Tag: Full Adder Using NAND Gates

Full Adder | Definition | Circuit Diagram | Truth Table

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, Cin (either 0 or 1)
  • Output variables = S, Cout where S = Sum and Cout = Carry

 

Step-02:

 

Draw the truth table-

 

Inputs
Outputs
ABCinCout (Carry)S (Sum)
00000
00101
01001
01110
10001
10110
11010
11111

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,

Watch this Video Lecture

 

Next Article- Half Subtractor

 

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