DESIGN THEORY OF JUNCTION TRANSISTORS 



1279 



Fig. 2(a) shows a structure for which the flow paths to the base con- 

 tact are substantially the same for all components of the base current. 

 Both the collector capacitance current and the diffusion loss base 

 current enter the base region substantially uniformly over the entire 

 area and follow the same path to the base contact. In Fig. 2(b) these two 

 currents have quite different flowpaths and the associated feedback 

 resistances are likewise very different. The general method of calcula- 

 tion is, however, the same in both cases. 



Another important effect is associated with modulation of the dc 

 voltage drop in the base region. The base current ordinarily has a dc 

 as well as an ac component, and a dc voltage drop occurs between the 

 base contact and the emitter junction. Since the base region thickness 

 changes when collector voltage changes, the dc resistance of the base 

 region is modulated by the collector voltage, producing a modulation 

 of the dc voltage between base contact and emitter.* This effect is most 

 easily represented by an ac voltage generator in series with the base 



EMITTER 



BASE 



COLLECTOR 



SECTION A -A 



EMITTER 



COLLECTOR 



Fig. 2 — p-n-p transistor structures. 



This effect was first pointed out by J. N. Shive. 



