A Novel Design Technique for Variable Non-recursive Digital Filter based on FrFT

摘要

Finite Impulse Response (FIR) filters with variable magnitude and phase characteristics in the pass-band (also called tunable digital filters), are often required in several signal processing applications. They are needed to perform a slightly modified task in accordance with the need that arises in real time processing. One such application is sample rate converter which employs various sample rates depending on the required signal quality and the available bandwidth of the channel and the data rate of the interfaces. If one applies the existing traditional constant filter design techniques, then for each rate change factor a new filter must be designed to satisfy the new desired characteristics. This results in higher computational complexity. Further the phase response of a window-based filter is directly proportional to the length of the filter at a particular frequency. Thus, filter length must be increased to tune the phase response which in turn increases complexity. To overcome this, a new method based on fractional Fourier transform is proposed here in order to modify the magnitude and phase characteristics of a filter. By analysing the behaviour of desired impulse response of FIR filter in various fractional Fourier domain, it is experiential that pass-band width and phase response can be made dependent on the changeable fractional order parameter.