Teledyne LeCroy SDA III-CompleteLinQ - Manual (Page 33)

Operator's Manual
Eye Parameters Dialog
The Eye Parameters right-hand dialog lets you choose which parameters you want to show on the
screen. You can also enter a slice width. The slice width is a percentage of the duration of a single bit (the
part of the pattern over which the extinction ratio is measured). Setting a percentage value indicates how
much of the central portion of the bit width to use.
Both the Jitter Measurements and the Eye Parameters can be on at the same time. They are shown sep-
arately on the table display. To turn off all eye parameter measurements, touch the "Turn off Eye
Params" button located on the left side of the adjacent Eye Diagram dialog.
Note: The oscilloscope's Measure table can also be displayed.
Eye Measurement Parameters
There are several important measurements are made on eye patterns. Many standards specify them as
part of required tests. Eye measurements mainly deal with amplitude and timing (outlined later in this
section). For information on setting up eye measurements, see
Set Up Eye Diagram .
Eye Amplitude
Eye amplitude is a measure of the amplitude of the data signal. The measurement is made using the dis-
tribution of amplitude values in a region near the center of the eye (the "slice width") selected by the user
(normally 20% of the distance between the zero crossing times). The simple mean of the distribution
around the 0 level is subtracted from the mean of the distribution around the 1 level. This difference is
expressed in units of the signal amplitude (normally voltage). This measurement algorithm is best suited
to eye diagrams that are rendered from optical rather than electrical signals. In the presence of inter-sym-
bol interference and/or equalization, it may not give reasonable results.
One Level
Simple mean of the 1 or high state of the eye within the selected slice width
Zero level
Simple mean of the 0 or low state of the eye within the selected slice width.
Eye Height
The eye height is a measure of the signal-to-noise ratio of a signal. The mean of the 0 level is subtracted
from the mean of the 1 level as in the eye amplitude measurement. This number is modified by sub-
tracting three times the standard deviation of both the 1 and 0 levels. The measurement provides an indi-
cation of the eye opening and is made on the central region (normally 20%, user changeable) of the UI
(bit period). This measurement algorithm is best suited to eye diagrams that are rendered from optical
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