Question

Which of the following is not a function of the NOT gate?
(A) stop a signal
(B) invert an input signal
(C) complement a signal
(D) Change the logic in a digital circuit

Answer 1

A NOT gate is one of the logic gates (or one can say a Boolean Operator) which can take only one input signal and gives one output signal. The NOT gate works by inverting the original signal. This means if the input signal is “1”, the NOT gate inverts it to give “0” as its output signal. This is also true when the input signal is “0”. We will use this basic definition of a NOT gate to answer our question.

Complete answer:
A NOT gate is a single input single output device. It is also known as an inverter gate because of its ability to invert the input signal. The Boolean expression for NOT gate is given as:
$\Rightarrow A\xrightarrow[NOT]{}\overline{A}$
We can also write the truth table for this Boolean expression above. This can be done as follows:

$A$	$\overline{A}$
0	1
1	0

Here, A is either of the two input logics, truth and false.
Now, we will use this above definition to check our options one by one.
(A) stop a signal: A NOT gate is an inverter gate and not a stopper gate. So, it cannot stop a signal.
Therefore, the first option is clearly incorrect.
(B) invert an input signal: A NOT gate inverts an input signal. This is the reason why it is also termed as an inverter.
Therefore, the second option is correct.
(C) complement a signal: A NOT gate complements (synonym for inverts) an input signal. This has been verified by its Boolean expression.
Therefore, the third option is also correct.
(D) Change the logic in a digital circuit: A NOT gate changes the logic in a circuit. This has been verified by its truth table.
Therefore, the fourth and the last option is also correct.
Hence, to stop a signal is not a function of the NOT gate.

Hence, option (A) is the correct option.

Note:
One should not confuse between a NOT gate and a Buffer gate. A Buffer gate is a non-inverting amplifier. Its main purpose is to take a weak signal and boost it up whereas an inverter or a NOT gate inverts a signal. These basic differences between these logic gates should be remembered so that one does not confuse between them while solving problems.