| 摘要 |
PURPOSE:To stabilize reproduced signal output levels without using any special optical system such as photo detector or the like by controlling semiconductor laser light output with the information from reproduced signal, releasing the system at the abnormal operating and driving laser under the specified conditions. CONSTITUTION:The signal read part consists of a preamplifier 10, signal mean level detecting circuit 12, phase inversion circuit 13, gate circuit 14 and a gate signal generating circuit 15 emitting the signal for opening a gate 14 at the inputting of the signal above the specified value. The output level of the gate 14 increases or decreases according to the increase or decrease of the output level of the circuit 12. Arrangement is so made that in the steady state where the output level of the circuit 12 is abobe the specified level the gate 14 is opened by the output of the circuit 15 and in the abnormal state where it becomes lower than the specified value the gate 14 is closed by the output of the circuit 15 according to this. Further, a laser driving circuit 1' drives a semiconductor laser 2 by a certain specified current when the gate 14 is closed and drives the semiconductor laser 2 by the current respectively increasing or decreasing with the increase or decrease in the output level of the gate 14 when the gate 14 is opened. |
