24-08-2013, 03:53 PM
VHDL Implementation of Reversible Logic Gates
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Abstract
Everyday new technology which is faster, smaller and
more complex than its predecessor is being developed.
The increase in clock frequency to achieve greater
speed and increase in number of transistors packed
onto a chip to achieve complexity of a conventional
system results in increased power consumption. Almost
all the millions of gates used to perform logical
operations in a conventional computer are irreversible.
Reversible logic is gaining interest in the recent past
due to its less heat dissipating characteristics. It has
been proved that any Boolean function can be
implemented using reversible gates. That is, every time
a logical operation is performed some information
about the input is erased or lost and is dissipated as heat.
Reversible logic has shown potential to have extensive
applications in future emerging technologies such as
quantum computing, optical computing, quantum dot
cellular automata as well as ultra low power VLSI
circuits, DNA computing to produce zero power
dissipation under ideal conditions. Reversible logic is
very essential for the construction of low power, low
loss computational structures which are very essential
for the construction of arithmetic circuits used in
quantum computation, nano technology and other low
power digital circuits. Recently, several researchers have
focused their efforts on the design and synthesis of
efficient reversible logic circuits. The important
reversible gates used for reversible logic synthesis are
Feynman Gate, New Gate and Fredkin gate.
Introduction:
Everyday new technology which is faster, smaller and
more complex than its predecessor is being developed.
The increase in clock frequency to achieve greater
speed and increase in number of transistors packed
onto a chip to achieve complexity of a conventional
system results in increased power consumption. Almost
all the millions of gates used to perform logical
operations in a conventional computer are irreversible.
That is, every time a logical operation is performed
some information about the input is erased or lost and is
dissipated as heat.
In digital design energy loss is considered as an
important performance parameter. Higher levels of
integration and new fabrication processes have
dramatically reduced the heat loss over the last
decades. The power dissipation in a circuit can be
reduced by the use of Reversible logic.
Reversible Logic Gates:
In this section, we describe all about reversible logic
and reversible logic gates. Though it is already briefly
described about garbage outputs, in this section we will
define it with more appropriate examples and figures.
Definition 2.1: Garbage is the number of outputs
added to make an n-input k-output Boolean function
((n, k) function) reversible. In other sense, a reversible
logic gate has an equal number of inputs and outputs
(k*k) and all the outputs are not expected. Some of the
outputs should be considered to make the circuit
reversible and those unwanted outputs are known as
garbage outputs. A heavy price is paid for every
garbage outputs.
Example 2.1: If we want to find the Exclusive-OR
between two variables in reversible computation, the
circuit will look like Fig. 2.1.
Advanced Reversible Logic
Gates:
In this section, we describe all about reversible logic
and advanced reversible logic gates. Though it is briefly
described about garbage outputs and these advanced
reversible logic gate can singly work as FULL ADDER,
FULL SUTRCTOR and more combinational circuits. In
this section we will define it with more appropriate
examples and figures.
CONCLUSION:
This paper presents VHDL CODE of all Reversible
Logic Gate, which provide us to design VHDL CODE
of any complex combinational circuit. Here we have
tried to make the VHDL code as much as possible. We
can simulate and synthesis it using Xilinx software and
also calculate the power consumption and compare it
with the irreversible Full Adder.