| 摘要 |
PURPOSE:To attain record/reproduction for both a read-only optical disk and an optical disk capable of write/erasion with the same deck, by using a critical angle method for focusing and then a heterodyne method and a push-pull method with selection in response to the type of a recording medium for tracking. CONSTITUTION:The output given from a 4-split photodiode 17 is applied to a driving coil 19 of a focus actuator through a phase compensating circuit and a driver 18 after an operation carried out to obtain a focus error signal by a critical angle method. For tracking error signals, a T.E1 obtained by a heterodyne method and a T.E2 obtained by a push-pull method are available. Both T.E1 and T.E2 are led to comparators 20 and 21 and then changed to an H level from an L level when the error signal exceeds a certain band value. The outputs of both comparators function as the control signals of analog switches 22 and 23. Then either one of both switches is turned on to apply the tracking error signal to a coil 25 of a tracking actuator through the phase compensating circuit and a driver 24. |
