[time-nuts] GPS: ADEV or MDEV?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Apr 23 12:35:33 UTC 2007


Question - does Vref drift matter for a GPSDO? It seems it is
> either too low to be of concern or the effect of Vref drift is in
> fact indistinguishable from OCXO frequency drift and is thus
> transparently compensated by any 3rd order loop?
>
> I don't know for sure, but is 1 ppm/day drift in Vref typical? If
> so given an EFC gain of 1 Hz / 10 MHz / 10 V = 1e-6 / V the
> net drift per day due to Vref is 1e-12 which is 50x below the
> quartz drift spec of say a hp 10811A (5e-10/day).
>
> Is the zener drift plot in Analog Devices AN-713 typical?
>
> /tvb
>   

Tom

Tempco (if the reference isnt in a temperature stabilised environment) 
and noise can be much more important if the drift is low enough.

That drift plot in AN713 is the for a bandgap reference.
However the attached plot from Woodward J Eicke's in April 1964 ISA 
transactions  paper shows similar drifts for discrete zener reference 
diodes.
Buried zeners can be much better.

Bruce
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