Design Theory of Junction Transistors

1.1 General Junction transistors have been in commercial production for nearly a year. A detailed understanding of their behavior is necessary both for the increasingly exacting requirements of modern circuit engineering and for the wise design of improved types. Design theory, by relating function to structure, can serve both these needs. The principal object of this paper is to develop in logical fashion a design theory for junction transistors. The product of the development is an equivalent circuit, founded on device physics, which predicts the circuit characteristics of junction devices in a simple and intelligible fashion. Although attention is concentrated on small signal transmission performance, some large signal aspects are also examined. 1271 1272 T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , N O V E M B E R 1953 1.2 Method and Assumptions The usefulness of the junction transistor derives primarily from the flow of holes or electrons across two closely-spaced p-n junctions, one of which is biased in the forward or conducting direction while the other is biased in the reverse or non-conducting direction. Development of design theory begins quite properly with analysis of this mechanism, which is considered, for simplicity, as a problem in the flow of holes and electrons in one dimension, at right angles to the p-n junctions. In the analysis, it is assumed that these carriers are controlled largely by the voltages applied to the junctions and that they move principally by diffusion.