A.
INTRODUCTION
A digital circuit is a
circuit where the signal must be one of two discrete levels. Each level is
interpreted as one of two different states (for example, on/off, 0/1,
true/false). Digital circuits use transistors to create logic gates in order to
perform Boolean logic. This logic is the foundation of digital electronics and
computer processing. Digital circuits are less susceptible to noise or degradation
in quality than analog circuits. It is also easier to perform error detection
and correction with digital signals. To automate the process of designing
digital circuits, engineers use electronic design automation (EDA) tools, a
type of software that optimizes the logic in a digital circuit. Jaeger, (1997: 226-233)
stated that In electronics, a logic gate is an idealized or physical device
implementing a Boolean function; that is, it performs a logical operation on
one or more logical inputs, and produces a single logical output. Depending on
the context, the term may refer to an ideal logic gate, one that has for
instance zero rise time and unlimited fan-out, or it may refer to a non-ideal
physical device. Signal must be a Boolean to establish a digital circuit.
Digital signal is stronger than the analog signal, that is more easily detected
and corrected when it occur an error
signal.
A digital circuit have
many advantages, one of the advantages of the use of a digital
circuit is a system used has an easy interface
device to be
controlled by a computer and software. That's why the information storage is done much more
easily in a digital system
compared to analog. However, the advantage is
reversed, this circuit also
has its drawbacks include the energy used each use
of this circuit is
quite a lot, in addition to
the components used is more expensive and
is very easy once
fragile. With digital systems, storage of information
will be easier to do, but it is wasteful energy, the components are expensive
and easy fragile.
The purpose of this article is to understand
digital circuit, recognize the basics of logic gates such as AND, OR, NOT, NOR,
XNOR, NAND and XOR gates, and Boolean algebra.
B. Logic Gates
In electronics, a logic gate is an idealized or physical device
implementing a Boolean function; that is, it performs a logical operation on
one or more logical inputs, and produces a single logical output. Depending on
the context, the term may refer to an ideal logic gate, one that has for instance
zero rise time and unlimited fan-out, or it may refer to a non-ideal physical
device. And, the writer will explain: NOT gate;
AND gate and NAND gate; OR gate
and NOR gate; XOR gate and XNOR gate;
a.
NOT
gate
NOT
gate or can also
be called by inverting (inverter) has
the function of reverse logic
input voltage at
its output. An inverter
(inverting) is a gate
with one input signal
and one output
signal where the output
state is always opposite to the
input state. Flips
in this case is to change into its opposite. Because the logic voltages
are only two conditions, namely high and low, or
"1" and "0", then the reverse logic voltage
means change "1" to "0" or otherwise change the zero
to one. (Tokheim, 1995). NOT
gate is also called an inverter, the gate has
only one input and one output. Boolean
algebra of logic equations
for NOT gate
output is Y
= A’. Become
a NOT gate output is always the
opposite of its input. If a given input
logic high, then the
output will be generated
logic low, and at low logic input is given then the
output will be generated
logic high.
Inverter or not gate, It takes one input signal.
In logic, there are usually two states, 0 and 1. The gate therefore sends 1
as output, if it receives 0 as input. Alternatively it received 1
as input, and sends 0 as output.
b.
AND
gate and NAND gate
AND
gate is a logic network with
multiple entry (input) and has only one way
out (output). AND gate has two or more than
two signal inputs
but only one
output signal. In
the AND gate to produce
a high output signal then all input signals must be of high
value. While the NAND gate
is a NOT-AND,
or an AND
function is reversed. In other words that the NAND gate will produce a low output
signal if all input signals of high
value. (Malvino, 1983). AND gate is
a logic gate consisting of two
or more inputs
and only one output.
AND gate output will
be high only if all inputs are
high, and if one
or more input
logic low then, output
will be low. Boolean algebra equations logic
gate is Y =
A.B In Boolean
algebra operations AND gate marked "time" or a "point". (Tokheim, 1995). NAND
gate is a combination of AND and NOT gates. NAND gate output
is always the opposite of the AND gate output for
the same input. So the output will be a
logic high if one or more of its inputs are
logic low, and the output to logic low
only when all its
inputs are logic high. Boolean algebra of
logic equations for the output of NAND gate
is Y =
A’.B’.
The
AND logic gate
output to logic one
only if both inputs
are logic one. From
this it can be concluded that the
gate has a logic
function of multiplying
the two input.
c.
