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In recent years, reversible logic circuits have applications in the emerging field of digital signal processing, optical information processing, quantum computing and nano technology. Reversibility plays an important role when computations with minimal energy dissipation are considered. The main purpose of designing reversible logic is to decrease the number of reversible gates, garbage outputs, constant inputs, quantum cost, area, power, delay and hardware complexity of the reversible circuits. This paper reveals a comparative review on various reversible logic gates. This paper provides some reversible logic gates, which can be used in designing more complex systems having reversible circuits and can execute more complicated operations using quantum computers. Future digital technology will use reversible logic gates in order to reduce the power consumption and propagation delay as it effectively provides negligible loss of information in the circuit. Keywords: Garbage output, Power dissipation, quantum cost, Reversible Gate, Reversible logic
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Special Conference Edition
, November, 2019
Bayero Journal of Pure and Applied Sciences, 12(1):
ISSN 2006 – 6996
A REVIEW ON REVERSIBLE LOGIC GATES
Galadima
1
,B.Y.,
Galadanci
1
Department of Physics, Bayero University, Kano, Nigeria)
4
Department of Physics
Corresponding Author:
ABSTRACT
ene
rgy dissipation are considered. The main purpose of designing reversible logic is to
compute
rs. Future digital technology will use reversible logic gates in order to reduce the
information in the circuit.
logic,
INTRODUCTION
In
present day technology, Reversible logic has
Applications of the
Reversible circuits can be
technology
(Markle & Drexler, 1996)
Trad
itional logic circuits are Irreversible which
result in energy dissipation and
information loss
(Biswas
et al
., 2014)
. Landaurer’s Research has
joules, where is k is
the Boltzmann’s constant
1961; Parhami, 2006). In 1973
, Bennett
reversible circuits (Bennett, 1973)
. The am
computation (Mamataj
et al
., 2014
circuits are those circuits
that do not lose
information.
Reversible logic
gates are required to design
reversible circuits (Biswas
etal
., 2014)
reversible logic
gate has equal input and output
etal
., 2014)
. In reversible circuit there should be
Misra, & Sen, (2017)
invented two kinds of
, November, 2019
Bayero Journal of Pure and Applied Sciences, 12(1):
242 - 250
A REVIEW ON REVERSIBLE LOGIC GATES
Galadanci
, G.S.M.,
1
Tijjani, A.
1
and Ibrahim,
M.
Department of Physics, Bayero University, Kano, Nigeria)
Department of Physics
, Yusuf Maitama sule university, kano.
Corresponding Author:
bygaladima.phy@buk.edu.ng
In recent years, reversible logic circuits have applications in the emerging field of digital
signal processing, optical information processing, quantum computing and nano
technology. Reversibility plays an important role when computations with minimal
rgy dissipation are considered. The main purpose of designing reversible logic is to
decrease the number of reversible gates, garbage outputs, constant inputs, quantum
cost, area, power, delay and hardware complexity of the reversible circuits. This paper
reveals a comparative review on various reversible logic gates
.
This paper provides some
reversible logic gates, which can be used in designing more complex systems having
reversible circuits and can execute more complicated operations using quantum
rs. Future digital technology will use reversible logic gates in order to reduce the
power consumption and propagation delay as it effectively provides negligible loss of
Keywords: Garbage output, Power dissipation, quantum cost, Reversible Gate, Reversible
present day technology, Reversible logic has
spread its popularity in numerous technologies,
due to their ability to reduce the power
dissipation which is the main requirem
ent in low
power VLSI design (Yelekar & Chiwande, 2011)
.
