A nonrepetitive waveform that rises or falls exponentially
from some initial value at some initial time, according to the logarithmic law
y(t) = eat
For a>0 the waveform rises without bound with increasing time t; for a<0 the
waveform decays to zero. One way in which logic signals can become corrupted as
they travel through a system is for their switching edges to become
exponentials.