1212 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



element values. Network resistances which contain both device and 

 external elements are primed. For example, 7^22 = Rii -\- Re -\- Rh , 

 where R22 = Tc -\- r^ . See also references 3 and 5. 



Taking the collector or output resistance, Fig. 2, for example, 



^6(^6 + r™) 



Rin = {Tc + Vb) — 



(1) 



Ri 



rt + n-\- Re 

 can be negative or positive depending upon the relative magnitudes 



of the two terms. Actually, of course, r„ has a phase factor and so is 

 frequency dependent. Frequencies wherein r^ is essentially resistive 

 will be assumed. For negative resistance, r„, must be large, R^ small and 

 Th not too small or else augmented by external resistance. Negative 

 resistance is thus predicted on a small-signal linear basis. The large- 

 signal behavior may be studied experimentally by adding sufficient 

 resistance as Re to the first or positive term to insure stability. This is 

 shown in Fig. 3 with the resultant characteristic. External base re- 

 sistance Rb has been added and R^ is zero. 



Fig. 3 illustrates the pattern of a three- valued characteristic : Regions 

 I and III are portions with positive slope, indicating stable operating 



-20 



-3 -2 -1 



Fig. 3 — Collector large-signal negative resistance characteristic. 



