# Logic Gates

LOGIC GATES • A logic gate is a digital circuit with one or more I/P but one O/P various types are used in logic gate.
• The digital circuit that can be analyzed with the help of Boolean algebra is called a logic Gate or logic circuit.

1. Basic Gate  - AND, OR, NOT
2. Exclusive Gate -  EX-OR  &  EX-NOR
3. Universal Gate  -  NAND & NOR

BASIC GATES

1. OR GATE – OR Gate is used to perform logical addition and OR Gate as two or more I/P signal & have one O/P signal. Let I/P – A,B & O/P-Y EXPRESSION:-

Y = A+B ; Read as A OR B gives Y.

Truth Table

 INPUT OUTPUT A B Y 0 0 0 0 1 1 1 0 1 1 1 1

2. AND GATE – The AND Gate is used to perform logical multiplication. It has two or more I/P Gate is high (1) only if all the I/P are high. EXPRESSION:-

Y = A.B ; Read as A AND B gives Y

Truth Table:-

 INPUT OUTPUT A B Y 0 0 0 0 1 0 1 0 0 1 1 1

3. NOT GATE :- NOT Gate is used to perform the inversion function also known as complementation.

The NOT Gate change 1 logical level to the opposite level. It change from 1 to a 0 & from to the 0 to a 1. EXPRESSION:-

Y = NOT A or A ; Read as INVERSE OF A gives Y.

Truth Table:-

 INPUT OUTPUT A Y 0 1 1 0

UNIVERSAL GATES

NOR and NAND are known as universal Gate because they can be used individually building block to build only logic circuit .The logic function AND or NOT using only NAND & only NOR.

1. NOR GATE:-

• In NOR Gate implies in OR Gate with an inverted Gate.
• The O/P of NOR Gate is high (1) only if all I/P are low (0). It has two or more I/P but it has only one O/P. EXPRESSION:-

Y = NOT OF A+B ; Read as NOT of A OR B gives Y.

Truth Table:-

 INPUT OUTPUT A B Y 0 0 1 0 1 0 1 0 0 1 1 0

2. NAND GATE:-

• NAND Gate implies on AND function.
• The O/P of NAND Gate is low only if all the I/P are high. EXPRESSION:-

Y = NOT of A.B ; Read as NOT OF A AND B gives Y

Truth Table:-

 INPUT OUTPUT A B Y 0 0 1 0 1 1 1 0 1 1 1 0

EXCLUSIVE GATES

1. EX-OR :- It has two or more I/P & one O/P the 0.

• The O/P of EX-OR is high only if both I/P are difference.
• The O/P of EX-OR is less only if both are same. EXPRESSION:-

Y = AB ; Read as A OR B But NOT BOTH gives Y

Truth Table:-

 INPUT OUTPUT A B Y 0 0 0 0 1 1 1 0 1 1 1 0

2. EX-NOR:-

( EX-OR+NOT)

• The O/P of EX-NOR Gate is high when both I/P are same.
• The O/P of EX-NOR is low when both I/P are difference. EXPRESSION:-

Y = AB ; Read as A AND B the SAME gives Y

Truth Table:-

 INPUT OUTPUT A B Y. 0 0 1 0 1 0 1 0 0 1 1 1

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