1. 1
Abstract—During designing of VLSI circuit, one would
concentrate in the optimization of different entities. Among these
entities, power dissipation is a critical parameter in the field of
modern VLSI design. In this paper, High speed low power
multiplier has been designed by adopting effective technique
called New Vedic VLSI Technique (NNVT). It increases the
performance by using carry look ahead adder as it can produce
carry bits faster. The proposed multiplier is implemented and
power analysis on a 012µm CMOS technology using
Microwind3.1. Based on the power analysis result it is shown
that when the carry look ahead adder is used, the power
consumption is 41.868 µw in 10ns while ripple carry adder causes
65.4µw power consumption in 10ns. The speed of the multiplier is
enhanced by using the Vedic multiplication technique. The
proposed high speed low multiplier can obtain 23.592 µw power
reductions in modified New Vedic VLSI Technique (NNVT)
when compared to convention multiplier. The high speed
processor requires high speed multipliers and the New Vedic
VLSI Technique (NNVT) suitable for this purpose.
Index Terms—Carry look ahead adder, Dsp processor, Low
power, Multiplier, NNVT.
I. INTRODUCTION
HIS the speed of the processor architectures such as
CISC, RISC etc is increased with the help of Arithmetic
operations in different digital circuits. The speed-up
process involves two important parameters viz. multiplication
and addition process. Though Multiplication is a less common
operation than addition, it is essential for many structures such
as microprocessor, digital signal processing and graphics
engines. Many of the DSP algorithms have the need of high
speed multiplier as the multiplication process dominates the
execution time in such algorithm.
New developments in the technology induce the need for
higher and higher speed in multipliers. Researchers are going
on to design multipliers to achieve high speed, regularity of
layout, low power consumption and thus less area or even
combination of them in multipliers.
Due to the increased complexity in various applications, not
only faster multiplier chips but also smarter and efficient
multiplying algorithms are necessary to implement in the
chips. Array multiplication algorithm and Booth multiplication
algorithm are the two most widely used multiplication
algorithms in the digital hardware. But these two algorithms
suffer by the drawback of large propagation delay associated
with it.
II. RELATED WORK
Multiplication algorithm will be used to demonstrate
method of designing different cells and thus they can fit into
large structure. The product of two unsigned (positive) binary
numbers forms the most basic form of multiplication process
which can be accomplished through the traditional method and
simplified to base 2. For instance, consider multiplication of
two positive 4-bit binary integers (1410 and 610). The
multiplication process can be done as.
1110:1410 Multiplicand
0110:610 Multiplier
……………..
1110
0000 Partial Product
1100
0000
……………….
01010100:8410 Product
S * T-bit multiplication is done by forming „N‟ partial
products of „S' bits each, and then obtaining the sum of the
appropriately shifted partial product which produces an S+T-
bit result „R‟ whereas Binary multiplication is just equivalent
to a logical „AND‟ operation. Therefore, the partial product
can be generated by logical „AND‟ of the appropriate bits of
the multiplicand and multiplier. Then, each column of partial
products must be added and carry values should be passed to
the next column, if any. If the multiplicand is denoted as
S=(Sm-1, Sm-2, ….., S1, S0) and the multiplier as T=(Tn-1, Tn-2,
…..,T1,T0). For unsigned multiplication, the product can be
obtained by the equation
There are various types of Multiplication [1] and Adders.
The various types of multiplications are Array Multiplication,
2‟s complement array multiplication, Serial/Parallel
multiplication, Wallace tree multiplication, Booth encoding.
The most familiar multiplication method is „add and shift‟
algorithm [2]. Next, in case of parallel multipliers, main
parameter that determines the performance of the multiplier is
the number of partial products (pp) to be sum. Then partial
products to be summed can be efficiently conquered by
Modified Booth algorithm [3] which is one of the most
popular algorithms. The speed improvements can be achieved
by Wallace Tree algorithm by reducing the number of
sequential adding stages.
