1
Logic Gates
-Jerome George Paliakkara
12-H
Acknowledgement
s
Firstly, I would like to express my
utmost gratitude to my teacher Ms.
Garima Uppadhyay who gave me the
golden opportunity to do this
wonderful project on the topic Logic
Gates; this taught me a lot about the
subject.
Secondly, I would also like to thank
my parents and friends who helped
me a lot in finalizing this project.
INDEX
Aim
Introduction
Integrated Circuits
Apparatus
OR Gate
10
AND Gate
NOT Gate
Combination of Gates
13
Bibliography
5
6
7
9
11
12
15
Aim
To study basic logic gates (OR, AND, NOT)
To study combination of gates and universal
logic gates (NAND, NOR)
To study the boolean expressions and truth
tables of these logic gates
To design an appropriate logic gate
combination for a given truth table
To study integrated circuits
Introduction
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.
Logic gates are commonly represented through Boolean
operators.
Logic gates are primarily implemented
using diodes or transistors acting as electronic switches.
The basic logic gates are OR, AND and NOT.
Integrated Circuits
The concept of fabricating an entire
circuit (consisting of many passive
components like R and C and active
devices like diode and transistor) on a
small single block (or chip) of a
semiconductor has revolutionized the
electronics technology. Such a circuit is
known as Integrated Circuit (IC).
The most widely used technology is the
Monolithic Integrated Circuit. This, in
effect, means that the entire circuit is
formed on a single silicon crystal (or
chip).
Depending on nature of input signals, ICs
can be grouped in two categories: (a) linear
or analogue ICs and (b) digital ICs.
a) Linear or analogue ICs
The linear ICs process analogue signals
which change smoothly and continuously
over a range of values between a maximum
and a minimum.
The output varies linearly with the input.
One of the most useful linear ICs is the
operational amplifier.
(b)Digital ICs
The digital ICs process signals that have
only two values.
They contain circuits such as logic gates.
Depending upon the level of integration
(i.e., the number of circuit components or
logic gates), the ICs are termed as
Small Scale Integration, SSI (logic gates
< 10)
Medium Scale Integration, MSI (logic
gates < 100)
Large Scale Integration, LSI (logic gates
< 1000); and
Very Large Scale Integration, VLSI
(logic gates > 1000).
Apparatus
LEDs
Diodes(generic)
Resistors
Jumper cables
DC supply (eg. Battery)
10
OR Gate
The OR gate is a digital logic gate that
implements logical disjunction.
A HIGH output (1) results if one or both the inputs to
the gate are HIGH (1). If neither input is high, a LOW
output (0) results.
Boolean expression: Y=A+B
Symbolic
Representation(OR)
11
Analogue Circuit(OR)
Truth Table of a 2 input OR
gate
A
Output Y = A+B
AND Gate
The AND gate is a basic digital logic gate that
implements logical conjunction.
A HIGH output (1) results only if both the inputs to the
AND gate are HIGH (1). If neither or only one input to
the AND gate is HIGH, a LOW output results.
12
Boolean expression: Y=A.B
Symbolic
Representation(AND)
Analogue Circuit(AND)
Truth Table of a 2 input AND
gate
A
Output Y = A . B
NOT Gate
In digital logic, an inverter or NOT gate is a logic
gate which implements logical negation.
A HIGH input (1) results in a LOW output (0) and a LOW
input (0) results in a HIGH output (1).
Boolean Expression: Y=A
Symbolic Representation(NOT)
13
Analogue Circuit(NOT)
Truth Table of a NOT gate
A
Y=A
Combination of
Gates
Universal Gates: NAND and NOR gates
are called universal gates because by
using NAND and NOR gates alone, the
outputs of OR, AND and NOT gates can
be obtained.
NOR Gate
14
Truth Table of NOR Gate
A
0
0
1
1
B
0
1
0
1
X = A+B
0
1
1
1
Y = X= (A+B)
1
0
0
0
NAND Gate
Truth table of NAND
A
0
0
1
1
B
0
1
0
1
OR from NOR
X = A.B
0
0
0
1
Y= X = (A.B)
1
1
1
0
NOT from NOR
AND from NOR
15
OR from NAND
AND from NAND
NOT from NAND
Bibliography
http://www.instructables.com/id/Diode-LogicGates-AND-OR/
https://en.wikipedia.org/wiki/Logic_gate
https://en.wikipedia.org/wiki/AND_gate
https://en.wikipedia.org/wiki/OR_gate
16
https://en.wikipedia.org/wiki/Inverter_(logic_gate)
https://en.wikipedia.org/wiki/Integrated_circuit
