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VENUS INTERNATIONAL COLLEGE OF TECHNOLOGY

PREPARED BY:DISHA D. PATELENROLMENT NO: 150810705004BRANCH: COMMUNICATION SYSTEM ENGINEERINGSUBJECT: CMOS CIRCUIT DESIGN-1(2720511)

GUIDED BY:BHARGAV SIRPROF. ANIRUDDH AMINHOD OF EC DEPT.

CMOS

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CONTENTS

• INTRODUCTION• ADDER MEANS• TYPES OF ADDERS HALF ADDER FULL ADDER RIPPLE CARRY ADDER LOOK AHEAD CARRY ADDER CARRY-SAVE ADDERS

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INTRODUCTION

• Digital computers perform various arithmetic operation Basic arithmetic operation is addition of two binary digits. The first three operations produce a sum whose length is one digit but when the last operation is performed sum is two digits. The higher bit is called carry. And lower bit is called sum. This operation is called half adder. The circuit which performs addition of three bits is a full adder.

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ADDER MEANS???

• An adder is a digital circuit that performs addition of numbers.

• In processor it is used to calculate addresses, table indices, and similar operations.

• It can be constructed for many numerical representations, such as binary-coded decimal or excess-3,the most common adders operate on binary numbers.

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TYPES OF ADDERS

• HALF ADDER• FULL ADDER• RIPPLE CARRY ADDER• LOOK AHEAD CARRY UNIT• CARRY-SAVE ADDERS

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HALF ADDER

The half adder adds two single binary digits A and B.

It has two outputs, sum (S) and carry (C).

Sum = AB’+A’B.Carry=A*B.

For half-adder design,an XOR gate & an AND gate

TRUTH TABLE

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FULL ADDER

A combinational circuit that adds 3 input bits to generate a Sum bit and a Carry bitWhere X,Y,Z are inputs and C & S are outputs.

Sum= X+Y+Z.

Cout= XY’+YZ’+ZX’.

TRUTH TABLE

X Y Z S C0 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 0

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RIPPLE CARRY ADDER

• It is possible to create a logical circuit using multiple full adders to add

• N-bit numbers.

• Each full adder inputs a Cin, which is the Cout of the

• previous adder.

• This kind of adder is called a ripple-carry adder, since

• each carry bit "ripples" to the next full adder.

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LOOK AHEAD CARRY UNIT

Carry Look Ahead (CLA) design is based on the principle of looking at lower adder bits of argument and addend if higher orders carry generated. This adder reduces the carry delay by reducing the number of gates through which a carry signal must propagate . As shown in fig. in the generation and propagation stage, the generation values, propagation values are computed. Internal carry generation is calculated in second stage. And in final stage, the sum is calculated. The flow chart of CLA is given in fig. and the architecture of CLA is given in fig.

Flow chart of CLA

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CARRY SAVE ADDER

• In Carry Save Adder (CSA), three bits are added parallelly at• a time. In this scheme, the carry is not propagated through the• stages. Instead, carry is stored in present stage, and updated as• addend value in the next stage [2]. Hence, the delay due to the

• carry is reduced in this scheme.

Block Diagram of CSA

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THANK YOU

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