Patent GB-1030698-A (GB)
Title: Improvements relating to colour television receivers
Inventor: JAMES IVANHOE JOHN PENFORD
IPC: H04N9/22
Filed: 1962-03-10
Abstract: 1,030,698. Colour television. ELECTRICAL & MUSICAL INDUSTRIES Ltd. March 6, 1963 [March 10, 1962], No. 9329/62. Addition to 1,021,092. Heading H4F. The invention relates to a receiver for use with a transmission consisting of a luminance signal Ey# = (0.30 ER + À59 EG + 0À11 E B )# together with colour difference signals E R # -E Y # and E B # - E Y # modulated in phase quadrature on a sub-carrier wave, and is concerned with eliminating an error in the reproduced colour which arises in the derivation of the green colour difference signal which exceeds the correct value E G #-E Y # by an amount equal to 1.7 (E Y # - E Y <SP>1</SP>), where Ey<SP>1</SP> corresponds to the conventional luminance signal and equals 0À30 E R # + 0À59 E G # + 0À11 E B #. The received signal is applied to a single-gun cathode-ray tube which reproduces the colours in a sequence and results in the green components being too bright. In carrying out the invention a correcting waveform cyclic at the colour sequence is also applied to modulate the tube and is given a phase such that the green light output is reduced relative to the red and blue light outputs. In contrast with the parent Specification, where the waveform amplitude is made to be proportional to saturation, in the present invention, the amplitude of the correcting waveform is controlled in dependence upon the product of luminance and saturation. In a first embodiment, Figs. 1 and 2 (not shown), the received signal is applied to a cathode-ray tube with a screen formed of a repeating sequence of vertical colour phosphors. The luminance signal is converted to an equienergy type of signal with the aid of a correction signal derived from the sub-carrier wave by synchronous detection at a specified phase angle, and the sub-carrier wave itself is converted to symmetrical form with the aid of sub-carrier modifier driven by a reference oscillation at twice the sub-carrier frequency. The cathoderay beam is gated by a signal at the third harmonic of the sub-carrier frequency to ensure beam impingement only at the centre of each phosphor stripe. In carrying out the invention, the cathode-ray beam is also modulated by a sinusoidal signal at sub-carrier frequency, the phase of the signal being selected so that negative peaks coincide with the scanning of the green stripes and the amplitude of the signal being controlled by passing it through an amplifier the gain of which is regulated by a signal derived by rectifying the received subcarrier wave. In a second embodiment, Fig. 3 (not shown), the received signal is applied to a cathode-ray tube with horizontal phosphor strips which is operated in either a continuous colour sequence (R G B R G &c.) or a reversing colour sequence (R G B G R &c.). In this second mode of operation the gating signal is at the sixth harmonic of the sub-carrier frequency and the correcting signal is at the second harmonic of the sub-carrier frequency. Reference is made to a receiver for operation with a sub-carrier signal which is of a suitable form not to require conversion to symmetrical form in the receiver.