Logic Gates

Logic Gates

A logic gate is simply an electronic circuit which takes one or more electronic signals as input to give an output signal.  

Basic Gates

NOT Gate

• It is an inverter circuit which has only one input signal and one output signal.
• It gives the complement of the input as the output.
• Symbol:

AND Gate

• It can have two or more input signals, but only one output signal.
• If any of the input is 0, output is 0.
• If all the inputs are 1, then the output is 1.
• Symbol:

OR Gate

• It can have two or more input signals, but only one output signal.
• If any of the input is 1, output is 1.
• If all the inputs are 0, then the output is 0.
• Symbol:

Universal Gates

NOR Gate

• It can have two or more input signals, but only one output signal.
• It is an inverted OR gate.
• If any of the input is 1, output is 0.
• If all the inputs are 0, then the output is 1.
• Symbol:

NAND Gate

• It can have two or more input signals, but only one output signal.
• It is an inverted AND gate.
• If any of the input is 0, output is 1.
• If all the inputs are 1, then the output is 0.
• Symbol:

Special Gates

XOR Gate

• The XOR( Exclusive OR ) gate can have two or more input signals, but only one output signal.
• If the input has an odd number of 1’s, output is 1 otherwise the output is 0.
• Its algebraic symbol is ⊕
• Symbol:

Q = A ⊕ B = (A’.B + A.B’)

XNOR Gate

• The XOR( Exclusive NOR ) gate can have two or more input signals, but only one output signal.
• If the input has an even number of 1’s, output is 1 otherwise the output is 0.
• Its algebraic symbol is ⊙
• Symbol:

Y = A ⊙ B = (AB)’ + AB