![]() It is obviously not the case in Figure 3-2-7, which means that it refers to IIR, not FIR filter.Īlso, Figure 3-2-7a clearly indicates interrelation between zeros and poles in the z plane. The poles of the FIR filter transfer function are located at the origin. All four poles of transfer function are located within the unit circle, which guarantees tha stability of IIR filters.Īccording to the location of poles in the z plane, it is easy to determine whether it refers to FIR or IIR filter. ![]() It doesn’t cause any problem as the location of poles is the only thing that matters. Transfer function zeros are denoted by small circles, whereas its poles are denoted by small crosses.Īs seen in Figure 3-2-7, one transfer function zero is located outside the unit circle. The word specification refers to the frequency response specification. You should be aware that without being familiar with these concepts, it is not possible to understand analyses and synthesis of digital filters.įigure 3-2-1 illustrates a low-pass digital filter specification. However, instability of the resulting filter, when bilinear transformation is used, may be caused only by the finite word-length side-effect.ģ.2.1 Basic concepts and IIR filter specificationįirst of all, it is necessay to learn the basic concepts that will be used further in this book. The resulting filter, obtained in this way, is always stable. The most popular and most commonly used converting method is bilinear transformation method. It is conversion from analog to digital filter. This is how an analog prototype filter is converted into an analog filter.Īfter the analog filter is designed, it is time to go through the last step in the digital IIR filter design process. The next step in the design process is scaling of the frequency range of analog prototype filter into desirable frequency range. A type of reference analog prototype filter to be used is specified according to the specifications and after that everything is ready for analog prototype filter design. The filter design process starts with specifications and requirements of the desirable IIR filter. It is the best method to use when designing standard filters such as low-pass, high-pass, bandpass and band-stop filters. The most commonly used IIR filter design method uses reference analog prototype filter.
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