An octave-tuning-range LC-VCO IC with a novel varactor is presented in this paper. The novel varactor, which is controlled by a single analog voltage, consists of three parallel-connected Inversion-MOS (IMOS)-based varactors, a PMOSFET level shifter, and two NMOSFETs as variable resistors. The control voltage is level shifted and applied to the IMOS-based varactors to widen the capacitance variation. In addition, NMOSFETs acting as variable resistors are employed to further extend the tuning range. The proposed LC-VCO IC is designed, fabricated, and fully evaluated on wafer in 45-nm CMOS SOI technology. The measured tuning range and phase noise of the proposed LC-VCO IC are 74.2% (2.21 GHz to 4.82 GHz) and -140.13 dBc/Hz, respectively. The proposed LC-VCO IC has realized an excellent measured FoMT of 201.8 dBc/Hz under a maximum dc power consumption of only 2.57 mW.