Abstract: Method and apparatus for extending a VCO tuning range. A shunt inductance connected in parallel with a varactor reduces the effective capacitance of the varactor and increases the capacitance ratio. This increases the VCO tuning range without increasing the tuning sensitivity variation and the phase noise.

Abstract: The present invention includes a Voltage Controlled Oscillator (VCO) having a resonant circuit capable of being quickly switched between two resonant frequencies in order to generate two different LO frequencies. In a preferred embodiment, the present invention includes a VCO having a dual-frequency resonant circuit attached to the VCO's resonant circuit input leads. The dual-frequency resonant circuit is constructed in a differential architecture in order to create a number "virtual ground" points within the circuit that nearly eliminate any ground currents, and thus minimize the time required to switch the resonant circuit between the two LO frequencies. The switching between two resonant frequencies is achieved by creating a short circuit across certain components within the circuit to eliminate them from the resonant circuit.