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Active filters may consist of a cascade of isolated resonators, with each resonator supplying a single pair of complexconjugate poles. This paper supplies a detailed analysis of some -amplifier resonators whose characteristics are well suited for practical filters. The calculations are facilitated by a set of sensitivity identities. One resonator, taken from the Sallen and Key catalog, is shown to have extremely low passive sensitivities: for all passive elements. Active multiplication is used to extend the usefulness of the circuit. Analysis of the dualintegrator feedback resonator shows that it is notably insensitive to amplifier parasitics. Finally, the dual-integrator concept is realized in a resonator that uses only two amplifiers. The several resonators supply a range of useful pole- 's from low values to several hundred.