The Logic NOT Function
The Logic NOT Function is simply a single input inverter that changes the input
of a logic level "1" to an output of logic level "0" and vice versa. The logic NOT function is so called because its
output state is NOT the same as its input state. It is generally denoted by a bar or overline
( ¯ ) over its input symbol which denotes the inversion operation. As
NOT gates perform the logic INVERT or COMPLEMENTATION function they are more
commonly known as Inverters because they invert the signal. In logic circuits this negation
can be represented by a normally closed switch.
Switch Representation of the NOT Function
If A means that the switch is closed, then NOT A or
simply A says that the switch is NOT closed or in other words, it is open. The logic NOT
function has a single input and a single output as shown.
NOT Function Truth Table
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The inversion indicator for a logic NOT function is a "bubble", ( O )
symbol on the output (or input) of the logic elements symbol. In Boolean algebra the Logic NOT Function follows the
Complementation Law producing inversion.
NOT gates or "Inverters" as they are more commonly called, can be connected
with standard AND and OR gates to produce NAND
and NOR gates respectively. Inverters can also be used to produce "Complementary" signals in
more complex decoder/logic circuits for example, the complement of logic A is
A and two Inverters connected together in series will give a double inversion which produces at
its output the original value of A.
When designing logic circuits and you need only one or two inverters, but do not have the space or
the money for a dedicated Inverter chip such as the 74LS04, you can easily make inverter functions using any spare
NAND or NOR gates by simply connecting their inputs together
as shown below.
NOT Function Equivalents
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