GB815999A - Improvements in or relating to scaling circuits - Google Patents

Abstract

815,999. Transistor and thermionic discharge tube two-stable state circuits. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. July 5, 1957 [July 17, 1956], No. 22162/56. Class 40 (6). [Also in Group XIX] In a circuit comprising first and second electronic switching devices, which are transistors or thermionic discharge tubes, interconnected so that when one is conducting the other is non-conducting, the emitters or cathodes are directly connected, with resistive coupling between the collector or anode of the first device and the base or grid of the second device, and a connection between the base or grid of the second device and a fixed potential. Input pulses applied to the emitters or cathodes render both devices non-conducting, bias on the base or control grid of the second device tending to cause it to conduct at the end of the pulse, an inductor in the collector or anode circuit of the second device being A.C. coupled to the base or grid of the first device to overcome the bias when the second device is switched from its conducting state. Where a number of stages are cascaded the A.C. coupling may be between the second device of a later stage and the base or grid of the first device of an earlier stage (see Group XIX). Transistors J1, J2 are cross-coupled by the common emitter resistor Rl and the resistors R3, R4 and R2. When transistor J1 is fully conductive, the collector potential is near earth so that the base of transistor J2 is carried positive and that transistor is non-conducting. Negative-going input pulses applied over diode D2 cause both transistors to cut-off and the base potential of transistor J2 falls until caught by diode D1 conducting. As the base of transistor J2 is lower in potential than that of transistor J1, transistor J2 conducts at the end of the input pulse. Since the base and emitter of transistor J2 are lower than earth the transistor J1 is cut off at the emitter and remains non-conducting until the next input pulse. Transistor J2 then cuts off at the emitter but due to the collector current flowing through the inductor L1, a negative pulse occurs which is fed over the secondary L2 to lower the base potential of transistor J1. Assuming the " memory " pulse is longer than the input pulse, transistor J1 is rendered conducting when the input pulse ceases the base potential is lower than that of transistor J2. The inductor L1 is critically damped by resistor R5 to give a single negative overshoot, and in a modification, Fig. 3, (not shown), the inductor L1 is connected to a shortcircuited delay line. In order to feed further binary stages a tertiary winding may be associated with the transformer L1, L2. Since the memory pulse from the transformer must be longer than the input pulse, the pulses from transistors in succeeding stages would have to be of increasing length. This may be avoided by coupling the stages over diodes having the characteristics shown in Fig. 4 with the result that the input pulse is fed to the emitter in the form shown in Fig. 5. An output may be derived from transistor J2 by employing a small resistor in the collector lead, and an output taken directly from the collector of transistor J1, Figs. 6 and 7 (not shown). Alternatively, an output may be derived from the connection to the diode D1, Fig. 8 (not shown), the anode of the diode being connected to the base of a third transistor, the output then appearing at the collector. Thermionic discharge tube circuit.-Thermionic discharge tubes V1, V2 are cross-coupled over the common cathode resistor R8 and the resistors R9, R10 and R 11. A positiveincoming pulse applied over diode V3 to the cathode causes the normally conducting tube V1 to cut off with the result that the grid potential of tube V2 tends to rise although limited by diode V5 and resistor R13, At the end of the input pulse tube V2 conducts in preference to tube V1 due to the higher grid potential. In order to reset the circuit a connection is taken from the transformer T2 to the grid of discharge tube V1 so that when the next input pulse causes the tube V2 to be rendered non-conducting a positive-going pulse is fed to the grid of tube V1. When the pulse ceases, tube V1 conducts rather than tube V2 due to the higher grid potential. A number of the circuits may be cascaded to form a counter (see Group XIX).