Logic gate

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Logic gate

A device that is use to implement the Boolean function is known as logic gate.

A computer carries out all operation by mean of combinations of signal passing through standard block of built-in circuit known as logic gate. A logic gate is an electronic device that is use to operate one or more input signal to produce standard output signal.

In a computer when we build an electronic device we combine a multiple logic gates of different types. There are many types of logic gates are available but we can discuss some of the most important ones.

#AND gate

#OR gate

#NOT gate

#NAND gate

#NOR gate

AND gate

An AND logic gate is created on the basis of multiplication operation. AND logic gate is electronic device that generate an output signal of 1 only if all input signal are also 1.

Example:

we connected two or more switches in series that behave as AND gate. The input current will reach the output point only when both the switch is in ON state. There will be no output if either one or both switch in OFF state.

Logic gate

Truth table of AND gate

The state of output signal depended on the combination of input signal.

Inputs Outputs
A B C=A.B
0 0 0
0 1 0
1 0 0
1 1 1

Block diagram of logic gate

Block diagram of logic gate

OR gate

An OR logic gate is created on the basis of addition operation. OR logic gate is electronic device that generate an output signal of 1 if any of input signal are also 1.

Example:

we connected two or more switches in parallel that behave as OR gate. The input current will reach the output point when any one or both the switch is in ON state. There will be no output only when the switch in OFF state.

or gate

Truth table of OR gate

The state of output signal depended on the combination of input signal.

Inputs Outputs
A B C=A+B
0 0 0
0 1 1
1 0 1
1 1 1

Block diagram of OR gate

Block diagram of OR gate

NOT gate

An NOT logic gate is created on the basis of complementation operation. NOT logic gate is electronic device that generate reverse of the input signal as output signal.  This is also known as inverter because it inverts the signal.

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The complementation operation is the unary operation that is defines on a single variable. NOT gate have always single value or signal input.

 Truth table of NOT gate

Input Output
A Ā
0 1
1 0

Block diagram of NOT gate

Block diagram of NOT gate

NAND gate

The NAND gate is the complemented of AND gate. The output of NAND gate is 1 if any one of the inputs is 0 and it will be 0 only when all input are 1.

Truth table of NAND gate

The state of output signal depended on the combination of input signal

Inputs Outputs
A B C= A+B
0 0 1
0 1 1
1 0 1
1 1 0

Block diagram of NAND gate

Block diagram of NAND gate

An AND gate followed by a NOT gate operates as a NAND gate. Output of the NAND gate is A.B that is fed as input to the NOT gate finally output is complement of A.B which is equal to (A.B) or A+B or A↑B.

Block diagram of NAND gate

 

NOR gate

NOR gate is the complemented of OR gate. Output of NOR gate will be 1 only when all input are 0, and it will be 0 if any input as a 1.

Truth table of NOR gate:

Inputs Outputs
A B C= A.B
0 0 1
0 1 0
1 0 0
1 1 0

 

Block diagram of NOR gate

Block diagram of NOR gate

An OR gate followed by a NOT gate operation as a NOR gate. Output of the OR gate is A+B that in turn is fed as input as input to NOT gate finally output is complement of A+B which is equal to A+BorA.Bor A↓B.

Block diagram of NOR gate

 

Complement of binary numbers

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