When I simulated IIP3 of a Double-balanced CMOS Mixer, I find the slope is not 3 but about 2.35, so selecting different input amplitude to extrapolate, the IIP3 result is different. Why dose this instance occur? When meeting this problem, how can I simulate IIP3?
I set amp_RF=-60dBm and amp_LO=0dBm,but the result was still strange which can be seen in the picture. I think the input amplitudes is small enough, isn't it?

Hi,

The simulation result is affected very much, for small signal levels, by tolerance options.
You can rerun the simulation by choosing reltol 0,0001, vastol 1e-6 and iabstol 1e-12.
You have to choose ep to a value only when the slope is close to 3.

Best regards,
Gavi