COMMON RECEPTION AND DECODING CIRCUIT FOR ZERO RETURN SIGNAL AND NON-ZERO RETURN SIGNAL

摘要

PURPOSE:To decode both a zero return signal and a non-zero return signal by deciding whether a received signal is a zero return signal or a non-zero return signal depending on a mean value of the received signal, selecting a clock for a zero return signal or a non-zero return signal and decoding the selected clock at a FF circuit. CONSTITUTION:An optical signal in a form of RZ and NRZ signal received by a photodetector 1 is converted into an electric signal therein, divided into two via an amplifier circuit 2, the one output is differentiated at a leading by a differentiating circuit 4, the differentiated output is inputted to a timing extraction circuit 5, from which a clock signal is generated. Moreover, a delay circuit 7 or 8 generates a 1st or 2nd clock resulting from retarding the RZ signal by a delay of phi1 or phi2 respectively so as to be fetched in a timing point when the data is established in order to decode the RZ signal at a FF circuit 10. A zero return signal and non-zero return signal identification circuit 6 compares a mean value of a received optical signal with a reference voltage to identify whether the received signal is the RZ signal or the NRZ signal, the result of identification is sent to a selection circuit 9, in which a 1st or 2nd clock is selected and a data inputted to the FF circuit 10 is decoded.