Circuit arrangement in colour television receivers

Claim 1

A CIRCUIT FOR A COLOUR TELEVISION RECEIVER FOR RECEIVING COLOUR TELEVISION SIGNALS OF THE TYPE IN WHICH TWO COLOUR SIGNALS ARE MODULATED IN QUADRATURE ON AN AUXILIARY CARRIER AND THE BURST SIGNAL IS CO-TRANSMITTED AS A SEPARATE SYNCHRONIZING SIGNAL DURING THE OCCURENCE OF A BACK PORCH BETWEEN TWO LINES, SAID CIRCUIT INCLUDING AN AMPLIFYING ELEMENT IN THE COLOUR CHANNEL OF THE RECEIVER FOR AMPLIFYING BOTH THE BURST SIGNAL AND THE COLOUR SIGNAL WHICH IS PRESENT DURING THE REST OF THE LINE PERIOD, MEANS APPLYING GATING PULSES TO SAID AMPLIFYING ELEMENT WHICH OPEN IT FURTHER DURING THE HORIZONTAL FLY-BACK PERIOD THAN DURING THE HORIZONTAL STROKE PERIOD, SAID GATING PULSES BEING DERIVED FROM AN OUTPUT ELECTRODE OF A SECOND AMPLIFYING ELEMENT HAVING AN INPUT ELECTRODE TO WHICH THE GATING PULSES ARE APPLIED, THE CIRCUIT ALSO INCLUDING MEANS FOR DERIVING AN AUTOMATIC CONTROL VOLTAGE, PROPORTIONAL TO THE AMPLITUDE OF THE BURST SIGNAL, FROM THE OUTPUT SIGNAL OF THE FIRST-MENTIONED AMPLIFYING ELEMENT WHEREIN THE IMPROVEMENT COMPRISES MEANS FOR APPLYING SAID CONTROL VOLTAGE AS AN AUTOMATIC BURST CONTROL VOLTAGE TO THE SECOND AMPLIFYING ELEMENT, A CLAMP CIRCUIT, MEANS CONNECTING THE OUTPUT ELECTRODE OF SAID SECOND AMPLIFYING ELEMENT TO AN INPUT ELECTRODE OF SAID FIRST MENTIONED AMPLIFYING ELEMENT BY WAY OF SAID CLAMP CIRCUIT, A SOURCE OF A VARIABLE BIAS VOLTAGE AT WHICH THE GATING PULSES DERIVED FROM THE SECOND AMPLIFYING ELEMENT MUST BE FIXED DURING THE HORIZONTAL STROKE PERIOD, AND MEANS APPLYING SAID BIAS VOLTAGE TO SAID CLAMP CIRCUIT, WHEREBY IN THE ABSENCE OF BURST SIGNALS CURRENT FLOW IN SAID INPUT CIRCUIT RESULTING FROM SAID GATING PULSES CHARGES SAID CLAMP CIRCUIT TO A POTENTIAL THAT CUTS OFF SAID FIRST MENTIONED AMPLIFYING ELEMENT DURING THE STROKE PERIOD.