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The wireless market drives the integration of RF circuits on common digital CMOS technologies. Full integration of the tank circuit, low-phase noise and high current efficiency are desirable for voltage-controlled oscillator (VCO) circuits. The design of fully-integrated non-relaxation VCOs in modern digital technologies is limited by the lack of high-quality passive components. For example, the quality of on-chip inductors is severely limited due to ohmic losses, especially in common CMOS technologies with low-resistivity substrates. Using transistor parasitics as tank capacitors, large active devices can be used in the VCO so current efficiency is optimized while phase-noise performance and a high center frequency are maintained. For a 0.7-2.7 V tune voltage range, a 200 MHz or 4.3% tuning range is available. This VCO can be used for 5 GHz wireless applications with a typical IF frequency of several hundred MHz.