BELL SYSTEM TECHNICAL JOURNAL 



20 



30° 



<0 120 

 < 



y 140 



O 



LU o 



Q 150 



i^H 160° 

 170° 

 180° 



.8 1.0 



1.4 1.6 



1.8 2.0 2.2 2.4 2.6 ^a 3.0 



Fig. 4 — Phase shift around the feedback path plotted as a function of |m/3| , 

 the absolute value of n0. 



IJ.I3 is a complex quantity which represents the ratio by which the amplifier and 



feedback (or more generally ix and /3) modify a voltage in a single trip around the 



closed path. 



First, there is a set of boundary curves indicated as A, B, C, D, E, F, G, H, I, and / 



which gives either limiting or significent values of |ju/3| and <i>. 



Secondly, there is a family of curves in which db change in gain due to feedback is 



the parameter. 



Boundaries 



A. Conditions in which gain and modulation are unaffected by feedback. 



B. Con3tant amplification ratio against small variations in |/3]. 



Constant change in gain, t- r-r , against variations in \fx\ and |/3|. 



I 1 — MP I 

 Stable phase shift through the amplifier against variations in ^g- 

 The boundary on which the stability of amplification is unaffected by feedback. 



C. Constant amplification ratio against small variations in |/x|. 

 Constant phase shift through the amplifier against variations in ^/x. 



The absolute magnitude of the voltage ted bark tt-^ — jr is constant against 



\-ariations in |/.i] and \/3\ . 



