PAL switching control circuit

In a receiver for processing a color television signal including a luminance component, deflection synchronizing components at respective line and field rates, and chrominance and burst components exhibiting a prescribed mutual timing relationship and alternating in phase on a line by line basis, a chrominance channel for processing said color signal, a plurality of color demodulators for demodulating selected phases of said chrominance component, means for providing line by line switching control of one of said demodulators, and wherein proper operation of said receiver requires that said demodulator be switched in correct timing synchronism with line by line alternation of signals received by said receiver, switching control apparatus comprising:

• a source of periodic trigger pulses occurring at said line rate;
• timing means coupled to said switching means and responsive to said trigger pulses for providing half line frequency timing signals for determining said line by line switching;
• means coupled to said chrominance channel and responsive to said burst component and said timing signals for deriving an identification signal when said demodulator switching occurs with incorrect timing synchronism, said signal deriving means exhibiting a fast response time relative to said line rate;
• and
• means for utilizing said identification signal, when present, as a supplementary trigger input to said timing means for resetting said timing means to provide timing signals corresponding to correct line by line timing synchronism.