—A wideband voltage-controlled oscillator (VCO) with a frequency range from 3GHz to 5GHz is presented. The VCO has two control inputs, one for band switching and one for continuous control of the output frequency. The VCO with a 4.4 tenability PMOS varactor was designed and fabricated in a TSMC 0.18- u m CMOS process. The phase noises at 1MHz offset are -124 dBc/Hz and -92 dBc/Hz for the oscillation frequency of 2.95 GHz and 5.03 GHz, respectively. Simulated data shows that the designed VCO is suitable for ultra-wideband system applications.