Design of reconfigurable digital filter based on continuously variable fractional delay and interpolation technique

This paper presents the design of interpolated continuously variable fractional delay based filter (ICVFD filter) with fine control over the cutoff frequency. In the ICVFD filter, each unit delay of the prototype lowpass filter is replaced by a continuously variable fractional delay (CVFD) element proposed in this paper. The CVFD element has the same multiplication complexity as that of the second order fractional delay structure used in the existing fractional delay based variable filter, however it provides fractional delays corresponding to the higher order fractional delay structures. Hence the proposed ICVFD filter provides wider cutoff frequency range compared to the existing fractional delay based filter. The ICVFD filter is also capable of providing variable bandpass and highpass responses. Design example shows that the ICVFD filter offers gate-count reduction of 24.6% over the variable filters published in the literature.