The combination of both Modified Booth algorithm and
Wallace Tree technique [4] can increase the performance of
one multiplier. But due to the increase in parallelism,
intermediate sums to be added and the amount of shifts
between the partial products will increase which reduces the
Low Power Multiplier using VEDIC Carry
Look ahead Adder Technique
S.Vijayakumar, Dr.J.Sundararajan, Dr.P.Kumar, S.Rajkumar
T
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 9 (2015)
© Research India Publications ::: http://www.ripublication.com
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2. 2
speed, increases the silicon area due to irregularity of structure
and also increases power consumption due to increase in
interconnect because of complex routing.
Alternatively, the serial-parallel multipliers [5] increases
speed to achieve better performance in terms of area and
power consumption. The selection of the type of multiplier
(parallel/serial) actually depends on the nature of application
in which we are using.
III. PROPOSED ARCHITECTURE
In this paper multiplier which increase speed and reduces
power using Vedic technique and carry look ahead adder is
proposed.
The proposed multiplier mainly consist of two parts
-Multiplication section (Vedic multiplication)
-Addition section (carry look ahead adder)
Fig . 1. NNVT-Proposed Archticture
A. Vedic Multiplication Technique
The primary advantage of Vedic mathematics is that it
reduces the typical calculations in conventional mathematics
to very simple one. The proposed Vedic multiplier [6] is based
on the “Urdhva Tiryagbhyam” sutra (algorithm) which
literally means “Vertically and crosswise”.
1) Vedic Multiplier for 2x2 Module
Consider two 2 bit numbers S and T where S = s1s0 and T
= t1t0. The Vedic multiplier can be implemented as shown in
Fig. 2.
Fig . 2. NNVT Method for two 2-bit Binary Numbers
First, the LSB were multiplied and which produces the
LSB of the final product (vertical). Next, the least significant
bit is multiplied with the next nearer bit of the multiplier and
then sum with the product of least significant bit of multiplier
and next nearer bit of the multiplicand (crosswise).
The resulted sum gives the second bit of the final product.
The resulted carry is added with the partial product which is
attained by multiplying the MSB to give the sum and carry. In
the final product, the carry be fourth bit and the sum is the
third bit.
This 2X2 Vedic multiplier module can be implemented
using four input AND gates & two half-adders as
specified in the block diagram shown in Fig. 3. Very precisely,
the total delay is only 2-half adder delays [7], after the
generation of final bit products, which is very similar to Array
multiplier.
Fig. 3. Block Diagram of 2x2 bit Vedic Multiplier
Thus we can switch over to the implementation of 4x4 bit
Vedic multiplier which makes use of the 2x2 bit multiplier as
a basic building block. The similar technique can be extended
for both input bits 4 & 8. But in case of higher no. of input
bits, little modification is required.
2) Vedic Multiplier for 4x4 Module
The 4x4 bit Vedic multiplier module can be obtained by
using four 2x2 VM as shown in Fig. 3. Let‟s analyze 4x4
multiplications, say S= s3 s2 s1 s0 and T= t3 t2 t1 t0. The finial
output of multiplication result is – p7 p6 p5 p4 p3 p2 p1 p0.
Now, s and t can be divided into two parts, t3 t2 & t1 t0 for T
and s3 s2 & s1 s0 for S. multiplication process is done by using
the fundamental of Vedic multiplication, that is, taking two bit
at a time and using 2 bit multiplier block and then addition
process is done using carry look-ahead adder. The
multiplication process is represented by the structure shown in
Fig. 4.
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3. 3
CLA1
CLA2
CLA3
t3t2s3s2t1t0s3s2t3t2s1s0t1t0s1s0
P7P6P5P4P3P2P1P0
STEP1
STEP2
STEP3
Fig. 4. Proposed block Diagram of 4x4 bit Vedic Multiplier
B. Carry Look ahead Adder
If the summation of circuit is used to compute the
sum of four or more numbers, it is better not to propagate the
carry result. Alternatively, three input adders can be used
which contributes two results: a sum and a carry.
