Absolute magnetic encoder

An absolute magnetic encoder comprising:

• a rotor provided with a first drum and a second drum fixed coaxially to a rotational member to be measured;
• a bipolar magnet formed on an external peripheral surface of the first drum;
• a multipolar track having Q-bit, where Q is a positive integer, magnetic poles formed at equiangular intervals on an external peripheral surface of the second drum;
• a reference track having Z, where Z is a positive integer, reference magnetic poles formed at equiangular intervals on the external peripheral surface of the second drum;
• an X-phase magnetic sensor and a Y-phase magnetic sensor which are disposed facing the external peripheral surface of the first drum and which output an X-phase signal and Y-phase signal that differ in phase by 90°;
• an A-phase magnetic sensor and a B-phase magnetic sensor which are disposed facing an external peripheral surface of the multipolar track and which output an A-phase signal and B-phase signal that differ in phase by 90°;
• a Z-phase magnetic sensor which is disposed facing an external peripheral surface of the reference track and which outputs a reference signal for indicating a position of the reference magnetic poles;
• a first rotor angle computing circuit for computing with P bits a rotational angle of the rotor on the basis of the X-phase signal and Y-phase signal;
• a second rotor angle computing circuit for computing with Q bits the rotational angle of the rotor on a basis of computational results of the first rotor angle computing circuit and on a basis of the A-phase signal, B-phase signal, and Z-phase signal;
• and
• an absolute signal generating circuit for generating an absolute signal that indicates an absolute rotational position of the rotor on a basis of computational results of the first and second rotor angle computing circuits.