METHOD AND DEVICE FOR MEASURING SIGNAL QUALITY OF DIGITAL INFORMATION TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To monitor a digital information transmission system whose bit error rate is unknown by deciding a bit error rate from an unknown input signal and generating a clock signal with an adjustable current threshold by using a scanning device to decide a signal parameter for signal quality with which the input signal is scanned by the scanning device. SOLUTION: An optical signal is supplied to a known scanning device 6 and an edge counter 7 as well through an optical comparator 1 and an amplifier 2. A search oscillator can be used instead of the edge counter. The counter 7 decides a bit error rate, transmits a preadjusted signal to a voltage controlled oscillator 17, and the oscillator 17 transmits a clock signal. Next, the bit error rate is synthesized with an input signal through a phase locked loop 16 and phase comparison with the input signal by the device 6. The device 6 transmits the bit error rate(BER) as a Q function through a device 12.