limits both the oscillator 39 s power output and frequency of operation that can be provided this can be eliminated by using oscillator devices having reactively tuned tank circuits the colpitts type cmos oscillator 20 shown in fig2 a is similar to that described in t gabara k tai m lau s pei r frye and p sullivan 34 a 27 mw cmos rf oscillator operating at 1 2 ghz 34 1994 ieee multi chip conference pp 15 19 however in fig2 a the resonant frequency of the tank circuit is electrically controlled to maintain near zero impedance in the tank circuit the reactance of the inductor 25 can be varied by adjusting the voltage v ml applied to the gate of a large area fet transistor 34 v ml is derived from v dd and the effective value of the variable inductance is l f v ml fig2 b is a cross section of the inductor 25 taken at line a a on fig2 c the spiral metallization 40 is applied to an insulative oxide layer 42 over the polysilicon gate electrode 44 that is connected to the control voltage v ml the spiral 40 is connected between junctions 34 c 34 and 34 d 34 in fig2 a the lightly doped polysilicon gate electrode 44 is deposited on a 100 150.