| 摘要 |
PURPOSE:To quickly switch systems by arranging a signal synthesizing circuit in the preceding stage of a time constant circuit, and using this time constant circuit in common between the current system and the stand-by system. CONSTITUTION:A signal synthesizing circuit 17 is arranged in the preceding stage of a time constant circuit 14, and the time constant circuit 14 is shared between the current system and the stand-by system. If trouble occurs in the current system, a switch SW is switched to supply the electric signal on an input terminal IN to a laser diode driving circuit 21, and the operation of a stand-by system 20 is started instead of a current system 10. In such a case, the bias current value supplied from a bis current control circuit 25 to a laser diode 22 is equal to the steady value of the current system already adjusted based on the output of the time constant circuit 14 during the operation of the current system 10. Thus, stable optical output control is performed even after switching from the current system to the stand-by system. |
