The simplest logic circuit is the Not gate. It performs the function called inversion, or complementation, and is commonly referred to as an inverter.

The purpose of the inverter is to make the output state the opposite of the input state. The two states associated with logic circuits are 1 and 0. A 1 state can also be referred to as a high, to indicate that the voltage is higher than in the 0 state. A 0 state can also be referred to as a low, to indicate that the voltage is lower than in the 1 state. If a 1, or high, is applied to the input of an inverter, a 0, or low appears on its output. If a 0, or low, is applied to the input, a 1, or high, appears on its output.