LOGIC CIRCUIT I (SS2 FIRST TERM)
LOGIC CIRCUIT
A logic gate is an elementary building block of a digital circuit. It processes one or more input signal in a logical fashion. Depending on the input value or voltage, the logic gate will either output a value of ‘1’ for ON or a value of ‘0’ for OFF.
Logic gates are digital
circuits and they utilize a binary numbering system known as binary code.
Binary code is the same language used by computer which uses only 1 or 0 as
numbers.
Gates have two or more
inputs, except a NOT gate which has only one input. All gates have only one
output. Usually the letters A, B, C and so on are used to label inputs and
output.
There are 3 common types
of Logic Circuits from which all other types are formed. They are
1. AND GATES
2.
OR GATE
3.
NOT GATE
An ‘OR’ gate is like two
or more switches in series. Only one switch need to be closed (ON or value of
1) in order to make the lamp (output C) turn ON with a value of 1.
|
INPUT |
INPUT |
OUTPUT |
|
A |
B |
C |
|
0 |
0 |
0 |
|
0 |
1 |
1 |
|
1 |
0 |
1 |
|
1 |
1 |
1 |
‘AND’ GATES: The AND
gate is a circuit that has two or more inputs and operates in such a
way
that:
Its output is 1 if and only if the two inputs are 1
Its output is 0 if any of the inputs is either 0 or 1 or
both are 0
TRUTH TABLE FOR “AND” GATE
|
INPUT |
INPUT |
OUTPUT |
|
A |
B |
C |
|
0 |
0 |
0 |
|
0 |
1 |
0 |
|
1 |
0 |
0 |
|
1 |
1 |
1 |
NOT GATE
NOT gate have only one
input and output. It reverses the input signal value. If the input is 1, the
output will be 0 and if the input is 0 then the output will be 1.
LOGIC SYMBOL FOR “NOT” GATE
TRUTH TABLE FOR “NOT”
GATE
|
INPUT |
OUTPUT |
|
A |
C |
|
0 |
1 |
|
1 |
0 |
“NOT” gate can be referred as inverter, whatever the input signal is the output is always the opposite.
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