**Logic Circuits**

Logic gates are physical devices that perform logical operations on one or more logic inputs to produce an output. They are mainly diodes or transistors though can also be constructed using electromagnetic rays. A **logic gate** is an elementary building block of a digital circuit. Most **logic gates** have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels. Both the input and output carry the binary valves ‘O’ which mean low or false ‘ I’ meaning high or true.

**Types of logic gates**

**AND gate**: Suppose we have two inputs AND gate A and B, the A.B denotes A and B which are both connected to the AND gate. This gate gives a high output if all inputs are high.

INPUT (A) | INPUT (B) | OUTPUT (A and B) |

0 | 0 | 0 |

1 | 0 | 0 |

0 | 1 | 0 |

1 | 1 | 1 |

**NOT gate**: Also called an inverter, the Not gate implements the logical negation. The Not gate outputs a voltage representing the opposite logic level of its input i.e. when the input is 0, the output will be 1 and vice versa.

INPUT (A) | OUTPUT (B) |

0 | 1 |

1 | 0 |

**OR gate**: The OR gate gives a high output, If at least one of the input is high. For a 2 input circuit with input A and B then A+B denote that A and B are both connected to the OR gate.

INPUT (A) | INPUT (B) | OUTPUT (A and B) |

0 | 0 | 0 |

1 | 0 | 1 |

0 | 1 | 1 |

1 | 1 | 1 |

** Uses of standard Logic Circuit**

- Logic gates are building blocks of hardware electronic components.
- It is used in activation of door bells.
- The AND gates use to combine multiply signals
- The NOT gate is used in building a switch.

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