Ghost cancelling system that cancels ghosts from video signals with a transversal filter

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide an improved ghost cancelling system which reduces the flickering low band fluctuation caused by the noise signals which are added to the reference signal for ghost cancellation, without stopping the waveform equalizing loop.
It is a further object of the present invention to provide a ghost cancelling system which is capable of following the ghost phase fluctuation caused by any change in the weather.
In accordance with the present invention, the foregoing objects are achieved by providing, a ghost cancelling system includes a transversal filter having a plurality of tapped delay lines, coefficient circuits, an adder and a tap coefficient memory, wherein the tapped delay lines operate as an input portion of the transversal filter and delay the input signal by a specified delay time, the tap coefficient memory maintains the value of each tap coefficient corresponding to the tapped delay lines, the coefficient circuits are connected to the corresponding delay lines and amplify the delayed output signal by the tap coefficients, and the adder sums the amplified output signals from the coefficient circuits and operates as an output portion of the transversal filter.
A subtractor subtracts the summed signal output from the output portion of the transversal filter from an input video signal containing a vertical synchronization cyclic reference signal and outputs the result of the subtraction operation to the input portion of the transversal filter.
A memory device maintains the waveform of the video signal output from the subtractor.
An error detector compares the video signal maintained in the memory device and a reference signal.
A control device controls the correction of the tap coefficients in response to an output from the error detector.
The control device includes, a judging device for judging whether an equilibrium condition exists wherein the ghost has been substantially cancelled from the video signal, a detecting device for detecting the tap coefficients, whose value exceeds a specified level, a correcting device for correcting the each tap coefficient until the equilibrium condition is reached but correcting only those tap coefficients detected by the detecting device after the equilibrium condition is reached, an output device for outputting the corrected tap coefficients to the tap coefficient memory in the transversal filter