Logic Gates

Logic Gates A logic gates is an electronic circuit that operates on one or more input signals to produce an output signal. The logic gate is...

Logic Gates

A logic gates is an electronic circuit that operates on one or more input signals to produce an output signal. The logic gate is used for binary operation and is the basic component of a digital computer. The function of gate is expressed by means of an algebraic expression.

In digital computer, there are three basic gates, which are:

• AND gate
• OR gate
• NOT gate

There are other gates derived from basic gates, which are:

• NAND gate
• NOR gate
• XOR gate (exclusive OR)
• XNOR gate (exclusive NOR)

Fig: Logic gates

1. AND Gate

AND gate is an electronic circuit which produces high (1) output when all inputs are high otherwise produce low (0) output. The output is equal to the product of the logic inputs.

Truth Table

Inputs		Output
A	B	F=A.B
0	0	0
0	1	0
1	0	0
1	1	1

Logic Symbol

2. OR Gate

OR gate is an electronic circuit which produces high (1) output when one of the input is high (1) otherwise produces low (0) output. The output is equal to the sum of the logic inputs.

Truth Table

Inputs		Output
A	B	F=A+B
0	0	0
0	1	1
1	0	1
1	1	1

Logic Symbol

3. NOT Gate

NOT gate is an electronic circuit whose output is the complement of the input i.e. it produces high (1) when input is low (0) and it produces low (0) output when input is high (1). It has only one input and output.

Truth Table

Inputs	Output
A	F=A|
0	1
1	0

Logic Symbol

4. NAND Gate

NAND gate is an electronic circuit which produces low (0) when all inputs are high (1) otherwise produces high (1). NAND gate is the combination of AND and NOT gate. 

Truth Table

Inputs			Output
A	B	A.B	F=(A+B)|
0	0	0	1
0	1	0	1
1	0	0	1
1	1	1	0

Logic Symbol

5. NOR Gate

NOR gate is an electronic circuit which produces high (1) output when all inputs are low (0) otherwise produces low (0) output. NOR gate is the complement of the OR gate and NOT gate. It is the complement of the OR gate.

Truth Table

Inputs			Output
A	B	A.B	F=(A+B)|
0	0	0	1
0	1	0	1
1	0	0	1
1	1	1	0

Logic Symbol

6. X-OR Gate (Exclusive OR gate)

XOR gate is an electronic gate which produces low (0) output when both the inputs are same otherwise produces high (1) output. 

Truth Table

Inputs						Output
A	B	A|	B|	A|.B	A.B|	Y= A.B| + A|.B
0	0	1	1	0	0	0
0	1	1	0	1	0	1
1	0	0	1	0	1	1
1	1	0	0	0	0	0

Logic Symbol

7. X-NOR Gate

XNOR gate is an electronic circuit which produces high (1) output when both inputs are same otherwise produces low (0) output. It is equivalent to an XOR gate followed by an inverter.

Truth Table

Inputs						Output
A	B	A|	B|	A|.B	A.B|	Y= A.B| + A|.B
0	0	1	1	0	0	0
0	1	1	0	1	0	1
1	0	0	1	0	1	1
1	1	0	0	0	0	0

Logic Symbol

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