Agilent Technologies N4906B Serial BERT User Manual page 171

Measurement Problems
Additional Information
Possible Cause
Additional Information
Example Log of Sync and Clock Loss
Agilent N4906B Serial BERT, User's Guide, October 2005
The output of your device may contain errors due to noise, although a
noisy waveform is not present at the output. The noise may originate
somewhere else within your device or system, causing random bit
errors to be passed on to other components. Therefore, your device
may have a good output waveform and still transmit random bit
errors.
Sync Loss Seconds
The sync loss seconds in this example may have been caused by high
bursts of errors or momentary clock loss. The clock signal from a clock
recovery module may have momentarily ceased. To confirm periods of
momentary clock loss, check the measurement log file.
In this example, the analyzer was in auto sync mode. If the analyzer
was in manual sync mode, the results would not have been measured
and displayed in the same way.
When the clock signal resumed, the received and ED reference
patterns could only be aligned if the synchronization functions were
activated. In manual sync mode, this would not have happened
because synchronization functions are only activated manually.
In manual sync mode, sync loss and high BER would have been
measured from the start of the momentary clock loss to the end of the
accumulation period.
Data in this measurement log file confirms that there were periods of
momentary clock loss.
Solving Problems
171