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Different Types of Signals

Signals can be classified into different categories, as given below.
  1. Continuous-time and discrete-time signals
  2. Periodic and non-periodic signals
  3. Odd and even signals

Continuous-time and Discrete-time Signals

Signals are represented mathematically as function of one or more independent variables. We classify signals as being either continuous-time (functions of a real-valued variable) or discrete-time (functions of an integer-valued variable).
In other words, a continuous-time signal has a value defined for each point in time and a discrete-time signal is defined only at discrete points in time.
(a) Continuous-time signal
(b) Discrete-time signal

Periodic and Non-Periodic Signals

A signal f(t) is said to be periodic if
f(t) = f(t ± nT)
where n is a positive integer and 'T' is the period. Thus, a periodic signal repeats itself every T seconds. Some periodic signals are shown in the figure.
Description: Description: 1236.png
Periodic signals
A signal not satisfying the above condition of Eq. is called a non-periodic signal. Examples of some non-periodic signals are e’, t, etc.

Odd and Even Signals

A signal f(t) is said to be odd if
f(t) = –f(–t)
Some examples of odd signals are sine functions, triangular functions and square function, as shown in  figure.
Description: Description: 1242.png
Odd signals
A signal f(t) is said to be even if
f(t) = f(–t)
Some examples of even signals are shown in figure.
Description: Description: 1249.png
Even signals

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