[sdiy] Adapting exponential convertor for single supply

[Phillip Gallo]

I have recently tried the Hackaday variant of the 'Perlman' type expo
converter. It wasn't the focus of what i was trying, but it met its
requirement.
I used it for a single supply VCO.

Earlier this summer, the SDIY list had a thread about a 250kHz to 3MHz
VCClock.
The thread provoked a quick bench-top project to produce an alternative to
CD/HC/HCT4046 solutions.

IThis project gave me the chance to try:
1) Rene' Schmitz - type linear CMOS osc
2) Hackaday converter
... and due to the above, allowed for a single supply +5Vdc VCClock.

I built this:

http://www.sdiy.org/philgallo/hfvco/cmosvco.jpg

My rough eval was of the VCO itself not the expo specifically. VCO
Frequency ('scope observations) seemed to demonstrate expo conformity for
voltages above the diode derived 'Ref' level and below the High Freq
(integrator/reset) droop.  Below 1Vdc it veers off but still allows for
very usable selectivity .

I didn't trim the VC scaling as the converter was part of a "utility" osc
and later changed to a more aggressive scale as i wanted a wide range
control response

I have only built one of these circuits so YMMV but It proved to be a good
solution for a HF utility clock for BBD, TOGs, and DigiDelay as it is wide
range (meeting original thread requirement) , stable and so easy to build.

p
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20170727/f4543315/attachment.htm>