Rotation detecting device and bearing having rotation detecting device

A rotation detecting device comprising:

• a plurality of magnetic encoders arranged in a coaxial ring arrangement and having respective number of magnetic poles different from each other;
• a plurality of magnetic sensors for detecting respective magnetic fields of those magnetic encoders, each of the magnetic sensors having a function of detecting information on the position of the magnetic encoders within each of the magnetic poles, each of the magnetic sensors includes
• a plurality of sensor elements arranged at respective positions displaced from each other within the pitch of the neighboring magnetic poles, each of the sensor elements is configured to obtain two phase signal outputs representative of sine and cosine curves and to accomplish detection of the position within the magnetic poles by interpolation between the two phase signal outputs, and a phase detector for determining the phase of the magnetic field signals in reference to the magnetic field signals detected by the sensor elements and outputting an ABZ phase signal including A-phase and B-phase pulse signals A and B, which are displaced 90° in phase from each other, and a Z-phase pulse signal Z indicative of start position;
• a phase difference detector for determining a phase difference of the magnetic field signals in reference to an output from the phase detectors;
• and
• an angle calculator for calculating the absolute angle of the magnetic encoders based on the phase difference so detected.