Agilent Technologies J-BERT N4903B, User Manual, Page: 209 / 572

N O T E
Adjusting the data input delay may cause momentary clock loss. If you select
Manual Sync mode, this may also result in sync loss.
• Burst sync mode is a special operating mode for measuring data in bursts of
bits, rather than one continuous stream of bits.
For more information, refer to
“Introduction to Burst Sync Mode” on page
211 .
N O T E
If the error detector is in Manual Sync mode, it is recommended that you keep an
eye on the SYNC LOSS light at the top of the instrument. There are various actions
that can lead to loss of synchronization. Check the SYNC LOSS any time you make
changes to the instrument.
What is False Synchronization?
For patterns other than PRBS, the error detector may gain sync at a point in the
pattern that meets the sync threshold, but is not the correct point where the internal
reference pattern and the received data pattern match. This is called false
synchronization.
N O T E
False synchronization cannot occur with PRBS patterns because a 1 bit
misalignment would cause a measurement of 50% or more errors. Thus, the BER
during a misalignment would always be greater than the sync threshold BER.
For example, consider a pattern of 1000 ones and 1000 zeros as shown in the
following figure. With reference alignment 1 the patterns are totally out of phase
and the error detector is measuring 100% errors. But as the reference moves closer
to optimum alignment, the percentage of errors gradually approaches zero
(reference alignment 2 and 3). For exact alignment, the sync threshold must be set
lower than the BER caused by a 1 bit misalignment, in this case 1E-3.
Setting up the Error Detector
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Agilent J-BERT N4903B High-Performance Serial BERT 209