| 摘要 |
PURPOSE:To prevent a timing shifting caused by a temperature change by securing a AND with a comparison value to the reference level of the output pulse of a sensor which detects the member attached to a spindle motor and the comparison value of zero level of the differential signal of the output pulse. CONSTITUTION:A reflective sensor 5 consists of a light emitting diode 51 and a phototransistor 52, and a sensor output pulse 100 is extracted out of the transistor 52. The pulse 100 is supplied to a comparator 6 and a differentiation circuit 7. The comparator 6 delivers a pulse 200 when its input exceeds a fixed level. While a comparator 8 delivers a pulse 400 when a differential signal 300 is >=0 volt. The AND is secured at pulses 200 and 400 by a AND circuit 9 and an index pulse 500 is delivered. A triangular reflecting plate 10 is attached to the side face 11 of a spindle motor. Then the reflected light given from the plate 10 is applied to the sensor 5. Thus it is possible to prevent the shifting of an index timing caused by the temperature change.
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