| 摘要 |
PURPOSE:To avoid giving an evil effect to the control signal and the reproduction signal despite the variations of transmittance and reflection factor of an optical parts and a disk, by using a circuit which obtains the means DC voltage component of the signal delivered from a pickup and an amplifying means which amplifies various control signals and reproduction signals with the gain corresponding to the output voltage of the above-mentioned circuit. CONSTITUTION:Voltage signals Pa-Pd delivered from photodetecting regions PDa-PDd of a photodetector 16 are supplied to a matrix circuit 19 as well as to a DC voltage converting circuit 24 and converted into the mean DC voltage VD. The output voltage level of the VD is dropped in response to the reduction of the voltage levels of signals Pa-Pd. In accordance with reduction of said voltage level, VCA circuits 25 and 26 increase the amplifying gain to compensate the reduction of the output levels of tracking and focus error detection signals respectively. Thus these signals are supplied to a tracking servo circuit 21 and a focus servo circuit 22 at a fixed level. |
