Patent GB-748060-A (GB)
Title: Matrixing apparatus for a color-television system
IPC: H04N9/66
Filed: 1954-05-12
Abstract: 748,060. Television. HAZELTINE CORPORATION. May 12, 1954 [June 5, 1953], No. 13923/54. Class 40 (3). Matrixing apparatus for a colour television system for developing from a pair of signals individually representative of different components of the colour of a televised object (e.g. the " I " and " Q " signals in the N.T.S.C. system) signals representative of other different components of the colour of the image (e.g. the R-Y, B-Y and G-Y colour-difference signals in the N.T.S.C. system) comprises an impedance network supplied with both pairs of signals and including three load circuits, the impedances of which are so proportioned and which are so interconnected that currents representative of the desired signals flow through the different load circuits. In one embodiment (Fig. 1), which is concerned with a colour television receiver designed to reproduce a colour picture from a composite colour signal of the type employed in the N.T.S.C. system, i.e. a signal comprising a carrier wave modulated by the total luminance signal (Y) of the object and a sub-carrier wave modulated in phase-quadrature by the colour-signals (I) and (Q), the impedance network 52 comprises three load circuits 53g, 53b, 53r, having a common terminal 54 and supplied via terminals 49, 50 and 49, 51 with the Q and I signals respectively with such polarity that currents representative of the colour difference signals G-Y, B-Y and R-Y flow in the resistors 55g, 55b, 55r, respectively. The actual colour difference signals are then taken from appropriate tapping-points on resistors 55g, 55b, 55s and fed to separate modulating grids, via terminals 31, 32, 33, of the tricolour picture tube 14 to the cathodes of which the luminance signal Y (derived from video amplifier 13) is supplied. In one example of a television system for which the present invention is suitable the colour difference signals comprise proportions of the I and Q signals as follows: R-Y=0.96 I + 0.62 Q; B-Y= - 1.11 I + 1.70 Q; G-Y=-0.27 1-0.65 Q and to derive such signals at terminals 31, 32 and 33 respectively, in addition to giving predetermined relative values to the whole and the tapped portions of the load resistors 55g, 55b, 55r, the input I and Q signals which are derived with predetermined polarity by means of the synchronous detectors 43, 44 and 40, 41 respectively are made to have relative values of 3.73 and 4.34 respectively by selecting the tapping points 48, 48 on the secondary winding of transformer 46 which supplies the colour sub-carrier to the detectors to give this ratio (3.73/4.34) of voltage relative to the voltage across the whole winding (terminals 47, 47). In a second embodiment (Fig. 3), allowing an increase in gain of the I and Q signals the latter signals are developed with like polarity in a detector unit 30 which supplies the I signals via a 0-1.5 Me. L.P.F. 61 and phase inverter 62 to the control grid of valve 63 and the Q signals via a 0-500 kc. L.P.F. to the control grid of valve 65 so that +I signals are developed in the anode circuit and -I signals in the cathode circuit of valve 63 and - Q signals in the anode and +Q signals in the cathode circuit of valve 65. With this arrangement currents representative of the G-Y, R-Y and B-Y colour difference signals flow in resistors 76, 79 and 74 respectively, the G-Y and R-Y signals being derived via terminals 31 and 33 respectively and the B-Y signal in the form - (B-Y) from terminals 32 in the tapped load resistor 78 and phase-inverter amplifier 71. In this embodiment the proportions of the I and Q signals which are combined to produce the colour . difference signals are determined by the gain of the valves 63, 65 and 71 and the resistors 74, 75, 76, 78 and 79. In a modification of the embodiment of Fig. 3, the B-Y signal is derived from the common cathode resistor 74 (valves 63 and 65 having individual cathode load resistors) and supplied to terminals 32 via a cathode-driven earthed grid triode (Fig. 4, not shown). Fig. 5 shows a further embodiment in which the output of video amplifier 13 (Fig. 1) is fed via terminals 91 to two band-pass filters 80, 81, the signals supplied to the latter being shifted in phase by 90 degrees by means of phase shifter 525 and the output of the filters supplying the synchronous detectors 40, 41 and 43, 44, via transformers 42 and 45, the turns ratio of which are as 4.35: 3.73 respectively. Colour difference signals are then derived via terminals 31, 32, 32 as in Fig. 1. In this manner the information carried by the I and Q signals is more efficiently utilized since the I signals (which have a wider band than the Q signals) and the Q signals are translated through channels (filters 81 and 80 respectively) which have pass-bands corresponding to the band widths of the transmitted I and Q signals.