User guide

The Fast Eye Mask measurement is first of all meant for production and screening
tests. It allows to determine very quickly whether the eye opening seen at the
output signal of a device is within specifications, that means, within certain timing
and voltage limits.
This is achieved by measuring the bit error rate at a limited number of test points.
The Eye Diagram allows a quick check for the DUT’s signal output, and determines
the signal quality. Due to the higher sampling depth of a BERT value, the eye
contour lines display the measured eye at a deeper BER level, for accurate results.
The Spectral Jitter measurement allows you to analyze the jitter inherent in the
output signals of your device under test (DUT) as a function of the frequency. This
measurement can be used for investigating the behavior of the DUT, for example
to identify crosstalk effects.
Before you can run any of these advanced measurements you have to properly set
the required parameters. After the test is complete you can view the results.
General Requirements
For any measurement to yield reasonable results the following requirements apply:
• The error detector must be correctly set up and synchronized with the pattern
sent from the DUT output port.
• Ideally, the sampling point should be aligned to the optimum sampling point
(for example, with the Auto Align function).
• For low bit rates below appr. 620 Mbit/s only the Error Location Capture
measurement works.
Please refer to “Bit Rate Range” on page 176 for a detailed explanation of the
limitations at low bit rates.
If the Serial BERT's pattern generator is used to send a data pattern to the DUT,
then also the following two conditions must be met:
• An appropriate pattern is selected.
• The pattern generator is correctly set up.
For examples, refer to the descriptions of the different measurements.
Optimizing Parameters
If the presented measurement results do not answer your questions adequately,
you can easily modify the setup parameters in the Properties dialog box. When
6 Advanced Analysis
228 Agilent J-BERT N4903B High-Performance Serial BERT
Fast Eye Mask
Eye Diagram
Spectral Jitter