GB1289963A - - Google Patents

Abstract

1289963 Cathode-ray tube displays EMI Ltd 2 Oct 1969 [11 Oct 1968] 48373/68 Heading H4T In a cathode-ray tube oscilloscope in which the beam is deflected in orthogonal directions at relatively high and low frequencies respectively, video signals are gated to the beam intensity control electrode during short intervals in each of the lower frequency deflection periods the times at which gating occurs being changed progressively in successive periods and further signals to form one or more markers on the display are gated to the intensity control electrode during respective selected high frequency deflection periods in each lower frequency deflection period. The invention is described in connection with an arrangement in which each of a plurality of video signals to be displayed is compared with the sawtooth ramp voltage producing the higher frequency deflection, (vertical line deflection) each video signal "standing-on" a progressively higher shift voltage so that during each period of the sawtooth a series of output voltages for application to the beam intensity control electrode is derived as the amplitude of each video signal coincides with the instantaneous sawtooth amplitude. For satisfactory display of slowly varying signals such as video signals a horizontal (lower frequency) deflection period between, e.g. 0-1 second and 20 seconds, depending on the rate of variation, is required but, because of the decay time of the screen phosphor fixed information such as markers will have faded by the end of the horizontal period and the present invention is concerned with the solution of this difficulty. As shown, the marker signal is produced by comparing a (manually adjustable) reference voltage from source 12 with the horizontal deflection waveform (of about 50 c.p.s.) from source 10, in a computer 11 which supplies via gate 13 a beam bright-up pulse having a duration equal to the period of the vertical (line) deflection generator 4 (of relatively high frequency) during each period of the horizontal deflection waveform so that a marker comprising a vertical line is produced on the display. The video signals each "standing-on" a different shift voltage are supplied from sources 6 1 -6 n to respective comparators 5 1 -5 n in which they are compared with the vertical deflection waveform from source 4 to produce a sequence of output signals via respective gates 7 1 -7 n during each period of the deflection waveform and the outputs from the gates are supplied to the beam intensity control (modulator) via a further gate 9 which is "opened" for the duration of one vertical deflection period at progressively later instants during successive periods of the horizontal deflection wave from source 10 under the control of the output of a comparator 15 supplied with the latter deflection wave and with a sawtooth of long period (e.g. suitable for the display of slowly varying waveforms). More than one marker may be displayed and the oscilloscope 1 may utilize electromagnetic deflection instead of electrostatic deflection.