A 2 GHz differentially tuned CMOS monolithic LC-VCO was designed and fabricated in 0.18-mum CMOS process. The VCO has a 16.15% tuning range (from 1.8998 GHz to 2.2335 GHz) due to a combination of analog and digital tuning technique (4-bit binary switch-capacitor array). The measured phase noise is -118.17 dBc/Hz at 1 MHz offset from 2.158 GHz carrier. With the presented smart switch, the phase noise varies no more than 3 dB at different digital control bits. The phase noise changes only about 2 dB in the tuning range due to the pn-junctions as the varactors. The VCO draws about 2.1 mA current from the 1.8 V power supply and could work in 1.5 V power supply