Agilent Technologies J-BERT N4903, User Manual

Page: 149 / 434

The burst sync ratio is an indication of how much of the burst signal
is in synchronization (and can therefore be used for counting bit
errors). The higher the value, the better.
•
Bad burst count
The bad burst count counts the number of bursts that are invalid (for
example, because synchronization failed or the BER of a
synchronized burst exeeds the sync threshold).
The following describes how changing the Gate In start and end points
can affect the evaluation of bursts.
Starting too soon
: If the Gate In signal is applied too soon, the error
detector will either not be able to recover the clock or synchronize the
pattern, and will thus mark the burst as a bad burst (thus increasing the
bad burst count). You can typically reduce the bad burst count by
starting the gating period later.
Burst
Attempted Settling Time ends here
Start too soon
CDR Settling Time
Synchronization Time
Settling/Synchronization fail here Gate Input
Data Input
Starting too late : If the Gate In signal is applied too late, the Bit Count
Time will be shortened, and thus the burst sync ratio will be low (which
forces the measurement of more bursts to obtain the necessary level of
reliability).
Data Input
CDR Settling Time
Synchronization Time
Burst
Gate Input
Start too late
Bit Count Time
End
Margin
Ending too soon : If the Gate In is deactivated too soon, the same
problems will occur as with starting the gate too late (see previous
point).
Setting up the Error Detector
4
Agilent J-BERT N4903 High-Performance Serial BERT 149
Gate In Start
Gate In End