Impedance mismatches on PCBs (printed-circuit boards) and backplanes can cause reflections that impair highspeed chip-to-chip connections. These reflections also create ISI (intersymbol interference), an echo of a previous bit superimposed on the current bit, which causes your system to become unreliable. To overcome the interference, you can employ various signal-processing techniques, including de-emphasis, in which you predistort the signal before transmission. You use an analog filter to make a CTE (continuous-time equalizer) in the transmission path in just a few minutes. You can best characterize a high-speed digital channel with S (scattering) parameters. S21, an insertion-loss plot, represents the signal attenuation by the channel as a function of frequency.
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