VCO simulation in spectreRF

hello,

I meet some problems in vco simulation.

(1)how can i get the curve of frequency or varactor capacitance versus tuning voltage in spectreRF? especially the curve of varactor capacitance vs tuning voltage.without it ,i don`t know the value of varactor in given controlling voltage,so i can`t fixate the frequency and tuning range in given voltage.
(2)some paper said(i can`t remember exactly) the phase noise is the lowest
when output voltage swinged at the border of current-controlled area and voltage-controlled area. but in my simulation in cadence spectreRF,the larger the output swing is ,the lower phase noise will be. that mean,phase noise is only determined by output swing. is it true ? i don`t know why,pls help me .

thanks in advance!

You can make a simple s-parameter simulation by connecting very large inductor to the tuning voltage source and and very large capacitor single port that will be used to observe the input impedance.
When you change the vtune supply, capacitance will also be changed then you can formulate that with reactance of a capacitor in calculator and you may put this formulae in "output that will be drawn" list. After that simply making a parametric s-parameter analysis will give you input impedance versus vtune volatge and then capacitance value by vtune..

Or better , if you have model parameters of that varactor in a formulae, you may simle dc simulation to find characteristic of tha diode by tuning volatge by making of a parametric simulation..