Electronics Logic Gates: NOT Gates
The simplest of all logic gates in electronics is the NOT gate, which is also called an inverter. A NOT gate has just one input, and its output is the opposite of the input. If the input is LOW, the output is HIGH. If the input is HIGH, the output is LOW.
A truth table is simply a table that lists every possible combination of input values and shows the resulting output for each combination. For an inverter, the truth table is simple. Because only one input exists, only two possibilities exist: The input is LOW, or it is HIGH.
Note that in truth tables, it’s common to use 0s and 1s to represent logic values rather than the terms HIGH and LOW.
Symbols such as the symbol for a NOT gate are often used in schematic diagrams for circuits that use gates. The NOT symbol is simply a triangle with the input at one end and the output at the other. The small circle on the output is called a negation bubble, which indicates that the output is inverted.