On 22/02/2021 20:47, alan victor wrote:
The approach I have taken is to gather the 2 port s parameters for a box full of say 3904. Then use the s data with a waveform arithmetic statement in LTSpice to get ft. As ft is an extrapolation of the low frequency gain on a 6dB per octave slope, it is pretty fast to evaluate. Recall, it is just a function of gm and Cbe; unity short circuit current gain crossing point. It does assist in validating the quality of some BIP models. I usually take the s data at the collector current where advertised ft peaks.
I'd be interested to know whose S-parameter data you've got for 2N3904?
Overall, your suggestion isn't worth much because S-parameters only model linear devices. The whole point about SPICE models is that they model the non-linear characteristics of devices. As a by-product they can also re-produce the S-parameters if the SPICE model is good. The converse is simply wishful thinking.
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Regards,
Tony
Tony Casey