Teledyne LeCroy SDA II - Manual (Page 10)

Serial Data Analysis II Software
matically set on each acquisition. The value set is the selected percentage of the signal amplitude (which
equals base - top).
The Slope selector determines which edges are measured when "Clock" is selected in the Signal Type
selector in the Signal dialog.. The choices for slope are Pos(itive), Neg(ative) or Both Select the choice
that corresponds to the edge type that is used for clocking of the data in your device, or that is of inter-
est in your analysis. For example, if you only latch data on positive edges, select Pos. If you clock on
both edges, you can select Pos or Neg rather than both in order to understand how the edge type affects
the jitter measurement.
The Hysteresis entry box sets the hysteresis level to use for edge detection, in units of vertical divisions.
The hysteresis is the vertical amount that the signal is required to travel beyond the crossing level to
allow detection of a crossing in the opposite direction. Incorporating hysteresis in the edge detection
algorithm prevents the software from finding false edges that would otherwise be detected due to noise
or other small glitches in the signal. The default value is 500mdiv, or 1/2 a division. When the input sig-
nals are properly scaled (i.e. to fill approximately 90% of the grid, vertically, this level of hysteresis should
be sufficient. When dealing with signals that result in closed eyes, a smaller value for hystersis may be
required.
More information about how the SDA analysis software determines the edge timing using the crossing
level can be found in the
Clock Recovery Theory section
NOTE: The Relative setting can potentially remove jitter by tracking slow level shifts between acqui-
sitions, if this is not desired, use the Absolute level setting.
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