Apparatus including a pair of angularly spaced sensors for detecting angle of rotation of a rotary member

An apparatus for detecting an angle of rotation comprising:

• a rotary magnet having a circumference in a plane of rotation on which four magnetic poles are spaced apart from each other at equal angular intervals;
• first and second magnetic sensors of a ferromagnetic material disposed adjacent and facing toward the circumference of the rotary magnet spaced apart from each other at an angular interval of (2n+1).pi./8, where n is an integer;
• a signal generating circuit connected to said first and second sensors for applying first and second sine wave signals thereto, respectively, which have a phase difference of .pi./2 in electrical angle between them;
• a synthesizing circuit receiving respective signals output from said first and second sensors, as a result of said applied first and second sine wave signals and rotation of said rotary magnet through an angle .theta. past said first and second sensors, for generating a synthesized signal based upon said received signals having a phase difference from the phase of said first sine wave signal corresponding to said angle .theta. of rotation;
• and
• a rotation angle detecting circuit receiving the synthesized signal output from said synthesizing circuit and receiving said first sine wave signal from said signal generating circuit for generating an output representing the angle of rotation based on said phase difference.