| 摘要 |
<p>A composite analog video signal is sampled at precise locations relative to the phase of the unmodulated color subcarrier along each horizontal line of the video signal. This provides a digitized signal with a constant phase relationship relative to the unmodulated subcarrier phase, which relationship may be used to remove sampling clock phase errors. The digitized samples are filtered by a digital bandpass filter to remove DC and second harmonic noise distortion. Two phase error measurements of the actual sampling clock phase are taken by averaging two sets of burst samples at 0 DEG and 180 DEG crossings, respectively, on selected horizontal lines. These phase error measurements are separately stored, and then are updated on selected alternate horizontal lines to cancel sampling nonlinearity errors. The updated signals are differenced to provide a phase error signal indicative of any sampling clock phase errors. The phase error signal is used to correct the phase of the sampling clock which is supplied to the sampling converter.</p> |
