A sensor unit for detecting an encoder at a predefined position, having a circuit device and a threshold signal present at the circuit device, and a magnetic field sensor. The magnetic field sensor has a supply and ground terminal and first and second outputs, and outputs an analog sensor signal that is dependent on the distance of the encoder, and a supply unit connected to the supply terminal of the magnetic field sensor, the supply unit having a control input, and the circuit device is connected to the magnetic field sensor. The circuit device is configured to provide the sensor signal as an amplified signal value, and the circuit device is configured to determine an amount from the difference between the amplified signal value and the threshold signal and to control the amplification of the signal value and the supply unit as a function of the magnitude of the amount.