Logic Gates

Learning outcomes: At the end of the lesson you should be able to: Identify gates symbols (NOT , AND, OR) Draw truth table for each of the above types of gate

Definition Logic gates are the building blocks of digital circuits. 

Gate A gate has two states either open or close open closed

Similarly 1 or 0 Logic gates process signals in only 2 state Either ON or OFF True or False

Logic Gates Each gate has 1 or more inputs and produces 1 output If the number of input(s) is X then the number of possible outcomes are 2x E.g. if number of input = 1 then the number of possible output will be 21 =2

NOT Gate NOT

NOT Gate The NOT gate is also known as an inverter The output of a NOT gate is the inverse of its input If A is the input then the output will be (NOT A) A A A

Truth Table of NOT Gate INPUT (A) OUTPUT () 1

AND Gate AND

AND Gate The output of an AND gate is True only if all inputs are True, otherwise the output is false A B Q 1 A B Q Q = A.B

OR Gate The output from an OR gate is True if any input is True, otherwise the output is false A B Q