# IEC Schmitt-trigger inverter (rectangular form)

Canonical URL: https://eloragrid.ai/symbols/iec-schmitt-trigger-inverter
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: 1
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: 1 element with hysteresis qualifier and output negation
Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted.
Related representation: [Schmitt-trigger inverter](https://eloragrid.ai/symbols/schmitt-trigger-inverter)

IEC inverter with the hysteresis mark, used to clean up slow edges while inverting the signal.

## In plain English

### What does IEC Schmitt-trigger inverter (rectangular form) mean?

This element combines the 1 additional drawing mark, the hysteresis mark and output negation. It inverts the signal while switching at two thresholds, which makes it a common choice for debouncing contacts with an RC network and for building simple relaxation oscillators.

### A simple example

When a Schmitt inverter forms part of an oscillator or delay with external resistors and capacitors, the drawing should keep those components next to the element and note the intended timing. The symbol alone gives no clue that it is part of a timing circuit.

### What the drawings help you do

Thresholds, hysteresis width and supply range are device data. Different logic families have markedly different thresholds even though the symbol is identical.

### This particular reference

IEC inverter with the hysteresis mark, used to clean up slow edges while inverting the signal. The Schmitt buffer has the same hysteresis mark but no output negation.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)
- [SN74HC14 — Schmitt-trigger inverters](https://www.ti.com/lit/ds/symlink/sn74hc14.pdf)


## What it represents

This element combines the 1 qualifier, the hysteresis mark and output negation. It inverts the signal while switching at two thresholds, which makes it a common choice for debouncing contacts with an RC network and for building simple relaxation oscillators.
When a Schmitt inverter forms part of an oscillator or delay with external resistors and capacitors, the drawing should keep those components next to the element and note the intended timing. The symbol alone gives no clue that it is part of a timing circuit.
Thresholds, hysteresis width and supply range are device data. Different logic families have markedly different thresholds even though the symbol is identical.

## How to read it

- Check for external RC parts that turn the inverter into a timing circuit.
- Confirm the output negation as well as the hysteresis mark.

## Information to show or reference

- Show both the hysteresis mark and the output negation.
- Keep associated RC components adjacent.
- Note the intended timing if used as an oscillator or debounce.

## Important distinction

The Schmitt buffer has the same hysteresis mark but no output negation.

## Facts

- Qualifier: 1, hysteresis mark, output negation
- Common circuits: Contact debounce, RC oscillator
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Hysteresis and negation qualifiers.
- [SN74HC14 — Schmitt-trigger inverters](https://www.ti.com/lit/ds/symlink/sn74hc14.pdf) — Texas Instruments. Manufacturer Schmitt-trigger inverter documentation.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.