1298 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



dimensional analysis of ohmic base region spreading resistance. The 

 resulting equivalent circuit has characteristics in good agreement Avith 

 experimental observations. In particular, collector capacitance, ohmic 

 base region spreading resistance and the current transmission three db 

 cutoff frequency may be computed with fair accuracy. The low fre- 

 quency values of the common base hybrid parameters may also be cal- 

 culated, but neglect of surface recombination and surface leakage re- 

 sults in serious errors in the short circuit current transmission factor h^i 

 and the open circuit collector conductance /i22 . The deviations of these 

 two parameters from calculated values are, however, both reasonable 

 and mutually consistent. The ohmic base layer spreading resistance, 

 which is the only base resistance of importance at high frequencies, is very 

 often much smaller than the low frequency base resistance appearing in 

 an equivalent tee network. 



Qualitative agreement of theory and measurement is excellent. The 

 variation of all parameters with emitter current and collector voltage 

 is within a few per cent that predicted from theory, 



6£ State of the Art 



Since this paper was deliberately limited in scope, it is pertinent 

 both to review its objectives and to point out significant omissions. The 

 principal objective sought was presentation of small signal transmission 

 design theory. No attempt was made to give a simple explanation of 

 the junction transistor, relating both its large signal and its transmis- 

 sion characteristics to simple physical assumptions. While the design 

 theory presented consolidates in one place some already published in- 

 formation, much remains to be done in assembling and integrating such 

 knowledge from its present widely scattered locations. 



In addition there exists a more detailed understanding of junction 

 transistor characteristics than can be found in the literature. For ex- 

 ample, units are found occasionally with negative hu • This is a result 

 of an easily modulated high resistance between base region and base 

 contact (high jLt6c). Publication of such information can reduce by a few 

 db the amount of head-scratching done by production engineers. 



Other phenomena for which explanations have been developed are 

 surface recombination and high carrier injection level effects. Despite 

 this, much work remains to be done. 



ACKNOWLEDGEMENTS 



The general point of view taken here has been much influenced by 

 discussions with J. A. Morton. Comments and criticisms by R. M. 

 Ryder have been particularly helpful in the preparation of this material. 



