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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



The considerations involved in supplying biases to a grounded collector 

 stage are rather similar to those discussed already for the grounded emitter 

 case. If the base is allowed to float, the collector current will be given ap- 

 proximately by equation (47) as discussed for the grounded emitter case. 

 A resistance between base and the negative side of the supply battery in 

 Fig. 24 will serve to decrease the collector current while a resistance between 

 base and ground will serve to increase it. In applications where it is deiired 

 to make full use of the high input impedance which this stage can afford, it 

 may be most desirable to let the base float as shown in Fig. 23. 



Fig. 23 — One practical arrangement of a grounded collector stage. 



Fig. 24 — Modification of Fig. 23 to obtain lower collector current. To raise collector 



current remove the resistance shown and connect a high resistance between 



base and ground. 



Frequency Response — General Remarks 



Shockley has shown that there are several different physical considera- 

 tions which lead one to expect a high-frequency cutoff in the response of 

 n-p-n transistors. The frequency at which cutoff occurs depends in a theoreti- 

 cally understandable way on such things as the geometry of the transistor 

 and the physical properties of the germanium from which it is made. If these 

 factors could all be controlled and varied at will, it would be possible to design 

 a transistor to have a specified cutoff frequency. 



One limitation comes about in the following way: In order to produce 

 transistor action, the electrons which are injected into the p layer at the 

 emitter junction must travel across this thin layer and arrive at the collector 

 junction. They do this principally by a process of diffusion and require a 

 finite (but small) amount of time to make the journey. If this time were 



