Design a combination of filters to reduce decline the attenuation in magnitude response

Abstract

Some biquad filters structures are characterized by a decreasing of the attenuation at high frequencies, caused by the final value of the output resistance of the operational amplifier. This decreasing of the attenuation occurs only for the some even orders filters, i.e. for the biquads, of which a higher order filter is composed. One possible solution is to replace the biquad with another biquad that does not have this property. The conversion of parameters of such biquads to each other biquad is described in the detailed steps. The results of the proposed numerical procedure are verified by simulation.