Abstract: A prototype ⅡR digital bandpass filter is derived from an analogous bandpass filter by using bilinear transformation. The formulas relating the digital bandpass filter's coefficients with its center frequency and bandwidth are obtained. Using N sections of such digital bandpass filter, a cascade ⅡR digital bandpass filter is constructed. Based on the specifications and the formulas given, the parameter N and bandwidth of prototype ⅡR digital bandpass filter can be obtained, and the unknown cascade ⅡR digital bandpass filter can be finally determined. The filter has few coefficients and a simple structure and it is easy to be designed. It is especially suitable for its implementations when using DSP.

Key words: prototype filter, bilinear transformation, cascade, IIR digital bandpass filter