| 摘要 |
PURPOSE:To stabilize focusing servo and stabilize recording at the head of a sector by inserting summing amplifiers in the input side and output side of an AGC circuit respectively, and adding specified voltage to each of them. CONSTITUTION:A summing amplifier 6 adds specified voltage V1 to a focus error signal 9, and the output 12 is inputted to an AGC circuit 7. A summing amplifier 8 adds specified voltage V2 to the output signal 11 of the AGC circuit 7 and a focus error signal 13 made by correcting the output by AGC control and summing amplifiers 6, 8 is obtained. The 0V point of the output signal 11 of the AGC circuit 7 does not always coincide with the focus point due to added voltage V1 added by the summing amplifier 6. Therefore, additional voltage V2 is added by the summing amplifier 8 to cancel additional voltage V1 to make 0V of the output signal 11 of the AGC circuit at the time of recording coincide with the focus point. Thus, 0V of the focus error signal 13 indicates the focus point at the time of recording, and shifting of focus point does not occur even when reproducing and recording operations are repeated alternately, and stable focus error signals can be obtained. |
