Logic Gates

Logic gate :-

Logic gates are the digital circuits which have two or more inputs and only one output, they takes as well as process the result only in logit 1 or logic 0 (only in binary number), here the word logic is used because the value of 0 and 1 is not fixed i.e. it depend on the complexity of the gates or circuits.

Basic Boolean Laws :-

  1. A+0 =A                                                                             0+0 =0, 1+0 =1
  2. A+1 =1                                                                             1+1 =1, 0+1 =1
  3. A+A =A                                                                             0+0 =0, 1+0 =1 
  4. A+A̅ =0                                                                             1+1 =1, 0+1 =1
  • A.0 =0                                                                              0.0 =0, 1.0 =0
  • A.1 =A                                                                              1.1 =1, 0.1 =0
  • A.A =A                                                                              0.0 =0, 1.0 =0
  • A.A̅ =0                                                                              1.1 =1, 0.1 =0

Types of gates :-

There are 8 types of gates in digital electronics from which the different circuit is created they are :

  1. AND Gate
  2. OR Gate
  3. NOT Gate
  4. Buffer Gate
  5. NAND Gate (NOT Gate combined with AND Gate)
  6. NOR Gate (NOT Gate Combined with OR Gate)
  7. X-OR Gate (Exclusive OR Gate)
  8. X-NOR Gate (Exclusive NOR Gate)

Basic logic gates :-

  1. AND Gate
  2. OR Gate
  3. NOT Gate
  4. Buffer Gate

1)  AND Gate :-

The AND gate is use for “product” operation in digital circuit.

Example : if the two inputs A, B passes through the AND gate the resultant output will be A.B

A can be 0 or 1 , similarly B can be 0 and 1.

So the possible combinations and their outputs can be shown in the truth table blow.

Truth Table :-

2) OR Gate :-

The OR gate is use for “adding” operation in digital circuit.

Example : if the two inputs A, B passes through the OR gate the resultant output will be A+B

The possible combinations and their outputs can be shown in the truth table blow.

Truth Table :-

3) NOT Gate :-

The NOT gate is use for “inversing” the input in digital circuit.

Example : if the input A passes through the NOT gate the resultant output will be A̅

Truth Table :-

4) Buffer Gate :-

The Buffer gate is use in long circuits to increase the propagation delay in circuits.

If the input A is passed from the buffer gate then the output will be same Which is A.

Truth Table :-

Universal Gates :-

Universal gates can be defined as the gates which is capable to do all operations of basic gates and by help of which almost any circuit can be formed. There are two universal gates NAND and NOR in digital electronics.

5) NAND Gate (NOT Gate combined with AND Gate) :-

The NAND gate is use for “ inverse product” operation in digital circuit. It work like AND gate but have inverse output of AND gate.

Example : if the two inputs A, B passes through the NAND gate the resultant output will be (A.B)’

The possible combinations and their outputs can be shown in the truth table blow.

Truth Table :-

6) NOR Gate (NOT Gate Combined with OR Gate) :-

The NOR gate is use for “ inverse Addition” operation in digital circuit. It work like OR gate but have inverse output of OR gate.

Example : if the two inputs A, B passes through the NOR gate the resultant output will be (A+B)’

The possible combinations and their outputs can be shown in the truth table blow.

Truth Table :-

There are two more gates exist which do the complex operations in digital electronics they are :

7) X-OR Gate (Exclusive OR Gate) :-

The X-OR gate or Exclusive OR gate is use to perform the OR operation with two AND Operation in the way that if A and B are two inputs and when it passes through X-OR gate it form the combination A̅.B + A.B̅ which is written in short AꚚB

The truth Table of X-OR gate is given below

Truth Table :-

8) X-NOR Gate (Exclusive NOR Gate) :-

The X-NOR gate or Exclusive NOR gate works opposite to X-OR gate, it is use to perform the inverse OR operation with two AND Operation in the way that if A and B are two inputs and when it passes through X-NOR gate it form the combination A̅.B̅+ A.B which is written in short AꙨB

The truth Table of X-NOR gate is given below

Truth Table :-

Logic gate :- Logic gates are the digital circuits which have two or more inputs and only one output, they takes as well as process the result only in logit 1 or logic 0 (only in binary number), here the word logic is used because the value of 0 and 1 is not fixed i.e. it depend on the complexity of the gates or circuits. Basic Boolean Laws :- A+0 =A                                                                             0+0 =0, 1+0 =1A+1 =1                                                                             1+1 =1, 0+1 =1A+A =A                                                                             0+0 =0, 1+0 =1  A+A̅ =0                                                                             1+1 =1, 0+1 =1 A.0 =0                                                                              0.0 =0, 1.0 =0A.1 =A                                                                              1.1…

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