[sdiy] Hybrid VCO

[Tim Parkhurst]

> -----Original Message-----
> From: Tim Ressel [mailto:madhun2001 at yahoo.com]
> Tim,
> 
> It seems like you can characterize the VCO over
> temperature, then add in corrections based on
> temperature. Temp should be the major drift factor.
> 
> --tr

Hi TR,

Yeah, using a temp sensor and a micro would have some advantages. It would
be a little simpler, and would allow you to do the same type of compensation
with a VCF or VCA too. I just saw reading the output freq of the VCO as the
most 'direct' route. Also, directly reading the VCO's output freq would
allow compensation for other non-temp related issues like component aging /
drift, power supply drift, and tracking / scaling issues. It would also
eliminate the step of having to characterize each VCO to create a
compensation table (probably only important if you were going to make a
bunch of these things). 

Perhaps a combination of both approaches might do the trick. Read the temp
sensor to perform fast, small adjustments (several hundred or even a few
thousand times per second), and compare the VCO output frequency against an
'ideal' to perform less frequent, larger adjustments (a little like leaving
the 'auto tune' switch ON all the time). 

-Tim Servo-



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