Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: fast NPN in LT Spice
Date: Wed, 05 Jun 2024 23:46:24 -0400
Organization: A noiseless patient Spider
Lines: 40
Message-ID: <q9a26jdroatud3o1hgaqve5r4bc6got063@4ax.com>
References: <eqsp5jde87vqs6du4a7djoalag7kpkuhkr@4ax.com> <v3j087$1bpc$1@nnrp.usenet.blueworldhosting.com> <4n2q5jln0sb9oqbfp81jm723tbjf7tol80@4ax.com> <v3j33n$2dk5$1@nnrp.usenet.blueworldhosting.com> <gkdq5jdq7gbe9pd5qekn1evt2gaa8unqhj@4ax.com> <v3jqnn$3prrc$1@dont-email.me> <ikir5jdbv9rbponup9btn3bcfsm5326ea2@4ax.com> <v3kiso$3u1if$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 06 Jun 2024 05:44:33 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="901be6abd0a8c7b73f8d4bbbfb09f4cb";
	logging-data="1430154"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+CedvMmD43w5BCfefo4Xpl"
Cancel-Lock: sha1:PuB5zuv29Lkyadgvzvrinvm/71Q=
X-Newsreader: Forte Agent 4.2/32.1118
Bytes: 2502

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.zip

Just why one model does one thing, while another does something 
else might be interesting to figure out.

RL