530 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1954 



Table I — Transistor Designs 



* First value calculated by Equation (9) ; second value is for diffusion through 

 base n-region only (i.e., t^ = 0). 



and materials were assumed and electrical parameters were calculated 

 from them by the Equations (1) to (11). MobiHties measured for low 

 resistivities by M. B. Prince^ were used in the calculations. 



Figures of Merit 



The last row of Table I gives (V25r6'Cc)^'^ which was discussed 

 previously as a gain-bandwidth figure of merit for a broad band common 

 emitter amplifier. It is also related to the maximum frequency at which 

 reliable oscillations may be obtained. The figure of merit WaTbCc is the 

 open circuit voltage feedback ratio at the alpha cutoff frequency and 

 gives some indication of the balance between the two time constants, 

 1/coa and rifCc . It is also approximately the ratio of input impedance to 

 output impedance in a common emitter broadband amplifier at high 

 frequencies. 



Comments 



It should be noted that the emitter depletion layer capacitance is 

 significant in all the p-n-i-p designs and that barrier transit time reduces 

 alpha cutoff frequency some forty per cent in the highest frequency 

 design. Despite this, it is probable that p-n-i-p or n-p-i-n germanium 

 junction triodes ^^^ll serve as oscillators and perhaps amplifiers at fre- 

 quencies as high as 3,000 mcps. 



