Mike,
A frequency offset is just a long term shift from nominal rate.
Wander is "slow" variations and jitter is "fast" variations of phase.
The separation between "slow" and "fast" is a bit arbitrary, but the 10
Hz division-line is handy as it describes different sources, where
wander is the in-bandwidth noise accumulation where as jitter is usually
damped pretty well by being outside of the jitter bandwidth.
See ITU-T G.810, G.813, G.823-825.
Cheers,
Magnus
On 06/27/2014 07:37 PM, bill wrote:
On 6/26/2014 2:39 AM, mike cook wrote:
A few dumb questions:
But first a quote from the ITU ( doc G.180 )
""4.1.12 (timing) jitter: The short-term variations of the significant
instants of a timing signal from
their ideal positions in time (where short-term implies that these
variations are of frequency greater
than or equal to 10 Hz).
DQ1 yes
DQ2 Frequency offset would come into the Wander category except it
defined differently.
DQ3 No
That gives my take on your q questions. Its been 23 years since I had
think about jitter and wander as chairman of T1X1.3 committee
Bill
K7NOM
4.1.15 wander: The long-term variations of the significant instants of
a digital signal from their
ideal position in time (where long-term implies that these variations
are of frequency less than
10 Hz).
NOTE – For the purposes of this Recommendation and related
Recommendations, this definition does
not include wander caused by frequency offsets and drifts.""
DQ1. These both refer to phase variations, so with the exception of
the frequency range specified, are they mathematically equivalent?
DQ2. The note on wander excludes frequency offsets, but that is not
specified for jitter, so do I have to include a frequency offset in
jitter measurements? It seems to me that it make no sense to do so.
DQ3. Can I deduce an underlying frequency offset from jitter (wander)
by taking an RMS value over some window of values?
regards,
Mike
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