Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 224)

Operator’s Manual
222
WE-OM-E Rev A
Measuring Jitter
The main Serial Data Analysis dialog provides access to all of the necessary controls for
measuring jitter. The primary controls include the signal source, crossing level, fit height, bit rate,
pattern length, and sample density. The latter three items are normally set by the acquisition
settings, as described in “Initial Setup for Jitter Measurement.” The Use Acq. Settings control
determines where these settings are made.
1. Select Serial Data… from the Analysis drop-down menu.
2. Select the desired source in the signal source control. This can be any channel, math, or
memory trace.
3. The Level is field determines the level at which the timing of each edge is measured. This
control can be set in percent or as an absolute voltage (or optical power level when an
optical module is being used). The percent setting determines the level based on the
amplitude of the most recent acquired waveform as a percentage of the mean ‘1’ level and
mean ‘0’ level, and is updated on each subsequent acquisition. The absolute level uses the
selected voltage or power level for all acquisitions. Find Level automatically sets the
absolute threshold based on the most recent acquired waveform. The preferred setting for
jitter measurements is the absolute level.
4. Set Fit Height to the desired size. The default of 15% is best for the broadest class of
waveforms. When a data waveform is “stressed” (using ISI, for example), the amplitude of
some transitions could be within the fit region, which will cause overestimation of jitter. In
these cases, reduce the fit region so that the lowest amplitude bit is well above the fit
region.
5. The Use Acq. Settings checkbox should be checked if an active signal is being measured.
This setting applies the timebase settings to the jitter measurement.
6. The Check Scope Setup button allows you to verify that the key acquisition parameters
are optimized for jitter measurement. For each setting that is found, you will be prompted to
require adjustment or not. The system will give a choice of whether to fix it automatically,
not to change it, or to fix this and all other adjustments that are found.
7. If a stored waveform is being measured, the bit rate, pattern length, and sample density
must be entered manually. These settings are not stored with the waveform so they must
be stored separately. One technique is to use the settings in the file name for the stored
waveform, for example: “40Gbps prbs7 256samples.trc”