Design of Low Power Vedic Multiplier Based on Reversible Logic

Sagar . Int. Journal of Engineering Research and Application www.ijera.com
ISSN : 2248-9622, Vol. 7, Issue 3, ( Part -2) March 2017, pp.73-78
www.ijera.com DOI: 10.9790/9622- 0703027378 73 | P a g e
Design of Low Power Vedic Multiplier Based on Reversible Logic
Sagar*, K Suresh Babu**
*(Pg Scholar, Department of Electronics and comm, Bangalore University, Bangalore-01)
** (Professor, Department of Electronics and comm, Bangalore University, Bangalore)
ABSTRACT
Reversible logic is a new technique to reduce the power dissipation. There is no loss of information in reversible
logic and produces unique output for specified inputs and vice-versa. There is no loss of bits so the power
dissipation is reduced. In this paper new design for high speed, low power and area efficient 8-bit Vedic
multiplier using Urdhva Tiryakbhyam Sutra (ancient methodology of Indian mathematics) is introduced and
implemented using Reversible logic to generate products with low power dissipation. UT Sutra generates partial
product and sum in single step with less number of adders unit when compare to conventional booth and array
multipliers which will reduce the delay and area utilized, Reversible logic will reduce the power dissipation. An
8-bit Vedic multiplier is realized using a 4-bit Vedic multiplier and modified ripple carry adders. The proposed
logic blocks are implemented using Verilog HDL programming language, simulation using Xilinx ISE software.
Keywords: Reversible Logic gates, Ripple carry Adder, Urdhva Tiryagbhyam Sutra, Vedic Mathematics.
I. INTRODUCTION
As the technology improves, the
requirement also changes so the complexity of
design. Power consumption has become the centre of
attention for digital system design. Landauer‟s
principle [1] states that in the irreversible logic the
heat coming from computation was due to the
destruction of information (wiping out bits of
information) but not due to the processing of bits.
Landauer showed that for every bit of information
that is erased during an irreversible logic
computation KTln2 joules of heat energy is
generated, where K is the Boltzmann constant and T
is the temperature in Kelvin at which the system is
operating. The heat generated due to the loss of one
bit of information is very small at room temperature
but when the number of bits is more as in the case of
high speed computational works like multiplication,
convolution, Fourier calculations, and signal
processing the heat dissipated by them will be so
large that it affects the performance and results in
the reduction of lifetime of the components.
A computation in which no information is
lost is known Reversible and the gates used in
designing are called reversible gates. This new
approach of designing using reversible logic gates
which reduces the power dissipation and improves
system response time. Bennett[2] showed that in
order to avoid energy dissipation in a circuit it must
be built from reversible circuits. Reversible logic
ensures zero information loss and low power
dissipation. This is so because reversible
computation does not require erasing any bit of
information and consequently it does not dissipate
any energy for computation.
Thus, Reversible logic circuits avoid energy
loss by not computing the computed information by
recycling the energy in the system. In the design of
reversible circuits, two restrictions should be
considered; firstly, Fan-out is not permitted and
secondly, Feedback from gate outputs to inputs is
not permitted. Due to these restrictions, synthesis of
reversible circuits can be carried out from the inputs
towards the outputs and vice versa. So, there is a
one-to-one mapping between input and output
vector. In an n-output reversible gate, the output
vectors are permutations of the numbers 0 to 2n - 1.
Multiplication is most importance in Digital
Signal Processing like Image and speech Processing.
To implement the hardware module of Discrete
Fourier, Cosine and Sine Transformations; large
numbers of complex multipliers are required. There
are so many novel designs and algorithms are
projected multiplier design is always a challenging
task and optimization required. The use of Vedic
mathematics reduces the calculation compared to
other multiplier design. Vedic mathematics is
methodology of arithmetic rules that allow simple
and effective speed implications. It provides some
effective algorithm that can be applied in complex
computation. Vedic mathematics was remade from
the antiquated Indian scriptures (Vedas) by “Sri
Bharati Krishna Tirtha” (1884-1660) after his
exploration on Vedas. He developed 16 sutras and
16 upa sutras after broad research in “Atharva
Veda”. It has been discovered that Urdhva
Tiryakbhayam is the most proficient among these.
The proposed 8-bit multiplier is based on the
“Urdhva Tiryakbhayam(UT)” sutra (algorithms ).
Urdhva Tiryakbhayam means “vertically and
crosswise”. Vedic multiplier also reduces transistor
count in multiplier which is also an additive feature,
improves the compactness of the system. This
implementation requires TG, PG, and HNG
RESEARCH ARTICLE OPEN ACCESS

