DESIGN AND DEVELOPMENT OF

EFFICIENT CARRY SELECT ADDER

Presented by:- ABIN THOMAS, S8, ECE FEBIN SEBASTIAN, S8, ECE

INTRODUCTION In electronics, an adder is a digital circuit that performs addition of numbers. Adders can be constructed for many numerical representations, such as BCD or

Excess-3, the most common adders operate on binary numbers. Adders plays major role in multiplications and other advanced processors designs. Carry Select Adder (CSLA) is one of the fastest adders used in many data-

processing processors to perform fast arithmetic functions. By gate level modification of CSLA architecture, we can reduce area, power and

delay. Based on this modification 16-b CSLA architecture have been developed and the

proposed design has reduced area, delay and power as compared with the regular CSLA .

RIPPLE CARRY ADDER(RCA)

This kind of adder is a Ripple Carry Adder, since each carry bit "ripples" to the next full adder.

The first (and only the first) full adder may be replaced by a half adder.

What is Carry select adder?

A carry-select adder is a particular way to implement an adder, which is a logic element that computes the (n+1 ) bit sum of two (n) bit numbers.

The carry-select adder is simple but rather fast than other adders.

Design 1:- Regular 16 bit CSLA Design 2:- 16 bit CSLA with BECDesign 3:- 16 bit EFFICIENT CSLA

OUR PROJECT

EXISTING SYSTEM

The carry-select adder generally consists of two Ripple Carry

Adders (RCA) and a Multiplexer .

Adding two n-bit numbers with a carry-select adder is done with

two adders (therefore two RCA).

In order to perform the calculation twice, one time with the assumption

of the carry being zero and the other assuming one.

Design 1:- REGULAR 16bit CSLA

Model of Carry Select Adder

Improvement to Design 1

The parallel RCA with Cin=1 is

replaced with Binary-Excess 1

converter( BEC).

=

Design 2:- Modified CLSA with BEC

=

IMPROVEMENT TO DESIGN 2

Design 3:- EFFICIENT CSLA

Tools used:

Iverilog 0.10.0 Isim Xilinx ISE 14.7 Xilinx Spreadsheet

Schematic and Simulation Results:-

Schematic of Design 1 (Regular Carry Select Adder)

Schematic of Design 2 (Carry Select Adder with BEC)

Schematic of Design 3 (Carry Select Adder without mux)

Simulation model of Design 1 (Regular Carry Select Adder)

Simulation model of Design 2 (Carry Select Adder with BEC)

Simulation model of Design 3 (Carry Select Adder without MUX)

COMPARISON

TYPE POWER(mW)

No. of Slices(= area)

DELAY(ns)

Regular CSLA 134 46 14.256

CSLA with BEC 133 31 12.188

Efficient CSLA 131 11 11.974

Comparison done in SPARTAN 6 FPGA xc6slx4-3tqg144

ADVANTAGES

Low power consumption Less area (less complexity) More speed compared to regular CSLA

CONCLUSION

A simple approach is proposed in this project to reduce the

area and power of CSLA architecture. The reduced number of

gates of this work offers the great advantage in the reduction of

area and also the power. The modified CSLA architecture is

therefore, low area, low power, simple and efficient for VLSI

hardware implementation.

REFERENCE

[1] Laxman Shanigarapu, Bhavana P. Shrivastava ”Area and power efficient carry select

adder” IJIRTS,Vol.1,2013

[2] B. Ramkumar, Harish M Kittur “Low power and Area efficient carry select adder,”IEEE Trans,Vol.20,Feb 2012.

[3] Y. Kim and L.-S. Kim, “64-bit carry-select adder with reduced area,” Electron. Lett., vol. 37, no. 10, pp. 614–615, May 2001.

[4] T. Y. Ceiang and M. J. Hsiao, “Carry-select adder using single ripple carry adder,” Electron. Lett., vol. 34, no. 22, pp. 2101–2103, Oct. 1998.

[5] Samir Palnitkar, “Verilog Hdl: A Guide to Digital Design and Synthesis”2005,2nd Edition.

[6] J. M. Rabaey, Digtal Integrated Circuits—A Design Perspective.Upper Saddle River, NJ: Prentice-Hall, 2001.

DELAY REPORT OF REGULAR CSLA-DESIGN 1

DELAY REPORT OF CSLA with BEC-DESIGN 2

DELAY REPORT OF EFFICIENT CSLA-DESIGN 3

POWER REPORT OF REGULAR CSLA-DESIGN 1

POWER REPORT OF CSLA with BEC-DESIGN 2

POWER REPORT OF EFFICIENT CSLA-DESIGN 3