COLOR DISPLAY SCANNING SYSTEM

1,237,732. Cathode-ray tube circuits. TEXAS INSTRUMENTS Inc. 17 Sept., 1968 [10 Oct., 1967], No. 44080/68. Heading H4T. In a colour display system employing a cathode-ray tube of the kind which emits light of different colours in response to impingement of electrons of different energies on the screen such different energies being produced by applying different accelerating voltages to the screen during successive line scans synchronously with the application to a beam current modulating electrode of signals representative of the different colours, the magnitude of the deflection current supplied to the deflection yoke is varied synchronously with the application of the different accelerating voltages to the screen such that the amount of deflection is independent of the beam energy and all lines are therefore of equal length. As shown, sequential pulses from a logic circuit 43 control a gating circuit 41 to pass the colour signals R (red), G (green) and B (blue) sequentially to the cathode 29 of the display tube 13 the screen electrode 20 of which is supplied via a switching circuit 47, also controlled by the pulses from circuit 43, with a high voltage step-waveform (the accelerating voltage) the steps of which occur synchronously with the sequential application of the colour signals to cathode 29. Circuit 43, in addition to supplying the positively going, sequential pulses I, II and III also supplies equivalent, negatively going, pulses IV, V and VI and both sets of pulses are operated on in a level adjusting circuit 54 such that when they are supplied to respective diode summing networks 55, 57, positively going and negatively going staircase (step) waveforms are produced. These waveforms, the levels of the different steps of which are individually adjustable in circuit 54, are then employed to control the conduction of respective NPN and PNP transistors Q2, Q3, which thus control the voltage at the junction of the conventional damper diode D1 and the primary W3 of fly-back transformer T1. This voltage is applied to the horizontal (line) deflection windings W1A, W1B and thus determines the range of the deflection current variation supplied to the windings from the horizontal transformer and transistor Q1 which with diode D1 and the primary W3 of transformer T1 operate in conventional manner. The parameters are such that the maximum range of deflection current variation is operative when the E.H.T. step voltage supplied by the switching circuit is a maxi