Sujet : Re: fast NPN in LT Spice
De : legg (at) *nospam* nospam.magma.ca (legg)
Groupes : sci.electronics.designDate : 06. Jun 2024, 05:46:24
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <q9a26jdroatud3o1hgaqve5r4bc6got063@4ax.com>
References : 1 2 3 4 5 6 7 8
User-Agent : Forte Agent 4.2/32.1118
On Tue, 4 Jun 2024 00:10:32 +1000, Bill Sloman <
bill.sloman@ieee.org>
wrote:
<snip>
Gosh, what a hideous mess, in many respects.
>
Do tell us why. You do claim to revel in electronic discussion.
Perhaps its the nonlinearity of the output stage, which is biased off.
So it's a switch, but the slow speed of the output, if engaged,
results in a stretched pulse.
The assertion that spice parameter Tf is related to spec sheet Ft is
only a guess.
The bfr92a model written into your simulation turns out to
be part of a more complete model published as a die-within-a-package.
There's little difference in performance when substituted into the
simulation.
If all the models with Tf<20ps are evaluated, you get unpredictable
results. Note that the bfr92a model doesn't actually meet this
limitation, but other similar models do (~bfr93). There are roughly
270 of them.
Each will either:
- fail to engage with the slow output detector.(31)
- act roughly like the original simulation.(217)
- oscillate at an unrelated frequency.(19)
- stall.(1)
- give incoherent wild results (2)
http://ve3ute.ca/query/Tf_20ps_vs_bfr92a.zipJust why one model does one thing, while another does something
else might be interesting to figure out.
RL