Angle determining apparatus and angle determining system

An angle detection apparatus producing an angle signal representative of a relative angle between the angle detection apparatus and a magnetic field source that is rotatable on a rotation axis and produces a magnetic field, the angle detection apparatus comprising

• first and second magnetic sensor units for detecting first and second magnetic components of the magnetic field of the magnetic field source, the first and second components oriented orthogonally to each other and lying in a plane running orthogonally to the axis of rotation of the magnetic field source,
• driving means for driving the first and second magnetetic sensor units, and
• control means coupled to the driving means, wherein in a first mode of operation the control means control an output signal of the first magnetic sensor unit so as to have a fixed value and the driving means drive the second magnetic sensor unit according to the same drive conditions as those applied to the first magnetic sensor unit at the time when the first magnetic sensor unit is controlled by said control means, so that an output signal of the second magnetic sensor unit is proportional to the tangent of said relative angle.