INTRODUCTION :
An AND gate is one of the three basic logic gates of digital
electronics. The AND gate is a two input and one output logic
gate. It combines the input A and B with the output Y following
the Boolean expression
Y = A.B
i.e Y equals A AND B
A high output results only if both inputs are high, otherwise
low results.
WORKING PRINCIPLE :
The working principle of a simple AND gate can be easily found
with the help of the electrical circuit :
Fig : Circuit Diagram of AND gate
Here a series combination of switches A and B are connected to
a battery and a bulb Y. The following conclusions can be easily
drawn from the working of the above electrical circuit :
• If both the switches A and B are open (i.e A=0, B=0), then
the bulb will not glow (i.e Y=0)
• If the switch A is closed and B is open (i.e A=1, B=0), then
the bulb will not glow (i.e Y=0)
• If the switch A is open and B is closed (i.e A=0, B=1), then
the lamp will not glow (i.e Y=0)
• If both the switches A and B are closed (i.e A=B=1), then
the bulb will glow (i.e Y=1)
Considering all the above cases, the following truth table for
AND gate can be deduced :-
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
REALISATION OF AND GATE USING
DIODES AND RESISTOR :
COMPONENTS REQUIRED:
1) Two PN junction diodes (IN4007)
2) Two resistors (470 Ω)
3) One LED
4) Connecting wires
5) Battery (6 or 9 volt)
CIRCUIT DIAGRAM :
CONSTRUCTION AND WORKING :
• Diodes D1 and D2 (IN4007) are taken and connected along
with resistors (470 Ω) and LED as shown in the circuit
diagram.
• A 9volt battery is connected to the circuit that provides
necessary voltage.
• When A=0, B=0, both D1 and D2 are forward biased and
conducts. The output Y will be the voltage drop across D1
or D2. Since diodes are ideal, no voltage drop occurs across
the diodes. Hence the output Y is 0. So, the LED doesnot
glow.
• A=1 and B=0, the diode D2 will conduct and D2 will
remain idle. Now, output Y is voltage across D2 and hence
it is 0. LED does not glow.
• A=0 and B=1, D1 will conduct and D2 will not conduct.
Output Y is voltage across D1, which is 0. Hence, LED will
not glow.
• A=1 , B=1, both D1 and D2 will not conduct , as they are
both reverse biased . The output Y is equal to battery
voltage, i.e equal to 1. Hence LED glows
USES :
AND gate can be used in circuits where something should only
activate if it is powered by multiple sources. For example, a
bunker may have a self-destruct mechanism, that will activate if
2 people press button simultaneously.
It can also be used to create a safety lock. An example would be
a room that can be remotely flooded with lava when a piston is
activated by pressing a button. To prevent accidental activation,
a lever and an AND gate could be implemented, requiring the
lever to be pulled in addition to the button being pressed. It can
also make a password lock where a few levers have to be pulled.
CONCLUSION :
A simple Diode and LED based AND gate is constructed. The
output is detected with the help of glow of an LED. Various
inputs were provided at the input and necessary output was
obtained depending upon the circuit (Y=A.B)
BIBLIOGRAPHY :
• http://en.wikipedia.org/wiki/Logic_gate
• http://hyperphysics.phyastr.
gsu.edu/hbase/electronic/and.html
• http://www.doctronics.co.uk/Subsystems/AND_gate.htm
• http://logic.ly/lessons/and-gate/
• http://www.physicshandbook.com/topic/topica/and%20gate
.htm
• http://www.wisconline.
com/objects/ViewObject.aspx?ID=DIG102
• www.iCBSE.com
