I am trying to make my VCO run across all different process corners.
For the slow corner I need a very small control voltage to drive the VCO at the same frequency as required in the fast and typical corners.
But how small can this voltage be? Can it be in micro volts? The Loop filter is as shown below.
At very low control voltages you may find that ground noise
(like, if you use an external loop filter cap) may be proportionally
more of a problem to phase noise / jitter. Also what happens
when your VCO control offset gets to the wrong side of gound?
If you have an active loop amp producing this near-ground
voltage, realize that all op amps lose gain as they approach
the rails, and your loop compensation may need work to
accommodate that in the corners.