Temperature compensation (Was Re: [sdiy] Exponential converter information)

[James Patchell]

The major temperature drift term in an expo converter is the scale factor 
(i.e. the number of Volts/Octave)...changing the reference current to the 
expo pair will only affect the offset drift.  To compensate for the scale 
factor drift you must use either a Tempco Resistor in the feedback loop of 
an op-amp...or use a multiplier (see my web page below for 
details...)...there are no easy fixes for compensating for the scale 
drift...I wish there were...

At 08:12 PM 6/20/2005 -0400, Aaron Bader wrote:

>Wow. That was a lot of information... thanks guys. I think I have my
>head on the ground in this area now.
>
>I've got plenty of ca3046's laying around, RCA production, so I think
>I'll put those to work. I missed the tempco order, so I think I'll
>either heat them or try some other idea.
>
>One idea that comes to mind in René's circuit (fig 3 at
>http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html) is to vary the
>Iref with temperature to compensate for shifts in gain... and
>temperature sensors like the LM335 are not that expensive.
>
>Any chance this idea is feasable?
>
>--
>
>"Not a bird not a leaf not a sound/And well after the close of time"
>         --Front 242
>
>Public Key: http://sparked.zadzmo.org/

         -Jim
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http://www.oldcrows.net/~patchell

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