Extra Element Theorem - Driving Point Impedances

Driving Point Impedances

As a special case, the EET can be used to find the input impedance of a network. For this application the EET can be written as:

Z_{in} = Z^{\infty}_{in} \left( \frac{1+\frac{Z^0_{e}}{Z}}{1+\frac{Z^{\infty}_{e}}{Z}} \right)

where

is the impedance chosen as the extra element
is the input impedance with Z removed (or made infinite)
is the impedance seen by the extra element Z with the input shorted (or made zero)
is the impedance seen by the extra element Z with the input open (or made infinite)

Computing these three terms may seem like extra effort, but they are often easier to compute than the overall input impedance.

Read more about this topic:  Extra Element Theorem

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