| 摘要 |
PURPOSE:To increase equivalently the gain margin of a servo system to improve the stability, by performing such control that average levels of optical beams for recording and reproducing are equal to each other approximately. CONSTITUTION:A controlling circuit 2 outputs a signal, which sets a bias level P2 of the optical beam, when a recording command signal 6 is ''1''. A controlling circuit 3 outputs a signal, which sets a level P3 to be superposed to the level P2 at the time point when a data modulation signal 7 becomes ''1'', when the signal 6 is ''1''. Meanwhile, a signal which is operated in the time, when a reproducing command signal 8 is ''0'', and sets an output level P1 of an optical beam generator 5 is outputted. In this constitution, parameters tA, tB, P1, P2, P3 are so set in circuits 2-4 that an average level PW=P2+tA.P8/tA.tB of the optical beam for recording is equal to an average level PR=P1 of the optical beam for reproducing. |
