#### akbarza

##### Member level 4

i am reading a pdf file with name:

THE GFT: A GENERAL YET PRACTICAL FEEDBACK THEOREM

R. David Middlebrook

( if search net, you can find it easily).

i am familiar with extra element theorem(eet) of middlebrook and zeet.

in related articles, often eet and zeet is used for impedance and not for voltage or current source generator.

in above mentioned article,

in page 8 is written:

If an “extra element” is an impedance Z, each contains

the ratio of Z to a certain driving point impedance seen by Z. If the extra element is a

controlled generator, such as Ai in Fig. 5(b), the denominator contains the ratio of

Ai to the negative of a return ratio seen by Ai, evaluated with the input ui set to

zero; the numerator contains the ratio Ai to the negative of a return ratio seen by Ai

evaluated with the output uo nulled.

can you explain it to me?how eet is used for current or voltage source ?

thanks