Patent GB-790407-A (GB)
Title: Matrixing apparatus for color-signal translating system
IPC: H04N9/67
Filed: 1954-09-06
Abstract: 790,407. Television. HAZELTINE CORPORATION. Sept. 6, 1954 [Oct. 6, 1953], No. 25780/54. Class 40 (3). A matrixing arrangement for a colour television receiver utilizing a N.T.S.C. type of signal comprises means for developing from the received chrominance modulated sub-carrier wave a pair of waves of sub-carrier frequency modulated, at the same phase angle, by signals representative, respectively, of the red, (R-Y), and blue, (B-Y), colour difference signals. In one embodiment (Fig. 1), the received colour sub-carrier (supplied by amplifier 18) is fed to a first resonant circuit M including a pair of coupled circuits 41, 43 and to a second resonant circuit 42, the former circuits being damped by resistors to have a pass-band of approximately 2.3-4.9 mc/s. (i.e. to pass the 3.6 mc/s. sub-carrier together with the lower side-band (1.3 mc/s.)) and an upper side-band of approximately 0.6 mc/s. of the I modulation component of the sub-carrier and the latter circuit being damped to pass a band of 3-4.2 mc/s. (i.e. the 3.6 mc/s. sub-carrier and the double side-band Q modulation components). The signal developed across circuit 43 (which is phase-shifted by 90 degrees because of the coupled circuits 41, 43) has each I modulation component in phase with the phase point of each Q modulation component of the signal developed across circuit 42 and by combining the latter signal with the former signal by means of connection 45, the transfer impedances of the circuits 41, 43 and 42 and the position of the " tap " connection 45 being suitably adjusted to satisfy the requirement R-Y=0.62Q+0.96I and B-Y= 1.70Q-1.10I, the desired R-Y and B-Y signals are developed as 0 degrees phase modulation of the sub-carrier frequency waves at terminals 80 and 81 respectively. The R-Y and B-Y modulation components are then derived by means of the synchronous detectors 46, 47 respectively, a reference wave at subcarrier frequency (from generator 27 and circuit 54) being employed as the heterodyning signal, and the detected components combined in adding circuits 48R and 48B with the brightness signal Y (supplied by amplifier 16) and fed to the appropriate control electrodes of the picture reproducing tube 17 in O.C. restorers 49R and 49B respectively. The green colour difference signal which is defined as G-Y= - 0.51 (R-Y) - 0.19 (B-Y) is then derived by combining these proportions of the outputs of adders 48R and 48B (by suitably proportioning the cathode circuit resistors 72, 73) this signal then being combined in adder 48G with the Y signal and fed via D.C. restorer 49G to the " green " electrode of tube 17. In order to ensure that the delay introduced by the comparatively wide band circuit M is the same as that of the narrower band circuit 42 an additional tuned circuit may be coupled between the circuits 41, 43 to increase the delay thereof (Fig. 3, not shown). Fig. 4, shows a second embodiment in which the G-Y signal is developed in the same manner as the R-Y and B-Y signals are developed in the arrangement of Fig. 1 by means of a coil 92 tightly coupled to the circuit 443 (equivalent to circuit 43, Fig. 1) the signal induced in this coil being combined with the signal in circuit 442 (equivalent to circuit 42, Fig. 1) in the correct polarity and amplitude to develop the G-Y signal as an 0 degrees phase modulation of the sub-carrier wave input to the synchronous detector 95. In this embodiment a - I signal is developed in coil 92 and to provide the - Q signal necessary to produce the green colour difference signal defined by G-Y= - 0.65 Q - 0.28 I an intermediate point of circuit 442 is earthed at a position such that the desired Q signal is available for connection to coil 92. In a modification of this arrangement the G-Y signal is obtained by connecting the synchronous detector 95 to a point on circuit 543 (Fig. 5) intermediate the end connected to synchronous detector 46 and the point of connection to circuit 42 and since this provides a - (G-Y) signal the desired G-Y signal is derived by supplying detector 95 with a reference wave (at sub-carrier frequency) from circuit 554 which is 180 degrees out-of-phase with that of the reference wave supplied to detectors 46 and 47. Specification 784,055 is referred to.