Voltage controlled oscillator is one of the fundamental building blocks in the frequency synthesizer architecture. A 4.224-GHz CMOS complementary cross-coupled LC-VCO is designed for multi-band OFDM (MB-OFDM) ultra-wideband (UWB) application. The tuning range of the VCO is from 3.77-GHz to 4.27-GHz or 12-, which was achieved through pMOS based varactors. The VCO core current consumption is 1.9-mA from a 1.8-V supply voltage. With the combination of source damping resistance of 40-Ω, multi-finger gate structure of pMOS based varactors the 2-μm x 284 fingers and tail biasing resistance of 232-Ω, the phase noise were simulated at - 94.7-dBc/Hz and -120.1-dBc/Hz at 100-kHz and 1-MHz offset, respectively. The VCO circuit is designed in Silterra 0.18-μm 1-poly 6-metal RFMOS process technology. ©2007 IEEE.