Method and apparatus for compensation of time base errors

DETAILED DESCRIPTION Basically, the present invention resides in an improved method and apparatus for compensating for variations in the time base of a video signal.
The apparatus includes means for delaying the video signal by a variable amount to compensate for the time base variations, and means for clamping the horizontal synchronizing pulses in the delayed video signal to a fixed reference level.
In accordance with the invention, the apparatus is provided with means for removing any random noise that might be superimposed on the synchronizing pulses prior to clamping, whereby such noise does not influence operation of the clamping means.
More specifically, the delay means of the apparatus preferably takes the form of a charge-coupled device (CCD) that is clocked by a variable rate clock signal supplied by a feedback control system.
The instantaneous frequency of the clock signal is adjusted automatically by the control system to lock the synchronizing pulses in the video signal output by the CCD to a fixed reference frequency corresponding to the average rate of the pulses.
The means for removing random noise superimposed on the successive time base pulses is provided by a circuit for clipping off a portion of each of the pulses and thereby removing most random noise that might be present in the pulses.
Following passage through the CCD to correct for any variations in the timing of the time base pulses, the video signal is passed through the means for clamping the successive noise-free (and now periodic) time base pulses to a fixed reference level.
In summary, then, the clamping means removes any voltage offsets that might be introduced into the video signal by the CCD to thereby prevent streaking from occurring in the resulting video picture, and the clipping circuit removes random noise from the time base pulses of the video signal, to insure that the clamping means is responsive only to voltage offsets caused by the CCD and thereby to prevent flicker from occurring in the resulting video picture