Patent ID: 7138796

Claim:
A rotation angle sensor, comprising: a rotor having a first area and a second area, wherein each area occupies 180 degrees or less of the circumference of the rotor, wherein the shape of the first area is different from the shape of the second area, such that the rotor is asymmetric about a plane that includes the axis of the rotor, wherein: the first area includes a measurement area, and the second area includes a measurement area, and the measurement area of the first area includes a predetermined number of salient poles, and the measurement area of the second area includes a plurality of salient poles; the number of poles in the second area is an integer multiple of the predetermined number, and the integer multiple is greater than one; and a stator, wherein the stator includes a first set and a second set of stator magnetic poles, wherein each set of stator magnetic poles includes windings, and the first set of stator magnetic poles is arranged on a first area of the stator, and the second set of stator magnetic poles is arranged on a second area of the stator, and the first area of the stator is located on an opposite side of the axis of the rotor with respect to the second area of the stator, wherein, when the rotor rotates, an output voltage signal of the second set of magnetic roles has a frequency that is equal to a frequency of an output signal of a winding of the first set of magnetic poles multiplied by the integer of the integer multiple.