Hi,
mmm, not sure if that discussion applies here:http://www.designers-guide.org/Forum/YaBB.pl?num=1207474039/9#9. It depends if your model it's symmetric or not. If the model isn't symmetric I wouldn't trust any of the simulations. If the model it's symmetric I would trust PSS and QPSS since transient sims for linearity can cause artifacts in FFT algorithm(although I don't know if spectre FFT algorithm it's a modified one that can take into account variable timesteps).
Hope it helps,

Hi,
Well I made a few experiments on my self guided with some papers and I found that "sweet spot" bias its so sensitive to all:process,input signal,load,degeneration...its too narrow that you can end up with less linearity,worse NF,worse gain and worse input matching all at once. The second order non-linearity effect with a degeneration basically causes the spike of linearity to disappear completely(depend on the magnitude of the degeneration), 2nd order products feedback and mixes with the fundamental and they create another 3rd order nonlinearity even if the third derivative of the current it's 0.
If you look at IEEE for high linearity LNA's people are using more complex structures that are more robust.
Hope it helps,
PS:a couple of references that I have at hand
"RF Circuit Implications of Moderate Inversion Enhanced Linear Region in MOSFETs",IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 51, NO. 2, FEBRUARY 2004,Bill Toole, Member, IEEE, Calvin Plett, Member, IEEE, and Mark Cloutier, Member, IEEE-->that paper I found very useful to carry out sims with my PDK.
"A Highly Linear Low-Noise Amplifier",IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 54, NO. 12, DECEMBER 2006,Sivakumar Ganesan, Edgar Sánchez-Sinencio, and Jose Silva-Martinez-->a high IIP3 LNA and revises two other approaches for high IIP3, also points the effect of second order nonlinearity and feedback.(in fact I did this little search on sweet spot because I've seen professor Silva in a symposium talking about this issues).