Schmitt Trigger

In electronics, a Schmitt trigger is a circuit with positive feedback and a loop gain greater than 1. 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 certain 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 circuit (latch). 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 open-loop controller configurations for noise immunity, and closed loop negative feedback configurations to implement bistable regulators, triangle/square wave generators, etc.