LeCroy SDA, Operator'S Manual

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SDA Operator’s Manual
The SDA measures eye patterns without using a trigger by using aforementioned the software
clock recovery to divide the data record into segments along the time values of the clock. For the
purpose of dividing the timeline into segments, the time resolution in the waveform record is
infinite. The samples occur at fixed intervals of 50 ps/pt (for a 20 GS/s sampling rate). The
samples are positioned relative to the recovered clock timing points and the segments delimited
by the clock samples are overlaid by aligning the clock samples for each segment. A
monochrome or color persistence display is used to show the distribution of the eye pattern data.
The jitter added by the measurement system (in this case) is from the sampling clock which, for
the SDA is very low: on the order of 1 ps rms.
Eye Violation Locator (ASDA Option)
The eye pattern is measured by overlaying segments of a continuous acquisition. Since the
complete data record is available, the location of individual bits can be determined by comparing
each bit interval in the original waveform to the selected mask. The mask is aligned horizontally
along the mean bit interval, and vertically along the mean one and zero level in the case of a
relative mask. Absolute masks exist for some standards and are defined in the vertical dimension
by specific voltage values. Figure 4 below shows this alignment. When mask testing is turned on,
the entire waveform is scanned bit-by-bit and compared to the mask. When a mask hit is
detected, the bit number is stored and a table of bit values is generated. The table is numbered
starting with the first bit in the waveform. This table can be used to index back to the original
waveform to display the waveform of the failed bit.
Figure 4. Eye Mask Alignment for Violation Locator
SDA-OM-E Rev H
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