Importance

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Abstract

A video/graphics overlay integrated circuit receives an analog composite video signal and a digital composite video signal and combines them in a predetermined format into an output composite video signal which is transmitted to a display device such as a television set. The digital video signal may be comprised of digital video, graphics data or a combination of digital video and graphics data. The digital video and graphics data are encoded by a digital encoder integrated circuit into a digital composite video signal. The digital composite video signal is coupled to the video/graphics overlay integrated circuit. An automatic phase correction circuit detects any phase difference between the burst signals of the analog composite video signal and the digital composite video signal. A phase control signal is generated by the automatic phase correction circuit and used to correct the phase and frequency of the digital composite video signal and ensure that it corresponds to the phase and frequency of the analog composite video signal. The automatic phase correction circuit uses the analog composite video signal as the master and adjusts the phase and frequency of the digital composite video signal until they are locked to the phase and frequency of the analog composite video signal. A numerically controlled oscillator generates an appropriate oscillating sinusoidal signal representing a burst frequency signal within the digital composite video signal. The phase and frequency of the oscillating sinusoidal signal are appropriately monitored and adjusted to correspond with the phase and frequency of the analog composite video signal.

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First Claim