Abstract: A rotational angle detecting apparatus includes a rotating member secured to one end of the rotating shaft of an object to be detected for rotation along with the rotating shaft which is rotatable in response to a change in a physical quantity. The apparatus further includes a non-rotating member fixedly positioned opposite to the rotating member, a magnetic field generating source disposed on one of the rotating member and the non-rotating member to generate a magnetic field, and a magnetic sensing element disposed on the other of the rotating member and the non-rotating member to generate an output signal which varies in dependence on the direction of the magnetic field.

Abstract: A rotational angle detecting apparatus employs a bridge circuit of four magneto-resistance elements arranged in a plane and placed in a fixed magnetic field so that the plane of the bridge circuit is parallel to the direction of the magnetic field and is rotatable around the axis perpendicular to the plane. One pair of diagonally disposed magneto-resistance elements further includes resistors respectively such that the direction of the potential difference obtained at one pair of opposite junctions of the bridge circuit is always constant although the magnitude thereof is varied depending on the direction of the magnetic field.The output potential difference from the bridge circuit is amplified by a D.C. amplifier including an operational amplifier and a transistor to deliver an output voltage across a collector resistor of the transistor.