306 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



is given by the expression 



'INP 



UT = ?'6 + ^e(l — Gi) 



(16)1 



where Gj is the current transmission given by (13). If Gi at dc is much' 

 greater than 1, then the input impedance and the current transmission 

 of the common emitter stage fall off at about the same rate and with 

 approximately the same corner frequency (wi). The input impedance 

 finally reaches a limiting value equal to r^ + Vb . 



A particularly useful interstage network is shown in Fig. 7(a). This 

 network is analyzed in Appendix II and Fig. 7(b) shoAvs a plot of the 



60 



50 



40 



30 



20 



Z 

 < 



z 



UJ 



10 



tr 

 cr 



D 

 U 



-10 



-20 



-30 



(a: 



EQUIVALENT CIRCUIT 



120 



140 



-160 10 



UJ 



m 

 cr 



-180 liJ 



Q 

 Z 



-200 ^ 



z 

 < 



-220 , 





10 



2 5p2 5,2 5.2 5,2 5 



-!•= in^ m^ in5 



10'= 



lO-^* 10^ 10= 



FREQUENCY IN CYCLES PER SECOND 



lO'' 



-240 ' 



260 



- -280 



10' 



Fig. 6 — Negative feedback applied to a common emitter stage. 



