A synthesis of an active RC filter with reduced GB effect of operational amplifier

In synthesizing RC filters by simulation of LCR filters, the advantages are simplicity of synthesis and low element sensitivities. Ordinarily, the operational amplifiers used in this synthesis method are all considered to have ideal characteristics which hold only at low frequencies. Researches on the effect of the frequency characteristics of the operational amplifiers on the filter characteristics have been done for Biquad circuits in several cases but none at all for higher-order active RC filters. In this paper, first, a synthesis method different from the conventional method is shown for a filter with finite zeros. Then a method for reducing the effect of the finite GB product on active RC filters is shown by contradicting the unnecessary phase-rotating component of the operational amplifiers with the entire circuit, assuming that all operational amplifiers used in the filter have the same GB product. Furthermore, actual circuits are synthesized and experiments are performed. As a result, the effectiveness of the proposed compensation technique is shown by the fact that the frequency range for possible synthesis is extended. Finally, a synthesis method and experimental results are shown for a filter with all poles.