Multiple-real-pole and multiple-critical-pole maximally flat RC active lowpass filters with sharp cut-off

Recently, an attempt has been made to design a multiple-real-pole/multiple-critical-pole maximally flat RC-active filter with sharp cut-off by including a multiple pair of concident jω-axis zeros (Wei and Chien 1985). This design technique unfortunately has two major drawbacks, i.e. (i) the passband response does not truly satisfy the maximally flat criterion with a consequent large deviation from the desired no-loss response and (ii) there is a limitation on the realizable number of third-order blocks with finite transmission zeros. A new design technique is therefore proposed here whereby all the aforementioned undesirable features are eliminated. The technique is also extended to cover the case of prescribed finite transmission zeros. Hence, this new technique offers a multiple-real-pole/multiple-critical-pole maximally flat lowpass RC-active filter with a sharp cut-off and also effective suppression of noise at prescribed frequencies. © 1991 Taylor & Francis Ltd.