final ppt

Implementation of 8-bit Conditional Sum adder and Parallel Prefix Adders for Fast

Addition

by B.Gayathri

K.Sushma

IntroductionThe csa generates two sets of outputs for a given group of

operand bts say n-bits. Each set includes n-sum bits and an outgoing carry. One set assumes that the incoming carry will be zero, while the other assumes that it will be one. Once the incoming carry is known, we need only to select the carrcet set of outputs by using a multiplexer without waiting for the carrry to further propagate the n-positions.

In ppa the aadition is done in parallel fashion there for it is said to be a parallel prefix adder, and some of the parallel prefix adders are

Brent-Kung Adder Kogge-Stone Adder Ladner-Fischer Adder

Conditional Sum Adder

Circuit Diagram of 8-bit CSA:

Top Model View of 8-bit CSA:

Simulated Waveform Using Modelsim:

CSA Mask layout Using I/O Pads:

Simulated Ouput Waveform Using Microwind Layout Editor:

Parallel Prefix Adders

Block Diagram of Parallel Prefix Adder:

STEP1: The pre-calculation stage is implemented by

STEP2: carry signals can be generated by using different prefix graphs.

STEP3: summation unit can be implemented by

Calculation of Carriers in Prefix Graph:

Tree Structure Diagrams of Parallel Prefix Adder:

Kogge-Stone Ladner-Fischer

Brent-Kung

Top Modules for Parallel Prefix Adders:

TOP VEIW OF 8-BIT KOGGE-STONE ADDER

TOP VIEW OF 8-BIT LADNER-FISCHER ADDER

TOP VIEW OF 8-BIT BRENT-KUNG ADDER

Simulated Waveform of KSA Using Modelsim:

KSA Mask layout Using I/O Pads:

Simulated Ouput Waveform of KSA Using Microwind Layout Editor:

Simulated Waveform of LFA Using Modelsim:

LFA Mask layout Using I/O Pads:

Simulated Ouput Waveform of LFA Using Microwind Layout Editor:

Simulated Waveform of BKA Using Modelsim:

BKA Mask layout Using I/O Pads:

Simulated Ouput Waveform of BKA Using Microwind Layout Editor:

Scope of Expansion:Radix-3Radix-4

Thanq u