It is known that forward crosstalk increases (for all
practical purposes) with increasing coupled length, but
has a pulse width that is constant. Backwards
crosstalk, on the other hand, rises quickly (within the
critical region) to a constant maximum, but has a
pulse width that increases with increasing coupled
length. Simulations using HyperLynx? LineSim? show
this very effectively and clearly. The tool can
illustrate how impedance loading of the victim
trace can impact the magnitude, and even the
polarity, of the backward crosstalk pulse.
HyperLynx also can be used to clearly illustrate
how the backward crosstalk pulse is twice the
propagation time through the coupled region plus
one rise time, how the crosstalk signal is
impacted by the relationship between the traces
and their reference planes and also with each
other, and how an aggressor AC signal's period
can interact with the length of the coupled region
to create some surprising crosstalk effects.