Logic Gate:-"Logic gate is an electronic circuit which operates on one or more input signals to perform a particular logical function and produce the perfect output"
Logic gates process signals which represent true or false. Normally the positive supply voltage +Vs represent true and 0V represents false.
Some important logic gates are: - AND gate, OR gate, NOT gate, NAND gate, NOR gate, EX-OR gate, EX-NOR gate..
Based on properties Logic gates are further classified into two types:
1. Basic Logic gates.
2. Universal Logic gates.
1. Basic Gates:-the basic gates are:-
i) AND Gate.
ii) NOT Gate.
iii) OR Gate.
iv) Exclusive OR Gate. &
v) Exclusive NOR Gate.
AND Gate:-If anyone of the two inputs is false then the output 'y'i s also false (equal to zero)
if both inputs are true then the output 'y' is also true (1)..
There fore by the above condition the logic expression for AND gate is given by
"Y=A.B"
OR Gate:-In OR gate the output Y is true when any one of the input is true or both the inputs are true.
There fore the expression for OR gate is given by
"Y=A+B"
NOT gate (inverter):-The output Y is true when the input A is NOT true, the output is the inverse of the input: Y = inversion of A.A NOT gate have one input. A NOT gate is also called an inverter.
EX-OR (Exclusive-OR) gate:- The output Y is true if either input A is true OR input B is true, but not when both of them are true: Y= (A . B|) OR (A|.B) i.e. = A Ex-OR B.
This is like an OR gate but excluding both inputs being true.
The output is true if inputs A and B are DIFFERENT.
EX-OR gates can only have 2 inputs.
EX-NOR (Exclusive-NOR) gate:- This is an EX-OR gate with the output inverted, as shown by the 'o' on the output.
The output Y is true if inputs A and B are the SAME (either both are true or both false):
Y = (A .B) + (NOT A. NOT B) EX-NOR gate has 2 inputs.
2.Universal Logic gates: - These are the gates by which all other basic gates can be realized...
The two universal gates are 1.NAND Gate. 2. NOR Gate.
NAND gate (NAND = NOT+AND):- This is an AND gate with the output inverted, as shown by the 'o' on the output.
The output is true if input A & input B are NOT both true: Y= complement (A .B)
A NAND gate can have two or more inputs, its output is true if NOT all inputs are true..
NOR gate (NOR = NOT +OR):-This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Y is true if inputs A OR B are true: Y = Complement (A + B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.
The output Y is true if inputs A OR B are true: Y = Complement (A + B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.
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