Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 226)

Operator’s Manual
224
WE-OM-E Rev A
Signal
The signal section allows for the selection of the source, which can be any
of the four active channels, a memory trace, or any one of the eight math
traces. The signal must be a voltage-vs.-time waveform captured using
the CIS timebase. Other types of waveforms will result in unpredictable
results.
The Clear Sweeps button resets the acquisition, and zeroes out all
averages and persistence maps. This control is also replicated by the front
panel Clear Sweeps button.
Crossing Level
The "Crossing Level" controls allow you to select the amplitude
at which the Fit Height is centered and the size of the fit height.
There are two modes for this control: Percent and Absolute.
Percent mode is the default and sets the level relative to the
amplitude of the signal. The Fit Height is set to 15% by default
and defines the vertical range over which the histogram for
each edge in the pattern is measured. Fit Height affects how
the jitter breakdown is determined when a stressed eye is
being measured. Eye patterns are “stressed” by adding ISI
(from a length of cable or backplane, for example) and by
adding periodic jitter to the signal. While the periodic jitter
impacts mainly the timing, ISI can have an impact on the rise
time and amplitude of the signal. High levels of ISI can reduce
the rise time of the signal significantly and can lead to
increased random jitter measurements if the fit height is large.
The default is optimum for most cases but when measuring
severely stressed eyes, the fit height may require adjustment.
For signals with large amounts of ISI, the fit height may need to
be reduced below 15%. In cases where there is very low jitter,
increasing the fit height will allow more data to be used in the
measurement, giving higher accuracy.
The Absolute selection allows the setting of an absolute level
for jitter measurements. The absolute level is in volts or watts,
depending on the module (electrical or optical) in the channel.
Fit Height is in volts (or watts), and the %target allows the
setting to be made as a percentage. The %target and Fit
Height controls are linked; changing one of the controls
automatically updates the other.
The Find Level control sets the absolute level to the center of
the signal amplitude. The control does not update until the On
checkbox is checked.