[sdiy] exponential converters

[Peter Grenader]

Re: 3046.  I have a circuit for an internal heater for that part I can post.
It's been tried and it did in fact give some sort of temp compensation.

I've also had real good success using a Linear Systems dual NPN, the LS312.
High gain and  matched within .2 mv.  Same price at a Mat, but available in
both T071 and 78 (better heat transfer to chip.

James Patchell wrote:

> 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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