Settling Time of VCO

What are the main parameter one should concider when he design for very low Settling time of wide band VCO.
What kind of Varactors (Companies and kind) are recommended for the design?

D.J
:?

We need some more informations as:
a) The VCO is used in the transmitter path or in the receiver path;
b) bandwidth of the modulating signal;
c) Frequency of operation and bandwidth
d) Output power;
e) type of modulating signal ( digital, analog, video, ecc )

Mandi

In general it is a feedback loop with a bandwidth and damping. Critical damping is usually best or slightly underdamped. For the bandwidth you have the countering problem of reference spurs going up and settling time going down as the bandwidth increases.