A NOT gate is the physical realization of complementation operation. It is an electronic circuit that generates the reverse of the input signal as output signal as output signal. It is also known as an inverter because it inverts the input.
Below Figure 5.6 shows the truth table and block diagram symbol for a NOT gate.
Recall that Complementation operation is unary operation defined on a single variable. Hence, a NOT Gate always has a single input. Below figure also shows that two NOT gates connected in Series given an output equal to the input. This is the gating counterpart of the law of the Double complementation. A = A.
