The present invention relates to a rotational angle detector for detecting the rotational angle of a rotor.
Japanese Laid-Open Patent Publication No. 2004-239670 discloses a steering angle sensor for detecting the rotational angle of a steering wheel for an automobile. The steering angle sensor includes a main gear that integrally rotates with the steering wheel, a detection gear engaged with the main gear and incorporating a magnet, and a magneto-resistance element for magnetically detecting the rotational angle of the detection gear.
The magneto-resistance element provides a microcomputer with a first analog signal, which has a sinusoidal shape that changes cyclically whenever the main gear (steering wheel) is rotated by 60 degrees (whenever the detection gear is rotated by 360 degrees), and a second analog signal, which has a sinusoidal shape with a phase shifted by one fourth of a cycle from the first analog signal. This enables the microcomputer to obtain the rotational angle of the steering wheel within the range of 0 to 60 degrees of the rotational angle of the steering wheel based on the combination of the first analog signal and the second analog signal provided from the magneto-resistance element. Thus, even after the steering wheel is rotated to a new rotational angle within the range of 0 to 60 degrees while the ignition switch is turned OFF, the microcomputer can immediately obtain the new rotational angle when the ignition switch is turned ON.