Wile designing an LNA, I have come across a test case where single tone PSS analysis with small amplitude suggests a circuit has net voltage loss while S-parameter analysis suggests there is net voltage gain. The input amplitude is small enough that the compression should not be an issue. I am doing PSS analysis with 0 output harmonics. All port impedances are properly taken into accout. Transient analysis is consistent with PSS and AC analysis is consistent with SP analysis. I am using ideal switches (sp1tswitch) from Cadence analogLib. Does anyone have had similar problem? Would love to hear your suggestions and comments.

Best regards,
Raz