Types of logic gates

use operators. The most common Boolean operators are AND, OR and NOT. Each operator has a standard symbol that can be used when drawing logic gate circuits.

AND gate

An AND gate usually has two inputs. AND tells us that both Input A AND Input B have to be 1 (or ON) in order for the output to be 1. Otherwise the output is 0.

The Boolean expression can be written as Q = A AND B.

The truth table would look like this:

Input A	Input B	Input Q
0	0	0
0	1	0
1	0	0
1	1	1

Input A	0
Input B	0
Input Q	0

Input A	0
Input B	1
Input Q	0

Input A	1
Input B	0
Input Q	0

Input A	1
Input B	1
Input Q	1

Logic gate diagrams would look like this:

AND gate symbol: a semicircle with two inputs (A&B) and one output (Q)

OR gate

An OR gate has two inputs. OR tells us that EITHER Input A OR Input B has to be 1 (or ON) in order for the output to be 1. Otherwise the output is 0.

The Boolean expression can be written as Q = A OR B.

The truth table would look like this:

Input A	Input B	Input Q
0	0	0
0	1	1
1	0	1
1	1	1

Input A	0
Input B	0
Input Q	0

Input A	0
Input B	1
Input Q	1

Input A	1
Input B	0
Input Q	1

Input A	1
Input B	1
Input Q	1

Logic gate diagrams would look like this:

OR gate symbol: a semicircle with a concave side, with two inputs (A&B) and one output (Q)

NOT gate

A NOT gate has just one input. NOT tells us that Input A has to be 0 (or OFF) in order for the output to be 1. Otherwise the output is 0. A NOT gate is sometimes called an inverter.

The Boolean expression is written as Q = NOT A.

The truth table would look like this: