4046 VCO experiment

Scott Gravenhorst chordman at earthlink.net
Thu Aug 17 10:32:52 CEST 2000


harrybissell at prodigy.net wrote:
>Hi everybody:
>
>Two thoughts
>
>1) Check out the internal VCO schematic of the 4046... its in
>ICAN-6101. Scott's circuit is still activating the CMOS Current
>Mirror... so basically the operation is still the same.
>
>2) Think about stealing the archetecture, but built with
>discrete CMOS chips... maybe 4007 for the capacitor reset
>section, and 4049UB for the rest... but absolute symmetry is
>required... each branch must be formed from devices in the same
>package. You need symmetry along the vertical axis...
>(matched right/left hand). Then... replace the current mirror with a
>discrete temp compensated current source.

If I were doing this for the education aspect, this would be an
interesting excercise, however, I really want this more to add
a special noise generator to my FatMan, and I'd like it to be as
simple as possible.  As far as VCO designs go I really want:
*simple*, like one IC if possible, linear and some kind of logic
compatible output such as pulse or square.  My intention is to
recreate my voltage controlled noise gen (pseudorandom clocked
by a linear VCO).  I really liked the effect of sweeping the
spectrum using a control voltage.  I know I can replicate the 
FatMan VCO, or I can use the first one I experimented with, the
LM13600 appnotes one.  The FatMan VCO has the advantage of a
readily available logic output, but it's at least 2 ICs and 
some trannies.  I want accurate linear tracking so that the VCO
can also act as a musical/tonal third VCO.

-- Scott Gravenhorst : On The Edge, but the Edge of What?
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