Blackman's theorem is a general procedure for calculating the change in an impedance due to feedback in a circuit. It was published by
Ralph Beebe Blackman in 1943,
was connected to
signal-flow analysis by
John Choma, and was made popular in the
extra element theorem The Extra Element Theorem (EET) is an analytic technique developed by R. D. Middlebrook for simplifying the process of deriving driving point and transfer functions for linear electronic circuits.
Much like Thévenin's theorem, the extra element ...
by
R. D. Middlebrook and the
asymptotic gain model of
Solomon Rosenstark
Solomon (), also called Jedidiah, was the fourth monarch of the Kingdom of Israel and Judah, according to the Hebrew Bible. The successor of his father David, he is described as having been the penultimate ruler of all Twelve Tribes of Israel ...
.
[ Blackman's approach leads to the formula for the impedance ''Z'' between two selected terminals of a negative feedback amplifier as Blackman's formula:
:
where ''ZD'' = impedance with the feedback disabled, ''TSC'' = loop transmission with a small-signal short across the selected terminal pair, and ''TOC'' = loop transmission with an open circuit across the terminal pair.][ The loop transmission also is referred to as the return ratio.][ Blackman's formula can be compared with Middlebrook's result for the input impedance ''Zin'' of a circuit based upon the extra-element theorem:][
:]