• Digital Circuit:-We are quite familiar with digital computers communication system, calculation watches etc. These have become an important part of our daily life. The operation of these system is based on the principles of digital techniques & these systems are referred to as digital system.

In an electronic calculator the input is given with the help of switches. This is converted into electrical signal which have two discrete values or levels one of these may be called as 'Low Level & other one as 'HIGH LEVEL.This type of signal is known as digital signal & the circuit inside the device calculation used to process these digital signal is known as 'DIGITAL CIRCUIT' The calculation is an example of digital system.

1) $\underline{ANALOG \ Signal}$ - The electrical signal whose amplitude varies continuously over specified range of time is called as analog signal. IT can take '00' value without the specified range. Sine wave is an example of analog signal

2) $\underline{DIGITAL \ SIGNAL}$:-It is an electrical signal whose amplitude varies in discrete over a specified range of time. It can take only two discrete values within the specified range. The square wave is an example of digital signal