**Half Adder-**

Before you go through this article, make sure that you have gone through the previous article on **Half Adder**.

We have discussed-

- Half Adder is used for the purpose of adding two single bit numbers.
- Half adders have no scope of adding the carry bit resulting from the addition of previous bits.
- To overcome this drawback, full adder comes into play.

In this article, we will discuss about Full Adder.

**Full Adder-**

- Full Adder is a combinational logic circuit.
- It is used for the purpose of adding two single bit numbers with a carry.
- Thus, full adder has the ability to perform the addition of three bits.
- Full adder contains 3 inputs and 2 outputs (sum and carry) as shown-

**Full Adder Designing-**

Full adder is designed in the following steps-

**Step-01:**

Identify the input and output variables-

- Input variables = A, B, C
_{in }(either 0 or 1) - Output variables = S, C
_{out}where S = Sum and C_{out}= Carry

**Step-02:**

Draw the truth table-

Inputs |
Outputs |
|||

A |
B |
C_{in} |
C_{out} (Carry) |
S (Sum) |

0 | 0 | 0 | 0 | 0 |

0 | 0 | 1 | 0 | 1 |

0 | 1 | 0 | 0 | 1 |

0 | 1 | 1 | 1 | 0 |

1 | 0 | 0 | 0 | 1 |

1 | 0 | 1 | 1 | 0 |

1 | 1 | 0 | 1 | 0 |

1 | 1 | 1 | 1 | 1 |

**Truth Table**

**Step-03:**

Draw K-maps using the above truth table and determine the simplified Boolean expressions-

**Also Read-** **Full Subtractor**

**Step-04:**

Draw the logic diagram.

The implementation of full adder using 1 XOR gate, 3 AND gates and 1 OR gate is as shown below-

To gain better understanding about Full Adder,

**Next Article-** **Half Subtractor**

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