Summary: A low-voltage 6-GHz-band monolithic LC-tank VCO has been fabricated using 0.2-µm CMOS/SIMOX process technology. The VCO features a tuning-range switching technique to achieve a wide tuning range. The output frequency range is between 5.71 and 6.21 GHz owing to the tuning-range switch. With the tuning-range switch on or off, the phase noise is about -100 dBc/Hz at 1-MHz offset and about -120 dBc/Hz at 10-MHz offset frequency at the supply voltage of 2 V.