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Nexxim Simulator >
VerifEye and QuickEye Analyses >
   QuickEye and VerifEye Technical Notes >
       Decision-Feedback Equalization           


Decision-Feedback Equalization

As in FFE, the number of DFE taps determine the number of unit intervals over which equalization is to operate. The decision-feedback equalizer keeps the results of the decision on the state of previous bits, then applies the weighted tap values to the previous bit waveforms to minimize ISI for the transition to the current bit state. The DFE weights can be automatically calculated using an algorithm similar to the algorithm used for FFE. While the FFE taps work towards canceling ISI both before the UI (precursors) and after the UI (post-cursors), DFE taps are limited to canceling post-cursors, because of the need to make a decision on a bit before its effect can be dealt with.

Figure 11 shows the QuickEye analysis of the same high-speed serial channel shown in Figure 8, but with 4 taps of DFE.

 

Figure 11. QuickEye analysis of channel with 4-tap DFE. Weights automatically calculated for DFE by Nexxim are (0.10439, 0.05148, 0.03139, and 0.02215)

Figure 12 shows the VerifEye analysis of the same high-speed serial channel shown in Figure 10, but with 4 taps of DFE.

 

Figure 12. VerifEye analysis of channel with 4-tap DFE. Weights automatically calculated for DFE by Nexxim are (0.10439, 0.05148, 0.03139, and 0.02215)

Decision-feedback equalization is set up in the Eye Probe, using the DFE_TAPS, DFE_LOCS, DFE_WEIGHTS, DECISION_HIGH, DECISION_LOW, and DECISION_THRESHOLD parameters.




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