DESIGN THEORY OF JUNCTION TRANSISTORS 1297 



cutoff" frequency calculated here. The difference is believed to be the 

 result of the fact that holes emitted around the emitter periphery have 

 much longer transit paths than do those emitted into the region directly 

 between the electrodes and consequently reduce significantly the cur- 

 rent cutoff frequency. 



The serious discrepancy in rb'2 is probably the result of the r^'i cal- 

 culation being very pessimistic because of neglect of peripheral emission 

 effects and of W2 and w^ being somewhat smaller than the assumed values. 

 Again it can be seen that the equivalent tee base resistance n = hn/h^^ 

 is 375 ohms, nearly seven times the high frequency resistance of 55 ohms 



5.4 Qualitative Comparison 



As might be expected, the qualitative agreement between theory and 

 observation is better than the quantitative. For example, Cc , /i22 , and 

 hi2 vary approximately as (Vc)~^^^ in fused junction units. Alpha cutoff 

 frequency increases as collector reverse bias is increased — a natural 

 result of the narrowing of the base region. The qualitative discrepancies 

 that are found are usually associated with large experimental deviations 

 from the assumptions of the analysis. 



5.5 Review of Design Calculations 



Numerical analysis of both drawn junction and fused junction tran- 

 sistors has shown rather good agreement of theory and experiment. 

 It is necessary, however, to modify some of the results empirically 

 because of lack of full understanding of some effects, such as leakage 

 and surface recombination. 



Qualitative agreement of measurements and theory is, of course, 

 much better than the quantitative correlation. For example, the de- 

 pendence of all of the parameters on emitter current and collector voltage 

 is almost exactly that expected from theory. Some of the dependence 

 on emitter currents involves high carrier injection level theory which 

 has been omitted from this study. 



6.0 SUMMARY 



6.1 Transmission Theory 



Design theory of the small signal transmission parameters of junc- 

 tion transistors is relatively complete. 



A one-dimensional analysis of minority carrier diffusion currents in 

 terms of short circuit admittances has been combined with a similar 

 analysis of depletion layer capacitances and an approximate three- 



