Tunable bandpass passive digital filter design

Sharp-cutoff filtering characteristics require a high-order filter. For a not-too-high filter order, IIR digital filters are required. In this paper, we present two methods for designing high-order tunable bandpass passive digital filters that can provide sharp-cutoff capability for real-time filtering applications. In the first method, a tunable bandpass digital filter is obtained from a lowpass to bandpass frequency transformed digital filter. In this method, a derived expression for each of the coefficients of the second-order and the decomposed second-order passive digital filter sections is used to achieve real-time digital tuning. In the second method, a tunable bandpass digital filter is obtained by cascading a lowpass and a highpass frequency transformed digital filters. These methods provide two feasible approaches from which realtime tunable sharp-cutoff bandpass passive digital filters can be designed.