Digital logic, an Inverter or NOT gate Digital logic, an Inverter or NOT gate | Page 13

Logic NOT Gates are available using digital circuits to produce the desired
logical function. The standard NOT gate is given a symbol whose shape is
of a triangle pointing to the right with a circle at its end. This circle is known
as an “inversion bubble” and is used in NOT, NAND and NOR symbols at
their output to represent the logical operation of the NOT function. This
bubble denotes a signal inversion (complementation) of the signal and can
be present on either or both the output and/or the input terminals.