EQUIVALENT CIRCUITS OF NETWORKS 



6oi 



The ''passive part" in Fig. 15, finally, preserves the open-circuit imped- 

 ance Zu , the feedback impedance Zn and the determinant Az of the com- 

 plete network. This network shows incidentally a close resemblance to one 

 already published.^ 



Fig. 13 — Equivalent circuit of an active four-pole; voltage impressed in series with the 

 output. 



Fig. 14 — Equivalent circuit of an active four-pole; voltage impressed in series with the 

 [ nput. 



2,2 + Z2, ^, 



z„ + z, 



V, 



-z, 



:©^ ^ 



.(z.-z.?-|5^) 



V2 



Fig. 15 — Equivalent circuit of an active four-pole; voltage impressed in series with the 

 output. 



It is well to emphasize that, while all the complete networks are equiva- 

 lent, this is not true for the ''passive parts." In fact from their derivation 

 it follows that none are equivalent. Specific circumstances may make it 

 desirable to perform transformations on the passive parts. For example, 

 it might be more convenient to work with a 11 than with a T network. Such 

 transformations are of course perfectly legitimate and raise the question of 

 choice of equivalent networks. A few remarks on this subject may be 



'Loc. cit. 



