A magnetic field sensor comprising a sensor arrangement (H), which is supplied by a supply device (IH) and generates a sensor signal. An evaluation device (ADC, R) to which the sensor signal is fed and which outputs a first output signal (AI). A feedback device (RV) to which the first output signal is fed and which controls the supply device. The regulation of the control loop closed with the feedback device improves the noise behavior of the magnetic field sensor. A method is disclosed for operating the magnetic field sensor.