An original composite eye diagram is reformulated by deliberately re-alignin g its component eye diagrams according to some appropriate standard. This 'forced-alignment' shifts the components in one or both of the time and voltage ayes. Notice is taken of the shift(s) fo r each channel, and that shift data is appended to the data structures for the original components. The content of the data structure can be read in its original form, or, read and force-aligned. A force-aligned composite eye diagram created from the re-aligned components can then be displayed, investigated and evaluated with any of the existing tools that are used to analyze eye diagrams, simply by instructing the process that reads a component eye diagram data structure to reform that component as it is being read. Automatic forced-alignment of the component eye diagrams involves two steps. First, fo r each component eye diagram some specified property an 'earmark' having a (time, voltage) value is measured. Individual earmarks may be the centroid of an eye opening for each channel in the group, or representative point of transition. Second, each component is offset in time, voltage, or both, according to the difference between its earmark and some forced-alignment reference that is associated with the enti re group of channels.That forced-alignment reference may be the earmark of a selected component eye diagram or an average of all of the earmarks in the group. Manual shifting of each component eye diagram by the operator is also possible. The forced-alignment shift data is appended to the eye diagram dat a structures. Patterns in the forced-alignment data can be discovered by inspection of a report showing th e amounts of forced-alignment shifting. Channels in the report can be sorted according to their degree of alignment.
FORCED-ALIGNMENT MEASUREMENT TOOLS FOR COMPOSITE EYE DIAGRAMS