Another important class of signals is exponential signals. In continuous
time, real exponentials are typically expressed in the form cet, whereas in dis-
crete time they are typically expressed in the form ca".
A third important class of signals discussed in this lecture is continuous-
time and discrete-time complex exponentials. In both cases the complex ex-
ponential can be expressed through Euler's relation in the form of a real and
an imaginary part, both of which are sinusoidal with a phase difference of 'N/2
and with an envelope that is a real exponential. When the magnitude of the
complex exponential is a constant, then the real and imaginary parts neither
grow nor decay with time; in other words, they are purely sinusoidal. In this
case for continuous time, the complex exponential is periodic. For discrete
time the complex exponential may or may not be periodic depending on
whether the sinusoidal real and imaginary components are periodic.
In addition to the basic signals discussed in this lecture, a number of ad-
ditional signals play an important role as building blocks. These are intro-
duced in Lecture 3.