Teledyne LeCroy Eye Doctor II - Manual (Page 38)

Eye Doctor II Software
Note: DFE taps is set to 7, the default is 3. The result looks significantly better when using 7 taps, because
on long runs of the same state, the input waveform continues to drift to larger magnitudes for more
than 3 UI.
In the following screen-shot we show Eye Doctor II's DFE Setup dialog. On the Equalizer dialog, the only
difference is the caption under the DFE button showing Enabled: DFE 7 taps. So, in the following screen-
shot, equalization is only being done by DFE.
The following screen-shot shows Eye Doctor II applying a reasonable transition time to the shift at the UI
boundaries. The shift reflects the DFE threshold shift, by moving each UI of the waveform relative to the
fixed center level. The transition time is automatically determined as a fraction of a UI, adjusted to be rea-
sonable at the greater of the oscilloscope's maximum bandwidth or 16GHz.
Case 2, with DFE equalization.
In this case, if the FFE is used instead of CTLE on the clock recovery path, the result is the same.
See for yourself and set Data Path to From FFE to see the result of training the FFE, and then change the
Data Path back to From Input so only the DFE does the equalization for the data out. The result should
look exactly like the previous screen-shot.
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