An LC oscillator is provided that achieves improved phase noise performance. A variable frequency oscillator includes a variable supply source, an oscillator tank circuit, a variable capacitance circuit comprising MOS switches, and an oscillator tank voltage common mode adjustment circuit. When the capacitance of the variable capacitance circuit is varied to vary an output frequency of the variable frequency oscillator, the common mode voltage is adjusted to reduce transitions of the MOS switches between an inversion state and a depletion state during excursions of an output signal through one cycle of oscillation.