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What are logic gates?
The main structural component of a digital system are logic gates. A Logic gate is the basic building block of a digital circuit that has two inputs and one output. The basic logic gates are divided into seven categories: AND, OR, XOR, NAND, NOR, XNOR, and NOT.
These are the important digital devices which are mainly based on the Boolean function. Logic gates carry the logical operations on single or multiple binary inputs and result in one binary output.
Basic Logic Gates Types
There are many logic gates used in digital systems. The basic gates are;
OR Gate
AND Gate
NOT Gate
XOR Gate
These gates can also be found in a composition of one or two gates. Thus, other gates like NAND, NOR, EXOR, and EXNOR Gates are formed.
OR Gate
The output of an OR gate is 1 when any of the inputs attain the state 1. When both inputs are 0 then output state is 0.
Boolean Expression of OR gate is
Y=A + B
The expression can be read as A ‘OR’ B.
The truth table of OR gate with two-input is given as
A | B | Y |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 1 |
AND Gate
The output of an AND gate is 1 when both of the inputs attain the state 1. Otherwise, it attains the state 0 (If any of the two inputs is 0 then output state will be 0).
Boolean Expression of AND gate is
Y=A .B
The expression can be read as A ‘AND’ B.
The truth table of AND gate with two-input is given as
A | B | Y |
0 | 0 | 0 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 1 |
NOT Gate
The output of an AND gate is 1 when the input did not attain the state 1, that is, the input attains the state 0. Otherwise, it attains the state 0 (If the input is 1 then output state will be 0).
Boolean Expression of NOT gate is
Y=A
The expression can be read as Y is equal to NOT A.
The truth table of NOT gate is given as
A | Y |
0 | 1 |
1 | 0 |
The three basic gates (OR, AND & NOT) when connected in different combinations then give us logic gates like NAND, NOR gates. These are the universal building blocks of digital circuits.
NAND Gate
The combination of AND & NOT gate is NAND logic gate.
Boolean Expression of NAND gate is
The output of a NAND gate is 1 when any of the inputs attain the state 0. Otherwise, it attains the state 0 (If the both input states are 1 then output state will be 0).
Truth Table of NAND Gate
A | B | Q |
0 | 0 | 1 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 0 |
NOR Gate
The combination of OR & NOT gate is NOR logic gate.
Boolean Expression of NOR gate is
NOR logic gate is a digital circuit having two or more inputs which creates an output. The output of NOR gate is the reverse output of logical OR gate. NOR logic gates are available using digital circuits to produce the appropriate logical function.
Truth Table of NOR Gate
A | B | Q |
0 | 0 | 1 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 0 |
XOR Gate (Exclusive OR gate)
The output of an XOR gate is 1 when only one of the inputs attain the state 1. When both inputs are 0 or 1 then the output state will be 0.
Boolean Expression of XOR gate is
Y=A.B +A.B
Y=A⊕ B
Truth Table of XOR Gate
A | B | Y |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 0 |
Conclusion
A Logic gate is the basic building block of a digital circuit that has two inputs and one output. The relationship of input and output is based on a certain logic. Logic gates are implemented by using electronic switches like diodes, transistors.
There are many logic gates used in digital systems. The basic gates are;
- OR Gate
- AND Gate
- NOT Gate
- XOR Gate
These gates can also be found in a composition of one or two gates. Thus, other gates like NAND, NOR, EXOR, and EXNOR Gates are formed.
