[sdiy] VCO drift

[Scott Gravenhorst]

I use a 4069UB VCO (René's design) in a synth and find it quite stable.
There is no noticable change in frequency against temperature.  The only
difference between René's actual schematic and mine is that I use a 
linear voltage to current converter, not an expo one.

=?iso-8859-1?q?Karl=20Dalen?= <karldalen at yahoo.se> wrote:
>In the Moog Rouge there is a buffer between  the current reference stage 
>and the expo trannies! What's  the real reason to do this? I can  imagine
>that 
>the buffer could add inaccuracy because of the offset  voltage drift with
>temp!
>( 5mV/deg C) and shifting the frequency  of both VCOs and VCF! Is this
>buffer
>there just because the emitter of the reference cannot sinc the summed
>currents 
>and instead are sinc'ed by the LF353's output stage?  Or is this a Vebo
>issue?
>Or is it because the 10k current limiting resistor causes a offset that
>makes this
>type of design some what unstable?  Any clues!
>
>VCO!
>
>How temperature sensitive are the thresholds levels in a 4069, 
>when used in oscillator designs in such as Renes CMOS VCO?
>Especially when configurated as a comparator with gain ad it
>goes hot?  (im not critiquing his design, they are nice.
>(no its more of a general CMOS questioning/aspect,)
>
>Also wouldn't a CMOS integrator also have quite high leakage
>currents due to esd diodes and other things, e.g i could see a 
>worst case leakage causing a drift of 5-30sec between cycles!
>(depending on manufacturer, process etc.)
>Perhaps not much to rant about but if a CMOS integrator VCOs
>run parallel a zero drift oscillator that 10sec drift would be close 
>to the edge of annoyingly fast phasing. At 5 sec drift i would call
>the VCO defect!
> 
>Thanks!
>KD
>
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>adressen http://se.docs.yahoo.com/travel/index.html 
>

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