Flat Magnitude Low-Pass Filters with a Pair of Imaginary-Axis Zeros

It is known that the cutoff rate of a maximally flat low-pass filter can be improved either by introducing a pair of imaginary-axis zeros or relaxing the flatness condition. Making use of both techniques simultaneously, this correspondence describes how to design an nth-order low-pass filter with (n − 2) degree of flatness at ω = 0 rad/s and also including a pair of imaginary-axis zeros. Advantageous performances of the filters obtained are also described. Copyright © 1978 by The Institute of Electrical and Electronics Engineers, Inc.