GB1235674A - Improvements in and relating to cathode ray tube display apparatus - Google Patents

Abstract

1,235,674. Cathode-ray tube displays; pulse circuits. NATIONAL RESEARCH DEVELOPMENT CORP. 11 Nov., 1968 [11 Aug., 1967], No. 37104/67. Headings H3P and H4T. In a line raster scanned cathode-ray tube display apparatus of the kind in which a signal to be displayed is compared with a periodic ramp waveform synchronized with the line scan of the tube to produce, on correspondence, a beam bright-up pulse so that the signal to be displayed is formed substantially at right angles to the scan lines by a series of bright dots, a reference pattern or grid is produced by means of a timing signal synchronized with the ramp waveform and including at least one rectangular pulse occurring during the ramp portion of the ramp waveform, the timing signal being utilized as beam bright-up pulses for an area of the tube screen which excludes, for each rectangular pulse, at least one band at right angles to the lines of the raster. The basic display comprising the trace 14, (Fig. 1a), corresponding to a waveform (X), Fig. 1 (c) to be displayed, is produced by "bright-up" of appropriate points 13 in a vertical line scanned raster 12 by means of the arrangement of Fig. 2 in which a differential amplifier 15 is supplied, at its respective inputs, with the display signal (X) and with a sawtooth wave (S) (also Fig. 1 (b)), synchronized with the sawtooth producing the raster 12, the amplifier producing a steep edge in its output signal, at the instants of correspondence between its two input signals. The output signals so produced then trigger a monostable circuit 16 to produce output pulses which are fed to a bright-up circuit 17 to brighten the beam at the required points 13. By using a plurality of amplifiers 15 each fed with a different display signal and with the same sawtooth (S) but with a different relative bias a like plurality of waveforms may be displayed. Fig. 3 shows the elements 15 and 16 of Fig. 2, together with the means for producing the reference pattern comprising a further differential amplifier 21 supplied with the sawtooth (S) and with the output of a bi-stable circuit 22 having as input the output of the amplifier 21. This arrangement operates to cause amplifier 21 to produce a transition between its two output levels (Fig. 4 (c)) when the sawtooth (S), Fig. 4 (a) corresponds to the reference input from resistor 23 such transition then triggering the bi-stable 22 to its other state (Fig. 4 (b)). Thus by adjustment of the reference input derived from the output of the bi-stable 22 the width of the output pulses from 22 may be adjusted. These pulses are then combined with the display bright-up pulses in a mixer 18 and fed to the bright-up circuit 19 to produce a dark band in which the display signal may be positioned and by suitably biasing the sawtooth (S) relative to the reference output from resistor 23 the position of this band may be controlled. The reference pulses controlling the pattern may also be produced by the arrangement of Fig. 5 in which the sawtooth (S) is fed to the positive input 26 of a differential amplifier 24 and to the inverting input 27 of a differential amplifier 25 the inverting input 28 of amplifier 24 receiving a D.C. voltage +Vc which is less than the peak amplitude of the sawtooth waveform and the positive input 29 of amplifier 25 receiving a D.C. voltage- Vd greater than the minimum amplitude of the sawtooth but less than the voltage Vc. The outputs of the amplifier in relation to the sawtooth wave (S) are shown in Fig. 6 (a), (b), (c) and the summed output in Fig. 6 (d).