Home » Digital Electronics

Designing of Half-Adder, Full Adder and making Full Adder using Half Adder

In this tutorial, we are going to learn about designing of Half-Adder, Full Adder and making Full Adder using Half Adder in Digital Electronics.
Submitted by Saurabh Gupta, on January 07, 2020

Half Adder

The logic circuit which performs the addition of 2 bits is called Half- Adder. It is a kind of combinational circuit. It contains two binary inputs "augend" and "addend" and two binary outputs Sum and Carry.

The Sum bit (S) and the Carry bit (C) are given according to the rules of Binary Addition which can be summarized in the form of truth table as,

ABSum (S)Carry (C)
0000
0110
1010
1101

K-Map Simplification

We use K-Map to obtain the expression for Sum and Carry bit which is as,

Half Adder 1

Upon obtaining the Boolean expressions, we can observe that Boolean Expression for Sum is nothing but the Exclusive OR function for two inputs and the Boolean Expression for carrying is the same as AND function. Thus, the circuit diagram for Half Adder can be drawn using an XOR gate and AND gate as shown in the above image.

Full Adder

Full Adder is an arithmetic circuit which performs the arithmetic sum of 3-input bits. It consists of 3 inputs and 2 outputs. One additional input is the Carry bit (C) in which represents the carry from the previous significant position.

Similarly, as in Half-Adder, we have two outputs Sum (S) and Carry (C), which can be obtained using the rules of Binary Addition and can be summarized in a Truth Table as,

ABCSum (S)Carry (C)
00000
00110
01010
01101
10010
10101
11001
11111

K-Map Simplification

We use K-Map to obtain the expression for Sum and Carry bit which is as,

Full Adder

The logic circuit for Full Adder can be drawn as,

Full Adder

Full Adder using Half Adder

A Full Adder can also be implemented using two half adders and one OR gate.

The circuit diagram for this can be drawn as,

Full Adder

And, it could be represented in block diagram as,

Full Adder

The Boolean expression for Sum and Carry is as,

    Sum     = A  B  C
    Carry   = AB + (A  B). C
            = AB + ( A. B + A. B). C
            = AB + A. BC + A. B. C
            = B (A + A. C) + A. B. C
            = B [(A+ A) (A + C)] + A. B. C
            = AB + AC + A. B. C
            = AB + C (B + A. B)
            = AB + C [(B + A) (B + B)]
            = AB + BC + AC





Comments and Discussions

Ad: Are you a blogger? Join our Blogging forum.





Languages: » C » C++ » C++ STL » Java » Data Structure » C#.Net » Android » Kotlin » SQL
Web Technologies: » PHP » Python » JavaScript » CSS » Ajax » Node.js » Web programming/HTML
Solved programs: » C » C++ » DS » Java » C#
Aptitude que. & ans.: » C » C++ » Java » DBMS
Interview que. & ans.: » C » Embedded C » Java » SEO » HR
CS Subjects: » CS Basics » O.S. » Networks » DBMS » Embedded Systems » Cloud Computing
» Machine learning » CS Organizations » Linux » DOS
More: » Articles » Puzzles » News/Updates


© https://www.includehelp.com some rights reserved.