Patent GB-1239052-A (GB)
IPC: H04N9/455
Filed: 1968-07-19
Abstract: 1,239,052. Colour television. TELEFUNKEN PATENTVERWERTUNG G.m.b.H. ' 19 July, 1968 [19 July, 1967; 19 Sept., 1967], No. 34432/68. Heading H4F. In a PAL receiver an arrangement ensures that the phase of the half-line frequency signal operating the switch-over phase reversal of the (R-Y) demodulating sub-carrier signal is correct. The colour bursts are combined (said term including performing a phase comparison with) with the switched demodulation signal and the resultant signal used to control the phase of operation of the switch-over signal generator. In the embodiments of Figs. 1 to 9, the " combination " is an additive process in addition means 15, whereas in the embodiment of Figs. 10 and 11, said phase comparing process is used. In Fig. 1, chrominance signals including the colour bursts are applied at terminal F, the colour bursts having place variations from line to line indicated at 14. The chrominance signals are synchronously demodulated at 2 with the direct output of sub-carrier oscillator 7 to give the (B-Y) signal and at 3 with the phase quadrative output of said oscillator to give the (R-Y) signal, 90 degrees place shifter 9 and PAL switch 10 causing a phase reversal on alternate lines. The thus phase alternated subcarrier 17, Figs. 2 and 3, is fed to addition means 15 for combination with the colour bursts. In the case of correct phasing of the switching signal from generator 11, the output of 15 has a large amplitude (b), Fig. 2, yielding on rectification a large D.C. signal (C) which is such as not to effect the operation of generator 11. With incorrect phasing of the switching signal (Fig. 3), the D.C. signal (C) is small, and so readjusts generator 11. In the embodiment of Fig. 4 (not shown), a combination of the output of switch 10 and the direct output of oscillator 7, is fed to the left input of addition means 15. This produces a small D.C. signal for the correct phase case and a large D.C. signal for the incorrect case. In the embodiment of Fig. 7, the +90 phased colour burst signals 14 are fed to addition means 15 and produced by summing at 24 the colour burst signals of the previous line. The D.C. signal for controlling generator 11 behaves as in the embodiment of Fig. 1. In the embodiment of Fig. 10, the output of the subcarrier generator 7 is, after being switched and alternately phase reversed at 10, phase shifted by 45 degrees. The phase thus alternates between + 45 degrees and + 225 degrees. The colour burst alternates in phase between Œ45 degrees. The phase discrimination 26 is of the type giving zero output for 0 and and 180 degrees phase difference between its input signals, and a maximum positive on negative signal for a phase difference of +90 and -90 degrees respectively. With correct phasing of the switch signal from generator 11, discriminator 26 gives a positive triangular output voltage, which does not affect generator 11 whereas incorrect phasing gives a negative output voltage, causing the generator to stop, leaving the switch 10 in such a position that when the generator 11 restarts, under the control of the positive discriminator output resulting from the applied constant phase subcarries, the correct phasing state is attained.