ByT.Mounika

Introduction Arithmetic operations like addition, subtraction,

multiplication, division are basic operations to be

implemented in digital computers using basic gates like

AND, OR, NOR, NAND etc.

Among all the arithmetic operations if we can implement

addition then it is easy to perform multiplication (by

repeated addition), subtraction (by negating one operand)

or division (repeated subtraction).

Binary addition is a fundamental operation in most digital

circuits

There are a variety of adders, each has certain

performance.

Each type of adder is selected depending on where the

adder is to be used.

Ripple carry adder is suitable for small bit applications

Basic adder circuit

A combinational circuit that adds two bits is called a half adder

A full adder is one that adds three bits

Full Adder

sum

carry3 inputs

Truth Table of fulladder

Input

A

Input

B

Input

C

sum carry

0 0 0 0 0

0 0 1 1 0

0 1 0 1 0

0 1 1 0 1

1 0 0 1 0

1 0 1 0 1

1 1 0 0 1

1 1 1 1 1

Ripple carry adderThe ripple carry adder is constructed by cascading full

adder blocks in series

The carryout of one stage is fed directly to the carry-in of

the next stage

For an n-bit ripple adder, it requires n full adders

Block diagram of 4 bit ripple adder

Truth table of ripple carry adderA1 A2 A3 A4 B4 B3 B2 B1 S4 S3 S2 S1 carry

0 0 0 0 0 0 0 0 0 0 0 0 0

0 1 0 0 0 1 0 0 1 0 0 0 0

1 0 0 0 1 0 0 0 0 0 0 0 1

1 0 1 0 1 0 1 0 0 1 0 0 1

1 1 0 0 1 1 0 0 1 0 0 0 1

1 1 1 0 1 1 1 0 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 0 1

DSCH SCHEMATIC

LAYOUT

AdvantagesWe can add two n-bit numbers easily

It is advantageous for less number of bit operations