Patent ID: 7122983

Claim:
A rotating angle detecting apparatus comprising: an angular resolver detecting a rotating angle and attached to a detected subject; a direct-current offset voltage applying circuit applying a direct-current offset voltage to an output from the angular resolver; an A/D converter A/D converting an output from the direct-current offset voltage applying circuit; and a computing unit applying an exciting voltage to the angular resolver and detecting a rotating angle of the angular resolver on the basis of an output from the A/D converter, wherein the direct-current offset voltage applying circuit comprises a differential amplifier, a first resistance connected between an inverting input of the differential amplifier and a reference potential, a second resistance for a negative feedback connected between an output and the inverting input of the differential amplifier, a third resistance connected in series between the angular resolver connected to the reference potential and a non-inverting input of the differential amplifier, and a fourth resistance connected between an offset potential and the non-inverting input, wherein values of the first resistance, the second resistance, the third resistance and the fourth resistance are set such that an output of the differential amplifier becomes equal to or more than a predetermined margin for preventing an erroneous ground fault detection in the computing unit, in a difference between a minimum output potential at a time when the angular resolver is not in a ground fault generated by a variation of the values of the first resistance, the second resistance, the third resistance and the fourth resistance and the direct-current resistance component of the angular resolver output coil, and a maximum potential at a time when the angular resolver is in the ground fault, wherein a magnification of said third resistance with respect to a direct-current resistance component of said resolver output coil is determined in such a manner that a difference between said minimum output potential and said maximum potential becomes equal to or more than said predetermined margin, and wherein values of said first resistance, the second resistance and the fourth resistance are set in such a manner that a gain of said differential amplifier defined such that the difference between said minimum output potential and said maximum potential becomes equal to or more than said predetermined margin becomes in a predetermined range, on the basis of the value of the third resistance determined by said magnification.