Agilent Technologies J-BERT N4903B, User Manual, Page: 473 / 572

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.
N O T E
The accumulated results table displays the total accumulated error ratio. Look in
the measurement log file to see the error ratio during the period of constant errors.
Solving Problems
9
Agilent J-BERT N4903B High-Performance Serial BERT 473
Possible Cause
Additional Information