Re: VCO's measured frequency is far away from it's simalated
At that frequency I would not find it surprising to be 6-8% off from simulated
(your process controls on many key components, are worse than that, let alone
the accuracy with which you may have (or not) modeled the parasitic loadings,
supply droop, wirebond effects and so on.
I have found trouble more than once, trying to test oscillation frequency at
probe. Supply can get mighty busy if you didn't build in enough on-chip
decoupling to kill internal switching spikes (Qswitching should be less than
10% of Qdecouple is my rule of thumb).
You will want to approach the problem with an orderly list of the possible
shortfalls, and knock them down one by one (preferably in simulation, by
adding realism for each until you see something start to make sense).