OR
gate and NOR gate
OR gate is one
of the basic logic gates that has 2 input channels ( input ) or more and an
output channel (output). Any number of input channels owned by an OR gate, it
still has the same working principle whereby the output conditions will
berlogic 1 if one or all input channels berlogic 1. Additionally berlogic
output 0. Similarly, NAND Gate, NOR gate
is a combination of an OR gate with a NOT gate in which the output of the OR
gate is connected to the line input of the NOT gate . Because the output of the
OR gate in " NOT " right the working principle of a NOR gate is the
inverse of the OR gate. The output is the complement or opposite of the OR
gate, which gives the state of logic 0 at the output level if one or more of
its inputs are logic 1. (Malvino, 1983). OR gate is the basic logic
gates that have two or more inputs and only one output.
OR gate output to
logic high when one or more input there is a logic
high, and the
output to logic low only when all inputs are
logic low. Boolean algebra of logic equations
for the OR gate output
is Y = A + B. In Boolean algebra operations
OR gate labeled "plus".
(Tokheim, 1995). NOR
gate is a combination of OR and NOT gates.
NOR gate output is
always the opposite of the OR
gate output for the same input. So the
output to logic low if one or more of its
inputs are logic high, and the output will be
a logic high only
when all inputs are logic low. Boolean
algebra of logic equations
for a NOR gate output
is Y = A+ B.
So
it can be said that
the OR gate has only a low output signal
if all input
signals low value. while the NOR gate
is the development of the OR gate.
The development of a NOT gate installation
at the output of the OR gate.
X-OR
gate will produce
a low output signal
if all input
signals low value or high value the input
of all other words that X-OR will produce low output
signal if the
input signal is all worth the same. And
X-NOR Gate
will produce a
high output signal if all input signals
of equal value (opposite of the X-OR gate). (Tokheim, 1995). Symbol of Exclusive
OR gate (XOR)
with two input variables
and one output, the
output at logic 1 if one input on the state of logic 0
or logic 1,
while the output at logic state 0 if both inputs same logic. Boolean
algebra of logic equations
for XOR gate
output is Y = A
B = AB’ + A’B (Tokheim, 1995). The
symbol of the arch Exclusive NOR (XNOR) with
two input variables
and one of
the output, the output at logic 1 when the input provided on the same logic as A
= 1 and B
= 1 or input A = 0 and B = 0. Whereas output
at logic 0 if
the input provided to the contrary.
Boolean algebra of
logic equations for XOR gate output is Y =
AB = A’B’+ A’B.
B = AB’ + A’B (Tokheim, 1995). The
symbol of the arch Exclusive NOR (XNOR) with
two input variables
and one of
the output, the output at logic 1 when the input provided on the same logic as A
= 1 and B
= 1 or input A = 0 and B = 0. Whereas output
at logic 0 if
the input provided to the contrary.
Boolean algebra of
logic equations for XOR gate output is Y =
AB = A’B’+ A’B.
So
it can be said that
the XOR gate has different input
signals, the output signal high value.
while the XNOR gate
is the development of the XOR gate.
The development of a NOT gate installation
at the output of the XOR gate.
C. Boolean Algebra
A Boolean algebra is a six-tuple
consisting of a set A, equipped with two binary operations ∧ (called "meet" or "and"), ∨ (called "join" or "or"), a unary operation ¬ (called
"complement" or "not") and two elements 0 and 1 (called
"bottom" and "top", or "least" and
"greatest" element, also denoted by the symbols ⊥ and ⊤, respectively), such that for all elements a, b and c of A, the
following axioms hold:
A Boolean
algebra with only one element is called a trivial Boolean algebra or a
degenerate Boolean algebra. (Some authors require 0 and 1 to be distinct
elements in order to exclude this case.) The simplest non-trivial Boolean
algebra, the two-element Boolean algebra, has only two elements, 0 and 1, and
is defined by the rules:
C.
Conclusion
Some benefit of logic gates are can be used to make any kind of
digital logic circuit like computer
circuit, television circuit, and robotic circuit. The aim gate is efficiency
component of circuit electric. So, if we not use logic gate we need big component
than we use logic gate. If we want use logic gate we must understand about
logic algebra.
D.
References
Firmansyah, sigit, Elektronika digital dan mikroprosesor, Penerbit
ANDI, Yogyakarta, 2005.
Tokheim, Roger L, Elektronika Digital edisi kedua, Penerbit
Erlangga, Jakarta, 1990.
Ilmu
computer(2007). http://ilmukomputer.org/wp-content/uploads/2007/10/anjars-gerbang-logika.pdf [18 Mei 2014]
