| 摘要 |
PURPOSE:To prevent a signal transmitted conventionally from an objective lens driver during track crossing from being caused by keeping the loop amplification factor from not being increased even when a light beam is between tracks. CONSTITUTION:When the light beam is crossing a track and between tracks, that is, on a mirror face, a focus error detection signal with high sensitivity is inputted to an amplifier 4 via a phase compensation amplifier 1. The focus detection signal in this case is detected at a high level signal and a sinusoidal wave signal at each track crossing is produced. The DC component of the signal is cut off by a capacitor 8 and a comparator 11 shuts off the noise component to detect only a high level and its detection output opens a switch 5. Since the loop amplification factor is decreased by the voltage division comprising resistors 2, 3, 6, it is possible to keep a constant loop amplification factor even during the track crossing. |
