[sdiy] Temperature Compensated VCO attempt - help?

[patchell]

    Can't comment on your question, as I am not using the OTA circuit that Scott
was using.  If you look at the schematic below, it is very similar to the
breadboard I have running right now, but I am using the Band Gap temp sensor that
Scott used instead, and altered which OTA was being used to control the Gain (I am
using two OTAs).

  http://www.silcom.com/~patchell/synthmodules/100-1007.pdf

Magnus Danielson wrote:

> From: patchell <patchell at silcom.com>
> Subject: Re: [sdiy] Temperature Compensated VCO attempt - help?
> Date: Sat, 01 Feb 2003 09:53:57 -0800
>
> Dear Jim and Scott,
>
> >     Very preliminary results...but I would say you have a winner here
> > Scott.  I haven't reduced what little data I have yet, but the expo
> > converter looks very stable.
> >
> >     Scale conformity I am getting is pretty much as before, although, I
> > haven't checked it over 8 octaves yet.  But over 5 octaves I am getting
> > about +/- 2 cents (same as before, no big surprise).
> >
> >     I need to get a few more points before I can calculate the tempco.
>
> Sounds good, but I still haven't got a comment on the possibility of a
> diffrential drive error of the OTA. Am I the only one seeing it or?
>
> Is it that my derivations deviates from your in some fundamental way?
> The single sided input will contribute to both the diffrential mode and common
> mode of the OTA input, where the output of the OTA is Iabc*Idiff/Icommon.
> You would get a scale error if you feed into both the diffrential and common
> mode input currents, right?
>
> BTW. I did the full linearized OTA derivation, but using a different
> linearization model, but it should not do any major thing other than switch a
> few signs.
>
> Cheers,
> Magnus

--
 -Jim
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