[sdiy] Temperature Compensated Exponential ConverterUsingSSM2164

[Ian Fritz]

At 01:58 AM 9/1/2009, Magnus Danielson wrote:

>Now that there seems like it is possible to get good cancelation, we need 
>to look at the practicality of achieving it.
>
>I think we need to have some heater/tempsensor hooked to it only for the 
>purpose of trimming.

Agree.  If you are trying for compensation to better than 100 pm/K, then 
you definitely need to characterize the temperature behavior with some 
measurements. I have shown how to do temperature measurement and cycling at 
home in my dial-a-tempco writeup:
http://home.comcast.net/~ijfritz/sy_cir9.htm

Don't forget that if you are measuring the whole VCO and not just the 
converter, you will need to be aware of other sources of drift, i.e., the 
linear drift of the VCO core.  If you are interested in just the expo drift 
-- "scale factor" -- drift then be sure to measure how the octave ratio is 
changing, not just some particular frequency.

The difference between "scale-factor" and "tuning" drift is explained in 
excruciating detail in my tempco theory writeup:
http://home.comcast.net/~ijfritz/sy_cir9.htm

I strongly encourage anyone taking on this kind of temperature-compensation 
to study the theory carefully, or else you will probably measure and report 
meaningless results.

Ian