| 摘要 |
1,196,313. Cathode-ray tube deflection circuits. SPERRY RAND CORP. 26 July, 1967 [31 Aug., 1966], No. 34418/67. Heading H4T. The two coils of the push-pull deflection yoke of a cathode-ray tube are connected via a switching arrangement to a single-ended digital type deflection waveform generator such that deflection current flows in one coil to step the beam from one edge of the screen towards the centre and then flows in the other coil to step the beam from the centre towards the opposite edge of the screen. Thus, as shown in the drawing, which is concerned with the X deflection system (the Y deflection system operating in a similar manner) deflection currents of a magnitude determined by binary weighted resistors 30, 32, 34, 36 and forming the analogue equivalent of the condition of n - 1 stages of the X register as the stages are sequentially set flow through either deflection coil 6 or deflection coil 8 of the push-pull yoke in accordance with the state of the nth stage of the register. The latter, in addition to conditioning the AND gates of the logic circuit 28, controls transistors 42 and 46 such that they are alternately cut-off thus causing respective transistors 2 and 4 to conduct alternately and complete the path for the deflection currents from + E to the common point 40. When the nth stage is " set " all the earlier stages are re-set and the register is again incremented in sequence. With this arrangement a count of 1110 or 0001 (considering n = 5) is indicative of zero beam deflection (i.e. the beam is in the centre of the screen) and to avoid this condition a resistor 38 is included to provide a fixed bias current for the deflection coils of such value that the " centre " position when the coils 6 and 8 are respectively operative is one-half of a unit step to the left and to the right respectively of the screen centre. To ensure linearity of deflection the voltage at point 40 is held constant independently of the magnitude of the deflection current by means of transistors 52, 54 the emitters of which are tied to a reference voltage 56 and which operate such that as the deflection current through transistors 2 or 4 increases the voltage drop across their base-to-emitter circuit also tends to increase thus causing the voltage on the bases of transistors 52 or 54 to tend to decrease resulting in an increase in the voltage from sources 48 or 50 on the bases of transistors 2 or 4 respectively so that the voltages on the emitters of the latter are held constant. |
