| 摘要 |
PURPOSE:To detect stably a recording irrespective of whether the difference of reflection factors of a substrate and the recording surface is large or small, by inputting a focus error signal to a differentiating circuit, providing an output of this differentiating circuit to a voltage comparator, and detecting the recording surface of an optical recording carrier. CONSTITUTION:As for a variation speed of a focus error signal which is generated when a focus sensitivity, namely, a condensed laser beam 15 crosses the reflecting surface, that of the time of crossing a recording surface 13a is higher than that of the time of crossing the surface of a substrate 13 of an optical recording carrier. By taking notice of a difference of this focus sensitivity, the recording surface is detected. By applying a focus error signal to a differentiating circuit 16, a differential signal for showing the focus sensitivity is obtained. By comparing it with a reference voltage VT by a voltage comparator 12, a signal surface detecting signal is obtained. In such a way, even in case when a difference of a reflection factor of the substrate 13 and a reflection factor of the recording surface is small, the signal surface detecting signal is obtained stably. |
