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Eye-Diagram Analyzer Reference
Performing Eye-Diagram Measurements
Use the NUMBER SAMPLES softkey for this purpose.
• Use the MEASURE EYE to initiate a number of automatic histogram measure-
ments on an eye-diagram.
• Use the r/f tim ON OFF softkey to enable rise time and fall time measurements
during the measure eye routine. This approximately doubles the measurement
time.
• Use the UPPER THRSHLD and LOWER THRSHLD softkeys to set the upper
and lower edges for rise time and fall time measurements. These softkeys
define the amplitude level to be used for the upper and lower parts of an
edge definition for the automatic measurement functions.
• The default upper threshold is 80%. The default lower threshold is 20%.
Measurement Definitions
Extinction Ratio This measurement is the ratio of the most prevalent high level to the most
prevalent low level over one bit interval. The measurement results are dis-
played in both linear and logarithmic (10log) forms of the ratio.
The peaks of the histogram are used to set initial limits for the computation of
the one and zero levels. The initial mean and sigma of the one level is based on
histogram data above the relative 50% point of the peaks. The limits for the
next evaluation of the histogram data are set to the initial mean plus-or-minus
one sigma. The new mean and sigma for the one level is determined. This pro-
cess iterates several times until the sigma becomes small and the mean con-
verges on the most prevalent one level. The determination of the most
prevalent zero level is based on the same algorithm, except the initial mean
and sigma of the zero level are based on histogram data below the relative 50%
point of the peaks.
1 Level (mean,
σ
) This measurement is the mean and sigma of the one level determined from a
20% window of a bit interval centered in the middle of the bit.
0 Level (mean,
σ
) This measurement is the mean and sigma of the zero level determined from a
20% window of a bit interval centered in the middle of the bit.
Eye Height This measurement is the difference between the mean minus-three sigma of
the one level and the mean plus-three sigma of the zero level.