Agilent Technologies J-BERT N4903, User Manual

Page: 379 / 434

Some phenomenon you might observe with the possible causes are
listed below:
Constant Errors (More Errored 0's than 1's)
A hardware failure may have occurred in your device. The errors
became constant at the point of failure.
Digital circuitry often has parallel architecture in which data lines are
multiplexed in stages into one serial data line. This example assumed
that a PRBS pattern was going through digital circuitry that had a total
multiplexing ratio of 256:1. The constant errors were produced from
one data line that became "stuck" high in the first stage of multiplexing.
The data line that was "stuck" high produced errored 0's 50% of the time
with the PRBS pattern. Therefore, at the serial rate, one out of every
512 bits was measured as an errored 0 (1/256 * 50% = 1/512). In addition,
the inverse of the error ratio was a multiple of 2.
In this example, the analyzer could have been in manual sync or auto
sync mode with 1E-2 as the sync threshold BER. If the sync mode
settings were different, the results would not have been measured and
displayed in the same way.
The BER in this example (approx. 2E-3) was greater than the default
sync threshold BER (1E-3). If the analyzer was in the default auto sync
mode, it would have activated the synchronization functions and
continually shifted the position of the reference pattern in an attempt
to find a lower BER.
Solving Problems
8
Agilent J-BERT N4903 High-Performance Serial BERT 379
Possible Cause
Additional Information