Transistor Trigger Circuits

Abstract

This paper concerns trigger and pulse circuits for transistors having emitter-to-collector current gain (such as point-contact units). The circuits are designed to permit reliable operation with transistors which are not completely uniform; they also allow reasonable variation of circuit parameters or bias voltages. Quantitative analysis is made possible by use of simplified circuit theory which divides the nonlinear characteristic of a transistor and its associated feedback and external resistances into quasi-linear regions. By this analysis, one can predict both the type of operation, i.e., monostable, bistable, and astable (oscillatory), and the amplitude and waveform of the output. A basic monostable circuit consists of a single transistor with a resistance in the base lead to provide feedback and a capacitance or, preferably, a transmission line as the emitter load. This circuit can be used to regenerate periodic or nonperiodic pulses, thereby providing a standardized output pulse shape, or to generate single pulses when initiated; it is possible to provide very intense short pulses (up to one ampere) even with transistors of low power-handling ability. The output pulses may be arbitrarily delayed with respect to the input, and amplitude discrimination against noise or spurious signals is also possible. Bistable circuits also use a single transistor with external resistances. It is shown that lack of reliability of previously used bistable single-transistor circuits can be overcome by proper arrangement of circuit parameters and bias supplies and, in some cases, by use of a nonlinear resistance (crystal diode) as the emitter load.