| 摘要 |
Delay induced apparent amplitude desensitization in a data signal channel and its accompanying worm-like distortion in an Eye Diagram Analyzer is avoided by altering the measurement to avoid the need for any substantial delay in the path of the data channel threshold comparison signals. In a first technique, only enough delay will be inserted in the data channels to produce the relative adjustments needed to compensate for skew between the data channels, as determined by a calibration operation, and it is these de-skewed, but otherwise un-delayed, data threshold comparison signals that are, in rapid succession, clocked into the latches whose difference registers a hit at a given (time, voltage) pair. The clock path delay is then varied from a minimal value to a sufficiently large value capable of spanning a desired the number of eye diagram cycles. In a second technique, the needed amounts of de-skew delay found by the calibration operation are noted, and then the actual delays in the data path are set back to zero. The clock path delay is swept as in the first technique. The de-skewing operation is then performed in post-processing that produces the eye diagram after the measurement is complete. In either technique, the short width of transitions in the data threshold comparison signals that are associated with threshold values near the extremes of data signal excursion are no longer swallowed by the finite bandwidth of a long delay line, since the delay lines in the data channel paths now either introduce only just enough delay to compensate for skew (and those amounts are very short), or, do not introduce any extra delay at all.
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