Patent GB-1074805-A (GB)
Title: Color video signal generating apparatus
IPC: G02B5/20
Filed: 1963-12-23
Abstract: 1,074,805. Colour television. NIPPON COLUMBIA KABUSHIKI KAISHA. Dec. 23, 1963 [Dec. 27, 1962], No. 50663/63. Heading H4F. A colour video signal generating apparatus for producing a plurality of continuous video signals of different colours comprises one image pick-up tube 1101, Fig. 11, with a photoelectric conversion layer 1102 and a filter 1103 which consists of filters 1103a and 1103b, Fig. 12, superimposed, the filters having strip elements 1103W and 1103W<SP>1</SP> which pass all the colours from an object, and strip elements 1103R and 1103B which cut off the red and blue colours respectively from an object. The strips of one filter may be arranged parallel or oblique to the strips of the other filter. The camera output video signal obtained at the output terminal 1110C of the video amplifier 1106, shown in Fig. 13a, comprises a non- modulated signal E( R ), E( G ), E (B) , and two ampli. tude modulated signals having side bands and fundamental wave frequencies f B  and f R , these modulated signals being produced by the periodic intersection of the colours blue and red by the strip filter elements, the-frequencies of the upper limits of the information being #f B  and αf R  (α#0À5; ##0À5). The cut-off frequency f c  of the load impedance or the video amplifier 1106 including the impedance is arranged to be f c  = (1 + α)f R  and the cut-off frequency (1 + #)f B  is determined according to the cut-off frequency (1-α)f R  such that the modulated signals are substantially symmetrical with their crossover point as the centre. The output signal of band-pass filter 1107R which has a pass-band of (f R αf R ) is shown in Fig. 13b. Fig. 13c shows the output signal of adder 1108BG which adds the signals of Figs. 13a and 13b with inverse polarities. The output signal of band-pass filter 1107B which has a pass-band (f B #f B ) is shown in Fig. 13d. Fig. 13e shows the output signal of adder 1108G which adds the signals of Figs. 13c and 13d with inverse polarities. 1109R and 1109B are demodulators and Figs. 13f and 13g show the red and blue video signals obtained at output terminals 1110aR and 1110aB and by linear coupling of these signals with the output signal at terminal 1110b the green video signal may be obtained. The carriers of f R  and f B  further produce beat components currents of (f R f B ), the component (f R  +f B ) is outside the band of the video amplifier 1106 but the component ( f R  - f B ) is mixed into the output signal of adder 1108G. To remove the beat component (f R  - f B ), beat frequency generator 1111 couples the output signals of the band-pass filters 1107R and 1107B non-linearly and produces a beat component (f R  -f B ) which is mixed into the output of adder 1108G in antiphase in adder 1112 and thus removes the unwanted beat component. The demodulation characteristic may be improved by uniformly projecting through the filter 1103 a certain amount of the colours red and blue or a colour including the two to the photo-electro conversion layer. By reducing substantially by half the transmission factor of the entire surface of the filter for the colours which have not been intercepted in strips, camera output video signals of all the colours may be obtained in the form of non- modulated video signals without using the linear coupling of the outputs of the respective terminals. In a further embodiment, Fig. 14, not shown, only colour red is obtained in the above manner the colour blue being obtained by inserting a semi-reflecting mirror in front of the strip filter followed by an ordinary filter which permits colour blue to pass therethrough, and a second image pick-up tube. The Specification includes a mathematical analysis of an embodiment described with reference to Fig. 1, not shown, in which only one colour video signal is obtained in the above manner described with reference to Fig. 11, the filter only having one set of strips. To reduce interference signals which are present in signals before they pass through the band-pass filters, gate circuits are included in the circuit which are driven by the separated carriers f R  and f B  at their frequencies to gate the output of the video amplifier, Figs. 7 and 8, not shown. In addition the separated carrier may be frequencydiscriminated (713) and.coupled to the scanning period generator of the image pick-up tube to control its scanning speed. In a further embodiment, Figs. 15 and 16, not shown, a filter is used such that f R  and f B  are the same, the carriers being separated by means of gate circuits which are switched at the desired phases.