This paper analyses general active filters that can be

applicable to EMI filter, active power filter, etc. It gives

generalized equations presenting insertion losses and input

impedances of various kinds of active filters, from which the

requirements and limitations of active filters can be identified.

Based on this analysis, the effectiveness of the active filters

presented in several literatures is investigated. With the results of

this study, an appropriate topology of an active filter for a

specific application can be selected with a good rationale.