DESIGN OF A NOVEL ENERGY EFFICIENT HYBRID ADDER

Under the Esteemed Guidance of

Dr.S.GOVINDARAJULU,

Professor, Dept. Of ECE,

RGMCET.

Submitted byY. Krishna Kalpana (11091A0455)

A. Guru Sai Prasanth (12095A0405)

G. Greeshma (11091A0436)

M. Harinath Reddy (11091A0438)

B. Anjan Kumar (11091A0406)

Introduction:• An energy efficient adder is designed based on a hybrid carry

computation.• In this design, addition takes place by considering the carry as

propagating forwards from LSB and backwards from MSB.• The incidence at a midpoint significantly accelerates the

addition.• This acceleration together with combining low cost ripple carry

and carry chain circuits, yields energy efficiency compared to other adder architectures.

• The adder is enhanced in a tree-like structure for further acceleration.

Block Diagram

Fig: The architecture of a complete n-bit hybrid adder.

Fig: A ripple carry adder (LSB’s) Fig: Carry look ahead adder (MSB’s)

Ripple Carry Adder :

The 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

DSCH of RCA(4 Bit) in Static Mode

RCA (8 BIT)

RCA(16 Bit)

Carry Look Ahead Adder

• A carry-look ahead adder improves speed by reducing the amount of time required to determine carry bits.

• The carry-look ahead adder calculates one or more carry bits before the sum, which reduces the wait time to calculate the result of the larger value bits.

Sum & Carry Generation :• Propagate P and Generate G in a CLA is given by, Pi=Ai Bi

Gi=Ai Bi

• The new expressions for the output sum and the carryout is given by,

Si = Pi Ci-1

Ci+1 = Gi +PiCi

SiCi+1

PiCi-1

Gi

Ci+1

Ai

Bi

Pi

Gi

Advantage of carry look ahead adder

• Like ripple carry adder we need not to wait for the propagation of carries to get the sum.

• That means it speed up the carry generation.

DSCH of Carry look ahead adder

CLA(8 Bit)

CLA (16 Bit)

HYBRID ADDER

• This is the combination of low-cost ripple –carry and carry-chain (carry look ahead) circuits, yields energy efficient compared to existing adders.

8 BIT

16 BIT

HYBRID ADDER POWER

COMPARISONADDER Bits DELAY

(ns)AREA POWER PDP

(Ws)RCA 8

BIT2.276 4297920

(Lambda2)5264.95 (um2 )

8.135uW 18.51x10-15

RCA 16 BIT

2.94 4868976(Lambda2)

5964.49 (um2 )

30.75uW 90.405x10-15

CLA 8 BIT

2.118 3581212(Lambda2)

4386.98 (um2 )

6.507uW 13.781x10-15

CLA 16 BIT

2.361 6571752(Lambda2)

8050.39 (um2 )

21.96uW 51.84x10-15

HYBRID ADDER

8 BIT

2.13 4389480(Lambda2)

537.113(um2 )

8.212uW 17.491x10-15

HYBRID ADDER

16 BIT

2.514 4389480(Lambda2)

5377.13(um2 )

13.24uW 33.28x10-15

DYNAMIC

RCA(8 BIT)

RCA (16 BIT)

CLA (8 BIT)

CLA (16 BIT)

DYNAMIC HYBRID ADDER (8 BIT)

DYNAMIC HYBRID ADDER (16 BIT)

COMPARISONADDER BITS DELAY

(ns)AREA POWER(mW) PDP (Ws)

RCA 8 BITS 1.282 4033080(Lambda2)4940.5234 (um)2

1.98 2.53x10-12

RCA 16BITS 2.111 5192748(Lambda2)6361.1163 (um)2

5.093 10.75x10-12

CLA 8 BITS 6.497 3792201(Lambda2)4645.44 (um)2

0.352 2.286x10-12

CLA 16BITS 21.47 7626895(Lambda2)9342.94 (um)2

0.702 15.07x10-12

HYBRID ADDER 8 BITS 4.857 4407191(Lambda2)5398.2280 (um)2

0.352 1.709x10-12

HYBRID ADDER 16BITS 13.185 8211225(Lambda2)10058.75 (um)2

1.043 14.37x10-12

Differences:

• General arithmetic circuits will consume power and energy.

• The hybrid adder can provide high energy efficiency compared with design compiler, different adders at high clock frequencies.

• Smaller area and power is achieved by using this hybrid architecture.

Advantages:

• Reduces time delay.• Has low energy and power consumption.• Smaller area can be achieved.• Addition can be made faster.

OPTIMIZATION RESULTS STATIC:

56.94% power efficient than RCA39.7% power efficient than CLA14.48% less delay than RCA

DYNAMIC:38.58% less delay than CLA79.52% power efficient than RCA

CONCLUSION

• An energy efficient hybrid adder was studied.

• Comparison of 8 bit, 16 bit with existing adders to the hybrid adder, targeting high frequencies showed less energy consumption was studied.

Thank you