OPTICAL RECEIVING CIRCUIT

摘要

PURPOSE:To assure the dynamic range of optical input without increasing the optimum SNR and variable gain width, by poligonal line approximation of the optimum value corresponding to an optical input of amplifier gain and to the APD amplification factor optimizing the SNR of APD. CONSTITUTION:An optical signal 11 is applied to an APD12 and the output is amplified at an amplifier 13 to be outputted at a terminal 15. The output of the amplifier 13 is applied to a level detector 14 and the output voltage V is connected to the inverting input of a comparator 52 consisting of operational amplifiers. The output voltage V2 of the comparator 52 is applied to an AGC control terminal of the amplifier 13 as an AGC voltage VAGC. The output voltage VAPD of a high voltage generating circuit 54 is inputted to the APD12 and an inverting input of a comparator 51 consisting of operational amplifiers. The VAGC is applied to a noninverting input of the comparator 53. Thus, the dynamic range of the APD can be assured without increasing the optimum SNR and the variable gain width.