User guide

Changes on the Pass/Fail, View, Graph, and Color tabs only affect the display
of the results. There is no need to repeat the measurement.
Variable Decision Threshold Method
The method used by this measurement is commonly known as Variable Decision
Threshold Method. It provides a "vertical" analysis of the eye opening seen by the
receiver. This method allows you to determine more than just the actual levels.
The Output Levels measurement also calculates the Q-factor (a measure that
describes the quality of the received signal) and derived values. These results can
assist you in characterizing the device. They can also enable you to predict very
low bit error rates that would take a long time to be measured.
Output Levels - Procedures
This section shows you how to set up and perform an Output Levels measurement.
As an example, we measure the output level behavior of a shielded cable.
This requires the following steps:
• Preparing the measurement (see “How to Prepare the Output Levels
Measurement” on page 265)
• Executing the measurement (see “How to Execute the Output Levels
Measurement” on page 266)
• Improving the Display (see “How to Improve the Output Levels Display” on
page 268)
• Changing the Properties (see “How to Change the Output Levels Properties”
on page 269)
• Using the different views (see “How to Use the Different Views” on page
269)
How to Prepare the Output Levels Measurement
To prepare an Output Levels measurement to test a shielded cable:
1
Disable the pattern generator outputs by pressing the 0V (Disable) button in
the PG Setup -> Data Output screen.
2
Use a shielded cable to connect the pattern generator's Data Out port and the
error detector's Data In port.
3
Terminate all non-connected pattern generator output ports with 50 Ω.
Advanced Analysis 6
Agilent J-BERT N4903B High-Performance Serial BERT 265