| 摘要 |
PURPOSE:To quicken a response for the switching on/off of power source or a sudden variation of an optical input by controlling a DC conversion circuit by ah amplification circuit so that a current to flow in an APD(avalanche photodiode) comes constant. CONSTITUTION:The current to flow in the APD 2 is converted into a voltage by the resistor R1 of a current detection circuit 3. The amplification circuit 4 organizes an inverting amplification circuit by the resistors R2, R3 and an operational amplifier OP1, and the DC conversion circuit 1 is controlled so that the output of the current detection circuit 3 coincides always with a reference voltage. Namely, the current to flow in the APD 2 is kept constant regardless of the magnitude of the optical input. The signal component of the APD 2 is transmitted to the amplification circuit including the operational amplifier OP2 of a next stage through a coupling condenser 5. Thus, because the current to flow in the APD can be made constant by controlling the bias voltage of the APD without using an F-AGC to control the multiplication factor of the APD, the response can be quickened. |
