A new S-Z replacement design technique of IIR digital filters

A new s--z replacement design technique of IIR digital filters is presented in the paper. The authors have derived concise relations between s and z. These relations are separately used to transform a referential analog lowpass normalized filter into a corresponding digital lowpass, high-pass, bandpass or bandstop filter. The technique has the same advantages as using the bilinear transformation design, that is, the steps of the design are simple and the use is convenient. Besides, it guarantees that all of the zeros and poles of the resulting digital filters are inside the unit circle. (Using the bilinear transformation, the zeros of the digital filter are on the unit circle). Using the technique, the authors have designed digital lowpass, highpass, bandpass and bandstop filters, including Butterworth, Chebyshev and elliptic filters. In all of these designs, not only the passband fluctuation and the passband width, but also the stopband attenuation are controlled very accurately. Ideal results have been obtained in all of these designs.