Patent GB-797378-A (GB)
Title: Improvements in or relating to colour television receivers
IPC: H04N11/14
Filed: 1955-11-11
Abstract: 797,378. Television. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 11, 1955 [Nov. 15, 1954], No. 32301/55. Class 40 (3). In a colour television receiver utilizing a received signal comprising a brightness component and an auxiliary carrier wave modulated by two signals each consisting of a combination of the brightness component with respective signals related to different colour aspects (e.g. the N.T.S.C. system) the whole of the received signal is supplied to two synchronous detectors via individual filter networks, the transmission characteristics of which are such that at least the lower frequencies of the brightness component in the output of each detector which are desired by detection of the auxiliary carrier wave are neutralized by the corresponding frequencies of the brightness component which the detector translates without transformation in frequency. With this arrangement the synchronous detectors supply actual colour signals instead of colour difference signals as in earlier known arrangements. In one of the described embodiments (Fig. 1) the output of the receiver video amplifier 6 which consists of a brightness signal occupying a frequency band o-fa (Fig. 2), and a colour signal comprising an auxiliary carrier wave of frequency fh modulated in phase quadrature by Blue and Red colour difference signals respectively and having frequency limits fb and fr, is supplied to a pair of synchronous detectors 16, 19 via filter networks 15, 18 the response characteristics of which are shown in Fig. 3 and (in full lines) in Fig. 4, respectively. A mathematical analysis of the system shows that the output of 16 and 19 contain actual Blue and Red representative signals respectively together with brightness signals in the frequency range fb-fa and fr-fa respectively. The brightness signals are suppressed by the filters 17, 20 and the resultant Blue and Red signals are then combined in 23 with the complete signal from video amplifier 6 to produce a Green plus brightness signal which is supplied to the green reproducing tube 30. The Blue and Red signals may be supplied to their respective reproducing tubes 32 and 31 either with the restricted bandwidths o-fb and o-fr determined by filters 17 and 20 respectively or suitable brightness components in the high frequency range and derived from video amplifier 6 via filters 35 and 33 may be combined therewith in adders 36 and 34 respectively. Alternatively, the outputs of the detectors 16 and 19 may be supplied to their respective reproducing tubes via filters, the characteristics of which allow desired portions of the high-frequency brightness components to be translated in addition to the Blue and Red components (Fig. 5, not shown). In a further embodiment (Fig. 6, not shown), the Blue and Red signals are derived as already described and the Green signal, together with high-frequency brightness signals is derived directly by synchronous detection at a predetermined phase angle, of the complete output signal from the video detector. Instead of employing three separate reproducing tubes (the component colour images from which are combined in register on a viewing screen) the derived signals may be supplied to individual guns of a tri-gun colour tube or, with correct control of the time sequence, to a three-colour single gun tube.