PROPERTIES AND APPLICATIONS OF H-p-H TRANSISTORS 561 



Collector Cutoff in the Grounded Collector Stage 

 In this case 



''^"^ ^ k. + i?L+ (r.+ i?,)(l -rjr:)] ■ ^^^^ 



+ (lAc)(r6 + Ra){re + Rl){\ + j^CcTc) 



and 





(74) 



For matched impedances (7?^ = 139,000 ohms and Rl = 2990 ohms), 



/cc = 320,000 cps 



G = 16.7 db. 



The cutoff frequency can be raised by decreasing either Rg or Rl . With 

 Rg = 139,000 and R^ = 25 ohms 



fee =9.77 megacycles 



G= 1.8 db 



The gain-bandwidth product in this case is 1.5(10)^. 



Noise 



The data now available on noise are insufi&cient to give an adequate 

 picture of the performance of n-p-n transistors in this respect. Such measure- 

 ments as have been made, however, make it clear that these devices are very 

 much quieter than early point-contact transistors reported on by Ryder and 

 Kircher. 



Transistor noise seems still to decrease with increasing frequency at a 

 rate of something like 11 db per decade. It also decreases as the thickness 

 of the p layer is decreased. 



Of the order of half a dozen units of various dimensions have been meas- 

 ured at 1000 cps and have shown noise figures as low as 8 db and as high 

 as 25 db. 



The dependence of noise figure on operating point has been measured for 

 only one transistor. As indicated in Fig. 28 and Fig. 29, these data show 

 that the noise figure improves as Vc is reduced and that it may be roughly 

 independent of collector current. These data were taken on a grounded 

 emitter stage with impedance match at the input terminals. Noise figure for 

 this connection varies shghtly with source impedance and has been found 



