| 摘要 |
PURPOSE:To discriminate the operational state of a focus servo circuit and to control the active or inactive states of a tracking servo circuit, by rectifying both positive and negative signals of a focus error signal, then detecting whether the rectified focus error signal stays under a prescribed level. CONSTITUTION:A focus error signal is applied to a preamplifier A, and the amplified tracking error signal is discriminated between positive and negative signal voltages by diodes 11 and 12 and then rectified. The reduction component of the rectification output of the diode 11 is delivered through an LPF connected to the diode 11; while the reduction component of the rectification output of the diode 12 is delivered through an LPF connected to the diode 12 respectively. A signal selecting circuit D selects the higher one of both output levels and delivers it. When a focus servo device has a stable operation, the output voltages of the circuit D is lower than the voltage of a reference voltage source 21. Then a comparator E generates a low voltage output, and a switch circuit 22 is controlled to an ON state. Therefore a tracking servo device becomes active. |
