85–110 GHz CMOS tunable nonreciprocal transmission line with 45 dB isolation for wideband transceivers

The first CMOS nonreciprocal transmission line (TL) for wideband tunable full-duplex transceiver front ends, having over 45 dB isolation in a bandwidth of 1.5 GHz and tuning range of 85–110 GHz, is demonstrated. Offering tunable nonreciprocal propagation, this structure is based on a parametric time-varying TL modulated by a 10 GHz signal through distributed capacitive mixing. Two capacitive mixers together with a biasing network form a resonant type of wideband matching. Implemented in a chip area of 0.245 mm2 in 65 nm CMOS, this nonreciprocal TL achieves over 45 dB isolation throughout its entire bandwidth, a maximum 6.5 dB insertion loss (IL) and over 10 dB return loss.