IRJET - Realization of Power Optimised Carry Skip Adder using AOI Logic

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 03 | Mar 2020 www.irjet.net p-ISSN: 2395-0072
© 2020, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 3198
REALIZATION OF POWER OPTIMISED CARRY SKIP ADDER USING AOI
LOGIC
ALMUKHTAR AHMED1, NASER ALINABE2
1Faculty of Engineering, Sabratha University, SABRATHA, LIBYA, ASSIST.PROF,DEPT.OF ELE &ELEC ENG,FACULTY OF
ENG,SABRATHA-LIBYA
2faculty of Education, ZINTAN UNIVERSITY, ZITAN, LIBYA, LECTURER, DEP OF MATH. FACULTY OF EDUCATION,
ZINTAN-LIBYA
------------------------------------------------------------------------***-----------------------------------------------------------------------
Abstract:- The binary adder is the critical element in most
digital circuit designs. The more important parameters in
VLSI design are power consumption, area and speed. And
since the binary adder is exist in most digital circuit
designs. In this paper a carry skip adder (CSKA)based
AND-OR INVERTER (AOI)logic is proposed in order to
reduce area and power consumption. The proposed adder
is simulated by Xilinx and compared with the conventional
CSKA based multiplexer logic
Key words-Carry skip adder (CSKA), AND-OR-INVERTER,
Xilinx Simulation.
1-INTRODUCTION
While designing an adder, lot of constraints comes into
picture. The tradeoff between speed and size being the
most important one. The most basic adder has a very small
area and is very easy to implement. But the delay involved
in obtaining the output is very huge. Hence the new
designs came to picture. But in current age the power
consumed by the device is also a very important
constraint.
Hence designing an adder which is very close in meeting
all these requirements is a very important. Apart from the
design, the technology we use to design the adder also
plays a huge role in the speed and size of the adder. Adders
are a key building block in arithmetic and logic units
(ALUs) and hence increasing their speed and reducing
their power/energy consumption strongly affect the speed
and power consumption of processors. There are many
works on the subject of optimizing the speed and power of
these units, which have been low-power/energy
consumptions, which is a challenge for the designers of
general purpose processors.
One of the effective techniques to lower the power
consumption of digital circuits is to reduce the supply
voltage due to quadratic dependence of the switching
energy on the voltage. Moreover, the sub threshold
current, which is the main leakage component in OFF
devices, has an exponential dependence on the supply
voltage level through the drain-induced barrier lowering
effect. Depending on the amount of the supply voltage
reduction, the operation of ON devices may reside in the
super threshold, near-threshold, or sub threshold regions.
Working in the super threshold region provides us with
lower delay and higher switching and leakage powers
compared with the near/sub threshold regions.
2- Full adder using MUX.
The Full adder using multiplexer is shown below in fig 1.
Fig1: full adder using Mux
The sum and carry of a full adder is given by:
Sum=A⊕B⊕C
Cout=Cin(A ⊕ B)+AB
Y=AS+BS
3- Carry Skip Adder Using Mux
The carry skip adder using mux is shown in Fig 2 .

Fig2: Carry skip adder using Mux
In carry skip adder four full adders are cascaded,
the calculations of sum and propagation are :
Sum s=a xor b xor cin.
Propagation p=a xor b.
And also done the same process done in the ripple
carry adder for generating carry(c3) of final full
adder.Propagation outputs of the four adders are p0,p1,p2
and p3 .And all the propagated outputs are given to the
one AND gate. The output of AND gate acts as a selection
line to the multiplexer, cin and c 3 are inputs to mux circuit
,this is nothing but skip logic.
In carry skip adder four full adders are cascaded,
same as the ripple carry adder and every full adder
calculating sum and propagation.
And also done the same process done in the ripple
carry adder for generating carry(c3) of final full
adder.Propagation outputs of the four adders are p0,p1,p2
and p3 .And all the propagated outputs are given to the
one AND gate. The output of AND gate acts as a selection
line to the multiplexer, cin and c 3 are inputs to mux circuit
,this is nothing but skip logic.
4- The CSKA based and-or-inverter
The proposed 4bit carry skip adder using and-or-inverter
is shown in fig 3
Fig :3 Four full adders using and-or-inverter
For example let us take 4 bit carry skip adder The
inputs of carry skip adder is ‘a’ and ‘b’. In carry skip adder
four full adders are cascaded, same as the ripple carry
adder and every full adder calculating sum and
propagation.
for generating carry(c3) of final full adder. Propagation
outputs of the four adders are p0,p1,p2 and p3 .And all the
propagated outputs are given to the one AND gate. The
output of AND gate is connected toAOI logic circuit this is
nothing but skip logic.
Initially cin =0,what the carry given to the next stage of
either c in or c3. We are having two cases of carry
production, those are best case and worst case.
In case of best case let us assume a=1010 and b=0110
P0= 0 xor 0= 0.
P1= 1 xor 1= 0.
P2= 0 xor 1 =1.
P3 =1 xor 0 =1.
P0,p1,p2 and ,p3 are given to the and gate , the output of
and gate is p= (0&0&1&1)=0.

A1=Cin and p=1&&0=0.
A2=C3 and p=1&&1=1.
4-Simulation and Results
The simulations are done by Xilinx version 12.3 using
32bit CSKA based Mux fig 4,and 32bit CSKA based and-or-
inverter fig 5 and the simulation results are shown below.
Fig 4: 32bit CSKA USING Mux
Fig5 : 32bit CSKA using and-or-inverter
4.1- CSKA based Mux simulation:
Fig6.1: RTL schematic view
Fig6.2: view technology schematic
Fig6.3: simulation results using Mux
4.2 CSKAbasedand-or-inverter simulation
Fig6.4: RTL Schematic View

Fig6.5: View Technology Schematic
Fig6.6: simulation results using and-or-inverter
5. Conclusion
In this paper, The carry skip adder based and-or-inverter
(AOI) is proposed and simulated using Xilinx.The
simulated results showed that it has less area and low
power consumption compared with traditional one and it
can be used in digital circuit design where the area and
power consumption are critical.
REFERENCES
[1] I. Koren, Computer Arithmetic Algorithms, 2nd ed.
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BIOGRAPHY
Dr. Almukhtar. A. Alhamrouni
received the BSC degree in
Communication Engg. From higher
institute of electronics, BeniWal-ed,
Libya in 1989, MSC degree in the
field of electronics from Belgrade
University ,Serbia in 2000. He
received Ph.D degree at Sam
Higginbottom Institute of Agriculture, Technology &
Sciences (Formerly AAI-DU) Allahabad in Electronics. His
processing and instrumentation .Currently He is working
as Assistant Prof at faculty of Engineering SARATHA
UNIVERSITY ,SABRATHA-LIBYA
area of interests Electronics, power electronics, Image

Dr. Naser. A. Alinabe ,He
Received his BSC and MSC
degree from Caspian Higher
Red Collage, Baku- Russia
(1988-1993) and Ph.D in
Control System from SHIATS,
Allahabad ,India 2016 . His is
interesting in Robotics and
Control system. Currently he is
Lecturer at ZITAN
UNIVERSITY, ZINTAN-LIBYA

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