as well as the simulation have been verified based on on-wafer measurements.