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A low-voltage low-phase-noise 5.5-GHz differential LC voltage-controlled oscillator (VCO) with quadrature outputs for direct and low intermediate frequency conversion is presented. The circuit is fully integrated in IBM's 65-nm radio-frequency complimentary metal-oxide-semiconductor process. Care has to be taken in achieving low phase noise, whereas the VCO core is powered from a low-voltage supply of 650 mV. The VCO incorporates a digitally controlled technique in order for the direct current to be adjusted in each oscillation band. Switching capacitors are adopted to enable the selection of the oscillating band, whereas differentially controlled varactors are used for fine tuning the circuit. Quadrature outputs are provided by two identical oscillators appropriately coupled. The oscillator has a wide tuning range, i.e., between 4.6 and 6.2 GHz (29%). The quadrature VCO core dissipates 8.71 mW from a voltage supply of 0.65 V, whereas its phase noise is -113 dBc/Hz at 1-MHz offset of a 5.5-GHz carrier. The whole circuit occupies 0.33 mm2 of die area.