An output signal of an opto-electric conversion element 1 is amplified by a differential type pre-amplifier 3 to a predetermined level and input to an ATC circuit 5 as a positive phase signal and an inverted phase signal. These signals are held in respective peak holding circuits 51 and 52 of ...http://www.google.de/patents/US5822104?utm_source=gb-gplus-sharePatent US5822104 - Digital optical receiving apparatus
