| 摘要 |
PURPOSE:To prevent the picture quality of a main picture from being deteriorated and to automate color matching between a main screen and a subscreen by inhibiting the demodulation and modulation of a main screen signal and executing the time-division multiplexing processing of the main screen signal and a contracted subscreen signal in accordance with the state of a composite video signal. CONSTITUTION:A phase detector 53 outputs a voltage signal corresponding a phase difference between a contracted subscreen signal and a color burst signal. A voltage control oscillator 54 generates a 1st and a 2nd carrier signal controlled in a direction synchronizing the frequency and phase with the color bust signal of the main screen signal based on the voltage signal. Thereby, the 1st and 2nd carrier signals are continuously adjusted so that the frequency and phase of the color burst signal included in the chrominance subcarrier of the contracted subscreen signal to used for chrominance signal modulation always coincides with the color burst signal of a chrominance subcarrier of the main screen signal. Thereby, time division multiplexing processing of the main screen signal and the contracted subscreen signal can be executed by one analog switch in accordance under the state of the composite video signal.
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