Teledyne LeCroy Eye Doctor II - Manual (Page 27)

Operator's Manual
Feed Forward Equalization (FFE)
A Feed Forward Equalizer (FFE) is implemented as a tapped delay line filter, with 1 tap per unit interval.
An FFE can compensate for Inter-Symbol Interference (ISI) due to preceding and following bits. For
details on the algorithm for the FFE filter, see
FFE Filter Algorithm .
When using SDAIII-CompleteLinQ, select the Linear Eq button on the SDAIII Framework dialog to con-
figure FFE. Otherwise, select the Equalizers button on the Eye Doctor II dialog to configure FFE.
To configure FFE:
1. Check the Enable checkbox in the Feed Forward Equalizer (FFE) section.
2. Specify the # Taps.
3. Specify how many of those taps should be precursor taps in the # Precursor Taps dialog.
Note: The number of precursor taps is often around half of the total number of taps.
4. Either check Auto Find Levels or manually enter the Upper Level, Lower Level and Decision Level.
5. Press the Train FFE button.
The Include In Training checkbox allows you to decide whether or not the Feed Forward Equalizer
should be trained when the Train FFE & DFE button is pressed on the Equalizer dialog. The ability to
exclude the FFE from training is particularly useful when specific tap values from the Feed Forward Equal-
izer have been entered by the user, which is discussed in the next paragraph.
While the best way to use the FFE is to train it, you can also enter the exact tap weights (if known) on the
FFE Details dialog (as follows). The Clear Taps button sets all of the taps to 0 except the first tap which is
set to 1. This is the pass-through state for the FFE.
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