Before knowing about the operation let us briefly discuss about what is an OR gate. OR gate is an device which has two inputs and one output and the output is 1 if any or both of the inputs are 0 and the output will be 0 only if the inputs are 0. The notation of an OR gate is given as

As we have already discussed that it has two inputs, in the picture A and B are the two inputs and it has only 1 output.

Now let us explain the operation of the OR gate logically. We have already gone through the basics of the fundamental logic of OR gate. Now to describe it through Boolean algebra we have to look through the truth table first.

As we have already discussed that it has two inputs, in the picture A and B are the two inputs and it has only 1 output.

Now let us explain the operation of the OR gate logically. We have already gone through the basics of the fundamental logic of OR gate. Now to describe it through Boolean algebra we have to look through the truth table first.

Truth Table

We can describe the operation of an OR gate through binary arithmetic also. From this point of view the operation of OR gate is similar to binary addition. So if we take the two inputs of an OR gate as A and B then the output will be equivalent to A+B. now the so called truth table will be like

Input 1 | Input 2 | Output |
---|---|---|

A | B | Y = A + B |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

The truth table clearly explains the logical operation of the OR gate and the circuit diagram given below totally supports the truth table. Now we will explain the truth table along with the diagram simultaneously. When the input A and B both are 0 then we can say that both the switches S1 and S2 are open and the output is also 0. Now when A is 1 and B is 0 then we can say S1 is closed and S2 is open so the signal transmits through only S1 and the output will be 1. Similarly when A is 0 and B is 1 then the output will also be 1. Finally when both A and B are 1 then S1 and S2 both are closed and the output will be 1. This is what we call OR operation.

OR gate is available in TTL and CMOS ICS, Where TTL is Transistor - Transistor Logic ICs and CMOS is Complementary MOSFET ICS. We will now discuss on the arrange of OR gate on both the ICs. In CMOS ICS. 4000 series is available in digital electronic 4071 is the CMOS IC number of inputs in each gate is two. 4075 is 3 - input OR gate and 4072 is 4 - input OR gate in CMOS ICs. A internal gate picture of 4071 can make you understand about this IC.

## IC 4071