Schmidt trigger circuit (Schmidt trigger circuit for short) is a kind of waveform shaping circuit. When any waveform signal enters the circuit, the output jumps between positive and negative saturation, resulting in a square wave or pulse wave output. Different from the comparator, the Schmitt trigger circuit has two critical voltages and forms a hysteresis region, which can prevent the noise in the hysteresis region from interfering with the normal operation of the circuit. For example, the remote control receiving line will be used by the sensor input circuit for shaping.