[time-nuts] App Notes Voltage References

[Bruce Griffiths]

Steve Rooke wrote:
> 2008/11/30 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
>   
>> Mark Sims wrote:
>>     
>>> If you want to play with the Xicor references,  I can recommend the device sold by Ebay zildjianboy7 (Doug Malone)  See current auction item 280289828315.   For $30 shipped,  it makes for a very handy meter checker / portable voltage reference.  Not as stable as the Geller Labs board,  but it runs on a 9V battery.
>>>
>>>       
>> Beware of their large flicker and wideband noise.
>> Because of the relatively high flicker noise, they wont, in practice be
>> anywhere near as stable as a good zener based reference
>> However they may be useful for checking lower resolution devices such as
>> a handheld DMM.
>>     
>
> Thanks, that's exactly the use I had intended one for.
>
> 73, Steve
>   
Steve

Since these devices actually store the reference voltage on an internal
capacitor, it would be interesting/informative to plot the output as a
function of time over several years/decades.
They haven't yet been available for long enough to establish their long
term stability in actual use.
I wonder if one can recharge the internal capacitor should this prove
necessary or if one wanted to adjust the output?
This probably requires access to an internal node.
During manufacture, a servo loop adjusts the output by changing the
voltage on the internal capacitor until the output reaches the voltage
of the external precision reference.
The servo loop is then opened trapping the required charge on the capacitor.

Bruce