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A 30 GHz trifilar-transformer-coupled quadrature voltage-controlled oscillator (QVCO) is proposed in this letter using 0.13 μm CMOS technology. The trifilar transformer provides dc decoupling as well as ac mutual coupling from drain, gate, and source nodes. The mutual coupling increases the overall quality factor while the gate/drain-to-source coupling provides quadrature coupling. The proposed 1:1:1 trifilar transformer realization has lower ohmic loss than the conventional trifilar transformer realization and is especially suitable for high-frequency applications. As a result, the proposed 30 GHz QVCO has a -195 dBc/Hz figure of merit (FOM) and a maximum 41.6 dB sideband rejection (SBR) at a 0.6 V supply.