the VCO gain is the measure how the output frequency changes with the control voltage
so it can be related directly how the MOS varactor capacitance will change with the change in the control voltage
if ur talking about ring oscillator , it is not controlled by the varactor , it is controlled by changing the current in the inverter so change the propagation delay ,
which control the output frequency of the ring oscillator
Fout \alpha 1/ ( \tau • N)
so the current control \tau , so u control the frequency
if ur talking about ring oscillator , it is not controlled by the varactor , it is controlled by changing the current in the inverter so change the propagation delay ,
which control the output frequency of the ring oscillator
Fout \alpha 1/ ( \tau • N)
so the current control \tau , so u control the frequency