Tektronix OM4006D, Руководство пользователя

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Operating basics
The Color Key colors:
If the prior symbol was in Quadrant 1 (upper right) then the current symbol
is colored Yellow
If the prior symbol was in Quadrant 2 (upper left) then the current symbol is
colored Magenta
If the prior symbol was in Quadrant 3 (lower left) then the current symbol
is colored light blue (Cyan)
If the prior symbol was in Quadrant 4 (lower right) then the current symbol
is colored solid Blue
Eye diagrams Eye diagram plots can be selected for appropriate modulation formats by clicking
on the eye-diagram icon and selecting an eye format. Supported eye formats
include
fi eld Eye (which is simply the real part of the phase trace in the complex
plane), Power Eye (which simulates the Eye displayed with a conventional
oscilloscope optical input), and Diff-Eye (which simulates the Eye generated by
using a 1-bit delay-line interferometer). As with the Constellation Plot you can
right-click to choose color options as well.
The fi eld Eye diagram provides the following measurements:
Q (dB): Computed from 20*Log10 of the linear decision threshold Q-factor
of the eye
Eye Height: The distance from the mean one level to the mean zero level
(units of plot)
Rail0 Std Dev: The standard deviation of the 0-Level as determined from the
decision threshold Q-factor measurement
Rail1 Std Dev: The standard deviation of the 1-Level as determined from the
decision threshold Q-factor measurement
In the case of multi-level signals, the above measurements will be listed in
the order of the corresponding eye openings in the plot. The top row values
correspond to the top-most eye opening.
The above functions involving Q factor use the decision threshold method
described in the paper by Bergano
1
. When the number of bit errors in the
measurement interval is small, as is often the case, the Q-factor derived from the
bit error rate may not be an accurate measure of the signal quality. However, the
decision threshold Q-factor is accurate because it is based on all the signal values,
not just those that cross a de
fi ned boundary.
1 N.S. Bergano, F.W. Kerfoot, C.R. Davidson, “Margin measurements in optical ampli fi er systems,” IEEE Phot.
Tech. Lett., 5, no. 3, pp. 304-306 (1993).
46 OM4000D Series Coherent Lightwave Signal Analyzer