Active RC realisation of a 3rd-order lowpass Butterworth characteristic

Two realisations of the 3rd-order lowpass Butterworth characteristic are discussed, in which all the capacitances, as well as all the resistances, are equal. The sensitivities of these circuits are evaluated and compared with those of the Huelsman realisation, in which only the capacitors are equal. It is shown that, from the sensitivity point of view, the Huelsman circuit is poorer than either of the two circuits discussed here.