Reversible circuits can be
found in the emerging fields of low power CMOS
design, optical information processing, DNA
computing, quantum computing and nano
(Markle & Drexler, 1996)
.
itional logic circuits are Irreversible which
information loss
. Landaurer’s Research has
proved that the amount of energy dissipated for
every irreversible bit operation is at
least kTLn2
the Boltzmann’s constant
and T is the temperature in Kelvin
(Landaurer,
, Bennett
showed
that in order to avoid kTLn2 joules of energy
dissipation in a circuit it must be built from
. The am
ount
of energy dissipated in a system bears a direct
relationship to the number of bits erased
during
., 2014
). Reversible
that do not lose
gates are required to design
etal
., 2014)
. A
gate has equal input and output
in order to have one to one mapping
(Biswas
. In reversible circuit there should be
no fan-out;
that is, each output will be used only
once
and for each input pattern there should be
unique output pattern.
In the year 2007 (James et al
., 2007)
a low power circuit using reversible logic that
provides single error correction
detection (SEC-
DED). The design was done
using a new 4 x 4 reversible gate called
Hamming Code Generating (HCG)
implementing hamming error coding and
detection circuits. A parity preserving H
Code Generating
(PPHCG) that preserves the
input parity at the output bits is used for
achievin
g fault tolerance for the hamming error
coding and detection circuits.
Rashmi, & Tilak, (2011)
invented a reversible
gate known as Binary Coded D
ecimal
correction logic (BSCL)
. The main purpose of
introducing this gate is either to find correc
logic for BCD subtraction or to pass same data
to the output.
Misra, & Wairya, (2015)
demonstrated a
reversible BCD adder and carry skip BCD adder
circuit based on three new t
ype of reversible
gates, namely;
Full adder subtraction (FAS), Half
adder su
btraction (HAS) and Overflow detection
(OD) gates, to optimize the ad
der
new type of reversible full adder using FAS gate
is the best circuit in terms o
f quantum cost.
utilizing those three new types of gates,
reversible n-digit BCD adder
and 1
skip BCD adder are proposed with its algorithm.
invented two kinds of
novel error control circuits such as hamming
code, parity generator and checker. To design
the HG-
PP (HG = Hamming gate, PP = Parity
http://dx.doi.org/10.4314/bajopas.v11i1.3
242
M.
2
In recent years, reversible logic circuits have applications in the emerging field of digital
signal processing, optical information processing, quantum computing and nano
technology. Reversibility plays an important role when computations with minimal
rgy dissipation are considered. The main purpose of designing reversible logic is to
decrease the number of reversible gates, garbage outputs, constant inputs, quantum
cost, area, power, delay and hardware complexity of the reversible circuits. This paper
This paper provides some
reversible logic gates, which can be used in designing more complex systems having
reversible circuits and can execute more complicated operations using quantum
rs. Future digital technology will use reversible logic gates in order to reduce the
power consumption and propagation delay as it effectively provides negligible loss of
Keywords: Garbage output, Power dissipation, quantum cost, Reversible Gate, Reversible
that is, each output will be used only
and for each input pattern there should be
., 2007)
implement
a low power circuit using reversible logic that
double error
DED). The design was done
using a new 4 x 4 reversible gate called
Hamming Code Generating (HCG)
for
implementing hamming error coding and
detection circuits. A parity preserving H
amming
(PPHCG) that preserves the
input parity at the output bits is used for
g fault tolerance for the hamming error
invented a reversible
ecimal
subtraction
. The main purpose of
introducing this gate is either to find correc
tion
logic for BCD subtraction or to pass same data
demonstrated a
reversible BCD adder and carry skip BCD adder
ype of reversible
Full adder subtraction (FAS), Half
btraction (HAS) and Overflow detection
der
circuits. The
new type of reversible full adder using FAS gate
f quantum cost.
By
utilizing those three new types of gates,
and 1
-digit carry
skip BCD adder are proposed with its algorithm.
code, parity generator and checker. To design
PP (HG = Hamming gate, PP = Parity
http://dx.doi.org/10.4314/bajopas.v11i1.3
8S
Special Conference Edition, November, 2019
preserving), NG-PP (NG = New gate) are
proposed for optimising the circuits. Based on
the proposed gates and few existing gates, the
hamming code and parity generator and checker
circuits are constructed. The reversible, major
metrics such as gate count, quantum cost, unit
delay, and garbage outputs, uses best
optimisation results compared to counterparts.
