For the LM13600 datasheet example, I can get: Vo/Vi = 1739 ∗ Iabc
or I can get: Vo/Vi = 870 ∗ Iabc
or, stretching, I can even get: Vo/Vi = 1948 ∗ Iabc
But I can't get the Vo/Vi = 940 ∗ Iabc that they claim is true.
I'd love to see how someone gets 940∗Iabc.
Chip
--- In PolySix@yahoogroups.com, "chipaudette" <chipaudette@...> wrote:
>
> Hi Johannes,
>
> If you're willing to explain your calculation of LM13600 gain, you can give the explanation in whatever forum you'd like!
>
> If you post it here, more people are likely to see it. And, if you don't mind, I can then copy select quotes over to my blog as necessary (with attributions, of course) when I go to use the information in future posts.
>
> If you were looking for an example to explain, I cannot see how the LM13600 datasheet (page 8) got the equation: Vo/Vi = 940 x Iabc for the circuit in Figure 2.
>
> If you can explain that one, then maybe I can take a crack at analyzing the one in the Polysix.
>
> Thanks!
>
> Chip
>
>
>
> --- In PolySix@yahoogroups.com, Johannes Hausensteiner <johau@> wrote:
> >
> > Hi Chip,
> >
> > I just finished watching the movie "The Cincinnati Kid". Whereas in
> > former years I would identify more with Steve McQueen nowadays I tend
> > more to the Edward G. Robinson character. It seems a little an
> > allegory to this LM1600 matter.
> > I am perfectly confident that I am able to understand and calculate
> > this VCA stage. But it is late today now (11 p.m.) and I hear my bed
> > calling my name :-)
> >
> > I take the challenge and I'll come back later, hopefully with some
> > figures!
> >
> > Johannes
> >
> >
> > P.S. I am not sure whether to answer to the list or your blog. What do
> > you prefer?
> >
> > On 2013-03-03 21:41, chipaudette wrote:
> > > What I find so difficult about the LM13600 is my inability to calculate what the transconductance should be for a given circuit configuration.
> > >
> > > For the VCA shown in the datasheet, the datasheet says that:
> > >
> > > Iout = Iin∗(2∗Iabc)/Idiode
> > >
> > > Seems simple enough, except I can't seem to use this equation to get anything reasonable. For example, the datasheet says that their example circuit results in Vout/Vin = 940 x Iabc. I can't see how they got that value from their circuit.
> > >
> > > Then, when i try to generalize to slightly different circuit setups (like the one that we're discussing in the polysix), I can't get any reasonable answer that comes close to the experimental result.
> > >
> > > Part of the reason could be that the assumptions in the datasheet, while accurate for the specific circuit that they drew, has important (critical) differences with how people (such as the Polysix designers) actually end up implementing their VCA. This page has a very interesting discussion...
> > >
> > > http://lushprojects.com/blog/2012/08/lm13700-missing-forumla/
> > >
> > > ...but it doesn't have quite enough detail to help me through all the way so that I can compute the gain vs Iabc relationship that I'm looking for.
> > >
> > > Bummer.
> > >
> > > Johannes, are you able to correctly calculate the gain of the LM13600 for the example in the datasheet or for the setup in the Polysix? It thwarted me....
> > >
> > > Chip
> > >