reversible gates as a whole improves the efficiency
of the digital systems.
The paper organization follows: In section
II, reversible logic and gates are discussed. Vedic
Multiplication and sutra is discussed in section III.
Proposed methodology for Vedic multiplier is in
section IV. In Section V, RTL Design
implementation of module using XilinxISE14.5.
Section VI, has results and discussion. Finally,
conclusion is given in Section VII.
II. REVERSIBLE LOGIC AND GATES.
Reversible logic is a promising computing
design which presents a method for constructing
computers with no heat dissipation. Reversible logic
is the one of the upcoming technology used to
reduce the heat generation due to the information
loss. In reversible logic the computation process is
reversible, i.e time-invertible. An n×n reversible
circuit consists of n inputs and n outputs with
mapping of each input pattern to a unique output
pattern assignment and vice versa. Optimization and
performance parameters of reversible logic are
Garbage outputs (GO) which do not contribute to the
reversible logic realization of the design. Quantum
cast (QC) refers to the cost of the circuit in terms of
the cost of a primitive gate. Gate count (NG) is the
number of reversible gates used to realize the
function. Gate level refers to the number of levels
which are required to realize the given logic
functions.
Features and design constrain of reversible logic.
 Reversible logic has an equal number of inputs
and outputs.
 Fan-out is not allowed.
 Feedback paths are not allowed.
 Every output that is not used in the circuit is a
garbage signal.
 The number of constants at the inputs of the
gates should be kept as low as possible.
Basic reversible gates used in design are listed below
1. Feynman Gate (FG)
Fig.1. Feynman Gate
Feynman gate is a 2*2 reversible gate as
shown in figure 3.2. The input vector is I (A, B) and
the output vector is O(P, Q) and outputs are defined
by P=A, Q=AB. Quantum cost of a Feynman gate
is 1.
2. Toffoil Gate (TG)
Fig.2. Toffoli Gate
Toffoli Gate is 3*3 gate. The input vector is
I (A, B, C) and the output vector is O(P,Q,R). The
outputs are defined by P=A, Q=B, R=AB C.
Quantum cost of a Toffoli gate is 5. It is used to
realize AND function; it is also used for realizing
XOR function.
3. Peres Gate (PG)
Fig.3. Peres Gate
In 3*3 Peres gate, the input vector is I (A,
B, C) and output vector is O (P, Q, R). The output is
given by P = A, Q = A B and R=AB C. Quantum
cost of a Peres gate is 4. It is used for realization of
half adder, Xor and And function.
4. HNG Gate.
Fig.4. HNG Gate
It is a 4x4 bit gate and its quantum cost is
six. The input vectors are I= (A, B, C, D) and output
vectors are O= (A, B, ABC, (AB)CABD).
It is used for designing full adders. HNG gate
produces sum and carry in the same and thereby
reduces the gate count and garbage outputs.

