**Introduction:-**

In this lesson we’re going to discuss logic gates and how they are applied to digital electronics. We’re going to talk about the three basic logic gates: And gate, Or gate and the Not gate. we’re going to construct some truth tables for these logic circuits so you can see how inputs and outputs relate to each other. we’re going to use these truth tables to provide boolean theorems and prove that they’re actually accurate and we’re going to express the outputs of logic circuits using boolean expressions and vice-versa.

**Logic Gate:-**

- A Logic Gate is a basic building block of the digital Circuit Electronics.
- A Logic Gate is used to make logical decisions in different circuits.
- A Logic Circuit use only Binary Numbers ‘0’ and ‘1’.
- ‘0’ is said to be as False or Low input and ‘1’ is said to be as True or High input.
- A Logic Gate can Have two or more inputs and only one output except Not Gate.

**Need of Logic Gate:-**

A Logic Gate is used to integrate the basic gates with two or more inputs to produce a single output so that a well defined component is defined.

logic Gates are basically one of the important part of the circuit. Logic gate consists of 3 basic gates.

**The Basic Gates:-**

The Logic Gates consists of 3 basic Gates:-

**1) And Gate:-**

- It is said to be a And Gate if and only if the output is ‘1’ when both the inputs are ‘1’ otherwise the output is taken as ‘0’ or low.
- The Symbol for And Gate is ‘.’ (DOT).
- For And gate the possible input and output combination are:-

0.0=0

0.1=0

1.0=0

1.1=1

**Truth Table For And gate:-**

A | B | Y=A.B |

0 | 0 | 0 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

The Above table Shows the Truth Table For And gate.

The Expression of the And Gate is given By –

Y=A.B

**Block Diagram For And Gate:-**

### ** Timing Diagram:-**

**2) OR Gate:-**

- It is said to be a OR Gate if and only if the output is ‘1’ when both the inputs or any one of the both inputs are ‘1’ otherwise the output is taken as ‘0’ or low.
- The Symbol for And Gate is ‘+’.
- For OR gate the possible input and output combination are:-

0+0=0

0+1=1

1+0=1

1+1=1

**Truth Table For OR gate:-**

A | B | Y=A+B |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

The Above table Shows the Truth Table For OR gate.

The Expression of the OR Gate is given By –

Y=A+B

**Block Diagram For And Gate:-**

### **Timing Diagram:-**

**3) NOT Gate:-**

- The Not Gate performs the complement of the input provided.
- It is also known as the Inversion or Complementation.
- NOT Gate has one input and one output.
- When input is taken as 0 or low then output is 1 or high and when input is taken as 1 then the output is 0.
- The Symbol for NOT Gate is ‘ (Complement Symbol).
- For OR gate the possible input and output combination are:-

0’=1

1’=0

**Truth Table For OR gate:-**

A | Y=A’ |

0 | 1 |

1 | 0 |

The Above table Shows the Truth Table For NOT gate.

The Expression of the And Gate is given By –

Y=A’

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