| 摘要 |
PURPOSE:To deliver a correct focus error control signal even though no pit signal is delivered with a no-signal state by using a DC voltage converting circuit which produces the mean DC voltage from the output signal of a pickup, a level detecting circuit which detects that an objective lens reaches the focus error control range and a set/reset flip-flop circuit. CONSTITUTION:For instance, a spot enters the no-signal surface of a disk 11 to produce a no-signal state. Thus no voltage change is produced to the voltage signal Vs which is delivered from a level comparator IC11. While the mean DC voltage V10 delivered from a DC voltage converting circuit 241 is kept at a level higher than the reference voltage V11 since an objective lens 17 is within a focus error control range. Therefore the output voltage VR of a level comparator IC10 keeps a negative polarity state, and as a result the output voltage VQ of an S-R FF circuit 242 receives no inversion of polarity. Then the voltage VQ is delivered continuously to a focus servo circuit 22 in the form of a lock signal. |
