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Logic gates
Logic gates are the basic building blocks of any digital system. Logic gates are electronic circuits. It has one or more inputs and only one output. The relationship between input and output is based on a particular logic.
In this, the input and output are in binary form, that is, the value of input / output will be only 0 (low) and 1 (high).
You can also read: What Is Boolean Algebra In Computer Science
Types of logic gates
Generally, there are three types of logic gates –
- AND gate
- OR gate
- NOT gate
There are many other types of logic gates which are based on these three logic gates. like :-
NAND GATE, NOR GATE, XOR gate.
AND Gate
AND GATE has two or more inputs but only one output. The output of AND GATE is high only when all the inputs are high. AND GATE performs the multiplication operation on two or more inputs. The operation of AND GATE is represented by (.).
Ex: X= A AND B
X= AB
Logical Diagram of AND Gate
Truth Table of And
| A | B | A.B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
OR GATE
OR GATE consists of two or more input signals and only one output signal. It is called OR GATE because the output is high when any one input or all the inputs are high. In OR GATE, addition operation is performed on two or more inputs. OR GATE operation is represented by (+) symbol.
Ex: X=A OR B
X= A+B
Logic Diagram of OR Gate
Truth Table of OR Gate
| A | B | A+B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Not Gate
NOT GATE has only one input and one output because its output state is opposite to the input state. That is, the input is high when the output is low. NOT GATE is also called complement, negation or inverter. The NOT GATE operation is displayed with a bar or (¯) symbol.
Ex: X = NOT A
X = A’
Logic Diagram of NOT Gate
Truth Table of NOT Gate
| A | A’ |
|---|---|
| 0 | 1 |
| 1 | 0 |
NAND GATE
On adding an AND GATE with NOT GATE, a new GATE is obtained which is called NAND GATE. It performs NOT and AND operations. What is NAND GATE is a compliment (¯) of AND GATE.
Ex: X = A NAND B
X = (AB)’
Logic Diagram of NAND Gate
Truth Table of NAND Gate
| A | B | (A.B)’ |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOR GATE
It is a combination of NOT and OR GATE. The GATE obtained by adding a NOT GATE and an OR GATE is called NOR GATE. What is NOR GATE is a compliment to OR GATE.
Ex: X = A NOR B
X = (A+B)’
Logic Diagram of NOR Gate
Truth Table of NOR Gate
| A | B | (A+B)’ |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
XOR GATE
XOR GATE is widely used in digital circuits although it is not a basic operation but it can be constructed using basic GATES (AND, OR, NOT) or by using universal GATE (NAND or NOR).
XOR can be used in half adder, full adder, and subtractor. XOR is also called Ex-OR.
Logic Diagram of XOR Gate
Truth Table of XOR Gate
| A | B | A⊕B |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Conclusion
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