1288 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



For the structure of Fig. 2(a), all current components are introduced 

 into the base layer relatively uniformly over its area. The dc component 

 and the (1 — a) or diffusion component originate within the layer vol- 

 ume, while the collector capacitance current is introduced from the 

 collector side of the layer, but this difference is of little consequence. The 

 transverse current density is largest at the base contact and diminishes 

 monotonically to zero at the layer edge opposite the contact. The feed- 

 back voltage to the emitter junction consequently rises most rapidly 

 close to the contact and becomes nearly constant as the opposite side 

 o{ the base region is reached. 



For the structure of Fig. 2(b), significant differences in flow paths are 

 apparent. The transverse current densities are zero at the center of the 

 unit and rise out to the edge of the emitter. Here the dc and (1 — a) com- 

 ponents of current density begin to decrease because of the increasing 

 cross-section of the base region, while the collector capacitance compo- 

 nents continues to increase because of the additional contribution from 

 the larger collector area. All components decrease in density beyond the 

 collector circumference. It is apparent that two feedback resistances 

 are required to describe the separate electronic functions in this case. 



4.3 Effective Feedback Resistances 



The resistance effects of importance are not the series resistances to 

 the flow of the various current components through the base region to 

 the base contact, but rather the feedback resistances defined by the 

 quotient of the average base contact to emitter junction voltage by the 

 current component producing the voltage. The calculations necessary to 

 determine such resistances are detailed in Appendix II. 



For the structure of Fig. 2(a), a single equivalent resistance given by 



\w/ w 



is sufficient. Both (1 — a) and Cc current components pass through this 

 resistance en route to the base terminal. In the structure of Fig. 2(b), 

 the (1 — a) or diffusion current component has an effective feedback 

 resistance off 



while the collector capacitance component of base current has associated 



t This value of r^j is an upper bound, since the assumptions are pessimistic. 



