JPS57207456A - Input signal interruption detecting circuit in relay device for digital signal transmission line - Google Patents

Abstract

PURPOSE:To prevent the generation of an error signal of a relay device, through the sure detection of broken state of an input signal with good accuracy, by comparing a peak value of a timing signal obtained from the input signal with a reference value. CONSTITUTION:An optical signal is inputted to a photo electric transducer 31 of a relay device of a digital transmission line using a self timing system, the signal is converted into an electric signal at the converter 31 and digitized at an equalizing amplifying circuit 32. An output waveform from the circuit 32 is inputted to a timing circuit 33, and the waveform of a clock frequency from the circuit 33 is inputted to an input signal interruption detecting circuit 36. An input waveform is clamped to a prescribed value at a clamp circuit 361 of this circuit 36, a peak value is detected at a peak value detection circuit 362 and added to a comparison circuit 364, where the peak value is compared with a reference voltage from a reference voltage generating circuit 363, and the output of the comparator 364 controls a gate circuit 37 provided between a discrimination circuit 34 and a electrooptic transducer 35. Thus, the interrupting state of the input signal is detected with good accuracy and the reliability of a relay device can be increased.