For ultra-wideband RF systems, a wide frequency tuning range of an LC-VCO is highly desired. Presented is an LC-VCO operating at 20GHz with differentially tuned MOS varactors. A simple voltage converter is used to generate the differential tuning voltages without compromising the VCO gain or phase noise. When implemented in 65nm CMOS technology, the VCO achieves 14.6-22.2GHz tuning range and exhibits a worst-case phase noise of -96dBc/sqrt(Hz) at 1MHz offset across the entire frequency range. The VCO core consumes 4mA of current from a 0.65V supply and occupies approximately an area of about 0.06mm2.