Many effort s have been applied to extend the capacitance coverage in the L C tank for the purpose of ultra broadband CMOS L C VCO design. But the analysis of the tuning situation shows that the varactor change shifts the working stat e of the oscillator. It is discovered that be sides the tuning range of capacitance in the LC tank, another restriction on the broadband CMOS differential VCO is the characteristic of the cross-coupled MOS pair which must be adjusted accompany with the varactor tuning to maintain the oscillation stat e. Dividing the cross-coupled MOSFET pair into switchable part s is a practice and effective method to meet the later condition. The de sign example of a VHF CMOS L C VCO demonstrates that the new schematic can get a breakthrough in the tuning range performance.