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Chapter 6: Concepts
Understanding Eye Scan Measurements
Understanding Eye Scan Measurements
Eye scan measurements are made possible by the logic analyzer's
ability to double-sample each channel using slightly offset delays and
by comparing the delayed samples using an exclusive-OR operation.
When the exclusive-OR output is high, the delayed samples are
different, and a transition is detected between the delay times.
Because of jitter and other variations in the sampled signal, an eye scan
measurement checks many clocks for each pair of delay values so that
it can report how often transitions occur between the two delay times.
Then, another pair of delay values is checked, and so on, until a whole
range of time is scanned for transitions.
Because the logic analyzer is able to adjust the threshold voltage for
channels, an eye scan measurement is able to repeat the scan for
transitions over time at many threshold voltage levels.