| 摘要 |
PURPOSE:To keep always the detection sensitivity of a servo system constant by assigning an upper limit to a semiconductor laser power and inserting a limiter which assignes a lower limit and closing a switch circuit after detecting that the servo system enters the normal operation. CONSTITUTION:The sum signal of focus or tracking detectors is used as a light quantity signal at least, and this signal is added to a light quantity control circuit 5 of a semiconductor laser through a filter 27 and a switch circuit 29. Since unnecessary signals may be recorded on a recording and reproducing disc 1 or already recorded signals are degraded if the quantity of light exceeds a certain value, the upper limit is assigned to the semiconductor laser power. A limiter 28 which assignes the lower limit is inserted for the purpose of preventing the degradation of the SN ratio of read signals. A switch circuit 29 is closed after detecting that the servo system enters the normal operation. |
