Patent GB-1177717-A (GB)
Title: Sinusoidal Time Base Systems
IPC: G01R13/24
Filed: 1967-11-22
Abstract: 1,177,717. Cathode-ray tube circuits; semiconductor pulse circuits. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 22 Nov., 1967 [2 Dec., 1966], No. 53258/67. Headings H3T and H4T. A time-base generator for a push-pull cathode-ray tube deflection system comprises two oscillators of like frequency generating damped sinusoidal waves each of which is triggered at different instants so that the output waves are of opposite phase. Thus as shown in Fig. 2, the trigger signal, comprising a negatively going step voltage 260, synchronized with the signal to be displayed as a deflection modulation of the time-base, is applied directly to the control grid of valve 211 in one oscillator 210 and after delay in a device 240 to the control grid of valve 221 in the second oscillator 220 both valves being normally conducting and the delay introduced by device 240 being equal to one-half period of the damped sinusoidal waves produced across similar tuned circuits 214, 215 and 224, 225. The latter circuits are connected to respective ones of the deflection plates 231 the amplitude of the waves being such that the substantially linear portions 310, 320 (Fig. 3 A and C) produce the actual beam deflection. This Figure also shows at B and D the two trigger signals displaced by the halfperiod time td. Since, due to the waves being damped, the amplitude of the second half-cycle of the wave A (Fig. 3) will be less than that of the first half-cycle of the wave C (Fig. 3) the slopes of the portion 310 will be less than the slope of the portion 320 and to compensate for this either the frequency or the amplitude of one of the waves may be adjusted so that the product of amplitude and angular frequency is the same for both waves. For adjusting the amplitude either the voltage of source 226 may be made slightly lower than that of source 216 or the amplitude of the trigger signal applied to valve 221 made lower than that applied to valve 211. Alternatively the triode valves may be replaced by pentodes and the adjustment effected by controlling the potential of the second grid. Fig. 4 shows an alternative arrangement which, by removing the heater-cathode capacitance of Fig. 2, is suitable for operation at frequencies of up to several thousand megacycles. In this arrangement the valves are normally non-conducting and capacitors 414, 434 having capacitances much larger than the frequency determining capacitors 413, 433 are connected in series with the coils 415, 435. When the positively going trigger pulse 470 is applied a substantial part of the anode currents is supplied by capacitors 414, 434 the resistors 416, 436 having a comparatively high value e.g. 5 K.ohms. The delay device 240 of Fig. 2 or 490 of Fig. 4 may take the form of a monostable multivibrator or of a coaxial line. Alternatively the step recovery diode circuit of Fig. 5A in which an input pulse 504 (also a Fig. 5B) produces an output pulse 505 (also b, Fig. 5B) after a delay td determined by the charge on the junction boundary of the diode 503 may be employed. This charge and consequently the delay may be adjusted by varying resistor 501.