Logic gates are the basic building blocks of any digital system. A logic gate is a electronic circuit having one or more than one input port(s) and only one output port. The relationship between its input(s) and output is determined by a certain logic.

It’s necessary to memorise the function, symbol as well as algebraic expression of some common logic gates introduced in this chapter.

Basic Operations

AND Gate

The AND gate only outputs a positive signal when all of its inputs are getting positive signal.

Expression: $F=A\cdot B=AB$. Intuitively the AND logic can be treated as multiplication.

Symbol:

OR Gate

The OR gate only outputs a negative signal when all of its inputs are getting negative signal.

Expression: $F=A+B$. Intuitively the OR logic can be treated as addition.

Symbol:

NOT Gate

The NOT gate will produce a signal different from its input.

Expression: $F=\bar{A}=A'$.

Symbol:

Other Operations