What is a Schmitt trigger and how do you calculate its hysteresis?

A Schmitt trigger is a comparator with positive feedback creating hysteresis, two different threshold voltages for rising and falling inputs. This prevents output oscillation from noisy inputs. Using an op-amp with positive feedback: Upper threshold VTH = Vref * (1 + R1/R2), Lower threshold VTL = Vref * (1 - R1/R2). Hysteresis width = VTH - VTL = 2*Vref*R1/R2. Non-inverting configuration provides wider hysteresis range. Schmitt triggers are essential for cleaning up noisy signals and in oscillator circuits.