Practical considerations in the design of active filters with particular reference to micropower requirements†

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Abstract
The effects of utilizing physical devices for the realization of active; band-pass filter sections which were designed with the aid of idealized mathematical models, are investigated. The assumptions made are pertinent to low-power drain requirements. The complete feasible range of component values is derived, showing that a. certain common arbitrary choice is, from some aspects, not optimal, nor is it always) feasible at all. The optimal choice from the viewpoint of imperfect amplifier usage and from that of passive element variation may or may not coincide, depending on the filter requirements ω0, A0 and Q. In any case, the designer in supplied with formulae in close form to choose optimally the component values with respect to these or another design criteria. Given an actual amplifier, upper bounds are derived, in a special case of interest, for the filter requirements which will not cause deviations larger than a prescribed percentage. Deviations due to passive element variations are also bounded, as a function of the maximum relative variations ΔR/R and ΔC/C, by a ‘ worst case ’ consideration.

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