LOCK DETECTION AND OPERATION ALARM DETECTION CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide a lock and operation alarm detection circuit for measuring a control voltage from a digital signal of an ABC circuit.

SOLUTION: A light signal outputted from an optical modulator 104 is converted to an electric signal and then is converted to a binary digital signal by a comparator circuit 108 in a digital control automatic bias control circuit 100. A phase comparator 109 compares the phase of a low-frequency signal applied to the optical modulator 104 with that of comparator output, and an adder-subtractor 110 outputs a value added and subtracted according to the code of the phase. A threshold determination circuit 121 operates an alarm circuit 123, when the output value of the adder-subtractor 110 is out of a prescribed range or the amount of change in the output value of the adder-subtractor 110 over a prescribed time interval is larger than a prescribed value.

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