| 摘要 |
An error voltage which includes serious fluctuation due to noise is applied to a LPF, and high frequency component due to noise is removed. The error voltage supplied through the LPF and a reference level, for example, 0-level voltage are supplied to a comparator. The comparator compares magnitude of theses two voltage each other, and outputs a signal which indicates polarity corresponding to the comparison result. As described herein above, by removing high frequency component included in the error voltage to be supplied to the comparator with the LPF, the polarity signal with reduced fluctuation due to noise and good quality can be obtained. Thus the polarity of an error voltage for controlling rotation of a disc can be judged correctly.
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