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Session 1620

Use of MATLAB in Design and Analysis of Analog Bandpass Filters to Meet Particular Specifications

Richard L. Martin United States Naval Academy

I. Introduction

An alternative title for this paper might be “Bandpass Filter Design - Not as Simple As You Thought - But Help is Not far Away”. One of the problems which has been noted with students working on design projects involving the use of analog filters is an appreciation for the effects of real filters. This is not meant as a knock against the present generation of students, but rather an acknowledgment of the difficulties faced as design requirements force students to apply more and more of those concepts which continue to crowd the various electrical engineering curricula.

In many instances, after basic first and second order analog filters are introduced, when signal processing applications require filters, “ideal” filters are assumed. For bandpass filters, signals within the pass band are assumed to pass through with constant gain while signals outside the pass band are assumed to be totally rejected. The notion that “ideal” filters may be easily implemented may also be reinforced as the students study the design of digital filters.

However, in our senior project design course and laboratory, real bandpass filters are frequently required which have particular pass band characteristics and out-of-band rejection requirements. Frequently a simple second order bandpass filter is implemented and expected to be “good enough?” Then as the filter’s performance is found to be seriously lacking, and the reality sets in of the difficulty encountered in meeting specifications for both pass band characteristics and out- of-band rejection, enthusiasm for filter design quickly wanes. However, use of the various functions and routines readily available and clearly presented in a student MATLAB text1 shows that the design process is not as daunting as it might otherwise seem, and the drudgery associated with rigorous filter design may be significantly reduced.

Contained in this paper is a procedure which begins with specifications for an analog filter which appear at first glance to be easily attained. Then the reader is guided through the process of designing the required filter starting with an intuitive “quick answer”. MATLAB’s frequency response plot capabilities are used to show how the results of the “quick answer” fail to meet the specs. Then the process moves on to a better, but still intuitive design, and finally to the application of a design process which utilizes several of MATLAB’s functions.

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Martin, R. (1999, June), Use Of Matlab In Design And Analysis Of Analog Bandpass Filters To Meet Particular Specifications Paper presented at 1999 Annual Conference, Charlotte, North Carolina. 10.18260/1-2--8021