| 摘要 |
PURPOSE:To stably conduct focusing control and tracking control by making a time constant of an automatic gain-controlling circuit small while a projecting amount of light from a laser is being changed. CONSTITUTION:A signal of a total amount of a reflecting laser light from an optical disc is supplied and amplified at a gain variable amplifier 1, to which a delay based on a time constant of a time constant circuit 7 is added thereby to form a gain control signal. The gain control signal is fed to the amplifier 1 to automatically control a gain. In the meantime, a focus error signal and a tracking error signal detected on the basis of the reflecting light from the optical disc are amplified respectively at gain variable amplifiers 2 and 3, and gain control signals obtained by adding the delay based on the time constant of the time constant circuit 7 to the amplified signals are sent to the amplifiers 2 and 3, thereby controlling gains. The focus error signal and tracking error signal amplified at the amplifiers 2 and 3 are output through pre-hold circuits 5 and 6 by a defect detection signal output from a defect detection circuit 4. |
