NOT gate (inverter)
A NOT gate, or inverter, outputs the opposite of its input: 1 becomes 0 and 0 becomes 1. Its symbol is a triangle with a small circle at its tip.
Easily confused with
How to read it
Kuphaldt’s Lessons in Electric Circuits calls the inverter a gate that outputs the exact opposite digital signal to its input. The small circle, the bubble, is the standard mark for inversion; the triangle without it is a buffer, which doesn’t invert. Boolean algebra writes NOT as a bar over the letter, Ā; an Illinois ECE 205 lecture notes that some authors write A′ instead, and a University at Buffalo course note writes ~A. Texas Instruments’ SN74HC04 holds six independent inverters on one chip.
Also searched as: ¬A, Ā, inverter symbol, NOT gate symbol, NOT gate truth table, triangle with a circle.
Truth table
| A | Y = Ā |
|---|---|
| 0 | 1 |
| 1 | 0 |
The two standard shapes
Distinctive shape ANSI/IEEE Std 91: a triangle with a circle at the tip. Rectangular shape IEC 60617-12: a box marked 1, with a circle at the output.
The rectangular form is a box marked 1 with the negation circle at its output. Texas Instruments’ guide to IEEE Std 91 defines the 1 as “the one input must be active” and the circle at an output as logic negation: an internal 1 produces an external 0.
Look-alikes
The buffer is the same triangle without the circle. A circle on another gate’s output, as on a NAND or NOR, is the same inversion bubble.
Read next
- Next in Logic gate symbolsNAND gateA NAND gate is an AND gate with its output inverted: the output is 0 only when all inputs are 1, and 1 otherwise. Its symbol is the AND gate’s D shape with a small circle at the output.
- In Logic symbolsNot symbol (¬)¬ means “not” in logic. ¬p, read “not p”, is the negation of p: it is true when p is false and false when p is true.
More logic gate symbols
The same shape elsewhere
Browse symbols drawn with circles, lines or triangles.
Sources
- Lessons In Electric Circuits, Volume IV: Digital, chapter 3, Logic Gates, Tony R. Kuphaldt, open textbook (Design Science License), Tony R. Kuphaldt (ibiblio), Digital signals and gates; The NOT gate
- Overview of IEEE Standard 91-1984: Explanation of Logic Symbols, SDYZ001A, 1996, Texas Instruments, Table 1; Table 2
- SNx4HC04 Hex Inverters (data sheet), SN74HC04 data sheet, Texas Instruments, 3 Description
- Interpreting Logic Gates (CSE111 lecture notes), H. Kershner, Spring 2009, University at Buffalo, Department of Computer Science and Engineering, The NOT gate
- ECE 205 Electrical and Electronics Circuits, Lecture 30, Prof. Umberto Ravaioli, Spring 2026, University of Illinois Urbana-Champaign, Slides 7–8, Boolean algebra and truth tables
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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