GB2005510A - PAL television signal time base corrector - Google Patents

Abstract

Relates to compensating those time base errors in a reproduced swinging burst colour television signal which are caused by inaccurate switching of the subcarrier burst and which result from the inability of a phase error detector from distinguishing phase errors due to burst switching errors from phase errors due to time base errors and which therefore treats both as time base errors with consequent inaccurate compensation of a time base error in the reproduced signal. In an embodiment the output error signal of the time base error detector is delayed by one line period 34, subtracted 32 from the undelayed error signal and the difference signal so formed passed directly and via an inverter 39 to a switch 36 which is changed over at line frequency so that a direct voltage signal appears at 41 whose average magnitude is determined predominantly by the switching error component. The signal at 41 is smoothed in an integrator 42 and the magnitude of the signal resulting therefrom determines the magnitude of a square wave signal produced by a generator 43. The square wave signal is arranged to be of opposite sign but of substantially the same magnitude as the switching error component so that when added to the detector output signal at 44 the switching error component is substantially removed. <IMAGE>