1. INTRODUCTION TO SIGNALS & SYSTEMS

2. SIGNAL
A signal is a function of time representing a physical variable, eg: voltage, current etc.
A signal is defined as a function of one or more independent variables.

3. CLASSIFICATION OF SIGNALS
Signals are basically classified into two different types as follows.
Continuous time signals
Discrete time signals

4. CT Signals
In continuous time signals the independent variable is continuous, and they are defined for a continuum of values

5. Example

6. DT Signal
Discrete time signals are defined only at discrete times and for these signals the independent variable takes on only a discrete set of values

7. Example

8. Representation
To distinguish between continuous-time and discrete time signals, we will use the symbol ‘t’ to denote the continuous time independent variable and ‘n’ to denote the discrete time independent variable.

9. Classifications of CT signals
The CT signals can be further classified into the following
Unit step
Unit ramp
Exponentional
Impulse

10. Unit Step Signal

11. Ramp Signals

12. System
A system can be viewed as a process in which input signals are transformed by the system or cause the system to respond in some way resulting in other signals as outputs.

13. CT system

14. DT system