Magnetic rotational-angle detector

A magnetic rotational-angle detector, comprising:

• a rotating drum having a magnetic medium, wherein the magnetic medium is alternately magnetized with a magnetization pitch λ at an arc-shaped outer periphery thereof in a circumferential direction and rotates in the circumferential direction;
• a plurality of magnetic sensor devices arranged in parallel with one another on a substrate placed oppositely to the outer periphery of the rotating drum wherein the plurality of magnetic sensor devices detects a change of intensity of a magnetic field of the magnetic medium by the rotation of the rotating drum;
• device arrays, each of which comprises a plurality of said magnetic sensor devices, positioned axisymmetrically with respect to a symmetric axis of the substrate, in an arrangement which cancels harmonic components of second and higher orders within output signals outputted from respective device arrays;
• and
• a differential amplifier connected to output terminals of the respective device arrays,
• wherein:
• the symmetric axis is an axis which passes through a barycentric position with respect to all the magnetic sensor devices on the substrate and is parallel to a rotary shaft of the rotating drum, wherein the barycentric position is located on a straight line extending in a radial direction of the rotating drum;
• each of the device arrays has the same number of the magnetic sensor devices and the same distance between adjacent magnetic sensor devices;
• a distance between a pair of magnetic sensor devices arranged at the same position in the device arrays is (2m+1±(1/14)) times the magnetization pitch λ (m is an integer);
• the respective device arrays comprise a power-supply terminal and a ground terminal connected to respective magnetic sensor devices, wherein the power-supply terminals and the ground terminals are arranged axisymmetrically with respect to the symmetric axis in the device arrays;
• and
• a position and a rotational angle of the rotating drum are detected by an output signal of the differential amplifier.