[sdiy] Hybrid VCO

[Tim Ressel]

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



--- Tim Parkhurst <tparkhurst at siliconbandwidth.com>
wrote:
> Hello All
> 
> It seems a LOT of effort goes into building a VCO
> that tracks well and has
> little or no drift with temperature. I was
> wondering, has anyone tried using
> a microcontroller as a 'feedback element' to adjust
> the frequency of a VCO
> to take out temp drift? The steps would be
> 
> 1) Micro uses A/D converter to sense CV
> 2) Micro calculates or looks up desired frequency
> 3) Micro measures frequency at output of VCO and
> adjusts input CV or
> charging current accordingly
> OR
> 3) Micro takes two quick samples of sawtooth wave,
> calculates frequency from
> slope and adjusts input CV or charging current
> 
> The second version of step 3 would be faster and
> might allow the micro to
> update the CV in lots of quick, small steps so that
> the compensation
> wouldn't produce audible frequency jumps. The end
> result might be a $500
> module, but I would think that a reasonably fast
> micro might be able to keep
> tabs on 2, 3 or even 4 VCOs (so that $500 might buy
> a quad ultra-stable VCO
> module). Also, this would take some of the tempco
> burden off of the analog
> circuitry, making it cheaper and easier to build.
> This is essentially a
> digitally tuned analog VCO, and I think you could
> dial in enough drift to
> keep the sound "phat" (in fact, you should be able
> to dial in exactly how
> much drift you'd like). I'm sure this has been done
> before in modern
> polyphonic systems, but I've never seen it done
> (real time) in a modular
> VCO. Any thoughts?
> 
> Tim Servo
> 
> 
> 
> 
>
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