They can be utilised as a low power error control
circuit applied in future communication systems.
Bhoi, K.B, & Misra, N.K. (2017) introduced a new
gate named as universal reversible QCA gate
(URQG) is proposed. It is a 3×3 gate that
realizes 13 standard functions with optimal gate
count. 2. The URQG gate is compared with the
existing reversible gates using standard Boolean
equations. The proposed gate outperforms the
existing gates in terms of design cost and
testing overhead. An n-bit comparator, was
synthesised where proposed URQG and existing
Feynman gates are cascaded together.
BASIC DEFINITIONS OF REVERSIBLE
LOGIC
1. REVERSIBLE FUNCTION
A function ∈ 
.
is called reversible if f is
bijective, i.e., if each input pattern is uniquely
mapped to a corresponding output pattern and
vice versa. Otherwise, it is called irreversible.
Clearly, if f is reversible, then its number of
inputs is equal to the number of outputs. In
other words, each reversible function  ∈ 
.
is
a bijection that performs a permutation of the
set of input patterns (Abdessied & Drechler,
2016). An irreversible function can be embedded
into a reversible specification by adding extra
variables to achieve a bijective function. An
embedding is not unique and the choice of
embedding can have a very significant effect on
the number of the variables of the resulting
function (Miller
et al
., 2009; Soeken
et al
.,
2015).
REVERSIBLE LOGIC GATE
A reversible logic gate is an n-input n-output
logic device with one-to-one mapping (Yelekar &
Chiwande, 2011), the number of inputs are
equal to the number of the outputs of the gates
in order to have a one-to-one mapping. This
generates a unique set of output vector for each
set of input vector (Biswas
et al
., 2014). This
prevents the loss of information which causes
power dissipation. In reversible logic, fan-out is
not possible and feedback or loops are not
allowed. Some features of a reversible logic
circuit are: Minimum input constants, Minimum
number of reversible gates and Minimum
number of garbage outputs.
REVERSIBLE CIRCUIT
A combinational reversible circuit is an acyclic
combinational logic circuit in which all gates are
reversible, and are interconnected without
explicit fan-outs and loops. Boolean functions
can be synthesized to a reversible circuit after
embedding them to reversible functions.
Therefore, in general a reversible circuit contains
n inputs with p primary inputs and c constant
inputs with p + c = n. At the output side, there
are m primary outputs and k garbage outputs
with k + m = n. Figure1 depicts the general
structure of a reversible circuit (Abdessied &
Drechler, 2016). A reversible circuit should be
designed using minimum number of reversible
logic gates, minimum input constant, minimum
number of garbage outputs.
Figure 1: Reversible Circuit Structure
GARBAGE OUTPUT
Unwanted output of reversible gate is called
garbage output. The output of reversible gate is
not used as a primary output or as input to
other gates is called garbage output. Garbage’s
outputs are needed in circuit to maintain
reversibility concept. Figure 2 shows an example
of reversible function f=

, the two
unused pins are the garbage outputs (Ankush &
Bhandari, 2016).
243
Special Conference Edition, November, 2019
Figure 2: Garbage output
CONSTANT INPUTS
This can be defined as the number of inputs
that are to be maintain constant at either 0 or 1
in order to synthesize the given logical function
(Thapiyal & Ranganathan, 2010).
QUANTUM COST
Quantum cost may be defined as the cost of the
circuit in terms of the cost of a primitive gate. It
is calculated by the number of primitive
reversible logic gates (1x1 or 2x2) required to
realize the circuit. The quantum cost of a circuit
is the minimum number of 2x2 unitary gates to
represent the circuit keeping the output
unchanged. The quantum cost of a 1x1 gate is 0
and that of any 2x2 gate is the same, which is
1(Smoline & David, 1996).
