JPS6459667A - Jitter measuring signal detector - Google Patents

Abstract

PURPOSE:To measure the jitter of a spindle motor with high accuracy and a high band by suppressing the decentering information with a reference signal provided at a reference signal. CONSTITUTION:A reference disk 1 for measuring a jitter having a triangular shape mark 10 is fitted to a spindle motor 2 to be measured and rotated in a measuring condition. A photodetector 3 detects the mark 10, a detecting signal is pulse width/voltage-converted, binarized by a processing part 4, and the output which resets a counter 5 is given to a D/A converter 8 as a clock. The counted value of the output of an oscillator 6 is supplied from the counter 5 to a subtracter 7 and the difference in a reference pulse width Tr is D/A- converted 8 and outputted through an LPF9. As this result, the number of the marks of the disk 1 and the decentering information accompanying the change of the duty of the detecting output are simultaneously detected, the jitter quantity due to the decentering is calculated backwards, subtracted from the number of the detections of marks, and thus, the jitter measurement of the spindle motor is executed.