# 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 Â± 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.

Periodic signals

A signal not satisfying the above condition of Eq. is called a non-periodic signal. Examples of some non-periodic signals are eâ€™, t, etc.

# Odd and Even Signals

A signal f(t) is said to be odd if
f(t) = â€“f(â€“t)

Some examples of odd signals are sine functions, triangular functions and square function, as shown in  figure.

Odd signals

A signal f(t) is said to be even if
f(t) = f(â€“t)

Some examples of even signals are shown in figure.

Even signals