Then the resulted sum and carry is to be fed into 2-inputs of
the subsequent 3-adder without await for the propagation of a
carry bits.
Thus, one can write,
COUT = Ci+1 = Li.Mi + (Li ^ Mi).Ci (2)
where "^" for exclusive OR.
Ci+1 = Ai + Pi.Ci (3)
Ai = Li.Mi (4)
Pi = (Li ^ Mi) (5)
where A-Generate and P-Propagate term.
C1=A0+P0.C0 (6)
C2=A1+P1.C1=A1+P1.A0+P1.P0.C0 (7)
C3=A2+P2A1+P2P1A0+P2P1P0C0 (8)
C4=A3+P3A2+P3P2A1+P3P2P1A0+P3P2P1P0C0 (9)
Fig. 5.Block diagram for carry look ahead adder
IV. RESULT
Fig. 6 Simulation Result for conventional multiplier (100ns)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 9 (2015)
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4. 4
V. CONCLUSION
Thus the low power multiplier has been designed using the
New Vedic VLSI Technique (NVVT). This multiplier is
designed with two different types of adder viz., ripple carry
adder and carry look-ahead adder and the obtained power
results were compared. Based on these power results, it has
been shown that carry look ahead adder is more efficient than
the other and the power difference between them is 23.592
µw. Hence our motivation to reduce power if finely fulfilled.
This work can be used for high speed DSP processor
applications.
VI. FUTURE WORK
The power obtained from proposed multiplier is to
decreased further by using a block Enable Technique
REFERENCES
[1] Neil H.E. Weste, David Harris and Ayan Banerjee, CMOS VLSI Design
, A circuits and system perspective, 3rd Edition, Pearson Education,
2005, pp. 345-358.
[2] M.Mottaghi Dastjerdi ,A.afzali Kusha,m.Pedram “BZFAD A Low
Power Low Area Multiplier Based on Shift and Add Architecture” IEEE
Trans. Very Large Scale Integr .(VLSI)Syst., Vol.17, no-2,pp302-306,
Feb. 2009.
[3] Nishat Bano (2012) “VLSI Design of Low Power Booth Multiplier”
International Journal of Scientific & Engineering Research. Vol. 3,
Issue 2, pp421-423, Feb.2012.
[4] Jagadeshwar Rao M, Sanjay Dubey (2012) “A High Speed Wallace Tree
Multiplier Using Modified Booth Algorithm for Fast Arithmetic
Circuits” IOSR Journal of Electronics and Communication Engineering
(IOSRJECE). Vol.3, Issue 1, PP 07-11, Oct. 2012.
[5] A. Aggoun, A.F. Farwan, M.K. Ibrahim and A. Ashur (2004) “Radix-2n
serial–serial multipliers” IEE Proc.-Circuits Devices System.. Vol. 151,
no. 6, pp503-509, Dec.2014.
[6] Swami Bharati Krishna Tritha, Vedic Mathematics, Motilal Banarsidass
Publisher, 1991, pp.26-35.
[7] Rejisha Krishnan, Mr.S.Vijayakumar, “Multiplierless FIR Filter Design
using Global Valued Numbering and Architecture” International
Computing, Communication and Networking Technologies (ICCCNT),
July.2014.
Fig. 7. Simulation Result for proposed multiplier (100ns)
TABLE I
POWER COMPARISONS PROPOSED AND CONVENTIONAL
MULTIPLIER
Type Power (µw)
10(ns) 100(10ns) 200(ns)
Conventional
multiplier
65.46µw 131 µw 149µw
Proposed
multiplier
41.868 µw 96.040 µw 123µw
Graph.1 conventional versus Proposed Multiplier
0
20
40
60
80
100
120
140
160
Conventional
Multiplier
Proposed
Multiplier
10 ns
100ns
200ns
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 9 (2015)
© Research India Publications ::: http://www.ripublication.com
7322