In electronics, a Schmidt trigger (in English: Schmitt trigger) is a comparator circuit with positive feedback.
For a standard Schmidt trigger, when the input voltage is above the positive threshold voltage, the output is high; when the input voltage is below the negative threshold voltage, the output is low; when the input is between the positive and negative threshold voltages, the output does not change. That is to say, when the output flips from a high level to a low level or from a low level to a high level corresponding to the threshold voltage, which is different when the input voltage changes, the output will change. Therefore, this component is named a trigger. This double-threshold action is called hysteresis phenomenon, indicating that the Schmidt trigger has memory. Essentially, the Schmidt trigger is a bistable multivibrator.
The Schmidt trigger can be used as a waveform shaping circuit, which can shape the analog signal waveform into a square wave waveform that can be processed by digital circuits. And because the Schmidt trigger has hysteresis characteristics, it can be used for anti-interference. Its applications include using it in open-loop configuration for anti-interference, and in closed-loop positive feedback/negative feedback configuration for implementing a multivibrator.