| 摘要 |
PURPOSE:To decide on the quality of an optical pickup properly by detecting a focusing control signal when accessing sampling positions on a reference information recording medium and an object information recording medium using a reference device equipped with a reference pick up and comparing the contents of both storage devices. CONSTITUTION:A focusing signal indicates the relative distance between an optical disk and an optical pickup and when characteristics of an optical pickup 1' are exactly the same with characteristics of a reference optical pickup, corre sponding focusing signals are exactly the same. The optical disk has an error based upon upward/downward movement of its recording surface due to surface undulation and curvature, but the use of the same optical disk cancels the error component originating from the optical disk. Data of a RAM7' and an EPROM14 are converted by D/A converters 15 and 16 into analog signals and a differential amplifier 17 calculates the difference between the both; and this difference Vi is compared by a comparator 18 with a specific reference voltage Vref and a signal indicating a defective is outputted when Vi>Vref. Consequent ly, the quality of the optical pickup is judged properly.
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