GB1370426A - Colour television systems - Google Patents

Abstract

1370426 Colour television N FARMER and B WINNING (trading as FARMERS) 26 Nov 1971 [28 Aug 1970 10 March 1971] 57415/73 and 57416/73 Divided out of 1370425 Heading H4F In a colour television receiver using a tube provided with two sets of parallel index electrodes which are connected to a resonant circuit, a chrominance signal containing information as to hue and saturation is controlled in phase by the index signal derived from the tube. The index signal may be at 88 KHz which is multiplied by 5 to derive a signal at 4À43 MHz corresponding to the colour sub-carrier of the PAL system. In one arrangement, Fig. 10 (not shown), two index signals at 4À43 MHz separated in phase by 120 degrees are respectively used to modulate (R-Y) and (B-Y) input signals, the outputs of the modulators being added and fed to the tube as a chrominance drive signal. In a modification (Fig. 11, not shown), the index signal at 4À43 MHz and two orthogonal signals from a reference oscillator at the same frequency are fed to a synchronous detector to derive two signals R1 and R2 which modulate the input signals. The relative amplitudes of R1 and R2 are related to the detection axes and may be used uncorrected if the widths of the phosphor stripes in the tube are unequal for the three colours; alternatively R1 and R2 may be corrected to give symmetrical hues in the output. In another arrangement, Fig. 12, the signals R1 and R2 are equal amplitude quadrature components derived by a frequency doubler 126 from a reference oscillator 125. Since the addition of these signals in unmodulated form results in a signal of 45 degrees phase, a corresponding phase shift is inserted at 127 in the chrominance sub-carrier, before it passes to the synchronous detector 128 which is supplied with reference signals derived from the index circuit 104 via frequency multiplier 107. The units 105 and 106 correct the phase of the index signal in accordance with any non-linearity in the beam scanning velocity. The signal A derived by adding the outputs of modulators 120 and 121 has a phase to hue relationship similar to the transmitted signal but suitable adjustment may be made to R1 and R2 to give symmetrical hues. When the chrominance signal is used to vary the scanning speed of the beam the saturation level is obtained by comparing the levels of the complementary hue in the luminance signal and in the sub-carrier. For this purpose (Fig. 13, not shown) the sub-carrier is synchronously detected and fed to a matrix to produce the matrixed level of the complementary hue, that is the sum-[(R-Y)-(B-Y)-(G-Y)] which is fed through a saturation correction circuit to the adder 108; a correction is also fed to the luminance drive 111.