s2p files for different bias

i am designing an LNA using the S2P file of the transistor @ certain gain and noise figure...but when i replaced that nonlinear model of the transistor instead of the s2p file..the whole S parameters of the transistor were changed leading to the change of the gain and NF curves as if i was using another transistor...
Isn't supposed that the s2p file and the nonlinear model to have the same S parameters at a certain DC bias ?!
thanks

some times it gives different S parameters but not much in difference
i have used one before gives about 1 or 2 dB change in S parameters

but the noise figure is completly different ,
u may use S parameter file

or if u have the capabilties u can characterize the tarnsistor using VNA and generate ur S2p file to be used in simulation

wish this help

khouly

sp analysis is small signal analysis based,
better use the nonlinear model

Hi,
I have faced the same problem when I designed an oscillator. so which one is true the ADS model or the company model?
Thanks.

S parameters should be more accurate (especialy if you measure it by yourself using TRL calibration), but they are accurate only for one bias conditions and one temperature.
Nonlinear model is less acurate, but it can be used in S-parameter analize, HB analize and DC analize with different temperatures.
About noise figure.
The same, S-prameters should be more accurate. Some of nonlinear transistor doesn't have noise parameters at all. Another thing is the simulator you use. I had a problem with GENESYS, noise figure for s-param and nonlinear model was completly different, but in ADS was simmilar.

You must be careful about the NONLIN models, cos some models include package parasitics, some don't. Anyway, I also noticed some differences in simulation using S-parameters or the NONLIN model of the active device.