III. VEDIC MULTIPLIER
Vedic mathematics reduces the calculation
compared to other multiplier design. Vedic
mathematics is methodology of arithmetic rules that
allow simple and effective speed implications. It
provides some effective algorithm that can be
applied in complex computation.
Urdhva Tiryakbhayam Sutra
The proposed 8-bit multiplier is based on
the “Urdhva Tiryakbhayam(UT)” sutra (algorithms).
UrdhvaTiryakbhayam means “vertically and
crosswise”. This UT sutra is a recognize from
“Sthapatya- Veda” (book on construction and
structural modeling as well as building designs),
which is an upa-veda (supplement) of “Atharva
Veda”. These sutra have been traditionally used for
multiplying two decimal number. This sutra also
applied for the binary number to make the proposed
algorithm suitable for the digital system. It is very
simple compare to the conventional method of
multiplication. Urdhva Tiryakbhyam Multiplication
Algorithms is generalized multiplication formula
applicable to all cases of multiplication. It means
“Vertically and Crosswise” method. The digits at the
two ends of the line are multiplied and the resultant
output is added with the previous carry. When there
are more lines involve in one step, all the results are
added with the previous carry. The least significant
digit of the number thus obtained after adding acts as
one of the result digits and the rest act as the carry
for the next step. Initially the carry bit is taken to be
as zero. It is faster and easier than other algorithms
like array and booths algorithms. For a “NxN”
multiplier, it requires “NxN” AND gates, “Nx(N-2)”
full adders and „N‟ half adders. But Vedic multiplier
requires only (N-1) adders. Figure 4 shows the steps
involve in 4-Bit Vedic multiplier.
Fig.4. Vedic multiplication steps
For 3-bit binary number (110) and (011)
multiplication using UT algorithm is shown in the
figure 5.
Fig.5. Multiplication of 3-Bit binary numbers using
UT algorithm.
The digits at the two ends of the line (cross
and vertical lines) are multiplied and the result is
added with the previous carry. If there are more lines
in one step, all the results are added with the
previous carry if generated. The least significant
digit of the numbers thus obtained after adding acts
as one of the result digits and the rest of numbers act
as the carry for the next step, where zero carry is
considered as an initial condition. This algorithm is
also true for the decimal numbers also.
IV. PROPOSED ARCHITECTURE.
The proposed 8x8 reversible vedic
multiplier multiply two binary numbers and give 16-
bit binary output. Peres gate and Feynman gates are
used for designing the multiplier. The beauty of UT
architecture is the generation of partial products and
additions are done concurrently. The proposed vedic
multiplier is design using reversible 2x2 and 4x4
vedic multiplier as its sub unit. Proposed 2x2, 4x4
and 8x8 vedic multiplier are describe below.
 2x2 Vedic Multiplier
It has two 2-bit binary number A and B as
input and 4-bit number S as output. Where A =a1a0
and B =b1b0 let output is S =s3s2s1s0 and c1and c2
are the carry generated in s1 and the s2, which is
shown in the figure 6.
Output is given as:
s0 = a0b0;
s1 = a1b0 + a0b1;
s2 = c1 + a1b1;
s3 =c2;
Fig.6. 2x2 Vedic multiplier using TG and PG gates.

There are four TG and two PG gates are
used in realizing 2x2 Vedic multiplier. Total six
reversible gates are used in this implementation.
Number of constants and number of garbage values
is six and quantum cost is 28. This implementation
looks same as array and booth multiplier, So 2-bit
Vedic multiplier does not give much advantage over
other methods but 4x4 and 8x8 does.
The 4x4 bit binary vedic multiplier can be
implemented using four 2x2 bit vedic multiplier unit.
Let 4x4 multiplications having input A= a3a2a1a0
and B= b3b2b1b0 and the output the multiplication
result is F= F7F6F5F4 F3F2F1F0. Using the
fundamentals of UT sutra, taking two bits at a time
and using four 2x2 multipliers, 4-bit binary
multiplication will be calculated. The 4x4 vedic
multiplier is shown in the figure 7.
Fig.7. 4x4 Vedic multiplier
This design consists of four 2x2 vedic
multiplier, and three 4-bit ripple carry adder circuit.
This purposed design reduces the delay because it
has property of concurrency. It has quantum cost of
144, constant input is 32 and garbage output is 44.
The proposed 4x4 vedic multiplier has less quantum
cost, constant inputs and garbage value as compare
to design proposed in [4],[5]and [6] This design is
used for implementing the proposed 8x8 vedic
multiplier.
The proposed 8x8 vedic multiplier block
diagram is shown in the figure 8. It is easily
implanted using four 4x4 vedic multiplier and three
8-bit ripple carry adder. This makes the design of
this proposed 8x8 multiplier very simple and
efficient compare to the array and booth type
multipliers. All the multipliers are made using PG
and TG reversible gates. And RCA is design using
HNG gates. So the designs are reversible in nature.
It has quantum cost of 720.
Fig.8. Proposed 8x8 Vedic multiplier.
 8-bit Reversible Ripple Carry Adder
Reversible adder is proposed using HNG
gate. In HNG gate if fourth input, D is made
constant zero and inputs is given through A and B
and carry to third input C then it act as reversible
one bit full adder and output is taken from R and S
respectively.
The proposed 8-bit reversible adder is form
using HNG gate having two 8-bit inputs and a carry
which is propagate from the list significant bit
(LSB) to most significant bit (MSB) also known as
ripple carry adder. The size of the reversible ripple
carry adder is very small and it is very simple to
design, so normally ripple carry adders are used for
cascading. Each HNG gate act as one bit full adder
so total eight HNG gates are required to built 8-bit
ripple carry adder. Output is represented as S0-S7
and „g‟ is the garbage. The 4 bit ripple carry adder is
made with same HNG gate. In proposed adder total
16 garbage values are produced and having quantum
cost of 48. The proposed reversible 8-bit ripple carry
adder is shown in the figure 9.
Fig.9. Proposed 8-Bit RCA using HNG Gate.
V. RTL DESIGN AND
IMPLEMENTATIOM
The design architectures are written in
VHDL language using Xilinx ISE 14.5 tool. The
VHDL codes are simulated using ISIM tool present
in the Xilinx and are implemented on Spartan LX45
board. The RTL design of 8x8 vedic multiplier and
8-bit ripple carry adder are as shown in figure 10 and
11 respectively.

