LeCroy SDA, Operator'S Manual

Page: 343 / 397

SDA Operator’s Manual
The SDA measures jitter by determining the timing between the edge crossings of the data signal
under test and comparing these measurements with the nominal unit interval (UI). A flow diagram
of the edge to edge jitter measurement is shown below. The total jitter is derived from the
histogram of timing error measurements. The histogram of measurements is accumulated and
the tails of the distribution are extrapolated to form an estimate of the histogram for a population
of 10
16
measurements. The extrapolated histogram is then integrated to determine the cumulative
distribution function, which forms the sides of the bathtub curve. The bathtub curve gives the eye
opening (or 1UI - Tj(UI)) for all bit error rates down to 10
-16
. The total jitter for a given bit error rate
is found by measuring the width of the bathtub curve at the y-axis value corresponding to the
desired bit error rate. The periodic jitter and data dependent jitter are measured directly on the
sequence of timing error measurements and the random jitter is found by measuring the
difference between the total jitter and the components of deterministic jitter.
SDA-OM-E Rev H
343