276 



where 



BELL SYSTEM TECHNICAL JOURNAL 



Z^ = 



Zp = 



1 — Fop 

 Zv.Z? 



(11) 



Zy, -{- Z^ 



This shows the now well-known fact that shunt feedback may be used to 

 reduce impedance. 



p- CIRCUIT 



f3- NETWORK 



■02' 



Fig. 4 — Impedance faced by the line at the shunt feedback end of a feedback ampHfier. 



Fig. 5 — Impedance faced by the hne connected to a bridge feedback amph"fier. 



The relation between the normal feedback F,v and the feedback ¥oj> in- 

 volved in (11) is, by (6) 



'^^^ (12) 



Vs - 





From (11) and (12) it follows that even with a very modest amount of nor- 

 mal feedback the reduction in impedance may be very large. For example, 



