Solution of a Transistor Transient Response Problem*

is desirable ‘in many k.J high-frequency and switching applications of transistors. A single transient response measurement can, in principle, yield frequency response information over a range of frequencies of width determined by the short-time resolution of the transient response measurement and the duration of the measurement. Further, measurement of the response to a unit step or unit impulse (delta function) of voltage or current applied at the input of the device allows its response to any other driving curve-shape to be calculated.’ Calculation of transistor transient response is complicated by the fact that a transistor is a distributed active element requiring an infinite number of passive elements (resistances and capacitances) and a finite number of current and/or voltage generators for its complete description by means of an equivalent circuit. Even transistor equivalent circuits having a finite number of elements can be excessively complicated.’ The situation is further complicated because transistors are bilateral instead of unilateral elements; hence, changes in the output circuit are reflected in the input and vice versa. The present work was undertaken to investigate the utility and practicality of calculating transistor transient response by bypassing both the equivalent-circuit transistor representation with an infinite number of elements or an approximate form of it with a finite number of elements. Transient response is calculated by dealing directly with the meromorphic functions arising from the solution of the small-signal linearized differential equations pertaining to transistor operation.3 Moll has treated the large-signal transient response of junction transistors by approximate methods of accuracy sufficient for many purposes.4 In addition, he has calculated the small-signal transient response by making use of the usual approximate expression for the short-circuit current transfer ratio CY. For a single mode of operation, the present work shows to what order of accuracy this approximation is valid and also yields more accurate results suitable for a quick and approximate oscilloscope determination of transistor