simulating for sigma delta noise folding due to charge pump nonlinearity

 Hi,

In the context of fractional plls, the nonlinearity in the PFD+CP transfer characteristic would result in  noise folding which would increase the low freq phase noise.

I want to create a simple setup to capture in spectre simulations using
1.) quantisation noise by using zvcvs ( just by plugging coefficents of NTF of sigma delta modulator(z domain TF))
2.) vcvs to create the nonlinear transfer char using pwl vector/data file (curve obtained from stand alone chargepump simulation  charge  Vs. delta phi (input phase difference))

If i cascade these two sources 1,2 can I really capture the folding effects(intermodulation )?
but what simualtion (ac/tran/pac ) is needed for this kind of situation?


Ofcourse modeling  modulator/chargepump in timedomain or using matlab for the same is fullblown exercise to capture it completely.

Thanks,
Vamshi