Fig.10. RTL of Proposed 8x8 Vedic multiplier
Fig.11. RTL of Proposed 8-bit RCA.
RTL (Resister Transfer Level) description
describes a circuit‟s registers and the sequence of
transfers between these registers but does not tell
about the hardware used to carry out these
operations. It is use to determine the size and
number of registers used.
VI. RESULTS AND DISCUSSIONS
All the blocks are modeled using Verilog
HDL. The simulation results of the proposed design
are verified using Xilinx ISE ISim. This achieves
functional verification of the conceptual design
which enables the developer to synthesize
(„compile‟) their designs, perform timing analysis.
Fig.12. Simulation result of 8-bit RCA.
Time delay and power comparisons
between proposed 8-bit reversible, non reversible
and [8] adders were observed and compared and
tabulated in Table 1.
Table 1. Time and Power Comparisons of proposed
logic.
Paramete
rs
Irreversible
RCA
Ref.
[8]
Proposed
Reversible
RCA
Time
Delay (ns)
11.2 ns 7.88
ns
7.4 ns
Power
(mw)
0.047 0.0114 0.0102
The above observations shows that the
proposed reversible ripple carry adder is time and
power efficient than irreversible logics and the
design proposed in [8].
Fig.13. Simulation Result of 8x8 Vedic Multiplier
Comparison between 8-bit Reversible
Vedic multiplier with the conventional multiplier
(Booth) and reversible multiplier [8] in terms of
parameters like time delay, power consume and area
utilized are shown in the table 2.
Table 2. Comparison of Multiplier designs.
Parameters Conv.
Booth
Multiplier
Ref [8] Proposed
Multiplier
Time Delay 27.72ns 21.44ns 20.249ns
Power (mw) 0.430mw 0.299mw 0.278mw
Area (no.
slice LUTs.)
171 -- 108
The proposed 8-bit reversible multiplier is
more efficient and optimized than the conventional
8-bit booth multiplier and design proposed in [8].
The power dissipation, speed and the area
utilization in terms of LUT is improved by 35.35%,
26.94% and 36.8% respectively with respect to
conventional booth multiplier. Also proposed design
has 5.5% power and 7% speed improvement over
design [8]. The improvement in power dissipation is
achieved by the 3*3 reversible gates, which are the
fundamental blocks of the proposed design but in
[8], Viswanath and Ponni utilized 4*4 gate (TSG).
The proposed Low power Reversible Vedic
multiplier and conventional booth structure are
implemented using VHDL programming language,
simulated and synthesized using Xilinx ISE 14.5 and
get implemented using Spartan xc6slx45-2csg324
FPGA kit.

VII. CONCLUSION
This paper presents the Urdhva
Tiryakbhayam Vedic Multiplier realized using
reversible logic gates. First a basic 2x2 UT
multiplier is designed and implemented using PG
and TG reversible gates. And this 2x2 UT multiplier
block is cascaded to obtain 4x4 multiplier with the
ripple carry adders which were required for adding
the partial products were constructed using HNG
gates and this 4x4 is used to construct proposed 8x8
Vedic multiplier design with 8-bit reversible ripple
carry adder using HNG gate to add the partial
product in single step.
The fast, low power and area efficient
reversible logic based adder and Vedic multipliers
with lower hardware complexity are integrated and
resulted that the power dissipation and speed of
operations of proposed design is reduced when
compared with the other design. Less number of
adders in the Vedic multiplier reduces the area and
power dissipation and increases the operation speed.
The proposed logic are implemented using Verilog
HDL programming language, simulated and
synthesized using Xilinx ISE 14.5i software. The
synthesized output resulted that the proposed
technique consumes approx the 35% of less power,
area of 36% less and the 26% of higher performance
compared to conventional circuit and 5% of less
power and 7% speed over [8].
ACKNOWLEDGEMENTS
I would like to thank my parent and
teachers, who have always been a source of
encouragement for me.
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[4]. Shams, M., M. Haghparast and K. Navi,
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Design of Low Power Vedic Multiplier Based on Reversible Logic

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