[sdiy] Log -> process -> AntiLog

[sbernardi at attbi.com]

An anti-log function is no more than our friendly exponential generator used 
for 1v/octave response. Run the output current into the virtual ground of an 
opamp with resistor in the feedback loop, and you have a voltage in, voltage 
out anti-log (i.e., exponential) conversion.
Note that your log converter should also use the matched transistor and 
temperature compensation (tempco resistor) that the expopnential generator does 
if you want temperature stability. In essensence, you swap the input and output 
on an anti-log generator.
Here's a good Bob Pease article on logarithic generators.
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=4321


Scott Bernardi
> I want to process the logarithm of a linear CV and then
> convert the result back to a linear CV (voltage, not current).
> 
> I know that a log amp can be made with an opamp, input
> resistor and within the negative feedback loop, a diode.  Is
> there some simple way to get the anti-log voltage output
> function ?  Can I simply swap the diode and resistor so that
> the signal passes through the diode and the resistor is in
> the neg. feedback loop?  If not, then how?
> 
> =========================================================  
> - A smoking gun is one that's already been fired.
> - That which gets rewarded, gets done.
> - What good are laws that only lawyers understand?
> - Government: The other religion.
> - The media's credibility should always be questioned.
> 
> "When you see a rattlesnake poised to strike, you do not 
> wait until he has struck before you crush him." 
>   -- FDR
> 
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: home1.gte.net/res0658s/FatMan/
> -- NonFatMan: home1.gte.net/res0658s/electronics/
>