hrkari,

   Have you tired autonomous envelope following analysis?  It is really
intended for handling modulated signals, however, it should probably
work for a sine wave input. It should be okay for IIP3 and the output
power spectrum. Not sure that it supports power sweeps so P1dB maybe
difficult, unless you want to generate an AM-modulated signal.

  BTW, the Virtuoso community website contains the SpectreRF app
notes for LNA, Mixer, VCO, and PA simulation. See the following link

http://www.cadence.com/community/virtuoso/wireless/tr.aspx?exclude=ams

                                                           Best Regards,

                                                              Sheldon