Not Gate Truth Table: Applications and Real World Uses

A NOT gate, also known as an inverter, is a logic gate which produces an output that is the opposite of its input. In other words:

  • If the input is high (1), the output will be low (0).
  • If the input is low (0), the output will be high (1).

It’s represented by a triangle with a small circle at the input, indicating that the input is inverted. The negated output is written as the input (in the above graphic, A) with a line on top.

Not Gate with Truth TableEvery possible output of a logic gate can be expressed using a truth table. Let's check out what the Not Gate Truth Table looks like in relation to the truth table of the other basic logic gates.

NOT Gates Truth Table

The truth table for a NOT gate is straightforward because it has only one input and one output. When the input is 0, the output is 1. When the input is 1, the output is 0.

Here’s what the NOT Gate Truth Table looks like compared to the other basic logic gates, like the AND OR NOT Gates.

Basic Logic Gates Truth Table

Truth tables are especially helpful when you are needing to know what the output will be on a gate that has multiple inputs. The above graphic shows all gates as having two inputs for clarity's sake, but these gates can have multiple inputs, making the truth table output incredibly useful.

Here’s an example of a 3-input XNOR Gate alongside its truth table. XNOR stands for eXclusive Not OR, and is the logical combination of a XOR (exclusive OR) and NOT Gate.

*notice the line above the output in the following graphic, that’s the boolean expression of the NOT Gate negating the output

3-Input XNOR Gate

So what’s the point of a NOT gate having one input and inverting that signal to the opposite? Let’s check out some real world examples of a NOT Gate!

Real World examples of a NOT Gate

To build any sort of non-trivial digital device, you must have NOT gates, or inverters.

*fyi, a non-trivial digital device a physical device, typically electronic, which computes a Boolean logical output (0 or 1) from Boolean input(s)

Any digital circuit can be constructed of just NOT and
AND gates (i.e. NAND gates), or NOT and OR gates (NOR gates). But you cannot use just AND or OR gates by themselves because any non-trivial digital circuit will require the inversion of some signals and you can’t do that with just AND or OR gates.

So every digital device that you have — smart phone, tablet, personal computer, etc. has millions or billions of transistors acting as inverters or NOT gates.

Check out WatElectronics post on the applications of the Not Gate. That post covers everything from NOT Gates with transistors, as a NAND Gate, NOR Gate, Multiplexer, integrated circuit (IC), and more. 

We hope that answers any and all questions you may have had about the NOT Gate and its Truth Table.

Final thoughts on the NOT Gates truth table

Having a single input and output, the NOT Gate along with its truth table may seem straightforward, but its role in digital electronics design is fundamental.

If this post was helpful, we wrote some others, like how Gates in Computer Science are used, you can check them all out in our engineering blog.

If you want a constant reminder of how NOT Gates and the other basic logic gates are used, snag a copy of Computer Engineering for Babies via the link below.