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A 27-GHz voltage-controlled oscillator MMIC (VCO-MMIC), featuring low phase noise of -115 dBc/Hz at a 1-MHz offset frequency and large output power of +3.7 dBm with low DC-power dissipation of 111 mW, was developed using a 0.18-mum SiGe BiCMOS process. A novel merged-transformer matching circuit, in which an inductor in an oscillation loop is reused as a primary inductor of the transformer, contributes to reducing the DC-power dissipation keeping a large output power. This matching circuit is also effective to suppress the bad influence due to the parasitic capacitance of the transformer. The figure of merit (FOM) of the VCO-MMIC is -187 dB. In our knowledge, this value indicates the best performance in 30-GHz class VCO-MMICs fabricated using Si-based technology.