Logic gates are the basic building blocks in digital electronics.
- These can have one or more inputs and produces only one output.
- Logic gate's input and output are 1 bit i.e., 0(LOW) or 1(HIGH).
- It performs logic operation according to its functionality and the logic associated with it.
- Such logic gates are NOT gate, OR gate, AND gate, NOR gate, NAND gate, XOR gate, XNOR gate.
NOT gate:
- NOT gate is also called as Inverter.
- This gate takes only one input and produces one output which is complement of the input.
- NOT gate is basically used to invert the input, hence it is called as Inverter.
- Logic expression for NOT gate is,
- \[Y=\bar{A}\]
- Here A is the input and Y is the output which is complement of A.
- Logic Symbol and Truth table for NOT gate is as follows,
- When A=0, output Y becomes complement of 0 i.e., Y=1.
- Similarly When A=1, Y becomes Y=0.
OR gate:
- The OR gate can takes two or more inputs and produces only one output.
- The OR gate output is 1(HIGH) when either of the inputs are 1(HIGH).
- If the first input is 1(HIGH), then it won't checks the other inputs and directly produces the output 1(HIGH).
- Logic expression for 2 input OR gate is,
- \[Y=A+B\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table of 2 input OR gate is as follows,
- Here, When either of A and B is 1(HIGH), the output Y becomes 1(HIGH).
NOR gate:
- NOR gate is the complement of OR gate i.e.,
- \[NOR=NOT(OR)\]
- NOR gate is constructed using NOT gate and OR gate.
- It can takes two or more inputs and produces only one output.
- The NOR gate output is 0(LOW) when either of the inputs is 1(HIGH).
- If the first input is 1(HIGH), then it won't checks the other inputs and directly produces the output 0(LOW).
- NOR gate is also known as Universal gate because it can be used as other basic gates such as NOT, OR, AND etc.
- Logic expression for 2 input NOR gate is,
- \[Y=\overline{A+B}\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table for 2 input NOR gate is as follows,
- Here, when either of A and B is 1(HIGH), the output Y becomes 0(LOW).
AND gate:
- The AND gate can takes two or more inputs and produces only one output.
- The AND gate output is 1(HIGH) when all the inputs are 1(HIGH).
- If the first input is 0(LOW), then it won't checks the other inputs and directly produces the output 0(LOW).
- Logic expression for 2 input AND gate is,
- \[Y=A.B\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table for 2 input AND gate is as follows,
- Here, when either of A and B is 0(LOW), the output Y becomes 0(LOW).
NAND gate:
- NAND gate is the complement of AND gate i.e.,
- \[NAND=NOT(AND)\]
- NAND gate is constructed using NOT gate and AND gate.
- It can takes two or more inputs and produces only one output.
- The NAND gate output is 0(LOW) when all the inputs are 1(HIGH).
- If the first input is 0(LOW), then it won't checks the other inputs and directly produces the output 1(HIGH).
- NAND gate is also known as Universal gate because it can be used as other basic gates such as NOT, OR, AND etc.
- Logic expression for 2 input NAND gate is,
- \[Y=\overline{A.B}\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table for 2 input NAND gate is as follows,
- Here, when either of A and B is 0(LOW), the output Y becomes 1(HIGH).
XOR gate:
- Here XOR stands for Exclusive-OR.
- The XOR gate can takes two or more inputs and produces only one output.
- The XOR gate output is 1(HIGH) when odd number of 1's are taken as inputs.
- Here, all the inputs will be checked no matter if first input is 0 or 1.
- Logic expression for 2 input XOR gate is,
- \[Y=A⊕B\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table for 2 input XOR gate is as follows,
- Here, when only one of the A and B is 1(HIGH), the output Y becomes 1(HIGH).
XNOR gate:
- Here XNOR stands for Exclusive-NOR.
- XNOR gate is the complement of XOR gate i.e.,
- \[XNOR=NOT(XOR)\]
- XNOR gate is constructed using NOT gate and XOR gate.
- The XNOR gate can takes two or more inputs and produces only one output.
- The XNOR gate output is 0(LOW) when odd number of 1's are taken as inputs.
- Here, all the inputs will be checked no matter first input is 0 or 1.
- Logic expression for 2 input XNOR gate is,
- \[Y=\overline{A⊕B}\]
- Here A and B are the inputs and Y is the output.
- Logic symbol and truth table for 2 input XNOR gate is as follows,
- Here, when only one of the A and B is 1(HIGH), the output Y becomes 0(LOW).
