OPTICAL RECEIVING CIRCUIT

PURPOSE:To operate an optical receiving circuit at high speed and to make the gain control of burst transmission efficient by setting the gain of an amplifier through the use of a current value in the light receiving device. CONSTITUTION:Current generated when an input signal is received by a light- receiving element 1 consisting of a photodiode is amplified when a pre-amplifier 2 converts current into voltage. Then, it is amplified by a variable gain amplifier 3 and is taken out by an output terminal 6. A part of the light-receiving current of the light-receiving element 1 consisting of the photodiode detects reception power by a power detection circuit 4, and a gain setting circuit 5 calculates a gain value which is set and sets/controls the gain of the variable gain amplifier 3. At normal time, the output of an amplitude detection circuit 7 is compared with a reference amplitude value, and the gain is controlled by the large or small value. The power detection circuit 4 consists of a current-voltage converter, an analog-digital converter and a peak detection circuit.