| 摘要 |
PURPOSE:To obtain the comparator reference voltage of a character signal by providing the titled circuit with a low pass filter to pass only the DC component of a CLOCK RUN IN signal added to the initial part of a character broadcasting signal multiplexed during a vertical feedback period. CONSTITUTION:In case of a character signal receiving mode, a character signal part from a video amplifier circuit 13 is applied to an analog switch 24 through a buffer amplifier 23. An analog switch 24 samples only the CLOCK PUN IN signal part from a CLOCK RUN IN smapling signal generated from a synchronous bit clock producing circuit 9 and applies the sampled signal part to a low pass filter 25. The low pass filter 25 transmits the DC part of the CLOCK RUN IN signal to a peak holding/clamping circuit 26. The peak holding/clamping circuit 26 holds the DC part for a period more than one horizontal period to make the DC part as comparator reference voltage of a comparator circuit 14. Consequently, the correct operation of the comparator 14 can be attained. |
