Logic gates are digital circuits that do processing of digital circuits. Gates have one or more inputs but only one output. There are three basic logic gates and they are named as OR gate, AND gate & NOT gate. These three gates can be combined in various ways to perform more complex arithmetic functions based on processed input digital signals.
There are two types of gates named as sequential gates and combinational gates. One type of logic gates called sequential gates, which have memory function, can process sequence of input digital values and outputs are based on sequences of applied inputs. Example of sequential gates are Flip-flops, Counters & Registers. Another types of logic gates called combinational gates, which do not have memory function, can process only instantaneous digital inputs and outputs are based on inputs applied at the moment of time. Examples of combinational gates are OR gate, AND gate, NOT gate, XOR gate, NAND gate, etc.
Different types of logic gates which will be discussed here are ;
- OR gate,
- AND gate,
- NOT gate,
- NOR gate,
- NAND gate,
- EXCLUSIVE OR gate, &
- EXCLUSIVE NOR gate.
OR gate
This gate can have two or more than two inputs but only one output. OR gate is named so because output signal will be high if any of the input signals are high. Truth table and symbol of OR gate with two inputs are given below ;
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| OR gate & Its Truth Table |
Output of OR gate is "X = A + B".
AND gate
This gate can have two or more than two inputs but only one output. AND gate shows output only when all the inputs are applied at same time. Truth table and symbol of AND gate with two inputs are given below ;
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| AND gate & its Truth Table |
Output of AND gate is "X = A . B".
NOT gate
This gate has only one input and one output. NOT gate always gives output opposite to that of input signal i.e., if input signal is 0 then output will be one and vice versa. Truth table and symbol of NOT gate are given below ;
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| NOT gate & Its Truth Table |
Output of NOT gate is "X =
Ā".
NOR gate
This gate can have two or more than two inputs but only one output. NOR gate is a combination of OR gate and NOT gate. NOT gate is connected to the output of OR gate. So the output of NOR gate is always opposite to that of OR gate. Truth table and symbol of NOR gate with two inputs are given below ;
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| NOR gate & Its Truth Table |
NAND gate
This gate can have two or more than two inputs but only one output. NAND gate is a combination of AND gate and NOT gate. NOT gate is connected to the output of AND gate like NOR gate. So the output of NAND gate is always opposite to that of AND gate. Truth table and symbol of NAND gate with two inputs are given below ;
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| NAND gate & Its Truth Table |
EXCLUSIVE OR (XOR) gate ;
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| Ex-OR gate & Its Truth Table |
EXCLUSIVE NOR gate
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| Exclusive NOR gate & Its Truth Table |
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