RECEIVING CIRCUIT OF OPTICAL SIGNAL

摘要

PURPOSE:To expand the dynamic range of automatic gain control (AGC) by controlling a program variable attenuator inputting an electric signal converted from an inputted optical signal by a signal obtained by digitizing DC voltage corresponding to the input optical signal level. CONSTITUTION:An optical signal inputted to a photoelectric conversion circuit 1 is converted into an electric signal and the electric signal is amplified by a signal amplifier 2 and inputted to the program variable attenuator 3. The circuit 1 detects also the DC voltage corresponding to the input optical signal level and an A/D converter 5 converts the DC voltage into a digital signal. The variable attenuator 3 is controlled by the digital signal from the converter 5 to keep the signal level from the amplifier 2 at a prescribed constant level and transfer its output from an output terminal 4 to the succeeding circuit. Since the attenuator 3 is controlled by the digital signal, the AGC operates in a wide dynamic range.