Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 220)

Operator’s Manual
218
WE-OM-E Rev A
WAVEEXPERT SDA
Introduction to WaveExpert SDA
The SDA software is standard on the SDA 100G and optional on the NRO 9000, and uses the
Coherent Interleaved Sampling (CIS) timebase to acquire samples of a serial data signal or clock.
SDA does not operate using the sequential timebase, so it is not available on the WE 9000. The
serial data analysis software measures the jitter on the acquired signal and provides readouts for its
components: total, random, deterministic, BUj, and data-dependent jitter. In addition to these
readouts, a number of graphical views of the jitter are also supplied.
WaveExpert SDA Theory
The SDA software uses waveforms from the CIS acquisition mode. This mode is used exclusively
to measure jitter because it provides the ability to lock to a repeating bit pattern, thus displaying a
voltage-vs.-time waveform that can be used to separate the data-dependent jitter. Another very
powerful feature of the CIS timebase that is exploited by the jitter software is its ability to acquire an
exact number of samples over each bit or UI. The number of samples per UI is settable in the
timebase from 8 to 2048, and the exact bit rate is determined during locking of the timebase which,
because it employs a phase-locked loop, provides a stable phase reference against which the
timing of the signal is measured.
The figure above shows how the coherent sampling clock provides a sequence of time slices of the
waveform. These time slices are fixed throughout the signal acquisition process, while the digitizer
divides the amplitude into vertical slices. The signal is, therefore, sampled against a fixed grid, and
any variations in amplitude or phase are measurable by number of “hits” in each x,y cell. The raw
jitter data is captured by accumulating the samples in a horizontal slice across this grid. Note that
because the WaveExpert can acquire up to 500M samples in a single waveform, a grid would