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

> 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