[sdiy] exponential vs linear vco cores

[Walker Shurlds]

Bipolar transistors have exponential current vs base voltage
characteristics, so you'll see a mixer op-amp feeding a bipolar
transistor current mirror on exponential.  I haven't looked at any
linear ones honestly but I'd imagine just an op amp and some resistors.

On Fri, 26 Feb 2010 12:27:11 +0100
cheater cheater <cheater00 at gmail.com> wrote:

> Antti,
> thanks for the round up, that was a good bit of info as usual from
> you. How are the different V/I built?
> 
> D.
> 
> On Fri, Feb 26, 2010 at 12:20, Antti Huovilainen <ajhuovil at cc.hut.fi>
> wrote:
> > On Fri, 26 Feb 2010, cheater cheater wrote:
> >
> >> I was wondering if someone knows a good article on the differences
> >> between exponential core and linear core VCOs?
> >> What is the difference in how they operate?
> >
> > The core itself is the same for both types, only the V -> I
> > converter differs. Exponential has inherently wide range, zero/low
> > per hz offset but suffers from heavy temperature dependency on CV
> > scale factor (needing tempco resistor or other compensation).
> > Linear has low tempco but needs trimming to get rid of constant per
> > hz offset and can't as easily get as wide range. Linear is much
> > harder to modulate (such as for vibrato) as modulations must be of
> > the form y = x*2^(mod) and the exponent operation must be
> > temperature compensated such that zero modulation will always mean
> > no DC scaling by temperature (to avoid detuning with temperature).
> >
> > For digital control I consider linear VCOs to be better bang for
> > the buck as you don't need to bother with tempco and can trim any
> > offsets digitally.
> >
> > Antti
> >
> > "No boom today. Boom tomorrow. There's always a boom tomorrow"
> >  -- Lt. Cmdr. Ivanova
> >
> 
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