Analog Electronics
A plain comparator switches over and over on noise near the threshold (chattering). The solution is hysteresis: positive feedback from the output to the non-inverting input creates two different thresholds.
The thresholds are VT± = ±Vsat · R1/(R1+R2). When the signal crosses the upper threshold the output flips and the threshold slides down; to flip back, the signal must fall below the lower threshold. As long as the noise band stays inside this window, the output remains clean.
The Schmitt trigger is one of the most-used blocks in analog design: cleaning up switch bounce, thresholding sensors, and serving as the core of oscillators.
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