Pal burst phase shift error corrector

Abstract

Time base errors in PAL subcarrier reference bursts, created in part by the operation of a video tape recorder, are detected by the recorder and used for detecting the phase shift error in phase angle switching between bursts on adjacent video signal lines which existed before the video signal was recorded. The video tape recorder timing errors detected on the bursts are first detected after the 90.degree. phase angle between successive bursts has been eliminated. Two sample and hold units then are alternately strobed, each at a point in time during a given tape recorder head pass wherein the error signals are normally most accurate, such that a first burst timing error is retained in one such unit and a next burst timing error is retained in said second unit. The outputs of these two sample and hold units are filtered and combined in an integrator for generating a voltage control signal whose amplitude varies as a function of the pre-existing burst shift error. This control voltage is fed to a phase shift unit which operates in response thereto to modify the phase of subsequent off-tape color reference bursts before error detection has been performed on such subsequent bursts.