HP 54750A, Руководство пользователя, Страница: 132 / 478

Eye , Mask and Eyeline Mode Measurement T utorials
Making Eyeline Measurements
(HP 83480A Option 001 only)
4
STOP
5
T o continue measurements , press:
4 RUN 5
Eyeline traces are often improved through averaging. T o activate averaging,
press:
4 Acquisition 5
NNNNNNNNNNNNNNNNNNNNNNNNNNNNN
Averaging on
Whatever the number of averages is set to , this number of waveforms
(complete record lengths) will be measured before a single averaged
eyeline trace is displayed. A tradeo exists between throughput and noise
reduction.
Error trace capture
Error trace capture allows you to isolate the waveform that caused a mask
violation. Before starting error trace capture , the following should be
considered in setting up the measurement to ensure that the desired number
of bits is displayed in the sequence leading to a mask violation.
Set the time base position to several bits , or time increment, above the
lowest allowable value to ensure the full sequence is seen. F or example , the
minimum setting at 622 Mbit/sec is 13.7 bits . T o view 10 bits , set the position
to greater than 24 bits . Similarly , at 2,488 Mbit/sec, the minimum setting is
54.7 bits , so set it to >65 bits .
Set up and align the mask. Y ou may need to wait several seconds to generate
enough waveforms to create an eye diagram suitable for mask alignment.
Note that the mask is aligned to the full eye closest to the left screen edge .
T o see the sequence leading to a mask violation, the mask must be adjusted
to the right edge of the screen. This is done by simply reducing the time
base position setting. Unless the mask is intentionally aligned again, it will
maintain its position in time .
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