PhaseStation 53100A User’s Manual V1.04 25-Apr-2022
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Second, the averaging process also helps to cancel uncorrelated noise from the two independent
reference oscillators. At taus beyond 1s where instrument noise doesn’t come into play, the result is
reminiscent of what would be obtained from a three-cornered hat measurement (Figure 63).
Given sufficient measurement time, it’s likely that the violet traces would approach each other closely at
taus greater than 1s, but only the cross ADEV technique can remove the instrument noise at shorter-
term taus. Comparing the two violet traces in Figure 63, the three-cornered hat solution remains
limited by the 53100A’s noise floor below t=1s, and it also does not support limit-line evaluation.
Finally, three-cornered hat measurements also require three different .TIM files to be saved and
reloaded for later inspection, making them less user-friendly than the cross ADEV approach in scenarios
where only one DUT needs to be measured.
Although this technique is capable of exceptional performance, there are also some subtle conditions
and caveats associated with cross ADEV measurements. Residual measurements of quiet DUTs (or the
instrument itself) may show substantially more variance than a conventional ADEV measurement would.
Cross ADEV plots are not subject to the fragmentation often seen in three-cornered hat measurements,
but in cases where the actual device performance is similar to or better than that of the instrument
itself, cross ADEV plots can display numerous divots and valleys at taus where the measurement has not
yet had time to settle. This effect is unlikely to be of concern when measuring real-world frequency
standards and sources, even at the most demanding performance levels, but may be a consideration in
two-port residual ADEV measurements where it risks underrepresenting the DUT’s true stability
performance.
Also note that for processing performance reasons, TimeLab limits the ADEV bin resolution in cross
ADEV traces to a maximum of 8 per decade.
Trace
→
Draw xDEV traces with spline interpolation (
i
)
may
be used if desired to smooth cross ADEV traces. While the accuracy at taus corresponding to the actual
Figure 63
Summary of Contents for PHASE STATION 53100A
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