fmax ft

Wondering anybody know how to plot fmax, ft when sweeping transistor current in LNA design? Thx.

ft:the frequency when current gain(h21)=1,
fmax:the frequency when max gain=1.
simulate h parameters and S parameters and then extrapolate h21 and max gain to 1(or 0dB),you will find ft and fmax

Thanks, icfarmer! As for the SpectreRF, I think it may because so many tools (digital/analog/RF/layout) can be integrated inside cadence environment, which makes simulation relatively easier.

icfarmer

There is one thing you did not say it clearly. When do the S/h-parameter simulation, is it nessary to do the matching network?

it doesn't need impedance matching.50 Ohm term is enough. ft and fmax tell us how high frequency the transistor can handle. they are of no dependence on impedance matching.

By impedence matching, I mean totally different thing which is part of the tool issue. I don't think I can "tune" the matching network (e.g. using smith chart), not necessary when simulating the ft or fmax.
but thanks for pointing that out.

Added after 5 hours 29 minutes:

icfarmer,

I think your method can get the ft and fmax @ specific bias current. But if I sweep the current, the DC bias point keep changing and at each of these points, should be a ft and fmax. However, h/s parameters are simulated in freq. domain.
My big issue is: how can I correlate these two factors? The diagram should be in 3-D, if I am not wrong.