Schmitt trigger circuit is a waveform shaping circuit. When a signal of any waveform enters the circuit, the output jumps between positive and negative saturation, producing a square wave or pulse wave output. Different from the comparator, the Schmitt trigger circuit has two critical voltages and forms a hysteresis area, which can prevent noise in the hysteresis range from interfering with the normal operation of the circuit. For example, remote control receiving circuits and sensor input circuits will use it for shaping.