THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOLUME XXXII NOVEMBER 1953 number 6 



Copyright, 196S, American Telephone and Telegraph Company 



Design Theory of Junction Transistors 



By J. M. EARLY 



(Manuscript received September 8, 1953) ^ 



The small signal ac transmission characteristics of junction transistors 

 are derived from physical structure and bias conditions. Effects of minority 

 carrier flow and of depletion layer capacitances are analyzed for a one 

 dimensional model. The ohmic spreading resistance of the base region of a 

 three dimensional model is then approximated. Short circuit admittances 

 representing minority carrier flow, depletion layer capacitances, and ohmic 

 base resistance elements are then combined into an equivalent circuit. Theo- 

 retical calculations are compared to observations for two typical designs. 



LO INTRODUCTION 



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. 



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