GB624022A - Improvements in or relating to time bases - Google Patents

Abstract

624,022. Saw-tooth generating circuits. CINEMA-TELEVISION, Ltd., and SOWERBY, J. M. Dec. 16, 1946, No. 37022. [Class 40 (vi)] In a voltage waveform generating circuit of the type which alternates between two distinct states, such as those giving rise to the scan and flyback in the case of a saw-tooth generator, the amplitude of the waveform is stabilized by preventing the instantaneous value of the waveform from exceeding that of a reference voltage. The Figure shows a Puckle type hard valve saw-tooth generator comprising valves 4 and 5 and a main capacitor 1, the positive and negative excursions of the lower plate of which are respectively limited by circuits comprising valves 17 and 6. In the latter circuit current through the right-hand side of cathode-coupled double triode 6 falls with the potential of point P. When it falls below a value determined by the bias EA on the right-hand side, the left-hand side conducts, applying a negative pulse to the suppressor grid of the phasereversing pentode 5 of the time-base, thus starting the flyback and causing the potential of point P to rise until the time base reverts to the scan condition or until rise in potential has been sufficient to cause the left-hand side of double triode 17 to conduct as well as the right, which is normally conducting, so that the potential across the common cathode resistor rises causing valve 16 to conduct and lower the grid potential of the discharging valve 4 of the time base, blocking it and thus initiating the scan. The value of potential at P when this occurs is determined by the voltage across resistor 12 and hence by the bias EB on the right-hand side of valve 17. Synchronization is effected by injecting a suitable waveform into the circuits of valves 6 and 17, or on to the guide valve 4 or valve 5.