1220 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



creation of optimized designs and, second, in the maintainance of 

 proper parameter controls in manufacture. Finally, the more detailed 

 the understanding, the more likely will be the creation of new circuits 

 and new devices. 



A complete analytical treatment will not be attempted here; con- 

 sideration will be limited to the equilibrium case and in particular to 

 the simple circuits described. 



II — Analysis 



In order to deal analytically with circuits and devices it is necessary 

 to have analytic expressions for the device characteristics. For small 

 signal analysis this is relatively easy. In large signal applications, as in 

 switching, the situation is not so simple. The problems arise because 

 of the high degree of nonlinearity wherein the simplifying assumptions 

 employed in small signal analysis are by no means valid. Further, it is 

 desirable to retain dc terms in many cases. 



The method to be employed here is the so called broken-line method 

 which involve^ approximating the negative resistance characteristic by 

 three intersecting straight lines. The assumption is made that there are 

 three distinct regions of operation in each of which the device is sepa- 

 rately linear, but involving different parameter values for each region. 



The approximation is shown in Fig. 12. The assumption that the 

 negative resistance characteristic can be simulated by three straight 

 lines is reasonably valid for gross considerations; for fine detail near the 



<:^ 



R,N 



R,N = rb+r- + 



'€ I 'm If ; 

 Rc+Pf^rc-rr, 



Tb 

 VW 



RiN = rb+rc-Tm + 



Tc (fm-r-c) 



Rf+re+ Tc-rpn 

 Fig. 10 — -Base driving point resistances. 



