The present teaching relates to a magnetic sensor comprising an input port, a magnetic field detecting circuit that generates a magnet detection signal, an output control circuit that controls operation of the magnetic sensor, and an output port. The magnetic field detecting circuit includes a magnetic sensing element that detects an external magnetic field and output a detection signal, a signal processing element configured to amplify the detection signal and removing interference from the detection signal, and an analog-digital conversion element configured to convert the processed detection signal into a magnet detection signal, and the output control circuit controls the magnetic sensor to operate in at least one of a first state and a second state responsive to at least the magnet detection signal, wherein the signal processing element comprises a folded cascode amplifier.