On the characteristics of monotonic L, Halpern, and parabolic filters

The design of analog filters is a well established theory. However, in spite of the great variety of filter types available (Butterworth, Chebyshev, elliptic, etc), there are some other less known filter types, such as monotonic L filters, Halpern, and parabolic ones, having many interesting and important characteristics which might be useful to the filter designer, such as group delay or step response, and that in some cases are superior to the classical filter types used by designers. In this work, we review the theory for these filter characteristics, compare them with classical filter functions and develop a graphical tool for the design of these analog filter functions. This tool guides the user in the approximation of monotonic L filters, Halpern filters, and parabolic ones. It presents in a graphical perspective the advantages and disadvantages of each one in the areas of group delay, magnitude and step response, making easier to the user determine the appropriate filter for a specific application