Continuous time versus discrete time signals
The signals illustrated in figure 1-6 are examples of continuous time signals it is important to note that continuous time does not imply that a signal is a math ematically continuous function but rather that it is a function of a continuous time variable
In some system the signals are represented only at discrete values of the in dependent variable between these discrete time instant the value of the signal may be zero undefined or of no interest
An example of such a discretetime or sample data signal is shown in figure 1-7a often the intervals between signal values are the same but they need not be
A distinction between discrete-time and quantized signals is necessary a quantized signal is one whose values may assume only a countable number of values or level but the changes from level to level may occur at any time figure 1-7b show an example of a quantized signal. A real-world situation that can be modeled as a quantized signal is the opening and closing of a switch
Discrete-time signals will be considered in chapter 8.