Circuit arrangement for synchronizing the sub-carrier oscillator in a color television receiver

Claim 1

A CIRCUIT ARRANGEMENT FOR SYNCHRONIZING THE SUBCARRIER OSCILLATOR IN A COLOR TELEVISION RECEIVER FOR USE IN A COLOR TELEVISION SYSTEM IN WHICH TWO COLOR SIGNALS MODULATE A SUB-CARRIER IN QUADRATURE AND THE BURST SIGNAL IS CO-TRANSMITTED AS A SEPARATE SYNCHRONIZING SIGNAL DURING THE OCCURRENCE OF A BACK-PORCH BETWEEN TWO LINES, WHICH CIRCUIT ARRANGEMENT INCLUDES A GATE CIRCUIT FOR AMPLIFYING AT LEAST THE BURST-SIGNAL, A FIRST PHASE-DISCRIMINATOR TO WHICH ARE APPLIED AT LEAST THE SAID BURST SIGNAL AND A SIGNAL DERIVED FROM THE OSCILLATOR, THIS FIRST PHASEDISCRIMINATOR FORMING PART OF THE NORMAL CONTROL LOOP OF THE SYNCHRONIZING CIRCUIT OWING TO THE FACT THAT FROM THIS PHASE-DISCRIMINATOR IS DERIVED THE CONTROL VOLTAGE FOR CONTROLLING THE FREQUENCY OF THE OSCILLATOR, AND A SECOND PHASE DISCRIMINATOR TO WHICH ARE APPLIED AT LEAST THE BURST SIGNAL AND A SIGNAL DERIVED FROM THE OSCILLATOR WITH A PHASE DIFFERING FROM THE PHASE OF THE CORRESPONDING SIGNAL APPLIED TO THE FIRST PHASE-DISCRIMINATOR IN A DEGREE SUCH THAT, IF REQUIRED WITH THE ADDITION OF MATRIX CIRCUITS, THE OUTPUT SIGNALS TAKEN FROM THE TWO PHASE-DISCRIMINATORS MAY BE REGARDED AS PRODUCED BY A DIFFERENCE IN DIRECTION OF DEMODULATION OF ABOUT 90*, WHEREIN THE IMPROVEMENT COMPRISES A PHASE-SHIFTING NETWORK CONNECTED BETWEEN AN OUTPUT TERMINAL OF THE SECOND PHASE-DISCRIMINATOR AND AN INPUT ELECTRODE OF THE GATE-CIRCUIT WHEREBY THE OUTPUT OF SAID PHASE SHIFTING NETWORK IS MIXED WITH SAID BURST SIGNAL.