| 摘要 |
PURPOSE:To make the output amplitude constant and to adjust a changeover circuit unifiedly by detecting an amplitude of a clamped electric signal so as to control a limiter stage number in matching with the optical signal level subject to amplitude modulation. CONSTITUTION:An electric signal inputted to a band limit filter 3 from a photoelectric conversion circuit 1 is converted into a waveform easily identified and the result is outputted to a multi-stage limiter circuit 7. The stage number in matching with an optical signal subject to amplitude modulation is selected by the electric signal and clamped to the amplitude close to the logic level and the result is outputted to an identification circuit 6 and a changeover circuit 8. The electric signal is used to control the limiter stage number to detect an output amplitude of the multi-stage limiter circuit 7 and to make it constant. Furthermore, the electric signal inputted to the identification circuit 6 from the multi-stage limiter circuit 7 is identified and recovered at the logic level by a comparator. Thus, the gain control adjustment for each circuit is not required by controlling the output amplitude through the changeover of the limiter stage number by the control of the changeover circuit in this way. |
