why dont you just build your own model from primitives and go from there (switches, ideal DAC's ideal comparators, etc)

Its a quasi tool I would say ..May be I am making some mistake. I am trying to find out..

Loose electron.. What you are saying is certainly one way of doing things but some high level sims in the tools like Matlab are quick and easy  , as you already know.

any one?  :)

Jefkat,

  Building high level models should be possible, it can also be
done ADE/Spectre. Only a few primitive cells are required:
delay, summer, gain, and quantizer should be enough, as
loose-electron pointed out. Using this approach you should
be able to directly realize the target transfer function and
build anything you need. In the attached sample is a second-order
loop. Using this approach, I have built first order, second order,
third-order MASH, band-pass, etc. They all work and show the
expected behavior.

                                                       Best Regards,

                                                         Sheldon