Dear gingerjiang
i have check ur circuit , it is good , and the nice thing about it , that u change the delay of the inverter by changing the load capacitance by the varactors used
mine is by changeing the current ,
i donot know which one will give u wide tuning range , u have to check it by simulatin , also u have to check the phase noise performance of each
and then decide which one will be more suitble ,
also u have to check how to add a voltage to current converter , to the current controlled ring oscillator
khouly