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BELL SYSTEM TECHNICAL JOURNAL 



mum phase" passive circuit.'^ Accordingly the phase shift, like the amplitude 

 variation, is also intermediate between a single R-C interstage and the flat 

 compensated pair of interstages. 



When variations between curve shapes are not too large, the shape can be 

 characterized by a single parameter which w^e take as the cutoff frequency 

 fc. Cutoff is defined as the frequency where the magnitude of a- is halved. 

 Some statistical data on cutofif frequency of different units made of N-type 

 and P-type germanium are plotted in Fig. 14. The P-material is somewhat 



(0 10 



?, 5 



u. 3 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 

 COLLECTOR VOLTAGE, Vj 



Fig. 15 — Cut-off frequency versus collector voltage. 



better, in keeping with the fact that the active charge carriers producing 

 the transistor effect in it are electrons having greater mobility than the holes 

 which are active in N-type germanium. 



As one changes the operating point of the transistor the frequency re- 

 sponse curve changes in such a way that the shape remains sensibly constant 

 on a logarithmic frequency scale, but the scale changes. The cutofif frequency 

 is usually roughly proportional to the collector voltage, with only minor 

 dependence on the other operating parameter, as shown in Fig. 15 unit AS62. 



* "Network Analysis and Feedback Amplifier Design," H. W. Bode, D. Van Nostrand 

 Publishing Co., 1945. 



