Lambda SR1, Руководство по эксплуатации, Страница: 209 / 317

SR1 Operation 209
© 2014 Stanford Research Systems
Eye Diagram Tab
The eye diagram is a plot of probability vs. amplitude and time with probability coded as color. The
Digitizer Display assembles overlays the signal transitions corresponding to the "Jitter Detection"
selection on the
digitizer panel and calculates the probability of the signal appearing at a given time with
a given amplitude. The probability is mapped to a user-selected color palette and an appropriately
colored point is plotted on the display. If the icon is active in the speedbar, the probability can be
directly examined by moving the mouse over the desired point.
By examining the probabilities, the Display computes four "envelope" traces corresponding to the inner
and outer limits of both the upper and lower portions of each transition. Selecting a trace from the
"Cursor 1" or "Cursor 2" control links that cursor to the selected trace. Note that unlike the graph,
clicking on a trace in the trace listing window of the Digitizer Display does
not link the cursor to that
trace. Checking "Lock X" locks the X value of the two cursors to the same value so that differences
between any of the envelopes can be read off directly on the cursor display bar.
Z-scale and Color Selection
The mapping from probability to color can be selected as linear, square root, or logarithmic with the "Z-
Scale" control. Linear mapping tends to produce the most "washed out" color display while logarithmic
produces the most intense color. The "Square Root" selection tends to be a good compromise between
the two extremes. A range of color palettes are available. Color palettes beginning with "Inverse" display
on a white background while the remaining palettes display on a black graph background.
Eye-Limits
The Digitizer Display can test both the width of the eye-opening and the maximum positive and negative
voltage of the input signal against pre-determined limits. To enable limit testing press the "Limits" button
on the Eye Diagram tab.
There are three sets of limits for the eye diagram. The Outer Limits, (not to be confused with the classic
television series of the same name) are two voltage values which specify the maximum positive and
negative values of the input signal.