antilog

[Ian Fritz]

I looked at this circuit some, too. There are approximations -- note the
equation on the right side of the page that has <approximately equal> marks.
I think there may be a couple of approximations there. Also I wondered about
noise, with the OTA input being attenuated to such a low level. Still,
probably worth having a closer look. And I still like tempco resistor
compensation. Once you realize how accurate it is and that the statement you
keep reading that it "can only work at one temperature" is *wrong*, then it
becomes much more attractive.

  Ian


----- Original Message -----
From: "Jim Patchell" <patchell at silcom.com>
To: <synth-diy at node12b53.a2000.nl>
Sent: Thursday, August 10, 2000 9:13 AM
Subject: Re: antilog


>
>
> "Fraser, Colin J" wrote:
>
> >
> > The LM13600 temperature compensation scheme looks really smart and might
be
> > the answer.
> > How come nobody noticed it hidden away at the end of the data sheet all
> > these years ?
> >
> > Colin f
>
>     Speaking for myself personally, it was because it was mislabed as a
"log"
> converter, so that was the first reason.  Second reason, if I had read the
text
> discribing it, I would have realized what it really was.
>
>     Paia seems to feel that it is good enough for a VCO.  I am going to
wait
> until I get my 9720 kit to reserve judgement.  I am mostly currious as to
how
> well it will actually perform the exponential function.  I am somewhat
concerned
> because the "temp sensor" is not exactly linear.  It very well me be that
this
> is not going to be a problem.  They seem to be operatin that OTA over a
very
> small input range which should keep it pretty linear.
>
>     -Jim
>
>