Low-Power and Area-Efficient Carry Select Adder

Presented by

P. SAI VARA PRASAD

M.Tech ,ECE DSCE,

Under the guidance of Dr.M.Suryanarayana Professor & HOD, Dept. of ECE

CONTENTS

ABSTRACT

INTRODUCTION

EXISTING SYSTEM

PROBLEMS IN EXISTING SYSTEM

PROPOSED SYSTEM

SOLUTION OF THE PROBLEM

SIMULATION RESULTS OF REGULAR CSLA

ADVANTAGES & APPLICATIONS

CONCLUSION

ABSTRACT

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 and power. Based on this modification 16-b square-root CSLA (SQRT CSLA) architecture have

been developed. The proposed design has reduced area and power as compared with the regular

SQRT CSLA . This work evaluates the performance of the proposed designs in terms of area,

power by hand with logical effort and through Xilinx ISE 14.2(Verilog HDL) and this will be implemented in FPGA (Sparton 6).

INTRODUCTION

In electronics, an adder or summer 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 processers designs

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.

REGULAR 16BIT SQRT CSLA

AREA EVALUATION METHODOLOGY OF REGULAR 16-b SQRT CSLA

Gate count=

57(HA+FA+MUX)

FA=39(3*13)

HA=6(1*6)

MUX=12(3*4)

PROBLEMS IN EXISTING SYSTEM

The problem in CSLA design is the number of full adders are increased then the circuit complexity also increases.

The number of full adder cells are more thereby power consumption of the design also increases

Number of full adder cells doubles the area of the design also increased.

SOLUTION OF THE PROBLEM

The parallel RCA with Cin=1 is replaced with Binary-Excess 1 converter( BEC).

four-bit BEC

Modified CLSABasic function of CLSA is obtained by using the 4-bit BEC together with the mux.

PROPOSED SYSTEM(16-b CLSA)

In this system we use the BEC to reduce the RCA circuits

Here based on the carry input the MUX will be select corresponding input

In this design we give the MUX inputs are RCA output and BEC output

Compare to regular design the area of the design is less

Contd…

AREA EVALUATION METHODOLOGY OF MODIFIED 16-b SQRT CSLA

GATE COUNT= 43(HA+FA+MUX+BEC) (13+6+12+1+1+10)

COMPARISION

GROUP REGULAR MODIFIED

GROUP 2 57 43

GROUP 3 84 61

GROUP 4 117 84

GROUP 5 147 107

RTL SCHEMATIC

Simulation Result

TOOL USEDProgramming language: VERILOG HDL

Tool : Xilinx ISE (10.2)

ADVANTAGESLow power consumption

Less area (less complexity)

More speed compare regular CSLA

APPLICATIONSArithmetic logic units

High Speed multiplications

Advanced microprocessor design

Digital signal process

CONCLUSION

A simple approach is proposed in this paper to reduce the area and power

of SQRT 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.

REFERENCES

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

[2] 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.

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

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