FEEDBACK AMPLIFIER DESIGN 



443 



where it is assumed that Am = 43 db, A = 29 db, x = 9 db, n = 3 and 

 y = 1/6. The Nyquist diagram for the structure is shown by Fig. 

 18. It evidently coincides almost exactly with the diagram postulated 

 originally in Fig. 9. 



< 



I 140 



(Q. 



120 





0.5 0.6 0.6 1.0 



2 3 4 5 6 



fo 



20 30 40 50 



Fig. 17 — Phase characteristic corresponding to gain characteristic of Fig. 16. 



Fig. 18 — Nyquist diagram corresponding to gain and phase characteristics of 

 Figs. 16 and 17. As in Fig. 8 the diagram is rotated to place the critical point at 

 - 1, rather than +1,0. 



With the characteristic of Fig. 16 at hand, we can return once more to 

 the calculation of the total design range corresponding to any given 

 feedback. From the useful band to the intersection of the cutoff 



