[sdiy] simulating low voltage LM13700 stuff

[Neil Johnson]

Chris McDowell wrote:
> a little bit ago, I posted here asking about low voltage filter designs. I later found that the 13700 works just fine at 3.3V, after designing a circuit for 5V and just giving it a shot.
>
> I'm finding that LTSpice will not simulate these designs at 3.3V. Anything with a 13700 seems to fall apart around 3.9V, from what seems to be some small constant offset. I get signals stuck on the rails in a filter design, 0.4V offset and no gain on a VCA design. I'm not experienced enough to see the pattern here of why it's falling apart this way, or why it would fail in LTSpice but work so well in real life. I've now tried three different LM13700 models, all with the same behavior. Does anyone here have any experience with this? Any idea why this might be happening?

Have you read through Don Sauer's site:
http://www.idea2ic.com/LM13600/SpiceSubcircuit/LM13700_SpiceModel.html

He has some detailed modelling notes on the LM13700 including low voltage.

Neil
-- 
http://www.njohnson.co.uk