Teledyne LeCroy SDA III-CompleteLinQ - Manual (Page 41)

Operator's Manual
Jitter Filter
You can optionally apply either a low-, high-, or band-pass filter to the TIE-vs.-time data measured on the
signal under test (configured on the Signal Input dialog of the Serial Data configuration screens). The filter
is applied as an FFT. You can configure the low and high frequencies used, along with the slope of the
transitions in dB per octave determining the drop-off between the pass band and stop band(s).
Acess the Jitter Filter dialog by touching the Jitter Filter button on the Jitter dialog.
Filter State - Turns the Filter On or Off.
Filter Type - Use this control to choose Lowpass, Highpass, or Bandpass as desired.
dB per Octave - Use this control to specify the slope of the transition from the pass band to the stop
band.
Cutoff Freq (1) - Shown when any filter type is selected.
Cutoff Freq (2) - Shown only when the Bandpass Filter Type is chosen.
For more information, see Set Up Jitter Measurements .
Jitter Pattern Analysis
In addition to the DDj calculations, the Pattern Analysis algorithm is a key part of the determine Tj, Rj
and Dj. The algorithm to determine Tj, Rj and Dj includes "stripping" the data-dependent jitter via pat-
tern analysis. For best results, acquire at least 100 iterations of the data pattern. Note that you do not
need to acquire the selected number of reps of the pattern in each acquisition: the oscilloscope will
accumulate iterations over multiple acquisitions, and keeps track of partial iterations as well.
DDj may be calculated using two methods:
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Repeating Pattern - DDj is measured by finding the average crossing time for each edge in the data
pattern and comparing it to the nominal crossing time, based on the expected bit rate of the sig-
nal under test. Repeating Pattern mode can be used for patterns up to 2^23-1 in length (meaning,
PRBS23). To apply this method, check the Repeating Pattern box.
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Non-Repeating Pattern- The average TIE value is calculated for edges with similar patterns of pre-
ceding N bits. To use this method, check the Repeating Pattern checkbox.
NOTE: If the number of iterations specified in the Min Reps selector are not in the data record when
using the Repeating Pattern method, Tj, Rj, Dj, and DDj all return with --- values showing on the jitter
measure table, and DDj, DCD, and ISI (if enabled for display) show 0 values despite the jitter type actually
being present.
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