AIM
TO STUDY ABOUT LOGIC GATES
INTRODUCTION
Logic gates are related with Boolean algebra, which differ from both ordinary and binary
algebra. In this the variable permitted to have only values true offalse usually written as 1 or 0. The
operation of logic gates is normally done by logic digital integrated circuits (IC’s). In another word
digital IC’s are logic circuits. The building block of digital computers and calculators. The basic digital
circuits are rather simple and will serve as an introduction to digital IC’s
CERTIFICATE
This is certified that SAVITA MENON is a student of this institution and the work on her project has
been completed under my supervision.
(RAJ KUMAR)
CONTENTS
1.
AIM
2.
ACKNOWLEDGEMENT
3.
CERTIFICATE
4.
INTRODUCTION
5.
LOGIC CIRCUIT
6.
SYMBOLS FOR VARIOUS GATES
7.
LOGIC GATES
(A)
OR GATE
(B)
NOT GATE
(C)
AND GATE
8.
CONCLUSION
CONCLUSION
The Logic Gates (OR Gate, AND Gate and NOT Gate) are the basic units
Of Digital Electronic Circuit.
ACKNOWLEDGEMENT
In presenting this investigatory project, I wish to express my thanks to my Physics Teacher Mr,
SANJEEV BANSAL who has supplied all the required information incorporated in the project.
I have put in my best efforst to make the project most authentic. Finally, I shall be failing in my
duty if I do not pay thanks to my project guide whose constant guidance and encouragement has helped
me a lot in the preparation of this project and also to Mr. …………………. The lab Asstt.
By :
SAVITA MENON
Class : XII – B
Roll No : Session: 2001-2002
NOT GATE
The not gate is a device which have one input and one output. Basically NOT Gate is a inverter.
If we give the input low, will be high And if the input given is high then output is low. NOT gate
can be realized making use of transistor.
Thus the operation of NOT gate is based on the following rule :The output of a NOT gate is 1 if input is 0 and vice-versa.
TABLE :TRUTH TABLE OF NOT GATE
INPUT
A
0
1
OUTPUT
Y
1
0
Boolean Symbol = Y = A
C
1
SV
0
R
Y
SV
SV
AND GATE
Look at two input of AND gate at figure (A). When both switches are in the ground position both
diode are conducting and the output is low. If SI is switched to +5 v and S-II is left in ground
position then the output is still low because D-2 still conducts continuously. If S-I is in ground
position and S-II is at +5v both diodes are pulled up to the supplied voltage because there is no
current through at the load resistance.
It is an all or nothing gate. I.e, All inputs must be high to get high output. Transistors, Mosfets
and other devices can also be used in the construction of AND Gates.
Thus operation of an AND Gate is based on the rule :The output of an and gate assumes 1, only if all the inputs assume 1.
TABLE 2 :TRUTH TABLE OF AND GATES
INPUT
A
0
0
1
1
OUTPUT
B
0
1
0
1
Y
0
0
0
1
Boolean Symbol = y = A.B.
OR GATE
Figure (A) shows two inputs OR gate when both switches are in the ground position. The
diodes are non-conducting and the output is low. If either switches is set to +5v, then its diode
conducts and the output is approximately 4.3 v. Infact both switches can be at 0v and output will
be low.
Thus operation of OR gate is based on the following rules :1.
The output of an OR gate assumes 1, If one or more inputs assumes 1.
2.
The output of an OR gate assumes 0, If both inputs assumes 0.
The action of logic circuits is usually summarized in the form of truth tables, which shows the
output for the combinations of the input signals.
INPUT
A
0
0
1
1
OUTPUT
B
0
1
0
1
Y
0
1
1
1
Boolean Symbol = Y = A+B
LOGIC GATE
Almost all-digital circuits are designed for two straight operations. This means using only two
non-adjacent points on the load line typically satrurated and cut off. As a result the output voltage has
only two states, either low or high.
Gate is a digital circuit with one or more input voltages but only one output voltage. The most
basic gates are called the NOT gate the OR gate & the AND gate. By connecting these gates in different
ways we can build circuits that performs arithmetic and other functions associated with the human brain.
Because they stimulate mental processes, gates are often called logic circuits.
LOGIC CIRCUITS
We know the unidirectional characteristics of a solid state semi conductor diode. When forward
biased this diode acts like a closed switch, i.e. it permits current to flow in a complete circuit, when
reverse biased it acts like an open switch. In digital electronics a gate is a logic circuits with one output
and one or more inputs. An output signal occurs for certain combinations of input signals.
Modern computers do may jobs from scientific computation to business accounting. Computers
are also used in the automatic control of manufacturing processors. These devices perform highly
complex jobs. They consist of arrangement of simple logic circuits.
To solve problems, a computer has to make decisions as it programme through the steps in the
problem solving. Computer circuits that make decisions and comparisons are called logic circuits.