Effects of excess phase in multiple-feedback active filters

The paper presents theoretical and experimental results showing that lagging "excess phase" of second-order active filter sections causes potentially large errors in the form of a characteristic skewing of the passband shape of multiple-feedback (MF) bandpass functions. It is shown that simple capacitive phase-lead methods eliminate the deviations. The situation is discussed in detail for the specific case of "follow-theleader-feedback" bandpass filters, but applies equally to other MF topologies. Experimental data are presented to demonstrate the effects of excess phase and to verity the correctness of the design process.