1.

What is the system function of all-zero filter or comb filter?(a) \(\frac{1}{M}(1+z^{-M} e^{j2πα})\)(b) \(\frac{1}{M}(1+z^M e^{j2πα})\)(c) \(\frac{1}{M}(1-z^M e^{j2πα})\)(d) \(\frac{1}{M}(1-z^{-M} e^{j2πα})\)The question was asked in examination.I need to ask this question from Structures for FIR Systems topic in chapter Discrete Time Systems Implementation of Digital Signal Processing

Answer»

The correct answer is (d) \(\frac{1}{M}(1-z^{-M} e^{j2πα})\)

Easy explanation: The system function H(z) which is characterized by the set of frequency samples is OBTAINED as

H(z)=\(\frac{1}{M}(1-z^{-M} e^{j2πα})\sum_{k=0}^{M-1}\frac{H(k+α)}{1-e^{j2π(k+α)/M} z^{-1}}\)

We view this FIR realization as a CASCADE of two filters, H(z)=H1(z).H2(z)

Here H1(z) REPRESENTS the all-zero filter or comb filter whose system function is given by the equation

H1(z)=\(\frac{1}{M}(1-z^{-M} e^{j2πα})\).



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