Whilst the standard deviation of the individual measures of TI will be
invariant with the number (N) of TI measurements made (provided the
environment doesn't change and the noise remains white), the standard
deviation of the averaged TI will decrease with increasing N until drift
and non white noise components dominate.
Bruce
Said Jackson wrote:
Yes, the TI will get more accurate with time. But the setup suggested in
previous email doesn't measure TI.
It measures the standard deviation of that TI. Big difference, two completely
different numbers. The SD number is essentially a measure of the absolute
amplitude of the noise. Since it is an absolute measurement, it doesn't
converge to 0ps.
That number will quickly converge to about 20ps to 50ps. It will not get
smaller with larger sample sets.
Please check the 5370 manual what standard deviation means, it will make sense
then.
Bye,
Said
Sent from my iPad
On Mar 12, 2011, at 9:27, [email protected] (Mike S) wrote:
At 12:00 PM 3/12/2011, Said Jackson wrote...
The average will approach 0.0 as the number of samples is increased, but not
the standard deviation.. The value displayed by their unit is standard
deviation.
If you're measuring jitter of an external signal, accuracy is obviously much
worse than the internal jitter. But if you're measuring TI, both the instrument
and signal jitter get reduced with more measurements, leaving a more accurate
TI, doesn't it?
Being designed and sold as a TI analyzer, that seems right. It seems the jitter
test is mostly to make sure the unit is operating properly.
If I recall correctly, internal jitter is affected by tweaking the 200 MHz
multiplier. Lacking a proper spectrum analyzer, that's the only calibration I
have been unable to do.
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