[volt-nuts] Ultra low noise reference

[Andreas Jahn]

> an exceptionally low-noise voltage reference (in the neighborhood of
> 1.25nV/root Hz).
>
This is the broadband noise which is only of interest if using a high speed
A/D converter. For integrating A/D converters the 0.1-10 Hz noise
(or even lower frequencies as I have learned now) are of interest.
The around 2-3 Hz corner frequency of the setup does not give much
advantage on precision measurements where integration times start from
2 seconds or more.

> One last thought; I have a couple of old proportional crystal ovens
> (salvaged from old military revivers, about 75C internal temp, controlled 
> to
> approx. 0.1C) that I'd like to use to house the assemblies.  What are some
> thoughts on enclosing the entire voltage reference circuit inside an oven?
> Would the heat inside the oven adversely affect the noise and voltage 
> drift
> of the opamp?  Better to put only the voltage reference IC or diode inside
> the oven?

I would put all within the oven minimizing the number of thermocouple
junctions (soldering points) with different temperatures.
But note: with higher temperature the ageing is accelerated
and the noise increases. So for some applications it might be better
to characterize the temperature drift and compensate it by measuring
the temperature.

(see diagram with a 3rd Order polynominal for approximating the
temperature error curve of a LT1027CCN8-5 reference voltage
the resulting error is in a 3uV band / 3V = around 1 ppm).

With best regards

Andreas
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ADC8_TC.PNG
Type: image/png
Size: 42751 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/volt-nuts/attachments/20110909/57e80bcc/attachment-0001.png>