[sdiy] exponential vs linear vco cores

[Antti Huovilainen]

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