Comparison of dynamic range properties of high-order active bandpass filters

The design procedures necessary for maximising dynamic range of cascade, f.l.f., i.f.l.f. and m.l.f. active-filter topologies, are presented and equations are derived for computing the total output-noise voltage contributed by internal-noise sources. Further, it is shown that the equivalent input noise of a second-order biquad section is dependent not only on circuit configuration and pole-Q, but in some cases also on the section gain. As a result, the total output noise of high-order filters may or may not be a function of the overall filter gain, depending on whether the equivalent input noise of the second-order section used as building block is not or is, respectively, a function of section gain. A comparison of the different topologies indicates that in addition to the advantage of being easy to design, the f.l.f. filter is the only topology whose output noise can remain constant regardless of the overall filter gain and the type of second-order used.