DELAY
The delay of a logic circuit is the maximum
number of gates in a path from any input line to
any output line. The definition is based on two
assumptions: (i) Each gate performs
computation in one unit time and (ii) all inputs
to the circuit are available before the
computation begins. (Mohammadi & Eshghi,
2009).
HARDWARE COMPLEXITY
Hardware Complexity refers to the total number
of logic operation in a circuit. Means the total
number of AND, OR and EXOR operation in a
circuit (Akbar
et al
., 2011).
REVERSIBLE LOGIC GATES
There are many number of reversible logic gates
that exist in present literature. Some of the
reversible gates are presented by (Ankush &
Bhandari, 2016). In this review we try to show
other reversible gates which are not presented
by (Ankush & Bhandari, 2016) and may be
useful to researchers. The reversible gates are
given below;
SG Gate
SG gate is also known as Sayem gate (Sayem&
Ueda, 2010) is a 4x4 reversible gate. The input
and output vector of this gate are, Iv = (A, B, C,
D) and Ov
=
,
DCAABDACBAAC ',',
.
The block diagram of this gate is shown in
Figure 3.
Figure 3: Sayem gate
BME Gate
BME gate is a 4 × 4 reversible gate
(Mahfuzzreza
et al
., 2013). The BME gate can be
described as: IV = (A, B, C, D); OV = (A, ABC,
ADC, A’BCD), where IV and OV are input
and output vectors respectively. Quantum cost
of BME gate is five (Garipelly
et al
., 2013).
Figure 4 shows a 4 × 4 BME gate.
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Special Conference Edition, November, 2019
Figure 4: BME Gate
BSCL Gate
Binary Coded Decimal Subtraction Correction
logic gate is a 6x6 reversible gate. The purpose
of this gate is either to find correction logic for
BCD subtraction or to pass same data to the
output depending on the control signal (Rashmi
et al
., 2011). Here F is the control signal as
shown in the figure if F is equal to 0, A, B, C, D
and E as it is passed to the output P Q R S and
T. If F is equal to 1, then output Q R S and T
depends on the value of E. If E is equal to 0
then Q R S and T is the nines compliment of the
input binary number A B C and D. If E is equal
to 1 then binary number 0001 is added to ABCD
to get the valid corrected subtraction result.
Figure 5: BSCL Gate
PTR Gate
PTR gate is a 4X4 Reversible gate that can work as a reversible full adder
Figure 6: PTR Gate
PAREEK GATE
PAREEK gate is a 4 × 4 reversible gate (Pareek
et al
., 2014). The PAREEK gate can be described
as: IV = (A, B, C, D); OV = (A, A’BAD,
A’B
AD
C, B
D), where IV and OV are input
and output vectors respectively. Quantum cost
of PAREEK gate is seven which is illustrated in
(Pareek
et al
., 2014). Figure 7 shows a 4 × 4
PAREEK gate.
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Special Conference Edition, November, 2019
Figure 7: Pareek Gate
RCQCA GATE
Reversible Conservative quantum dot Cellular
Automata gate is a 4 × 4 reversible gate (Misra
et al
., 2018). Quantum cost of 6. This gate is
utilised for Sequential circuit synthesis of
reversible functions
Figure 8: RCQCA Gate
URQG GATE
Universal Reversible Quantum dot Cellular
Automata Gate is a 3x3 reversible gate (Bhoi
et
al
., 2017). Based on reversibility given the
outputs logic P, Q, R the inputs A, B, C can be
computed. The reversible URQG gate is a
universal gate and can implements 13 standard
functions. By combining two URQG gate N-bit
comparator can designed.
Figure 9: URQG Gate
HCG GATE
A 4x4 reversible gate, Hamming Code
Generating gate (James
et al
., 2007) is depicted
in Figure 10. HCG gate is one-through gate
which means that one of the input variables is
also output. Hamming error coding and
detection circuit can be implemented using this
gate
Figure 10: HCG Gate
246
Special Conference Edition, November, 2019
HAS GATE
Half Adder Subtraction gate is a 3x3 reversible
gate which is helpful for the design of reversible
BCD adder and carry skip BCD adder circuit. The
HAS gate has a quantum cost 5. It consist of
four XOR gates, two controlled-V and one
controlled-V
+
gate. This gate can implement the
operation of haif adder and full subtraction.
