[sdiy] exponential converters

[James Patchell]

Well, I am afraid there really isn't anything that will do that (as a 
chip).  You will need to actually construct one, but it doesn't take very 
many parts.  You can build a decent converter using a dual opamp and a dual 
transistor (PNP for source, NPN for sink).

         You will find circuits all over the internet.  You will find quite 
a few on my webpage below.

One problem you will have to address is what to do about the built in scale 
drift of 3300ppM/C.  If you are going to use the converter to control 
pitch, you will need to compensate for this drift.  For non critical 
applications, I don't bother.  There are several ways to compensate for 
this drift.  One is to use a temperature compensating resistor (the 
infamous +3300ppM Tempco Resistor), Temperature control, or electronic 
compensation (I discuss this on my webpage)....The tempco resistor methode 
uses the fewest components.

As far as dual transistors go, I prefer to use the CA3046 for moderate 
precision and the MAT04 for high precision.  The CA3046 is more than 
adequate for VCOs, and is very cheap (about 50 cents).

Hope this gives you a start.

         -Jim

At 08:24 PM 3/18/2004 -0500, Guillaume Fairfield wrote:
>Hello all,
>
>I'm looking for an IC that performs an exponential conversion of a voltage 
>to a current...you know, the 1v/OCT thing.
>Preferably something that is still in production.
>Anything helps though.
>
>Thanks
>
>Guillaume
>
>

         -Jim
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