low-temp-drift ssm2164 VCO

[Rene Schmitz]

Hi Roman, 

(and welcome to the Club of the Solid State compensated!)

>Let me have the pleasure of presenting new (for me)
>VCO with *no* tempcos and *no* heater, but still
>not bad in terms of temperature stability.
>This circuit was born in discussion with
>Paul Maddox in private mail.
>It is based on my beloved SSM2164 quad VCA chip,
>and it's ten times more stable than my last VCO.
>It isn't stable as a rock, but still enough for me
>to make next module with it.
>
>I did thermal tests using finger for heating, and
>blowing air for cooling, so I guess temperature
>change was about 10-15 deg. Over this range
>the frequency drifted like this:
>
>4Hz	0,2%
>100Hz	0,5%
>550Hz	0,1%
>1.5k	couldn't notice
>11k	0,3%
>
>Any comments, and improvement tips appreciated

After I had seen yours, I was thinking about the idea of makeing a SSM2164
based oscillator, too. (But I have nothing build yet!!!) I think I'll use a
similar scheme as in my other *no* tempco *no* heater compensated
oscillators for compensation. (Hence the strange welcome above. ;-) This
would be similar to your circuit, but I'd place an opamp arround the gain
stage to form a divider but with only temperature dependant division. (Not
an attenuator. The gainstage is in the feedback loop of the opamp.) This
should turn the temperature dependancy into its reciprocal (perhaps only
when we let the stage have some gain, and if the tempco is only a
*factor*). But then it should cancel out totally. I have sucessfully used
such a scheme - with a diffamps tempco term turned into the reciprocal by
an opamp. Check www.uni-bonn.de/~uzs159/vco2.html to read all about it.

Bye
 René


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