The NOT gate (inverter)
The NOT gate, also called an inverter, has one input and gives the opposite value: 0 becomes 1 and 1 becomes 0. In formulas it is written with a bar over the letter: Ā, read “not A”.
Formula Y = Ā
Truth table
| A | Y |
|---|---|
| 0 | 1 |
| 1 | 0 |
Try it Click the inputs to change them.
Y1
Where it is used
Whenever a circuit needs the opposite of a signal: a light that turns on when it gets dark, or a multiplexer that lets input A through when the select signal is not 1 (see the multiplexer).
The small circle on the tip of the symbol means “invert”. You will see the same circle on NAND, NOR and XNOR.
Build it yourself
Connect both inputs of a NAND gate together and it becomes a NOT gate. Try it in the NOT from NAND challenge.