Teledyne LeCroy Eye Doctor II - Manual (Page 42)

Eye Doctor II Software
Case 3, with 6dB de-emphasis and 7 tap DFE.
Let's see if more DFE taps help. Note the somewhat tighter distributions at the crossings.
Case 3, with 6dB de-emphasis and 15 tap DFE.
The previous screen-shot shows the DFE Details dialog (accessed by touching Edit/View DFE Setup). The
tap values are shown and can be changed. In addition, the number of taps in use are shown along with
Clock Adjust (also shown on Eye Doctor II's Clock Recovery dialog as Deskew). This screen-shot shows
the Training decided that 10ps of deskew was needed. Since the Eye diagram horizontal scale is
16.7ps/div we clearly see 10ps if it was not deskewed. The need for this deskew is almost certainly due to
the group delay of the CTLE, only present on the clock recovery path, so its group delay caused a skew
between the data and the recovered clock.
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