Ghost cancelling system and method of controlling such a system

Claim 1

A ghost cancelling system comprising: 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 which 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 means for maintaining the waveform of the video signal output from the subtractor; an error detection means for comparing the video signal maintained in the memory means and a reference signal; and control means for controlling the correction of the tap coefficients in response to an output from the error detection means, the control means including, means for judging whether an equilibrium condition exists wherein the ghost has been substantially cancelled from the video signal, means for detecting the tap coefficients, whose value exceeds a specified level, means for correcting each tap coefficient until the equilibrium condition is reached but correcting only those tap coefficients detected by the detecting means after the equilibrium condition is reached, means for outputting the corrected tap coefficients to the tap coefficient memory in the transversal filter.

Claim 6

A system according to any preceding claim, wherein the control means further includes means for calculating the specified level, which level depends on a noise signal contained in the video signal.

Claim 7

A system according to any preceding claim, wherein the control means detects the tap coefficients which have absolute values equal to or greater than the specified level.

Claim 8

A system according to any preceding claim, wherein the control means judges whether the equilibrium condition exists by counting the number of times the tap coefficients are corrected.

Claim 9

A system according to one of claims 1 to 6, wherein the control means judges whether the equilibrium condition exists by the difference between the new tap coefficients and the old tap coefficients.

Claim 12

A system according to one of claims 1 to 6, wherein the control means judges whether the equilibrium condition exists by the difference between the new error signal and the old error signal, wherein the error signal is defined as a difference between the reference signal and a difference signal, with the difference signal being defined as the difference in the output of the subtractor for a specified interval.

Claim 15

A system according to any preceding claim, wherein the control means corrects the tap coefficients by a specified amount which depends on the noise signal included in the video signal.

Claim 18

A method for controlling a ghost cancelling system having a transversal filter comprising: delaying an input signal by a specified delay time, amplifying the delayed signal by tap coefficients which correspond to a tapped delay line, summing the amplified signals, subtracting the summed signals from an input video signal containing a vertical synchronization cyclic reference signal, outputting the results of the subtracting operation to the transversal filter, maintaining the waveform of the output video signal in a memory, comparing the video signal being kept in the memory with a reference signal, and controlling the correction of the tap coefficients in response to an output from an error detect section by : distinguishing whether an equilibrium condition exists wherein all ghosts have been substantially eliminated from the video signal; calculating a specified value which depends on a noise signal contained in the video signal; detecting the tap coefficients which are equal or greater than the specified value; and correcting only those tap coefficients whose value exceeds the specified value.

Claim 19

A method for controlling a ghost cancelling system having a transversal filter comprising: delaying an input signal by a specified delay time, amplifying the delayed signal by tap coefficients which correspond to a tapped delay line, summing the amplified signals, subtracting the summed signals from an input video signal containing a vertical synchronization cyclic reference signal, outputting the results of the subtracting operation to the transversal filter, maintaining the waveform of the output video signal in a memory, comparing the video signal being kept in the memory with a reference signal, and controlling the correction of the tap coefficients in response to an output from an error detect section by : distinguishing whether an equilibrium condition exists wherein all ghosts have been substantially eliminated from the video signal; calculating a specified value which depends on a noise signal contained in the video signal; detecting the tap coefficients which are equal or greater than the specified value; and correcting only those tap coefficients whose value exceeds the specified value.