Abstract: The present paper shows that by a bilinear transformation of elliptic minimal Q-factors analogue filters the IIR half-band filters could be obtained, having twice less number of multipliers with respect to the standard realization. By adjusting the frequency axes of the analogue and digital filters we achieve that the transfer function poles of the IIR filter lie on the imaginary axis of the z-plane, thereby the half of coefficients in the denominator of the transfer function reduces to zero. Hence, the filters could be realized with a decreased number of multipliers. The following realization structures were considered: cascade, parallel, the structure based on the parallel connection of two allpass networks and the wave digital lattice. The efficient realization for filters separating 1/3 of the band is also presented. The IIR filters derived from the elliptic analogue prototype of minimal Q-factors have approximately minimal radii of poles compared to other elliptic filters. It was shown that efficacious filters of very good characteristics could be realized, which divide the operating band in the ratio 1:2 or 1:3.
Keywords: Discrete system, half band filter, IIR filter, cascade structure, parallel structure, wave digital lattice, elliptic filter, allpass network.