(Misra
et al
., 2015).
Figure 11: HAS Gate
FAS GATE
Full Adder Subtraction gate is a 4x4 reversible
gate. FAS gate can perform the operation of full
adder and full subtraction. The gate has a
quantum cost of 8. It consist of six XOR gates,
two controlled-V and one controlled-V
+
. (Misra
et al
., 2015).
Figure 12: FAS Gate
OD GATE
Over flow Detection gate is a 5x5 reversible
gate. The OD gate has a quantum cost of 10. It
consist of seven XOR gates, four controlled-V
and two controlled-V
+
gate. OD gate is used for
overflow detection. (Misra
et al
., 2015).
Figure 13: OD Gate
PPHCG GATE
Parity Preserving Hamming Code Generating
gate is a 4 x 4 Parity Preserving Reversible gate.
The outputs preserve the input parity (James
et
al
., 2007).This gate can be used for achieving
fault tolerance for the hamming error coding and
detection.
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Special Conference Edition, November, 2019
Figure 14: PPHCG Gate.
NG-PP
The NG-PP structure is utilised of 5-input and 5-
output. The input parity to output parity is
conserved. Hence this gate is a conservative
gate. Further, it holds the bijective mapping, it
also the reversible gate. The QC of NG-PP gate
is 5(Misra
et al
., 2017). It can singly perform the
logic operation of parity generator and checker.
Figure 15: NG-PP Gate
HG-PP GATE
A 5 x 5 conservative reversible logic gate named
HG-PP is shown in Figure16.. It depicts the same
count of 1’s in the output as well as input,
further maintain the bijective-mapping property
of the reversibility. Hence this gate is reversible
as well as conservative. The QC of HG-PP gate is
4(Misra
et al
., 2017). This gate is helpful for the
design of hamming code.
Figure 16: HG-PP Gate
COMPARATIVE STUDY
Various reversible gates and different circuits
associated with these gates are discussed here.
And also comparisons have been made among
the existing circuit in terms of various
parameters such as quantum cost, garbage
output, constant input, gate count and delay.
Comparison between existing reversible gates is
shown in Table 1.
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Special Conference Edition, November, 2019
Table 1: Comparison between Reversible Logic Gates
Reversible Gates Quantum cost Types
SG Gate(Sayem& Ueda, 2010) Unknown 4x4
BME Gate(Mahfuzzreza
et al
., 2013). 5 4x4
BSCL Gate (Rashmi
et al
., 2011) Unknown 6x6
PAREEK Gate (Pareek
et al
., 2014) 7 4x4
RCQCA Gate (Misra
et al
., 2018). 6 4x4
URQG Gate (Bhoi
et al
., 2017). Unknown 3x3
HCG Gate (James
et al
., 2007) Unknown 4x4
HAS Gate (Misra
et al
., 2015). 5 3x3
FAS Gate (Misra
et al
., 2015). 8 4x4
OD Gate (Misra
et al
., 2015). 10 5x5
PPHCG Gate (James
et al
., 2007) 6 4x4
NG-PP Gate (Misra
et al
., 2017) 5 5x5
HG-PP Gate (Misra
et al
., 2017) 4 5x5
CONCLUSION
In this paper, a survey of various works is
carried out in the field of reversible logic with
respect to reversible circuits which form the
basic building block of quantum computers. This
paper presents the reversible gates which are
not shown in (Ankush & Bhandari, 2016) and
which are gathered from the literature till now.
The paper can further be extended towards the
digital design development using reversible logic
circuits which are helpful in quantum computing,
low power CMOS, nanotechnology,
cryptography, optical computing, DNA
computing, digital signal processing (DSP),
quantum dot cellular automata, communication,
computer graphics, etc.
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