| 摘要 |
PURPOSE:To set the multiplication factor of a light receiving element to an optimum value without setting specially a means to correct the temperature fluctuation of the multiplication characteristic of the light receiving element by providing a clipping circuit at a control voltage circuit for the amplifier when a variable amplifier is controlled by the output signal from an error amplifying circuit. CONSTITUTION:By the output signal from an error amplifying circuit 16 to compare and amplify the voltage corresponding to the peak value of the output signal and the set voltage, the gain of a variable gain amplifying circuit 13 to amplify a light-receiving signal is controlled. A clipping circuit 31 is set to the circuit of a gain control signal and the voltage is impressed through a current limit circuit 33 to a light-receiving element 11. Consequently, while a light-receiving level is small, the impressed voltage for the light-receiving element 11 is limited by the current limit circuit 33, and by the clipping circuit 31, the control voltage for the variable gain amplifying circuit 13 is limited in the specified range and the amplifying gain is constantly kept. Thus, the multiplication factor of the light-receiving element at the time of the minimum light reception can be set to the optimum value. |
