[volt-nuts] Ultra low noise reference

[Dave M]

I've been following the "Traveling Standards" thread (and its aberrations). 
It took me a while to find it, but the postings reminded me of an article 
that I had read in Electronics Design magazine some years ago.  The article 
by Walt Jung 
(http://www.waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf) 
describes a technique using a 10V reference IC and an AD797 opamp to build 
an exceptionally low-noise voltage reference (in the neighborhood of 
1.25nV/root Hz).

The circuit, as drawn, uses an AD587 10V reference IC, buffered by an AD797. 
After looking the circuit over again (after having lost it for many years), 
I'm thinking about getting some parts and building a few copies of it, using 
a variety of voltage references, such as the LM399 and 1N829 (I have a few 
left over from days long past).  Almost any type of voltage reference could 
be used in front of the opamp, and a variety of output voltages provided 
with a bit of gain in the opamp.  Possibilities are intriguing.  In terms of 
voltage stability and drift, the AD587 doesn't look particularly attractive, 
considering today's available references that's why I'm thinking about other 
types of references.

I'm not an engineer, but spent a number of years as a calibration tech, and 
later, as an engineering tech.  Precision voltage and frequency equipment 
continue to hold my interest, even though I've been away from it for several 
years.  I'd be interested in hearing a discussion of the pros and cons of 
the circuit described in the article.

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?

Thanks for comments,
David
dgminala at mediacombb dot net