| 摘要 |
PURPOSE:To improve the performance of response without losing stability in the control of sensitivity, by switching an input sensitivity stepwise at a feedforward control means, when a level of an input signal is changed to a level of a by-pass signal sufficiently lower than that of a main signal or its inverting level. CONSTITUTION:A station ST1i (where i=1-n) is connected in series via an optical transmission line 30. The transmission line 30 is provided with a by-pass 2i of a passive branching circuit comprising a half mirror. An input optical signal to each ST is converted into an electric signal at a photoelectric converting element P, amplified at a preamplifier A1 and a main amplifier A2, compared with a threshold voltage Vth by a comparator CMP, converted into a binary signal and given to a signal processing section in the ST. When the function is stopped at the ST11, the input to the ST12 is changed rapidly from the level of the main signal to that of the by-pass signal, and when the function is restored, the input is changed rapidly to the inverting level. Gain controlling signals Vc1, Vc2 corresponding to the main signal and the by-pass signal are selected at the feedforward controlling circuit FF, summed to a control signal of a feedback controlling circuit FB and the main amplifier A2 is controlled stepwise. |
