Logic gate – A digital circuit which either allows a signal to pass through or stops it, is called gate. Such gate allows the signal to pass through only when some logical conditions are satisfied. Hence they are called logic gate.
There are three types of basic logic gates.
1) OR gate It is a device having two or more inputs and one output. In Boolean algebra, the term OR is represented by (+) and Boolean expression for OR gate is A + B = Y, indicates Y equals A OR B.
2) AND gate It is a device having two or more inputs and one output. In Boolean algebra, the term AND is represented by dot (.) and the Boolean expression A.B= Y, indicates Y equal A AND B.
3) NOT gate It is device which has one input and one output. In Boolean algebra the term NOT is represented by bar symbol (-) and the Boolean expression A = Y, indicates that Y equals NOT A.
A continuous time varying current or voltage signal is called analogue signal.
An electronic circuit which gives out any type of analogue signal is called analogue circuit.
A signal which has to travel of voltage (represented by 0 and 1) is called digital signal.
It is a table that shows all possible input combinations for a logic gate. It is also called a table of combination.