JPS57123756A - Demodulating circuit - Google Patents

Abstract

PURPOSE:To increase a discrimation margin and to obtain a highly reliable demodulation output by discriminating between ''1'' and ''0'' by extracting the fundamental signal of a demodulated signal through an LPF when demodulating a signal processed by frequency shift modulation. CONSTITUTION:The output of a multivibrator 2 is processed by prescribed-time delay 5, the trailing edges of the pulse waveforms of the output 2a of the vibrator 2 and the output 5a of the circuit are detected by differentiators 6 and 7, and the result of OR8 between both differential outputs is inputted to an FF9. A timer 10, on the other hand, monitors an elapse time from the trailing edge of the pulse waveform and sends its output to a timer 11. The timer 11 sends an output 11a when the differential output 12a of a limiter 1 continues for the elapse time, and its differentiated value and the output of the circuit 12 are ORed 14 to apply the result to the other reset terminal of said FF. The output of the FF9 is passed through an LPF3 to send its fundamental wave component to a discriminating circuit 4, which discriminates between ''1'' and ''0'' with a large discrimination margin, thereby obtaining a demodulation output.