User guide

This graph shows the extrapolation of the optimum Q-factor and the optimum
threshold level from a limited number of measured points.
The measured data points to be used for the calculation have to be within a
contiguous BER range. This range is defined by specifying the Min BER for Q (lower
threshold) and the BER Threshold (upper threshold). Both thresholds can be set
in the lower section of the View tab.
The Q-factor can only be calculated if for both high and low level rails two or more
points fall within the defined BER range. For reliable results use at least five
measured points.
To ensure proper settings, activate the Show Measured Points function on the
Graph tab and switch to the BER vs. Threshold graph. Move the upper BER
threshold marker (vertical line) so that a sufficient number of measured points is
included for the calculation:
From these points, the following QBER vs. Threshold graph is generated:
This graph illustrates the calculation of the Q-factor (65 in the figure above) as the
best fit line through the calculated points. This method makes the calculation
reproducible. For details see “Q-factor Results” on page 279.
Furthermore, the following parameters can be set on the View tab of the
Properties dialog box:
You can calculate measurement parameters for:
• BER Threshold
Advanced Analysis 6
Agilent J-BERT N4903B High-Performance Serial BERT 275
QBER vs. Threshold Graph
Calculate