User guide

We do not need to know the exact BER values at x+ and x-. It is sufficient to assure
that BER(x-) is greater than 10
-12
and BER(x+) is lower than 10
-12
at a confidence
level of 95 %.
The algorithm then assumes that x
L
(for the left-hand slope of the bathtub curve)
is in the middle of the bracketing interval. After repeating the procedure to
determine x
R
(for the right-hand slope), it calculates the total jitter peak-to-peak
like in the standard timing/jitter measurement.
The duration of a Fast Total Jitter measurement depends on:
• the BER threshold
• the bit rate
• the sample delay step size
• the contribution of random jitter
• the contribution of deterministic jitter
Compared to a conservative bathtub measurement, the Fast Total Jitter
measurement can reduce the measurement time by more than a factor of 40.
Typical test times are approximately 20 minutes at 10Gbit/s and slightly more than
one hour at 2.5 Gbit/s for a measurement at the 10
-12
BER threshold with an overall
confidence level better than 90%.
Advanced Analysis 6
Agilent J-BERT N4903B High-Performance Serial BERT 249
Measurement Duration