562 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



to be a minimum when the source impedance is roughly equal to the input 

 impedance of the stage. 



It must be emphasized that this functional dependence of noise figure 

 on operating point and source impedance has been measured for only one 

 transistor. Further measurements may show that these results are not 

 typical. 



20 



CD 18 



o 



UJ 



o 



Z 16 



UJ 



a. 



8 10 12 



Vc IN VOLTS 



18 20 



Fig. 28 — Noise figure increases with increasing collector voltage. 



20 



UJ 



(D 



U '8 



UJ 



a 

 ? 16 



UJ 



tr. 

 o 1^ 



<o 12 



o 



z 



40 



60 



80 



120 140 160 180 

 Ic IN MICROAMPERES 



200 220 240 260 



Fig. 29 — Noise figure does not vary much with collector current. 



Final Comments 



In this paper we have attempted to present what is known about the 

 circuit performance of n-p-n transistors. Since these devices are still under- 

 going exploratory development and since only a limited number has been 

 produced, it is obviously impossible to give statistical data on reproduc- 

 ibility or on such reliabihty factors as the effect of ambient temperature. 



It is much too soon to know what properties may be achieved after further 

 development, but the results obtained to date seem encouraging and worth 

 reporting. 



