Introduction to Digital Electronics - Logic Gates

Introduction to Logic Gates

          Logic gate serve as a building block to digital logic circuit using combinational logic. Most logic data have two inputs and one output. At any given moment, every terminal is in one of the binary conditions; low(0) or high(1), represented by different voltage levels. In most logic gates, the low state is approximately zero volts, while the high state is approximately five volts positive. Some circuits may have only a few logic gates while others such as microprocessor may have millions of them.

Types Of Logic Gates

AND Gate:AND Gate is a logic gate whose output is 1 if all it inputs are 1, otherwise 0. The Expression for AND Gate is given as

C=A.B

OR Gate:OR Gate is a logic gate whose output is 1 if any of its input is 1, otherwise 0 i.e if all the input is 0 the output will be 0. The expression for OR Gate is given as

C=A+B

 



NOT Gate:NOT Gate is a logic gate whose output is an inverse of its input. i.e if input is 0 the output would be 1. However unlike others, NOT Gate has just 1 input. The expression for NOT Gate is given as

C=A'

 

NAND Gate:NAND Gate is an inverse of an AND Gate. Its output is 1 if all or one of its input is 0.The expression for NAND Gate is given as

C=A'.B'

 

NOR Gate:NOR Gate is also an inverse of an OR Gate.In other words NOR Gate is OR Gate been reversed. i.e the output is 0 if any of its input is 1. The expression is given as

C=A'+B' or C=(A+B)'

 

Exclusive OR or XOR Gate: XOR Gate is a logic gate whose output is 1 if one of the input is true but 0 if both is 1 or both is 0.The expression is given as

C=A'B+AB'

 

Exclusive NOR or XNOR Gate: XNOR Gate is a logic gate whose output is 1 if all input is 0 or 1.The expression is given as

C=AB+A'B'