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1. Logic Gates
Logic gates are those digital circuit which works according to some
logical relationship between input and output voltage.
Logic gates works only on 0(LOW) and 1(HIGH).
Remember:
–True= ON = 1
–False = OFF=0
Logic gates turn ON when a certain condition is true, and OFF when
the condition is false

2. What are logic gates?
Output depends on the logic gate and the input
Input is one of two states – high or low
Output is one of two states – high or low
 There are seven types of logic gates
 The number of output combination will be 2N .(where N is no. of
input)
 Truth tablet is means for describing how logic circuit’s output depends
upon logic levels at input.
Boolean expression is representationof output of logic gate , through
which we can make truth table.

3. Classification of Gates
Logic gates one classified as:-
1. basic gates :- NOT, AND, OR.
2. universal gates :- NAND , NOR .
3. Special purpose gate :- X-OR , X-NOR.

4. NOT is the most simple logic gate.
NOT gate has one input terminal and one output terminal.
Output is complement or inversion of its applied input.
 Another name for a NOT gate is inverter, because it inverts (makes
opposite) the input
NOT Gate

5. AND has two input terminal and one output terminal.
AND gate perform multiplication function.
When both inputs are high, output is high otherwise output is low.
AND Gate

6. OR gate has two input terminal and one output terminal.
OR gate performs addition function.
Output is high when any one or more input is high otherwise output is
low.
OR Gate

7.  NAND gate has two and more input terminal and one output terminal.
 NAND gate is combination of NOT and AND gate.
 Output of NAND gate is complement of Product of it’s input.
 If any one input is low, output is high. If all inputs is high, output is low
NAND Gate

8.  NOR gate has two and more input terminal and one output terminal.
 NOR gate combination of Not gate and OR gate.
 Output of NOR gate is complement of sum of it’s input.
 If both inputs are low, output is high. If one of the input is high, output
will be low.
NOR Gate