Practical Filter Design Part 8

62 PRACTICAL FILTER DESIGN PART 8 by H. Baggott The Chebishev section has one of the steepest cut-off profiles of all types of filter. Unfortunately, it also has a limiting deficiency: a ripple in the pass band. The Chebishev filter can be dimensioned in various ways: the ripple is at all times limited to a certain value. This part of the series includes the Chebishev design tables for a ripple of 0.1 dB. The Chebishev function is one of the most effective functions for realizing a filter: it combines a pronounced bend at the cut-off point with a sharp profile. This combina- tion also results in ringing, which, by care- ful design can fortunately be kept within a given value. There is, however, a direct relation between the cut-off profile and the ringing: if the former is made steeper, the latter becomes more pronounced; and if the ringing is kept to a small value, the profile is less steep. In practice, a compro- mise is reached, be-cause in virtually all applications a ripple e...