Coupled Forms

The first publication on the active RC filter (ARC) appeared in 1938 (Scott). J.G. Linvill (1954) is one of the first pioneers of modern active filter theory. At first, electron tubes were used as amplifying elements. They were expensive and had very large power consumption. Filter circuits with only one amplifying element were therefore preferred, but they turned out to be sensitive for variations in resistance and capacitance values and particularly sensitive to the gain of the electron tubes. In practice, it was not possible to design usable active RC filters of higher order because of the very high sensitivities. This has led to extensive research to find active filter structures that are less sensitive to the component errors.