Nonsaturating Pulse Circuits Using Two Junction Transistors

Junction transistors have been supposed to be too slow for many pulse applications. However, if they are used in a way in which their collector voltage is never permitted to become zero, saturation does not occur and the switching times achieved may be as low as several times the reciprocal of wo, the radian cut-off frequency of ¿. This time will be less than a microsecond for junction triodes presently available. Saturation is prevented through use of breakdown diodes which terminate switching transients by their breakdown. They may also serve other functions in the circuit. A binary counter described has stable points dependent upon the breakdown diodes and passive components, these points being virtually independent of the transistor or its temperature-sensitive Ic0. A class of two-transistor pulse circuits is described including a binary counter which with one kind of junction triode operates at 1.25 mc. Monostable and astable circuits of the same general nature are shown. The pulse requirements for switching of the binary counter are analyzed in some detail. It is shown that the switching charge is the significant quantity and that a crude estimate of the charge required is l/¿0 times the difference in conduction currents of the two transistors in the stable state.