DesignCon 2002

A fundamental assumption of both QuickEye and VerifEye is that the drivers and channel
are linear time-invariant systems. QuickEye and VerifEye are based on the principle of
superposition, which makes use of this assumption [6].
The step response is the waveform at the far end of the channel to a single transition at
the input, from low to high or high to low. To obtain the response of the overall channel,
individual step responses for rising and falling edges are superposed. The result is the
channel response shown in Figure 8.
Figure 7: Intermediate QuickEye waveforms for the RC example. Rising edges are shown as solid
curves; falling edges as dashed. When all these transitions are added together, we get the waveform
in Figure 8.
While it is relatively easy to calculate the effects of ISI with the QuickEye algorithm,
random transmit jitter is much more difficult. The most accurate method is to do a
Monte-Carlo method: each transition is displaced a random amount from the nominal
time, depending on the probability distribution of the random jitter, but this greatly
increases simulation time, as there needs to be at least several different jittered transitions
for each bit in the original stream.