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16 The PCB Design Magazine • July 2016 improved optimization algorithms, and illus- trate how optimization moves worst case chan- nels within design targets (lower left corner, all plots) while providing improved margin for all channels. For the largest system, Figure 4 shows op- timization improvement by contrasting simu- lated eye heights using both the original algo- rithm (left) and the improved algorithm (right). Each point in the plots represents one channel. For each channel, the X axis plots simulated eye height using the original (baseline) SerDes cod- settings had been derived that moved chan- nel performance within design targets for the worst-case channels (gold and black). The axes in Figure 2 are aligned for easier comparison. As similar PCB/SerDes combinations were deployed in systems of differing scale, perfor- mance was examined for all scenarios. The plots in Figure 3 compare the eye openings using de- fault SerDes coding (blue) against optimized coding (red) for three system sizes: large (left), medium (center) and small (right). These sim- ulations add additional system-level jitter and Figure 3: Default vs optimal eye openings for large, medium, and small systems. Figure 4: Eye heights contrasted, original (left) and improved (right) optimization algorithms. NEW SI TECHNIQUES FOR LARGE SYSTEM PERFORMANCE TUNING