Design of low complexity variable digital filter with large cutoff frequency range based on second order frequency transformation and interpolation

This paper presents the design of low complexity variable digital filter with large cutoff frequency range based on the second order frequency transformations and interpolation technique. It provides tunable lowpass as well as bandpass responses, making it suitable for applications such as cognitive radios which need to support multiple communication standards on a single mobile terminal. The design example of the proposed interpolated second order frequency transformation based filter (ISFT filter) has the wide cutoff frequency range of 0.0523π to 0.9477π. For this cutoff frequency range, ISFT filter offers 12.5% reduction in the number of multiplications over the fast filter bank based filter for approximately the same gate-count, and 39.3% and 30% reduction in the number of multiplications and gate-count respectively over the spectral parameter approximation based filter.