Patent GB-1266336-A (GB)
IPC: H04N9/093
Filed: 1968-08-13
Abstract: 1,266,336. Automatic frequency control. MARCONI CO. Ltd. 26 June, 1969 [13 Aug., 1968], No. 38701/68. Heading H3A. In a colour television camera of the component camera tube type registration as respects at least the horizontal direction of scanning is effected by comparing changes in the output signals from one component camera tube with changes in the output signals from another and utilizing the resultant comparison to control the scanning in one of the tubes. In a four tube camera luminance signals are applied to terminal Y IN , Fig. 1, and successively delayed half a colouring channel picture element in each of two delay networks DL1, DL2. The output from delay network DL1 is fed to a utilization terminal Y OUT . The output from the delay network DL2 and the input to delay network DL1 are respectively fed over filters BP1, BP2 to the first inputs of two analogue multipliers, e.g. Hall effect devices, AM1, AM2. The second inputs to the multipliers are derived over filter BP3 from the red chrominance channel via input terminal R IN . The outputs from multipliers AMI, AM2 are fed to the two input terminals of a comparator C, e.g. a differential amplifier, the output of which is fed to a further analogue multiplier AM3, the output of which is passed over delay line storage system DS having a delay equal to one line period. The output of delay line DS is recirculated to the second input of multiplier AM3 via an optional low-pass filter LPF and also constitutes the frequencycontrolling output at terminal CO. Where the arrangement comprises only three tubes, one of these is taken as reference and the other two corrected to it (Fig. 2, not shown). Separate correction networks may be used for each colour channel, or a single network employing timedivision, the input to the filter BP3 being switched between the colour channels in succession and a corresponding number of switched delay line storage systems being employed (Fig. 3, not shown). In the arrangement of Fig. 1 the multiplier AM3 may be followed by an analogue to digital converter which feeds via a one-line delay store into a digital generator: the output from this feeds the output terminal and the second input to the multiplier via a digital to analogue converter (Fig. 4, not shown). In a modification of this, the comparator feed into an analogue to digital converter and the following multiplier (DM3) is of digital type, the recirculating loop being digital and the output terminal (CO) fed via a digital to analogue converter (Fig. 5, not shown). The arrangement may be modified for correcting vertical registration: the luminance input terminal Y IN , Fig. 6, then feeds successive delay networks VDL1, VDL2 each giving a delay of one frame. The input and output of delay network VDL1 then feed the two inputs of a differential amplifier VD2, while the input and output of delay network VDL2 are similarly applied to a second differential amplifier VD1. The outputs from differential amplifiers VD1, VD2 feed the first inputs of multipliers VAM1, VAM2, respectively, from which point the arrangement is similar to that of Fig. 1, except that the delay store VDS has delay of one field. The Specification also describes a further modification capable of correcting errors which are both in the horizontal and vertical direction (Fig. 7, not shown). A manually operated switch, e.g. a push-button may be provided whereby any of the arrangements described may be brought into circuit to provide correction when desired.