Patent GB-1154002-A (GB)
Title: Improvements in Colour Television Receivers
Inventor: BROUSMICHE ROGER
IPC: H04N9/24
Filed: 1966-09-14
Abstract: 1,154,002. Colour television. ATELIERS DE CONSTRUCTIONS ELECTRIQUES DE CHARLEROI (A.C.E.C.). 14 Sept., 1966 [15 Sept., 1965] No. 41010/66. Heading H4F. A circuit for a colour television receiver utilizing a beam-indexing cathode ray tube having vertical strips of luminescent material of red, green and blue colour response arranged in the respective sequence BRGRB &c. with index strips emitting ultraviolet light coinciding with the blue strips, comprises two chrominance demodulators 15 and 16, Fig. 1, producing narrow band signals of the form 0À25(R<SP>1</SP>- Y<SP>1</SP>) + 0À59 (B<SP>1</SP> - Y<SP>1</SP>), i.e. ¢ (B<SP>1</SP> - G<SP>1</SP>) and - 0À63(R<SP>1</SP> - Y<SP>1</SP>) + 0À2(B1 - Y<SP>1</SP>), i.e. “(- 2R<SP>1</SP>+B<SP>1</SP>+G<SP>1</SP>) respectively which modulate cos wt. and cos 2 wt. oscillations respectively having zero envelope delay in balanced modulators 22 and 23, w being the frequency of the indexing signal, and are added in amplifier 24 and applied to the grid 3 of tube 1. A luminance demodulator 14 produces a wide band signal Y<SP>1</SP> which is modified by the chrominance signals from demodulators 15 and 16 to form a signal of the form Y<SP>1</SP>+0À37(R<SP>1</SP>- Y<SP>1</SP>)+0À2(B<SP>1</SP>-Y<SP>1</SP>), i.e. “(2R<SP>1</SP>+G<SP>1</SP>+B<SP>1</SP>) at the output of adder amplifier 26 which is applied to the cathode 2 of tube 1. The ultraviolet light emitted from the index strips is detected by photo-electric cell 5 and the resulting variable amplitude current is fed to a filter 19. The output voltage of filter 19 is a sinusoidal oscillation of frequency f equal to the frequency of the fundamental component of the current produced in detector 5. The output voltage is of variable amplitude and when frequency f does not correspond exactly to the natural frequency f 0  of filter 19 the current of detector 5 and the output voltage of filter 19 are out of phase. This phase difference and the amplitude variations are connected in amplitude limiter amplifier 20 comprising a selective transmission device so that the output signal of amplifier 20 is a sinusoidal oscillation cos wt. of frequency w = 2#f identical with that of the fundamental harmonic of the photo-electric current of cell 5 and having zero envelope delay. This output signal is applied to balanced modulator 22 and via frequency doubler 21 to balanced modulator 23. The selective transmission device which ensures zero envelope delay, i.e. constant phase close to a predetermined frequency, comprises a number N (at least one) of independent resonant circuits tuned to the predetermined frequency f o  in which exceeding of the predetermined frequency by carrier f produces an increase in the phase of the transmitted signal, and a number N + 1 of independent resonant circuits tuned to f 0  in which exceeding of f 0  by f produces a decrease in the phase of the transmitted signal, the elements of the resonant circuits being selected so that for slight frequency deviations the phase remains constant. The specification describes in detail the operation of selective transmission devices with reference to Figs. 3, 4 and 5 (not shown). In the embodiment referred to above the red luminescent material employed is less efficient than the other intervals hence two red strips to each blue and green strip. When luminescent materials of equal efficiency are used the strips may be deposited in the sequence two blue strips, red strip, two green strips, red strip, two blue strips &c., the index strips being deposited in the intervals between the blue strips, Fig. 8 (not shown). In this arrangement the output signal of the luminance adder amplifier 26 comprises equal quantities of the components of the primary colours, i.e. <SP>1</SP>/ 3 (R<SP>1</SP>+G<SP>1</SP>+B<SP>1</SP>), while in the first arrangement the quantity of red component was double that of the blue or green component. The contiguous strips of the same colour may be united. The received signals may be according to the N.T.S.C., S.E.C.A.M. or P.A.L. systems.