VIDEO/SOUND DEMODULATION CIRCUIT

摘要

PURPOSE:To correct distortions after detection by applying envelope detection to a video intermediate frequency signal prior to passing through a delay circuit then adding its output polarity to the control voltage of a voltage controlled variable oscillator so that a phase variation in a detection circuit generated by the variation of a modulation factor is cancelled. CONSTITUTION:VIF signals obtained from a terminal A are divided into two systems; as to the former system, the modulation factor is detected through peak detection circuits 8 in order to detect the above signals' envelope. In addition, detected signals are convoluted to controlled signals of the voltage controlled variable oscillator VCO 5 and VCO 5's outputs are controlled so that phase differences generated in amplification stages of detection circuits 1 are corrected. As regards the latter system, delay circuits 7 make its signal system delay and multiplication detection is applied by means of VCO 5 output signals as well as the detection circuits 1, phases of which are corrected after compensating delayed times in the peak detection circuits 8. And videos/sounds of the detected signals are obtained from a terminal B. Thus phase distortions of videos/sounds generated by rapid variation of the modulation factor of VIF signals can be mitigated.