Editing Schmitt trigger (section)

{{Short description|Electronic comparator circuit with hysteresis}}
{{More citations needed|date=March 2021}}

[[File:Hysteresis sharp curve.svg|thumb|upright=0.8|[[Transfer function]] of a Schmitt trigger. The horizontal and vertical axes are input voltage and output voltage, respectively. ''T'' and −''T'' are the switching thresholds, and ''M'' and −''M'' are the output voltage levels.]]

In [[electronics]], a '''Schmitt trigger''' is a [[comparator]] circuit with [[hysteresis]] implemented by applying [[positive feedback]] to the noninverting input of a comparator or differential amplifier.  It is an [[passivity (engineering)|active circuit]] which converts an [[analog signal|analog]] input signal to a [[digital signal|digital]] output signal. The circuit is named a ''trigger'' because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high. When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called ''[[hysteresis]]'' and implies that the Schmitt trigger possesses [[memory]] and can act as a [[bistable multivibrator]] (latch or [[Flip-flop (electronics)|flip-flop]]). There is a close relation between the two kinds of circuits: a Schmitt trigger can be converted into a latch and a latch can be converted into a Schmitt trigger.

Schmitt trigger devices are typically used in [[signal conditioning]] applications to remove noise from signals used in digital circuits, particularly mechanical [[Switch#Contact bounce|contact bounce]] in [[switch]]es.  They are also used in [[Feedback|closed loop]] [[negative feedback]] configurations to implement [[relaxation oscillator]]s, used in [[function generator]]s and [[switched-mode power supply|switching power supplies]].

[[Image:Smitt hysteresis graph.svg|thumb|250px|Comparison of the action of an ordinary [[comparator]] (A) and a Schmitt trigger (B) on a noisy analog input signal (U).  The green dotted lines are the circuit's switching thresholds. The Schmitt trigger tends to remove noise from the signal.]]

In signal theory, a schmitt trigger is essentially a one-bit [[Quantization (signal processing)|quantizer]].