Filter design, be it active, passive, or switched capacitor, is traditionally a mathematically intensive pursuit. There are many architectures and design methods to choose from. Two methods of high order bandpass filter design are discussed herein. These methods allow the filter designer to simplify the mathematical design process and allow LTC’s switched capacitor filters (LTC®1059, LTC1060, LTC1061,LTC1064) to be utilized as high quality bandpass filters.
The first method consists of the traditional cascading of non-identical 2nd order bandpass sections to form the familiar Butterworth and Chebyshev bandpass filters. The second method consists of cascading identical 2nd order bandpass sections. This approach, although “nontextbook,” enables the hardware to be simple and the mathematics to be straightforward. Both methods will be described here.
This note will first present a finished design example and proceed to present the design methodology, which relies on tabular simplification of traditional filter design techniques.